Repolarization heterogeneity and rate dependency in a canine rapid pacing model of heart failure.

BACKGROUND: Repolarization heterogeneity and rate dependency have long been established as factors contributing to arrhythmogenic risk. However, there are conflicting observations regarding the nature and extent of ventricular repolarization heterogeneity that complicate understanding of arrhythmogenic mechanisms. To explore these disparate findings, we studied ventricular repolarization heterogeneity and rate dependency in a canine, rapid pacing model of heart failure. METHODS AND
RESULTS: We studied ventricular repolarization heterogeneity and rate dependency in 10 canine hearts (5 normal and 5 after 1 month of rapid pacing at 240 beats per minute) by analyzing 64 body surface electrocardiograms, 64 epicardial, and 190 intramural plunge electrograms. We estimated mean ventricular depolarization and repolarization times from R- and T-wave peaks of the root-mean-square electrocardiogram (body surface) and local depolarization and repolarization times using activation-recovery interval (ARI) methods from recordings obtained during a range of fixed rate pacing. In addition, we estimated local epicardial and transmural gradients of ARIs to assess cardiac locations of greatest spatial repolarization heterogeneity. We compared changes in repolarization at different rates between normal and heart failure hearts. Findings documented prolongation of repolarization, repolarization rate dependency, and increased repolarization gradients in the heart failure hearts compared with control as observed from body surface, epicardial, and transmural measurements. Maximum local epicardial and intramural ARI gradients were comparable both in heart failure and control hearts. Intramural ARI distributions tended to be more irregular in the heart failure hearts compared with the systematic epicardium to endocardium ARI increase observed in control animals.
CONCLUSIONS: This study documented prolongation of repolarization, increase in both epicardial and transmural repolarization gradients, and irregularity of transmural distribution in a rapid pacing canine model of heart failure compared with control animals. The findings support previously published results of increased repolarization heterogeneity and repolarization prolongation observed in rapid pacing models of heart failure. New findings are the irregularity of transmural heterogeneity and the ability of noninvasive root-mean-square electrocardiogram R-T intervals to estimate mean ventricular repolarization duration in the setting of rapid pacing models of heart failure. These findings suggest increased arrhythmogenic risk in this model and potentially in patients with heart failure.