Risk factors for amputation are influenced by competing risk of death in patients with critical limb ischemia

Eva Torbjörnsson; Lena Blomgren; Ann-Mari Fagerdahl; Lennart Boström; Carin Ottosson; Jonas Malmstedt

doi:10.1016/j.jvs.2019.07.074

Risk factors for amputation are influenced by competing risk of death in patients with critical limb ischemia

J Vasc Surg. 2020 Apr;71(4):1305-1314.e5. doi: 10.1016/j.jvs.2019.07.074. Epub 2019 Nov 6.

Authors

Eva Torbjörnsson¹, Lena Blomgren², Ann-Mari Fagerdahl³, Lennart Boström¹, Carin Ottosson³, Jonas Malmstedt⁴

Affiliations

¹ Department of Clinical Science and Education, Karolinska Institutet, Stockholm, Sweden; Division of Vascular Surgery, Department of Surgery, Södersjukhuset AB, Stockholm, Sweden.
² Department of Cardiothoracic and Vascular Surgery, Faculty of Medicine and Health, Örebro University Hospital, Örebro, Sweden.
³ Department of Clinical Science and Education, Karolinska Institutet, Stockholm, Sweden; Wound Centre, Södersjukhuset AB, Stockholm, Sweden.
⁴ Department of Clinical Science and Education, Karolinska Institutet, Stockholm, Sweden; Division of Vascular Surgery, Department of Surgery, Södersjukhuset AB, Stockholm, Sweden. Electronic address: jonas.malmstedt@sll.se.

PMID: 31706801
DOI: 10.1016/j.jvs.2019.07.074

Abstract

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.

Keywords: Competing risk analysis; Critical limb ischemia; Major amputation.

MeSH terms

Aged
Amputation, Surgical*
Female
Humans
Ischemia / mortality
Ischemia / surgery*
Limb Salvage
Lower Extremity / blood supply*
Male
Peripheral Arterial Disease / mortality
Peripheral Arterial Disease / surgery*
Registries
Retrospective Studies
Risk Factors
Sweden