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. |