Predicting heart attack risk

CORONARY plaques are blockages that cause narrowing and hardening of the heart’s blood vessels, often causing angina (chest pain). When plaques rupture, they can lead to blood clot formation, which blocks off the blood supply to the heart or the brain, resulting in a heart attack or a stroke. Why plaques rupture is not known, but if doctors could accurately identify when plaques are about to rupture, patients could be managed and treated accordingly, potentially preventing substantial numbers of heart attacks and other serious coronary events.

A team of researchers led by Nikhil Joshi, at the British Heart Foundation Centre for Cardiovascular Science in Edinburgh, U.K., investigated the use of two radioactive tracers, 18F-sodium fluoride (NaF) and 18F-fluorodeoxyglucose (18F-FDG). These simple and relatively inexpensive tracers are injected into patients’ veins, and then the patients undergo a PET-CT (positron emission tomography-computed tomography) scan that is commonly used in cancer diagnosis. Earlier research had suggested that 18F-NaF and 18F-FDG might be able help doctors identify characteristic features in the hearts of patients at high risk for serious coronary events, but this was the first systematic investigation into whether they could be used in this way.

Joshi and colleagues investigated 18F-NaF and 18F-FDG in 40 patients who had recently had a heart attack (myocardial infarction) and in another 40 patients who had stable angina. In nearly all (37, or 93 per cent) of the heart attack patients, the highest coronary uptake of 18F-NaF (as revealed by the PET-CT scan) was seen in the area of the recently ruptured plaque that had led to the heart attack. 18F-FDG did not exhibit the same effect, with no significant difference in uptake between “innocent” and “culprit” plaques. In the group of patients with angina, the researchers identified increased uptake of 18F-NaF in the plaques of nearly half (18, or 45 per cent) of the patients. More detailed and invasive intravascular ultrasound imaging confirmed that the areas of increased 18F-NaF uptake were associated in most cases with the high-risk features that often lead to rupture and serious coronary events.

“Until now,” Joshi was quoted as saying, “there have been no non-invasive imaging techniques available which can identify high-risk and ruptured coronary plaques in patients with heart disease. For the first time, we have shown that this is possible.”