Dose-response association of implantable device-measured physical activity with long-term cardiac death and all-cause mortality in patients at high risk of sudden cardiac death: a cohort study

Background Cardiovascular implantable electronic devices (CIEDs) with physical activity (PA) recording function can continuously and automatically collect patients' long-term PA data. The dose-response association of implantable cardioverter-defibrillator (ICD) and cardiac resynchronization therapy defibrillator (CRTD)-measured PA with cardiovascular outcomes in patients at high risk of sudden cardiac death (SCD) was investigated. Methods In total, 822 patients fulfilling the inclusion criteria were included and divided into three groups according to baseline PA tertiles: tertile 1 (< 8.04%,n = 274), tertile 2 (8.04-13.24%, n = 274), and tertile 3 (> 13.24%, n = 274). The primary endpoint was cardiac death, the secondary endpoint was all-cause mortality. Results During a mean follow-up of 59.7 +/- 22.4 months, cardiac death (18.6% vs 8.8% vs 5.5%, tertiles 1-3,P < 0.001) and all-cause mortality (39.4% vs 20.4% vs 9.9%, tertiles 1-3,P < 0.001) events decreased according to PA tertiles. Compared with patients younger than 60 years old, older patients had a lower average PA level (9.6% vs 12.8%,P < 0.001) but higher rates of cardiac death (13.2% vs 8.1%,P = 0.024) and all-cause mortality (28.4% vs 16.7%,P < 0.001) events. Adjusted multivariate Cox regression analyses showed that a higher tertile of PA was associated with a lower risk of cardiac death (hazard ratio (HR) 0.41, 95% confidence interval (CI): 0.25-0.68, tertile 2 vs tertile 1; HR 0.28, 95% CI: 0.15-0.51, tertile 3 vs tertile 1,P-trend < 0.001). Similar results were observed for all-cause mortality. The dose-response curve showed an inverse non-linear pattern, and a significant reduction in endpoint risk was observed at the low-moderate PA level. The HR for cardiac death was reduced by half with 12.32% PA (177 min), and the HR for all-cause mortality was reduced by half with 11.92% PA (172 min). Subgroup analysis results indicated that older adults could benefit from PA and the range for achieving optimal benefits might be lower. Conclusions PA monitoring may aid in long-term management of patients at high risk of SCD. More PA will generate better survival benefits, but even low-moderate PA is already good especially for older adults, which is relatively easy to achieve.