Regional ischemia increases sensitivity of left ventricular relaxation to volume in pigs

Regional ischemia impairs early diastolic filling due, in part, to changes in left ventricular relaxation. This study uses open-chest pigs instrumented with high-fidelity pressure transducers to investigate the effect of regional ischemia on the active component of relaxation independent of the passive effects of filling and the effect of left ventricular filling and stretch on the rate, duration, and extent of relaxation. During regional ischemia, active relaxation was impaired in the nonfilling ventricle, with a slower rate of relaxation. Stretching the myocardium as the ventricle fills slows the rate of relaxation more during regional ischemia than during normal perfusion, reflecting an increased sensitivity to stretch due to filling and an increased dependence of relaxation on volume. The duration of relaxation depends on the effect of regional ischemia on the end-diastolic pressure-volume relation. Stronger baseline contractile function results in an upward shift in the end-diastolic pressure-volume relation during regional ischemia and no net effect on the duration of relaxation. If this curve is shifted upward, the duration of relaxation shortens. All these effects combine to reduce the atrioventricular pressure gradient and left ventricular filling during regional ischemia.