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Cardiac arrhythmias in the fetus and newborn
Seminars in Fetal & Neonatal Medicine (2006) 11, 182e190
a v a i l a b l e a t w w w. s c i e n c e d i r e c t . c o m
j o u r n a l h o m e p a g e : w w w. e l s e v i e r. c o m / l o c a t e / s i n y
Cardiac arrhythmias in the fetus and newborn Christopher Wren* Department of Paediatric Cardiology, Freeman Hospital, High Heaton, Newcastle upon Tyne NE7 7DN, UK
KEYWORDS Arrhythmia; Bradycardia; Fetus; Neonate; Tachycardia
Summary Arrhythmias are potentially life-threatening problems in the fetus and newborn. Appropriate management depends on accurate diagnosis. Atrioventricular re-entry is the most common type of supraventricular tachycardia in both the fetus and newborn. It should be distinguished from other types of tachycardia e such as atrial flutter, atrial ectopic tachycardia, permanent junctional re-entry tachycardia, and ventricular tachycardia. Neonatal and fetal bradycardias are less common clinical problems. Sustained bradycardia is most often caused by complete atrioventricular block. It can be mimicked by the more common but benign occurrence of non-conducted atrial premature beats. ª 2006 Elsevier Ltd. All rights reserved.
Introduction Sustained tachycardias and bradycardias are important clinical problems in the fetus and newborn. The physiological properties of the fetal and neonatal myocardium make it intrinsically more vulnerable to high or low ventricular rates.1 Arrhythmias that would not be dangerous later in childhood can be life-threatening early in life. Arrhythmias can be noticed incidentally in the newborn because of bradycardia, tachycardia or irregularity of rhythm, but the most common presentation is with heart failure, usually as a result of sustained tachycardia. Fetal arrhythmias might be noted incidentally or because of the presence of heart failure (hydrops fetalis).
Tachycardias in the newborn Atrioventricular re-entry tachycardia is the most common mechanism of supraventricular tachycardia (SVT) in the * Tel.: C44 191 223 1082; fax: C44 191 223 1314. E-mail address: [email protected]
newborn. The arrhythmia circuit involves normal conduction over the atrioventricular (AV) node and retrograde conduction from ventricle to atrium over an accessory muscular atrioventricular connection (and is known as orthodromic AV re-entry). About a third of accessory connections are capable of anterograde conduction, which is recognized as WolffeParkinsoneWhite syndrome on the electrocardiogram (ECG) in sinus rhythm. The clinical presentation of tachycardia is usually with heart failure, ranging from tachypnoea and poor feeding to cardiogenic shock. The differential diagnosis obviously includes infection and metabolic problems. Sinus tachycardia in an ill baby may be over 200 beats/min, but AV re-entry tachycardia is rarely slower than 270 beats/min (unless the baby is preterm). Recording a 12-lead ECG allows accurate measurement of the heart rate and confirmation of the diagnosis (Fig. 1). Termination of tachycardia is most easily achieved by intravenous administration of adenosine at a dose of 150e 300 mg/kg given by rapid bolus injection (Fig. 2). Adenosine is metabolized very quickly and the dose can be repeated as necessary.2 Facial immersion in iced water or facial application of an ice pack is also usually effective.
1744-165X/$ - see front matter ª 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.siny.2005.12.001
Cardiac arrhythmias in the fetus and newborn
183
Figure 1 Atrioventricular (AV) re-entry tachycardia. A recording from a neonate with a ventricular rate of around 290 beats/min. P waves are clearly seen in the ST segment in lead V1 (arrow). The short RP interval is typical of AV re-entry.
Other drugs are rarely required for termination of tachycardia. The dangers of verapamil in early infancy are well recognized, and this drug is no longer recommended.3 Synchronized electrical cardioversion will be effective but is usually unnecessary and is not easily repeated.
Once sinus rhythm is restored the baby’s condition will improve. There is a strong likelihood of recurrence of tachycardia in the short term, so pharmacological treatment is usually advised. Treatment with a beta-blocker, a class IC drug such as flecainide4,5 or amiodarone6,7 will usually achieve arrhythmia suppression. Most babies will
Figure 2 Adenosine in atrioventricular (AV) re-entry tachycardia. Administration of intravenous adenosine to a neonate with orthodromic AV re-entry tachycardia. Note that tachycardia terminates with a non-conducted P wave (solid arrow). There is then a sinus bradycardia with obvious ventricular pre-excitation (open arrow). As the sinus rate accelerates the delta wave disappears and the QRS returns to normal e the same morphology as in tachycardia.
184 not be prone to attacks after 6 or 12 months, after which treatment is usually withdrawn. Atrial flutter usually presents at or before birth.8,9 It is caused by re-entry within the right atrium. ECG diagnosis is often straightforward with saw-tooth flutter waves best seen in leads II, III and aVF (Fig. 3). In the newborn, the atrial rate is usually around 400 beats/min with 2:1 AV conduction, giving a ventricular rate of around 200 beats/min. Sinus rhythm can be restored by DC cardioversion or transoesophageal pacing. Recurrence of atrial flutter is rare and pharmacological treatment is usually not required. Atrial ectopic tachycardia usually presents as a sustained arrhythmia in early infancy. It is caused by an automatic focus in the left or right atrium and can be difficult to distinguish from sinus tachycardia (Fig. 4). Short-term treatment might be required, but the arrhythmia usually resolves by 6 months of age.10,11 Permanent junctional reciprocating tachycardia is a type of orthodromic AV re-entry with an accessory connection near the coronary sinus, which conducts relatively slowly and only in a retrograde fashion.12 It is easily recognized from the ECG (Fig. 5). Adenosine is only transiently effective. Drug treatment with a beta-blocker, flecainide or amiodarone is required, and spontaneous resolution is unusual rather than very unusual. The definitive treatment is radiofrequency ablation later in childhood.
Ventricular tachycardia in the newborn Paediatricians seem to be reluctant to consider the diagnosis of ventricular tachycardia (VT) in infancy, and most cases are initially mistaken for SVT. If the QRS in tachycardia is abnormal, then the diagnosis of VT should be considered more likely.13,14
C. Wren
Incessant idiopathic infant ventricular tachycardia This arrhythmia is often incessant on presentation with secondary poor ventricular function. It more commonly presents later in infancy but may occur earlier. The ECG usually shows a right bundle branch block and superior axis morphology (Fig. 6), predicting an origin in the inferior left ventricle. The underlying cause is probably a microscopic tumour (myocardial hamartoma) in most cases. Drugs such as amiodarone and flecainide are usually effective in controlling the arrhythmia.15 The VT usually resolves by 5 years of age and drug treatment can be withdrawn.
Accelerated idioventricular rhythm in the newborn The incidence of this arrhythmia is unknown, as it is usually asymptomatic and transient and may go undetected. The VT is not much faster than sinus rhythm (usually by less than 25%).16 It usually has a left bundle branch block pattern (presumably a right ventricular origin) and shows intermittent sinus rhythm (Fig. 7). The QRS widening is relatively subtle but is obvious if sinus beats are available for comparison. This arrhythmia will usually respond to a beta-blocker, flecainide or amiodarone if treatment is considered necessary. It usually resolves spontaneously with no long-term sequelae.
Bradycardias in the newborn Most bradycardias in the newborn are transient and benign. Intermittent bradycardia associated with apnoea is particularly common in prematurity.
Figure 3 Atrial flutter. A recording from a neonate with idiopathic atrial flutter. The flutter rate is 460 beats/min with 2:1 conduction giving a ventricular rate of 230 beats/min. ‘Saw tooth’ flutter waves are best seen in leads II, III and aVF.
Cardiac arrhythmias in the fetus and newborn
185
Figure 4 Atrial ectopic tachycardia. The PR interval is prolonged and P waves are in the terminal portion of the previous QRS (best seen in lead V1). The presentation was with apparent ‘dilated cardiomyopathy’ but myocardial impairment was secondary and improved once the arrhythmia was controlled.
Congenital complete atrioventricular block is the most common significant cause of sustained bradycardia. It is often recognized during labour and can result in emergency caesarean section for presumed fetal distress. The ECG
shows a regular normal atrial rhythm and a regular dissociated ventricular bradycardia (Fig. 8). The most common cause is maternal connective tissue disease (which is often asymptomatic).17 Anti-Ro antibodies cross the placenta and
Figure 5 Permanent junctional reciprocating tachycardia. An incessant arrhythmia with a characteristic appearance. Note the very long RP interval and the deeply inverted P waves in leads II, III and aVF. This is a type of orthodromic atrioventricular (AV) re-entry over a relatively slowly conducting concealed right posteroseptal pathway.
186
C. Wren
Figure 6 Incessant idiopathic ventricular tachycardia of infancy. A rapid, wide QRS tachycardia with a right bundle branch block pattern and a QRS axis of around ÿ90 . The shorter secondary R wave in V1 suggests VT. Ventricular dissociation is not easy to see but the rhythm strip at the bottom does suggest irregular P waves superimposed on the T waves. The origin of the VT is presumably from the posterior left ventricle.
can damage the developing conduction system. Complete AV block is sometimes associated with structural abnormalities such as left atrial isomerism or congenitally corrected transposition. Management in the newborn depends mainly
on the ventricular rate. If the rate is below 55 beats/min, pacing is usually advocated.18 Several arrhythmias may masquerade as AV block but can be differentiated by careful ECG analysis. Non-conducted
Figure 7 Ventricular tachycardia in infancy. The QRS is relatively narrow but is obviously wide compared with the sinus beat seen in leads V4e6. There is 1:1 VA conduction in the first 3/4th of the recording but slower dissociated P waves are seen after the sinus beats in the last 1/4th.
Cardiac arrhythmias in the fetus and newborn
187
Figure 8 Complete atrioventricular block. A recording from a neonate whose mother has Sjo ¨gren’s syndrome. The atrial rate is normal at 140 beats/min. The ventricular rate is 65 beats/min and there is complete AV dissociation. The QRS complexes are normal. The baby had a structurally normal heart and there was no immediate indication for pacemaker implantation.
atrial premature beats are common and, if frequent, will produce a bradycardia, which is irregular (Fig. 9).
Tachycardia in the fetus Fetal tachycardia is an important cause of fetal morbidity and mortality. Reliable diagnosis in utero has been
possible only since the introduction of fetal echocardiography. The mechanisms of tachycardia occurring prenatally are similar to those presenting postnatally. Most reports only distinguish between SVT (1:1 AV relationship) (Fig. 10) and atrial flutter (very rapid atrial rate, usually with 2:1 AV conduction) (Fig. 11). The rate of fetal tachycardia is of no real help in defining the mechanism, as
Figure 9 Non-conducted atrial premature beats. The rhythm here is sinus but every third, fourth or fifth P wave occurs prematurely with a different morphology from a normal P wave. The early P wave occurs within the ST segment and is therefore not conducted, producing a pause.
188
C. Wren
Figure 10 Fetal supraventricular tachycardia. An M mode sweep from right atrium (RA) to left ventricle (LV). Both show a rate of 240 beats/min. IVS, interventricular septum; TV, tricuspid valve.
most tachycardias occur at about 240 beats/min. Atrial flutter usually has a rate of 440e480 beats/min, which, with 2:1 conduction, gives a ventricular rate of 220e240 beats/min.19 Ideally, we should try to make a more precise diagnosis than ‘SVT’, although this is obviously more difficult without an ECG. There are reports of the use of echocardiography or Doppler to assess the relative timing of atrial and ventricular activations, although in practice this is
difficult.20 The aim is to distinguish between tachycardia with a short VA time (usually atrioventricular re-entry) and tachycardia with a long VA time, usually atrial ectopic tachycardia or PJRT). Confirmation of the mechanism is usually possible only postnatally. Treatment of fetal tachycardia usually involves oral drug administration to the mother or e rarely e parenteral administration of agents to the fetus. Digoxin used to be the mainstay of treatment and verapamil was often the
Figure 11 Fetal atrial flutter. M mode recordings showing a right atrial (RA) rate of 480 beats/min and aortic (Ao) opening at 240 beats/min, evidence of atrial flutter with 2:1 atrioventricular conduction.
Cardiac arrhythmias in the fetus and newborn
189
Figure 12 Fetal complete atrioventricular block. Superimposed traces of flow in the aorta (above) and foramen ovale to show atrioventricular dissociation and ventricular bradycardia.
second choice. Digoxin has relatively little effect in suppressing infant SVT, and intravenous verapamil is recognized as potentially hazardous in early infancy. The more recent use of anti-arrhythmic drugs such as amiodarone and flecainide has led to an increased efficacy of treatment and a reduction in mortality.21,22
Bradycardia in the fetus Bradycardia in the fetus is often defined as a rate of less than 100 or 110 beats/min. Transient bradycardias are common and benign. Bradycardia during labour might result from fetal distress. The most important cause of sustained fetal bradycardia is complete atrioventricular block. As in the newborn, this might be associated with left atrial isomerism but is usually related to maternal anti-SSA antibodies. Complete atrioventricular block is recognized on the echocardiogram or Doppler tracing from a normal atrial rate and regular ventricular bradycardia (Fig. 12). The prognosis depends on the ventricular rate and presence or absence of structural heart disease or hydrops. Preterm delivery is usually not advised. Although maternally administered sympathomimetics can increase the ventricular rate, they have not been shown to improve outcome. Similarly, steroids and other treatments are not proven to influence atrioventricular conduction. Management is usually conservative. The main differential diagnosis of AV block in the fetus, as in the newborn, is nonconducted atrial premature beats. They are common and benign and have a bigeminal pattern, producing a regular bradycardia.
Practice points Atrioventricular re-entry is the most common type of supraventricular tachycardia in the neonate. Adenosine is effective in neonates if given in an appropriate dose. Amiodarone or flecainide will be needed for 6e12 months to prevent recurrence. Other types of tachycardia, such as atrial flutter, atrial ectopic tachycardia, permanent junctional re-entry tachycardia and ventricular tachycardia, require precise diagnosis before treatment.
Research agenda The influence of site and mode of pacing of neonatal AV block on the late development of dilated cardiomyopathy. Efficacy of treatment of fetal tachycardias. Efficacy of attempts to influence progression/ regression of fetal AV block.
References 1. Rudolph AM. Congenital diseases of the heart: clinico-physiological considerations. Armonk, NY: Futura; 2001.
190 2. Dixon J, Foster K, Wyllie J, Wren C. Guidelines and adenosine dosing in supraventricular tachycardia. Arch Dis Child 2005;90: 1190e1. 3. Garson Jr A. Medicolegal problems in the management of cardiac arrhythmias in children. Pediatrics 1987;79:84e8. 4. O’Sullivan JJ, Gardiner HM, Wren C. Digoxin or flecainide for prophylaxis of supraventricular tachycardia in infants. J Am Coll Cardiol 1995;26:991e4. 5. Perry JC, Garson Jr A. Flecainide acetate for treatment of tachyarrhythmias in children: review of world literature on efficacy, safety, and dosing. Am Heart J 1992;124:1614e21. 6. Etheridge SP, Craig JE, Compton SJ. Amiodarone is safe and highly effective therapy for supraventricular tachycardia in infants. Am Heart J 2001;141:105e10. 7. Burri S, Hug MI, Bauersfeld U. Efficacy and safety of intravenous amiodarone for incessant tachycardias in infants. Eur J Pediatr 2003;162:880e4. 8. Lisowski LA, Verheijen PM, Benatar AA, Soyeur DJ, Stoutenbeek P, Brenner JI, et al. Atrial flutter in the perinatal age group: diagnosis, management and outcome. J Am Coll Cardiol 2000;35:771e7. 9. Casey FA, McCrindle BW, Hamilton RM, Gow RM. Neonatal atrial flutter: significant early morbidity and excellent long-term prognosis. Am Heart J 1997;133:302e6. 10. Baursfeld U, Gow RM, Hamilton RM, Izukawa T. Treatment of atrial ectopic tachycardia in infants <6 months old. Am Heart J 1995;129:1145e8. 11. Salerno JC, Kertesz NJ, Friedman RA, Fenrich Jr AL. Clinical course of atrial ectopic tachycardia is age-dependent: results and treatment in children <3 or 3 years of age. J Am Coll Cardiol 2004;43:438e44. 12. Dorostkar PC, Silka MJ, Morady F, Dick M. Clinical course of persistent junctional reciprocating tachycardia. J Am Coll Cardiol 1999;33:366e75.
C. Wren 13. Davis AM, Gow RM, McCrindle BW, Hamilton RM. Clinical spectrum, therapeutic management, and follow-up of ventricular tachycardia in infants and young children. Am Heart J 1996; 131:186e91. 14. Pfammatter JP, Paul T. Idiopathic ventricular tachycardia in infancy and childhood: a multicenter study on clinical profile and outcome. J Am Coll Cardiol 1999;33:2067e72. 15. Villiain E, Bonnet D, Kachaner J, Le Bidois J, Cohen L, Piechaud JF, et al. Tachycardies ventriculaires incessantes idiopathiques du nourrisson. Arch Mal Coeur Vaiss 1990;83: 665e71. 16. Perry JC. Ventricular tachycardia in neonates. PACE 1997;20: 2061e4. 17. Eronen M, Siren MK, Ekblad H, Tikanoja T, Julkunen H, Paavilainen T. Short and long-term outcome of children with congenital complete heart block diagnosed in utero or as a newborn. Pediatrics 2000;106:86e91. 18. Villain E, Martelli H, Bonnet D, Iserin L, Butera G, Kachaner J. Characteristics and results of epicardial pacing in neonates and infants. PACE 2000;23:2052e6. 19. Krapp M, Kohl T, Simpson JM, Sharland GK, Katalinic A, Gembruch U. Review of diagnosis, treatment, and outcome of fetal atrial flutter compared with supraventricular tachycardia. Heart 2003;89:913e7. 20. Fouron J-C, Fournier A, Proulx F, Lamarche J, Bigras JL, Boutin C, et al. Management of fetal tachyarrhythmia based on superior vena cava/aorta Doppler flow recordings. Heart 2003;89:1211e6. 21. Frohn-Mulder IM, Stewart PA, Witsenburg M, Den Hollander NS, Wladimiroff JW, Hess J. The efficacy of flecainide versus digoxin in the management of fetal supraventricular tachycardia. Prenat Diagn 1995;15:1209e13. 22. Kleinman CS, Nehgme RA. Cardiac arrhythmias in the human fetus. Pediatr Cardiol 2004;25:234e51.
a v a i l a b l e a t w w w. s c i e n c e d i r e c t . c o m
j o u r n a l h o m e p a g e : w w w. e l s e v i e r. c o m / l o c a t e / s i n y
Cardiac arrhythmias in the fetus and newborn Christopher Wren* Department of Paediatric Cardiology, Freeman Hospital, High Heaton, Newcastle upon Tyne NE7 7DN, UK
KEYWORDS Arrhythmia; Bradycardia; Fetus; Neonate; Tachycardia
Summary Arrhythmias are potentially life-threatening problems in the fetus and newborn. Appropriate management depends on accurate diagnosis. Atrioventricular re-entry is the most common type of supraventricular tachycardia in both the fetus and newborn. It should be distinguished from other types of tachycardia e such as atrial flutter, atrial ectopic tachycardia, permanent junctional re-entry tachycardia, and ventricular tachycardia. Neonatal and fetal bradycardias are less common clinical problems. Sustained bradycardia is most often caused by complete atrioventricular block. It can be mimicked by the more common but benign occurrence of non-conducted atrial premature beats. ª 2006 Elsevier Ltd. All rights reserved.
Introduction Sustained tachycardias and bradycardias are important clinical problems in the fetus and newborn. The physiological properties of the fetal and neonatal myocardium make it intrinsically more vulnerable to high or low ventricular rates.1 Arrhythmias that would not be dangerous later in childhood can be life-threatening early in life. Arrhythmias can be noticed incidentally in the newborn because of bradycardia, tachycardia or irregularity of rhythm, but the most common presentation is with heart failure, usually as a result of sustained tachycardia. Fetal arrhythmias might be noted incidentally or because of the presence of heart failure (hydrops fetalis).
Tachycardias in the newborn Atrioventricular re-entry tachycardia is the most common mechanism of supraventricular tachycardia (SVT) in the * Tel.: C44 191 223 1082; fax: C44 191 223 1314. E-mail address: [email protected]
newborn. The arrhythmia circuit involves normal conduction over the atrioventricular (AV) node and retrograde conduction from ventricle to atrium over an accessory muscular atrioventricular connection (and is known as orthodromic AV re-entry). About a third of accessory connections are capable of anterograde conduction, which is recognized as WolffeParkinsoneWhite syndrome on the electrocardiogram (ECG) in sinus rhythm. The clinical presentation of tachycardia is usually with heart failure, ranging from tachypnoea and poor feeding to cardiogenic shock. The differential diagnosis obviously includes infection and metabolic problems. Sinus tachycardia in an ill baby may be over 200 beats/min, but AV re-entry tachycardia is rarely slower than 270 beats/min (unless the baby is preterm). Recording a 12-lead ECG allows accurate measurement of the heart rate and confirmation of the diagnosis (Fig. 1). Termination of tachycardia is most easily achieved by intravenous administration of adenosine at a dose of 150e 300 mg/kg given by rapid bolus injection (Fig. 2). Adenosine is metabolized very quickly and the dose can be repeated as necessary.2 Facial immersion in iced water or facial application of an ice pack is also usually effective.
1744-165X/$ - see front matter ª 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.siny.2005.12.001
Cardiac arrhythmias in the fetus and newborn
183
Figure 1 Atrioventricular (AV) re-entry tachycardia. A recording from a neonate with a ventricular rate of around 290 beats/min. P waves are clearly seen in the ST segment in lead V1 (arrow). The short RP interval is typical of AV re-entry.
Other drugs are rarely required for termination of tachycardia. The dangers of verapamil in early infancy are well recognized, and this drug is no longer recommended.3 Synchronized electrical cardioversion will be effective but is usually unnecessary and is not easily repeated.
Once sinus rhythm is restored the baby’s condition will improve. There is a strong likelihood of recurrence of tachycardia in the short term, so pharmacological treatment is usually advised. Treatment with a beta-blocker, a class IC drug such as flecainide4,5 or amiodarone6,7 will usually achieve arrhythmia suppression. Most babies will
Figure 2 Adenosine in atrioventricular (AV) re-entry tachycardia. Administration of intravenous adenosine to a neonate with orthodromic AV re-entry tachycardia. Note that tachycardia terminates with a non-conducted P wave (solid arrow). There is then a sinus bradycardia with obvious ventricular pre-excitation (open arrow). As the sinus rate accelerates the delta wave disappears and the QRS returns to normal e the same morphology as in tachycardia.
184 not be prone to attacks after 6 or 12 months, after which treatment is usually withdrawn. Atrial flutter usually presents at or before birth.8,9 It is caused by re-entry within the right atrium. ECG diagnosis is often straightforward with saw-tooth flutter waves best seen in leads II, III and aVF (Fig. 3). In the newborn, the atrial rate is usually around 400 beats/min with 2:1 AV conduction, giving a ventricular rate of around 200 beats/min. Sinus rhythm can be restored by DC cardioversion or transoesophageal pacing. Recurrence of atrial flutter is rare and pharmacological treatment is usually not required. Atrial ectopic tachycardia usually presents as a sustained arrhythmia in early infancy. It is caused by an automatic focus in the left or right atrium and can be difficult to distinguish from sinus tachycardia (Fig. 4). Short-term treatment might be required, but the arrhythmia usually resolves by 6 months of age.10,11 Permanent junctional reciprocating tachycardia is a type of orthodromic AV re-entry with an accessory connection near the coronary sinus, which conducts relatively slowly and only in a retrograde fashion.12 It is easily recognized from the ECG (Fig. 5). Adenosine is only transiently effective. Drug treatment with a beta-blocker, flecainide or amiodarone is required, and spontaneous resolution is unusual rather than very unusual. The definitive treatment is radiofrequency ablation later in childhood.
Ventricular tachycardia in the newborn Paediatricians seem to be reluctant to consider the diagnosis of ventricular tachycardia (VT) in infancy, and most cases are initially mistaken for SVT. If the QRS in tachycardia is abnormal, then the diagnosis of VT should be considered more likely.13,14
C. Wren
Incessant idiopathic infant ventricular tachycardia This arrhythmia is often incessant on presentation with secondary poor ventricular function. It more commonly presents later in infancy but may occur earlier. The ECG usually shows a right bundle branch block and superior axis morphology (Fig. 6), predicting an origin in the inferior left ventricle. The underlying cause is probably a microscopic tumour (myocardial hamartoma) in most cases. Drugs such as amiodarone and flecainide are usually effective in controlling the arrhythmia.15 The VT usually resolves by 5 years of age and drug treatment can be withdrawn.
Accelerated idioventricular rhythm in the newborn The incidence of this arrhythmia is unknown, as it is usually asymptomatic and transient and may go undetected. The VT is not much faster than sinus rhythm (usually by less than 25%).16 It usually has a left bundle branch block pattern (presumably a right ventricular origin) and shows intermittent sinus rhythm (Fig. 7). The QRS widening is relatively subtle but is obvious if sinus beats are available for comparison. This arrhythmia will usually respond to a beta-blocker, flecainide or amiodarone if treatment is considered necessary. It usually resolves spontaneously with no long-term sequelae.
Bradycardias in the newborn Most bradycardias in the newborn are transient and benign. Intermittent bradycardia associated with apnoea is particularly common in prematurity.
Figure 3 Atrial flutter. A recording from a neonate with idiopathic atrial flutter. The flutter rate is 460 beats/min with 2:1 conduction giving a ventricular rate of 230 beats/min. ‘Saw tooth’ flutter waves are best seen in leads II, III and aVF.
Cardiac arrhythmias in the fetus and newborn
185
Figure 4 Atrial ectopic tachycardia. The PR interval is prolonged and P waves are in the terminal portion of the previous QRS (best seen in lead V1). The presentation was with apparent ‘dilated cardiomyopathy’ but myocardial impairment was secondary and improved once the arrhythmia was controlled.
Congenital complete atrioventricular block is the most common significant cause of sustained bradycardia. It is often recognized during labour and can result in emergency caesarean section for presumed fetal distress. The ECG
shows a regular normal atrial rhythm and a regular dissociated ventricular bradycardia (Fig. 8). The most common cause is maternal connective tissue disease (which is often asymptomatic).17 Anti-Ro antibodies cross the placenta and
Figure 5 Permanent junctional reciprocating tachycardia. An incessant arrhythmia with a characteristic appearance. Note the very long RP interval and the deeply inverted P waves in leads II, III and aVF. This is a type of orthodromic atrioventricular (AV) re-entry over a relatively slowly conducting concealed right posteroseptal pathway.
186
C. Wren
Figure 6 Incessant idiopathic ventricular tachycardia of infancy. A rapid, wide QRS tachycardia with a right bundle branch block pattern and a QRS axis of around ÿ90 . The shorter secondary R wave in V1 suggests VT. Ventricular dissociation is not easy to see but the rhythm strip at the bottom does suggest irregular P waves superimposed on the T waves. The origin of the VT is presumably from the posterior left ventricle.
can damage the developing conduction system. Complete AV block is sometimes associated with structural abnormalities such as left atrial isomerism or congenitally corrected transposition. Management in the newborn depends mainly
on the ventricular rate. If the rate is below 55 beats/min, pacing is usually advocated.18 Several arrhythmias may masquerade as AV block but can be differentiated by careful ECG analysis. Non-conducted
Figure 7 Ventricular tachycardia in infancy. The QRS is relatively narrow but is obviously wide compared with the sinus beat seen in leads V4e6. There is 1:1 VA conduction in the first 3/4th of the recording but slower dissociated P waves are seen after the sinus beats in the last 1/4th.
Cardiac arrhythmias in the fetus and newborn
187
Figure 8 Complete atrioventricular block. A recording from a neonate whose mother has Sjo ¨gren’s syndrome. The atrial rate is normal at 140 beats/min. The ventricular rate is 65 beats/min and there is complete AV dissociation. The QRS complexes are normal. The baby had a structurally normal heart and there was no immediate indication for pacemaker implantation.
atrial premature beats are common and, if frequent, will produce a bradycardia, which is irregular (Fig. 9).
Tachycardia in the fetus Fetal tachycardia is an important cause of fetal morbidity and mortality. Reliable diagnosis in utero has been
possible only since the introduction of fetal echocardiography. The mechanisms of tachycardia occurring prenatally are similar to those presenting postnatally. Most reports only distinguish between SVT (1:1 AV relationship) (Fig. 10) and atrial flutter (very rapid atrial rate, usually with 2:1 AV conduction) (Fig. 11). The rate of fetal tachycardia is of no real help in defining the mechanism, as
Figure 9 Non-conducted atrial premature beats. The rhythm here is sinus but every third, fourth or fifth P wave occurs prematurely with a different morphology from a normal P wave. The early P wave occurs within the ST segment and is therefore not conducted, producing a pause.
188
C. Wren
Figure 10 Fetal supraventricular tachycardia. An M mode sweep from right atrium (RA) to left ventricle (LV). Both show a rate of 240 beats/min. IVS, interventricular septum; TV, tricuspid valve.
most tachycardias occur at about 240 beats/min. Atrial flutter usually has a rate of 440e480 beats/min, which, with 2:1 conduction, gives a ventricular rate of 220e240 beats/min.19 Ideally, we should try to make a more precise diagnosis than ‘SVT’, although this is obviously more difficult without an ECG. There are reports of the use of echocardiography or Doppler to assess the relative timing of atrial and ventricular activations, although in practice this is
difficult.20 The aim is to distinguish between tachycardia with a short VA time (usually atrioventricular re-entry) and tachycardia with a long VA time, usually atrial ectopic tachycardia or PJRT). Confirmation of the mechanism is usually possible only postnatally. Treatment of fetal tachycardia usually involves oral drug administration to the mother or e rarely e parenteral administration of agents to the fetus. Digoxin used to be the mainstay of treatment and verapamil was often the
Figure 11 Fetal atrial flutter. M mode recordings showing a right atrial (RA) rate of 480 beats/min and aortic (Ao) opening at 240 beats/min, evidence of atrial flutter with 2:1 atrioventricular conduction.
Cardiac arrhythmias in the fetus and newborn
189
Figure 12 Fetal complete atrioventricular block. Superimposed traces of flow in the aorta (above) and foramen ovale to show atrioventricular dissociation and ventricular bradycardia.
second choice. Digoxin has relatively little effect in suppressing infant SVT, and intravenous verapamil is recognized as potentially hazardous in early infancy. The more recent use of anti-arrhythmic drugs such as amiodarone and flecainide has led to an increased efficacy of treatment and a reduction in mortality.21,22
Bradycardia in the fetus Bradycardia in the fetus is often defined as a rate of less than 100 or 110 beats/min. Transient bradycardias are common and benign. Bradycardia during labour might result from fetal distress. The most important cause of sustained fetal bradycardia is complete atrioventricular block. As in the newborn, this might be associated with left atrial isomerism but is usually related to maternal anti-SSA antibodies. Complete atrioventricular block is recognized on the echocardiogram or Doppler tracing from a normal atrial rate and regular ventricular bradycardia (Fig. 12). The prognosis depends on the ventricular rate and presence or absence of structural heart disease or hydrops. Preterm delivery is usually not advised. Although maternally administered sympathomimetics can increase the ventricular rate, they have not been shown to improve outcome. Similarly, steroids and other treatments are not proven to influence atrioventricular conduction. Management is usually conservative. The main differential diagnosis of AV block in the fetus, as in the newborn, is nonconducted atrial premature beats. They are common and benign and have a bigeminal pattern, producing a regular bradycardia.
Practice points Atrioventricular re-entry is the most common type of supraventricular tachycardia in the neonate. Adenosine is effective in neonates if given in an appropriate dose. Amiodarone or flecainide will be needed for 6e12 months to prevent recurrence. Other types of tachycardia, such as atrial flutter, atrial ectopic tachycardia, permanent junctional re-entry tachycardia and ventricular tachycardia, require precise diagnosis before treatment.
Research agenda The influence of site and mode of pacing of neonatal AV block on the late development of dilated cardiomyopathy. Efficacy of treatment of fetal tachycardias. Efficacy of attempts to influence progression/ regression of fetal AV block.
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