Local myocardial function following coronary occlusion in cats. Effect on non-ischaemic regions.

Abstract

The mechanical function and perfusion in ischaemic and non-ischaemic myocardium after coronary occlusion was studied in 10 cats using pressure-length loop analysis and radiolabelled microspheres. Measurements in three regions--ischaemic, adjacent normal and remote normal myocardium--all showed different responses to coronary occlusion. In the ischaemic region loop area, segment shortening and tissue flow were markedly reduced. In the adjacent normal region, both loop area and segment shortening as well as flow increased. In the remote normal region, neither loop area, segment shortening nor flow showed consistent changes. End-diastolic segment length increased in all regions, most in the ischaemic region and least in the remote region. The increased end-diastolic segment length in all regions after coronary occlusion indicates activation of the Frank-Starling mechanism as an attempt to maintain stroke volume. However, the end-diastolic segment length did not increase uniformly for all normal myocardium: it depended on the proximity to the ischaemic region. Increased contractile function in the adjacent normal myocardium due to non-uniform distribution of the Frank-Starling effect is the most likely mechanism behind the left ventricle's ability to partially compensate for loss of contractile mass during acute regional ischaemia in anaesthetized cats.