Heart rate reserve (HRR) during physical or pharmacological stress is a sign of cardiac autonomic function and sympathetic reserve, but it can be reduced during exercise for confounders such as poor motivation, drugs or physical fitness. In this study we sought to assess the prognostic meaning of HRR during dipyridamole stress echocardiography (DSE) in patients with abnormal chronotropic response to exercise. From 2004 to 2019, we prospectively acquired and retrospectively analyzed 379 patients (age 62 ± 11 years; ejection fraction 60 ± 5%) with suspected (n = 243) or known (n = 136) chronic coronary syndromes, referred to DSE for chronotropic incompetence during upright bicycle exercise-electrocardiography test defined as HRR used [(peak HR - rest HR) / (220 - age) - rest HR] ≤80% in patients off and ≤62% in patients on beta-blockers. All patients were in sinus rhythm and underwent DSE (0.84 mg/kg) within 3 months of exercise testing. During DSE, age-independent HRR (peak/rest HR) ≤1.22 was considered abnormal. All patients were followed-up. All-cause death was the only outcome measure. HRR during DSE was normal in 275 (73%) and abnormal in 104 patients (27%). During a follow-up of 9.0 ± 4.2 years, 67 patients (18%) died. The 15-year mortality rate was 23% in patients with normal and 61% in patients with abnormal HRR (p < 0.0001). At multivariable analysis a blunted HRR during DSE was an independent predictor of outcome (hazard ratio 2.01, 95% confidence intervals 1.23-3.29; p = 0.005) with age and diabetes, while neither inducible ischemia nor ongoing beta-blocker therapy were significant predictors. In conclusion, a blunted HRR during DSE predicts a worse survival in patients with chronotropic incompetence during exercise test. HRR during DSE is an appealingly simple biomarker of cardiac autonomic dysfunction independent of imaging, exercise and beta-blocker therapy.
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