A hypothetical protocol for the provisional use of perfusion imaging with exercise stress testing

Abstract

Background: Previous literature suggests that the results of myocardial perfusion imaging (MPI) add little to the prognosis of patients who exercise >10 metabolic equivalents (METS) during stress testing. With this in mind, we attempted to determine if a provisional injection protocol could be developed in which a patient would not receive an injection of radioisotope if adequate exercise was achieved without symptoms and a negative ECG response. This protocol would save a substantial amount of time, radiation exposure, and cost.

Methods: All patients who underwent a stress SPECT MPI over a 6.5-year period from 2004 to 2010 were included. Patients who would have been considered for a standby injection protocol were: exercise stress, age < 65, no known coronary artery disease (CAD), and an interpretable ECG. Patients were retrospectively divided into two groups based on whether they would have received radioisotope or not. Criteria for not injecting included a maximal predicted heart rate ≥ 85%, ≥10 METS of exercise, no symptoms of chest pain or shortness of breath, and no ECG changes (ST depression or arrhythmia). The two groups were then compared based on MPI results and all-cause mortality derived from the Social Security Death Index.

Results: A total of 24,689 patients underwent SPECT MPI during this period, and 5,352 would have been eligible for a provisional injection protocol. There were 3,791 (70.8%), who would have been injected and 1,561 (29.2%), who would not have been. Perfusion results were abnormal in 5.9% of non-injected group compared to 14.4% in those who would have been injected. After a mean follow-up of 60.6 ± 21.4 months, 1.1% had died in the non-injected cohort compared to 2.2% in the injected group.

Conclusion: A provisional injection protocol defined as age < 65, normal rest ECG, no history of CAD, and high level exercise with a negative ECG response and no symptoms has a very low 5-year all-cause mortality and low yield of MPI. If adopted it would decrease radiation exposure and save time and health care costs without jeopardizing prognosis.