Cholesterol and atherosclerosis: a contemporary perspective

Monumental advances in the field of lipid metabolism and its relationship to atherosclerotic cardiovascular disease have been achieved during the last half century. Epidemiologic studies have defined lipid disorders as highly significant independent risk factors for coronary heart disease, along with diabetes mellitus, hypertension and smoking. Primary and secondary prevention studies including the Coronary Primary Prevention Trial, Helsinki Heart Study, and the Coronary Drug Project have shown that lowering the atherogenic low density lipoproteins (LDL) and very low density lipoproteins (VLDL) whilst raising the high density lipoproteins (HDL) significantly decreases the risk for coronary disease. Striking evidence that aggressive therapy (to sharply lower LDL and raise HDL with newer drugs) prevents progression and induces regression of coronary narrowing has been obtained in numerous recent studies using quantitative coronary arteriography. An interesting and unexpected lesson learned from these arteriographic studies was that a highly significant reduction within months in several studies in coronary events was out of proportion to improvements in luminal narrowing. Recently, three major clinical trials to assess the effects of cholesterol reduction by the newly discovered HMG CoA reductase inhibitors (statins) have been published. Pravastatin significantly reduced coronary events in hypercholesterolemic patients [mean LDL-Chol. = 5.0 mM/L (192 mg/dl)] without a history of myocardial infarction. In a secondary prevention study, simvastatin also reduced coronary complications in hypercholesterolemic patients [mean LDL-Chol. = 4.9 mM/L (190 mg/dl)] with pre-existing coronary disease. Very recently, pravastatin treatment significantly reduced coronary events and stroke in patients with a history of myocardial infarction and average cholesterol levels [mean LDL-Chol. = 3.6 mM/L (139 mg/dl)], representing the majority of patients with coronary disease. In all these studies, reduction in cardiovascular events was approximately one-third. In subgroup analyses, men, women, elderly, smokers and hypertensives benefited from cholesterol lowering. There was no significant increase in non-cardiovascular causes of death. In the United States of America, the National Cholesterol Education Program (NCEP) Adult Treatment Panel, representing major health organizations, developed national guidelines on the detection, evaluation and treatment of high blood cholesterol in adults. In a given patient, the Panel recognizes the importance of weighing all cardiovascular disease risk factors including age (men > 45 years, postmenopausal women), family history of premature coronary disease, smoking, hypertension, diabetes and HDL-Cholesterol (< 35 mg/dl) in determining how aggressive therapy should be. The patient with manifest coronary heart disease (CHD) is given a special position as such patients are at highest risk for recurrent events. Major goals of therapy are to lower the LDL-Cholesterol to 2.6 mM/L (< 100 mg/dl) in the CHD patient. In non-CHD patients with two or more risk factors, the LDL-Cholesterol goal is 3.4 mM/L (130 mg/dl). In those with fewer risk factors, the goal is 4.2 mM/L (160 mg/dl). These guidelines should be modified as appropriate for Singapore. Patients with elevated triglycerides usually have low HDL-Cholesterol levels and often represent a heterogeneous group who may have other concurrent abnormalities including the presence of small dense LDL, insulin resistance, hypertension, obesity, overt diabetes and combined hyperlipidemia. Such patients merit individualized treatment. The prevalence of this syndrome may be more common in Singapore and requires further investigation. Current therapeutic guidelines emphasize the need for weight loss and dietary restriction of total and especially saturated fat (< 7% to 10% total calories), cholesterol (< 200 to 300 mg/day), and exercise. (ABSTRACT TRUNCATED)