Laukkanen JA; Kurl S; IKhan H; Kunutsor SK;

Heart rhythm [Heart Rhythm] 2021 Mar 06. Date of Electronic Publication: 2021 Mar 06.

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.