Atherosclerosis and heart disease

Atherosclerosis is the hardening and narrowing of the arteries. The process begins with damage to the endothelium, a single layer of cells that line the arteries. Once the endothelium becomes damaged, platelets and white blood cells can become caught and migrate through the wall of the artery (the intima), where they become macrophage cells and begin actively accumulating low-density lipoprotein (LDL) cholesterol. These fatty clumps and streaks (visible in the arteries of many adults by the age of 30) become lesions called plaques that obstruct blood flow through the artery and attract deposits of calcium, worsening the condition .

Risk factors for this narrowing (atherosclerosis) include high lipid levels in the blood, smoking, diet, ageing, and stress. Ageing also reduces the elasticity of the arteries, making any blockage or narrowing more difficult for the blood to flow past.

A thickening of the wall of the carotid artery (the artery in the neck that supplies the brain with blood) is a sign of atherosclerosis. This intima media thickening (IMT) has been shown to progress more rapidly in people with HIV, with HIV infection independently contributing as much risk as many other traditional risk factors.^{1,2 3 4}

Coronary artery disease results when atherosclerosis occurs in the arteries that provide blood and oxygen to the heart. This can result in chest pain or angina, which may precede a heart attack. Other factors that increase the risk of heart disease are obesity, high blood sugar levels, and lack of exercise.

High LDL cholesterol is associated with narrowing of the arteries when other risk factors such as hypertension, diabetes, obesity, and smoking are present. If triglyceride levels are also high, LDL cholesterol particles can persist longer and cause more damage to the arteries. Therefore, high triglyceride levels, while not a cardiac risk in the absence of high LDL, are an additional risk factor if LDL levels are high.

HIV infection itself may also contribute to the development of atherosclerosis by causing gaps to open up in the endothelium of blood vessels (which promotes plaque formation), as well as inducing apoptosis of endothelial cells.⁵

Elevated levels of the inflammation marker C-reactive protein (CRP) are independently associated with increased acute myocardial infarction risk, as is HIV infection itself. In one study, an elevated CRP level was associated with a more than doubled risk of subsequent heart attack and HIV infection alone was slightly less than that (OR 1.93). Not surprisingly, having both HIV and an elevated CRP raised the risk more than fourfold. Other researchers have found that elevated CRP levels also correlate with more rapid intima media thickening, which itself is a marker of increased cardiac risk.² CRP testing (which just requires a blood sample) may be another useful tool in monitoring cardiovascular risk.⁶