Inappropriate use drags on SPECT MPI’s prognostic value

An abnormal SPECT MPI does an excellent job stratifying risk in patients with appropriate indications for known or suspected heart disease but its value is diminished in cases of inappropriate use. These findings from a community-based evaluation validate the use of SPECT MPI, according to researchers, but they may apply only to low-risk patient populations.

In 2009, the American College of Cardiology, American Society of Nuclear Cardiology, the American College of Radiology and other groups created a set of appropriate use criteria (AUC) to help guide physicians in SPECT MPI’s use in patient care. That prompted Rami Doukky, MD, of Rush University Medical Center in Chicago, and colleagues to evaluate the impact of AUC on SPECT MPI’s prognostic value using a prospective cohort study. They published their results online Sept. 10 in Circulation.

Twenty-two physicians from 11 practices in metro Chicago participated in the study. The study included 1,511 consecutive patients who underwent outpatient SPECT MPI between Aug. 15, 2007, and May 15, 2010. Applying the 2009 AUC, patients were stratified as having either appropriate or uncertain appropriateness tests (combined under the term appropriate in the analysis) or inappropriate tests. The primary endpoint was all-cause mortality and secondary endpoints were the composite of death or MI or the composite of cardiac death or MI.

Patients were followed for a mean 27 months. Of the total MPI referrals, 51.6 percent were appropriate, 2.9 percent uncertain and 45.5 percent inappropriate. Eleven percent of patients had myocardial perfusion defects.

In patients who had an appropriate or uncertain SPECT MPI, an abnormal scan predicted an increase in the risk of death, cardiac death, the composite of death or MI and the composite of cardiac death or MI. An abnormal SPECT MPI scan did not predict major adverse cardiac events compared with patients who had a normal scan.

Doukky and colleagues acknowledged that the rate of inappropriate use in their analysis was higher than results from other studies. They noted that in their study most of the scans were performed before the 2009 AUC were published and integrated into practice.

They emphasized the cost and health consequences of inappropriate use. “[A]lthough MPI is considered cost-effective overall, the diminished prognostic value with inappropriate testing could have serious implications on the overall cost-effectiveness of MPI, not to mention unnecessary radiation exposure," they wrote. “In fact, minimizing inappropriate use is probably the best and most cost-efficient way to limit the radiation exposure in the community.”

Their analysis showed that patients in the inappropriate group were more likely to be asymptomatic with a lower likelihood of coronary artery disease and a lower 10-year Framingham coronary heart disease risk. In an accompanying editorial, Raymond J. Gibbons, MD, and Todd D. Miller, MD, of the Mayo Clinic in Rochester, wrote that consequently the results likely apply only to similar low-risk patient populations.

The editorial writers also pointed to the high variability between the inappropriate use rates for physicians, which ranged from 10 percent to 77 percent. “To the degree that there is similar, if not greater, variability in physicians across the country, the ‘group’ results presented here may not apply to many individual physicians or many practices with higher or lower rates of inappropriate studies,” they suggested.

Gibbons and Miller added that the issue of limited generalizability hounds other AUC studies. “This study is one step along the road to quality improvement, the ultimate goal of the AUC.”

The study was funded by a grant from Astellas Pharma U.S.