Microvolt T-wave alternans and beat-to-beat variability of repolarization during early postischemic remodeling in a pig heart

BackgroundRepolarization variability is considered to predict sudden cardiac death. T-wave alternans (TWA) has been the subject of exhaustive research, whereas beat-to-beat variability of repolarization (BVR) is a new parameter that possibly predicts proarrhythmia. How these parameters interact has not been tested.ObjectiveThe purpose of this study was to compare TWA and BVR as predictors of proarrhythmic substrate early after myocardial infarction (MI).MethodsIn nine pigs, MI was induced by 1-hour occlusion of the left anterior descending coronary artery. Cardiac magnetic resonance imaging was performed at day 21. Six sham pigs served as control. Spectral TWA was tested during right atrial pacing before induction of MI and after 21 days. BVR was calculated from 60 consecutive QT intervals.ResultsMagnetic resonance imaging showed transmural MI. TWA was negative in all pigs at clinical threshold rate and equally present in MI versus sham pigs at higher rates (170 bpm: 55% vs 50% positive TWA). In MI pigs, BVR of QT intervals increased significantly during acute ischemia (2.44 ± 0.43 ms vs 3.55 ± 0.41 ms, P <.01) and even more on day 21 (5.80 ± 1.12 ms), but it differed significantly from sham (2.14 ± 0.54 ms, P <.01). A clinical ventricular tachycardia induction protocol was positive in 2 of 8 MI pigs and in none of 6 shams.ConclusionIn early remodeling after MI, BVR at intrinsic heart rate was a consistent phenomenon, whereas TWA during atrial pacing or baseline QT-interval changes were not. TWA and BVR could reflect different post-MI remodeling processes. BVR may be a new technique for predicting a potentially proarrhythmic substrate in the early postinfarction period.