Incremental Prognostic Value of Ankle-Brachial Index in High Atherosclerosis Risk Patients: Prediction model assessment on ABILITIES Study

Background: Previous studies have demonstrated association between ankle–brachial index (ABI) and cardiovascular disease (CVD), and confirmed patients with high atherosclerotic risk (AR) had worse prognosis. But after controlling traditional risks, the prognostic value of ABI with all-cause mortality and CVD-cause mortality remains unclarified, especially lack of prediction model assessment. Methods 2988 valid participants were separated into 0-0.40, 0.41–0.89, 0.90–0.99, and 1.00-1.40 four ABI subgroups, and followed up by six year. Factors related to all-cause mortality and CVD-cause mortality were observed by multivariate Cox regression analysis, log-rank test and nomogram. Restricted cubic splines (RCS) were used to explore relationship with ABI and mortality. Incremental discrimination was evaluated by net reclassification index (NRI), integrated discrimination improvement (IDI), and decision curve analysis (DCA). Results RCS and Kaplan–Meier survival curve all manifested abnormal ABI levels increased mortality. Compare with normal value, among 0-0.40 and 0.41–0.89 subgroup, adjusted HR of all-cause mortality was 2.12, 95% CI (1.63–3.17), and 2.06, 95% CI (1.35–2.90), respectively. HR of CVD-cuase mortality was 2.39, 95% CI (2.41–3.09), and 2.29, 95% CI (1.83–2.87), respectively. RCS presented reverse J-shaped relationship with ABI and mortality. Nomogram indicated ABI as a strong risk, occupied the second weight. Adding ABI to traditional AR model, NRI, IDI, and DCA was 0.11, 0.12, and 0.18, respectively. Conclusion Combining ABI with traditional AR can improve all-cause mortality and CVD mortality prediction. Routine ABI evaluation and intensive intervention were pressing needed, especially in high AR patients.