To Örebro University

OBJECTIVE: Patients with critical limb ischemia (CLI) have a high risk of amputation and death. Death is a competing risk that affects the estimated amputation risk. Our aim was to find the specific risk factors for amputation for patients with CLI using competing risk analyses and compared these results with those from standard Cox regression analysis.

METHODS: Patients who had undergone revascularization for CLI (2009-2013, with follow-up data until 2017) in Stockholm were identified from the Swedish National Registry for Vascular Surgery. The main outcome was major amputation. The risk factors for amputation were assessed using competing risk analysis and compared with the risk factors for amputation-free survival identified using Cox proportional hazards regression analysis.

RESULTS: Of 855 patients with CLI, 178 had required a major amputation and 415 had died during the 8-year follow-up period. In the competing risk regression, age (subdistribution hazard ratio [sub-HR], 0.98; 95% confidence interval [CI], 0.97-1.00), ambulatory status (independent vs bedridden; sub-HR, 4.10; 95% CI, 2.14-7.86), and ischemic wound vs rest pain (sub-HR, 3.03; 95% CI, 1.72-5.36) were associated with amputation, considering death as a competing risk. In contrast, Cox regression analysis identified female vs male (hazard ratio [HR], 0.77; 95% CI, 0.64-0.94), age (HR, 1.02; 95% CI, 1.01-1.03), renal impairment (HR, 2.08; 95% CI, 1.61-2.67), ambulatory status (independent vs bedridden; HR, 3.45; 95% CI, 2.30-5.18), and ischemic wound vs rest pain (HR, 2.41; 95% CI, 1.78-3.25) as risk factors.

CONCLUSIONS: The risk factors associated with amputation differed when analyzing the data using competing risk regression vs Cox regression. The differences between the analyses indicated that a risk exists for biased estimates using standard survival methods when a strong competing risk such as death is present.