Biventricular pacing has an advantage over left ventricular epicardial pacing alone to minimize proarrhythmic perturbation of repolarization

Introduction: Cardiac resynchronization therapy (CRT) by simultaneous biventricular pacing is now widely accepted as a new therapeutic option for patients with severe congestive heart failure (CHF). Recent studies have shown comparable hemodynamic benefits of left ventricular (LV) pacing alone. The clinical usefulness of CRT, however, might be compromised by potential exaggeration of arrhythmogenic substrates through a modification of ventricular repolarization. Methods and Results: We compared ECG parameters during sinus rhythm (SR), atrioventricular synchronous pacing at the right ventricular apex (RV_endP), at LV epicardium (LV_epiP), and at both sites (BiVP) in acute homodynamic studies of 14 CHF patients scheduled for CRT (QRS duration = 144 ± 23 msec, LVEF = 27 ± 10%). The maximum rate of increase in LV pressure (LVdp/dt_max) was decreased significantly during RV_endP, whereas it was increased similarly during LV_epiP and BiVP compared with SR. QTc was increased during RV_endP (by 10.2%) and LV _epiP (by 26.1%). QTc dispersion (QTc_max-QTc_min in the six precordial leads) was also increased during LV_epiP (by 66.5%). These parameters were unaffected during BiVP. JTc was unchanged, and the interval from the peak to the end of the T wave (Tc_peak-end) was increased slightly (by 19.3%) during RV_endP. Both JTc and Tc _peak-end were increased dramatically during LV_epiP (by 18.2% and 55.4%, respectively), but increased only modestly during BiVP (by 6.6% and 15.8%, respectively). Conclusions: LV_epiP causes much greater increase in spatial dispersion of ventricular repolarization than BiVP in CHF patients. BiVP may have a substantial advantage over LV_epiP to minimize the proarrhythmic perturbation of ventricular repolarization in association with CRT.