Left ventricular ORS widening decreases Emax without lowering VO2-PVA relation in dog hearts

We observed a few rare spontaneous cases of a suddenly widened QRS wave of left ventricular ECG associated with a simultaneous decrease in left ventricular (LV) contractility (Emax, end-systolic pressure-volume ratio) in excised cross-circulated dog heart experiments. The decreased Emax was not associated with a descent of the relation between cardiac oxygen consumption (VO2) and LV systolic pressure-volume area (PVA, a measure of total ventricular mechanical energy). This result is intriguing because ventricular VO2-PVA relation generally changes its elevation in proportion to Emax under various inotropic interventions. We suspected the unusual observation to reflect no change in myocardial contractility despite ventricular asynchrony augmented by an intraventricular conduction defect.