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CHICAGO -- When used off-guideline, myocardial perfusion imaging didn't hold significant predictive value for cardiovascular events, a study showed, perhaps due to few events in the low-risk population studied in community practice.
An abnormal finding in a scan that didn't fit appropriate use criteria was associated with 2.3- to 11.8-fold odds of subsequent major adverse cardiac events, but with wide confidence intervals, Rami Doukky, MD, of Rush University Medical Center in Chicago, and colleagues found.
Appropriate or uncertain single photon emission CT (SPECT) perfusion scans held consistently significant hazard ratios of 3.1 to 3.7 for events, they reported here at the American Society of Nuclear Cardiology meeting and simultaneously online in Circulation: Journal of the American Heart Association.
"Inappropriate SPECT was generally associated with a low absolute rate of hard events, rendering myocardial perfusion imaging ineffective in risk assessment," Doukky told attendees.
The findings were important as the first large study validating the 2009 appropriate use criteria agreed upon by all the relevant cardiology societies, "supporting their clinical utility," Raymond J. Gibbons, MD, and Todd D. Miller, MD, both of the Mayo Clinic in Rochester, Minn., acknowledged in an accompanying editorial.
However, they cautioned against interpreting the results as that SPECT perfusion imaging performs "differently" in inappropriate use. The test for interaction between appropriateness and SPECT's performance in prediction didn't reach statistical significance on any endpoint, remaining above a P-value of 0.43 for all, Gibbons and Miller pointed out.
The study was large at 1,511 consecutive patients in 11 outpatient, community-based private practices in the Chicago area from Aug. 15, 2007, through May 15, 2010.
And patients were followed fairly long, a mean of 27 months, for major adverse cardiac events.
Yet the 54% who got inappropriate myocardial perfusion imaging SPECT had only five deaths (none from cardiac causes) and two myocardial infarctions (MIs).
While that limited the power of the study to find prognostic value in inappropriate use of the imaging technique, other aspects of the study added up to poor generalizability, according to the editorialists.
Only 11% of the cohort had an abnormal SPECT study and 2.8% had severe ischemia, while "the inappropriate patients were an even lower-risk subset of this low-risk group."
Moreover, the 45% inappropriate rate was more than twice as high as any previously published inappropriate rate, Gibbons and Miller pointed out.
But those published reports from tertiary care centers likely reflected the higher risk populations seen there, as well as publication bias, Doukky countered at the session.
"This finding has major implications if it is representative of other community practices in the country," the editorialists wrote. Doukky suggested that was the case, but added that as payers have implemented the criteria in reimbursement, the inappropriate use rate has come down substantially in the community.
But with 85% of the about 5.8 million myocardial perfusion imaging studies performed each year in the U.S. done in the outpatient setting at a cost of $800 to $1,000, "the diminished prognostic value with inappropriate testing could have serious implications on the overall cost-effectiveness of myocardial perfusion imaging, not to mention unnecessary radiation exposure," his group wrote.
Another concern was the high degree of variability between physician categories and between individual clinicians, Gibbons and Miller added. The inappropriate use rate ranged from as low as 10% to as high as 77% among the 22 physicians in the study (P<0.001).
The rate was 47% among the 20 primary care physicians and 28% among the two cardiologists in that group (P<0.001).
Inappropriate and appropriate use were associated with a similar rate of coronary angiography and revascularization after adjustment for clinical covariates. But time to intervention was shorter among individual physicians with higher inappropriate imaging rates (P=0.01 and P=0.001), "perhaps with little time to evaluate response to medical therapy," the researchers noted.
"We need more studies such as this one to better define the variability in inappropriate rates, the most common inappropriate indications, and the prognostic value of appropriate use criteria in other populations," the editorialists concluded. "This study is one step along the road to quality improvement, the ultimate goal of the appropriate use criteria."
The study was funded by an investigator-initiated grant from Astellas Pharma.
Doukky reported serving on the Advisory Board of Astellas Pharma.
Gibbons reported consulting for Lantheus Medical Imaging and receiving speaking honoraria from AstraZeneca.
Miller reported consulting for Astellas Pharma.
- Reviewed by Zalman S. Agus, MD Emeritus Professor, Perelman School of Medicine at the University of Pennsylvania and Dorothy Caputo, MA, BSN, RN, Nurse Planner
Circulation: Journal of the American Heart AssociationSource Reference: Doukky R, et al "Impact of Appropriate Use on the Prognostic Value of Single-Photon Emission Computed Tomography Myocardial Perfusion Imaging" Circulation 2013; DOI: 10.1161/CIRCULATIONAHA.113.002744.
Circulation: Journal of the American Heart AssociationSource Reference: Gibbons RJ, Miller TD "SPECT Appropriateness: Does It Matter for Patient Outcomes?" Circulation 2013; DOI: 10.1161/CIRCULATIONAHA.113.005595.