Developing physical Activity and Sedentary behaviour thresholds for the Secondary prevention of Heart disease (DASSH): a cohort mortality survival tree analysis

Background: The dose–response relationship between physical activity and sedentary behaviour (SB) with mortality in people with coronary heart disease (CHD) is unclear. The aim was to identify moderate-to-vigorous physical activity (MVPA) and SB thresholds for mortality risk. Methods: This prospective cohort study comprised Australian participants aged ≥ 45 years with self-reported CHD (2006–2020). Self-reported MVPA (min/wk) and SB (hr/day) were the exposures. Cardiac and all-cause mortality were the main outcomes. Survival regression trees identified MVPA and SB thresholds influencing mortality survival rate. Cox regression models and the C-statistic were used to examine the thresholds, comparing them to public health guidelines. Results: The cohort included 40,156 participants (mean (SD) age, 70.3(10.3) years; 15,278 females (38%)). During a median follow-up of 11.1 (IQR,6.2–14.4) years, 2,497 cardiac and 12,240 all-cause deaths were recorded. The threshold for MVPA and all-cause and cardiac mortality was ≥ 146 min/wk and ≥ 96 min/wk, respectively. For SB, the threshold for mortality was < 5–6 h/day. Sex-specific differences in thresholds for MVPA and SB were found. All MVPA and SB thresholds had equivalent associated risk reductions and predictive abilities for cardiac and all-cause mortality to the public health guidelines. Conclusion: The newly identified thresholds suggest that the public health physical activity guidelines are suitable for reducing risks of all-cause mortality in people with CHD. For reducing risks of cardiac mortality, the threshold is suggested to be much lower. The SB suggested thresholds for reducing risks of mortality are 5–6 h/day. Further research is required to explore these thresholds and sex-specific differences.