The importance of the determination of the myocardial area at risk in the evaluation of the outcome of acute myocardial infarction in patients

Abstract

On the basis of animal studies, we postulated that the size of the perfusion field (risk area) of an occluded coronary artery would be an important determination of outcome in patients with acute myocardial infarction. To test this hypothesis, we measured size of the risk area in 27 patients with acute myocardial infarction by the intracoronary injection of 99mTc-macroaggregated albumin and gated nuclear imaging. After injection of the albumin spheres (5.3 ± 1.4 hr after the onset of chest pain) streptokinase was administered and in 16 of 27 patients (59%) effective thrombolysis was achieved. Since none of the patients had evidence of a prior acute myocardial infarction, the 3 day nuclear left ventricular ejection fraction (LVEF) was considered an index of infarct size. Response to thrombolysis was analyzed according to success or failure of reperfusion and the size of the risk area (small risk area less than 25%, large risk area greater than 25% of left ventricular surface area). Standard clinical indexes correlated poorly with size of the risk area: electrocardiographic variables (r = .37), left ventricular end-diastolic pressure 9r = .23), cardiac index (r = .55), and the LVEF obtained from a right anterior oblique contrast ventriculogram (r = .31). The coronary vessel responsible for the acute myocardial infarction significantly influenced size of the risk area (left anterior descending, 38 ± 5% [mean ± SD] vs circumflex or right coronary artery, 17 ± 4%). However, knowledge of the site of coronary occlusion within a vessel was not helpful in predicting the size of the area at risk. For example, sizes of risk areas in patients with proximal and mid left anterior descending coronary occlusions were similar (38 ± 8% vs 33 ± 14%). When the 3 day LVEF response was analyzed as a function of risk area subset, patients with large risk areas had significantly lower LVEFs than those with small risk areas (33 ± 9% vs 56 ± 50%, p < .01). A strong inverse linear relationship was demonstrated between the 3 day LVEF and size of the risk area in those patients with persistent coronary occlusion (r = .91, y = -1.19x + 75). All cardiogenic deaths occurred in patients with risk areas greater than 33% of the left ventricular area (p < .001 vs small risk area). In conclusion, these studies demonstrate that accurately measured risk area is a major prognosticator of outcome in those patients with acute myocardial infarction in whom reperfusion fails or occurs relatively late. These findings underscore the importance of the determination of risk area in patients in whom the efficacy of infarct-limiting agents is being assessed.