Discordant Alternans of Repolarization in Atrium Initiates Atrial Fibrillation and is Suppressed by Verapamil
Kenji Hiromoto
Authors: Hiroki Shimizu; Tetsuzou Kanemori; Bi-Hua Tann; Yoshio Furukawa; Kenji Hiromoto
8:00 - 6:00

Background: Alternans of repolarization in ventricular myocardium as beat-to-beat change was recognized to induce the serious ventricular arrhythmias in the experimental model and T wave alternans from surface ECG was widely used as a marker of sudden cardiac death. On the other hand, atrial fibrillation (AF) was initiated on the basis of heterogeneous repolarization. However, it remained unclear whether the alternans of repolarization in atrium was associated with AF.Methods: The study population consisted of 19 patients who performed electrophysiological study for atrial tachyarrhythmia. A standard bipolar electrode catheter was positioned in high lateral right atrium and two Franz catheters were positioned in the free wall and septum in atrium for recording monophasic action potentials (MAP) simultaneously. After propranorol (0.2mg/kg) and atropine (0.04mg/kg) was administrated as autonomic block, MAPs were recorded during steady state (>1min) pacing starting at a cycle length (CL) of 400ms and then at faster CLs by 10ms decrements from HRA. We measured the duration from the onset of upstroke to 90% repolarization of the MAP (APD90). If discordant alternans (DA), which is defined as the phenomenon of two spatially distinct regions exhibiting APD90 alternans of opposite phases, was present during pacing, verapamil was administrated in this group and MAPs were recorded again. Results: Rapid pacing in 13 of 19 (68%) patients developed concordant alternans to DA at a mean cycle length 207 plusminus 19 ms. AF was initiated after the induction of DA in 8 patients among those. (P=0.012) AF was not initiated in all 6 patients who could not be induced DA. After the administration of verapamil, the longest pacing CL at which DA was induced was decreased significantly compared with that before the administration (207 plusminus 19 vs. 178 plusminus 17 ms, respectively, P<0.0001). Conclusion: Rapid atrial pacing induced DA that was associated with the initiation of AF and suppressed by verapamil. It was suggested that temporal repolarization heterogeneity that was reduced by calcium channel blocker might provide the substrate for AF.