The power of exercise: SPECT MPI in active patients may be unnecessary

Many older patients undergoing an exercise stress test may not need molecular imaging to provide a clear picture of cardiovascular health. Evidence suggests that SPECT MPI may not provide any additional information for those who are nimble enough to reach a certain level of exertion and show no signs of CAD or cardiovascular distress. These and similar findings point to potential radioisotope injection guidelines to reduce radiation dose and cost of healthcare for these patients, according to research presented at the International Conference on Nuclear Cardiology and Cardiac CT, held May 5 to 8 in Berlin.

Milena Henzlova, MD, PhD, a professor of medicine and cardiology at Mount Sinai Medical Center in New Yor City, and colleagues reviewed the use of SPECT myocardial perfusion imaging during exercise stress tests to gauge the added value of the molecular imaging technique for active patients.

Researchers at Mount Sinai Medical Center reviewed all cases of stress SPECT MPI from 2004 to 2010, including a total of 24,689 patients. Hypothetical parameters for determining patients’ eligibility for MPI and radioisotope injection divided subjects retrospectively into two groups. Those who had readable ECGs, were under the age of 65 and could exercise more than 10 METS and reach 85 percent of their projected maximum heart rate with no signs of chest pain, arrhythmia or other symptoms of distress were considered ineligible for radioisotope injection based on these new guidelines for SPECT MPI candidacy. Those who were elderly and could potentially not reach this level of exercise or who had cardiac symptoms or shortness of breath and unclear ECG were considered eligible for stand-by radioisotope injection.

The results of dividing patients into these two hypothetical camps of eligibility and ineligibility for injection were compared to actual radioisotope administration and SPECT MPI data for these patients. A total of 5,352 patients would have been eligible for stand-by injection and based on clinical information about patient stress tests, 3,791 would have received injection during their stress test.

The findings showed that 1,561 patients eligible for injection would not have ended up receiving radioisotope injection under the new guidelines based on clinical data from their actual stress tests. Abnormal perfusion was found in 5.9 percent of those who would not have been injected and 14.4 percent for those who would have been injected. Follow up at a mean of five years showed a 1.1 percent mortality rate for those ineligible for injection under the new protocol versus 2.2 percent in those who would have been injected. These rates were compared to all-cause mortality based on the Social Security Death index.

Initial data from this study suggest that the use of these new guidelines for determining whether SPECT MPI is necessary and beneficial could reduce radiation dose significantly and potentially improve patient throughput and clinical practice.

“A provisional injection protocol defined as age greater than 65 [years], normal rest ECG, no history of CAD and a high level exercise with negative ECG response and no symptoms, has a very low five-year all-cause mortality and low yield of MPI,” concluded the authors. “If adopted it would decrease radiation exposure, save time and health care costs without jeopardizing prognosis.”