Modulation of Atrial Repolarization by Site of Pacing in the Isolated Rabbit Heart

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Abstract
Background Single-site or multisite atrial pacing may reduce the incidence of atrial fibrillation in humans. The therapeutic mechanisms may include synchronization of atrial repolarization (repolarization “memory”) and/or decreased dispersion of atrial repolarization. These responses have not been well documented in intact atria. Methods and Results Monophasic action potential recordings were made from six atrial epicardial sites in 39 isolated perfused rabbit heart preparations during 3 hours of continuous right atrial, left atrial, or biatrial pacing. Action potential recordings obtained at times 0, 45, 90, 135, and 180 minutes were computer analyzed for activation time (AT) and 90% action potential duration (APD) at each site. No consistent relationship could be demonstrated between APD and AT at any time during atrial pacing (all P>.05). On average, left atrial APDs were longer than right atrial APDs by up to 6.3 ms at all times, regardless of the site of pacing (P≤.05). At all times, dispersion of atrial repolarization was minimized by left atrial pacing compared with right atrial pacing (21.6±9.1 versus 32.4±15.1 ms, respectively, at time 0; P<.05). Biatrial pacing provided no further reduction in dispersion of repolarization compared with left atrial pacing (all P>.05). Conclusions No relationship can be demonstrated between atrial AT and APD in the isolated rabbit heart preparation. This differs from ventricular repolarization “memory,” which is demonstrable under the same conditions. Left atrial APD is, on average, longer than right atrial APD, suggesting spatial heterogeneity in repolarization. Dispersion of atrial repolarization is minimized by left atrial pacing in this preparation with no further advantage to biatrial pacing.