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Ankle brachial index improved cardiovascular risk prediction
Combining ankle brachial index and the Framingham risk score may help improve treatment recommendations.
The ankle brachial index may provide experts with a convenient option for predicting cardiovascular risk.
“Based on our results, more health care professionals are now likely to consider using the ankle brachial index in cardiovascular risk prediction,” said Gerry Fowkes, PhD, professor of epidemiology and director of the Wolfson Unit for Prevention of Peripheral Vascular Diseases at the University of Edinburgh, Scotland.
Fowkes and colleagues from Scotland and other sites worldwide conducted a meta-analysis to determine the efficacy of the ankle brachial index in the prediction of cardiovascular risk, independent of the Framingham risk score. The analysis included 16 population cohort studies.
Together, the studies included 24,955 men and 23,339 women without a history of CHD. The mean age of participants was between 47 and 78 years.
Promising findings
The ankle brachial index revealed a reverse J-shaped distribution in the risk of death, with a normal (low risk) index of 1.11 to 1.40. According to the researchers, in men with a low ankle brachial index, the 10-year cardiovascular mortality was 18.7% (95% CI, 13.3% to 24.1%) and in men with a normal index, mortality was 4.4% (95% CI, 3.2% to 5.7%; HR=4.2; 95% CI, 3.3 to 5.4).
In women, 10-year cardiovascular mortality was 12.6% (95% CI, 6.2% to 19.0%) for those with low risk ankle brachial index and 4.1% (95% CI, 2.2% to 6.1%; HR=3.5; 95% CI, 2.4 to 5.1) for those with normal risk.
Despite adjusting for the Framingham risk score, hazard ratios remained elevated (2.9 for men [95% CI, 2.3 to 3.7] vs. 3.0 for women [95% CI, 2.0 to 4.4]), according to the study.
“Our most important finding was that, independently of the Framingham Risk Score, individuals with a low ankle brachial index had a two- to three-fold increase in cardiovascular events and mortality, compared with those with a normal ankle brachial index,” Fowkes told Endocrine Today.
Compared with the overall rates of 10-year total mortality, cardiovascular mortality and major coronary events over the range of Framingham risk categories without ankle brachial index included, a low ankle brachial index (0.90 or less) was related to a largely increased risk of mortality and major coronary events in both men and women across all Framingham risk score categories, according to the study.
Women in the lowest Framingham risk score category had especially high rates of mortality and both men and women with an ankle brachial index between 0.91 and 1.10 had higher morality and event rates, compared with those with normal ankle brachial index. However, the level of increase was less for those with an ankle brachial index of 0.90 or lower. Mortality and event rates were also higher across most Framingham risk score categories in participants with an ankle brachial index greater than 1.40.
Improving risk prediction
“This information is important for health care professionals involved in the primary prevention of CVD because it shows that the ankle brachial index may have a role in more accurately assessing an individual’s future risk,” Fowkes said.
When incorporating the use of ankle brachial index with the Framingham risk score, the researchers observed an effect on the prediction of events, particularly in women. The receiver operating characteristic curve, when using only the Framingham risk score to predict major coronary events, was 0.646 (95% CI, 0.643 to 0.657). With the addition of ankle brachial index, the curve was 0.655 (95% CI, 0.643 to 0.666) in men. In women, the curve was 0.605 for Framingham risk score (95% CI, 0.590 to 0.619) and 0.658 after the addition of ankle brachial index (95% CI, 0.644 to 0.672).
“The ankle brachial index when used with the Framingham Risk Score can improve cardiovascular risk prediction. However, the development of a new risk score incorporating the ankle brachial index is warranted,” he said. – by Stacey L. Adams
For more information:
- JAMA. 2008;300:197-208.