Multidetector computed tomography for coronary artery disease screening in asymptomatic populations: evidence-based analysis.
OBJECTIVE
This evidence-based health technology assessment systematically reviewed the published literature on multidetector computed tomography (MDCT) angiography (with contrast) as a diagnostic tool for coronary artery disease (CAD), and applied the results of the assessment to health care practices in Ontario.


OBJECTIVE
Coronary artery disease is the leading cause of death in the western world. Occlusion of coronary arteries reduces coronary blood flow and oxygen delivery to the myocardium (heart muscle). The rupture of an unstable atherosclerotic plaque may result in myocardial infarction. If left untreated, CAD can result in heart failure and, subsequently, death. According to the Heart and Stroke Foundation of Canada, 54% of all cardiovascular deaths are due to CAD. Patient characteristics (e.g., age, sex, and genetics), underlying clinical conditions that predispose to cardiac conditions (e.g., diabetes, hypertension, and elevated cholesterol), lifestyle characteristics, (e.g., obesity, smoking, and physical inactivity), and, more recently, determinants of health (e.g., socioeconomic status) may predict the risk of getting CAD. In 2004/2005, The Ontario government funded approximately 15,400 percutaneous (through the skin) coronary interventions and 7,840 coronary bypass procedures for the treatment of CAD. These numbers are expected to reach 22,355 for percutaneous coronary interventions and 12,323 for coronary bypass procedures in 2006/2007. It was noted that more than one-half of all first coronary events occur in people without symptoms of CAD. In Ontario in 2000/2001, $457.9 million (Cdn) was spent on invasive ($237.4 million) and noninvasive ($220.5 million) cardiac services. The use of noninvasive cardiac tests, in particular, is rising rapidly.


METHODS
Computed tomography (CT) is a medical imaging method employing tomography where digital geometry processing is used to generate a 3-dimensional image of the internals of an object from a large series of 2-dimensional X-ray images taken around a single axis of rotation. Multidetector computed tomography is performed for noninvasive imaging of the coronary arteries. Computer software quantifies the amount of calcium within the coronary arteries and calculates a coronary artery calcium score. Compared with conventional CT scanning, MDCT can provide smaller pieces of information and cover a larger area faster. Advanced MDCT technology (that is, 8-, 16-, 32-, and 64-slice systems) can produce more images in less time. For general CT scanning, this faster capability can reduce the length of time people are required to be still during the procedure and thereby reduce potential movement artifact. However, the additional clinical utility of images obtained from faster scanners compared with the images obtained from conventional CT scanners for current CT indications (i.e., nonmoving body parts) is unknown.


METHODS
The Medical Advisory Secretariat completed a computer-aided search limited to English-language studies in humans from 1998 to 2007 in multiple medical literature databases, including MEDLINE, EMBASE, The Cochrane Library, and INAHTA/CRD. Case reports, letters, editorials, nonsystematic reviews, and comments were excluded. Additional studies that met the inclusion and exclusion criteria were obtained from reference lists of included studies. Inclusion and exclusion criteria were applied to the results according to the criteria listed below. The Grading of Recommendations Assessment, Development and Evaluation (GRADE) system was used to evaluate the overall quality of the body of evidence (defined as 1 or more studies) supporting the research questions explored in this systematic review.
Screening the asymptomatic population for CAD using MDCT does not meet World Health Organization criteria for screening; hence, it is not justifiable. Coronary artery calcification measured by MDCT is a good predictor of future cardiovascular events. However, MDCT exhibits only moderately high sensitivity and specificity for detection of CAD in an asymptomatic population. If population-based screening were implemented, a high rate of false positives would result in increased downstream costs and interventions. Additionally, some cases of CAD would be missed, as they may not be developed, or not yet have progressed to detectable levels. There is no evidence for the impact of screening on patient management. Cardiovascular risk factors are positively associated with the presence of coronary artery calcification and cardiovascular events; however, risk factor stratification to identify high-risk asymptomatic individuals is unclear given the current evidence-base. Safety of MDCT screening is also an issue because of the introduction of increased radiation doses for the initial screening scan and possible follow-up interventions. No large randomized controlled trials of MDCT screening have been published, which indicates an important area of future research. Lastly, the policy implications for MDCT screening for CAD in the asymptomatic population are significant. There is no evidence on the long-term implications of screening, and the potential impact on the resources of the health care system is considerable.