Abstract & Commentary
By John P. DiMarco, MD, PhD, Professor of Medicine, Division of Cardiology, University of New Mexico, Albuquerque. Dr. DiMarco is a consultant for Novartis and does research for Medtronic and Guidant.
Synopsis: Asymptomatic atrial fibrillation occurs commonly after radiofrequency ablation procedures for atrial fibrillation. Thus, a symptom only based follow-up substantially overestimates the true success rate of AF ablation procedures.
Source: Hindricks G, et al. Perception of Atrial Fibrillation Before and After Radiofrequency Catheter Ablation: Relevance of Asymptomatic Arrhythmia Recurrence. Circulation. 2005;112:307-313.
Hindricks and colleagues performed a careful study on the relationship between symptoms and the recurrence of atrial fibrillation after radiofrequency catheter ablation. One hundred fourteen patients with symptomatic atrial fibrillation were included in this perspective study. Ninety-six patients had paroxysmal atrial fibrillation and 18 had persistent atrial fibrillation. Sixty of 114 patients had lone atrial fibrillation. Forty-eight patients had a history of hypertension and 21 patients had some form of organic heart disease. The mean left ventricular ejection fraction was 62 ± 8%, with a left atrial diameter measured at 40 ± 6 mm. After enrollment, but before ablation, a continuous 7-day ambulatory ECG was recorded in all patients. Each patient was given a detailed symptom log to complete during the 7-day monitoring period. Similar 7-day continuous ambulatory ECG’s were repeated immediately after ablation and at 3, 6, and 12 months of follow-up. Documentation of greater than 30 seconds of atrial fibrillation was considered a sustained AF recurrence. Recordings of atrial flutter were analyzed separately. A total of 108 of the 114 patients completed 6 months of follow-up. Of these 108 patients, 10 with early recurrences of atrial fibrillation underwent a second ablation procedure. ECG analysis was performed by a physician blinded to the patient’s name and symptom log. Each episode of atrial fibrillation was classified as symptomatic or asymptomatic.
The ablation procedure involved circular left atrial linear lesions around the ostia of the pulmonary veins as guided by electroanatomic mapping. Additional linear lesions across the roof of the left atrium and between the circular lesions and the mitral annulus were also placed. During the 7-day recording prior to ablation, 81% of the patients had atrial fibrillation. Of these, 5% had only asymptomatic episodes, 35% had only symptomatic episodes, and 57% had both symptomatic and asymptomatic episodes. Immediately after ablation, 78 of 114 patients had documented atrial fibrillation, with 22% of the patients having only asymptomatic episodes, 21% only symptomatic episodes, and 57% a mixture of symptomatic and asymptomatic episodes. At 3, 6, and 12 months of follow-up, 57%, 50%, and 64% of patients, respectively had only sinus rhythm during follow-up recordings. Among the patients with documented recurrences, 38%, 37%, and 36% had only asymptomatic episodes at these 3 time points. A decrease in total AF duration was, however, observed. Prior to ablation, the median total arrhythmia duration was 38 hours during the 7-day ECG monitoring period. Immediately after ablation, this declined to 36 hours, then to 23 hours after 3 months, 17 hours after 6 months, and 10 hours after 12 months.
During follow-up, patients initially were continued on a beta blocker and an antiarrhythmic drug (flecainide or amiodarone) for at least 3 months. After 3 months, medication could be continued on an individual basis. At 6 and 12 months, over 70% of the patients were still receiving a beta blocker and 40% of patients were still taking an antiarrhythmic drug after 12 months. There was no difference in the measured heart rate during AF episodes. It remained between 100 and 110 bpm at all time points. No patient characteristics were identified that could distinguish between patients with symptoms or no symptoms during atrial fibrillation. Atrial flutter was documented in a small proportion of patients, however, all patients with atrial flutter also had atrial fibrillation during the 7-day electrocardiograms.
Hindricks et al conclude that asymptomatic atrial fibrillation occurs commonly after radiofrequency ablation procedures for atrial fibrillation. They argue that a symptom only based follow-up substantially overestimates the true success rate of AF ablation procedures.
The role of catheter ablation in the management of patients with atrial fibrillation is expanding but remains controversial. This paper by Hindricks et al provide important insights into how we should interpret the current literature. Almost all of the patients in this study had a history of highly symptomatic episodes of atrial fibrillation. The ablation procedure was reasonably effective for reducing or eliminating symptoms. However, as the data show, careful monitoring demonstrates that asymptomatic atrial fibrillation may still occur and this impacts the potential clinical value of the procedure.
Most of the patients in this study would not have had conventional criteria for initiation of anticoagulation. However, as atrial fibrillation ablation procedures are extended to older patients and those with risk factors for stroke, the presence of asymptomatic atrial fibrillation during follow-up will certainly influence our enthusiasm for recommending the procedure. For many patients, symptoms during atrial fibrillation can be controlled with medications, but their major desire is to avoid a need for long-term anticoagulation. The data presented here show that discontinuation of warfarin after an ablation in patients with stroke risk factors is difficult to justify. A large fraction of patients may still have only asymptomatic episodes of atrial fibrillation. We do not know how much atrial fibrillation is necessary to elevate stroke risk in these patients. Is there some lower limit that can be considered safe? The minimum duration required to count as a sustained episode in this study was only 30 seconds, but the median duration was 10 hours during the 7-day monitoring period. At the present time, we don’t know if this amount increases the risk of stroke enough to warrant long-term anticoagulation. Current guidelines are very conservative and suggest that all patients with any atrial fibrillation and stroke risk factors should receive prophylaxis.