Comparison of the effects of epicardial and endocardial cardiac resynchronization therapy on transmural dispersion of repolarization.

BACKGROUND: Despite significant improvements in cardiac output and functional capacity with cardiac resynchronization therapy (CRT), incidence of sudden cardiac death still remains high. Reversal of physiological myocardial activation sequence during epicardial pacing increases the transmural dispersion of repolarization (TDR). The aim of this study was to compare the effects of endocardial and epicardial biventricular pacing on repolarization parameters in the same patient group. METHODS: Seven patients who had transseptal endocardial left ventricle (LV) lead placement, in whom epicardial CRT had failed due to coronary sinus (CS) lead dislodgement after successful implantation, were admitted to the study. LV endocardial leads were implanted through the inter-atrial septum in a lateral position. ECGs were scanned before and after successful epicardial and endocardial biventricular pacing and analyzed using digital callipers. ECG markers of TDR (TpTe and TpTe/QT ratio) were measured and compared. RESULTS: Baseline QRS durations (161.7+/-15.9 vs 162.2+/-17.8 ms, p = 0.95), TpTe values (107.1+/-20.5 vs 108.5+/-17.6 ms, p = 0.89) and TpTe/QT ratios (0.24+/-0.05 vs 0.24+/-0.03, p = 0.88) were similar before epicardial and endocardial CRT. QRS interval reduction was similar (-28.3+/-11.6 vs -29.1+/-11.4 ms, p = 0.89) in both groups. Compared to transseptal endocardial CRT, epicardial CRT was associated with a significant increase in TpTe (17.1+/-19.5 vs -12.6+/-18.9 ms, p = 0.01) and TpTe/QT ratio (0.03+/-0.04 vs -0.02+/-0.03, p = 0.04). CONCLUSION: Transseptal LV endocardial pacing is associated with significant reduction in TDR characteristics compared to epicardial pacing in CRT. Further studies are warranted to determine whether these effects may contribute to reduction of arrhythmias in patients with CRT. This article is protected by copyright. All rights reserved