Atrial Fibrillation After Radiofrequency Ablation of Type I Atrial Flutter

ABSTRACT & COMMENTARY

Synopsis: Patients with a history of atrial fibrillation and left ventricular dysfunction undergoing an ablation procedure for atrial flutter should be advised of the appreciable risk of atrial fibrillation after the procedure.

Source: Paydak H, et al. Circulation 1998;98:315-322.

Paydak and colleagues analyzed acute procedural success and the occurrence of atrial fibrillation after catheter ablation of type I atrial flutter. One hundred ten patients who had type I atrial flutter as their predominant rhythm and underwent atrial flutter ablation in the authors' laboratory formed the study group. The mean age was 62 ± 14 years, and 78% of the patients were male. Structural heart disease was noted in 71 of 110 patients. Atrial flutter had been present for 25 ± 36 months before the procedure. Forty percent (44/110) had a prior history of atrial fibrillation, but, in 23 of these patients, only a single episode of atrial fibrillation had been documented. Electrophysiologic studies were carried out in all patients to document atrial flutter and to determine the direction of rotation in the circuit. Radiofrequency ablation was performed using stepwise overlapping energy applications in a line in the isthmus beginning at the mitral annulus and concluding at the inferior vena cava. Recurrence of atrial fibrillation or atrial flutter was documented during long-term clinical follow-up.

The ablation was an acute success in 108 of 110 patients. Ninety patients manifested bidirectional conduction block across the ablation line. In four patients, atrial flutter could no longer be induced, but complete isthmus block was not achieved. Conduction across the isthmus was not measured in 14 patients early in the series. The mean number of radiofrequency applications was 14 ± 8, with more lesions required in patients with atrial enlargement.

The mean follow-up duration was 20 ± 9 months. Type I atrial flutter recurred in six patients: One of two patients with persistently inducible flutter, three of 18 patients with suppression of flutter induction only, and two of 90 patients with both no inducible flutter and bidirectional isthmus block at the end of the procedure experienced recurrences. Three additional patients experienced atypical atrial flutter during follow-up. Each of these latter patients also had episodes of atrial fibrillation.

Spontaneous atrial fibrillation occurred after the ablation procedure in 28 (25%) patients. The cumulative risk for atrial fibrillation was 12% at one month, 23% at one year, and 30% at two years. Increased age, a history of atrial fibrillation before the initial procedure, a left ventricular ejection fraction of less than 50%, and atrial enlargement were univariate predictors of recurrence. Cox regression analysis revealed that a history of spontaneous atrial fibrillation and a depressed left ventricular ejection fraction were the two significant independent risk factors. Patients with both of these risk factors had a 74% (14 of 19) risk for post-procedure atrial fibrillation.

Paydak et al conclude that patients with a history of atrial fibrillation and left ventricular dysfunction undergoing an ablation procedure for atrial flutter should be advised of the appreciable risk of atrial fibrillation after the procedure. In such patients, continued anticoagulation and antiarrhythmic therapy are likely to be necessary.

COMMENT BY JOHN P. DiMARCO, MD, PhD

Radiofrequency ablation has become standard, first-line therapy in patients with paroxysmal supraventricular tachycardia (PSVT). In patients with accessory pathway mediated tachycardias on patients with atrioventricular nodal reentrant tachycardia, initial success rates are high (> 90%), and late recurrence after an initial procedure is uncommon (< 5%). The critical part of the circuit in these arrhythmias that is targeted during ablation is relatively easy to identify and can usually be ablated with a single, discrete lesion. Ablation of atrial flutter is a more complex procedure. In contrast to patients presenting with PSVT, patients with atrial flutter more frequently have a history of other atrial arrhythmias and significant structural heart disease. The landmark papers by Feld et al (Circulation 1992;86:1233-1240) and Cosio et al (Am J Cardiol 1993;71:705-709), which described the anatomical basis of the reentrant circuit in atrial flutter, permitted the use of radiofrequency ablation techniques to be extended to this arrhythmia. The paper by Paydak et al delineates both the successes and pitfalls of this approach.

Two improvements in techniques have enhanced the effectiveness of radiofrequency ablation in patients with atrial flutter. Since the circuit in type I flutter passes through a critical isthmus defined by structural boundaries, an anatomic approach that does not require complex electrophysiologic mapping is, therefore, possible. Simply creating a linear lesion across the circuit should be sufficient to prevent the arrhythmia. The effect of the ablation can be assessed during the procedure by measuring block across the ablation line using a standard technique that involves simple analysis of atrial activation in response to pacing from both sides of the ablation line. Using these techniques, a high rate of acute procedural success can be achieved.

The long-term results of atrial flutter ablation are considerably inferior to ablation results in patients with PSVT. Atrial flutter frequently develops in the setting of progressive heart disease, and other disturbances of atrial electrophysiology are frequently present. Even though a discrete portion of the flutter circuit that is susceptible to ablation can usually be identified, patients will frequently require additional therapy after the procedure. The data presented in this study indicate that we should be cautious in explaining the potential benefits of ablation procedures to patients with atrial flutter. In patients who have never experienced atrial fibrillation and who have normal ventricular function, ablation is likely to provide at least short-term complete relief of symptoms. However, in patients with both of these clinical variables, ablation of atrial flutter is likely to be only partially effective, and additional long-term therapy is likely to be required.