VERAPAMIL REDUCES TACHYCARDIA-INDUCED ELECTRICAL REMODELING OF THE ATRIA

Background Prolonged periods of atrial fibrillation or rapid atrial pa cing induce shortening of the atrial effective refractory period (AERP ), which is thought to be related to the lower success rates of variou s antifibrillatory treatments when the arrhythmia has lasted for a lon ger period of time. Methods and Results To investigate whether an incr ease in intracellular calcium could be the stimulus for electrical rem odeling, the effects of verapamil on shortening of the AERP in respons e to 24 hours of rapid atrial pacing (300 bpm) were studied in five ch ronically instrumented conscious goats during infusion of saline or ve rapamil. During rapid atrial pacing, the ventricular rate was kept con stant by ventricular pacing (150 bpm). The AERP was measured by progra mmed electrical stimulation at basic cycle lengths of 430, 300, and 20 0 ms. Verapamil had no effects on the AERP before rapid atrial pacing. However, in the course of 24 hours of rapid atrial pacing, the AERP s hortened significantly less (27% to 58%) in the presence of verapamil compared with control (at 430, 300, and 200 ms, P<.001, P<.01, and P<. 01, respectively). Also, after cessation of pacing, complete recovery of the AERP during verapamil infusion occurred much sooner than in the control experiments. Despite a significant reduction in electrical re modeling, there was only a minimal reduction in inducibility of atrial fibrillation by verapamil (34% versus 39% in the control experiments, P=.03). Conclusions Electrical remodeling of the atrium during rapid atrial pacing was significantly attenuated by verapamil. This suggests that electrical remodeling of the atrium is triggered by the high cal cium influx during rapid atrial pacing rates.