Electron-beam computed tomography screening for asymptomatic coronary artery disease.

Abstract

S CREENING FOR preclinical disease with computed tomography scanning is controversial in radiological and clinical practice circles at the present time. There are opponents and advocates. There is an entrepreneurial point of view as well as an academic point of view. Proponents use anecdotal stories about disease detected and lives saved. Opponents demand rigorous scientific evidence of efficacy of screening. Only future studies can provide the necessary evidence. Then, current proponents will be viewed as either inappropriate enthusiasts or visionaries; similarly, opponents will be deemed as correctors or obstructionists. Possibly the scientific evidence will give some credence to both advocates and opponents by identifying the specific subgroups in the population that are appropriate for screening while arguing against screening the general population of asymptomatic adults. Screening with computed tomography scanning comes in 4 general categories: whole-body screening, screening for lung cancer, screening for colon cancer, and screening for coronary artery disease (CAD). The general public is becoming more sophisticated and knowledgeable about health care issues and is understandably lured by the promise of early detection of disease at a preclinical stage when a cure or effective treatment may be possible. Although the general public's biggest fear is associated with a development of cancer, less fear is often associated with development of CAD. CAD is the single largest killer of Americans. Over one-half million Americans die of CAD each year. This represents about 1 of every 5 deaths. This year, more than 1 million Americans will have a new or recurrent coronary event (defined as a new myocardial infarction [MI] or sudden death from CAD), and 650,000 will experience their first MI. More than 12 million Americans have a history of symptomatic CAD. CAD is the leading cause of premature, permanent disability in the US labor force. Annual health costs for CAD are $111.8 billion. Atherosclerosis is the major cause of CAD. Atherosclerosis develops over several decades and often remains asymptomatic until the development of an acute, life-threatening event. One half of sudden CAD deaths and one half of first MIs occur in persons without previous symptoms. Comprehensive studies have identified risk factors for atherosclerosis including older age, male sex, family history of premature CAD, elevated levels of total cholesterol and low-density lipoprotein cholesterol (LDL-C), reduced high-density lipoprotein cholesterol (HDL-C) levels, hypertension, physical inactivity, obesity, diabetes mellitus, and cigarette smoking. 2 These traditional CAD risk factors, however, fail to explain a large proportion of CAD events. 3 The associations of other factors including serum triglycerides, lipoprotein(a), small LDL particles, homocysteine, markers of inflammation, and coagulation factors with CAD are being investigated; however, a causal link between these factors and CAD has yet to be documented with certainty. 4 Thus, at this time, individuals can be screened for traditional CAD risk factors as well as newer ones to determine their predisposition for CAD; however, it is not always clear what therapeutic recommendations should be made and not all of the identifiable risk factors can be modified. Additionally, many individuals with asymptomatic coronary atherosclerosis will be considered to be at low risk based on identification of these risk factors alone. There are 2 strategies to screen for CAD. 5 One strategy is to screen for modifiable risk factors such as elevated LDL-C, hypertension, and smoking, and the second is to identify individuals with preclinical, asymptomatic CAD. 5 Researchers from the Framingham Heart Study developed a scoring system for estimating the 10-year risk of a coronary event based on an individual's age, sex, total and HDL-C, systolic blood pressure, history