Catheter Ablation in Children With Accessory A-V Pathway

Do Short-Term Results Predict Long-Term Success?

Corresponding Author

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• catheter ablation
• Wolff-Parkinson-White syndrome

Wolff- Parkinson-White syndrome affects up to 0.3% of the population and is diagnosed in about 20,000 patients per year in the United States. The limited efficacy of antiarrhythmic therapy and the replacement of surgical ablation led to the increased use of catheter ablation for long-lasting elimination of conduction over accessory A-V pathways (1). Although initial reports of catheter ablation mainly included adult patients, its use has progressively expanded to pediatric patients (2). In fact, pediatric electrophysiologists perform a large number of the ablation procedures in patients with accessory A-V pathways. The success and safety of catheter ablation is constantly evolving due to an increase experience in these procedures and an improvement in technology. Initially, catheter navigation was guided only by fluoroscopy, while mapping was limited to interpretation of timing and characteristics of intracardiac electrograms. Now catheter navigation can also be guided by non-fluoroscopic mapping systems and even robotically maneuvered catheters, reducing radiation exposure and improving catheter stability. Despite these improvements in experience and technology, there is still limited information regarding the long-term success and safety of catheter ablation in the pediatric population who have Wolff- Parkinson-White syndrome.

Because the success rate in ablating accessory pathways is high, one has to ask when to perform catheter ablation in children with accessory A-V pathways? The decision is straightforward when the arrhythmia is life-threatening as it occurs with atrial fibrillation and rapidly conduction accessory pathways or when the patients has recurrent symptomatic AV reciprocating tachycardia that is not controlled with antiarrhythmic therapy. However, a lack of symptoms does not mean that the patient is at low risk of malignant arrhythmias (3,4). Of course, there are limitations to using certain catheters and equipment in children with low weight and size reducing the likelihood of procedural success. Before recommending an invasive electrophysiology study and possible ablation in children with an accessory A-V pathway, it is important to know the risks as well as the long-term success of the procedure. There are several possible complications that are not always consistently reported in the literature. In addition to complications related to vascular access and transseptal puncture, the site where radiofrequency current needs to be delivered can determine specific risks. For example, when ablation needs to be performed close to the atrioventricular conduction system, a coronary artery, or the valves. Still many centers have excellent success and a low complication rate with catheter ablation in children. However, the long-term efficacy following catheter ablation in children is not well known since most studies have only included follow-up of up to 1 year. In patients with overt accessory pathways, electrocardiographic loss of the delta wave is encouraging. However ablation may eliminate antegrade A-V conduction through the accessory pathway, but with eventual recovery of retrograde conduction. Under these conditions, patients may remain asymptomatic if the conditions for reentry are not met by spontaneous atrial or ventricular premature beats.

In this issue of JACC: Clinical Electrophysiology, Backhoff et al. (5) report the long-term outcome after radiofrequency ablation of accessory A-V pathways in 296 children with a median 11.6 years of age who were followed for a median of 5.6 years. The authors used a navigation mapping system in addition to intracardiac electrograms and ablation was performed with a non-irrigated 4 mm. tip electrode catheter. The ablation protocol used a total of 30 s of radiofrequency energy application if accessory pathway conduction was interrupted within 15 s after the start of the ablation. The ablation procedure was considered successful if there was no return of accessory pathway after 30 min of observation. There was an initial success of 91%, with failed ablations higher in right sided and multiple accessory pathway patients. Only 7 patients had epicardial accessory pathways and this accounted for 2 failed ablations. Recurrence of accessory pathways conduction occurred in 8% of children within the first year (early recurrence) and in another 2% thereafter (late recurrence) Therefore, when analyzing long-term efficacy up to 5 years post-ablation, elimination of accessory pathway conduction was achieved in only 80.7% of patients. In this study patients did not undergo a repeat electrophysiology if they remained asymptomatic and the electrocardiogram did not show ventricular pre-excitation. Consequently, we may conclude that even in this long-term study, some patients with recurrence of retrograde conduction over the accessory A-V pathway may be undiagnosed. It is well known that due to anatomical reasons, the margin of safety for conduction is better in the retrograde than in the antegrade direction (6). Therefore, a partially damage accessory A-V pathway is more likely to lose antegrade than retrograde conduction. Six patients, who had late recurrence of accessory pathway conduction, had left sided accessory pathways. Although not unexpected, a higher number of radiofrequency current applications, longer procedure duration and longer fluoroscopy time were associated with failed procedures. The majority of patients did not have concomitant structural heart disease. Cardiomyopathy was present in 8 patients, Ebstein anomaly in 7 patients, and complex congenital heart disease in 5 patients. One patient had a femoral vein thrombosis followed by a pulmonary embolus.

Results of this study are important when counseling patients and family regarding long-term outcome after ablation. Results also emphasizes the fact that short-term results do not necessarily predict long-term success. This is especially relevant in the pediatric population as the size of the patient may restrict the selection of diagnostic catheters available, and this in turn may make localization of the accessory pathway conduction more difficult. In addition, in the pediatric population, the risk of procedural complications may be higher and of greater consequence.

How can we improve persistent elimination of accessory pathway conduction following radiofrequency catheter ablation? The authors used a 30-min observation period after elimination of accessory A-V pathway conduction. Could the results be different if patients were observed for 60 min to identify early recurrence of accessory A-V pathway conduction? Targeting accessory pathway potentials instead of earliest atrial or ventricular activation may reduce the number of radiofrequency applications and improve success (7). Measuring temperature at the electrode tip and monitoring impedance have limited roles in estimating tissue temperature, which is the main determinant of lesion formation during ablation. Recently the use of externally irrigated electrode catheters with contact force sensors and catheter stability determination (8) have been shown to facilitate the creation of a durable lesion. Refinement in mapping of accessory A-V pathways and advances in radiofrequency energy delivery have the potential to improve long-term outcome of catheter ablation in children. Prospective studies are needed to determine whether these advances translate into safer and more successful procedures.

• 2018 American College of Cardiology Foundation