Coronary artery disease is currently the leading cause of death and disability in the United States. Doctors have identified risk factors for treating and delaying cardiac disease, and testing has increasingly become more sophisticated. One of these tests that doctors order and assess carefully is the coronary artery calcium score, or CAC. While it is an independent predictor of coronary artery disease, the score is combined with information from conventional cardiac risk factors to provide very useful information.
In coronary artery disease, a fatty material called plaque narrows the coronary artery diameters and limits blood flow crossing the heart. This most common cause of heart disease in both women and men leads to chest pain, heart attack, arrhythmia, and in advanced cases, heart failure. Coronary artery calcium screening is done with an electron beam CT scan which looks for coronary calcium on the cardiac vessel walls. Calcification within the arteries can be one of the earliest signs of heart disease and can precede any signs and symptoms of the disease.
In 1990 Arthur Agatston (the same cardiologist we know from the South Beach Diet fame) and his colleagues showed that individuals with high coronary calcium scores were at 10 times the risk of developing coronary artery disease than those with lower scores. Other studies showed that individuals with coronary calcium scores above the 75th percentile for their age were 11 times more likely to develop a cardiac event compared to those having scores in the lower 25th percentile, and those individuals with significantly elevated scores in the 90th percentile were 23 times more likely to develop coronary artery disease.
Testing results start with a score of 0 (zero), which is when no calcium is seen. A score of 80 or above is associated with an increased likelihood of coronary artery disease, independent of the presence or absence of any other risk factors. Risk increases with higher calcium scores, and a result of over 400 is quite significant. That being said, scores can rise into the thousands, with 3,000 being close to the upper limit.
If this is the case, why aren't all patients (as a screening measure) subject to calcium scans as part of their routine health care? The scan is painless, is usually completed within 15 minutes, and involves less than 60 seconds of actual scanning time in most cases. The major reasons are the cost, the absence of a need for excess radiation, and the fact that most people can be risk stratified without such a scan. First, the test is of low value in those who are already at low risk of coronary artery disease, and who don't have significant risk factors. The Framingham Risk score, which is a combination of risk factors evaluated that include high blood pressure, age, smoking status, diabetes, obesity, cholesterol and physical activity can help define risk noninvasively. So in those at low risk of developing cardiac disease, the test is not useful.
In those where cardiac risk is high, such as people who have several risk factors, have suffered a cardiac event, or have illness relatable to cardiac disease, the score adds little. Those individuals will have more conclusive testing for cardiac disease and active modification of risk factors by their doctors, whether by medication, intervention, or increased lifestyle modification. So the scan isn't additionally helpful either in this situation.
Scanning may be most helpful in intermediate risk cases where doctors are deciding whether to add medication or make major modification in risk factors. Much stricter control of blood sugar, blood pressure, or cholesterol may be undertaken with an intermediate risk score. This allows such drugs as statins, for instance, to be started. Prevention is far preferable to treatment of an already occurred event.