Simple, cheap test an accurate measure of hardening of the arteries in patients with HIV

A simple and cheap test to measure hardening of the arteries appears to be effective in HIV-positive patients, according to a study published in the July 11^th edition of AIDS. Investigators in Spain found that a low ankle-brachial index (ABI) in patients with HIV was correlated with carotid intima-media thickness (IMT), a traditional measure of hardening of the arteries, or atherosclerosis.

Cardiovascular disease is a growing concern for patients taking anti-HIV treatment. Unfortunately many patients only have cardiovascular disease diagnosed when they have already developed symptoms and have developed hardening of the arteries.

A standard test to check for hardening of the arteries is an IMT ultrasound. But these tests are expensive and are not always available. But an alternative test is an ABI. This involves placing a blood pressure cuff around the arm and ankle. It is simple and inexpensive, and results of IMT and ABI tests in HIV-negative patients have been shown to be correlated.

However, tests showing that ABI is a reliable measure of hardening of the arteries have generally been performed in older patients with a high prevalence of diabetes. Investigators were concerned that HIV-positive patients at risk of hardening of the arteries tend to be younger and have a lower prevalence of diabetes. Furthermore, studies measuring hardening of the arteries in patients with HIV using ABI have yielded conflicting results (see here and here).

They therefore conducted a study involving 139 HIV-positive patients. They had both ABI and IMT tests to see if the results were equal predictors of hardening of the arteries in patients with HIV. The study was conducted between early 2006 and late 2007.

The mean age of the patients was 46 years, 73% were men, 79% were taking antiretroviral therapy, 58% had a viral load below 50 copies/ml and mean CD4 cell count was 502 cells/mm³.

There was a high prevalence of risk factors for cardiovascular disease in the study population, with 61% being smokers, 29% having high blood pressure, 11% having a family history of heart disease and 22% experiencing body fat changes associated with antiretroviral therapy. Overall, 46% of patients had three or more risk factors for heart disease. A moderate Framingham risk score (an accepted measure of the risk of cardiovascular disease) was present in 17% of patients, with 18% having a high Framingham score.

Just over a fifth of patients (22%) had carotid IMT greater than 0.8mm, suggestive of hardening of the arteries. This was associated with older age, high blood pressure, and a high Framingham score (all p < 0.001).

Further multivariate analysis showed that a low ABI score (below 0.90), high blood pressure, and age were all independently associated with IMT above 0.8mm (all p < 0.001). When the investigators restricted their analysis to patients with two or more risk factors for cardiovascular disease, they found that a low ABI score, smoking, and age were all predictors of IMT (p < 0.001).

An ABI score below 0.90 had been shown in earlier studies to be associated with increased IMT.

All the patients in the current study with ABI above 0.90 were men, and their IMT was significantly higher (0.95 vs. 0.66mm, p = 0.005) than that seen in patients with normal ABI. These patients also had more traditional risk factors for heart disease (four vs. two, p = 0.015), and had lower CD4 cell counts (220 cells/mm³ vs. 450 cells/mm³, p = 0.009) than patients with normal ABI.

High ABI (above 1.40) has also been associated with greater IMT thickness in older HIV-negative patients. But this was not the case in this study.

“We found that patients with a low ABI, according to the accepted cut-off point value for [the] general population, had a high carotid IMT, suggesting that, in HIV-infected patients, this value may be a surrogate marker of subclinical atherosclerosis”, comment the investigators.