Blunted heart rate response during dipyridamole stress SPECT is associated with cardiovascular outcomes in an all-comers cohort

Abstract Background Dipyridamole stress cardiac 99mTc-SPECT (DS-SPECT) is commonly used to detect myocardial ischemia. Blunted heart rate response (BHRR) during pharmacologic stress has been associated with adverse outcomes. This study evaluated the significance of BHRR in an unselected real-world DS-SPECT cohort and compared it with routine imaging findings. Methods In this single-center retrospective cohort study, all adult patients who underwent dipyridamole stress SPECT without adjunct exercise between 2014 and 2017 were included. Clinical data were obtained from the electronic medical record and structured pre-test interviews, and patients were followed through September 2020. 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 found association of BHRR with cardiovascular death (HR 8.09, 95% CI:1.06–61.91, p < 0.05). Patients with abnormal DS-SPECT imaging and BHRR had a nearly fourfold increased risk of adverse cardiovascular events (HR 3.79, 95% CI: 1.24–11.63, p < 0.05). Moreover, individuals demonstrating both abnormal imaging results and BHRR experienced the highest rate of all-cause mortality (HR 2.93, 95% CI: 1.1–7.7, p < 0.01). Overall, BHRR significantly correlated with increased all-cause and cardiovascular mortality. Conclusions In unselected patients referred to DS-SPECT, BHRR was associated with cardiovascular mortality. Moreover, in our population group, when combined with abnormal imaging results, BHRR significantly increases the association with DS-SPECT for cardiovascular morbidity and all-cause mortality. These findings may support future inclusion of BHRR in DS-SPECT studies.