Activation-Repolarization Coupling in the Normal Swine Endocardium

BACKGROUND: While abnormalities of activation and repolarization play an important role in arrhythmogenesis, little information is available on the interaction between their spatial dispersions in the heart. This study examined the effects of activation spread on the spatial distribution of the repolarization properties during different depolarization patterns. METHODS AND RESULTS: Left ventricular (LV) endocardial activation and repolarization patterns were mapped in 13 healthy pigs. LV local activation, repolarization, and activation-recovery interval (ARI) times were determined from the intracardiac unipolar electrograms, color-coded, and superimposed on a three-dimensional anatomic map of the ventricle generated with a nonfluoroscopic mapping system. ARI values correlated with the duration of monophasic activation potential recorded from onset of activation to time of 90% repolarization (r=.97, P<.01). Activation time range of the left ventricle was 42+/-5 ms (mean+/-SEM) during sinus rhythm and 54+/-5 ms during right ventricular septal pacing. ARI inversely correlated with the corresponding activation times during both sinus (r2=.76+/-.03) and paced (r2=.77+/-.02) rhythms. The longest ARIs were located at the sites of earliest activation and shortest at the latest activation areas, with gradual shortening between them. CONCLUSIONS: The spatial distribution of repolarization is dependent on the activation pattern. Repolarization dispersion in the healthy swine heart is relatively small as the result of tight coupling of the action potential duration to the activation process, assigning longer ARIs to sites activated earlier. This coupling reduces global and regional dispersion of repolarization and may serve as an important antiarrhythmic mechanism present in normal myocardium.