Comparison of the natural history of irregular and smooth coronary lesions: insights into the pathogenesis, progression, and prognosis of coronary atherosclerosis.

The coronary arteriograms of 255 patients who had two to four arteriograms within 2.6 +/- 1.7 years were reviewed. Two hundred three patients had lesions on at least one arteriogram; among the 167 patients without coronary surgery, there were 48 complex irregular lesions (suggesting a ruptured plaque and/or thrombosis) and 141 smooth lesions with follow-up, and 73 irregular and 164 smooth lesions with preceding arteriograms available. Severe irregular lesions (> or = 90% diameter occlusion) progressed to total occlusion (46%) more often than did severe smooth lesions (11.5%) (p < 0.01). Less severe lesions usually did not progress, with no difference in incidence of progression between irregular and smooth lesions (27.8% vs 23.9%). Irregular lesions > or = 80% usually occurred as a result of progression in less severe smooth lesion or occurred in areas that were minimally diseased or appeared normal, whereas smooth lesions > or = 80% had usually not changed since the previous arteriogram. Irregular lesions very rarely became smooth. A study of lesions in 36 patients with surgery was confirmatory. We conclude that plaque rupture is a common mechanism for progression of coronary disease but is not a common pathway for the growth of smooth lesions; irregular lesions remain irregular for years. There is no relationship between the severity of smooth plaques and their likelihood to rupture. Progression of coronary disease can occur by either of two modes: (1) gradual growth of a smooth-walled plaque or (2) plaque rupture with marked progression to a severe irregular lesion. Because most smooth and most irregular lesions remain stable for years, except possibly for > or = 90% irregular lesions, there is no anatomic finding that justifies urgent revascularization. Instability is a clinical diagnosis.