Cardiorespiratory Fitness and the Risk of Serious Ventricular Arrhythmias: A Prospective Cohort Study.

Cardiorespiratory fitness (CRF) is an established risk factor for cardiovascular disease outcomes. However, the relationship of CRF with risk of ventricular arrhythmias (VAs) is unknown. We aimed to assess the prospective association of CRF with the risk of serious VAs. Cardiorespiratory fitness, as measured by maximal oxygen uptake, was assessed using a respiratory gas exchange analyzer in 2299 middle-aged men in the Kuopio Ischemic Heart Disease prospective cohort. We corrected for within-person variability in CRF levels using data from repeated measurements 11 years apart. During median follow-up of 25.3 years (interquartile range, 18.7-27.2 years), 73 serious VAs were recorded. The age-adjusted regression dilution ratio of CRF was 0.58 (95% CI, 0.53-0.64). In analysis adjusted for age, the hazard ratio (HR) for serious VAs per 1-SD increase in CRF was 0.64 (95% CI, 0.49-0.84). The association persisted on additional adjustment for body mass index, systolic blood pressure, history of hypertension, prevalent coronary heart disease, smoking, history of diabetes, cholesterol level, alcohol consumption, and physical activity (HR, 0.67; 95% CI, 0.51-0.88). The corresponding adjusted HRs (95% CIs) were 0.29 (0.14-0.59) and 0.32 (0.15-0.65), respectively, comparing the top vs bottom tertiles. The associations were stronger on correction for regression dilution bias, remained consistent on exclusion of men with a history of coronary heart disease, and did not vary importantly in several relevant clinical subgroups. Cardiorespiratory fitness is inversely associated with future risk of serious VAs, independently of several cardiovascular disease risk factors. Further research is needed to assess the causal relevance of these findings.