Alterations of Myocardial Function during Early Stages of Mild Experimental Ischemia in Dogs Determined by Left Ventricular Pressure-Wall Thickness Loop

Abstract

Alterations of regional left ventricular myocardial function immediately after coronary artery branch ligation as related to the total left ventricular function were determined by utilizing left ventricular pressurewall thickness loop in 6 anesthetized open-chest dogs. End-diastolic wall thickness was decreased immediately from 11.54±0.50mm (standard error of the mean) of control to 10.99±0.50mm in 5 to 10min after ligation (p<0.05), while regional myocardial work calculated as the loop area, was also decreased from 27.5±6.1 to 19.3±5.8×10³dyn/cm (p<0.05), indicating that the local Frank-Starling curve at the myocardium was depressed during ischemia. At the site where the ligation did not have effect, end-diastolic wall thickness and the regional work did not change significantly. Analysis of the shape of the loop revealed that the myocardial shortening was incomplete during the systolic ejection phase, and that the myocardial relaxation occurred very early in the ventricular relaxation phase after ischemia without alterations in the isovolumic contraction phase. These findings are compatible with those reported on isolated cardiac muscle strips during anoxia. The left ventricular pressure-wall thickness loop is superior to the pressure-length loop in that the former can be applied easily for clinical purposes and that the former utilizes a more direct relationship of pressure to its generator than the latter. Thus, primary alterations of myocardial function during ischemia were clarified accurately by utilizing the present method in the left ventricle in situ.