Abstract Body (Do not enter title and authors here): Introduction: Resting Heart Rate (HR) and Heart Rate Variability (HRV) reflect autonomic control, and are implicated as prognostic factors. We aimed to evaluate the prognostic value of HR and HRV in a cohort from a nationwide telemedicine network.
Methods: We assessed unique ECGs recorded from patients ≥16 years-old, from the tele-ECG database of the Telehealth Network of Minas Gerais, Brazil, between 2010 and 2017. Variables of interest were HR and standard deviation of normal RR intervals (SDNN). Self-informed data were collected: sex, age, risk factors (hypertension, dyslipidemia, diabetes, smoking) and comorbidities (myocardial infarction, Chronic Obstructive Pulmonary Disease, and Chagas disease). Outcomes of interest were all-cause and cardiovascular mortality, assessed by ICD codes reported in death certificates, through linkage with the Mortality Information System. Cox regression was applied to evaluate the association between HR and HRV and the outcomes, in 4 models: 1. Unadjusted; 2. Adjusted for sex and age; 3. Model 2 + risk factors + clinical comorbidities; 4. Model 3 + HRV or HR, respectively.
Results: At total 992.611 individuals were included, median age of 55 years, 60% women. In 6 years, there were 33.292 deaths (3,37%), 21% due to cardiovascular causes. Patients who died had higher prevalence of all risk factors and comorbidities, as well as higher HR: 76 (IQR 66-87) vs. 74 (IQR 65-83) bpm, p<0.001 and lower HRV: 84 (IQR 51-127) vs. 114 (IQR 74-153), p<0.001. After adjustments (model 4), all HR quartiles were independently associated a progressively increased risk of all-cause mortality, being 88% higher for the 4^th quartile (HR=1.88 (95%CI 1.77–1.89). Similarly, the 1^st and 2^nd HRV quartiles remained associated with increased all-cause mortality (1^st quartile HR=1.42 (95%CI 1.37–1.47) in the final model. For cardiovascular mortality, HR was also an independent predictor, with a progressively higher risk, with a 77% increase (HR=1.77 95%CI 1.65–1.91) in the 4^th quartile. HRV was also an independent predictor of cardiovascular death, with a 33% risk increase (HR=1.33, 95%CI 1.23–1.44) for the 1^st quartile. Male gender, age, and all risk factors and comorbidities were also independent predictors of all-cause and cardiovascular mortality.
Conclusions: In a large cohort of Brazilian adults, baseline HR and HRV were independent predictors of all-cause and cardiovascular mortality, after adjustment for clinical variables and autonomic indexes.