Clinical study
Infarct expansion versus extension: Two different complications of acute myocardial infarction

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Abstract

Precordial S-T segment mapping studies have suggested that extension of acute transmural myocardial infarcts occurs in up to 80 percent of patients within 6 days. To determine the morphologic nature of extension 76 consecutive acute myocardial infarcts aged 30 days or less were studied. All infarcts had been clinically diagnosed and proved at autopsy. Extension (histologically more recent foci of contraction band necrosis around an infarct) was found in only 13 infarcts (17 percent). However, “expansion” (acute dilatation and thinning of the area of infarction not explained by additional myocardial necrosis) was present in 45 infarcts (59 percent). Severe expansion did not develop until 5 days after infarction and was greater with transmural and first infarcts. Clinically diagnosed extension manifested by new pain, S-T segment elevation, rise in serum creatine kinase level and increased congestive heart failure occurred in 14 of the 76 patients (18 percent). At autopsy these clinical extensions were associated with expansion alone in three patients, with extension alone in two and with both in nine. The study shows that expansion is a common complication of acute myocardial infarction that can worsen cardiac function through left ventricular dilatation and can mimic or possibly cause infarct extension. In contrast, extension with additional myocardial necrosis is an infrequent accompaniment of acute myocardial infarction and is usually a result of hypoperfusion.

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This study was supported by Grant P50-HL-17655-03 from The National Institutes of Health, U.S. Public Health Service, Bethesda, Maryland.

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