Blunted Heart Rate Response Enhances Prognostic Value of Dipyridamole Stress SPECT for Cardiovascular Morbidity and Mortality in All-Comers

Background Dipyridamole stress cardiac 99mTc Single Photon Emission Computed Tomography (DS-SPECT) is a common method for detecting myocardial ischemia in selected patients. Blunted heart rate response (BHRR) during pharmacological stress is a known risk factor for mortality and morbidity. With increasing prevalence of referred patients with significant comorbidities, often excluded in studies, an all-comers population was evaluated to better represent the patients undergoing DS-SPECT. This study aimed to determine the prognostic significance of BHRR compared to DS-SPECT imaging results. Methods We conducted an all comer, single-center, retrospective cohort study. All patients subjected to DS-SPECT, years 2014 to 2017, were included. Results Study population consisted of 388 patients, 227 (58.5%) had normal imaging results, and 245 (63.1%) exhibited BHRR. During a mean follow-up of four years, multivariable analysis identified BHRR as the strongest independent predictor of cardiovascular death (HR 8.09, CI: 1.2–11.6, p < 0.05). Patients with abnormal DS-SPECT imaging and BHRR had a nearly fourfold increased risk of adverse cardiovascular events (HR 3.79, CI: 1.06–61.91, p < 0.05). Moreover, individuals demonstrating both abnormal imaging results and BHRR experienced the highest rate of all-cause mortality (HR 2.93, CI: 1.1–7.7, p < 0.01). Overall, BHRR significantly correlated with increased all-cause and cardiovascular mortality. Conclusions In unselected patients referred for DS-SPECT, BHRR was an independent predictor of cardiovascular mortality, stronger than imaging findings. When combined with abnormal imaging results, BHRR significantly improves the prediction value of DS-SPECT for cardiovascular morbidity and all-cause mortality. These findings suggest inclusion of BHRR in DS-SPECT studies.