SEQUENCE AND DISPERSION OF VENTRICULAR REPOLARIZATION ON THE ENDOCARDIUM AND EPICARDIUM Studies using the monophasic action potential mapping technique in humans and pigs

Materials and Methods: Monophasic action potential (MAP) were recorded, using the CARTO mapping system and NaviStar catheters, during sinus rhythm from the endocardium at 43 ± 15 LV or RV sites in 8 patients, at 61 ± 18 LV and/or RV sites in 10 pigs and during atrial pacing from the endo- and epicardium at 211 ± 54 LV and RV sites in additional 10 pigs. Local activation time (AT), MAP duration (MAPd) and end-of-repolarization time (EOR) were calculated at each site and 3-dimensional maps of AT, EOR and MAP duration on the endo- and epicardium were obtained. Results: (1) The EOR sequence followed the sequence of activation on the endocardium in 8/10 patient maps and in 18/18 LV and 4/5 RV pig maps as well as on the epicardium in 8/9 pig maps. (2) A positive correlation between the EOR and the AT was found on the endocardium in 7/10 patient maps and in 19/19 LV and 5/5 RV pig maps as well as on the epicardium in 9/10 pig maps. A negative correlation was found between the MAPd and AT on the endocardium in 8/10 patient maps and in 16/19 LV and 4/5 RV pig maps as well as on the epicardium in 8/10 pig maps. (3) In pigs, the total dispersions of AT, EOR and MAPd were 57 ± 10, 84 ± 20, and 75 ± 21 ms respectively, which were significantly greater than the respective epi- and endocardial dispersions. The epicardial dispersions of AT, EOR and MAPd for both the RV and LV were significantly greater than that of each ventricle alone. (4) Both in pigs and in patients, the maximum dispersions in EOR were 57 ± 23 ms on the epi-, 61 ± 24 ms on the endocardium and 84 ± 20 ms on both, which were significantly greater than the dispersions between adjacent sites, remote sites and paired epi- and endocardial sites. Conclusions: (1) Detailed mapping of endo- and epicardial repolarization in vivo using the MAP mapping technique is feasible. (2) Repolarization gradients exist over both the endo- and epicardium in pigs and in humans. (3) Both the epi- and endocardium of the two ventricles contribute significantly to the global DVR. (4) The global DVRs are poorly estimated from MAP recordings at a few adjacent or remote sites, suggesting the importance of obtaining global information in the evaluation of the DVR. (5) The apico-basal and septo-lateral gradients are predominant repolarization gradients, as compared to the epicardial-endocardial gradients (6). The EOR sequence follows the activation sequence, suggesting that the latter is an important determinant of the former. The magnitude of the progressive MAP shortening with progressively later activation, relative to local AT, is a critical factor governing the direction and pattern of the EOR