Further information: Coronary Artery Disease: Pathologic Anatomy and Pathogenesis (see p593), Arterial Compliance (see p1811), Atrial Fibrillation and Flutter (see p1955), and Sudden Cardiac Death (see p2039) from Cardiovascular Medicine, 3rd Edn*

In 1985 and 1986 respectively, two articles were published in Circulation [1,2] that reported that myocardial platelet thrombi were embolic and that the emboli were a cause of acute coronary syndromes (ACS). Although prior histopathological studies had shown intramyocardial microemboli and microvascular obstruction (MVO) were present in patients with ischemic cardiac death, the association between culprit coronary morphology and intramyocardial emboli had not been reported. Therefore, the investigators in this study [3] determined to evaluate the frequency of intramyocardial microemboli and MVO in sudden cardiac death from acute coronary thrombosis. Differentiating between plaque rupture and plaque erosion were important elements of the study. Plaque rupture was defined as “disruption of a fibrocellular cap overlying a pool of lipid with pultaceous debris,” and plaque erosion was defined as “surface ulceration of the upper plaque layers without rupture into a lipid core.”

Through analysis at autopsy of coronary arteries of 44 hearts, 26 plaque ruptures and 21 erosions were found, and there was a mean of 4.5 microemboli per heart. Microemboli and MVO occurred in eroded plaques more often, and although all vessels contained fibrin and platelets, microemboli and occluded intramyocardial vessels were more common in the LAD of the coronary artery. The mean stenosis of the culprit lesion was 74% in the arteries with microemboli and 75% in those without (P=NS). Intramyocardial microemboli were more common in plaque erosion than in plaque rupture.

The investigators concluded that plaque erosion was dominant in the histopathology of clot embolization causing sudden cardiac death, was more likely to occur in vessels of less than 120 µm, and was associated with focal necrosis.

[1] Falk E. Unstable angina with fatal outcome: dynamic coronary thrombosis leading to infarction and/or sudden death. Autopsy evidence of recurrent mural thrombosis with peripheral embolization culminating in total vascular occlusion. Circulation 1985;71:699-708

[2] Davies MJ, Thomas AC, Knapman PA, Hangartner JR. Intramyocardial platelet aggregation in patients with unstable angina suffering sudden ischemic cardiac death. Circulation 1986;73:418-27

[3] Schwartz RS, Burke A, Farb A, et al. Microemboli and microvascular obstruction in acute coronary thrombosis and sudden coronary death. J Am Coll Cardiol 2009;54:2167-73

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