Heart Scans Only Useful in Specific Situations When Statins Are Prescribed

Researchers from the University of California San Francisco (UCSF; USA) designed a statistical model to forecast whether it was practical to do the scan, using data from the Multi-Ethnic Study of Atherosclerosis (MESA) and other sources. They modeled the effects of statin therapy in 10,000 55-year-old women with high cholesterol and a 10-year risk of coronary heart disease of 7.5%. The model predicted that prescribing statins to all of them would prevent 32 heart attacks, cause 70 instances of statin-induced muscle disease, and add 1,108 years to their cumulative life expectancy.

Then, the investigators looked at how a coronary artery calcium (CAC) test could be used to target statin therapy only in those women the test showed were at heightened risk of coronary heart disease. They found that this strategy would save money on statin costs and expose fewer women to side effects from statins but would not prevent as many heart attacks. Moreover, the test itself exposes the women to a small risk of radiation-induced cancer and costs about USD 200 to USD 400 per scan.

The researchers concluded that as long as the price of a statin remained low— USD 0.13 a pill—and did not reduce quality of life for patients, it was not cost-effective to perform a CAC test. But if the price of the pill were more costly—USD 1 or more—or if taking them reduced patients’ quality of life, then it did make sense to use the CAC test.

The result is somewhat surprising, given all the evidence that has accumulated over the last decade that the test strongly predicts heart attacks, said the lead author, Mark Pletcher, MD, MPH, an associate professor of epidemiology and biostatistics, and medicine, at UCSF. The study was published online March 11, 2014, in the journal Circulation: Cardiovascular Quality Outcomes.

Traditional prediction models, such as the Framingham-based risk equations, work imperfectly, and clinicians have long tried to find better ways to figure out which patients would benefit most from taking statins, which can cause side effects, such as decreased cognitive function, muscle aches, and cataracts.

“The prevailing wisdom is that if you have a test that predicts heart attacks, you should use it,” Dr. Pletcher said. “But even a test that is strongly predictive of future events, like a coronary artery calcium scan, does not itself improve outcomes. If it is used to keep some people off of statins that would otherwise take them, then fewer people will get protection from using statins, and more people will have heart attacks.”

The study integrated data from MESA and many other sources to create a cost-effectiveness model. The researchers tested whether changing the other model inputs made a difference, and it turned out that the only critical factors were the cost of statins and the degree to which they decreased quality of life for patients.

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