Cardiac arrhythmias in infants and children

Cardiac Arrhythmias in Infants and Children ROGER

A. H U R W I T Z

UNTIL RECENTLY arrhythmias~[n pediatrics seldom were encountered, rarely diagnosed and even "l~ss commonly treated. However, along with new methods of cardiac diagnosis and treatment came a heightened awareness of arrhythmias in infants and children. Nevertheless, standard textbooks of pediatric cardiology and those on arrhythmias still devote only single chapters to the problem of pediatric arrhythmias. This monograph is intended to familiarize the pediatric house officer and practitioner with the most commonly encountered and/or dangerous dysrythmias of infancy and childhood. The pathophysiology will be discussed in light of new methods of electrophysiology, such as bundle of His recording. Each arrhythmia, however, will be based on the ECG and recognition via this standard diagnostic technic. The reader must be familiar with standard ECG nomenclature. Each tracing presented has been taken from a patient at Riley Hospital for Children during the years 1967-1972. At the conclusion of this monograph is a formulary.

ANATOMY AND PHYSIOLOGY OF THE NORMAL CONDUCTION SYSTEM Certain tissues of the heart are specialized for impulse initiation and propagation (Fig. 1 ). The sinoatrial (SA) node, derived from muscle cells of the sinus venosus, is located in the superior portion of the right atrium, near the entrance of the superior vena cava. Sinoatrial node fibers are thought to be in continuity with specific pathways extending to distal atrial musculature, left atrium and atrioventricular (AV) NoTE: The studies reported here have been made possible in large part through grants from the Riley Memorial Association.

SINO-ATRIAL NODE

ATRIO-VENTRIC NODE

MAIN ATRIO-VENTRICULAH BUNDLE (BUNDLE OF HIS) RIGHT BRANCH OF BUNI

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system.

1.--Diagrammatic representation of the normal heart and conducting

junctional tissue, t This latter area is on the right side of the atrial septum, near the coronary sinus. Most atrial nerve fibers enter the A V junction, but a few bypass the area and enter more distal conducting tissue near the bundle of His. z The term " A V junction" refers to the area between the atrial specialized cells and bundle of His, while the " A V node" is a smaller, central area. It lies on the right interatrial septum above the septal leaflet of the tricuspid valve. The bundle of His continues from the AV junction. The bundle then runs onto the muscular septum and bifurcates into right and left branches at the membranous portion of the interventricular septum. There is further branching, with termination in Purkinje fibers interspersed in the ventricular myocardium. The cardiac impulse begins in the SA node, travels through the atria at 1,000 mm/second, slows to 20 m m / s e c o n d in the AV junctional area and speeds to 4,000 m m / s e c o n d through Purkinje fibers. These cells have the ability to conduct the cardiac impulse and initiate it spontaneously: they possess "autom~aticity." Normally, the SA node has the highest degree of automaticity, and thus initiates the impulse. When another group of cells initi.ates the impulse, rhythm is called "ectopic." Automaticity differs from "excitability" which is the property that permits a cell to be stimulated. Though cardiac function depends on certain of these inherent properties, extraneous events may alter these cardiac properties. Changes in oxygenation, electrolyte balance, acid-base status, catecholamine levels and many drugs profoundly influence the cardiac electrophysiology.

TABLE 1.---HEARTRATEAT VARIOUSAGES (Beats per Minute) AGE

MINIMUM

MEAN

0-24 hours 1-7 days 8-30 days 1-3 months 3-6 months 6-12 months 1-3 years 3-5 years 5-8 years 8-12 years 12-16 years

85 100 115 115 115 115 100 55 70 55 55

119 133 163 154 140 140 126 98 96 79 75

MAXIMUM

145 175 190 205 205 175 190 145 145 115 115

SD*

16.1 22.3 19.9 18.6 21.0 18.7 19.8 18.0 16.1 15.0 13.5

*SD, Standard deviation.

NORMAL PEDIATRIC VALUES Accurate pediatric diagnosis is predicated upon knowledge of the normal at the age in question. Cardiac rate and speed of conduction have wide variations in infants and children, being especially age and activity dependent. N o r m a l values are included in Table 1.3 It is interesting that the newborn's rate is often below 100, and usually is slower during the first week than during the next few months. The fastest rate occurs at about 1 month of age. The P - R interval generally seems to increase with age. Though also tending to increase with age, the Q R S duration has less correlation. Premature infants have a very short Q R S duration, usually less than 0.04 seconds. 4 Generally, a narrow QRS complex never is considered abnormal; however, a Q R S duration longer than 0.10 seconds is abnormal in any preadolescent patient. NORMAL (SINUS)

RHYTI~M,BRADYCARDIA AND TACHYCARDIA

The SA node is the normal pacemaking site. Sinus rhythm occurs when ( 1 ) rate is normal; ( 2 ) sequence of P, QRS and T is maintained; ( 3 ) P - R interval is normal; and (4) P wave is upright in standard leads I and II. Sinus bradycardia occurs when the rhythm is normal and the rate is less than 100 in an infant, less than 80 in a child or less than 60 in a teenager. It m a y occur normally, during sleep or in those in good physical condition, e.g., athletes. Vagal stimulation such as gastrointestinal manipulation m a y induce bradycardia. Slow rates are also associated with increased intracranial pressure, jaundice or myxedema. Drugs, notably digitalis, antiarrhythmia preparations and cer-

tain anesthetic agents, may result in bradycardia. Sinus tachycardia may occur with any activity that" stimulates the adrenergic system. Fever almost always causes tachycardia, usually 10-15 beats/1 °F of temperature elevation. Hemodynamically, tachycardia increases cardiac output. Since tachycardia does encroach on the diastolic filling period, it decreases myocardial efficiency. At rates more than twice normal, myocardial performance and cardiac output may be reduced. Interestingly, children with congenital heart disease exhibit maximal exercise rates of 175, significantly less than those with repaired lesions (185) or those with normal hearts (195) .5

SINUS ARRHYTHMIA Sinus arrhythmia is very common in normal children. It represents a disturbance in the rhythmic production of the impulse in the SA node. However, each ventricular contraction is preceded by an atrial systole with a constant P-R interval (Fig. 2). There is a cyclic variation in rate, often corresponding to the respiratory cycle. Commonly, the rate increases toward the end of inspiration and slows with expiration.

SUPRAVENTRICULAR ARRHYTHMIAS PREMATURE SYSTOLE Supraventricular premature contractions are uncommon in normal children. They are associated frequently with a diseased myocardium, being found with myocarditis, carditis of rheumatic fever or following cardiac surgery. They usually produce no symptoms, but if recurrent they may produce a feeling of "palpitations." Since some degree of ventricular filling and emptying occurs despite an ectopic supraventricular beat, the hemodynamic effects of these prematures are minireal. When they occur there is a premature ventricular complex preceded by a P wave differing in contour from the normal P wave (Fig. 3). Additionally, the ectopic beat usually has a long P-R interval. Often leads I and II have a positive P wave deflection, but if there is a left atrial ectopic focus, there may be inversion of the P. Should the origin be in AV junctional tissue, the impulse may spread in both directions, giving rise to a negative P in II, III and aVF. Due to retrograde conduction, the P may precede, follow or coincide with the QRS. There may be no P wave if the retrograde impulse fails to discharge the atria. With most supraventricular prematures the QRS contour is normal. There may be no compensatory pause or one less than fully compensatory. If shifting or wandering of the pacemaker occurs, this may be due to ectopic.impulse formation or exaggeration of a sinus arrhythmia. Since supraventricular prematures carry only slight risk

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F[c,. 2 (top).----Sinus arrhythmia in an otherwise normal child.

FIG. 3 ( bottom ).--Numerous atrial premature contractions.

and little impairment of hemodynamics, treatment rarely is necessary. Therapy should be directed at a possible underlying cause. When the premature beats occur frequently or repetitively, they may precipitate an attack of supraventricular tachycardia, and suppressive therapy should be considered in these cases. PAROXYSMAL SUPRAVENTRICULAR TACHYCARDIA

(PST)

Since it is difficult to diagnose the exact site of impulse formation, "supraventricular tachycardia" is currently accepted as including paroxysmal atrial tachycardia. Periodic cardiac acceleration is frequent. However, only a fraction of such attacks are true PST. Though infrequent in pediatrics, PST is the most common tachycardia found in infants and children, with an estimated incidence of 1 in 25,000. 6 Of added significance is the fact that the disease is potentially life-threatening, but easily treatable and usually curable.

The basic etiology in most cases is not known. Paroxysmal supraventricular tachycardia usually is found in patients with otherwise normal hearts. In such "susceptible" individuals, environmental factors such as hyperventilation, exercise, changes in position and stressful situations may precipitate paroxysms. Paroxysmal supraventricular tachycardia also is associated with acute infections and myocarditis, including that caused by Echo virus. 7 Currently, PST often is acquired during cardiac surgery. It is common especially after repair of complete transposition of the great vessels. 8 Paroxysmal supraventricular tachycardia also is a complication of cardiac catheterization. 9 Digitalis toxicity may cause PST, often with associated AV heart block. 1° Certain congenital defects have a high association of PST, the most notable being Ebstein's deformity of the tricuspid valve in which PST occurs in approximately 40% of cases. 11 Forty per cent of patients with the Wolff-Parkinson-White syndrome have been reported to have paroxysmal tachycardia, lz, 13 The hemodynamic effects of PST depend upon the cause of the arrhythmia, the previous condition of the patient's heart, the ventricular response and the duration of tachycardia. 14 To a certain point cardiac output increases as rate increases; however, as ventricular filling is compromised output decreases. Paroxysmal supraventricular tachycardia has more adverse effect on hemodynamics than does a simple sinus tachycardia. An increase in oxygen consumption and a fall in cardiac output of 13 % have been reported.l.~ Clinically, in the absence of associated morphologic abnormalities, PST initially produces little impairment of cardiac output; however, there is an early drop in systemic blood pressure, an elevation in atrial pressures and low stroke volumes. When the tachycardia is of longer duration, cardiac output also falls. Paroxysmal supraventricular tachycardia is the most common tachycardia encountered in infants and children. Boys are affected in approximately 65% of cases, x6 It is commonly a disease of infancy, with most initial attacks occurring before 3 months of age. Though a few children have no apparent signs or symptoms and are diagnosed during routine examination, most, especially infants, do have some distress. They may be irritable, coughing and have poor color. The rate usually is too fast to count accurately; murmurs are insignificant. At least one third of infants with PST present in failure. It usually requires the presence of tachycardia for 2 a. ~ 8 hours before the occurrence of congestive failure in the presence of an otherwise normal heart. An x-ray film of the chest may show cardiac enlargement, and in those with failure, pulmonary congestion also may appear. This vascular engorgement clears within 48 hours after conversion of the tachycardia; however, cardiomegaly may persist for periods up to 1 month (Fig. 4).

FIG. 4.--X-ray film of the chest of infant severely ill (A) with PST. Mild cardiac enlargement persists (B) 1 week postconversion. Silhouette is normal (C) 8 months later. Diagnosis depends upon electrocardiographic verification (Fig. 5). Infants and children with PST have a rapid succession of premature beats occurring at a rate usually ranging between 180 and 300. By definition, a succession of six supraventricular prematures is considered a paroxysm. 14 Since the supraventricular origin is often ectopic, the P waves may have a different configuration from those observed during sinus rhythm. More often, however, the P waves are superimposed on the T waves, masking P wave recognition. The ventricles usually respond regularly to every supraventricular impulse. For this to occur there must be ( 1 ) normal atrial musculature, contracting well and not developing flutter or fibrillation; and (2) normal AV junctional tissue able to conduct this rapid an impulse without developing heart block. Actually, a "block" may be clinically beneficial, since it may slow ventricular action enough to prevent or decrease the development of congestive heart failure. The QRS complexes usually are normal in contour. When widening occurs it may reflect abnormal conduction in the bundle branches, resulting from the arrival of impulses during the relative refractory period. Though AV junctional tachycardia is less common than atrial tachycardia in children, it may occur during the course of carditis (usually rheumatic), catheterization, cardiac surgery or digitalis toxicity (Fig. 6). 18 It may be difficult to differentiate this from atrial tachycardia; however, the QRS complexes may be aberrant, and the P waves frequently are inverted and close to the QRS. Though PST may convert immediately to sinus rhythm, often there

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are abnormal rhythms during the transition period. Conversion may follow one of several patterns: (1) asystole lasting up to 6 seconds; (2) slight ventricular slowing followed by sudden conversion; (3) slowing, asystole and then conversion; (4) ventricular tachycardia, a prefibrillatory ventricular arrhythmia and premature beats followed by sinus rhythm; and (5) immediate conversion.18 Episodes of ventricular tachycardia and flutter also may occur (Fig. 7). Following an attack, a patient may have prolongation of ventricular conduction or unusual repolarization even in the absence of digitalis. A patient with an isolated attack of PST may have an entirely normal E C G after conversion. Frequently, however, there may be non~ specific S-T changes for a number of days. Those more susceptible to repetitive attacks may show atrial premature beats, often coupled or in groups, or the Wolff-Parkinson-White syndrome which will be discussed later. A few children may demonstrate PST, sinus rhythm, and Wolff-Parkinson-White syndrome at different times. Patients with underlying heart disease who develop PST have an exaggerated course. These children may be affected severely in a very short time. This has been shown graphically when tachycardia develops during cardiac catheterization. It has been suggested recently that tachycardia may cause distress and may potentiate or initiate hypoxic 10

spells in patients with tetralogy of Fallot. 19 There are cases in which PST has caused severe cyanosis and hypotension in such patients. When the tachycardia is treated, the distress abates. The management of tetralogy spells with the beta-adrenergic blocking agent, propranolol, is somewhat predicated on the theory that control of cardiac rate may help prevent the occurrence of hypercyanotic spells. Paroxysmal supraventricular tachycardia is usually discovered, especially in infants, as a medical emergency. Occasionally, the tachycardia may revert spontaneously or may be intermittent. Usually, urgent treatment is necessary. The simplest, quickest and safest method FIG. 6 (top).---Sinus rhythm (11) alternating with runs of junctional tachycardia (AVF).

FIG. 7 ( bottom ).--Electric conversion of a moribund infant with paroxysmal tachycardia: (1) tachycardia with block and aberrancy; (2) after one shock, very rapid PST; (3) after second shock, V F occurs and ( 4 ) rapidly converts to ventricular tachycardia which ( 5 ) has varying block and ( 6 ) spontaneously converts to sinus. All occurred over 3 0 - 4 5 seconds.

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of therapy involves parasympathetic stimulation. Carotid sinus pressure usually is tried first, and consists of compression of one carotid artery firmly against the vertebral column. If PST converts, there usually is a rapid conversion. Neosynephrine and other sympathomimetics, in doses large enough to raise systemic blood pressure, may be effective. Occasionally, Neosynephrine coupled with carotid pressure is more efficacious than either alone. Unfortunately, these procedures usually are not effective in converting PST of infancy. Digitalis is the most effective and widely used agent for conversion of PST in pediatric patients. Its antiarrhythmic properties include augmentation of vagal tone, sensitization of the carotid sinus and slowing of conduction through AV junctional tissue. In addition, digitalis has inotropic properties advantageous to those patients in congestive heart failure. Digoxin is used most commonly: When given parenterally, initial effect occurs within minutes. Frequently, especially when dealing with a morphologically normal heart, digoxin affects cardioversion before the total calculated amount of digoxin is administered. Moreover, the dose necessary for conversion frequently is less than that necessary to control congestive heart failure from congenital deformities. Therefore, careful ECG monitoring is essential. Digitalis is effective in converting at least 80% of PST in infants and children. 6 The drug is contraindicated in the presence of ventricular tachycardia and must be administered cautiously when there are low potassium levels, in the presence of myocarditis, when digitalis toxicity may be the cause of PST (a rare phenomenon), when PST with AV block occurs or when renal function is impaired. Other antiarrhythmic drugs should be reserved for cases recalcitrant to digitalis. Quinidine and procaine amide are similar drugs which increase the refractory period of atrial muscle and decrease automaticity of ectopic pacemakers. These drugs are almost as effective as digitalis in aborting an acute episode of PST, but potentially are more dangerous since they possess negative inotropism. 20 They may be used in conjunction with digitalis in patients difficult to control. Propranolol, a beta-adrenergic sympathetic blocking agent, has also been efficacious in management of PST. zl It is especially effective in PST associated with digitalis toxicity. 2z Propranolol is known to reduce cardiac output approximately 10%; thus, it must be used cautiously. Verapramil, a new agent used in Europe, has been reported highly successful in converting PST. z~ New methods of conversion include electrical stimulation. Countershock causes rapid depolarization of the entire heart, and allows the sinus node to resume its pacemaking role. Electric cardioversion is useful particularly in those patients whose E C G pattern suggests ventricular tachycardia. Since this method of treatment is so rapid, it is sometimes initial therapy in the most ill patients. 24 Secondary arrhyth12

mias may occur in previously digitalized patients during countershock; thus, extreme care must be taken to ensure the absence of digitalis toxicity or electrolyte imbalance prior to conversion, z5 Intracardiac atrial stimulation also may be effective. This is done with a temporary transvenous pacemaker that may suppress the abnormally conducting tissue by overdriving a different atrial site. z6 Although many infants and some children have only a single known attack of PST, prophylaxis to prevent further attacks is indicated. A low-maintenance dose of digitalis is advised. If PST has occurred as a single isolated attack, therapy should be maintained for 6 months. In those with recurrent attacks, digitalis a n d / o r other drugs found most effective should be continued indefinitely. The prognosis for infants and children with PST is quite good. If the attack occurs before 6 months of age and is not associated with other morphologic or conduction system anomalies, 8 0 % - 9 0 % will have no further problems after initial conversion. Repetitive attacks are more likely to occur in those with structural abnormalities. Recurrence is most likely when Wolff-Parkinson-White syndrome is present.

WOLFF- PARKINSON-WHITE SYNDROME The classic Wolff-Parkinson-White syndrome is the most common form of ventricular preexcitation. The sinus impulse bypasses the normal conduction pathway and activates ventricular muscle earlier than when the impulse travels through normal AV junctional tissue. The abnormal impulse moves over accessory pathways or may progress through normal pathways in an anomalous manner. Wolff-Parkinson-White syndrome occurs in nearly 0.1% of unselected infants and children and is found in 0.5% of children referred for cardiac evaluation, z7 It is more frequent in males than females. There have been enough situations in which multiple family members had Wolff-Parkinson-White syndrome to suggest a familial nature to the anomaly, z8 Approximately 50% of children with the syndrome are reported to have additional morphologic cardiac lesions, z7 They most frequently have Ebstein's deformity of the tricuspid valve. Cardiomyopathy, tricuspid atresia, corrected transposition of the great vessels and dextrocardia also have been reported in patients with preexcitation. Wolff-Parkinson-White syndrome is diagnosed by characteristic E C G findings (Fig. 8 ) : (1) a short P-R interval of less than 0.07 seconds in infants and of less than 0.10 seconds in older children; (2) a prolonged QRS duration of more than 0.06-0.08 seconds in infancy and of more than 0.09 seconds in older children; and (3) notching or slurring (delta waves) in the initial portion of the QRS complex. Additionally, there may be inverted P waves, S-T segment changes and 13

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F[o. 8.--Wolff-Parkinson-White syndrome, type B. tachycardia. Analysis of the precordial leads allows division of the Wolff-Parkinson-White s y n d r o m e into two types: ( A ) large R waves are present in the right precordial leads, a n d ( B ) large negative reflections are seen in the right precordial leads. Casual inspection of the E C G suggests a spurious diagnosis of ventricular hypertrophy. Physiologic studies show m i n i m a l h e m o d y n a m i c changes in patients with the syndrome. T h e r e m a y be early onset and ejection f r o m one or both ventricles, z9 H o w e v e r , m o s t patients have no significant asynchrony and no physiologic i m p a i r m e n t unless a further a r r h y t h m i a Occurs.

P a r o x y s m a l tachycardia is the m o s t c o m m o n a r r h y t h m i a in patients with Wolff-Parkinson-White s y n d r o m e . T h o u g h the m e c h a n i s m for its f o r m a t i o n is not defined entirely, it seems to be caused by a circus m o v e m e n t of the excitatory wave. A s u p r a v e n t r i c u l a r impulse is conducted normally, but reenters the atrium in a retrograde direction via the accessory pathway. 80 T h e t a c h y c a r d i a then m a y persist through a repetitiye mechanism. T h o u g h P S T occurs in a b o u t half of the patients with the syndrome, the incidence of t a c h y c a r d i a in infants with the s y n d r o m e approaches 8 0 % . 31 T h e s e children have p r o b l e m s during the acute attack similar to those with PST. It is only after conversion of the tachycardia to a slower rate that the diagnosis of Wolff-Parkinson-White s y n d r o m e m a y be m a d e . M o r e o v e r , the s y n d r o m e m a y alternate with sinus rhythm. T r e a t m e n t of Wolff-Parkinson-White s y n d r o m e is difficult and unpredictable because the pathology m a y be due to variation in conduc14

tion and refractory period in single or multiple pathways. Treatment of an attack of PST has been described. However, when digitalis is administered, the necessary dose is often larger than that commonly used for the simple variety of PST. If the patient has Wolff-Parkinson-White syndrome but no spells of tachycardia, therapy is not indicated. However, when PST becomes recurrent, a preventive regimen must be attempted. Often quinidine or procaine amide, sometimes converting the syndrome complexes to normal intraventricular conduction, may be helpful in preventing ectopic tachycardias. These drugs work by increasing the refractory period in the accessory pathways. Propranolol also has been effective in treatment and prevention of tachycardia,zz Electrical stimulation has been used successfully for termination of attacks of PST. The mode of action is through premature atrial depolarization by direct atrial stimulation or ventricular stimulation with retrograde atrial activity. In cases recalcitrant to maintenance drug therapy, permanent pacemakers employing radio frequency or magnetic control for use at the start of tachycardia have been successful, even once in an infant. 83 Newer surgical methods also are being investigated. These are (1) creation of complete heart block with insertion of a permanent pacer and (2) interruption of the abnormal pathways. The prognosis for patients with the syndrome depends primarily on the associated lesions, the frequency of attacks of PST and the response to treatment. Problems range from none to sudden death. However, when the syndrome is discovered at a young age, the prognosis is quite good. Intermittency of the syndrome is reported to occur in approximately 30% of cases. 27 In this latter report, when sinus rhythm became established, it persisted to the exclusion of Wolff-ParkinsonWhite syndrome. 27 Furthermore, the presence of sinus rhythm coincided with abatement of PST. ATRIAL FLUTTER Atrial flutter is tachyarrhythmia characterized by regular, atrial, P wave oscillations. Theories to explain its development include those of a circus movement and of a unifocal origin. In circus movement the initiating impulse travels relatively slowly, without having a cessation of activity. Thus, the same impulse may reenter atrial muscle it already traversed and reactivate this area. In the unifocal theory a single atrial focus produces an impulse that spreads uniformly to the atrial periphery. This focus must fire at a high speed for a long period of time and must not produce the picture of another more typical atrial tachycardia. In atrial flutter, actual mechanical atrial contraction occurs. Hemodynamic consequences depend upon the ventricular response. In 15

general, h e m o d y n a m i c s a p p r o a c h n o r m a l as the v e n t r i c u l a r rate approaches normal. W h e n the v e n t f i c u l a r response is relatively slow (less t h a n 1 5 0 - 2 0 0 ) , the cardiac o u t p u t is n e a r l y n o r m a l . T h e pathology of flutter is that of the u n d e r l y i n g disease state. T h e clinical picture is variable. Males are affected with flutter m o r e t h a n twice as c o m m o n l y as are females. T h e a r r h y t h m i a m a y p r e s e n t in utero a n d has b e e n d i a g n o s e d by fetal E C G w h e n the fetal h e a r t beat was noted to be irregular. 34 T h o u g h a few patients with atrial flutter have associated defects, m o s t flutter occurs in infants with n o

TABLE PATIENT

2 . - - P A T I E N T S WITH ATRIAL F L U T T E R O R FIBRILLATION, 1 9 6 7 - 1 9 7 1 : RILEY HOSPITAL FOR CHILDREN

ONSET AGE

SM PM

Birth* Birth*

EC AT

Birth 3 years

JA

OTHER KNOWN LESIONS

ASD 20t None

Predominant Flutter Digitalis Spontaneous

None Myopathy; MI,$ Marfan's 1 month None

TP

12 years

JW

3 years

BT

13 years

EM

5 years

LB

METHOD OF CONVERSION

PRESENT STATUS

Digitalis None

Living 3 months: sinus Living 1 year: WPW syndrome Living 8 months: sinus Died day of surgery

D / C countershock

Living 9 months: sinus

Predominant Fibrillation Myopathy, Quinidine MI* D / C countershock Mlfl: AS§ Ebstein's

Digitalis Digitalis

12 years

Single ventricle RF,¶ MI~t

AG

14 years

RF,¶ MI~t

D / C countershock

KM

14 years

RF,¶ MI~t

D / C countershock

JP

13 years

RF,¶ MIt

Digitalis, D/C countershock

JV

14 years

RF,¶ MI~t

D / C countershock

D/C countershock

*Prenatal. t A S D 2 °, Secundum atrial septal defect. SMI, Mitral insufficiency.

§AS, Aortic stenosis. ¶RF, Rheumaticfever.

]6

Living 1 year: sinus Living 3 years: sinus, prosthetic valve Living 3 years: slow fibrillation Died age 7 years: recurrent fibrillation Living 4 years: sinus, prosthetic valve Living 2 years: sinus, prosthetic valve Living 6 months: sinus, prosthetic valve Living 5 years: slow fibrillation, prosthetic valve Living 3 years: slow fibrillation, prosthetic valve

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Fro. 9.--Atrial flutter-fibrillation (top) and sinus rhythm (bottom). Infant successfully converted with digitalis. morphologic malformations. The arrhythmia is quite rare (Table 2 ) . Symptomatology usually depends on the duration of tachycardia and the ventricular response. Typical presentation is similar to that for PST, except that in over half the cases of flutter diagnosis is made prior to or at delivery. 35 Onset during the ensuing few months also is common. Most flutter that occurs beyond infancy is associated with other cardiovascular lesions which produce large, irritable atria. Atrial flutter must be diagnosed by E C G (Fig. 9). The characteristic atrial oscillations are most clearly seen in leads II, III, a V F and the right precordial leads. These are very regular, have a similar contour in each individual case and occur at an average rate of 300 per minute. Usually, the ventricular response is less rapid but m a y be irregular. In some instances the QRS is widened and repolarization is also affected. There m a y be associated arrhythmias, commonly A V block and atrial fibrillation. Treatment includes agents used for PST. Digitalis seems most efficacious, though less than half the patients have rapid conversion. 3~ Another group of patients may have spontaneous conversion, often after initial attempts at therapeutic conversion have failed. Prognosis relates to the degree of cardiac disability. The prognosis for an infant with flutter and associated cardiac lesions or with atrial flutter-fibrillation is very poor. Most of this group do not survive infancy. In a series of 27 infants without either of these conditions, 3 died. 35 If an infant lives beyond his 1st year, chances for asymptomatic survival are good. The prognosis for older children with "acquired flutter" rests almost exclusively on the associated cardiac problem. ATRIAL FIBRILLATION This is rhythm in which there are continuous, irregular atrial oscillations associated with a variable degree of A V block, resulting in an 17

irregular ventricular rhythm. Almost always there is abnormal atrial tissue, with dilatation and often disease of the sinus node/G An episode of atrial fibrillation may be initiated by multiple atrial premature beats and usually is sustained by multiple reentry circuits. Rather marked hemodynamic alterations contribute to the clinical picture in this arrhythmia. Important pathophysiologic mechanisms are (1) irregular, ineffective atrial contractions which impair ventricular filling; (2) irregular ventricular rhythm in which the altered end-diastolic volume produces an abnormal stroke volume; and (3) extreme tachycardia in response to exertion, resulting in a restricted cardiac output during exercise. Added to these are the usual myocardial and/or valvular lesions, also causing an alteration of hemodynamics. Atrial fibrillation rarely is encountered in pediatrics; when discovered, it almost always is associated with severe underlying cardiac pathology. The clinical features depend largely on the presence of the associated lesions. It may occur in the "paroxysmal" type, and in these few cases the hearts usually are normal morphologically. Fibrillation commonly is of the "permanent" type, and most often is found with mitral valve disease (postrheumatic) and atrial septal defects (see Table 2). Those with septal defects are usually adult patients. Symptoms similar to those of PST may occur with fibrillation, but usually the clinical status is that caused by the total cardiac problem. From the arrhythmia standpoint, slower ventricular responses are associated with less severe symptomatology. During exercise, patients with fibrillation develop extreme tachycardia. This may partly explain the poor tolerance to stress exhibited by these patients. An "irregular irregularity" to the pulse and a pulse deficit suggest the diagnosis. Electrocardiography confirms the presence of atrial fibrillation (Fig. 10). The atrial oscillations, ranging from 400-700 per minute, are much more rapid than flutter waves. The deflections vary in size, shape and regularity. They are seen best in right precordial leads. Ventricular deflections show variation in the QRS complexes and R-R interval. When the ventricular response is rapid (approaching 150), there is often aberrancy, with widening of the QRS complexes. Treatment must begin with an appraisal of the total cardiac condition. Causative factors and the presence or absence of congestive failure are initial considerations. Almost all children with fibrillation have had congestive failure. Digitalis then should be used, not only for its inotropic effect but for control of rapid ventricular response. This is accomplished through an indirect vagal effect and a direct effect on the AV junction. Maximal therapeutic effect is said to occur when the apical rate drops to 70-90 and the pulse deficit disappears. Occasionally, conversion occurs during digitalization, but usually quinidine or countershock is necessary. Before such measures are employed, it must be decided whether conversion to sinus rhythm is indicated. Generally, 18

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FIG. 10.--Atrial fibrillation with slow ventricular response. those in whom fibrillation is chronic and due to severe degrees of myocardial damage a n d / o r enlargement are difficult to convert and even more difficult to maintain in sinus rhythm. Furthermore, the synchronized atrial addition to cardiac output will be no more than 1 0 % 15%. Quinidine is successful in converting 5 0 % - 8 0 % of patients, while direct current countershock has been found effective in up to 90% .37 After conversion, quinidine maintenance usually is employed. Prognosis of atrial fibrillation in children is generally poor, depending to a large extent on the underlying pathology. Most children develop fibrillation in response to severe rheumatic valvular disease. In an early study, Gibson reported 14 of 21 children with rheumatic heart disease and fibrillation dying during the study period, with average survival less than 2 years. 38 Currently, better methods of therapy and surgical intervention have appreciably lowered mortality (see Table 2).

VENTRICULAR PREMATURE CONTRACTIONS Premature ventricular contractions (PVCs), sometimes called "extra systoles," constitute the most common ectopic rhythm. These beats disrupt the normal mechanism and arise from cells in the His-Purkinje system. No single mechanism can explain the occurrence of PVCs. The great majority are triggered or produced by the preceding beat. The reentry theory illustrates this concept. The premise states that in the 19

myocardium are one or more areas of tissue with slower refractory states. Following a normally conducted beat, this tissue remains refractory and is not responsive to the next impulse until a later time. It may then serve as an ectopic focus from which the impulse then proceeds through the heart as a premature beat. Another commonly accepted theory is that of an ectopic focus. This theory is attractive, since any alteration of the variables normally controlling conduction may be enough to trigger an ectopic site. Parasystole, comprising yet another theory, has a regular and persistent focus coexistent with the dominant sinus pacemaker. This extra focus usually is located deep in ventricular tissue and normally is protected from depolarization by the normally conducted impulse. Thus, the parasystolic focus usually initiates separate impulses. Normal cardiac function is altered by premature beats. The origin of the impulse and the time of appearance in the cardiac cycle determine the speed and sequence of conduction. Generally, the extent of hemodynamic alteration depends upon the degree of prematurity, frequency, and site of ectopy. 14 Hemodynamic effects relate to the location of the PVC in the cardiac cycle. Thus, the stroke volume varies inversely with the degree of prematurity of the beat; i.e., the earlier the beat, the more significant is the stroke deficit (Fig. 11 ). The first beat following the pause after a PVC may have greater than normal contractility and stroke volume; however, the total effects usually are negative. Differing from this general finding is the fact that in newborns the normal contraction following a PVC does not have a pressure higher than normal. 39 The frequency of PVCs is significant, Numerous premature beats, especially those in couples or groups, may lower cardiac output seriously. The site of origin of the PVC also is important. Beats arising from the base of the left ventricle result in lowest systemic pressures; those from the left ventricular apex are next in alteration; and those from right ventricular sites cause least alteration. Ectopic beats are less effective than those normally conducted, producing contractions before the ventricles are completely filled. This results in a lowered cardiac output with a normal expenditure of work, thus decreasing myocardial efficiency. Premature ventricular beats occur at all ages. In pediatric practice PVCs are seen most commonly during infancy and adolescence. Though most adults with premature beats have underlying heart disease, PVCs usually are found in children with otherwise normal hearts. Causative factors include inflammatory and myocardial disease. The following alterations in environment may predispose to PVCs: (1) hypoxia, (2) autonomic effects, (3) visual reflexes, (4) catecholamine stimulation and (5) changes in acid-base or electrolyte balance. Drugs may also stimulate PVCs. Premature contractions are more frequent at slow heart rates, and are usually abolished by exercise. Moreover, 20

,ll

|

,

FIG. 11.--Effect of ventricular prematures on left ventricular pressure. Lowest pressure achieved with prematures; highest pressure with normal beat following premature contractions. when exercise provokes P'v Cs, additional further heart disease should be suspected. Usually children with PVCs have no symptoms. Occasionally, there are complaints of "palpitations," precordial pain or anxiety and sweating. Those who have symptoms usually have multiple PVCs. There may be no physical findings, especially if the premature beat is a late one that is strong enough to produce a palpable pulse. Normal rhythm often is interrupted by the PVC, which is then followed by a "compensatory pause." Auscultation may reveal a variance in the heart sounds as well as in the rhythm. The E C G is diagnostic (Fig. 12). Salient features are prematurity of the beat and bizarre configuration of the QRS complex. This QRS is generally of greater duration than the normal complex. The S-T segment may also be unusual. Coupling usually refers to groups of complexes with a normal beat and early PVC; "bigeminy" is similar, but the premature beat is later in the cycle, producing a palpable, but weaker pulse. 21

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~!.Iiiiiti~it!!fil Fz6. 12.--Sinus beat followed by premature ventricular contraction-bigeminy. The clinical significance of the different types of premature beats is not known definitely. Certain characteristics suggest a more serious situation: (1) development with exercise; (2) a very wide QRS complex; (3) multifocal origin of PVCs; and ( 4 ) groups of premature beats. In addition to the greater likelihood for myocardial disease, these conditions may herald future deleterious arrhythmias, such as ventricular fibrillation. Treatment usually is not necessary. If there is underlying heart disease and the premature beats produce symptoms or are likely to trigger more severe arrhythmias, treatment should be undertaken. Elimination of any environmental cause (as ingestion of epinephrine compounds) or treatment with mild tranquilization are safest modes of therapy. Commonly used antiarrhythmic drugs are quinidine sulfate, procaine amide, and diphenylhydantoin. Prognosis is related significantly to the underlying cardiac condition. In most children PVCs have no known cause. They have a variable course: they may persist for years, disappear or even become frequent enough to cause symptoms or trigger further arrhythmias. 22

VENTRICULAR TACHYCARDIA Ventricular tachycardia ( V T ) is a rare but serious arrhythmia. When 6 or more ventricular premature beats occur in succession, they constitute a paroxysm of VT. 14 Such attacks are often preceded by various combinations of ventricular premature beats. The mechanisms underlying production of V T are similar to those said to cause PVCs: ectopic focus, reentry and parasystole. These may alter conduction a n d / o r automaticity. The most important factor leading to V T is the relationship of onset of attack to position in the cardiac cycle. Paroxysms may be initiated if ( 1 ) ectopic activity occurs during the vulnerable phase of the absolute refractory period; (2) the ventricle becomes responsive to subthreshold stimuli during a hyperexcitable period; or (3) the threshold for successive premature beats is lowered following a PVC. Actually, different mechanisms may be operative at different times. 4° The hemodynamic effects of V T are similar to those of PST. There is a fall in cardiac output and blood pressure. Actually, V T produces a greater charge than does PST. The severity relates to the underlying state of the myocardium, the duration of tachycardia and the absolute rate. Ventricular tachycardia is a rare arrhythmia in pediatrics. It has been seen with congenital defects, infections, hypoxia, electrolyte imbalance and severe myocardial disease. However, in most cases etiology is obscure. The clinical picture resembles that of PST, but usually is more severe. It often occurs in those with underlying cardiac disease and usually produces more significant hemodynamic change. There may be palpitations, substernal pain, dyspnea, syncope, shock or congestive failure. Short episodes may produce little more than discomfort, even when repetitive. Attacks lasting longer than 24 hours usually cause significant hemodynamic alterations and seldom abate spontaneously. Physical examination reveals a fast (more than 150) rate and almost constant rhythm. Heart sounds often vary in intensity. The E C G is necessary when diagnosing V T (Fig. 13). However, the diagnosis may be difficult, since PST and V T are very similar in appearance. Usual criteria for V T are as follows: (1) beats are ectopic and conform to isolated PVCs seen before the paroxysm; (2) the QRS is wide and aberrant; (3) the relationship of the first beat of the paroxysm and preceding normal beat is the same as with an isolated PVC; and (4) the ventricular rate of over 150 is almost regular, faster than the atrial rate and independent of atrial control. TM If diagnosis is uncertain and the clinical condition warrants, more precise diagnosis may be made by bundle of His recording. This technic can differentiate between V T and supraventricular tachycardia by the position of the His spike relative to the atrial and ventricular contractions. 23

iliiiii i[iiii

~

FIG. 13.--Ventricular tachycardia; AV dissociation also present.

Treatment of V T depends on the seriousness and urgency of the condition. Variables to be considered are clinical status and type and duration of the tachycardia. Isolated short runs of single focus V T are probably benign, but prolonged paroxysms or recurrent paroxysms deserve treatment. Drug therapy may be reasonably effective. Intravenous lidocaine may control the tachycardia, but cannot be used for maintenance. Quinidine and procaine amide can control 7 0 % - 8 0 % of V T in adults; however, large doses of procaine amide have been necessary in some recalcitrant children. 41, 4z In one case propranolol was added to control the tachycardia. 4z Unless congestive heart failure is present, digitalis is contraindicated in treatment of VT. Electric countershock, which is usually effective in terminating a paroxysm of VT, usually is reserved for a severely ill child or one in whom drug therapy has been ineffective. Other modes of therapy not reported in children are the "precordial thump" and pacing. Pennington et al. converted 12 episodes Of V T by a sharp blow to the chest by the physician's hand. 4a Overdrive pacing also has been effective. The prognosis is variable. In the presence of associated cardiac disease there is at least a 50% mortality. Most infants and children with V T have otherwise normal hearts; however, there is always a risk of ventricular fibrillation and death. VENTRICULAR FIBRILLATION ( V F ) Ventricular fibrillation is a most serious cardiac arrhythmia. It is a terminal event in at least half the patients dying of cardiac disease, and may also lead to ventricular asystole. Ventricular fibrillation is not always a final event in a patient with an irreparably damaged heart; patients with V F have been resuscitated and even discharged from acute care. Ventricular fibrillation usually occurs when the automaticity of ventricular pacemaker tissue is increased, often in a seriously damaged 24

heart. There are numerous theories regarding electrophysiologic initiation and maintenance of VF. A current unifying concept is that V F is initiated by impulses arising from one or more loci; however, these impulses cannot be normally conducted. Areas of refractory tissue result in disorganized conduction and establish reentry circuits. The abnormal conduction and excitability perpetuate the arrhythmia. TM The fibrillation threshold significantly increases during metabolic acidosis. 44 Hypoxia, anesthesia, cardiac surgery and myocardial injury have produced VF, especially in the presence of preexisting cardiac disease. Ventricular fibrillation has occurred during hypothermia (at body temperature below 28 ° C) and following chest trauma. Electric current also may produce fibrillation; lightning and improperly grounded electrical devices may cause VF. During countershock an impulse during repolarization may produce VF. The mechanism usually postulated for spontaneous development of V F is that of a PVC falling on the T wave downslope of the preceding beat. The hemodynamic consequence of V F is a rapid decrease of effective circulation. A few cases may revert spontaneously; however, almost all quickly progress to a fatal outcome. Though the atria may continue to contract, they propel at most 10% of resting cardiac output into the pulmonary circulation and even less into the aorta. 45 Following conversion to a normal rhythm, hemodynamic alterations persist, though there is a return to near normal function when the heart is not damaged severely. Clinically, the diagnosis must be suspected in any patient who has a sudden loss of pulse, heart sounds and blood pressure. Obviously, those with previously impaired hemodynamics or severe arrhythmias (as ventricular tachycardia or heart block) are at greater risk than those with normal hearts. The E C G (Fig. 14) shows bizarre ventricular osFIG. 14.--Complete AV block developing ventricular tachycardia, followed by rapid and slow, coarse VF.

2

25

cillations. The waves are coarse, irregular and occur at a rate of 1 5 0 300. Occasionally, a progression of VT-flutter-fibrillation may be observed. The ventricular waves may then proceed through coarse fibrillation to fine fibrillation to terminal, slow, aberrant complexes. Active and rapid treatment is imperative. T o be effective, defibrillation must begin within 4 minutes of onset of fibrillation. TM Direct current cardioversion, closed-chest compression and artificial respiration all may be necessary. The closed-chest (cardiac) massage may not terminate fibrillation, but is effective as a t e m p o r a r y means of assisting circulation until countershock therapy can convert the heart. Attention also must be paid to possible hypoxia and acidosis. A very important aspect of therapy is prevention or prophylaxis. Care must be taken when subjecting an3t patient with severe cardiac disease a n d / o r arrhythmia to an event potentially stressful to the heart. Monitoring is essential, especially during induction of anesthesia and during surgery. Prognosis depends on the underlying state of the heart and on the immediacy and efficacy of treatment of the attack. Analysis of adult mortality rates demonstrates an especially p o o r outlook for patients in congestive heart failure prior to the bout of VF, despite temporary conversion.

ATRIOVENTRICULAR BLOCK (AVB) Atrioventricular heart block refers to a disturbance in the A V conduction system. This is an abnormal situation in which the atrial impulse is delayed or completely fails to reach the ventricles. The "block" may be partial ( I o or 2 °) or complete (3 o ). FIRST DEGREE A V B (1 o A V B ) This is a partial A V B in which the P - R interval is greater than normal. Normal values vary with age and heart rate (Table 3). As the

TABLE

3 . - - U P P E R L I M I T OF NORMAL P - R INTERVAL IN SECONDS PULSE

Age Years

< 70

70-90

90-110

110-130

> 130

0-1½ 1½-6 7-13 > 13

0.16 0.17 0.18 0.19

0.15 0.165 0.17 0.18

0.145

0.135 0.145 0.15 0.16

0.125 0.135 0.14 0.15

0.155

0.16 0.17

Modified from Ashman & Hull, Essentials of Electrocardiography for the student and practitioner of medicine, Macmillan Co.

26

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block becomes more severe, there is prolongation of the conduction time; however, there are no dropped beats. Bundle of His recordings have shown the block to occur in the intraatrial region, A V tissue or bundle of His. Delay in the AV tissue is most common. Pathologic specimens have shown abnormalities caused by inflammation, degenerative disease and congenital anomalies. Generally, 1 °AVB causes no hemodynamic impairment. Certain physiologic adjustments may shorten the P-R interval; in response to assumption of the upright position or during exercise, the P-R interval may normalize. These changes reflect increase in sympathetic tone and abolition of vagal influence. First degree A V B is relatively common in pediatrics. Prolongation of the P-R interval is commonly present during active carditis caused by rheumatic fever. There may be 1 ° AVB in 60% of such cases. The incidence approaches 30% in rheumatic fever without carditis. 46 Furthermore, 2 % of normals, 4 0 % of those with febrile illnesses, 5 % of cases with glomerulonephritis, and 1 0 % - 2 0 % of children with atrial septal defects have 1 ° AVB. Prolongation of P-R is almost universal in those patients receiving digitalis preparations. Thus, it is hazardous to include 1 ° A V B as a definite criterion for the diagnosis of rheumatic carditis. However, a P-R interval changing during the course of the disease has more significance. The clinical picture reflects the underlying cardiac condition. It is almost impossible to diagnose 1 o AVB without an ECG which shows regularly recurring, normally shaped P waves (Fig. 15). The P-R interval is prolonged and there is a normal AV relationship. First degree A V B requires no treatment. Generally, the prognosis is 27

excellent. When it occurs during rheumatic carditis, 1 ° AVB has no direct relationship to ultimate cardiac prognosis. However, a few cases have been documented in which lesser degrees of block have evolved into more advanced AVB. SECOND DEGREE A V B ( 2 ° A V B ) Second degree AVB is a form of partial heart block in which some atrial impulses fail to reach the ventricles in a heart usually paced from the sinus node. Classically, the 2 ° A V B is divided into type I (Wenckebach) in which there is progressive prolongation of the P-R interval until a ventricular beat is dropped, and type II (Mobitz II) in which the P-R interval is constant and there is a regular dropping of a ventricnlar beat. More recently o n the basis of E C G and bundle of His recordings, there has been proposed a new classification based upon duration of the QRS complexes. 47 Current pathophysiologic studies center upon localization of the site of delay. The block may occur anywhere from the A V node to the major bundle branches. It has been thought that most cases with type I block have delay in the AV tissues, while type II block occurs at a site distal to the bundle of His. Physiologic effects depend primarily upon the ventricular rate; if this is reasonably rapid, there are only slight alterations in the hemodynamics. If the rate is slow, the stroke volume will be large. Those ventricular beats preceded by a relatively short P-R interval have the greatest pressure and volume. A heart with chronic block and slow rate may have a relatively high systemic pressure. However, following the acute development of block, the pressure may transiently drop (Fig. 16). Sympathetic stimulation (as with exercise) a n d / o r reduced vagal tone may produce a more normal rhythm and speed up the atrial and ventricular rate. The incidence of 2 ° AVB in infants and children is relatively rare. It may be observed as an isolated entity, but usually is acquired from infections (as rheumatic carditis), severe hypoxia or following cardiac surgery. It may be associated with congenital defects, the most common being corrected transposition of the great arteries. The clinical picture relates to underlying cardiac disease and degree of hemodynamic impairment caused by the arrhythmia. In 2 ° AVB with slow cardiac rates, there may be dizziness or syncope. Physical examination may disclose varying heart sounds and murmurs o r gallops caused by the altered stroke volume. The diagnosis of 2 o AVB is established by the E C G (Fig. 17). The Wenckebach type has a progressive lengthening of the P-R interval until no QRS complex follows the P wave. The following beat has the shortest P-R interval. There also may appear to be a shortening of the 28

i m

FXG. 16.--Partial (2:1 ) AVB acquired during catheterization. Note wider pulse pressure in A; after spontaneous conversion (B) there is smaller pulse pressure but higher absolute pressures. Patient also had severe congenital heart disease.

cycles. In type II the P-R interval is constant. However, at certain set intervals a ventricular beat is dropped, resulting in a rather constant atrial-ventricular ratio. Frequently, the QRS complex is widened, indicating an intraventricular conduction problem. Treatment of 2 ° A V B generally consists of treatment for the underlying condition. If the ventricular rate becomes slow, cardiac output may be decreased, necessitating therapy with atropine sulfate, isoproterenol or even pacemaker stimulation. The prognosis for patients with 2 ° A V B is related directly to any underlying pathology. A patient with carditis may make an eventual complete recovery. However, if block is persistent it may cause problems eventually, even if the arrhythmia is an isolated defect. Some observers feel that those with wide QRS complexes are more prone to FIo. 17.--Apparent 2°AVB with 2:1 AV response. With this prolonged P-R it is doubtful that there is definite capture.

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serious disturbances. 47 There has been a progression of 2 ° AVB to complete block. This has been reported during infancy. 48 At this point low cardiac output or Stokes-Adams attacks may occur and cause the patient to become seriously ill. COMPLETE HEART BLOCK Complete AVB (3 ° A V B ) rarely is seen in routine pediatric practice. However, it may cause profound cardiovascular alterations and symptomatology. Loosely defined, complete block consists of independent atrial and ventricular firing, with the ventdcular rate considerably lower than the atrial rate. Conceptual knowledge regarding electrophysiology has been cladfled by recent technics employing microelectrode and bundle of His studies. Meticulous histologic studies of hearts at postmortem examination have shown the block to occur proximal to the AV node, in the AV tissue, proximal to the bundle of His or distal to the bundle of His. Congenital 3 o A V B may occur as an isolated entity. There may be complete absence or fibrotic degeneration of the continuous pathway at any site between atria and bundle of His. Lev et al. demonstrated the block to occur proximal to or at the A V node in 6 of 7 patients examined at autopsy. They postulated the block to be caused by malformation of the central fibrous body during absorption of the bulbus. 49 Other histologic investigations of "congenital" 3 ° A V B have shown absence of a portion of the A V node and fibrosis of various parts of the conducting pathway. Hearts with "acquired" 3 o A V B have shown inflammation and degenerative, traumatic and infiltrative lesions. It may be difficult to decide whether fibrosis represents a congenital deformity from an in utero condition or manifests extrauterine infection. The hemodynamics of 3 ° A V B depend mainly upon the site of block, ventricular rate and status of the total heart. In general, the more proximal the block, the more normal are hemodynamic and physiologic responses. If the conducting system is blocked before the bundle of His, negation of parasympathetic stimuli or sympatheti c stimulation (as with exercise) often accelerate heart rate by 1 0 % 3 0 % , However, this augmentation rarely exceeds 10% when the block is more distal. Though cardiac output may drop 50% after acute development of 3 ° AVB, output-gradually returns toward low normal values. Compensatory mechanisms include prolonged diastolic filling, very large stroke volumes, widened pulse pressure and high degree of oxygen extraction by the tissues. These factors tend to minimize development of congestive heart failure. Concurrently, myocardial contractility usually is normal. Though exercise and stress may increase rate and cardiac output, the increment is small. Hemodynamics are relatively normal in those with 3 ° AVB and faster ventricular rates. 30

Stepwise acceleration of the rate by use of pacemakers generally increases cardiac output until rates over 100 are reached. Synchronization of atrial and ventricular beats to provide proper ventricular filling from the atria has only a small effect on output. When done experimentally, output has increased only 7 % - 8 % .50 Complete heart block is being seen more frequently in pediatrics. This is due to (1) an awareness of the problem; (2) an increased number of patients undergoing cardiac surgery for repair of complex lesions; and (3) better methods of diagnosis and treatment that prolong the life of patients with 3 ° AVB. The etiology of complete block is not known always. Generally, it is classified as acquired or congenital. The most frequent and serious form of acquired 3 ° A V B is that following cardiac surgery. This arrhythmia most commonly occurs during repair of lesions requiring placement of large patches (ventricular septal defect, tetralogy of Fallot), dissection of pathologic muscle (subaortic stenosis, cardiomyopathy) o r placement of sutures near the AV node (Mustard's complete repair of transposition of the great arteries). Myocardial inflammation, as carditis of acute rheumatic fever, is probably the next most common cause for acquired 3 ° AVB. This arrhythmia also may occur during the course of viral or diphtheritic myocarditis. Transient block also may arise from severe metabolic problems, as with neonatal hypocalcemia a n d / o r acidosis. It also has been associated with infiltrative disease and tumors of, or contiguous to, the heart. Congenital corrected transposition of the great arteries was found in 8 of 18 cases of congenital complete block in one series. ~z Large atrial septal defects and endocardial fibroelastosis also are commonly found in association with 3 ° AVB. There are no morphologic lesions in the hearts of approximately half of those with congenital complete block. The clinical picture has great variation. Those with acquired 3 ° AVB and those with associated congenital defects have a more serious course. The most significant symptom is a Stokes-Adams attack, manifest by transient loss of consciousness. There may be all gradations of severity from dizziness to death during such an episode. Other possible symptoms are those associated with congestive heart failure and intolerance of stress. This latter is illustrated by the severe illness of infants or patients in the immediate postoperative phase of cardiac surgery. These patients are often gravely ill when their hearts cannot respond with the usual compensatory tachycardia. Physical examination may reveal evidence of failure or reflect the findings of additional malformations. Third degree AVB always results in a slow pulse which usually appears regular. The rate is in the range of 4 0 - 8 0 , with only slight to moderate acceleration after exercise. Pulses are often bounding. Sharply rising venous pulses (cannon waves) that are not related to ventricular activity may be seen. There 31

is usually variation in heart sound intensity, and third a n d / o r fourth sounds are often heard. Almost all patients with 3 ° A V B have ejectiontype murmurs varying in intensity from beat to beat. These murmurs are thought to reflect the large, but variable, stroke volume crossing the semilunar valves. Middiastolic murmurs, representing large flow across normal A V valves, may also be heard. These systolic and diastolic murmurs can be heard in the absence of associated lesions. Moreover, 60% of children with isolated 3 ° A V B have cardiomegaly upon x-ray examination. The E C G is vital to diagnosis (Fig. 18). The ventricles are regularly beating at slow rates, while the atria are beating normally. There is dissociation between atrial and ventricular firing. In almost half the cases the P-P interval containing a QRS complex is shorter than in those not containing a ventricular complex. The R - R interval is usually regular. The ventricular complexes are of two main types: (1) normal width and duration, thought to represent block above the His bundle, and (2) notched, slurred and prolonged, probably representing idioventricular pacemaking with perhaps associated bundle branch block. The site of block m a y be better determined by bundle of His study. Generally, those with normal QRS complexes have been shown by His recordings to have block proximal to the bundle of H i s . 5z These are almost always congenital in etiology. Patients with surgically acquired 3 °AVB demonstrate a block distal to the bundle of His and have more aberrant QRS complexes. Treatment usually is instituted when there are symptoms of low FIG. 18.--Complete (3 °) AVB. The narrow QRS complexes indicate a focus above the bundle of His and often are found in congenital block, such as this case. ~~ti:~-~-I~T-~:~ii~iiit!iq q 1 Vl

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cardiac output or Stokes-Adams attacks. Almost all patients with acquired 3 °AVB require treatment. This is so especially in those who develop block during cardiac surgery. Many patients with 3°AVB never have symptoms and require no therapy. Most of these asymptomatic children have congenital 3 °AVB and otherwise normal hearts. Treatment of 3°AVB is less than satisfactory. When block is acquired, initial therapy is directed at the acute process. Treatment of hypoxia and acidosis may improve conduction. In those with acutely acquired block, steroids may help reduce local inflammation and edema, thus restoring more normal conduction. Atropine sulfate may be transiently successful in increasing rate, but only in those with pacemaking from a site proximal to the bundle of His. Sympathomimetic amines, especially isoproterenol, are useful in increasing automaticity and also may increase output through inotropic action. Unfortunately, these drugs are difficult to administer. Furthermore, there is the danger of increased myocardial irritability; this may then precipitate VT and// or VF. Prolonged use of sympathetic amines may result in tachyphylaxis. Also, areas of myocardial fibroses have been demonstrated in laboratory animals subjected to prolonged isoproterenol administration, and epinephrine overdosage has caused myocardial injury. 53 Glucagon has also been shown to increase rate and cardiac output transiently when given intravenously. 54 However, the drug is experimental, must be given parenterally and has very short duration of response. Though digitalis may decrease rate slightly, it generally increases cardiac output and should be administered in cases of congestive failure. It is especially effective in those with fixed rate pacemakers who have continuing cardiac failure. 55 Artificial pacemakers are the most effective mode of therapy. These may be temporary or permanent. Temporary pacemakers may be inserted transvenously or attached to the epicardium at surgery. They are extremely beneficial during the acute phase of acquired 3 °AVB, and greatly facilitate the postoperative course. Since many patients with 3°AVB have complications during anesthesia and surgery, it would be advisable also to insert a pacemaker prophylactically before any elective surgical procedure such as permanent pacemaker implantation. ~6 Permanent pacing is the treatment of choice in all patients with Stokes-Adams seizures and in most patients with surgically acquired 3 °AVB, especially those with residual cardiac defects. This has been accomplished effectively in infants as small as 8 lb at Riley Hospital for Children. The most practical unit is a fixed rate pacemaker. Unfortunately, battery life does not exceed 2 years, so that surgery for battery replacement must be performed every 18-24 months. Currently, atomic powered pacemakers with a longevity of at least 5 years are being investigated. The prognosis for infants and children is variable. When 3 °AVB is acquired from a cause other than cardiac surgery, complete recovery 33

is probable. Block resulting from surgery carries a poor prognosis; early reports cited mortality as high as 80% .57 The early postoperative period is especially dangerous. Those with residual defects are at greatest risk. The high postoperative mortality has prompted use of pacemakers--both temporary and permanent. Late reversion to a more normal conducting system has been reported up to 9 months postoperatively, but most convert by one month. Unfortunately, a few patients with early supraventricular pacing may develop 3 °AVB as a late occurrence. The sudden onset of 3 ° A V B may even cause death. Generally, with careful early control and judicious use of long-term pacemaking, the mortality rate in postoperative 3 °AVB is now in the range of 2 0 % . Congenital 3 ° A V B carries a better prognosis. This is partly related to the intrinsically faster site, usually proximal to the bundle of His. Especially worrisome are infancy and other periods of stress. Of great importance is the presence or absence of associated cardiac defects. If there are no other lesions mortality approaches 5 %, while the presence of further cardiac defects raises mortality to 50% .~z Thus, it seems advisable to catheterize patients with 3 °AVB; if further defects are present they should be corrected if possible and permanent pacemaking must be considered.

BUNDLE BRANCH BLOCK Bundle branch block is an electrophysiologic condition with intraventricular conduction delay. The E C G has a widened (slowed) QRS, which usually is slurred or aberrant in configuration. The arrhythmia is classified as right or left bundle branch block. RIGHT BUNDLE BRANCH BLOCK Right bundle branch block is subdivided into incomplete ( I R B B B ) and complete ( R B B B ) block. Both of these are fairly common in pediatrics. Incomplete block is also called right-sided intraventricular conduction delay and also may be named for the E C G pattern of the right precordial leads, i.e., "rsR' or rsr'" (Fig. 19). Other criteria for diagnosing IRBBB include a QRS of normal duration (always less than 0.10 seconds) and terminal slowing of right-sided vectors. This may produce right axis deviation and criteria for right ventricular hypertrophy. Some observers consider all cases of I R B B B to reflect ventricular hypertrophy; however, this concept is not universal. Electrophysiologically, there is mild slowing of conduction through the right bundle. The condition is a graphic one and does not alter cardiac hemodynamics. Many normal infants have IRBBB, and this may persist until 2 - 5 years of age. The E C G usually is considered abnormal only when the terminal R' is quite large. Incomplete block also may 34

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I FT-,I L.w r4v: FIG. 19.--Incomplete right bundle branch block. This tracing is compatible with right ventricular hypertrophy. The patient had an atrial septal defect.

be present in conditions of altered chest contour, as "straight-back syndrome," pectus excavatum, asthma and cystic fibrosis. Incomplete block commonly is associated with congenital heart disease; over 90% of patients with atrial septal defects have a typical rsR' complex. Interestingly, only half of those who undergo repair of this defect lose the IRBBB. 58 Patients with coarctation of the aorta frequently have an rsr' picture, perhaps due to abnormal conduction into the hypertrophied posterobasal portion of the left ventricle. This, then, is not a conduction delay, but rather a manifestation of left ventricular hypertrophy. Incomplete block is a benign entity that requires no treatment and carries an excellent prognosis. Complete bundle block is a conduction disturbance seldom seen in pediatrics except after surgical trauma. The diagnosis rests upon the ECG which has ( 1 ) QRS duration greater than 0.10 seconds; (2) wide slurred S in I and V6; and (3) slurred R' in III, aVR and V1 (Fig. 20). 59 This reflects terminal intraventricular slowing, due to unopposed right-sided forces. There usually is right axis deviation and an appearance of right ventricular hypertrophy. However, it is impossible to interpret true ventricular hypertrophy in a patient withRBBB. Complete bundle block causes no hemodynamic alterations. It may be found in conditions causing right ventricular hypertrophy, but almost always is seen following intracardiac surgery. Those undergoing tetralogy of Fallot repair usually develop RBBB, while those with ventricular septal defect or pulmonary stenosis have a varying incidence of postoperative RBBB. The etiology for the conduction deficit is most probably the ventricular myotomy. 60 Complete bundle block is relatively benign. Of course, if there should develop a left branch block as well, the condition could lead to complete heart block. The prognosis in patients who postoperatively dem35

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Fallot. onstrate R B B B with left axis d e v i a t i o n ( c a u s e d p r o b a b l y by left " h e m i - b l o c k " ) h a v e a m o r e g u a r d e d p r o g n o s i s . This g r o u p has a high incidence of late c o m p l e t e h e a r t b l o c k o r e v e n m a y h a v e S t o k e s - A d a m s seizures or s u d d e n death. 61 A n a t t e m p t m u s t be m a d e at s u r g e r y to p r e v e n t this c o n d u c t i o n d i s t u r b a n c e . O t h e r w i s e , t r e a t m e n t consists of careful o b s e r v a t i o n and p a c e m a k e r i m p l a n t a t i o n as necessary. L E F T BUNDLE BRANCH BLOCK

(LBBB)

L e f t b u n d l e b r a n c h b l o c k is s e l d o m seen in pediatrics. It is c a u s e d by a deficit in c o n d u c t i o n t h r o u g h all or p a r t of the left bundle. T h e diagnosis is o n e b a s e d on E C G criteria of ( 1 ) Q R S d u r a t i o n greater t h a n 0.10 seconds; ( 2 ) a s u p r a v e n t r i c u l a r p a c e m a k e r ; ( 3 ) b r o a d , slowly inscribed R waves in I, V 5 , V 6 ; ( 4 ) absent Q w a v e s in I, V 5 , V 6 ; ( 5 ) b r o a d and slurred S w a v e s in V 1 , a n d V 2 ; a n d ( 6 ) S - T a n d T segments opposite to the m a j o r Q R S deflection (Fig. 2 1 ).62 L e f t b u n d l e b r a n c h b l o c k p r o d u c e s little alteration in n o r m a l h e m o d y n a m i c s . T h u s , patients with L B B B h a v e few signs. If the b l o c k o c c u r s in a diseased FIG. 21.--Left bundle branch block. Patient is postoperative.

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heart, as usually is the case, the clinical and hemodynamic picture is caused by the associated pathology. Left bundle branch block may alter the heart sounds, resulting in a paradoxically split second sound and soft first sound. Left bundle branch block rarely is encountered as an isolated "congenital" anomaly, but more often is acquired during the course of myocarditis or drug therapy. It also has been found in patients with other congenital heart defects, as single ventricle, eridocardial fibroelastosis, Ebstein's disease and following surgical repair of subaortic stenosis. Generally, the prognosis for patients with LBBB is good. Treatment is not indicated. DIGITALIS TOXICITY

Digitalis intoxication is included in this monograph since cardiac glycoside toxicity is a common cause of arrhythmias. Despite the fact that digitalis is used to treat certain arrhythmias, overdosage can produce almost every type of arrhythmia. The frequency of intoxication relates to the narrow range between maximum drug efficacy and toxicity. Full digitalization usually occurs when 6 5 % - 7 0 % of the toxic dose is administered; early signs of toxicity are seen at 40% of the lethal dose. 63 Though digitalis intoxication may be encountered after accidental ingestion of the drug, it usually is seen in infants and children receiving cardiac glycosides therapeutically. Certain general factors modify tolerance to digitalis: (1) amount of digitalis in the body; (2) physiologic adjustments; (3) electrolyte alterations; (4) sympathetic and parasympathetic tone; and (5) presence of other drugs. In pediatric practice there are especially important situations that predispose to digitalis toxicity: (1) renal insufficiency--70%-80% of administered digitalis is excreted through the kidneys; (2) myocardial abnormality--myocarditis increases cardiac irritability; (3) hypoxia--there is increased myocardial retention of digitalis, correlating with the elevated risk of toxicity in cyanotic patients and those with cor pulmonale; (4) hypokalemia and hypomagnesemia--this may be exaggerated by concurrent use of diuretic agents; and (5) prematurity--perhaps due to immaturity of the sympathetic and parasympathetic system. It is difficult to diagnose digitalis toxicity from the clinical picture, especially in infants and small children. The nausea and vomiting so frequently encountered may also be a manifestation of congestive heart failure. Worsening of failure also may occur with digitalis toxicity. Slowing of pulse and/or arrhythmias suggest the diagnosis, but an ECG is mandatory for diagnosis and management. The ECG is useful in separating digitalis effect from toxicity. The drug generally causes sinus slowing, sinus arrhythmia, and prolongation 37

of the P-R interval. If the sinus rate drops below 100 in infants or below 80 in older children, early toxicity should be suspected. Any arrhythmia not seen prior to digitalis administration should be considered evidence for toxicity (Fig. 22). Commonly encountered toxic arrhythmias are marked sinus bradycardia, sinus block, atrial premature contractions, junctional rhythms, advanced A V block and A V dissociation. 64 Premature ventricular contractions occur less commonly. Digitalis blood levels now are being analyzed in an attempt to better correlate the dose-response-toxicity relationship. This is done by radioimmunoassay. Though blood levels show a reasonable correlation with clinical status there is a marked overlap. ~ In a further effort to detect digitalis toxicity, salivary electrolytes have been measured. One group has shown that salivary potassium and calcium levels are higher in those with digitalis toxicity than in those not toxic. 66 Unfortunately, these studies are difficult and not easily reproducible. The prevention of digitalis toxicity is of prime concern. The total condition of the patient before and during digitalis administration must be known. Obviously, the digitalis preparation must be fully understood. Most pediatric cardiologists recommend use of a single preparation, commonly digoxin. It has an onset of action within minutes when given parenterally, and precludes use of other "rapid-acting glycosides." Digoxin effects peak serum and tissue levels in a smooth manner, especially when administered orally. It also has the safety of being relatively short-acting; the half life is approximately 24 hours, and most of the drug is excreted within 2 - 3 days after cessation of therapy, s7 Digoxin usually is administered on a dose/weight basis; however, the recommended "calculated" dose may even cause toxicity. Since digitalis may be given easily, but not removed easily, ensuing doses FIG. 22.--~inus rhythm (11), slower junctional rhythm and AV dissociation ( Vl ) in patient with probable digitalis toxicity. ~ - , 1 :

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should not be ordered without reevaluation of the patient. Electrocardiogram monitoring is mandatory during initial digitalization. Frequent rhythm strips are necessary when increasing dosage. When the patient's course or ECG suggests the possibility of digitalis toxicity, the drug must be withheld. After signs of intoxication are gone (usually in 1-3 days), administration of the drug may be resumed in a lower dose. Hypokalemia should be corrected, but the use of potassium as therapy for digitalis toxicity is very dangerous. Potassium must not be given in the presence of advanced AV block. Chelation therapy, employing E D T A to reduce serum calcium, may be useful. When tachyarrhythmia occurs, lidocaine, procaine amide, quinidine or diphenylhydantoin may be eflective. Gv Though electroconversion is useful, this torm of therapy is dangerous, since further ventricular arrhythmias may occur in a person with high digitalis levels. 67 Electrical pacing, especially for advanced AVB, may be necessary.

ELECTROLYTE ABNORMALITIES POTASSIUM Alteration in potassium level profoundly affects cardiac electrophysiology, especially in the patient receiving digitalis. This ion influences cardiac contractility, conductivity, excitability and automaticity. Though most of the body's potassium is contained in cells, serum levels are fairly reliable in determining cardiac effects and indications for therapy. 14 As a rule, serum values of 3.0-7.0 m E q / L seldom are associated with significant cardiac alterations; moreover, arrhythmias usually occur when potassium levels are grossly abnormal. Hypokalemia is usually seen in the presence of alkalosis. This occurrence is often encountered after diuretic therapy. In the presence of a normal heart, hypokalemia seldom causes arrhythmia, though occasional premature atrial or ventricular contractions may occur. 68 However, in the presence of myocardial disease and digitalis, arrhythmias such as ectopy or paroxysmal tachycardia with block may be seen. Hyperkalemia may produce profound changes in the rhythm of a normal heart. High potassium levels often are seen in patients with renal insufficiency. There may be sinus arrest, which may progress to marked intraventricular conduction delay, depression of all atrial activity and complete heart block with idioventricular rhythm (Fig. 23). The treatment for alterations in potassium is primarily elimination of the cause. In hypokalemia, careful addition of potassium and withholding of digitalis may be necessary. Hyperkalemia is more difficult to treat. Cessation of potassium intake, administration of alkalinizing solutions, competitive substitution with sodium or calcium and elimi39

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FIG. 23.--Extreme hyperkalemia.Tracing in right hal/is after partial correction of electrolyteproblem. nation of potassium by cation exchange resins or dialysis may all be necessary. CALCIUM Calcium has a significant role in the excitation-coupling of contraction and in complementing the inotropic effects of cardiac stimulatory drugs. Generally, calcium is antagonistic to the effect of potassium on the heart. As an isolated entity, hypocalcemia seldom causes severe arrhythmias. Sinus arrest and occasional premature beats may occur. Hypercalcemia of moderate degree seldom affects normal hearts. However, calcium has synergy with digitalis and may potentiate or aggravate digitalis toxicity. When the myocardium is diseased, rapid elevation of calcium level may produce ectopic beats, paroxysmal tachycardia or varying degrees of heart block. 14 ARRHYTHMIAS IN THE NEWBORN Up to 90% of otherwise healthy prematures have transient arrhythmias. 69 These include marked sinus bradycardia (some with junctional escape beats), premature atrial and ventricular beats, and varying degrees of AVB. It is possible that immaturity of the sympathetic and parasympathetic systems contributes to the arrhythmic episodes. Reinforcing this premise are the abnormalities encountered during periods of autonomic stimulation, such as feeding, suctioning and esophageal irritation. Moreover, the older and larger prematures have less frequent and severe arrhythmias. Term infants seldom have arrhythmias, and if there is no additional cardiac anomaly the occasionally encountered arrhythmia seldom persists. 40

T r e a t m e n t is u s u a l l y expectant. If the i n f a n t shows n o sign of additional cardiac lesions a n d shows n o sign of distress, the child requires only close o b s e r v a t i o n . A p r o l o n g e d b r a d y a r r h y t h m i a or t a c h y a r r h y t h m i a does r e q u i r e i n t e r v e n t i o n . C a u t i o n in use of any t h e r a p y m u s t again be advised. This especially is true when a d m i n i s t e r i n g digitalis to a p r e m a t u r e infant.

T A B L E 4.---CARDIAC LESIONS O F T E N ACCOMPANIED BY ARRHYTHMIAS CONGENITAL DEFECTS

Atrial septal defects (primum and secundum) Left ventricle to right atrial shunt Subaortic stenosis (IHSS and discrete) Ebstein's deformity

Corrected transposition Single ventricle Anomalous pulmonary Venous return (partial and total) Endocardial Fibroelastosis

ARRHYTHMIA

90% 10%-20% Most (90%)

W-P-W*

1%-5 %

RBBB W-P-W* Atrial flutter SVTf 1*AVB 2* and 3*AVB W-P-W,* SVTt 1* and 2°AVB SVT,t wandering Atrial pacemaker IRBBB 1*AVB

Most (90%-95 % ) Up to 50% 20%-50%

3°AVB W-P-W*

ACQUIRED HEART DISEASE

Rheumatic fever Acute (with carditis)

Chronic Acute carditis, especially: Viral myocarditis Diphtheria Tumors, most commonly: Myxomas (atrial) Rhabdomyxomas

INCIDENCE

IRBBB IOAVB IRBBB

ARRHYTHMIA

50% 10%-15% 1%-5 % Fairly common Occasionally 90% 10%-20% Occasional Occasional INCIDENCE

Sinus tachycardia 1°AVB 2°AVB AV dissociation PVCs Atrial flutter Atrial fibrillation

Almost all 80% Not rare Not rare Not rare Fairly common Fairly common

Arrhythmia; most commonly PVCs commonly PVCs, AVB

Not rare

Atrial arrhythmias Ventricular arrhythmias

Not rare Not rare

*W-P-W, Wolff-Parkinson-White syndrome.

tSVT, Supraventriculartachycardia.

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ACKNOWLEDGMENT The secretarial efforts of Miss Becky Holland and Mrs. LaVonne Stout have been invaluable in the preparation of this manuscript. REFERENCES I. James, T. N.: The connecting pathways between the sinus node and A-V node and between the fight and left atrium in the human heart, Am. Heart J. 66:498, 1963. 2. Shelf, L., and James, T. N.: A new electrocardiographic concept: Synchronized sino-ventricular conduction, Dis. Chest 55:127, 1969. 3. Ziegler, R. F.: Electrocardiographic Studies in Normal Infants and Children (Springfield, Ill.: Charles C Thomas, Publisher, 1951 ). 4. Liebman, J., Romberg, H. C., Downs, T. D., and Agusti, R. : The Frank QRS Vectocardiogram in the Premature Infant in Hoffman, I., and Raymor, R. (eds.) : Vectorcardiography--1965 (Amsterdam: North Holland Publishing Company, 1966). 5. Hurwitz, R. A., and Goldberg, S. J.: Maximal cardiac rate before and following repair of cardiac lesions, J. Sports, Med. & Phys. Fitness 10:165, 1970. 6. Keith, J. D., Rowe, R. D., and Vlad, P.: Heart Disease in In[ancy and Childhood (2nd ed.; New York: The Macmillan Company, 1967). 7. Cherry, J. D., John, C. L., and Meyer, T. C.: Paroxysmal atrial tachycardia associated with Echo 9 virus infection, Am. Heart J. 73 : 681, 1967. 8. El-Said, G., Rosenberg, H. S., Mullins, C. E., Hallman, G. L., Cooley, D. A., and McNamara, D. G.: Dysrhythmias after Mustard's operation for transposition of the great arteries, Am. J. Cardiol. 30:526, 1972. 9. McIntosh, H. D.: Cardiac catheterization: Arrhythmias, Circulation (supp.) 37-III:27, 1968. 10. Meltzer, L. E., and Kitchell, J. B.: The incidence of arrhythmias associated with acute myocardial infarction, Prog. Cardiovas. Dis. 9:50, 1966. 11. Bialostozky, D., Horwitz, S., and Espina-Vela, J.: Ebstein's malformation of the tricuspid valve, Am. J. Cardiol. 29:826, 1972. 12. Littman, D., and Tarhomer, H.: The Wolff-Parkinson-White syndron0e, Am. Heart J. 32: I00, 1946. 13. Mark, H., and Luna, L. S.: Treatment of Wolff-Parkinson-White syndrome, Am. Heart J. 83:565, 1972. 14. Bellet, S.: Clinical Disorders o / t h e Heart Beat (3d ed.; Philadelphia: Lea & Febiger, 1971 ). 15. Wright, J. S., Fabian, J., and Epstein, E. J.: Immediate effect on cardiac output of reversion to sinus rhythm from rapid arrhythmias, Brit. M. J. 3:315, 1970. 16. Lundberg, A. : Paroxysmal tachycardia in infancy, Acta paediat., supp. 143, 1963. 17. Gasul, B. M., Arcilla, R. A., and Lev, M.: Heart Disease in Children (Philadelphia: J. B. Lippincott Company, 1966). 18. Hellerstein, H. K., Levine, B., and Fell, H.: Electrocardiographic changes following carotid sinus stimulation in paroxysmal ventricular tachycardia, J. Lab & Clin. Med. 38:820, 1951. 19. King, S. B., and Franch, R. H.: Production of increased right-to-left shunting by rapid heart rates in patients with tetralogy of Fallot, Circulation 44:265, 1971. 20. Berry, K., Garlett, E. L., Bellet, S., and Gefter, W. I.: Use of Pronestyl in treatment of ectopic rhythms, Am. J. Med. 11:431, 1951. 44

21. Giannely, R.: Propranolol in the treatment and prevention of cardiac arrhythmias, Ann. Int. Med. 66:667, 1967. 22. Turner, J.: Propranolol in the treatment of digitalis-induced and digitalis resistant tachycardias, Am. J. Cardiol. 18:450, 1966. 23. Bein, G., and Wolf, D.: The Treatment of Supraventricular Paroxysmal Tachycardia in Infants and Children with Verapramil, Vol. XX (Vienna: Congress of Cardiology and Pneumology, 1970). 24. Linde, L. M., Turner, S. W., and Awa, S.: Present status and treatment of paroxysmal supraventricular tachycardia, Pediatrics 50:127, 1972. 25. Lown, B., Kleiger, R., and Williams, J.: Cardioversion and digitalis drugs: Changed threshold to electric shock in digitalized animals, Circulation Res. 17:519, 1965. 26. Hunsaker, M. R., and Khoury, G. M.: Management of supraventricular tachycardia by atrial stimulation, J. Pediat. 77:454, 1970. 27. Swiderski, J., Lees, M. H., and Nadas, A. S.: The Wolff-Parkinson-White syndrome in infancy and childhood, Brit. Heart J. 24:561, 1962. 28. Schneider, R. G. : Familial occurrence of Wolff-Parkinson-White syndrome, Am. Heart J. 78:34, 1969. 29. March, H. W., Seizer, A., and Holtgren, H. N.: Mechanical events during anomalous atrioventricular excitation (WPW syndrome), Circulation 22: 784, 1960. 30. Durrer, D., School, L., Schuilenburg, R. M., and Wellens, H. J.: Role of premature beats in the initiation and termination of supraventricular tachycardia in the W-P-W syndrome, Circulation 36:644, 1967. 31. Engle, M. A. : Wolff-Parkinson-White syndrome in infants and children, Am. J. Dis. Child. 84: 692, 1952. 32. Gianelly, R., Griffin, J. R., and Harrison, D. C.: Propranolol in the treatment and prevention of cardiac arrhythmias, Ann. Int. Med. 66:667, 1967. 33. Dreifus, L. S., Arriaga, J., Watanabe, Y., Downing, D., Haiat, R., and Morse, D.: Recurrent WoIff-Parkinson-White tachycardia in an infant, Am. J. Cardiol. 28:586, 1971. 34. BlumenthaJ, S., Jacobs, J. C., Steer, C. M., and Williamson, S. W.: Congenital atrial flutter: Report of a case documented by intrauterine electrocardiogram, Pediatrics 41:659, 1968. 35. Moiler, J. H., Davachi, F., and Anderson, R. C.: Atrial flutter in infancy, J. Pediat. 75:643, 1969. 36. Bailey, G. W. H., Brainoff, B. A., Hancock, E. W., and Cohn, K. E.: Relation of left atrial pathology to atrial fibrillation in mitral valvular disease, Ann. Int. Med. 69 : 13, 1968. 37. Lown, B.: Electrical reversion of cardiac arrhythmias, Brit. Heart J. 29:469, 1967. 38. Gibson, S.: Auricular fibrillation in childhood and adolescence, J.A.M.A. 117:96, 1941. 39. Arcilla, R. A., Lind, J., Letterquist, P., Oh, W., and Gessner, I. H. : Hemodynamic features of extrasystoles in newborn and older infants, Am. J. Cardiol. 18:191, 1966. 40. Scherf, D., and Bornemann, C.: Tachycardias with alternation of the ventricular complexes, Am. Heart J. 74:667, 1967. 41. Gelband, H., Steeg, C. N., and Bigger, J. T., Jr.: Use of massive doses of procaine amide in the treatment of ventricular tachycardia in infancy, Pediatrics 48 : 110, 1971. 42. Dimich, I., Steinfeld, L., Richman, R., and Lasser, R.: Treatment of recurrent paroxysmal ventricular tachycardia, Am. Heart J. 79: 811, 1970. 43. Pennington, J. E., Taylor, J., and Lown, B.: Chest thump for reverting ventricular tachycardia, New England J. Med. 283:1192, 1970. 45

44. Gerst, P. H., Fleming, W. H., and Maim, J. R.: Increased susceptibility of the heart to ventricular fibrillation during metabolic acidosis, Circulation Res. 19:63, 1966. 45. Spach, M. S., and Scarpelli, E. M.: Circulatory dynamics and the effects of respiration during ventricular asystole in dogs with complete heart block, Circulation Res. 10: 197, 1962. 46. Mirowski, M., Rosenstein, B. J., and Markowitz, M.: A comparison of atrioventricular conduction in normal children and in patients with rheumatic fever, glomerulonephritis, and acute febrile illnesses, Pediatrics 33:334, 1964. 47. Dreifus, L. S., Watanabe, Y., Haiat, R., and Kimbris, D.." Atrioventricular block, Am. J. Cardiol. 28:371, 1971. 48. Kelly, D. T., and Rose, R. D.: Mobitz type II atrioventricular block in a newborn, Pediatrics 50: 333, 1972. 49. Lev, M., Silverman, J., Fitzmaurice, F. M., Paul, M. H., Cassels, D. E., and Miller, R. A.: Lack of connection between the atria and the more peripheral conduction system in congenital atrioventricular block, Am. J. Cardiol. 27: 481, 1971. 50. Snyder, J. H., Bender, F., Kitchin, A. H., Zitnik, R. S., Donald, D. E., and Wood, E. H.: Atrial contribution to stroke volume in dogs with chronic heart block, Circulation Res. 19:33, 1966. 51. Sarachek, N. S., and Leonard, J. L.: Familial heart block and sinus bradycardia, Am. J. Cardiol. 29:451, 1972. 52. Kangos, J. J., Griffiths, S. P., and Blumenthal, S.: Congenital complete heart block, Am. J. Cardiol. 20:632, 1967. 53. Piscatelli, R. L., and Fox, L. M.: Myocardial injury from epinephrine overdosage, Am. J. Cardiol. 21:735, 1968. 54. Hurwitz, R. A.: Effect of glucagon on dogs with acute and chronic heart block, Am. Heart J. 81:644, 1971. 55. Benchimol, A., Palmero, H. A., Liggett, M. S., and Dimond, E. G.: Influence of digitalization on the contribution of atrial systole to the cardiac dynamics at a fixed ventricular rate, Circulation 32:84, 1965. 56. McNally, E. M., and Benchimol, A.: Medical and physiological considerations in the use of artificial cardiac pacing, Am. Heart J. 75:380, 1968. 57. Lillehei, C. W., Sellers, R., Bonnabeau, R., and Eliot, R.: Chronic post surgical complete heart block, J. Thoracic & Cardiovas. Surg. 46:436, 1963. 58. Chen, S., Arcilla, R. A., Moulder, P. V., and Cassels, D. E.: Postoperative conduction disturbances in atrial septal defect, Am. J. Cardiol. 22:636, 1968. 59. Guntheroth, W. G.: Pediatric Electrocardiography (Philadelphia: W. B. Saunders Company, 1965). 60. Gelband, H., Waldo, A. L., Kaiser, G. A., Bowman, F. O., Malta, J. R., and Hoffman, B. V.: Etiology of right bundle branch block in patients undergoing total correction of tetralogy of Fallot, Circulation 44: 1022, 1971. 61. Godman, M. J., Roberts, N. K., and Izukawa, T.: His bundle analysis of conduction disturbances following repair of ventricular septal defect and tetralogy of Fallot, Circulation (abstract) 46:11:37, 1972. 62. Scott, R. C.: Left bundle branch block: A clinical assessment, Am. Heart J. 70:535, 1965. 63. Robinson, S. J.: Digitalis therapy irt infants and children, J. Pediat. 56:536, 1960. 64. Neil, C. A.: Recognition and treatment of congestive heart failure in infancy, Prog. Cardiovas. Dis. 7:399, 1965. 65. Beller, G. A., Smith, T. W., Abelmann, W. H., Haber, E., and Hood, W. B., Jr.: Digitalis intoxication: A prospective clinical study with serum level correlations, New England J. Med. 284:989, 1971. ,t6

66. Wotman, S., Bigger, T., Jr., Mandel, I. D., and Bartelstone, H. J.: Salivary electrolytes in the detection of digitalis toxicity, New England J. Med. 285: 871, 1971. 67. Mason, D. T., Zelis, R., Lee, G., Hughes, J. L., Spann, J. F., Jr., and Amsterdam, E. A. : Current concepts and treatment of digitalis toxicity, Am. J. Cardiol. 27:546, 1971. 68. Pick, A.: Arrhythmias and potassium in man, Am. Heart J. 72:295, 1966. 69. Church, S. C., Morgan, B. C., Oliver, T. K., and Guntheroth, W. G.: Cardiac arrhythmias in premature infants, J. Pediat. 71:542, 1967.

T H E N E X T ISSUE In May Dr. Barbara Maria Korsch and Elaine Firestone Aley of Childrens Hospital of Los Angeles and the University of Southern California School of Medicine will discuss Pediatric Interview Technics. The authors point out that the traditional doctor-patient relationship is severely threatened. Patients from all walks of life are voicing deep disappointment at the lack of personal interest and warmth their doctors show. Though the authors agree there are undoubtedly a host of factors contributing to this discontent, they believe poor communications between the doctor and patient is one of the most critical, in the pediatrician's case, often between himself and the patient's parents. It is this factor they will discuss in their monograph, giving sample interviews between pediatricians and parents of patients, with suggestions for better communications.

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