Abstract
BackgroundHigh levels of physical activity (PA) and heart rate variability (HRV) are associated with cardiovascular benefits in patients with cardiovascular diseases. HRV, representing cardiac autonomic function, is positively associated with PA. However, the impacts of PA and cardiac autonomic function on cardiovascular outcomes were not analysed in the same study population. This lack of evidence supported our hypothesis that PA might contribute to cardiovascular benefits via enhanced cardiac autonomic function.MethodsPatients with implantable cardioverter defibrillator (ICD) or cardiac resynchronisation therapy defibrillator (CRT-D) implantation were included from the SUMMIT registry. HRV and PA values were assessed during the first 30–60 days post device implantation using a continuous home monitoring system. Causal mediation analysis was conducted to explore the possible mediation function of HRV in the association of PA with long-term cardiac death and all-cause mortality in patients at a high risk of sudden cardiac death.ResultsOver a mean follow-up period of 47.7 months, 63 cardiac deaths (18.9%) and 85 all-cause death events (25.5%) were observed among 342 patients with ICD/CRT-D implantation. A positive linear association between HRV and PA was demonstrated and the β value of HRV was 0.842 (95% confidence interval [CI]: 0.261–1.425, P = 0.005) in the multiple linear regression analysis. Multivariable Cox proportional hazards analysis revealed that high levels of PA (≥11.0%) and HRV (≥75.9 ms) were independent protective factors against cardiac death (PA: hazard ratio [HR] = 0.273; 95% CI, 0.142–0.526, P < 0.001; HRV: HR = 0.224; 95% CI, 0.103–0.489, P < 0.001) and all-cause mortality (PA: HR = 0.299; 95% CI, 0.177–0.505, P < 0.001; HRV: HR = 0.394; 95% CI, 0.231–0.674, P = 0.001). Causal mediation analysis demonstrated partial mediation effects of PA that were mediated through HRV on cardiac death (mediation proportion = 12.9, 95%CI: 2.2–32.0%, P = 0.006) and all-cause mortality (mediation proportion = 8.2, 95%CI: 1.6–20.0%, P = 0.006).ConclusionsHRV might be a modest mediator in the association between high levels of PA and the reduced risks of cardiac death and all-cause mortality in ICD/CRT-D recipients. This finding supports that enhanced cardiac autonomic function might be one of the underlying mechanisms by which regular PA contributes to cardiovascular benefits.
Highlights
Physical activity (PA) refers to any bodily movement resulting from skeletal muscle action, which can reflect the status of energy expenditure or exercise intensity of an individual [1, 2]
Dysfunction of the autonomic nervous system plays a crucial role in the clinical course of cardiovascular disease (CVD), and low levels of heart rate variability (HRV) indices are associated with increased risks of cardiovascular adverse events and mortality [16, 17]
Patients who underwent implantable cardioverter defibrillator (ICD) or cardiac resynchronisation therapy defibrillator (CRT-D) implantation between May 2010 and April 2014 were included upon meeting the following criteria: 1) ICD or CRT-D implantation in accordance with the recommendations outlined in the current guideline [19]; 2) the equipment with a remote home monitoring system and initiation of continuous monitoring after implantation; 3) capacity to supply available data related to daily HRV and physical activity (PA); 4) age of the patients ≥18 years at implantation; and 5) life expectancy > 1 year after device implantation
Summary
Physical activity (PA) refers to any bodily movement resulting from skeletal muscle action, which can reflect the status of energy expenditure or exercise intensity of an individual [1, 2]. Previous studies have reported that high levels of PA can protect against cardiovascular adverse events, cardiovascular death, and all-cause mortality in individuals with or without cardiovascular diseases (CVDs) [3,4,5]. High levels of physical activity (PA) and heart rate variability (HRV) are associated with cardiovascular benefits in patients with cardiovascular diseases. The impacts of PA and cardiac autonomic function on cardiovascular outcomes were not analysed in the same study population. This lack of evidence supported our hypothesis that PA might contribute to cardiovascular benefits via enhanced cardiac autonomic function
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