The impact of the left ventricular pacing polarity and localization during cardiac resynchronization therapy on depolarization and repolarization parameters

Objective: Reversal of myocardial activation sequence during cardiac resynchronization therapy (CRT) may increase the transmural dispersion of repolarization (TDR), which may lead to ventricular arrhythmias. Quadripolar left ventricular (LV) leads offer 10 different pacing configurations. However, little is known about the role of pacing polarity on repolarization patterns. Our study aimed to investigate the impact of LV pacing polarity on depolarization and repolarization parameters in the same substrate in the same patient group. Methods: This study prospectively analyzed 20 patients who were consecutively admitted and underwent CRT-D implantation with quadripolar LV leads. Two bipolar pacing vectors and two unipolar vectors, also called extended bipolar pacing vectors, from the same pacing sites were selected for comparison. Electrocardiogram markers of depolarization and repolarization were measured and compared. Results: Bipolar LV pacing was associated with a significantly shorter QRS duration (basal, unipolar vs. bipolar, 135.1±17.8 vs. 119.3±14.5, p<0.01; non-basal, unipolar vs. bipolar, 134.4±15.7 vs. 121.9±10.3, p<0.01) and Tp-Te value (Basal, unipolar vs. bipolar, 119.1±36.7 vs. 97.6±27.9, p<0.05; non-basal, unipolar vs. bipolar, 117.9±36.3 vs. 98.6±20.4, p<0.05) than those in unipolar pacing. LV pacing from basal and non-basal segments had no differential effect on the repolarization parameters. Conclusion: The LV pacing polarity significantly affects QRS duration but not repolarization patterns regardless of the pacing site in the same substrate. From the perspective of basal and non-basal segments, the LV pacing site has no differential effect on the repolarization parameters. Keywords: