Bi-ventricular pacing improves pump function only with adequate myocardial perfusion in canine hearts with pseudo-left bundle branch block.

Bi-ventricular (BiV) pacing is an effective therapy for the treatment of cardiac electromechanical (EM) dysfunction. The reason(s), however, for therapy non-response in approximately one-third of the subjects remains unclear, especially as it relates to myocardial perfusion and pacing location. In this study, we examined how acute BiV pacing response may be related to underlying myocardial perfusion coupled with pacing near or distant to the area of perfusion. In 10 open-chest anesthetized canines, coronary blood flow to the left ventricular (LV) anterior wall (AW: n = 5) and lateral wall (LW: n = 5) was controlled during four pacing conditions: right atrial, right ventricular (pseudo-left bundle branch block; [pseudo-LBBB]), BiV-LW and BiV-AW. Local EM function (piezo-electrical crystals and electrodes), along with global hemodynamic parameters, were measured during all pacing conditions at three coronary perfusion rates (>= 0.40 mL/min/g, 0.20-0.40 mL/min/g and <0.20 mL/min/g). A positive BiV therapy response was assessed by a significant increase in the maximum cardiac output compared with the pseudo-LBBB condition. Despite no improvement in QRS duration, BiV-LW pacing improved LV function compared with the pseudo-LBBB pacing condition (P value <0.01). This improvement with BiV-LW pacing was seen above a certain myocardial perfusion threshold and was independent of any increases in regional coronary blood flow with BiV pacing. At lower myocardial perfusion rates, LV function was not improved with BiV pacing at any location. This study underscores the significance of even mild ischemia on BiV pacing response.