ENERGETICALLY OPTIMAL LEFT-VENTRICULAR PRESSURE FOR THE FAILING HUMANHEART

Background An energy-starved failing heart would benefit from more eff ective transfer of the mechanical energy of ventricular contraction to blood propulsion. However, the energetically optimal loading conditio ns for the failing heart are difficult to establish. In the present st udy, we analyzed the optimal left ventricular pressure to achieve maxi mal mechanical efficiency of the failing heart in humans. Methods and Results We determined the relation between left ventricular pressure-v olume area and myocardial oxygen consumption per beat (VO2), stroke wo rk, and mechanical efficiency (stroke work/VO2) in 13 patients with di fferent contractile states. We also calculated the optimal end-systoli c pressure that would theoretically maximize mechanical efficiency for a given end-diastolic volume and contractility. Left ventricular pres sure-volume loops were constructed by plotting the instantaneous left ventricular pressure against the left ventricular volume at baseline a nd during pressure loading. The contractile properties of the ventricl e were defined by the slope of the end-systolic pressure-volume relati on. In patients with less compromised ventricular function, the operat ing end-systolic pressure was close to the optimal pressure, achieving nearly maximal mechanical efficiency. As the heart deteriorated, howe ver, the optimal end-systolic pressure became significantly lower than normal, whereas the actual pressure remained within the normal range. This discrepancy resulted in worsening of ventriculoarterial coupling and decreased mechanical efficiency compared with theoretically maxim al efficiency. Conclusions Homeostatic mechanisms to maintain arterial blood pressure within the normal range cause the failing heart to dev iate from energetically optimal conditions.