Percentage of age-predicted cardiorespiratory fitness and risk of sudden cardiac death: a prospective cohort study.

Abstract Background The inverse associations between cardiorespiratory fitness (CRF) and vascular outcomes are previously established. However, there has been no previous prospective evaluation of the relationship between percentage of age-predicted CRF (%age-predicted CRF) and risk of sudden cardiac death (SCD). Objective We aimed to assess the association of %age-predicted CRF with SCD risk in a long-term prospective cohort study. Methods Cardiorespiratory fitness was assessed using the gold standard respiratory gas exchange analyser in 2,276 men who underwent cardiopulmonary exercise testing. The age-predicted CRF estimated from a regression equation for age was converted to %age-predicted CRF using (achieved CRF/age-predicted CRF)*100. Hazard ratios (HRs) (95% confidence intervals, CIs) were calculated for SCD. Results During a median follow-up of 28.2 years, 260 SCDs occurred. There was a dose-response relationship between age-predicted CRF and SCD. A 1 standard deviation increase in %age-predicted CRF was associated with a decreased risk of SCD in analysis adjusted for established risk factors (HR 0.60; 95% CI 0.53–0.70), which remained consistent on further adjustment for several potential confounders including alcohol consumption, physical activity, socioeconomic status and systemic inflammation (HR 0.73; 95% CI 0.62–0.85). The corresponding adjusted HRs (95% CIs) were 0.34 (0.23-0.50) and 0.52 (0.34-0.79) respectively, when comparing extreme quartiles of %age-predicted CRF levels. The HRs for the associations of absolute CRF levels with SCD risk in the same participants were similar. Conclusions Percentage of age-predicted CRF is continuously, strongly and independently associated with risk of SCD and it is comparable to absolute CRF as a risk indicator for SCD.