Usefulness of Postexercise Ankle-Brachial Index to Predict All-Cause Mortality
What is the usefulness of postexercise ankle-brachial index (ABI) in predicting all-cause mortality?
This was an observational study of consecutive patients referred for ABI measurement before and after the fixed-grade treadmill or symptom-limited exercise component to a noninvasive vascular laboratory from January 1990 to December 2000. The subjects were classified into two groups. Group 1 included patients with an ABI of ≥0.85 before and after exercise, and group 2 included patients with a normal ABI at rest, but <0.85 after exercise. Survival analysis was done using Cox proportional hazard modeling, adjusted for confounding factors.
A total of 6,292 patients underwent ABI measurements with exercise during the study period. Propensity score matching of the groups was performed to minimize observational bias. Overall mortality, as determined using the United States Social Security death index, was the endpoint. The 10-year mortality rate of groups 1 and 2 was 32.7% and 41.2%, respectively. An abnormal postexercise ABI result independently predicted mortality (hazard ratio, 1.3; 95% confidence interval, 1.07-1.58; p = 0.008). Additional independent predictors of mortality were age, male gender, diabetes, and hypertension. After the exclusion of patients with a history of cardiovascular events, the predictive value of an abnormal postexercise ABI remained statistically significant (hazard ratio, 1.67; 95% confidence interval, 1.29-2.17; p < 0.0001).
The authors concluded that postexercise ABI is a powerful independent predictor of all-cause mortality and provides additional risk stratification beyond the ABI at rest.
This study suggests that the postexercise ABI might not only help in diagnosing peripheral arterial disease in more patients, but could also independently identify patients at a greater mortality risk who would have remained unidentified using conventional testing. It appears that the use of postexercise ABI testing might help identify a subgroup of patients with a normal ABI value at rest who have a coronary artery disease risk equivalent and subsequent greater mortality, in a noninvasive and cost-effective manner. These findings need to be validated in larger prospective multicenter studies, and postexercise ABI should be compared with other modalities for the early detection of atherosclerotic vascular disease such as brachial artery reactivity testing, carotid intima medial thickness, or electron-beam computed tomography.
Keywords: Coronary Artery Disease, Propensity Score, Atherosclerosis, Proportional Hazards Models, Brachial Artery, Ankle Brachial Index, Peripheral Arterial Disease, Survival Analysis, Hypertension, Peripheral Vascular Diseases, United States
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