Modulation of atrioventricular conduction by ablation of the "slow" atrioventricular node pathway in patients with drug-refractory atrial fibrillation or flutter

Istituto di Cardiologia, Universita degli Studi, Milan, Italy.

OBJECTIVES. We hypothesized that modulation of atrioventricular (AV) node 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 pathway. BACKGROUND. In patients with atrial fibrillation or flutter not amenable to a direct atrial approach, ablation of the His bundle is performed to induce complete AV block. This procedure causes pacemaker dependence. 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 sinus rhythm, in six during atrial flutter and in two during atrial fibrillation. 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 increased from 1.6 +/- 0.5 to 3.0 +/- 0.6 (p = 0.02) in six patients with atrial flutter. Mean ventricular rate decreased from 157 +/- 38 to 67 +/- 10 beats/min in two patients with atrial fibrillation. Complete AV block was induced in two patients (transient in one, permanent in one). During a follow-up period of 5.8 +/- 3.5 months, 11 patients experienced a recurrence of atrial fibrillation at 60 to 95 beats/min. No patient had progression to any degree of AV block. CONCLUSIONS. Ablation of the slow AV node pathway allows reduction of ventricular rate during atrial fibrillation or flutter 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.

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