The effect of variation in the interval between right and left ventricular activation on paced QRS duration

Pacing of the RV and LV is a promising technique for treating patients with dilated cardiomyopathy and bundle branch block. The salutary effects of biventricular pacing may be due to resynchronization of LV activation. Currently, available biventricular pacemakers and implanted defibrillators produce simultaneous ventricular output pulses. The purpose of the current study was to assess the effects of variation in the timing of RV and LV activation, using the paced QRS duration as a marker of resynchronization. Twenty-six patients undergoing transvenous biventricular pacemaker implantation were studied. After stable lead positions were achieved, activation of the LV and RV was varied over a range of +/- 50 ms and the QRS duration measured on a 12-lead ECG. Only 6 (23%) of the 26 patients had maximal shortening of the paced QRS with simultaneous activation of the LV and RV. The shortest paced QRS duration was most often produced by an LV to RV interval of -30 ms (LV activation preceding RV activation). Optimization of LV to RV interval resulted in an additional 13% shortening of the paced QRS compared to simultaneous activation (P < 0.0001). Patients with leads located on the lateral or anterolateral walls of the LV were more likely to benefit from preexcitation of the LV than did patients with leads in the posterior position. Results of this study suggest that the ability to program the LV to RV interval may be useful to optimize the benefit of biventricular pacing.