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Morphometric and histological study of coronary plaques in stable angina and acute myocardial infarctions.

OBJECTIVE
To compare the morphological difference of coronary plaques in acute myocardial infarction and stable angina to clarify the occurrence basis of these two different myocardial events.


METHODS
Sixty-eight acute myocardial infarction cases and 34 stable angina postmortem cases were studied. The coronary arteries were dissected en block, fixed, decalcified, sectioned at a 3 mm interval and processed routinely for histologic examination. A computor-aided planimeter was used to measure plaque and lipid core area.


RESULTS
Among the total 4089 coronary blocks in acute myocardial infarction, 2087 (51.0%) had a lipid core over 40% of the plaque area; while among the total 2030 blocks in stable angina, only 209 (10.3%) had a lipid core over 40% of the plaque area (P < 0.05). Sixty-one of the 68 (89.7%) acute myocardial infarction cases had thrombi among which 56 occurred on ruptured plaques; while no thrombus was found in stable angina. In addition, atheroemboli were found in most of the thrombus-negative acute myocardial infarction cases (6/7) but none in SA cases.


CONCLUSIONS
Acute myocardial infarction and stable angina had different morphologic basis of the coronary plaques. The former had more plaques with a large lipid core than the latter. Acute myocardial infarction was caused mainly by plaque rupture and associated thrombus. But atheroembolus could be another very important cause of acute myocardial infarction.