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The ankle-brachial index as a predictor of survival in patients with peripheral vascular disease
M M McDermott1, J Feinglass, R Slavensky
1Division of General Internal Medicine, Northwestern University Medical School, Chicago, Illinois.
Objective:
To determine whether the ankle-brachial index (ABI) predicts survival rates among patients with peripheral vascular disease.
Design:
A retrospective survival analysis of patients with abnormal ABIs who visited the authors' blood-flow laboratory during 1987. The National Death Index was used to ascertain survival status for all patients up to January 1, 1992. Kaplan-Meier and Cox proportional hazards analyses were used to determine the relationship between increasing lower-extremity ischemia, measured by ABI, and survival time. Clinical characteristics controlled for included age, smoking history, gender, and comorbidities, as well as the presence of lower-extremity rest pain, ulcer, or gangrene.
Setting:
A university hospital blood-flow laboratory.
Patients/Participants:
Four hundred twenty-two patients who had no prior history of lower-extremity vascular procedures and who had ABIs < 0.92 in 1987.
Results:
Cumulative survival probabilities at 52 months' (4.3 years') follow-up were 69% for patients who had ABIs = 0.5-0.91, 62% for patients who had ABIs = 0.31-0.49, and 47% for patients who had ABIs < or = 0.3. In multivariate Cox proportional hazard analysis, the relative hazard of death was 1.8 (95% confidence interval = 1.2-2.9, p < 0.01) for the patients who had ABIs < or = 0.3 compared with the patients who had ABIs 0.5-0.91. Other independent predictors of poorer survival included age > 65 years (p < 0.001); a diagnosis of cancer, renal failure, or chronic lung disease (p < 0.001); and congestive heart failure (p < 0.04).
Conclusion:
The ABI is a powerful tool for predicting survival in patients with peripheral vascular disease. Patients with ABIs < or = 0.3 have significantly poorer survival than do patients with ABIs 0.31-0.91. Further study is needed to determine whether aggressive coronary risk-factor modification, a work-up for undiagnosed coronary or cerebrovascular atherosclerotic disease, or aggressive therapy for known atherosclerosis can improve survival of patients with ABIs < or = 0.3.