974-39 Differential Response of Left Ventricular Work Efficiency and Inotropy to Dobutamine in the Failing Canine Heart

Left ventricular work efficiency (LVWE), a measure of the efficiency of energy transfer from LV to systemic circulation, declines as heart failure (CHF) becomes more severe. We compared changes in the response of LVWE and inotropy to dobutamine as progressively more severe CHF was induced by tachypacing. Seventeen dogs (weights 19–24kg) were instrumented with micromanometer catheters, Ultrasonic crystals and a pacemaker and paced at 215–240bpm over 3 weeks. Ventricular volumes and pressures were digitally acquired at baseline and weekly over 3 weeks. Pressure-volume area (PVA), external work (EW), end-systolic pressure-volume relation slope (Ees) and arterial elastance (Ea) were derived from variably loaded beats after IVC occlusion. The LVWE was calculated as EW/PVA. Measurements were made with and without dobutamine (DOB) at 10μg/kg/min.ResultsBaselineCHF 1CHF 2CHF 3EW(mmHg*ml)1308±6631050±542861±633*738±506*% † on DOB+80±34+133±71+145±89+222±188*LVVVE(%)52±842±10*36±10*33±11*% † on DOB+65±27+77±26+108±77*+115±1.2*Ees (mmHg/ml)5.1±2.93.8±1.62.9±1.6*2.5±1.0*% † on DOB+269±159+135±118*+125±31*+131±58*peak+dP/dt (mmHg/s)1680±4821312±354*1008±178*1080±325*% † on DOB+162±63105±49*108±52*+81±42*Ea/Ees ratio2.0±083.7±2.4*4.1±2.2*4.1±1.6*% ↓ on DOB–78±11–72±9–73±9–65±4**p<0.05 vs baselineThe inotropic responsiveness of the LV is significantly reduced in CHF as demonstrated by the response of Ees and +dP/dt to DOB. However, EW on DOB in CHF is not significantly different than at baseline (1924±1205 vs 2269±1051mmHg*ml). This is caused by a greater increase in LVWE on DOB in CHF Improved LVWE and Ea/Ees coupling is an important mechanism for enhanced LV pump performance in CHF and helps counterbalance the reduction of inotropic responsiveness of the LV as CHF progresses