Does risk for major adverse cardiac events in patients undergoing vasodilator stress with adjunctive exercise differ from patients undergoing either standard exercise or vasodilator stress with myocardial perfusion imaging?

BACKGROUND: In patients with functional limitations, the use of adjunctive exercise with vasodilator stress has advantages over vasodilator stress alone in single photon emission computed tomography myocardial perfusion imaging (MPI) for technical reasons and with regards to more effective cardiac risk stratification. Whether patients who undergo vasodilator with adjunctive exercise stress MPI possess clinical characteristics and cardiac risk that differs from those who undergo standard exercise or vasodilator stress MPI is unknown.
METHODS: Prospectively collected data on 19,367 consecutive patients referred for stress MPI to a tertiary care center (9,331 [48%] underwent exercise-only, 3,793 [20%] underwent vasodilator plus exercise, and 6,243 [32%] underwent vasodilator-only) were analyzed. Perfusion data were scored using the ASNC 17-segment with a summed stress score (SSS) < 4 = normal, 4-8 = mildly abnormal, and > 8 = moderate to severely abnormal. Patients were followed a mean of 1.96 ± 0.95 years. Demographics, clinical characteristics, and the occurrence of major adverse cardiac events (cardiac death or nonfatal myocardial infarction) were compared between the three stress modality groups.
RESULTS: Comparison of demographics and clinical characteristics revealed significant differences in gender, age, cardiac risk factors, and stress MPI between the three stress modality groups (P < .001). In follow-up, cardiac event-free survival of patients in the vasodilator plus exercise stress group was significantly higher than those in the vasodilator-only group but lower than those in the exercise-only group (P < .001). Annualized cardiac event rates of patients in the vasodilator plus exercise stress group were significantly lower than those in the vasodilator-only group for all three categories of the SSS (P < .001). After multivariable adjustment, with exercise-only as reference category, vasodilator plus exercise and vasodilator-only stress emerged as independent predictors (more likely occurrence) of cardiac death, while vasodilator-only stress emerged as an independent predictor (more likely occurrence) of cardiac death or nonfatal myocardial infarction. With vasodilator-only as the reference category, exercise-only and vasodilator plus exercise stress emerged as independent predictors (less likely occurrence) of cardiac death as well as of cardiac death or nonfatal myocardial infarction.
CONCLUSIONS: Patients undergoing vasodilator plus exercise stress MPI possess clinical characteristics and cardiac risk that differs significantly from those undergoing either standard exercise or vasodilator stress MPI and places them in a lower risk category compared to vasodilator stress alone.