Myocardial perfusion imaging (MPI) with SPECT, an important diagnostic test to identify candidates for coronary angiography and revascularization, is also the single medical test with the highest radiation burden and potential cancer risk. The steady increase in MPI exams performed in the United States motivated the American Heart Association to issue a statement emphasizing appropriate patient selection to maximize the benefit-to-risk ratio of cardiac imaging and to improve the safety of patients undergoing cardiac imaging procedures. The implementation of appropriate use criteria can help achieve these objectives.
Cardiologists at John H. Stroger Jr. Hospital of Cook County and Rush University Medical Center in Chicago analyzed the records of over 1,500 patients to determine the impact of appropriate use of SPECT MPI on the benefit-to-risk ratio of testing in men and women and on their lifetime attributable risk of developing cancer. They confirmed that inappropriate MPI use is indeed associated with excess cancer risk. In an article published in the Journal of Nuclear Medicine, they also reported that appropriate use of SPECT MPI can close the gender gap in radiation risk if younger, low-risk female patients were not tested.
The 1,511 consecutive patients who had a SPECT MPI between August 2007 and May 2010 were enrolled from 11 cardiology and primary care physicians’ practices in greater metropolitan Chicago. They were prospectively followed up for a mean of 27 months. Twenty two major cardiac events occurred and 29 patients had revascularizations within six months during the follow-up time period.
Based on 2009 appropriateness criteria guidelines, each patient was categorized as having had an appropriate, inappropriate, or uncertain MPI study. MPI appropriateness was determined on the basis of surgical risk, prior revascularization type and date, imaging findings and date, pretest CAD likelihood, ability to exercise, electrocardiogram interpretability, and Framingham risk 10 year coronary heart disease risk. A total of 779 studies (51.6%) were categorized as appropriate, 44 (2.9%) as uncertain, and 688 (45.5%) as inappropriate. Patients in the inappropriate group were younger, predominantly women, had lower prevalence of coronary artery disease (CAD) and coronary risk factors, and were less likely to have an abnormal MPI finding.
Lead author Rami Doukky, MD, of the Division of Cardiology and colleagues calculated lifetime attributable risk for each patient on the basis of accepted risk estimates. MPI benefit-to-risk ratios were defined by the annualized predicted major adverse cardiac events-to-lifetime attributable risk ratio and the predicted 6 month revascularization -to-lifetime attributable risk ratio.
The researchers determined that patients with an inappropriate MPI had significantly higher lifetime attributable risk, lower predicted major adverse cardiac event-to-lifetime attributable risk ratio, and lower predicted 6 month revascularization-to-lifetime attributed risk ratio. There was a significant difference between men and women in all risk ratio categories. However, for the appropriate and uncertain groups, the sex gap in lifetime attributable risk was neutralized.
“Until radiation saving protocols are widely implemented, appropriate patient selection will remain the primary means to reducing exposure to ionizing radiation from MPI,” the authors wrote. “Implementing the appropriate use criteria can lead to substantial reduction in radiation burden in the population, further emphasizing the role of appropriate use criteria as an invaluable quality measure.”
Appropriate use criteria needed for SPECT MPI testing. Appl Radiol.