Energetics of the fibrillating ventricle

We have proposed a new mechanical index, equivalent pressure-volume area (ePVA), as a measure of the total mechanical energy of a fibrillating ventricle. ePVA is an analogue of the pressure-volume area (PVA) of a contracting ventricle and the specific area surrounded by the horizontal pressure-volume line at the pressure of ventricular fibrillation (VF) and the end-systolic and end-diastolic pressure-volume relations in the beating state in the pressure-volume diagram. In the isolated, cross-circulated heart preparation, we obtained myocardial oxygen consumption (VO2) during VF and ePVA at various left ventricular volumes in the control, epinephrine, propranolol and hypothermia runs. ePVA was highly linearly correlated with VO2 in all runs (r = 0.95, 0.98, 0.96 and 0.90, respectively). We also determined equivalent heart rate (eHR) as an estimate of the contraction frequency of individual myocytes in a fibrillating ventricle from mechanically unloaded VO2 in beating and fibrillating states. Using both ePVA and eHR, VO2 during VF was estimated and correlated with directly measured VO2. Estimated VO2 almost agreed with measured VO2 in all runs. We conclude that ePVA is a primary determinant of VO2 during VF, and that VO2 of a fibrillating ventricle can be reasonably accounted for by the combination of ePVA and eHR. This paper is a review of our previous studies on the energetics of a fibrillating ventricle.