Impaired subsidiary pacemaker function in patients with a right bundle branch block created prior to complete catheter ablation of the AV junction.

The impact of a right bundle branch block (RBBB), inadvertently created prior to complete ablation of the atrioventricular (AV) junction, on the intrinsic subsidiary pacemaker function was investigated. In 31 patients suffering from intractable supraventricular tachyarrhythmia, catheter ablation of the AV junction was performed using direct current (n = 13) or radiofrequency (n = 18) energy. In 16/31 patients a RBBB was created prior to complete AV ablation. Subsidiary pacemaker function was evaluated after a mean period of 5 months. Following 5 min of ventricular pacing (70 beats.min-1) escape interval and spontaneous heart rate were measured. In patients with a RBBB there was a trend towards a longer escape interval (2979 +/- 2559 vs 1867 +/- 1254 ms, P = ns) and a significantly lower intrinsic heart rate (38 +/- 14 vs 47 +/- 8 beats.min-1, P < 0.05). Pacemaker dependency was only observed among patients with a RBBB (4/16 vs 0/15, P < 0.05). HV intervals were shorter in those energy discharges resulting in a RBBB as compared to those inducing a complete heart block (52 +/- 8 vs 66 +/- 6 ms, P < 0.05). Creation of a RBBB prior to complete ablation of the AV junction results in impaired intrinsic subsidiary pacemaker function; the most proximal catheter position should be carefully sought to minimize the risk of pacemaker dependency.