Editorial

Coronary artery calcium scoring: A valuable tool in primary care

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In 1984, Jim Fixx, who wrote The Complete Book of Running,1 went out for his daily run and died of a massive heart attack. He was 48. Unbeknownst to him, he had 3-vessel coronary artery disease.

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His case illustrates the difficulty of diagnosing coronary artery disease in patients who have no symptoms of it. For many, the initial presentation is myocardial infarction or death. Until recently, there was no reliable way to diagnose subclinical coronary artery disease other than angiography, and there is still no way to rule it out. As a result, physicians have concentrated less on diagnosing subclinical disease and more on assessing the risk of myocardial infarction.

ASSESSING RISK

The risk factors for coronary artery disease (age, male sex, smoking, hypertension, and cholesterol) have been well known for half a century. By combining risk factors with the appropriate weighting, it is possible to predict an individual’s risk of a myocardial infarction.

In 2013, the American College of Cardiology/American Heart Association (ACC/AHA) guidelines applied this risk-based approach to prescribing statins for primary prevention.2 Instead of focusing on low-density lipoprotein cholesterol concentration, which by itself is a poor predictor of myocardial infarction, they recommended using the Pooled Cohort Equation3 to determine the risk of a cardiovascular event within 10 years. For patients at high risk (> 7.5%), the benefits of a statin generally outweigh the harms. For those at low risk (< 5%), the opposite is true. For patients in between, there is room for shared decision-making.

Debate has focused on the predictive accuracy of the equation, the threshold for treatment, and the fact that almost all men over 60 qualify for treatment.4 These objections stem from the focus on risk rather than on diagnosis of the underlying disease.

Because one-third of “high-risk” patients never develop cardiovascular disease,5 the risk-based approach necessitates overtreatment. Those without disease cannot benefit from treatment but nonetheless suffer its side effects, cost, and inconvenience. Raising treatment thresholds (eg, treating only patients whose 10-year risk exceeds 10%) improves the ratio of patients with disease to those without but also misses diseased patients who have few risk factors. “Low risk” is not “no risk.”

TESTING FOR DISEASE IN THOSE AT INTERMEDIATE RISK

Diagnostic testing is preferred if such testing is safe and inexpensive.

In this issue of Cleveland Clinic Journal of Medicine, Parikh and colleagues6 review coronary artery calcium scoring, a diagnostic test for coronary artery disease. They conclude that calcium scoring is strongly predictive but should be reserved for patients at intermediate risk to help them decide about treatment. This is clearly the right approach, but the authors leave the term “intermediate” undefined, and their clinical examples offer little guidance as to where the borders lie.

The ACC/AHA guidelines specify a narrow intermediate range (5.0%–7.4%). For these patients, calcium scoring could reclassify most as being at high or low risk, helping to clarify whether statins are indicated.

However, only 12% of patients fall into this category.7 What about patients at higher risk? Could they be reclassified as being at low risk if their calcium score was 0?8 Conversely, could some low-risk patients discover that they are at high risk and perhaps take action?

The ACC/AHA guidelines recommend against calcium scoring in these circumstances. One concern was that calcium scoring had not been tested with the Pooled Cohort Equation. Another concern related to cost and radiation exposure, but as Parikh et al point out, the cost has now fallen to less than $100, and radiation exposure is similar to that with mammography.

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