126 The respective incidences of heart rhythm disorders change throughout childhood, from fetal life, through newborn infants, and up through the teen years to adulthood. In adults, the most common form of supraventricular tachycardia (SVT) other than atrial fibrillation is atrioventricular nodal reentrant tachycardia (AVNRT). In contrast, in the newborn infant, this diagnosis is unusual, whereas accessory pathway (AP)–mediated tachycardia is the most common form of SVT seen. Through childhood, AVNRT becomes progressively more likely and is common in teenagers.1 Specific arrhythmia mechanisms are much more common in children and adults. Atrial flutter can be seen in the newborn period, with atrial rates in the range of 400 to 600 beats/min, but once converted back to normal sinus rhythm, most will never require therapy or ablation.2 Neonates can exhibit hydrops caused by in utero SVT, but most can be managed with medication once they are born. Furthermore, the natural history of SVT in infants is fairly well characterized, particularly when Wolff-Parkinson-White (WPW) syndrome is present.3 Most will experience spontaneous resolution by 1 year of age, and this argues strongly for avoiding invasive procedures in infants if possible. Occasionally, incessant SVT, especially persistent junctional reciprocating tachycardia (PJRT), or other mechanisms such as atrial ectopic tachycardia or junctional ectopic tachycardia can be difficult to manage and rarely require catheter ablation. It is generally agreed that once the child reaches 3 to 4 years of age, if SVT is still occurring clinically, it is unlikely that the substrate will spontaneously resolve. The specific situation of congenital heart disease (CHD) should be noted. Certain forms of CHD are highly associated with arrhythmias. Most importantly, patients with Ebstein anomaly of the tricuspid valve have a high incidence of coexisting WPW syndrome, generally because of right-sided APs.4 One subtype of hypertrophic cardiomyopathy is associated with WPW syndrome, specifically Danon disease, a form of glycogen storage disease caused by LAMP-2 mutation.5 In patients who have had repair of CHD, a variety of tachyarrhythmias are seen, generally in the late postoperative period, sometimes decades later. This topic is discussed in Chapter 127. Intraatrial reentry tachycardia, also known as postoperative atrial flutter, is seen commonly after extensive atrial surgery, such as a Senning or Mustard procedure, but can also be seen after any operation that involves an atriotomy including repair of tetralogy of Fallot, ventricular septal defect, atrial septal defect, or other conditions.6 The first case reports and single-center reports concerning a catheter ablation in children appeared in the early 1990s, but organized multicenter research quickly followed. There are now reasonable benchmarks for likely success rates, complication rates, and recurrence risks based on these multicenter studies. The collaborative Prospective Assessment after Pediatric Cardiac Ablation (PAPCA) study began enrolling patients on April 1, 1999, in an effort to better determine success rates, complications rates, and the time course of recurrence following initially successful ablation. The PAPCA study included children up to 16 years old with either AP tachycardias or AVNRT. The first PAPCA report included 2761 patients and reported an initial procedural success rate of 95.7%, which was higher for left-sided (97.8%) than for right-sided (90.8%) pathways.7 Acute complications were uncommon (approximately 4%). The incidence of AV block was 1.2% of all procedures, but 2.1% of AVNRT and 3.0% of septal AP procedures. Success rates were high in younger aged children and teenagers, and complication rates were similar. The second PAPCA report focused on recurrence.8 This study involved 517 successfully ablated substrates (540 attempted; 95.7%). Recurrence rate 12 months after ablation related to substrate type (AP, AVNRT) and AP location. It was highest for right septal pathways (24.6%) and lowest for left septal AP and AVNRT (both 4.8%). Serial echocardiography results after ablation was the subject of the third PAPCA report.9 Previously, only anecdotal or retrospective nonblinded data had been reported addressing the issue of potential cardiac structural damage (e.g., valvar regurgitation, perforation, coronary occlusion) by ablation.10 In the small hearts of pediatric patients, this has been an important concern. Of the total 481 patients (follow-up at 2, 6, and 12 months) who were recruited, two-dimensional echocardiography was obtained before and at intervals following the ablation procedure, and these studies were reviewed by a reference laboratory in a blinded fashion. Moderate valve regurgitation was uncommon (0.12%), and severe valve abnormalities were not seen at all. With the exception of the association of mild tricuspid valve regurgitation to right free wall AP and AVNRT, there was no other association of ablation targets to valve proximity. No intracardiac thrombosis or ventricular wall motion or function problems were found. Since the publication of the PAPCA studies, technology has changed, with both the availability of catheter cryoablation and reports of the use of three-dimensional (3D) mapping as a technique for avoiding fluoroscopy exposure. The risk of inadvertent AV block has been lowered substantially with the use of cryoablation.11,12 Only transient block has been reported. This compares to the data for RF ablation that consistently has shown a 1% risk of AV block for slow AV node modification for AVNRT, 3% for ablation of anteroseptal APs, and 10% for midseptal APs.13 Since the beginning of the catheter ablation era, there has been concern about the fate of the coronary arteries, because of the frequent close anatomical proximity of the catheter ablation to the tricuspid and mitral valve annulus. It is thought that high coronary flow dissipates any heat that reaches to coronary arteries, and results have shown, with few exceptions, no evidence of gross catheter ablation damage using standard ablation techniques for APs. However, the concern for potential catheter ablation damage to coronary arteries has never completely receded. There have been occasional but persistent case reports of coronary damage, especially in small children.14 Further animal investigation demonstrated catheter ablation effects by more sensitive tests, such as ultrasound, suggesting that perhaps the absence of gross catheter ablation damage did not negate the potential cellular damage that could lead to clinical problems in the future, in the older pediatric population, and in adults.15 Although there are essentially no reports of the late development of coronary artery disease following catheter ablation, no prospective studies investigating the status of the coronary arteries have been performed. From the factors and available data detailed earlier, it appears reasonable that indications for catheter ablation in pediatric patients should vary with age and symptoms. The 2002 NASPE Expert Consensus Conference reported guidelines for the indications of ablation in children by applying the American Heart Association (AHA) and American College of Cardiology (ACC) definitions used for other published indications: class I, class II, and class III (Box 126-1)16. No other consensus guidelines for pediatric indications have been developed; however, several reports continue to stimulate opinion and discussion. A recent joint expert consensus statement from the Pediatric and Congenital Electrophysiology Society and the Heart Rhythm Society addressed the topic of management of asymptomatic younger patients with WPW syndrome. Traditionally, the risk of sudden death in asymptomatic individuals has been thought to be low (0.1% per year), but it is clear that these data, accumulated for adults, do not necessarily apply to the pediatric population. There have always been reports of pediatric patients with sudden death as their first sign of WPW, but the actual risk of this event has been difficult to determine. The availability of electrophysiology testing, the high success rate, and low complication rate of catheter ablation have prompted many clinicians to take an aggressive approach to studying asymptomatic pediatric patients with WPW syndrome and offering catheter ablation when safe and feasible. The recent consensus document supports the use of noninvasive testing for risk stratification, specifically exercise treadmill testing to identify individuals who have had a spontaneous loss of preexcitation indicating low risk.17 Another approach is the use of the Holter monitor to identify intermittent preexcitation. For individuals who are 8 to 21 years old and exhibit constant preexcitation but are asymptomatic, transvenous or esophageal electrophysiology study was judged reasonable, primarily to evaluate the shortest preexcited RR interval during atrial fibrillation, with subsequent catheter ablation depending on the findings. The decision concerning ablation also depends on the proximity of the pathway to critical structures, such as the conduction system or coronary arteries, and the inducibility of AV reciprocating tachycardia. Another frequently discussed issue is ablation in infants and small children. Data from individual centers suggests that younger and smaller patients appear to have a higher risk of complications, although small numbers of patients limit meaningful statistical analysis. Blaufox et al.18 showed good success rate in their 14 small patients (18 procedures) weighing less than 15 kg. They reported a higher incidence of complications that were significantly associated with greater total RF applications. The consensus is that ablation is recommended only in dire circumstances in this population and, when necessary, limiting RF application duration to 20 seconds.
Ablation in Pediatrics
Indications for Ablation in the Pediatric Age Group
Incidence of Heart Rhythm Abnormalities by Age and Congenital Heart Disease
General Procedural Success and Complication Rates That Inform Indications
Consensus Indications (Class I, II, III) for Catheter Ablation in Children
Ablation in Pediatrics
