A low CD4 cell count is associated with an increased risk of heart attack for patients with HIV, US investigators report in the online edition of the Journal of Acquired Immune Deficiency Syndromes. Even after taking into account traditional risk factors for cardiovascular disease, a CD4 cell count under 200 cells/mm3 was associated with a significantly increased risk of incident heart attack.
“Our data reinforce the emerging hypothesis that treatment of HIV infection decreases the risk of cardiovascular disease”, write the investigators.
High of rates of cardiovascular disease are seen in patients with HIV. A number of reasons have been suggested for this including a high prevalence of traditional risk factors such as smoking, the side-effects of HIV treatment, and the inflammatory effects of infection with the virus.
The large SMART treatment interruption study showed that a CD4 cell count below 350 cells/mm3 was associated with an increased risk of cardiovascular disease, and patients with traditional risk factors for such illnesses are especially encouraged to start HIV treatment before their CD4 cell count falls to this level. However, other research has yielded inconsistent findings about the relationship between CD4 cell count and heart attack risk.
Therefore, researchers in Boston wished to gain a firmer understanding of the relationship between CD4 cell count and viral load and heart attack risk.
They analysed heart attack rates in 6517 HIV-positive patients who received care between 1998 and 2008. Analyses were conducted to see if CD4 cell count and viral load were associated with an increased risk of heart attack, independent of traditional risk factors and the use of HIV treatment.
A total of 273 patients (4%) experienced a heart attack. These were older than those who did not have a heart attack (54 vs. 46), and more likely to high blood pressure (57% vs. 25%), diabetes (28% vs. 16%), high lipids (33% vs. 29%), smoking (55% vs. 50%), kidney disease (14% vs. 7%), and a history of coronary heart disease (35% vs. 9%) – all traditional risk factors for heart disease.
In addition, those who had a heart attack were more likely to have a CD4 cell count below 200 cells/mm3 (41% vs. 25%), or a viral load above 100,000 copies/ml (20% vs. 10%).
The investigators’ first set of statistical analysis showed that a CD4 cell count below 200 cells/mm3 doubled the risk of heart attack (OR, 2.00; 95% CI, 1.48-2.71, p < 0.0001). A viral load above 100,000 copies/ml was also associated with a significant increase in the risk of heart attack (OR, 2.23; 95% CI, 1.37-3.65, p = 0.001).
By contrast, a viral load below 400 copies/ml was associated with a 44% reduction in the risk of heart attack (p = 0.003).
The investigators repeated their analysis, this time controlling for traditional risk factors.
A CD4 cell count below 200 cells/mm3 remained significant (OR, 1.74%; 95% CI, 1.07-2.81, p = 0.02). In addition, the investigators found that each 50 cell/mm3 increase in CD4 cell count significantly reduced the risk of heart attack (p = 0.002).
However, the significant relationship between viral load and heart attack risk disappeared.
But further analysis that took into account traditional risk factors for heart attack, but excluded CD4 cell count, showed that a viral load above 100,000 copies/ml was associated with a significant increase in heart attack risk (OR, 2.16; 95% CI, 1.26-3.69, p = 0.01), and a viral load below 400 copies/ml was protective against the risk of a heart attack (p = 0.02).
“We demonstrate that decreased CD4 cell count is significantly associated with an increased risk of myocardial infarction and is second only to hypertension in terms of its effect size as a risk factor”, comment the investigators. They add that a CD4 cell count below 200 cells/mm3 was a much more important risk factor for heart attack than treatment with any antiretroviral drug. Indeed, the investigators failed to find a significant relationship between any antiretroviral and an increased risk of heart attack.
They conclude, “treatment of HIV infection to improve immunological function is likely to be an important component of cardiovascular prevention for patients with HIV.”
Triant VA et al. Association of immunologic and virologic factors with myocardial infarction rates in a US healthcare system. J Acquir Immune Defic Syndr, online edition, 2010 (for free abstract and paid-for full-text click here).