In vivo effects of mid-myocardial pacing on transmural dispersion of repolarization and conduction in canines

Objective: In our previous in vitro study mid-myocardial relative to epicardial pacing decreased transmural dispersion of depolarization (TDR) and prevented ventricular arrhythmia. We therefore hypothesized that in vivo mid-myocardial pacing in canines has a similar effect. Methods and results: Using custom-made electrodes, monophasic action potentials were simultaneously recorded in vivo from left ventricular epicardial (Epi), mid-myocardial (Mid) and endocardial (Endo) layers of canines (n = 12). TDR was significantly increased at Epi (44.6 +/- 6. 4 ms; 14.2 +/- 5.1 ms; and 13.8 +/- 5.4 ms for Epi, Mid and Endo pacing, respectively; P < 0.001), and similarly at Mid and Endo pacing (P = 0.855). This result was reproducible after ibutilide administration (n=12). TDR was augmented at each layer pacing and significantly increased at Epi (78.1 +/- 15.9 ms; 46.8 +/- 16.0 ms; and 46.5 +/- 15.2 ms for Epi, Mid, and Endo pacing, respectively; P < 0.001), but was similar at Endo and Mid pacing (P = 0.965). TDR at 3 cm from left ventricular apex pacing site was similar between Mid and Endo pacing, and still significantly increased at Epi pacing. At 3 cm distance, the first activation myocardium was still the epicardium at Epi, while sequence transformed from mid-myocardium to endocardium at Mid pacing. Conclusion: Mid as compared to Epi pacing significantly decreases TDR and remains this advantage on the distant myocardium away from the pacing site. (C) 2015 The Authors. Published by Elsevier Ireland Ltd.