CT CAC Screening: Bolstered By Data, But Debate Rolls On

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CT coronary artery calcium (CAC) screening for low- or intermediate-risk individuals remains a topic of great debate among providers, with strong, varied opinions about when and if to introduce the test into the patient care continuum. Despite the critics of the screening technology, new clinical data and society initiatives have resulted in steady gains of acceptance.

Screening debate

Critics pounced when President Barack Obama received a CT CAC scan as part of his routine 2010 annual physical examination. It was suggested that he was too young, at age 49, to undergo a risk assessment for a future heart attack. Furthermore, critics said CAC scans lack scientific evidence to demonstrate a clinical benefit. Yet, Obama actually met the guidelines proposed by the Society for Heart Attack Prevention and Eradication (SHAPE), a Houston-based organization whose mission is to improve heart health through early screening.

Rita F. Redberg, MD, a cardiologist at the University of California, San Francisco, and editor of Annals of Internal Medicine, remains adamant about what she considers a paucity of clinical trial evidence showing that CAC positively affects clinical outcomes. In 2010, Redberg publicly stated that Obama would have been better advised to kick his nicotine habit, and skip the imaging test.

"I always look at tests in terms of how they can help you to feel better, be healthier or live longer," Redberg says. "Coronary calcium doesn't offer that. It has radiation exposure risks, but no known benefits." Redberg and other critics say they will dismiss the test until a randomized clinical trial generates definitive proof that CT CAC screening saves lives by helping to avoid MI.

This position infuriates physicians, such as Matthew J. Budoff, MD, director of cardiac CT at Harbor-UCLA Medical Center in Torrance, Calif.

"Based on Redberg's opinion, cardiologists should go home, and patients should die until these randomized trials are conducted," says Budoff. "Randomized trials are rare because they are too expensive and it would be unethical to randomize patients to a placebo because we already know calcium scoring is effective."

After 20 years of extensive testing and increased support from many U.S. cardiologists, CT CAC scans still are not widely accepted. Also, most insurers deny payment for calcium screening and the U.S. Preventive Services Task Force has recommended against the test. One exception is the Texas Heart Attack Prevention Bill signed into law by Texas Gov. Rick Perry in August 2009, which requires payors to compensate for heart attack preventive imaging screening tests.

Framingham's shortcomings

It is clear to Budoff as well as other cardiologists and cardiothoracic radiologists that CT CAC scans address shortcomings of the Framingham Risk Score (FRS), which remains the standard test to determine the likelihood of middle-aged individuals suffering a future MI. FRS reliably identifies high-risk patients, but it is less reliable at detecting patients with an intermediate- or low- to intermediate-risk.

Based on an assessment of 1,416 men and 707 women, mostly asymptomatic, one study found that almost two-thirds of women and one-quarter of men with substantial atherosclerosis will be missed if subjects are excluded from further screening because they are characterized as low risk by FRS (Am J Roentgenol 2010;194:1235-1243).

"As our study suggests, the presence of coronary artery calcium detects more patients with coronary atherosclerosis than does the Framingham risk-assessment score," says study author Kevin M. Johnson, MD, chief of diagnostic radiology at Yale University School of Medicine, New Haven, Conn.

"Often, we don't know what to do with these low- to intermediate-risk patients," says Charles S. White MD, chief of thoracic radiology at the University of Maryland Medical Center in Baltimore.

Compared with the "extremely indirect Framingham scoring methods," White considers CT calcium scoring an easier way to get a direct view of the presence and amount of atherosclerotic damage to the coronary arteries. "A CT CAC scan provides information that none of these predictive methods previously did," he says. "For the proper population, it incrementally provides more information."

Better information leads to better patient management, notes John J. Mahmarian, MD, director of nuclear and cardiovascular CT at Methodist DeBakey Heart and Vascular Center in Houston. Equipped with the data of a CAC