[Modulation of atrioventricular conduction in patients with atrial fibrillation or flutter. Immediate and long-term results].

The modulation of atrioventricular (AV) conduction by radiofrequency catheter ablation of the "slow" AV node pathway reduces the ventricular rate during atrial flutter (AFL) or fibrillation (AF), without affecting AV conduction during sinus rhythm. In this study the acute and long-term effects of AV node modulation in 41 patients with AFL-AF are presented. The arrhythmia was paroxysmal in 34 and chronic in 7 patients, and was responsible in all patients for severe symptoms of heart failure. The procedure was performed during sinus rhythm in 23, AFL in 8, AF in 10 patients, and caused respectively an increase in Wenckebach cycle from 330 +/- 64 to 452 +/- 91 ms (p < 0.001), and a reduction in ventricular rate from 182 +/- 53 to 95 +/- 40 b/min (p < 0.001) and from 170 +/- 40 to 90 +/- 27 b/min (p < 0.001). The arbitrary endpoint of the procedure (Wenckebach cycle > 500 ms during sinus rhythm, maximum heart rate < 100 b/min during AFL-AF) was achieved in 19/41 patients; permanent complete AV block was induced in 6 "non-responder" patients (15%). At a mean follow-up of 15 +/- 7 months (range 1-31) all patients reported a substantial subjective improvement and a better exercise tolerance--as documented by a quantitative questionnaire concerning quality of life--without any recurrence of acute pulmonary edema, syncope or severe hypotension. In 5 patients during paroxysmal AFL-AF, and in 1 patient with chronic AF, a heart rate higher than 120 b/min was documented, and in 3 cases it was associated with severe palpitations. No late AV block occurred. The mean number of hospital-emergency room admissions per patient per year decreased from 3.9 before to 0.2 after the modulation. Considering complete AV block (6 patients, 15%) and clinical failures (6 patients, 15%), the success of the procedure was 70%, and was independent of the rhythm at the time of the procedure; the percentage of AV block was nevertheless higher during AFL-AF (22 vs 9%). Both endpoints of the procedure (Wenckebach cycle > 500 ms; heart rate < 100 b/min) were confirmed to be good predictors of long-term efficacy; on the other hand, a Wenckebach cycle < 430 ms was demonstrated to represent a specific marker of late failure. In conclusion, the study confirms that modulation of AV conduction is feasible in 70% of patients with AFL-AF: in these patients the procedure allows the long-term control of ventricular rate and a substantial improvement in quality of life, avoiding the need for His ablation and pacemaker implantation. "Non-responder" patients can be acutely identified and should be therefore considered condidates for His ablation during the same session.