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.