乌鸦传媒

EDINBURGH, Scotland, July 8 -- Taking the ankle brachial index into account may improve the accuracy of Framingham cardiovascular risk prediction, a meta-analysis found.

Inclusion of the index in the Framingham risk score would reclassify the risk category and modify treatment recommendations for about 19% of men and 36% of women, Gerry Fowkes, Ph.D., of the University of Edinburgh, and colleagues reported in the July 9 issue of the Journal of the American Medical Association.

The ankle brachial index, a quick and easy measure using a Doppler, is commonly used in vascular practice to assess atherosclerosis and the severity of peripheral artery disease, the investigators said.

It is calculated by dividing the lower measure of systolic blood pressure in the posterior tibial or the dorsalis pedis artery in the ankle by the brachial systolic pressure in the arm.

The accurate identification of those at risk for major cardiovascular or cerebrovascular events remains a serious public health challenge, the researchers wrote.

Although the Framingham risk score is often considered the reference standard, its accuracy is limited, tending to overestimate risk in low-risk populations and underestimate risk in high-risk groups, they said.

Because the ankle brachial index has been related to an increased incidence of mortality, myocardial infarction, and stroke, the researchers wanted to determine whether the index provides predictive information on cardiovascular risk independent of Framingham scores.

So they conducted an individual participant data meta-analysis that included 16 studies identified from a search of MEDLINE (1950 to February 2008), Embase (1980 to February 2008) and other sources.

During 480,325 person-years of follow-up of 24,955 men and 23,339 women, the risk of death according to the index had a reverse J-shaped distribution with a normal (low risk) index of 1.11 to 1.40.

The 10-year cardiovascular mortality in men with a low index (≤ 0.90) was 18.7% (95% confidence interval 13.3% to 24.1%).

With a normal index (1.11 to 1.40), it was 4.4% (95% CI 3.2 to 5.7%), amounting to about a four times greater risk of cardiovascular disease for men with a low index (HR 4.2, 95% CI 3.3 to 5.4).

Corresponding mortalities in women were 12.6% (95% CI 6.2% to 19%) and 4.1% (95% CI 2.2% to 6.1%) (HR 3.5, 95% CI 2.4 to 5.1).

The risks remained elevated after adjusting for the Framingham score (2.9 for men and 3.0 for women).

A low index (0.90 or less) was associated with approximately

twice the 10-year total mortality, cardiovascular mortality, and major coronary event rate compared with the overall rate in each Framingham risk category.

Inclusion of the ankle brachial index in cardiovascular risk stratification using the Framingham score would result in reclassification of the risk category and modification of treatment recommendations for approximately 19% of men (4,106 of 21,433) and 36% of women (8,154 of 22,486), the researchers said.

In predicting the 10-year risk of total cardiovascular heart disease, these results indicate that approximately one in five men would have their broad category of risk reduced from that predicted by the Framingham score alone to that found with inclusion of the ankle brachial index.

These changes from higher to lower categories of risk would likely affect decisions to start preventive treatment, such as lipid-lowering therapy.

In contrast, the main effect for women would be that one in three women would change from low risk according to the Framingham score alone (less than 10%) to a higher risk level.

The researchers cautioned that the proportion of individuals affected by inclusion of the index is approximate because of the methods of estimating cardiovascular heart disease and possible confounding within the Framingham categories.

The ankle brachial index is a potentially useful tool for prediction of cardiovascular risk, the researchers said. In contrast to measurement of coronary artery calcium and carotid intima-media thickness, it is easy to use in the primary care physician's office and in community settings, they wrote.

The equipment is inexpensive (a hand-held Doppler costs less than $600), the procedure takes less than 10 to 15 minutes, and it can be done by a suitably trained nurse or other healthcare professional.

The results of this study indicate that when using the Framingham risk score, adding the ankle brachial index may be justified to improve risk prediction and advice on ways to reduce that risk, the researchers said.

A new risk equation incorporating the index and relevant Framingham risk variables could more accurately predict risk, and "our intention is to develop and validate such a model in our combined data set," the authors concluded.

Sanofi-aventis/BMS provided an unrestricted educational grant for data processing and initial statistical analysis. The Framingham Offspring Study is supported by a National Institutes of Health grant. The inCHIANTI and Women's Health and Aging studies are supported by the Intramural Research Program, National Institute on Aging, National Institutes of Health. Dr. Fowkes reported receiving honoraria and consulting fees from sanofi-aventis/BMS for purposes other than this research.

Comment