Improved left ventricular mechanics from acute VDD pacing in patients withdilated cardiomyopathy and ventricular conduction delay

Background-Ventricular pacing can improve hemodynamics in heart failure pat ients, but direct effects on left ventricular (LV) function from varying pa cing site and atrioventricular (AV) delay remain unknown. We hypothesized t hat the magnitude and location of basal intraventricular conduction delay c ritically influences pacing responses and that single-site pacing in the de lay-activated region yields similar or better responses to biventricular pa cing. Methods and Results-Aortic and LV pressures were measured in 18 heart failu re patients (mean+/-SD: LV ejection fraction, 19+/-7%; LV end-diastolic pre ssure, 25+/-8 mm Hg; QRS duration, 157+/-36 ms). Data under normal sinus rh ythm were compared with ventricular pacing (VDD) at varying sites and AV de lays (randomized order). Right ventricular (RV) apical or midseptal pacing had negligible contractile/systolic effects. However, LV free-wall pacing r aised dP/dt(max) by 23.7+/-19.0% and pulse pressure by 18.0+/-18.4% (P<0.01 ). Biventricular pacing yielded less change (+12.8+/-9.3% in dP/dt(max), P< 0.05 versus LV). Pressure-volume analysis performed in 11 patients consiste ntly revealed minimal changes with RV pacing but increased stroke work and lower end-systolic volumes with LV pacing. Optimal AV intervals averaged 12 5+/-49 ms, and within this range, AV delay had less influence on LV functio n than pacing site. Basal QRS duration positively con-elated with %Delta dP /dt(max) (P<0.005), but pacing efficacy was not associated with QRS narrowi ng. Conduction delay pattern generally predicted pacing sites with most eff ect. Conclusions-VDD pacing acutely enhances contractile function in heart failu re patients with intraventricular conduction delay. Single-site pacing at t he site of greatest delay achieves similar of greater benefits to biventric ular pacing in such patients. These data clarify pacing-effect mechanisms a nd should help in candidate identification for future studies.