LOW-ENERGY INTRACARDIAC SHOCKS DURING ATRIAL-FIBRILLATION - EFFECTS ON CARDIAC-RHYTHM

The effect on ventricular rate of intracardiac shocks for atrial fibri llation was studied in 13 patients receiving 95 shocks. Shocks were sy nchronized to the R wave and were delivered after R-R intervals >500 m sec, with increasing strength (20 to 400 V). In 10 patients, conversio n to sinus rhythm was achieved in this way. Noneffective shocks increa sed the mean first postshock R-R interval (compared with 20 V as basel ine), for shocks greater than or equal to 140 V. The R-R prolongation correlated with the shock level (r = 0.936, p < 0.01). Subsequent R-R intervals were comparable to baseline. A similar trend toward longer f irst postshock intervals was observed for effective shocks. However, t he maximal first R-R interval after noneffective shocks had no relatio n to the voltage. The number of pauses >1500 msec tended to increase w ith voltage (noneffective shocks). Pauses >2500 msec were exceptional (4 of 85 noneffective shocks). No symptomatic bradycardia occurred. In subsequent intervals (cycles 2 through 10) no pauses >2500 msec were noted. It is concluded that atrial defibrillation attempts between the right atrium and coronary sinus prolong R-R intervals, in relation to administered energy, but without the need for backup pacing.