Aug. 18, 2011 -- An imaging test that identifies calcium in the coronary arteries of the heart is a more accurate indicator of heart attack risk in seemingly healthy people than a widely used test that measures inflammation, a new study shows.
Researchers say coronary artery calcium (CAC) testing can better identify people with normal cholesterol who could benefit from treatment with cholesterol-lowering statin drugs than the C-reactive protein (CRP) blood test.
Statins were once prescribed only to people with high cholesterol, but that changed following the publication of a practice-changing study known as the JUPITER trial in 2006.
JUPITER found that patients with normal cholesterol benefited from treatment with statins when they had elevated levels of inflammation, as measured by CRP.
Patients in the study with normal cholesterol and elevated CRP who took statins had fewer heart attacks than patients with the same characteristics who did not take the drugs.
Based on the findings, it was estimated that an additional 6.5 million adults in the U.S. might benefit from treatment with statins.
But the new study suggests that far fewer patients would actually benefit.
The study included 950 participants in another trial followed for an average of just under six years who also had normal cholesterol and elevated CRP levels.
All the participants underwent CT scans to look for evidence of calcium in the coronary arteries, which is an indicator of possible plaque buildup and heart disease.
Checking for Heart Risk With CAC Testing
Even though all of the study participants would have been candidates for statins under the JUPITER guidelines, CAC testing indicated that about half had a very low risk for heart attack or stroke.
Three out of four heart attacks, strokes, or other blood-clot-related events over the follow-up period occurred in the 25% of patients with the highest CAC scores, and almost all heart attacks (95%) occurred in people with some measurable level of calcium in their coronary arteries.
"The JUPITER trial suggested that all of the people in our patient population should be treated with statins, but our analysis suggests that half are at very low risk," cardiologist and study researcher Michael J. Blaha, MD, of Baltimore's Johns Hopkins Ciccarone Preventive Cardiology Center, tells WebMD.
Blaha believes CAC imaging will prove to be a better test for assessing cardiovascular risk than CRP in generally healthy patients for whom treatment decisions are unclear.
He adds that a trial like JUPITER is needed to determine if patients treated with statins based on CAC findings have fewer heart attacks and strokes.
Cardiologist Robert Bonow, MD, who is a past president of the American Heart Association (AHA), says until such a trial is done it will not be clear if coronary calcium screening influences treatment and changes outcomes.
The AHA does not recommend coronary artery calcium screening for patients with a low or high risk of heart disease, but it concludes that the test may be of use in average-risk patients who are not having symptoms such as chest pain.
Bonow, who is a professor of medicine at Chicago's Northwestern Feinberg School of Medicine, says one potential downside to the screening test is that it might lead to even more testing and potentially unnecessary invasive treatments like angioplasty.
"It is human nature to want to do something about a blockage when it is found, even if that blockage is not causing any symptoms," he says.
Blaha believes this concern is unfounded.
"CAC should be used to establish risk, but it should play no part in driving more testing," he says, adding that angioplasty should be considered only in patients with chest pain or other symptoms indicative of heart disease.