CT CAC Screening: Bolstered By Data, But Debate Rolls On
Screening debateCritics 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 shortcomingsIt 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 scan, an emerging clinical paradigm indicates that outcomes improve for asymptomatic patients who are aggressively treated with lipid-lowering drugs, he says.
The 2008 JUPITER trial, for instance, found that aggressive rosuvastatin (Crestor, AstraZeneca) therapy for asymptomatic patients, with normal LDL cholesterol and increased high-sensitivity C-reactive protein, led to a 44 percent reduction in cardiac events compared with patients given a placebo (N Engl J Med 2008;359(21):2195-2207).
"In light of [JUPITER's] results, how would you respond to a calcium score of 600?" Mahmarian asks. "It would change your whole management strategy. Now, you would have to be extremely aggressive with drug therapy."
|Coronary Calcium Prevalence by Framingham Risk Score (FRA)|
|The prevalence of categories of CAC scores compared across 10-year FRA strata. |
Proof is in the dataResults from the MESA and Heinz-Nixdorf RECALL trials have added to the burgeoning evidence that encourages the use of CT CAC screening in lower-risk adults.
In MESA, an ethnically diverse mix of 6,814 patients received baseline CT CAC, then were monitored for 18 months. Results from 175 consecutive coronary catheterization procedures performed on these subjects during that time were evaluated to determine the relationship between baseline CAC and the severity of coronary stenosis (J Am Coll Cardiol 2007;49:594-600).
MESA's senior investigator João A. Lima, MD, a cardiologist at Johns Hopkins University School of Medicine in Baltimore, established a direct relationship between total Agatston score at baseline, the severity of stenosis and the number of diseased vessels. Only 4 percent of MESA patients who underwent invasive coronary angiography had a baseline Agatston calcium score of zero.
The population-based Heinz-Nixdorf RECALL study, the German version of MESA, demonstrated the value of CAC for reclassifying FRS (J Am Coll Cardiol 2010;56:1397-1406). CAC reassessments were especially valuable for subjects who were initially classified as intermediate risk for a future cardiac event.
In Heinz-Nixdorf RECALL, Raimund A. Erbel, MD, of the University Clinic Essen, Germany, and colleagues monitored the cardiovascular health of 4,129 asymptomatic adults (mean age, 60) for five years after baseline Framingham risk assessments and calcium scores. The results showed that 14 percent of the subjects, initially deemed intermediate risk from their Framingham scores, were reclassified as high risk based on additional information from their calcium scores. Slightly more than 60 percent were shifted to the low-risk group.
As an early indicator of risk, CAC could be used as the basis for ordering risk-modifying medications and encouraging the patient to adopt healthier lifestyles, Erbel said during an ACC.09 presentation.
However, CAC performed with relatively expensive electron-beam CT scanners proved uneconomical for saving lives in the Heinz-Nixdorf RECALL study. The quality adjusted life years saved was surprisingly high at $37,633. Erbel notes that further studies with multi-detector CT should be pursued to better appreciate its cost-effectiveness.
One dimension of cost appears to have been answered by the EISNER trial, an ongoing prospective registry managed by Daniel Berman, MD, director of cardiac imaging and nuclear cardiology at Cedars-Sinai Medical Center in Los Angeles.
A comparison of 1,427 middle-aged volunteers who received baseline CAC and Framingham screenings and 713 who received Framingham scoring alone suggests that concerns about increased downstream testing and medical costs could be overblown. All participants were asymptomatic, but had at least one risk factor for heart disease in addition to their age.
Four years after baseline testing, Berman and colleagues determined that the cost of downstream testing for patients with CAC Agatston scores of less than 100 was about $25. More testing was observed for patients with scores higher than 400, but the relatively higher costs of their diagnosis and therapy as attributed to appropriate responses to their higher clinical risks (J Am Coll Cardiol 2011;57(15):1622-1632).
The study authors concluded that patients who underwent CT CAC scanning with a subsequent risk factor counseling session that included an assessment of their calcium took more steps to improve their health without increasing downstream medical costs compared with those who did not receive calcium scanning.
Broadening guidelinesSuch findings encouraged a consortium of nine cardiology-related societies, led by the American College of Cardiology Foundation, to issue expanded appropriate use guidelines for CAC in 2009.
Compared with the 2009 guidelines, the 2007 criteria deemed CT CAC screening appropriate only for asymptomatic adults at intermediate-risk (a 10 to 20 percent 10-year probability of a cardiac event) based on their Framingham scores. The 2009 guidelines also deemed it reasonable to screen patients at low- to intermediate-risk (a 6 to 20 percent 10-year probability).
Positive clinic findings and an expanded potential patient base have helped SHAPE better position itself to chip away at payor and provider resistance. Founded in 2005, SHAPE aims to reduce the incidence of heart attacks—especially for asymptomatic patients—through education and provider certification, according to its Founder and President Morteza Naghavi, MD.
The SHAPE guidelines recommend either CAC or carotid artery intimal-media thickness scanning with diagnostic ultrasound for two groups of asymptomatic adults: at-risk men ages 45 to 75 and at-risk women ages 55 to 75.
Improving CAC screening acceptance has been an uphill battle, made more difficult for SHAPE because of political miscues. It drew criticism, for example, for avoiding peer review of its guidelines and publishing them in an industry-sponsored supplement of the American Journal of Cardiology (2006;98[2A]:2H-15H).
Legal victories & bottom lineYet, SHAPE has made progress, especially on the legislative front. In Texas, it helped lay the groundwork for the first state law requiring insurers to cover CAC and carotid ultrasound screening. Enacted in 2010, the statute requires insurers to pay up to $200 every five years to beneficiaries who meet the SHAPE guidelines for the two types of scans. Similar legislation has been proposed in Florida.
Now in its second year, SHAPE's Centers of Excellence program is drawing attention to its cause. Sixteen programs across the U.S. are certified and another 30 programs are working toward certification, says Jeffrey J. Fine, PhD, SHAPE's program director.
The onsite training program encourages participants to shift focus from consumer-oriented marketing to educational efforts aimed at primary care, family physicians and obstetrician/gynecologists. They perform many FRS assessments, which places them in a good position to identify at-risk, asymptomatic patients who would benefit from screening, he says.
Education revolves around informing physicians about consensus CAC guidelines and published trials describing the benefits and risks of screening.
The program's financial elements aim at affordable pricing. Many participants are charging patients $99 out-of-pocket for a CT CAC screening exam. Even at larger facilities there is a push to contain costs, and SHAPE's model Center for Excellence at Cedars-Sinai is charging $185, Fine says.
Hospitals that have completed certification are performing nearly 10 screenings per day, compared with an average of about two CAC tests at facilities that rely on direct-to-consumer advertising. Cedars-Sinai, which has provided CAC scanning for 20 years, also saw volume growth in three months of experience with the program, he says,
Financially, 10 referrals per day translates into roughly $300,000 in revenue per year for an imaging department and potentially more than $1 million in additional imaging services annually from patients diagnosed with significant heart disease, Fine says.
Central data collection by SHAPE is seeking to longitudinally measure the program's performance over time and may allow site-specific benchmarking.
Despite progress, the slow pace of change is agonizing for cardiologists and radiologists who believe that CAC scans can save lives. "We see tragedies every day of patients who are walking around
asymptomatic and then drop dead," Budoff says. "We're just asking for a chance to allow providers to examine coronary calcium screening more closely, and to be more proactive in identifying patients at an earlier stage of their atherosclerotic disease."