Kinetics of Atrial Repolarization Alternans in a Free-Behaving Ovine Model

Kinetics of Atrial Repolarization Alternans. Introduction: Repolarization alternans (Re‐ALT), a beat‐to‐beat alternation in action potential repolarization, promotes dispersion of repolarization, wavebreaks, and reentry. Recently, Re‐ALT has been shown to play an important role in the transition from rapid pacing to atrial fibrillation (AF) in humans. The detailed kinetics of atrial Re‐ALT, however, has not been reported so far. We developed a chronic free‐behaving ovine pacing model to study the kinetics of atrial Re‐ALT as a function of pacing rate. Methods: Thirteen sheep were chronically implanted with 2 pacemakers for the recording of broadband right atrial unipolar electrograms and delivery of rapid pacing protocols. Beat‐to‐beat differences in the atrial T‐wave apex amplitude as a measure of Re‐ALT and activation time were analyzed at incremental pacing rates until the effective refractory period (ERP) defined as stable 2:1 capture. Results: Atrial Re‐ALT appeared intermittently but without periodicity, and increased in amplitude as a function of pacing rate until ERP. Intermittent 2:1 atrial capture was observed at pacing cycle lengths 40 ms above ERP, and increased in duration as a function of pacing rate. Episodes of rapid pacing‐induced AF were rare, and were preceded by Re‐ALT or complex oscillations of atrial repolarization, but without intermittent capture. Conclusion: We show in vivo that atrial Re‐ALT developed and increased in magnitude with rate until stable 2:1 capture. In rare instances where capture failure did not occur, Re‐ALT and complex oscillations of repolarization surged and preceded AF initiation. (J Cardiovasc Electrophysiol, Vol. 23, pp. 1003‐1012, September 2012)