The influence of preload on post-systolic shortening in ischaemic myocardium.
Post-systolic shortening is a wall motion abnormality defined as shortening of cardiac muscle after the end of ejection and usually regarded as a manifestation of ischaemia. This study was designed to determine whether changes in preload may alter the magnitude of ischaemia-induced post-systolic shortening. Eleven beagles were anaesthetized (halothane 0.8%) and instrumented for measurement of pressures, flows and dimensions in the apical subendocardium supplied by the left anterior descending coronary artery. Myocardial ischaemia was obtained by tightening a micrometer-controlled snare around the left anterior descending coronary artery. Post-systolic shortening, calculated as end-systolic length minus minimum length divided by end-systolic length, was measured at different levels of preload. Increasing the preload from 4 to 17 mmHg caused a significant reduction in post-systolic shortening (8.9% vs. 12.9%, P < 0.05, Student's paired t-test); post-systolic shortening was negatively correlated with coronary perfusion pressure (r = 0.35, P < 0.01) and positively correlated with systolic bulging. This study demonstrates that the amount of post-systolic shortening depends on the volume status, which therefore has to be taken into account in interpreting regional wall motion abnormalities, such as those detected by echocardiography.
Dalmas
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Nuffield Department of Anaesthetics, University of Oxford, Radcliffe Infirmary, UK.
Wanigasekera
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Marsch
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Ryder
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Wong
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Foëx
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D000818:Animals; D004285:Dogs; D005260:Female; D008297:Male; D009200:Myocardial Contraction; D017202:Myocardial Ischemia / Q000503:physiopathology*; D013599:Systole; D016277:Ventricular Function, Left; D017725:Ventricular Pressure