Therapeutic Implications of Coronary Artery Calcium Using Cardiac Computed Tomography

The objective of this document is to review the clinical applicability of coronary artery calcium (CAC) scoring in both asymptomatic and symptomatic patients at risk for cardiovascular disease. We begin by describing the pathological basis of atherosclerosis, the characteristic stages of atherosclerotic plaque development, and the mechanism and role of arterial calcification in advanced atherosclerotic lesions. We also explain the utility of CAC scoring in cardiovascular risk assessment, discuss the most current clinical methods for measuring CAC, and examine major clinical studies reporting CAC scores in both asymptomatic and symptomatic heart patients. Lastly, the current recommendations for CAC scoring as stated by the American College of Cardiology/American Heart Association (ACC/AHA) are outlined, and a number of considerations for future research are provided. Atherosclerosis begins when certain factors cause chronic endothelial injury, which eventually leads to the build up of fibrofatty plaques in the intima of arterial blood vessels. In time, blood vessel walls can weaken, thrombi can form and plaques can send emboli to distal sites. There are six characteristic stages of plaque development. Mature plaques may be calcified in an active process comparable to bone remodeling, where calcium phosphate crystals coalesce among lipid particles inside arterial walls. Calcification is only present in atherosclerotic arteries, and the site and levels of calcium are non-linearly and positively associated with luminal narrowing of coronary vessels. Calcification is also postulated to stabilize vulnerable plaques in atherosclerotic vessels. Recent studies have shown that CAC scoring can improve the management of both asymptomatic and symptomatic heart patients. Electron beam computed tomography (EBCT) and Multidetector computed tomography (MDCT) are two fast cardiac CT methods used to measure CAC. No matter what technique one uses, CAC is scored with either the Agatston or the "volume" score system. The ACC/AHA currently finds it is reasonable for asymptomatic patients with intermediate Framingham risk scores ( FRS) to undergo CAC assessment because these patients can be re-stratified into the high risk category if their CAC scores are >= 400. Conversely, CAC measurement in asymptomatic patients with low or high FRS is not warranted. There is also no evidence to suggest that high risk asymptomatic patients with no detectable coronary calcium should not be treated with secondary prevention medical therapy. For symptomatic patients, the ACC/AHA recommends CAC assessment as a second line technique to diagnose obstructive CAD, or when primary testing modalities are not possible or are unclear. Furthermore, they do not recommend the use of CAC measurement to determine the etiology of cardiomyopathy, to help identify patients with acute MI in the emergency room, or to assess the progression or regression of coronary atherosclerosis. Future research needs to incorporate calcium scores with percentile rankings, larger population samples, more women with at least intermediate Framingham risk, sufficient numbers of non-Caucasians, reports on cost-effectiveness, and data on populations with Chronic Kidney Disease, End Stage Renal Disease and Diabetes.