Use of cardiac stress tests with imaging in patients without a diagnosis of coronary heart disease surged in the U.S. over an 18-year span, according to a study published in the Oct. 7 issue of the Annals of Internal Medicine. Almost one in three of those tests was ruled as rarely appropriate.

Many studies that assessed trends over time in cardiac stress test use relied on Medicare data, and analyses designed to spot disparities focused on gender rather than race or ethnicity. To broaden the scope, Joseph A. Lapado, MD, of New York University Langone Medical Center in New York City, and colleagues used two national databases: the National Ambulatory Medical Survey and the National Medical Care Survey.   

For their study, they looked at data from visits between 1993 and 2010 to office-based physicians and hospital-based outpatient clinics by patients who did not have a diagnosis of coronary heart disease. Within those visits, they identified if a cardiac stress test was performed or ordered.

They also assessed the appropriateness of the test, based on criteria established by various medical societies. They defined a test as rarely appropriate if the patient had no chest pain or angina as a reason for the visit or had ischemic equivalents.

Lapado et al found that the average annual rate of visits that led to a cardiac stress test being done or referred grew from 28 per 10,000 visits in 1993-1995 to 45 per 10,000 visits in 2008-2010. They saw no trend toward more frequent testing after adjusting for patient characteristics, risk factors and provider characteristics.

Cardiac stress tests with imaging commanded an increasing proportion of all stress tests over time. In 1993-1995, 59 percent of all tests used imaging. That grew to 87 percent in 2008-2010.

They determined that at least 30 percent of cardiac stress tests with imaging and 14 percent of stress tests without imaging were rarely appropriate, for a cost of $507.1 million ($494 attributed to tests with imaging, 2013 dollars). In addition, the imaging tests exposed patients to an estimated 10.2 million mSv of unnecessary radiation a year, and potentially 491 cases of future cancers.

The upward trend in cardiac stress test use carried through all races and ethnicities, although test rates were lower in Hispanics than other groups.

“[W]e provide novel evidence that national growth in cardiac stress test use can largely be explained by changes in population demographics, clinical risk factors, and provider characteristics rather than changes in physician ordering behavior,” they wrote. “In contrast to overall growth, the brisk increase in the use of imaging in cardiac stress tests was largely unexplained by these factors, and a substantial portion was for patients in whom imaging is rarely appropriate.”  

Their findings suggest that at least in the case of cardiac stress tests, physician decision making is not contributing to health disparities. “However, reducing disparities in the burden of cardiovascular disease remains an important concern.”