Baseline characteristics
A total of 2,988 eligible participants with available baseline data were enrolled in this cohort. Through careful calculation, the missing participants did not significantly affect the major results. Our research demonstrated that all subjects were under treatment for secondary prevention. The PAD prevalence in these patients was 27.2%. The average ABI was 1.10 ± 0.12 (mean ± SD). Table 1 presented the baseline characteristics of our subjects. According to the degreeof lower extremity arterial st-enosis, from normal to borderline, moderate, and severe stenosis. ABI value was subdivided into four subgroups including 1.0-1.40, 090-0.99, 0.41–0.90, and 0-0.40. Among all variables examined, our research revealed moderate and severe stenosis subgroups had hypertension, had chronic renal insufficiency, high FRS risk stratification, higher proportion of male subjects, old enough, had MI history and PCI history, smoking state and suffered from ischemic stroke. Of note, there was no significant statistical difference on dyslipidemia, level of Cr, DBP, and CABG history. Meanwhile, in contrast with the reference group, participants were more likely to be treated with ARB.
All-cuase Mortality, CVD Mortality, and Survival Analysis of ABI Subgroups
As Table 2 represented, among 0-0.40, 0.41–0.89, 0.90–0.99, and 1.00-1.4 four subgroups, all-cause mortality were 50%, 38.1%, 23.7%, and 22.4%, respectively. CVD mortality were 33.6%, 20.2%, 13.5%, and 9.1%, respectively. After multivariable adjusted, Cox regression models revealed that compared with 1.0-1.40 subgroup, among 0-0.40, 0.41–0.90, and 0.91-1.0 subgroups, HR of all-cause mortality were 2.12, 95% CI (2.39–2.98), 2.06, 95%CI (1.35–2.90), and 1.86, 95%CI (1.54–2.89), respectively. And HR of CVD-cause mortality were 2.39, 95%CI (2.41–3.09), 2.29, 95%CI (1.83–2.87), and 2.02, 95%CI (1.73–2.81), respectively. The Kaplan–Meier curves illustrated the survival rate decreasing with lower levels after 6 years follow-up, (P < 0.001; Fig. 2). In Fig. 3, below the horizontal dotted line represents null risk. This figure indicated after multivariable adjusted, cubic spline models with nodes presented reverse J-shaped with ABI value whether all-cause mortality or CVD mortality.From the Fig. 3, there was a significant increasing tendency in all-cause mortality and CVD mortality with lower andhigher levels after 6 yearsfollow-up. (P < 0.001).
Reclassificationof Model with and without ABI for All-cause Mortality and CVD-cause Mortality
In table 3, after adding ABI to AR,for all-cause mortality and CVD-cause mortality, the NRI was 11%, 95% CI (0.09–0.19) and 12%, 95% CI (0.10–0.21), respectively. Meanwhile, for all-cause mortality and CVD-cause mortality, IDI was all 18%, 95% CI (0.07–0.23) and 95% CI (0.08–0.23), respectively.
Nomogram to Predict All-cause Mortality and CVD-cause Mortality
Nomogram was derived from Cox proportional hazard model. It assessed risk factors that might predict all-cause mortality and CVD mortality. To estimate mortality probability, first obtain and add point values foreach variable (i.e. age, ABI, BMI, TC and so on ) by connecting vertical line intercepts to the horizontal “score” bar. Theaccumulated “total score” bar then aligns with the probability axis of model. From figures 4 A and B, nomogram also demonstrated mortality of risk factors included gender, age, SBP, stroke, DM, MI history, PCI history, smoking state, CABG history, glucose, BMI, LDL-C, and ABI value. Of noted, among these risk factors, age, ABI value, BMI, LDL-C, glucose, and SBP occupied major probability weight. Especially, when ABI value was from 0.0 to 1.4, match score calculated among all-cause mortality and CVD-cause mortality was from zero to 70 and from zero to 60, respectively.
DCA Plot of Classic AR Model and Model with ABI to Predict All-cause Mortality and All-cause Mortality
DCA was clinical benefit of model plotting the net benefit versus threshold probabilities. The grey line assumed that allpatients with mortality, whereas the black line assumes none with mortality. The blue dotted line was the clinical benefit of AR model, and red dotted line was the clinical benefit of adding ABI value to AR model. DCA plot demonstrateda significant positive benefit at predicting all-cause mortality and CVD-cause mortality, at a threshold probability of 18% where the red line diverges from the blue line.