Analysis of regional myocardial function, dimensions, and wall thickness in the characterization of myocardial ischemia and infarction.

Disorders of contractile function constitute one of the earliest events to follow acute coronary occlusion, and occur in the central ischemic region within approximately 10 seconds. Measurements of regional myocardial dimensions and function in the central, border, and normal zones around an area of ischemia allow assessment of such changes, and when these disorders are persistent after permanent coronary occlusion they may offer an indirect means for assessing the severity and extent of myocardial ischemia and infarction. Recent experimental studies that used pairs of miniature ultrasonic crystals implanted within the subendocardium of open-chested and chronically instrumented, unanesthetized dogs indicate that functional function may be studied simultaneously in these regions; a holosystolic bulge rapidly develops in the central zone of ischemia while hypokinesis is apparent in marginal zones bordering the central region. It has been shown that function in the marginal zone reflects the balance between oxygen supply and demand and may be favorably or unfavorably influenced by acute therapeutic interventions. This finding suggests that the extent of an ischemic region may be altered by such therapy.Our studies further indicate that regional changes in dynamic wall thickness closely parallel the characteristics of shortening of nearby subendocardial segments, indicating that measurement of wall thickness alone may be useful for characterizing regional function. Studies in chronically instrumented animals also have established that the miniature crystals are useful for measuring regional dimensions and function over prolonged periods of time; for example, reduction in end-diastolic dimensions that reflex tissue loss over a 3- to 4-week period after coronary occlusion is substantially greater in the central ischemic regions than in the marginal zones. It is proposed that persistent changes in myocardial function and progressive alterations changes in dimensions over time offer indirect measures of the extent and severity of ischemic damage and infarction. With the development of improved echocardiographic or other clinically applible methods, such measurements may be a useful tool for assessing the effects of therapy on myocardial infarct size.