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DIAGNOSIS AND TREATMENT OF PEDIATRIC ARRHYTHMIAS
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PEDIATRIC CARDIOLOGY
+ .OO
DIAGNOSIS AND TREATMENT OF PEDIATRIC ARRHYTHMIAS Christopher L. Case, DMD, MD
Pediatric primary care practitioners are truly on the "front line" in the diagnosis and treatment of many childhood arrhythmias. The increased vigilance of these primary care providers, combined with advances in the recording technologies of arrhythmias, has resulted in an increased number of infants, children, and adolescents who are being correctly diagnosed with rhythm disturbances. This article deals with the general principles of pediatric arrhythmia diagnosis and treatment and individually discusses some of the more frequently encountered arrhythmias in children. GENERAL PRINCIPLES
A few general principles should be remembered by practitioners who are considering the management of suspected arrhythmias in children: 1. As with many disease processes in children, the symptoms of arrhythmias in pediatric patients may vary depending on the ages of these children. Classic symptoms of an arrhythmia described by mature individuals (eg., palpitations, heart racing, and dizziness) may not be elicited from children until the age of 5 years. For younger children, arrhythmia symptoms may be described in more obtuse ways (e.g., chest discomfort) or not at all. Periods of fussiness in infants may be the only evidence of paroxysmal sustained arrhythmias. 2. Recording suspected arrhythmias in children is necessary before advancing a diagnosis or instituting a treatment. Important and long-lasting mistakes can be made if any child is assumed to have a specific arrhythmia on the basis of history or physical examination.
From the Department of Pediatric Cardiology, Cook Children's Medical Center, Fort Worth, Texas
PEDIATRIC CLINICS OF NORTH AMERICA ~~~~
~
VOLUME 46 * NUMBER 2 * APRIL 1999
347
348
CASE
3. The urgency of a workup of suspected arrhythmias in children depends on symptom severity, cardiac structure and function considerations, and the activity profiles of these patients. Children with suspected arrhythmias with any alteration of consciousness (i.e., syncope or dizziness) need expeditious workups. Arrhythmias in children with compromised cardiac function or structure (e.g., cardiomyopathy or congenital heart disease [CHD]) should be investigated as soon as possible even if symptoms are minimal. Children in competitive athletic activities also need prompt investigation of suspected arrhythmias. 4. The physical examination of children with important arrhythmias may be entirely normal. Frequently, children present to their primary care providers ”in between” arrhythmia events. These patients’ complaints must not be dismissed because of the paucity of findings during the physical examination. 5. If an ECG, Holter monitor, or event monitor is needed, the results should be interpreted by someone who is familiar with the scope of pediatric arrhythmias. Frequently, sinus tachycardia in normal children may be misinterpreted as a pathologic tachycardia. 6. Treatment of pediatric arrhythmias should be guided by the severity of the arrhythmias, the activity of the patient, and the structure and function of the heart. Although drug therapy is the traditional means to treat arrhythmias, nonpharmacologic treatment of arrhythmias (i.e., ablation therapy or pacemaker or defibrillator placement) is sometimes the more efficacious therapy and may be preferred by these patients and their parents. 7. If evaluating an acute arrhythmia with hemodynamic compromise (e.g., cardiogenic shock or loss of consciousness), ”think simple.” If the rhythm is fast or disorganized, the patient should be cardioverted or defibrillated. If the rhythm is slow, cardiopulmonary resuscitation should be initiated. DIAGNOSTIC PRINCIPLES History
The cornerstone of a good arrhythmia evaluation starts with history taking. Eliciting details of the suspected arrhythmia event sets the stage for the depth and timeliness of the subsequent evaluation. If the child is too young to provide details of the event, these must be elicited from the parent or any other mature person who witnessed the event. Many children complain of their hearts “going fast,” which may be a normal phenomenon or a pathologic event. Pathologic tachycardias that are reentrant in nature start and stop suddenly. Some children provide histories of their hearts racing with a sudden onset and abrupt termination. Sometimes this occurs at rest but may also be exacerbated by exercise. Distinguishing reentrant tachycardias that occur only with exercise from sinus tachycardia may be difficult. Paroxysmal arrhythmias in children may be associated with other symptoms, including shortness of breath, pallor, cyanosis, chest pain, dizziness, or alteration of consciousness. A temporal sequence of these associated symptoms as they relate to any perception of heart palpitations or tachycardia is important to obtain. If these associated symptoms precede, or occur in the absence of, the sensation of tachycardia or palpitations, the arrhythmia described may be a secondary event. For example, many children describe symptoms of functional
DIAGNOSIS AND TREATMENT OF PEDIATRIC ARRHYTHMIAS
349
chest pain followed by a reflex sinus tachycardia. Alternatively, reentrant supraventricular tachycardia (SVT) can be accompanied by chest discomfort from insufficient coronary perfusion during the SVT episode. Another example is hyperventilation syndrome, which can produce respiratory distress with a "reflex" sinus tachycardia. Alternatively, reentrant SVT can cause shortness of breath from presumed poor cardiac output. In the workup of loss of consciousness, the cause for arrhythmia should always be pursued. Historical information concerning palpitations preceding the syncope is important. Information concerning the activity of these children before and after the syncopal episode, the pulse rate (if taken during the episode), and associated symptoms described earlier can help to guide further workup. Family history of early cardiovascular death or arrhythmia is important to ascertain so as to aid in the diagnosis of familial arrhythmia states, such as hypertrophic cardiomyopathy and Wolff-Parkinson-White (WPW) and long QT syndromes. Physical Examination
The physical examinations of children who have suspected arrhythmias are important but may be normal. Attention to ruling out other disease processes (e.g., fever, anemia, or endocrine problems) that can explain an adaptive arrhythmia (i.e., sinus tachycardia or bradycardia) is important. Any abnormality in the cardiovascular examination should be aggressively pursued because the prognosis and treatment of a particular arrhythmia are dependent on the cardiac structure. For example, single, premature beats (atrial or ventricular) with a normal cardiac structure are (for the most part) considered benign if they are not exacerbated by exercise. Conversely, single, premature beats in children with poor cardiac structure or function may signify a significant risk for subsequent morbidity or mortality. Noninvasive Adjunctive Tests
Any pediatric arrhythmia evaluation probably necessitates a good 12-lead ECG. The ECG needs to be properly performed and properly interpreted. Attention should be paid to the heart rate, atrioventricular relationships, the presence and absence of premature beats, intervals (i.e., PR, QRS, and QT), and the presence or absence of hypertrophy. Sometimes the 12-lead ECG can give good evidence as to the diagnosis, especially if the suspected arrhythmia is captured on the recording. Even if the suspected arrhythmia is not present, the ECG can give clues as to the suspected rhythm disturbance by showing phenomena such as a delta wave (WPW), atrioventricular block (bradycardia), or long QT interval (long QT syndrome). A 24-hour rhythm recording (Holter monitor) may also aid in diagnosing an episodic arrhythmia event. The frequency of symptoms, especially if a paroxysmal arrhythmia is being sought, can limit the usefulness of the Holter monitor to diagnose a specific rhythm disturbance. Holter monitors are particularly useful in illustrating slow heart rate events in the assessment of asymptomatic bradycardia. Event recorders are more useful in capturing intermittent arrhythmia events. Several event recorders are commercially available. Some models (loop recorders) require these children to always wear the device. The arrhythmia event is
350
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recorded by pushing a button on the device. These monitors are useful in recording short-duration arrhythmias or suspected arrhythmias with aberrations of consciousness. Other event monitors require these patients to record the arrhythmia by interfacing the device (during the suspected event) with a telephone for recording. Obviously, such models (”pacer tracers”) are better for sustained arrhythmia events (at least 3-4 min in duration) that do not impair the sensorium. Exercise testing rarely can be helpful in the evaluation of an arrhythmia. Occasionally, SVT can be provoked during an exercise test. Also, the nature or extent of a patient’s bradycardia (secondary to sinus node incompetence or atrioventricular node disease) may be evaluated with graded exercise testing. Finally, some evaluations of pediatric arrhythmias may require additional cardiac imaging to investigate the structure and function of the heart. Sometimes, the physical findings of the cardiac examination need to be clarified with a chest radiograph or an echocardiogram. The specifics of the cardiac structure can help predict the risk for the cardiac arrhythmia in regard to sudden cardiac death or can help to select patients for specific treatment modalities. TREATMENT PRINCIPLES
Traditional treatment strategies for chronic arrhythmias in children have mostly relied on the use of antiarrhythmic drug therapy. In the past decade, catheter ablation techniques have evolved so that the substrates for most sustained pediatric tachycardias (i.e., SVT or ventricular tachycardia [VT]) can be destroyed in the context of a single catheterization session lasting 3 or 4 hours. With successful ablation therapy, patients can be rendered both tachycardia and medication free for the rest of their lives. Because catheter ablation therapy has been performed for less than a decade, some caution regarding its long-term effects is warranted; however, when the issues of long-term medical therapy versus catheter ablation techniques are discussed with parents, many choose ablation for the treatment of their children’s arrhythmias. ”Parental choice” is the most common indication for catheter ablation procedures in the pediatric age group. Catheter ablation is the procedure of choice for any child, regardless of age or size, who has a life-threatening event from a tachyarrhythmia and whose substrate is amenable to an ablation procedure. Medications are still used by many physicians to treat pediatric patients with tachyarrhythmias. In children with normal hearts, most medications are well tolerated. Depending on the symptoms of the arrhythmia, some medications can be started on an outpatient basis (e.g., digoxin or p-blockers for patients with SVT). Stronger antiarrhythmic therapy (class I or I11 medications) is usually started in the hospital because of the possibility of proarrhythmia. This phenomenon is more common in children with structural heart disease or significant arrhythmias but also has been reported in children with normal hearts and relatively benign rhythm disturbance^.^ Cardiac pacing is still the therapy of choice for children with bradycardia. The devices involved in permanent pacing techniques are sufficiently small to be used safely in most infants and children. More sophisticated implantable devices that not only pace the heart but also can terminate tachyarrhythmias may also be useful in treating pediatric patients with arrhythmias. Antitachycardia pacemakers and implantable defibrillators have become more common treatment options for children with severe forms of bradycardia-tachycardia syndromes?
DIAGNOSIS AND TREATMENT OF PEDIATRIC ARRHYTHMIAS
351
SPECIFIC ARRHYTHMIAS Supraventricular Tachycardia
Supraventricular tachycardia is the most common sustained tachyarrhythmia in children. Most commonly in children younger than 12 years of age, the SVT is caused by an accessory atrioventricular connection; in teenage years, atrioventricular node reentry tachycardia is also an important cause of SVT.* In accessory connection-mediated tachycardia, the common tachycardia circuit (i.e., orthodromic tachycardia) is comprised of antegrade conduction down the atrioventricular node and retrograde conduction up the accessory connection. If the accessory connection also has antegrade conduction properties, the term WPW is applicable. With WPW, the surface ECG shows the characteristic short PR interval and wide QRS (Fig. 1). Patients with WPW not only can have orthodromic tachycardia but also can have antidromic tachycardia. The circuit of antidromic tachycardia involves antegrade conduction down the accessory connection, with retrograde conduction up the atrioventricular node or alternative accessory connection. WPW patients are also prone to have atrial flutter with rapid conduction down the accessory connection. Tachycardias associated with WPW and that involve antegrade conduction down the accessory connection may be dangerous and associated with sudden cardiac death. The risk for sudden cardiac death in patients with WPW is 1%every 10 years. For this reason, any child with WPW and a syncopal tachycardia episode should be considered for a catheter ablation procedure. The classic ECG characteristic of accessory connection-mediated orthodromic tachycardia is a narrow QRS tachycardia with a retrograde P wave inscribed after the QRS in the ST segment. (Fig. 2). Antidromic SVT has a wide QRS morphology and resembles VT. Both antidromic and orthodromic SVT are reentrant in nature, so they can have an abrupt onset and termination. Acute termination of orthodromic SVT can be accomplished by vagal ma-
Figure 1. ECG of a patient with Wolff-Parkinson-White. wide QRS.
Note the short PR interval and
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CASE
Figure 2. ECG of a child with orthodromic SVT. Note the retrograde P waves in the ST
segments. neuvers or with medications. Adenosine (100 &kg) given intravenously and rapidly breaks the orthodromic circuit at the level of the atrioventricular node. Other intravenous medications, such as verapamil, digoxin, procainamide, propranolol, and amiodarone, can also be used to acutely terminate SVT. Intravenous verapamil is contraindicated in infants and small children. It can be used cautiously in older children, but is probably best avoided altogether in the pediatric population. Long-term medical treatment of patients with orthodromic SVT usually involves digoxin or @-blockertherapy. Other medications, such as flecainaide, procainamide, sotalol, amiodarone, and verapamil, are used for more recalcitrant SVT. Digoxin should be avoided in children with WPW because of its potential proarrhythmia effects. It can enhance the conduction properties of the accessory pathway, resulting in a more rapid ventricular rate during atrial flutter and an increased risk for sudden death. Radiofrequency catheter ablation has become an important treatment of chronic atrioventricular reentrant tachycardia. Success rates for radiofrequency catheter ablation and accessory connections depend on the age of the patient, structures of the heart, pathway location, and operator experience. In general, success rates in experienced centers range between 85% and Premature Beats
Premature beats, either atrial or ventricular, are common in children. Atrial or ventricular premature beats that occur in the context of children with normal hearts and are extinguished with exercise generally have a benign natural history. Generally, premature ventricular beats with structural heart disease (e.g., postoperative CHD) or poor cardiac function ( e g , cardiomyopathy) are associated with an increased risk for sudden cardiac death? Stratifying such patients so as to identify treatment alternatives to mitigate sudden death risk is a subject of ongoing investigation in pediatric electrophysiology.
DIAGNOSIS AND TREATMENT OF PEDIATRIC ARRHYTHMIAS
353
Ventricular Tachycardia
Ventricular tachycardia in children is rare compared with the incidence of SVT. Because of this fact, VT is often misdiagnosed and treated as SVT in children. The wide QRS tachycardia in children should be considered to be ventricular tachycardia until proven otherwise. The "wideness" of the QRS in pediatric VT may be subtle, so vigilance is important. The presence of atrioventricular dissociation during tachycardia is diagnostic of VT. Sometimes, VT may still exhibit a 1:l ventricular-atrial relationship (Fig. 3). In children, VT occurs in the context of a normal heart or, more importantly, with structural heart disease. In infants, VT can be associated with hamartomatous growths on the ventricle^.^ These automatic VTs may be responsive to medications but may also necessitate surgical ablation procedures because of hemodynamic compromise. Many VTs of this nature resolve as these children mature. Ventricular tachycardia can be associated with repaired CHD. Children with heart lesions, such as repaired tetrology of Fallot, can have VT that presents as sudden cardiac death.6Antiarrhythmic medications, surgical or catheter ablation procedures, and defibrillator placement may be needed for control of this variety of VT. Other types of VT occur in children with normal hearts5 One such VT has a left bundle branch block morphology with an inferior axis. This VT is automatic in nature, catecholamine sensitive, and originates in the muscle of the right ventricular outflow tract. Another VT seen in children with normal hearts is thought to be secondary to reentry around the Purkinje network of the left posterior fascicle. Treatment regimens for both of these varieties of VT include no intervention, antiarrthymic medications, or ablation procedures. Atrioventricular Block
Symptomatic bradycardia in children requiring cardiac pacing usually involves diseases of the atrioventricular node. Children with congenital complete
Figure 3. ECG of an 8-month-old child with ventricular tachycardia. Note that in certain leads (Ill) the QRS morphology is not overtly wide.
atrioventricular block (CCAVB) may present at any age because of symptoms of bradycardia (e.g., fatigue or syncope). Also, many of these children are asymptomatic and are diagnosed because of a low resting heart rate on physical examination. The only recognized therapy for CCAVB is permanent cardiac pacing. Most patients with CCAVB, even if asymptomatic, are believed to need permanent pacing during their lifetime to avoid the possibility of sudden cardiac death.9 Most children with CCAVB and structurally normal hearts are born to mothers with serologic evidence of systemic lupus erythematosus. All mothers of children born with CCAVB need to be evaluated for connective tissue disease. The risk for CCAVB in subsequent pregnancies may be as high as 16%.’ Atrioventricular block may also be acquired after surgery for certain types of CHD. These surgeries usually involve closure of a ventricular septa1 defect. Patients with atrioventricular block that persists beyond 14 days need permanent cardiac pacing. Cardiac pacing is required to avoid rare episodes of sudden cardiac death. Dual-chambered pacing is preferable to single-chamber pacing in the ventricle. Dual-chamber pacing ensures atrioventricular syncrony, which may be important to maximize hemodynamics in patients with structurally abnormal hearts. SUMMARY
The work up of arrhythmias encountered in the pediatric patient is usually initiated by primary care providers. Proper treatment of pediatric arrhythmias necessitates recording the suspected rhythm disturbance and an evolution of the underlying cardiac structure and function. References 1. Buyon J, Hiebert R, Cope1 J, et a1 Autoimmune-associated congenital heart block Demographics, mortality, morbidity and recurrence rates obtained from a national neonatal lupus registry. J Am Coll Cardiol31:1658-1666, 1998 2. Case C, Sokoloski M, Gillette P: Device therapy for arrhythmias. In Deal B, Wolff G, Gelband H (eds): Current Concepts in Diagnosis and Management of Arrhythmias in Infants and Children. Armonk, NY, Futura Publishing, 1998, pp 401-426 3. Danford D, Kugler J, Deal B, et a 1 The learning curve for radiofrequency ablation of tachyarrhythmias in pediatric patients. Am J Cardiol 75:587-590, 1995 4. Fish F, Gillette P, Benson D Proarrhythmia, cardiac arrest and death in young patients receiving encainide and flecainide. J Am Coll Cardiol 18:35&365, 1991 5. Garson A Jr: Ventricular arrhythmias. In Gillette P, Garson A Jr (eds): Pediatric Arrhythmias: Electrophysiology and Pacing. Philadelphia, WB Saunders, 1990, pp 427-500 6. Garson A Jr, Nihill M, McNamara D, et al: Status of the adult and adolescent after repair of tetralogy of Fallot. Circulation 59:1232-1240, 1979 7. Garson A Jr, Smith RT Jr, Moak JP, et al: Incessant ventricular tachycardia in infants: Myocardial hamartomas and surgical cure. J Am Coll Cardiol 106194126, 1987 8. Ludomirsky A, Garson A Jr: Supraventricular tachycardia. In Gillette P, Garson A Jr (eds): Pediatric Arrhythmias: Electrophysiology and Pacing. Philadelphia, WB Saunders, 1990, pp 380-426 9. Michaelsson M, Jozon A, Risenfeld T Isolated congenital complete atrioventricular block in adult life: A prospective study. Circulation 9244249,1995
Address reprint requests to Christopher L. Case, DMD, MD Cook Children’s Medical Center 801 7th Avenue Fort Worth, TX 76164
PEDIATRIC CARDIOLOGY
+ .OO
DIAGNOSIS AND TREATMENT OF PEDIATRIC ARRHYTHMIAS Christopher L. Case, DMD, MD
Pediatric primary care practitioners are truly on the "front line" in the diagnosis and treatment of many childhood arrhythmias. The increased vigilance of these primary care providers, combined with advances in the recording technologies of arrhythmias, has resulted in an increased number of infants, children, and adolescents who are being correctly diagnosed with rhythm disturbances. This article deals with the general principles of pediatric arrhythmia diagnosis and treatment and individually discusses some of the more frequently encountered arrhythmias in children. GENERAL PRINCIPLES
A few general principles should be remembered by practitioners who are considering the management of suspected arrhythmias in children: 1. As with many disease processes in children, the symptoms of arrhythmias in pediatric patients may vary depending on the ages of these children. Classic symptoms of an arrhythmia described by mature individuals (eg., palpitations, heart racing, and dizziness) may not be elicited from children until the age of 5 years. For younger children, arrhythmia symptoms may be described in more obtuse ways (e.g., chest discomfort) or not at all. Periods of fussiness in infants may be the only evidence of paroxysmal sustained arrhythmias. 2. Recording suspected arrhythmias in children is necessary before advancing a diagnosis or instituting a treatment. Important and long-lasting mistakes can be made if any child is assumed to have a specific arrhythmia on the basis of history or physical examination.
From the Department of Pediatric Cardiology, Cook Children's Medical Center, Fort Worth, Texas
PEDIATRIC CLINICS OF NORTH AMERICA ~~~~
~
VOLUME 46 * NUMBER 2 * APRIL 1999
347
348
CASE
3. The urgency of a workup of suspected arrhythmias in children depends on symptom severity, cardiac structure and function considerations, and the activity profiles of these patients. Children with suspected arrhythmias with any alteration of consciousness (i.e., syncope or dizziness) need expeditious workups. Arrhythmias in children with compromised cardiac function or structure (e.g., cardiomyopathy or congenital heart disease [CHD]) should be investigated as soon as possible even if symptoms are minimal. Children in competitive athletic activities also need prompt investigation of suspected arrhythmias. 4. The physical examination of children with important arrhythmias may be entirely normal. Frequently, children present to their primary care providers ”in between” arrhythmia events. These patients’ complaints must not be dismissed because of the paucity of findings during the physical examination. 5. If an ECG, Holter monitor, or event monitor is needed, the results should be interpreted by someone who is familiar with the scope of pediatric arrhythmias. Frequently, sinus tachycardia in normal children may be misinterpreted as a pathologic tachycardia. 6. Treatment of pediatric arrhythmias should be guided by the severity of the arrhythmias, the activity of the patient, and the structure and function of the heart. Although drug therapy is the traditional means to treat arrhythmias, nonpharmacologic treatment of arrhythmias (i.e., ablation therapy or pacemaker or defibrillator placement) is sometimes the more efficacious therapy and may be preferred by these patients and their parents. 7. If evaluating an acute arrhythmia with hemodynamic compromise (e.g., cardiogenic shock or loss of consciousness), ”think simple.” If the rhythm is fast or disorganized, the patient should be cardioverted or defibrillated. If the rhythm is slow, cardiopulmonary resuscitation should be initiated. DIAGNOSTIC PRINCIPLES History
The cornerstone of a good arrhythmia evaluation starts with history taking. Eliciting details of the suspected arrhythmia event sets the stage for the depth and timeliness of the subsequent evaluation. If the child is too young to provide details of the event, these must be elicited from the parent or any other mature person who witnessed the event. Many children complain of their hearts “going fast,” which may be a normal phenomenon or a pathologic event. Pathologic tachycardias that are reentrant in nature start and stop suddenly. Some children provide histories of their hearts racing with a sudden onset and abrupt termination. Sometimes this occurs at rest but may also be exacerbated by exercise. Distinguishing reentrant tachycardias that occur only with exercise from sinus tachycardia may be difficult. Paroxysmal arrhythmias in children may be associated with other symptoms, including shortness of breath, pallor, cyanosis, chest pain, dizziness, or alteration of consciousness. A temporal sequence of these associated symptoms as they relate to any perception of heart palpitations or tachycardia is important to obtain. If these associated symptoms precede, or occur in the absence of, the sensation of tachycardia or palpitations, the arrhythmia described may be a secondary event. For example, many children describe symptoms of functional
DIAGNOSIS AND TREATMENT OF PEDIATRIC ARRHYTHMIAS
349
chest pain followed by a reflex sinus tachycardia. Alternatively, reentrant supraventricular tachycardia (SVT) can be accompanied by chest discomfort from insufficient coronary perfusion during the SVT episode. Another example is hyperventilation syndrome, which can produce respiratory distress with a "reflex" sinus tachycardia. Alternatively, reentrant SVT can cause shortness of breath from presumed poor cardiac output. In the workup of loss of consciousness, the cause for arrhythmia should always be pursued. Historical information concerning palpitations preceding the syncope is important. Information concerning the activity of these children before and after the syncopal episode, the pulse rate (if taken during the episode), and associated symptoms described earlier can help to guide further workup. Family history of early cardiovascular death or arrhythmia is important to ascertain so as to aid in the diagnosis of familial arrhythmia states, such as hypertrophic cardiomyopathy and Wolff-Parkinson-White (WPW) and long QT syndromes. Physical Examination
The physical examinations of children who have suspected arrhythmias are important but may be normal. Attention to ruling out other disease processes (e.g., fever, anemia, or endocrine problems) that can explain an adaptive arrhythmia (i.e., sinus tachycardia or bradycardia) is important. Any abnormality in the cardiovascular examination should be aggressively pursued because the prognosis and treatment of a particular arrhythmia are dependent on the cardiac structure. For example, single, premature beats (atrial or ventricular) with a normal cardiac structure are (for the most part) considered benign if they are not exacerbated by exercise. Conversely, single, premature beats in children with poor cardiac structure or function may signify a significant risk for subsequent morbidity or mortality. Noninvasive Adjunctive Tests
Any pediatric arrhythmia evaluation probably necessitates a good 12-lead ECG. The ECG needs to be properly performed and properly interpreted. Attention should be paid to the heart rate, atrioventricular relationships, the presence and absence of premature beats, intervals (i.e., PR, QRS, and QT), and the presence or absence of hypertrophy. Sometimes the 12-lead ECG can give good evidence as to the diagnosis, especially if the suspected arrhythmia is captured on the recording. Even if the suspected arrhythmia is not present, the ECG can give clues as to the suspected rhythm disturbance by showing phenomena such as a delta wave (WPW), atrioventricular block (bradycardia), or long QT interval (long QT syndrome). A 24-hour rhythm recording (Holter monitor) may also aid in diagnosing an episodic arrhythmia event. The frequency of symptoms, especially if a paroxysmal arrhythmia is being sought, can limit the usefulness of the Holter monitor to diagnose a specific rhythm disturbance. Holter monitors are particularly useful in illustrating slow heart rate events in the assessment of asymptomatic bradycardia. Event recorders are more useful in capturing intermittent arrhythmia events. Several event recorders are commercially available. Some models (loop recorders) require these children to always wear the device. The arrhythmia event is
350
CASE
recorded by pushing a button on the device. These monitors are useful in recording short-duration arrhythmias or suspected arrhythmias with aberrations of consciousness. Other event monitors require these patients to record the arrhythmia by interfacing the device (during the suspected event) with a telephone for recording. Obviously, such models (”pacer tracers”) are better for sustained arrhythmia events (at least 3-4 min in duration) that do not impair the sensorium. Exercise testing rarely can be helpful in the evaluation of an arrhythmia. Occasionally, SVT can be provoked during an exercise test. Also, the nature or extent of a patient’s bradycardia (secondary to sinus node incompetence or atrioventricular node disease) may be evaluated with graded exercise testing. Finally, some evaluations of pediatric arrhythmias may require additional cardiac imaging to investigate the structure and function of the heart. Sometimes, the physical findings of the cardiac examination need to be clarified with a chest radiograph or an echocardiogram. The specifics of the cardiac structure can help predict the risk for the cardiac arrhythmia in regard to sudden cardiac death or can help to select patients for specific treatment modalities. TREATMENT PRINCIPLES
Traditional treatment strategies for chronic arrhythmias in children have mostly relied on the use of antiarrhythmic drug therapy. In the past decade, catheter ablation techniques have evolved so that the substrates for most sustained pediatric tachycardias (i.e., SVT or ventricular tachycardia [VT]) can be destroyed in the context of a single catheterization session lasting 3 or 4 hours. With successful ablation therapy, patients can be rendered both tachycardia and medication free for the rest of their lives. Because catheter ablation therapy has been performed for less than a decade, some caution regarding its long-term effects is warranted; however, when the issues of long-term medical therapy versus catheter ablation techniques are discussed with parents, many choose ablation for the treatment of their children’s arrhythmias. ”Parental choice” is the most common indication for catheter ablation procedures in the pediatric age group. Catheter ablation is the procedure of choice for any child, regardless of age or size, who has a life-threatening event from a tachyarrhythmia and whose substrate is amenable to an ablation procedure. Medications are still used by many physicians to treat pediatric patients with tachyarrhythmias. In children with normal hearts, most medications are well tolerated. Depending on the symptoms of the arrhythmia, some medications can be started on an outpatient basis (e.g., digoxin or p-blockers for patients with SVT). Stronger antiarrhythmic therapy (class I or I11 medications) is usually started in the hospital because of the possibility of proarrhythmia. This phenomenon is more common in children with structural heart disease or significant arrhythmias but also has been reported in children with normal hearts and relatively benign rhythm disturbance^.^ Cardiac pacing is still the therapy of choice for children with bradycardia. The devices involved in permanent pacing techniques are sufficiently small to be used safely in most infants and children. More sophisticated implantable devices that not only pace the heart but also can terminate tachyarrhythmias may also be useful in treating pediatric patients with arrhythmias. Antitachycardia pacemakers and implantable defibrillators have become more common treatment options for children with severe forms of bradycardia-tachycardia syndromes?
DIAGNOSIS AND TREATMENT OF PEDIATRIC ARRHYTHMIAS
351
SPECIFIC ARRHYTHMIAS Supraventricular Tachycardia
Supraventricular tachycardia is the most common sustained tachyarrhythmia in children. Most commonly in children younger than 12 years of age, the SVT is caused by an accessory atrioventricular connection; in teenage years, atrioventricular node reentry tachycardia is also an important cause of SVT.* In accessory connection-mediated tachycardia, the common tachycardia circuit (i.e., orthodromic tachycardia) is comprised of antegrade conduction down the atrioventricular node and retrograde conduction up the accessory connection. If the accessory connection also has antegrade conduction properties, the term WPW is applicable. With WPW, the surface ECG shows the characteristic short PR interval and wide QRS (Fig. 1). Patients with WPW not only can have orthodromic tachycardia but also can have antidromic tachycardia. The circuit of antidromic tachycardia involves antegrade conduction down the accessory connection, with retrograde conduction up the atrioventricular node or alternative accessory connection. WPW patients are also prone to have atrial flutter with rapid conduction down the accessory connection. Tachycardias associated with WPW and that involve antegrade conduction down the accessory connection may be dangerous and associated with sudden cardiac death. The risk for sudden cardiac death in patients with WPW is 1%every 10 years. For this reason, any child with WPW and a syncopal tachycardia episode should be considered for a catheter ablation procedure. The classic ECG characteristic of accessory connection-mediated orthodromic tachycardia is a narrow QRS tachycardia with a retrograde P wave inscribed after the QRS in the ST segment. (Fig. 2). Antidromic SVT has a wide QRS morphology and resembles VT. Both antidromic and orthodromic SVT are reentrant in nature, so they can have an abrupt onset and termination. Acute termination of orthodromic SVT can be accomplished by vagal ma-
Figure 1. ECG of a patient with Wolff-Parkinson-White. wide QRS.
Note the short PR interval and
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CASE
Figure 2. ECG of a child with orthodromic SVT. Note the retrograde P waves in the ST
segments. neuvers or with medications. Adenosine (100 &kg) given intravenously and rapidly breaks the orthodromic circuit at the level of the atrioventricular node. Other intravenous medications, such as verapamil, digoxin, procainamide, propranolol, and amiodarone, can also be used to acutely terminate SVT. Intravenous verapamil is contraindicated in infants and small children. It can be used cautiously in older children, but is probably best avoided altogether in the pediatric population. Long-term medical treatment of patients with orthodromic SVT usually involves digoxin or @-blockertherapy. Other medications, such as flecainaide, procainamide, sotalol, amiodarone, and verapamil, are used for more recalcitrant SVT. Digoxin should be avoided in children with WPW because of its potential proarrhythmia effects. It can enhance the conduction properties of the accessory pathway, resulting in a more rapid ventricular rate during atrial flutter and an increased risk for sudden death. Radiofrequency catheter ablation has become an important treatment of chronic atrioventricular reentrant tachycardia. Success rates for radiofrequency catheter ablation and accessory connections depend on the age of the patient, structures of the heart, pathway location, and operator experience. In general, success rates in experienced centers range between 85% and Premature Beats
Premature beats, either atrial or ventricular, are common in children. Atrial or ventricular premature beats that occur in the context of children with normal hearts and are extinguished with exercise generally have a benign natural history. Generally, premature ventricular beats with structural heart disease (e.g., postoperative CHD) or poor cardiac function ( e g , cardiomyopathy) are associated with an increased risk for sudden cardiac death? Stratifying such patients so as to identify treatment alternatives to mitigate sudden death risk is a subject of ongoing investigation in pediatric electrophysiology.
DIAGNOSIS AND TREATMENT OF PEDIATRIC ARRHYTHMIAS
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Ventricular Tachycardia
Ventricular tachycardia in children is rare compared with the incidence of SVT. Because of this fact, VT is often misdiagnosed and treated as SVT in children. The wide QRS tachycardia in children should be considered to be ventricular tachycardia until proven otherwise. The "wideness" of the QRS in pediatric VT may be subtle, so vigilance is important. The presence of atrioventricular dissociation during tachycardia is diagnostic of VT. Sometimes, VT may still exhibit a 1:l ventricular-atrial relationship (Fig. 3). In children, VT occurs in the context of a normal heart or, more importantly, with structural heart disease. In infants, VT can be associated with hamartomatous growths on the ventricle^.^ These automatic VTs may be responsive to medications but may also necessitate surgical ablation procedures because of hemodynamic compromise. Many VTs of this nature resolve as these children mature. Ventricular tachycardia can be associated with repaired CHD. Children with heart lesions, such as repaired tetrology of Fallot, can have VT that presents as sudden cardiac death.6Antiarrhythmic medications, surgical or catheter ablation procedures, and defibrillator placement may be needed for control of this variety of VT. Other types of VT occur in children with normal hearts5 One such VT has a left bundle branch block morphology with an inferior axis. This VT is automatic in nature, catecholamine sensitive, and originates in the muscle of the right ventricular outflow tract. Another VT seen in children with normal hearts is thought to be secondary to reentry around the Purkinje network of the left posterior fascicle. Treatment regimens for both of these varieties of VT include no intervention, antiarrthymic medications, or ablation procedures. Atrioventricular Block
Symptomatic bradycardia in children requiring cardiac pacing usually involves diseases of the atrioventricular node. Children with congenital complete
Figure 3. ECG of an 8-month-old child with ventricular tachycardia. Note that in certain leads (Ill) the QRS morphology is not overtly wide.
atrioventricular block (CCAVB) may present at any age because of symptoms of bradycardia (e.g., fatigue or syncope). Also, many of these children are asymptomatic and are diagnosed because of a low resting heart rate on physical examination. The only recognized therapy for CCAVB is permanent cardiac pacing. Most patients with CCAVB, even if asymptomatic, are believed to need permanent pacing during their lifetime to avoid the possibility of sudden cardiac death.9 Most children with CCAVB and structurally normal hearts are born to mothers with serologic evidence of systemic lupus erythematosus. All mothers of children born with CCAVB need to be evaluated for connective tissue disease. The risk for CCAVB in subsequent pregnancies may be as high as 16%.’ Atrioventricular block may also be acquired after surgery for certain types of CHD. These surgeries usually involve closure of a ventricular septa1 defect. Patients with atrioventricular block that persists beyond 14 days need permanent cardiac pacing. Cardiac pacing is required to avoid rare episodes of sudden cardiac death. Dual-chambered pacing is preferable to single-chamber pacing in the ventricle. Dual-chamber pacing ensures atrioventricular syncrony, which may be important to maximize hemodynamics in patients with structurally abnormal hearts. SUMMARY
The work up of arrhythmias encountered in the pediatric patient is usually initiated by primary care providers. Proper treatment of pediatric arrhythmias necessitates recording the suspected rhythm disturbance and an evolution of the underlying cardiac structure and function. References 1. Buyon J, Hiebert R, Cope1 J, et a1 Autoimmune-associated congenital heart block Demographics, mortality, morbidity and recurrence rates obtained from a national neonatal lupus registry. J Am Coll Cardiol31:1658-1666, 1998 2. Case C, Sokoloski M, Gillette P: Device therapy for arrhythmias. In Deal B, Wolff G, Gelband H (eds): Current Concepts in Diagnosis and Management of Arrhythmias in Infants and Children. Armonk, NY, Futura Publishing, 1998, pp 401-426 3. Danford D, Kugler J, Deal B, et a 1 The learning curve for radiofrequency ablation of tachyarrhythmias in pediatric patients. Am J Cardiol 75:587-590, 1995 4. Fish F, Gillette P, Benson D Proarrhythmia, cardiac arrest and death in young patients receiving encainide and flecainide. J Am Coll Cardiol 18:35&365, 1991 5. Garson A Jr: Ventricular arrhythmias. In Gillette P, Garson A Jr (eds): Pediatric Arrhythmias: Electrophysiology and Pacing. Philadelphia, WB Saunders, 1990, pp 427-500 6. Garson A Jr, Nihill M, McNamara D, et al: Status of the adult and adolescent after repair of tetralogy of Fallot. Circulation 59:1232-1240, 1979 7. Garson A Jr, Smith RT Jr, Moak JP, et al: Incessant ventricular tachycardia in infants: Myocardial hamartomas and surgical cure. J Am Coll Cardiol 106194126, 1987 8. Ludomirsky A, Garson A Jr: Supraventricular tachycardia. In Gillette P, Garson A Jr (eds): Pediatric Arrhythmias: Electrophysiology and Pacing. Philadelphia, WB Saunders, 1990, pp 380-426 9. Michaelsson M, Jozon A, Risenfeld T Isolated congenital complete atrioventricular block in adult life: A prospective study. Circulation 9244249,1995
Address reprint requests to Christopher L. Case, DMD, MD Cook Children’s Medical Center 801 7th Avenue Fort Worth, TX 76164