Coronary Heart Disease
Coronary artery disease is the leading cause of death in the United States and most of the industrialized Western world. In contrast, it is much less common in Asia, the Near East, Africa and South and Central America. Inexplicably, death from coronary heart disease has declined in the United States since the late 1960’s.
Atherosclerosis is a thickening and hardening of medium-size and larger arteries with narrowing of the arterial lumen by atherosclerosis plaques. Its cause is multifactorial. Preventable risk factors, genetic susceptibility, local arterial hemodynamic factors, and sex influence the development of atherosclerosis.
The fatty streak, consisting of lipids and lipoid proteins, located in the intima of the vessel with the overlying endothelium intact is the earliest from of atherosclerosis. This yellow fatty streak seen in childhood is not necessarily a precursor of adult atherosclerosis and occurs in populations in which atherosclerosis is uncommon; it is presumably reversible at this stage. Around age 25, in populations in which atherosclerosis is common, the fibrous plaque begins to develop. It is white, elevated, and may compromise the arterial limen. Reversibility is questionable when fibrous tissue and intimal proliferation are present. In more advanced stages, deposition of fibrin and platelets and necrosis of tissue with growth of new vessels may occur. Cholesterol, calcification and haemorrhage within the atherosclerosis plaque from complicated plaques. The intimal surface may ulcerate, thrombose and occlude the vessel. Mechanical, chemical or immunological injury that begins with the fatty streak may cause progression of the atherosclerosis lesion. Different arteries appear to have different degrees of susceptibility to atherosclerosis lesions; the coronary arteries are particularly susceptible, mostly within the first 6 cm of origin. Plaques tend to occur at arterial bifurcations, possibly due to the turbulent flow in these areas.
Atherosclerosis lesions in the coronary arteries may be detected during life by coronary arteriography (Figure 1). When a radiopaque contrast agent is injected into a coronary artery, atherosclerotic plaques appear as narrowings in the column of contrast as it travels down the artery. Narrowing pf vessels is described as a per cent diameter narrowing. Lesions > 50 per cent are probably hemodynamically significant, causing approximately 75 per cent narrowing of cross-sectional area, while lesions > 75 per cent are definitely significant, producing 95 per cent cross-sectional narrowing. The gradation of obstruction at coronary angiography is approximate and often underestimates the actual degree of obstruction. Complete obstruction of a vessel at angiography is usually represented by a stump, the distal portion of the vessel often opacified via collateral circulation.
Figure 1. A, Normal left coronary arteriogram in the right anterior oblique projection. LM = Left main coronary artery; LAD = left anterior descending coronary artery; LC = Left circumflex coronary artery. B, Normal right coronary arteriogram in the left anterior oblique projection. PDA = Posterior descending artery.
Dr. Afsaneh Jeddi