Discordant repolarization alternans-induced atrial fibrillation is suppressed by verapamil

Background Ventricular alternans of repolarization produces serious ventricular arrhythmias in experimental models. The present study investigated the role of alternans of atrial repolarization in patients with atrial fibrillation (AF). Methods and Results Electrophysiological studies were performed in 19 patients without structural heart disease. Monophasic action potentials (MAP) were recorded with 2 Franz catheters during steady state pacing, starting at a cycle length (CL) of 400 ms with subsequent decrements of 10 ms. Duration from the onset of upstroke to 90% repolarization of the MAP were measured. If discordant alternans (DA) was present during pacing, verapamil was administrated, and MAP measurements were repeated. Rapid pacing resulted in concordant alternans to DA in 13 of 19 (68%) patients. AF was initiated after the induction of DA in 8 of 13 patients (p=0.012). Verapamil treatment resulted in a significant decrease in the longest pacing CL at which DA was induced (207 19 vs 178 17 ms, p<0.0001). Conclusions Rapid atrial pacing induced DA and was associated with initiation of AF. Furthermore, induction of DA was suppressed by verapamil. Reducing the spatiotemporal repolarization heterogeneity may be how the calcium-channel blockade prevents initiation of AF.