Indirect measurement of infarct size. Correlative variability of enzyme, radionuclear angiographic, and body-surface-map variables in 34 patients during the acute phase of first myocardial infarction

To gain a correlative perspective of indirect indications of the size of a myocardial infarct, we measured several body-surface electrocardiographic variables and several enzyme and radionuclear angiographic indicators of an infarct's size in 34 patients during the acute phase of first infarction. We found that bivariate correlations ranged widely, from an r value of 0.05 to an r value of 0.92, but were significantly (p<0.001) higher when variables from the same technique were correlated (mean r, 0.60 ± 0.27), as opposed to correlations of variables from different techniques (mean r, 0.27 ± 0.18). Trivariate comparisons among techniques produced significantly (p<0.001) higher r values, but the highest, an r value of 0.76 (total wall motion abnormality score; peak lactic dehydrogenase level; ST-segment integral maximum), indicated that even in this best case, only about 60 percent of the variation of one variable was dependent on or due to the two other variables. These data demonstrate that multiple indirect quantitative indicators of myocardial injury can vary widely in their correlations within the same population of infarcts, and much remains unknown in their relationships during the acute phase. Caution should be exercised, therefore, in their clinical application to predict an infarct's size in individual patients with acute myocardial infarction.