Calcium Scans Pick Up Controversy in Cardiology
August 26, 2011
Coronary artery calcium scans might be the best thing since sliced risk scores or the worst example of "medicine gone wild," garnering strong and divisive opinions in cardiology.
The noncontrast CT screening test is vying for a role in determining which otherwise low- to moderate-risk patients may need more aggressive cardiovascular prevention.
When news broke last week of a study in The Lancet suggesting that calcium scans predicted risk of cardiovascular events better than high-sensitivity C-reactive protein (CRP) in a relatively healthy population like that in the JUPITER trial, major networks carried breathless statements about the technology:
· "Before you go on a cholesterol medication, I want you to ask your doctor about this: A coronary artery calcium test." -- Dr. Richard Besser on ABC
· "Unless you do the imaging, you are really playing Russian roulette with your life." -- Dr. Arthur Agatston in a CNN report
While these reports were criticized in Forbes and the healthcare media watchdog Health News Review, some leading cardiologists find themselves just as impressed by coronary artery calcium screening.
"Of the options available to add on top of typical risk prediction, calcium is clearly emerging as the winner," James de Lemos, MD, of the University of Texas Southwestern Medical Center in Dallas, said in an email to MedPage Today.
Agreement, though, is far from universal, which isn't surprising given the complexity of atherosclerosis, according to Howard S. Weintraub, MD, clinical director of the NYU Center for the Prevention of Cardiovascular Disease.
"There are so many different agendas we can view this with; there's no surprise this is not something that has uniform vision from all the individuals involved," he explained in an interview with MedPage Today.
Calcium Scores for Risk Reclassification
Statin therapy guided by traditional risk factors enumerated in the Framingham risk score, which uses age, gender, cholesterol, smoking status, and blood pressure, can provide an important first step in prediction but leaves much to be desired. The estimated risk is based on population data.
"That's one of the reasons the interventions we have been practicing haven't been as robust in reducing risk as we'd like," Weintraub said. "In order to be able to more appropriately apply prevention, we need to have a better scheme of testing to truly identify risk."
The high-risk population by traditional factors clearly needs lifestyle intervention and consideration of a statin medication, and calcium score won't change that decision making.
But persistent rates of heart attack and other events in the intermediate- and low-risk groups suggest that traditional factors are missing important clues of impending danger.
Calcium scanning has looked good in studies reclassifying risk.
In one large cohort study published in the Journal of the American College of Cardiology earlier this year, calcium score independently predicted 25% elevated risk of coronary events and 12% elevated risk of death from any cause.
It improved prediction by 23.8% over what Framingham score, body mass index, and known cardiovascular disease could do compared with a 10.5% improvement by high-sensitivity CRP.
Based on results like these, the American Heart Association updated its guidelines in 2010 to call calcium scans "reasonable" in intermediate-risk patients, putting it on par with echo screening of carotid intima-medial thickness (IMT).
The Society for Heart Attack Prevention and Eradication now recommends calcium and carotid IMT scans for all intermediate-risk people ages 45 to 80 and for men 35 and older who are diabetic or have a family history of premature coronary disease.
Another advantage of coronary scans, according to some reports, is their power for patient motivation.
Calcium scores moved patients to get to work on their heart disease risk factors -- reducing blood pressure, LDL cholesterol, and waist circumference compared with patients who didn't get the scan, another JACC study reported in March.
A meta-analysis in the Archives of Internal Medicine suggested that noninvasive imaging may not be very motivating for physicians to change prescribing.
But "you'd be surprised how if you tell a 55-year-old that his cholesterol is 260, he's going to look at you and go 'Okay, yeah, I know that's high,'" Weintraub said. "However, if you tell a 55-year-old he has the arteries of a 75-year-old, that tends to get his attention."
Not Just a Simple Test
Calcium scanning got all the wrong kind of attention initially from many physicians.
"There has been a lot of controversy around calcium scoring because most of the early proponents owned their equipment and had a huge conflict of interest," William W. O'Neill, MD, chief medical officer of the University of Miami Health System, noted in an email to MedPage Today and ABC News.
High-sensitivity CRP has faced the same concern, with the pivotal JUPITER trial of statins in lower-risk, high-CRP patients led by a patent holder on the CRP blood test, Paul Ridker, MD, MPH, of Brigham and Women's Hospital in Boston.
Also, "many of us were initially bothered by the way calcium scanning was introduced, as a for-profit test marketed directly to the community, without good evidence to support its use," de Lemos explained in an email.
Calcium scans, generally, aren't reimbursed by insurance, with the exception of coverage mandated by a 2009 Texas state law. The average out-of-pocket cost runs about $100 elsewhere.
Recent studies have redeemed the test in many minds, but there's still no randomized trial showing that coronary artery calcium-guided therapy leads to better outcomes, de Lemos noted.
But no screening method has such large-scale clinical trial evidence, noted Amit Khera, MD, MSc, a cardiologist at UT Southwestern.
The widely used Framingham risk score hasn't been tested in a randomized trial. Even CRP, for which the randomized JUPITER trial demonstrated benefit of treating patients with high CRP as their sole risk factor, doesn't have gold standard evidence since JUPITER didn't include a low CRP arm.
"What we need from our imaging colleagues are trial data, not assumptions of what might work without formal evaluation," Ridker argued in an email to MedPage Today.
"Remember, the imaging community also assumed for years that statins would reduce coronary artery calcium scores, but when trials were finally done this turned out to be a completely wrong assumption," he noted.
The lack of change in calcium score with treatment can be troubling to some physicians and patients, Weintraub noted.
And that often leads to unnecessary catheterization and stenting, "so actual costs to the healthcare system are very high," added Steven E. Nissen, MD, chair of cardiovascular medicine at the Cleveland Clinic, who called calcium scanning "one of the worst examples of 'medicine gone wild'" in an email to MedPage Today and ABC News.
Incidental findings are a well-known concern with CT imaging, including when imaging coronary arteries for calcium.
Radiation, too, is an issue.
One calcium scan confers the equivalent of 10 chest X-rays or two mammograms, which could be expected to result in cancer in nine per 100,000 persons tested, according to an analysis done by Khera at the time the Texas law passed.
Though one-third the radiation a person gets on average from the sun and environment are offset by a potential reduction in cardiovascular deaths, the cancer risk is important when talking about asymptomatic individuals, Khera noted.
"In the absence of evidence, why use a test that is associated with radiation, cost, and leads to a number of downstream consequences instead of a simple panel of blood tests along with data on age, smoking, and blood pressure?" Ridker questioned in an email.
Competition or Collaboration?
Yet it may not be an either-or situation between calcium scanning and other noninvasive screening methods.
In the JACC cohort study that showed incremental predictive power of calcium scoring, its combination with high-sensitivity CRP had better discriminatory power than either measure alone.
"I think ultimately it's going to be a combination of things," Weintraub told MedPage Today. "We've known for a long time that CRP and calcium scores don't necessarily coincide."
Calcium in the arteries points to stable plaque, while inflammatory markers like high-sensitivity CRP indicate vulnerability of plaque to rupture, he noted.
Carotid IMT images the coronary arteries with ultrasound, eliminating the radiation concerns, and may be particularly useful for risk prediction in younger people in whom the calcium score is likely to be zero.
Some evidence also suggests carotid IMT is a better predictor of stroke risk, whereas calcium score may be a better predictor of coronary events, Khera noted.
So which test or combination of tests you choose may depend to some degree on the individual patient, he suggested.
"We're in the sorting out period right now," he told MedPage Today. "The positive is these are all potential new tools that can be used, and they all have some value. It's just figuring out how to use each test and where they should be used and what to do about them."