Cardiac Mechanoenergetics and Coronary Circulation

Abstract

Coronary circulation variously modifies cardiac performance. We have been characterizing the left-ventricular mechanoenergetics modified by interventions related to the coronary circulation by fully using the Vo2—PVA—Emax framework, in which Vo2 is myocardial oxygen consumption, PVA is the systolic pressure-volume area as a measure of the total mechanical energy generated by ventricular contraction, and Emax is the end-systolic maximum elastance as an index of ventricular contractility. This framework has been powerful in analyzing cardiac mechanoenergetics under various physiological and pathophysiological inotropic conditions. Coronary hypoperfusion depresses Emax, PVA, and Vo2 at a given preload and lowers the volume-loading Vo2—PVA relation in a parallel manner until the coronary reserve exhausts at a high PVA: coronary hyperperfusion does the opposite. These mechanoenergetic responses to changes in coronary perfusion partly resemble those to negative and positive inotropism. Postischemic reperfusion causes myocardial stunning, characterized by disproportionately increased coronary flow and Vo2 despite depressed Emax, resulting in a twice-normal oxygen cost of Emax. This type of mechanoenergetic change contrasts with ordinary negative inotropism. We also referred to some other interventions accompanying changes in coronary perfusion. By using Emax and PVA, we have thus been able to characterize left-ventricular mechanoenergetics related to primarily and secondarily modified coronary circulation in a manner such as could not have been possible otherwise.