MODULATION OF ATRIOVENTRICULAR-CONDUCTION BY ABLATION OF THE SLOW ATRIOVENTRICULAR NODE PATHWAY IN PATIENTS WITH DRUG-REFRACTORY ATRIAL-FIBRILLATION OR FLUTTER

Objectives. We hypothesized that modulation of atrioventricular (AV) n ode conduction, allowing a reduction in ventricular rate during atrial fibrillation or flutter without affecting AV conduction during sinus rhythm, might be achieved through ablation of the ''slow'' AV node pat hway. Background. In patients with atrial fibrillation or flutter not amenable to a direct atrial approach, ablation of the His bundle is pe rformed to induce complete AV block. This procedure causes pacemaker d ependence. Methods. Fourteen patients with drug-refractory paroxysmal atrial flutter or fibrillation underwent ablation of the slow AV node pathway. Radiofrequency current was delivered in six patients during s inus rhythm, in six during atrial flutter and in two during atrial fib rillation. Results. The anterograde effective refractory period of the AV node was prolonged from 270 +/- 50 (mean +/- SD) to 390 +/- 87 ms (p = 0.005) and the Wenckebach cycle from 346 +/- 33 to 458 +/- 75 ms (p = 0.004) in six patients during sinus rhythm. Mean AV ratio increas ed from 1.6 +/- 0.5 to 3.0 +/- 0.6 (p = 0.02) in six patients with atr ial flutter. Mean ventricular rate decreased from 157 +/- 38 to 67 +/- 10 beats/min in two patients with atrial fibrillation. Complete AV bl ock was induced in two patients (transient in one, permanent in one). During a follow-up period of 5.8 +/- 3.5 months, 11 patients experienc ed a recurrence of atrial fibrillation at 60 to 95 beats/min. No patie nt had progression to any degree of AV block . Conclusions. Ablation o f the slow AV node pathway allows reduction of ventricular rate during atrial fibrillation or butter while maintaining intact AV conduction during sinus rhythm. Modulation of AV node conduction is effective in most patients as an alternative to His bundle ablation for control of ventricular rate in paroxysmal atrial fibrillation or flutter.