Associations of cardiovascular and all-cause mortality events with oxygen uptake at ventilatory threshold.

BACKGROUND: Oxygen uptake (VO2) at ventilatory threshold (VT), is a cardiopulmonary exercise testing parameter which may be a proxy for peak VO2. We aimed to assess the associations of VO2 at VT with sudden cardiac death (SCD), fatal coronary heart disease (CHD) and cardiovascular disease (CVD), and all-cause mortality.

METHODS AND RESULTS: VO2 at VT was assessed during a submaximal exercise test using respiratory gas analyzers in the Kuopio Ischemic Heart Disease cohort of 1639 middle-aged men. Hazard ratios (HRs) (95% CIs) were assessed. During a median follow-up of 25.6years, 121 SCDs, 202 fatal CHDs, 312 fatal CVDs, and 703 all-cause mortality events occurred. VO2 at VT was correlated with peak VO2 (r=0.90) and linearly associated with each outcome. Comparing extreme quartiles of VO2 at VT, the HRs (95% CIs) for SCD, fatal CHD, fatal CVD, and all-cause mortality on adjustment for established risk factors were 0.37 (0.18-0.78), 0.32 (0.18-0.57), 0.45 (0.30-0.69), and 0.50 (0.38-0.64) respectively. The HRs were 1.02 (0.36-2.91), 1.43 (0.63-3.25), 1.46 (0.79-2.71), and 1.02 (0.69-1.51) respectively on further adjustment for peak VO2. Addition of VO2 at VT to a CVD mortality risk prediction model containing established risk factors significantly improved risk discrimination and reclassification at 25years.

CONCLUSIONS: There are linear and inverse associations of VO2 at VT with fatal cardiovascular and all-cause mortality events, which are dependent on peak VO2. Inclusion of VO2 at VT in the standard established risk factors panel significantly improves the prediction and classification of long-term CVD mortality risk.