Is there a true increase in myocardial stiffness with acute ischemia?

Based on experimental observations, an increase in intrinsic regional myocardial stiffness can be demonstrated during complete coronary occlusion at rest when there is dyskinesia. There is decreased chamber compliance as well during coronary occlusion, while the zero volume intercept of the ventricle in diastole is larger, changes that may relate in part to regional ultrastructural alterations at the sarcomere level. Postpacing studies suggest that decreased chamber compliance also occurs in that setting, but with an opposite shift upward of the diastolic pressure-volume relation, which may relate to reperfusion effects. The factors involved in such changes in stiffness undoubtedly are multiple, and also include delayed ventricular relaxation, which can be magnified at rapid heart rates, effects of nonuniformity, and possibly the timing of loading conditions during individual contractions. The relative influence of these multiple factors undoubtedly varies with the conditions and duration of acute ischemia.