Dependence of instantaneous transfer function on regional ischemic myocardial volume

To obtain the instantaneous left ventricular transfer function curve (instantaneous TFC) under conditions of regional ischemia, sinusoidal accelerations ranging from 30 to 150 Hz were applied to a small area of the epicardium of cross-circulated isovolumic canine left ventricle, and the contralateral acceleration was measured under control and during regional coronary occlusion (n = 11). The TFC is the ratio of the output to input acceleration amplitudes. The instantaneous TFC was characterized as a single-peaked configuration under control coronary perfusion. However, TFCs progressively changed from a single-peaked to a double-peaked configuration during regional ischemia. To quantify this change in instantaneous TFC, we defined an index D as the mean squared difference of TFC during ischemia from TFC during control. Index D was linearly related to the percent mass of the ischemic region at 40 minutes after onset of ischemia. We conclude that 1) transfer function curves are sensitive measures of myocardial heterogeneity and 2) the fractional ischemic weight of the ventricle is a major factor in determination of the deformation in instantaneous TFC at the later stages of regional ischemia.