Changes in left ventricular wall dimensions during regional myocardial ischemia

Abstract

The relation between changes in left ventricular wall systolic thickening and other measures of left ventricular function were studied during regional ischemia in 14 open chest pigs. A fixed decrease in coronary peak blood flow from 46 ± 5 (standard error) to 13 ± 2 ml/min was produced using a screw clamp and flow probe placed around the left anterior descending coronary artery. Myocardial wall thickness was measured with a calibrated harpoon mercury strain gauge placed through the apical portion of the left ventricle and recorded continuously with left ventricular systolic pressure, the first derivative of left ventricular pressure rise ( dP dt ) and pressure-derived peak velocity of contraction. During systole, the left ventricle thickened by 10.7 ± 2.1 percent of its total average thickness of 12.7 ± 0.7 mm. Within 6 seconds of the onset of ischemia total myocardial wall thickness decreased from 1.356 ± 0.135 to 0.592 ± 0.081 mm ( P < 0.001) or to 45.2 ± 5.1 percent of the control value. During ischemia, changes were noted in both the isovolumic and the ejection phases of systole in addition to left ventricular wall thinning of 0.282 ± 0.02 mm at enddiastole. There was no significant change in left ventricular pressure or its derived values. In two experiments isolated wall thickness alternans was observed. These studies indicate that myocardial wall thickness is more sensitive than ventricular pressure as a measure of local changes in myocardial function during regional myocardial ischemia.