The prognostic association between resting heart rate and cardiac death-Myocardial perfusion defects as a potential mechanism

Objective: Elevated resting heart rate (RHR) is a robust risk factor for cardiac events, and recent clinical trial evidence suggests lowering RHR may reduce cardiac risk among individuals with elevated RHR and known coronary artery disease (CAD). This study sought to elucidate the extent to which myocardial perfusion defects explain the association between RHR and cardiac death among individuals with known or suspected CAD undergoing myocardial perfusion imaging (MPI). Methods: This retrospective cohort study included 3708 individuals with known or suspected CAD who underwent clinically indicated MPI with positron emission tomography (PET MPI). Stress, rest, and stress-induced myocardial perfusion defect sizes were measured objectively by automated computer software as percent of left ventricular myocardium hypoperfused. RHR was measured by electrocardiography prior to rest PET MPI. Cardiac and non-cardiac death information was obtained through the National Death Index. All analyses were stratified by beta blocker (BB) use. Results: RHR was consistently associated with the presence of significant myocardial perfusion defects, though associations were stronger among BB than non-BB users. Among BB users, RHR was strongly associated with an increased risk of cardiac death in adjusted models before (hazard ratio [HR]. =. 2.6 comparing RHR. ≥. 80. bpm vs. RHR. <. 60, p<. 0.05) and after (HR. =. 2.4, p<. 0.05) including stress myocardial perfusion defect size in the model. Results were similarly strong among non-BB users. Conclusions: Resting heart rate was independently associated with cardiac death, however there was little evidence suggesting this association was explained by the presence of myocardial perfusion defects.