Internal atrial defibrillation: effect on sinus and atrioventricular nodal function and implanted cardiac pacemakers.

Internal atrial defibrillation (IAD) has been extensively evaluated for clinical efficacy but the need for concomitant demand pacing and the effect of IAD shocks on pacemaker function is not well studied. We prospectively evaluated: (1) the incidence of bradycardia as a result of IAD shocks; and (2) effect of these shocks on functioning of implanted cardiac pacemakers. Consecutive consenting patients with atrial fibrillation (AF) requiring cardioversion or undergoing electrophysiological study were selected for IAD. IAD shocks were delivered using the right ventricle to right atrium (RV-RA), right ventricle to superior vena cava (RV-SVC), right atrium to axillary patch (RA-AX), and right atrium to left pulmonary artery or coronary sinus (RA-LPA/CS) lead configurations. Mean RR interval before and after the shocks and the time interval from shock delivery to first QRS complex were analyzed for unsuccessful and successful shocks. Pacing and sensing function was analyzed in patients with previously implanted pacemakers. Twenty-five patients, 18 men, mean age 67.9 +/- 10 years were included in the study. A total of 305 shocks (264 unsuccessful, 41 successful) were analyzed. For unsuccessful shocks the mean post-IAD shock RR interval (795 +/- 205 ms) and the time to first post-IAD shock QRS complex (970 +/- 438 ms) were both significantly greater than the pre-IAD shock RR interval (685 +/- 131 ms, P < 0.001). The increase in post-IAD shock RR interval and time to first post-IAD shock QRS complex was seen with all four lead configurations used. With successful shocks the mean post-IAD shock sinus cycle length (1,105 +/- 450 ms) and time to first post-IAD shock QRS complex (1,126 +/- 443 ms) were both also significantly greater than the pre-IAD shock RR interval (766 +/- 172 ms). Nine patients (36%) had episodes of significant bradycardia after shock delivery. Shocks of up to 20 J using the RA-LPA/CS lead configuration did not affect pacemaker function. IAD can result in transient bradycardia related to sinus and atrioventricular nodal effects requiring backup ventricular pacing. Shocks can be safely delivered using RA-LPA or RA-CS lead configurations in patients with implanted bipolar cardiac pacemakers.