Altered LV inotropic reserve and mechanoenergetics early in the development of heart failure

Department of Medicine, University of Texas Health Science Center at San Antonio, and South Texas Veterans Health Care System-Audie Murphy Division, San Antonio, Texas 78284 To test the hypothesis that alterations in left ventricular (LV) mechanoenergetics and the LV inotropic response to afterload manifest early in the evolution of heart failure, we examined six anesthetized dogs instrumented with LV micromanometers, piezoelectric crystals, and coronary sinus catheters before and after 24 h of rapid ventricular pacing (RVP). After autonomic blockade, the end-systolic pressure-volume relation (ESPVR), myocardial O 2 consumption (M O 2 ), and LV pressure-volume area (PVA) were defined at several different afterloads produced by graded infusions of phenylephrine. Short-term RVP resulted in reduced preload with proportionate reductions in stroke work and the maximum first derivative of LV pressure but with no significant reduction in baseline LV contractile state. In response to increased afterload, the baseline ESPVR shifted to the left with maintained end-systolic elastance ( E es ). In contrast, after short-term RVP, in response to comparable increases in afterload, the ESPVR displayed reduced E es ( P