Whether sequential biventricular pacing provides substantial benefits over conventional simultaneous stimulation remains unclear, particularly regarding the differences between ischemic and non-ischemic patients. The purpose of this study was to evaluate the acute effect of interventricular pacing interval (V-V) optimization on left ventricular (LV) systolic performance and dyssynchrony in ischemic versus non-ischemic patients.

Sixty-nine consecutive patients underwent cardiac resynchronization therapy. Within 3 days after implantation, V-V was optimized by measuring (every 20-millisecond interval) LV systolic performance (LV outflow-tract velocity-time-integral, LVOT VTI) and LV dyssynchrony (using tissue Doppler imaging). Optimal pacing configuration was the one achieving maximal increase in LVOT VTI.

Optimized sequential pacing provided a significant improvement in LVOT VTI compared to simultaneous stimulation (from 138 ± 42 to 163 ± 38 mm, P < .001) and was associated with a significant reduction in LV dyssynchrony (from 33 ± 31 to 19 ± 24 milliseconds, P < .001).

The increase in LVOT VTI and LV ejection fraction after implantation was greater in non-ischemic as compared to ischemic patients (P < .001). However, V-V optimization yielded a larger improvement in LV systolic performance in ischemic patients (P = .03). Consequently, the 2 groups showed comparable response after V-V optimization. A significant correlation was observed between LV scar tissue and optimal V-V interval (r = 0.58, P < .001), with a larger extent of scar related to a larger level of LV preactivation, probably reflecting slow intra-LV conduction.

Optimized sequential biventricular pacing further increased LV systolic performance as compared to simultaneous stimulation, particularly in ischemic patients where the presence of a large scar was correlated with a larger LV preactivation.