Ultrasonic detection of myocardial infarction by amplitude analysis.

Myocardial infarctions were produced in dogs by occluding the left anterior descending artery; the dogs were killed at varying times, from 30 minutes to 8 days. Prior to sacrifice, Thioflavin S was injected intravenously. The excised heart was scanned by a B-scanner interfaced with a computer that permitted quantification of signal amplitude. The heart was sectioned, photographed, and studied pathologically. Infarcted myocardium showed high ultrasonic reflectivity with average amplitudes 1.4--2.6 times that of normal muscle. Perfusion-histomorphologic evidence of infarction correlated best in infarcts of 24 hours or less; older infarcts were generally underestimated. Tissue changes, sources of false-positive and false-negative findings, signal processing, and potential clinical utility are discussed.