Theoretical analysis on the relationship between left ventricular energetic efficiency and acute infarct size

Energetic efficiency is an important indicator of cardiac function in acute myocardial infarction. However, the relationship between cardiac energetic efficiency and infarct size is not perfectly elucidated. In this study, the relationship is analysed by means of simulation using a theoretical model of the guinea pig left ventricle. In simulation with varied ratios of infarct area, pressure-volume area (PVA), which is an index of total mechanical energy by ventricular contraction, and myocardial oxygen consumption (MVO₂) are calculated for each infarct ratio. Then, change of PVA when MVO₂ alters (PVA/MVO₂) as a well-known index of energy conversion efficiency is evaluated. In addition, PVA/VO₂, which represents a ratio of PVA change to alteration of mean oxygen consumption of myocytes except for infarct myocytes, is introduced as an index for real energetic efficiency. In simulation results, PVA/MVO₂ increases but PVA/VO₂ decreases as infarct area expands, because with expansion of infarct area PVA decreases but VO₂ remains almost unchanged because of larger shortening of myocytes. This implies that the enlargement of shortening of noninfarcted myocyte to compensate for depression of cardiac output is a potential cause of myocardial remodelling.