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Abstract & Commentary
Synopsis: Young patients with inducible AV reentrant tachycardia or multiple accessory pathways should undergo ablation, if possible.
Source: Pappone C, et al. N Engl J Med. 2003;349: 1803-1811.
The optimal management of asymptomatic individuals in whom preexcitation is noted on an electrocardiogram has long been controversial. Although atrioventricular (AV) reentrant tachycardia is the most common presenting arrhythmia in patients’ manifest preexcitation, occasional patients may present with rapidly conducting atrial fibrillation or even ventricular fibrillation and cardiac arrest. Catheter ablation in patients with preexcitation is both very effective and is associated with a low risk of complications in experienced hands. Despite this, however, current guidelines do not recommend invasive evaluation of most asymptomatic individuals.
In this paper from 2 Italian centers, Pappone and colleagues report the results of a randomized trial of prophylactic catheter ablation in previously asymptomatic patients with Wolff-Parkinson-White syndrome (WPW). Pappone et al had previously reported results of a prospective follow-up after a diagnostic electrophysiologic study in patients who did not undergo catheter ablation.1 In that prior study, they had shown that the ability to induce AV reentrant tachycardia or sustained atrial fibrillation, younger age, and the presence of multiple accessory pathways were risk factors for future arrhythmic events.
In the current study, they randomized patients with high-risk characteristics at their baseline study to either ablation or routine follow-up. Based on their previous experience, patients were considered high risk if they were younger than 35 and had inducible AV reentrant tachycardia or atrial fibrillation. Ablation was performed using standard techniques. Follow-up was maintained after the procedure with periodic ECG monitoring and clinic visits.
Among the 224 patients who underwent a baseline study, 148 were classified as being at low risk, and 76 were classified as being at high risk. Four high-risk patients withdrew consent and were excluded from the study. As a result, there were 37 high-risk patients in the ablation group and 35 in the control group. In both groups, the age range was 15-30 with an equal distribution of men and women. Most patients had relatively short refractory periods of their accessory pathways. The median anterograde refractory period was 240 msec in both groups at baseline and 200 msec after isoproterenol. About one-third of the patients in both groups had multiple accessory pathways, an unusually high proportion. AV reentrant tachycardia was the most commonly inducible arrhythmia (63% in both groups). In about one-half of these patients, the AV reentrant tachycardia was observed to degenerate into atrial fibrillation. Nonsustained atrial fibrillation was the inducible arrhythmia in 37% of the patients.
Catheter ablation was successful in all 37 patients in the ablation group. Two of these patients had arrhythmic events during a median follow-up of 27 months. In both patients, the arrhythmic events were AV nodal reentrant tachycardia. Both of these patients successfully underwent a second ablation procedure for modification of the slow AV nodal pathway and have remained arrhythmia-free.
The 35 control patients were followed for a median of 21 months. All patients continued to manifest ventricular preexcitation on their electrocardiograms. Twenty-one of the 35 patients (60%) had an arrhythmic event during follow-up. The arrhythmic event was supraventricular tachycardia in 15 patients, atrial fibrillation in 5 patients, and cardiac arrest with resuscitation from ventricular fibrillation in 1 patient. The latter patient had multiple septal accessory pathways documented at his original study.
Among the 148 asymptomatic patients who were thought to be at low risk, only 6 (4%) developed arrhythmic events during follow-up, and none died suddenly. In the control group, all patients who had inducible AV reentrant tachycardia later developed arrhythmic events. Among the patients who had only inducible nonsustained atrial fibrillation, 53% remained asymptomatic during the 5-year follow-up.
Pappone et al recommend expanding recommendations for invasive evaluations of asymptomatic patients with WPW. They recommend that patients without inducible AV reentrant tachycardia or sustained atrial fibrillation at baseline and patients older than 35 should not undergo prophylactic ablation. Young patients with inducible AV reentrant tachycardia should have their accessory pathways ablated. However, patients with only inducible nonsustained atrial fibrillation may be followed since arrhythmic events are less common. Finally, this paper confirms that patients who have multiple accessory pathways are at particularly high risk and should undergo ablation if possible.
Comment by John DiMarco, MD, PhD
This paper confirms the safety and efficacy of catheter ablation in patients with WPW. Pappone et al selected a relatively young group of patients whom they characterized as "high risk" based on their prior experience. Given the known effectiveness of catheter ablation in patients with accessory pathways, it is not surprising that there was a difference in arrhythmic events during follow-up between the ablation group and the control group. There are, however, several factors in addition to those mentioned here that should also be considered when deciding whether to proceed with an electrophysiologic study and possible catheter ablation in an asymptomatic patient.
The surface electrocardiogram can often be used to localize an accessory pathway. Anteroseptal, epicardial, and midseptal accessory pathways may be technically challenging to ablate. With anteroseptal pathways, there is an increased risk of producing AV block since the accessory pathway is located close to the normal conduction system. In a truly asymptomatic patient, I would hesitate to attempt an ablation in this situation even if AV reentry could be induced. The recent introduction of cryo-thermal ablation techniques, which allow monitoring of conduction during the lesion before permanent damage is inflicted, however, may make even these patients candidates for ablation. Patients with epicardial or midseptal pathways also present problems. In these patients, standard techniques for ablation on the AV ring may not be successful and higher-risk procedures with ablations either via a pericardial approach or an approach through the coronary venous system may be required. In these patients also, I would not recommend ablation until symptoms had developed.
In the past, noninvasive techniques were used to assess future risk for sudden death in patients with WPW. These techniques were usually based on the disappearance of preexcitation on the surface electrocardiogram either at normal rates or with exercise. Although this may be a predictor of a short anterograde effective refractory period, there is not a good correlation between antegrade and retrograde refractory periods, and this technique is not effective for assessing risk for AV reentrant tachycardia. However, most patients will survive an episode of AV reentry and, if they have intermittent preexcitation, rapid rates during atrial fibrillation are uncommon.
Based on the data in this paper and the previous paper from this group, it now seems that individuals younger than 35, or perhaps 40, in whom a delta wave is found consistently on routine electrocardiograms should be offered electrophysiologic study. If AV reentrant tachycardia is induced and the pathway is not in a high-risk location, then ablation should be performed.
Dr. DiMarco, Professor of Medicine, Division of Cardiology, University of Virginia, Charlottesville, is on the Editorial Board of Clinical Cardiology Alert.
1. Pappone C, et al. J Am Coll Cardiol. 2003;41:239-244.