Coronary plaque erosion without rupture into a lipid core. A frequent cause of coronary thrombosis in sudden coronary death

Coronary risk factors and plaque morphology in men with coronary disease who died suddenly

BACKGROUND

Cigarette smoking and abnormal serum cholesterol concentrations are risk factors for acute coronary syndromes, but the underlying mechanisms are poorly understood. We studied whether cigarette smoking and abnormal cholesterol values may precipitate acute coronary thrombosis and sudden death resulting from either rupture of vulnerable coronary plaques or erosion of plaques.

METHODS

We examined the hearts of 113 men with coronary disease who had died suddenly and also analyzed their coronary risk factors. We found an acute coronary thrombus in each of 59 men, and severe narrowing of the coronary artery by an atherosclerotic plaque without acute thrombosis (stable plaque) in 54. Cases of acute thrombosis were divided into two groups: 41 resulting from rupture of a vulnerable plaque (a thin fibrous cap overlying a lipid-rich core), and 18 resulting from the erosion of a fibrous plaque rich in smooth-muscle cells and proteoglycans. Vulnerable plaques that had not ruptured were counted in each heart.

RESULTS

Cigarette smoking was a risk factor in 44 (75 percent) of the men with acute thrombosis, as compared with 22 (41 percent) of the men with stable plaques (P<0.001). The mean (+/-SD) ratio of serum total cholesterol to high-density lipoprotein (HDL) cholesterol was markedly elevated in the men who died of acute thrombosis with plaque rupture (mean, 8.5+/-4.0) but only mildly elevated in the men without acute thrombosis (5.5+/-2.4; P<0.001) and in the men with thrombi overlying eroded plaques (5.0+/-1.8; P<0.001). Multivariate analysis showed an association between an elevated ratio of serum total cholesterol to HDL cholesterol and the presence of vulnerable plaques (P<0.001).

CONCLUSIONS

Among men with coronary disease who die suddenly, abnormal serum cholesterol concentrations - particularly elevated ratios of total cholesterol to HDL cholesterol - predispose patients to rupture of vulnerable plaques, whereas cigarette smoking predisposes patients to acute thrombosis.

Angioscopic assessment of coronary lesions underlying thrombus

This study examines the characteristics of coronary lesions in which thrombus is found as assessed by angioscopy before percutaneous transluminal coronary angioplasty in patients with various coronary syndromes. Our findings demonstrate that the plaque underlying intracoronary thrombus is usually yellow and/or disrupted, and support in vitro observations that lipid-rich plaques are highly thrombogenic and that disruption of these plaques is associated with in situ thrombosis.

Inflammation, aspirin, and the risk of cardiovascular disease in apparently healthy men

BACKGROUND

Inflammation may be important in the pathogenesis of atherothrombosis. We studied whether inflammation increases the risk of a first thrombotic event and whether treatment with aspirin decreases the risk.

METHODS

We measured plasma C-reactive protein, a marker for systemic inflammation, in 543 apparently healthy men participating in the Physicians' Health Study in whom myocardial infarction, stroke, or venous thrombosis subsequently developed, and in 543 study participants who did not report vascular disease during a follow-up period exceeding eight years. Subjects were randomly assigned to receive aspirin or placebo at the beginning of the trial.

RESULTS

Base-line plasma C-reactive protein concentrations were higher among men who went on to have myocardial infarction (1.51 vs. 1.13 mg per liter, P<0.001) or ischemic stroke (1.38 vs. 1.13 mg per liter, P=0.02), but not venous thrombosis (1.26 vs. 1.13 mg per liter, P=0.34), than among men without vascular events. The men in the quartile with the highest levels of C-reactive protein values had three times the risk of myocardial infarction (relative risk, 2.9; P<0.001) and two times the risk of ischemic stroke (relative risk, 1.9; P=0.02) of the men in the lowest quartile. Risks were stable over long periods, were not modified by smoking, and were independent of other lipid-related and non-lipid-related risk factors. The use of aspirin was associated with significant reductions in the risk of myocardial infarction (55.7 percent reduction, P=0.02) among men in the highest quartile but with only small, nonsignificant reductions among those in the lowest quartile (13.9 percent, P=0.77).

CONCLUSIONS

The base-line plasma concentration of C-reactive protein predicts the risk of future myocardial infarction and stroke. Moreover, the reduction associated with the use of aspirin in the risk of a first myocardial infarction appears to be directly related to the level of C-reactive protein, raising the possibility that antiinflammatory agents may have clinical benefits in preventing cardiovascular disease.

Cell dysfunction in atherosclerosis and the ischemic manifestations of coronary artery disease

Many of the cellular mechanisms and dysfunctions that underlie atherosclerotic plaque formation have been identified, including adverse interactions between atherogenic lipids and the arterial endothelium, loss of endothelium-dependent dilation, accumulation of inflammatory cells and mediators of inflammation in the intima of the arteries, and a decline in anticoagulant defenses. Several studies have shown that these mechanisms, which appear to be active throughout the pathogenesis and progression of atherosclerosis, are reversible within days, weeks, or months with effective lipid-lowering therapy. In addition, the findings of large-scale trials of 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitors suggest that the rapid improvement observed in trial participants is attributable to a reversal of endothelial and vascular wall dysfunctions rather than to a reduction in plaque size. The accumulated evidence indicates that improved endothelial function can benefit patients who have angina pectoris and/or are at risk for myocardial infarction. Current understanding of the cellular mechanisms of atherogenesis also suggests avenues of future research to refine treatment approaches and further improve outcomes for patients with coronary artery disease.

Atherosclerotic plaque rupture in symptomatic carotid artery stenosis

PURPOSE

Plaque rupture is often the precipitating event in acute coronary syndromes. We hypothesized that a similar process occurs in stenotic carotid plaques in association with ischemic neurologic symptoms. Our purpose was to examine several morphologic features of stenotic carotid plaques and to determine which characteristics are more commonly associated with plaques obtained from patients with symptomatic carotid artery disease than with those from patients with asymptomatic carotid artery disease.

METHODS

Forty-four carotid endarterectomy specimens (from 25 asymptomatic and 19 symptomatic patients) were analyzed with pentachrome staining and light microscopy. The asymptomatic patients and symptomatic patients had similar mean percent stenosis (77% vs 74%). Other risk factors, including hypertension, diabetes mellitus, coronary artery disease, smoking history, serum cholesterol, and triglyceride levels, were similar between groups.

RESULTS

Patients with symptomatic carotid artery disease were found to have more frequent plaque rupture, fibrous cap thinning, and fibrous cap foam-cell infiltration when compared with the asymptomatic group. Plaque rupture was seen in 74% of symptomatic plaques and in only 32% of plaques from asymptomatic patients (p = 0.004). Fibrous cap thinning was noted in 95% of symptomatic plaques and in 48% of asymptomatic plaques (p = 0.003). Infiltration of the fibrous cap with foam cells was also significantly more common in the symptomatic plaques (84% vs 44% of asymptomatic plaques; p = 0.006). In addition, intraplaque fibrin was more common in symptomatic plaques than in asymptomatic (100% vs 68%; p = 0.008). No significant differences were found between the two groups with respect to plaque hemorrhage, the presence of a necrotic core, luminal thrombus, smooth muscle cell infiltration, eccentric shape, and plaque type (fibrous, necrotic, or calcified).

CONCLUSIONS

As in the coronary artery system, rupture of the atherosclerotic plaque may play an important role in the pathogenesis of ischemic stroke caused by carotid artery stenosis. The process of inflammation, involving foam-cell infiltration of the fibrous cap, may contribute to rupture of the atherosclerotic plaque.