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CT Angiography in Low-risk Patients Leads to More Tests and Treatment

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Cardiac imaging Undergoing a coronary CT angiography (CCTA) often leads to greater use of medications and significantly more additional testing including invasive catheterizations in low-risk patients compared to similar patients who did not undergo CT angiography, a new study shows.

In the first large population study to look at both patient and physician behavior following a CT scan screening test for coronary stenosis, researchers led by Dr. John McEvoy, a cardiology fellow at Johns Hopkins Medical Center in Baltimore compared testing and medication prescription and use following the screening test in 2,000 Korean men and women who took part in a health promotion trial.

McEvoy told The Hub in a phone interview from Ireland that the study grew out of a collaboration dating back to 2009 between Dr. Roger Blumenthal, director of the Ciccarone Center for the Prevention of Heart Disease at Johns Hopkins, and Dr. Hyuk-Jae Chang at Yonsei University in South Korea.

“The study Dr. Chang was conducting was looking at the association of risk factors with different plaque types,” McEvoy said. “We thought that, given the opportunity of studying low-risk, asymptomatic patients who undergo a CT angiography, it would be interesting to look at the downstream medical treatment they received following screening.”

What they found suggests that low-risk patients without symptoms don't benefit in the short term from knowing whether or not plaque has been detected using CT angiography. Not surprisingly physicians may be inclined to be more aggressive with prescriptions or follow up tests. “It is intuitive that if someone undergoes a scan and some disease is found that there will additional testing and treatment,” McEvoy said. “So we weren’t surprised by the study results. We were more interested in carefully documenting just how much medication and additional testing was done after the test.”

In the study published online ahead of print publication in the Archives of Internal Medicine the researchers compared 1,000 asymptomatic participants in the SNUBH health-screening program in South Korea who elected to undergo the CT angiography, with a matched group of 1,000 participants in the program who elected not to undergo CT angiography.

The average age for both groups was 50, and 63 percent were men. Both groups had similar baseline heart disease risk factors and none had experienced angina or other symptoms. Their current use of statins, aspirin, anti-hypertensive, and oral hypoglycemic drugs were documented at the index visit, as were BMI, history of hypertension, diabetes, and total cholesterol.

For the CCTA group, their scans were analyzed by experienced independent investigators who documented plaque deposits that were larger than 1 millimeter squared within or adjacent to the vessel lumen. Those in the CCTA group were given their results, and all 2,000 patients were followed over 18 months. In both groups, the treating physicians ordered all prescriptions and additional testing. Study follow-up exams were scheduled at 90 days and 18 months after the initial visit.

In the CCTA group 785 screening scans (79 percent) were negative. The remaining 215 patients (21 percent) were defined as CCTA positive. There were 392 narrowed segments in 215 patients. A total of 52 patients (5 percent) had greater than 50 percent stenosis, and 21 patients (2 percent) had greater than 75 percent stenosis.

While there was no difference in the two groups at baseline for statin use, following CCTA, statins were prescribed more often among those with a positive CCTA compared to the control group that did not undergo CCTA. At the 90-day follow-up visit 34 percent of the CCTA group positive for stenosis were taking statins compared to 8 percent of those who did not undergo CT angiography. At the 18-month visit statin use declined to 20 percent of the CCTA group remaining on statins compared to 6 percent of the non-CCTA group.

Inversely, those with a negative CCTA were less likely to be on statins at the 90-day and 18-month follow-up visits than patients in the control group. Similarly, those with a positive CCTA were nearly 7 times more likely to be taking aspirin at the 90-day visit compared to those in the non-CCTA group, and that too declined at the 18-month visit with the positive CCTA group 4 times more likely to be taking aspirin compared to the non-CCTA group.

There were no significant differences in use of anti-hypertensive and oral hypoglycemic drugs between the two groups. A total of 55 patients (5.5 percent) in the CCTA group underwent additional tests including invasive catheterization compared to 22 patients (2.2 percent) of the non-CCTA group at 90 days.

At 18 months there was one patient admitted to the hospital in the CCTA group for unstable angina and 1 cardiac death occurred in the control group. McEvoy said that they had wanted to look at cardiac events as part of the follow-up study, but that 18 months in this low-risk group was too short for that.

What they could say was that screening CCTA suggesting coronary atherosclerosis was associated with a sustained increase in aspirin and statin use. In addition, an abnormal result was also associated with more resource-intensive secondary tests and invasive revascularizations outside of evidence-based guidelines. In terms of implications of the study for screening low-risk patients, co-author Blumenthal, noting that a CT angiography test can cost between $600 and $1,000, said the results affirm the current guidelines for CT angiography of the American Heart Association.

“Before we advocate for a particular screening test, we need to demonstrate its potential benefit and define the patient populations for whom the test would be useful,” Blumenthal said.

McEvoy emphasized that the people in this study had these scans as part of a study of plaques so it was not at all the common scenario of patients seeing their cardiologist and being given a CT scan. Nevertheless there is some evidence of increasing use of CT angiography in low-risk, asymptomatic patients. “No one knows how many low-risk patients are undergoing these scans,” McEvoy said. “Because of the non-invasiveness and the quality of the result it may be tempting for a cardiologist to consider the test in certain patients without symptoms but who might have other factors that are associated with heart disease. But most cardiologists would consider other tests first because the cost, radiation and contrast bolus used for CT angiography make the risk-to-benefit ratio too high.”

By Michael O’Leary, contributing writer, Health Imaging Hub

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