ACTIVATION-REPOLARIZATION COUPLING IN THE NORMAL SWINE ENDOCARDIUM

Background While abnormalities of activation and repolarization play a n important role in arrhythmogenesis, little information is available on the interaction between their spatial dispersions in the heart. Thi s study examined the effects of activation spread on the spatial distr ibution of the repolarization properties during different depolarizati on patterns. Methods and Results Left ventricular (LV) endocardial act ivation and repolarization patterns were mapped in 13 healthy pigs. LV local activation, repolarization, and activation-recovery interval (A RI) 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 val ues correlated with the duration of monophasic activation potential re corded from onset of activation to time of 90% repolarization (r=.97, P<.01). Activation time range of the left ventricle was 42+/-5 ms (mea n+/-SEM) during sinus rhythm and 54+/-5 ms during right ventricular se ptal pacing. ARI inversely correlated with the corresponding activatio n times during both sinus (r(2)=.76+/-.03) and paced (r(2)=.77+/-.02) rhythms. The longest ARIs were located at the sites of earliest activa tion and shortest at the latest activation areas,with gradual shorteni ng between them. Conclusions The spatial distribution of repolarizatio n is dependent on the activation pattern. Repolarization dispersion in the healthy swine heart is relatively small as the result of tight co upling of the action potential duration to the activation process, ass igning longer ARIs to sites activated earlier. This coupling reduces g lobal and regional dispersion of repolarization and may serve as an im portant antiarrhythmic mechanism present in normal myocardium.