Noninvasive radioactive tracer may predict risk for MI

Use of radioactive tracer 18F-sodium fluoride during combined PET and CT may be an effective, noninvasive method of identifying ruptured and high-risk coronary plaques.

In a prospective study, 40 patients with MI and 40 with stable angina underwent combined PET and CT with radioactive tracers 18F-sodium fluoride and 18F-fluorodeoxyglucose, and invasive coronary angiography. All of the patients were older than 50 years and were recruited from the Royal Infirmary of Edinburgh between February 2012 and January 2013.

The 18F-sodium fluoride tissue-to-background ratios of culprit plaques were compared with nonculprit plaques among patients with acute MI. In patients with MI, 18F-sodium fluoride uptake was compared with histology in carotid endartectomy specimens from patients with symptomatic carotid disease. In patients with angina, uptake in those with stable angina was compared with results from IVUS.

Culprit plaque was associated with the highest 18F-sodium fluoride uptake in 93% of patients with MI, with a median maximum tissue-to-background ratio of 1.66 (interquartile range [IQR]=1.4-2.25) compared with the highest nonculprit ratio of 1.24 (1.06-1.38; P<.0001). No significant difference in 18F-fluorodeoxyglucose uptake was observed between culprit and nonculprit plaques (IQR=1.71; 95% CI, 1.4-2.13 vs. IQR=1.58; 95% CI, 1.28-2.01). Investigators noted that uptake of this tracer was frequently obscured by myocardial uptake.

Substantial 18F-sodium fluoride uptake was observed at the site of all carotid plaque ruptures. This uptake was significantly associated with signs of calcification activity and cell death.

Among patients with stable angina, 45% had plaques with focal 18F-sodium fluoride uptake, with a maximum tissue-to-background ratio of 1.9 (IQR=1.61-2.17) compared with 1.02 (IQR=0.82-1.17) in those with no uptake. Plaques with 18F-sodium fluoride uptake were significantly more likely than those with no uptake to have positive remodeling (P=.0004), microcalcification (P=.002) and necrotic core (P=.001) on IVUS.

“Until now, there have been no noninvasive imaging techniques available which can identify high-risk and ruptured coronary plaques in patients with heart disease,” Nikhil Joshi, MD, of the British Heart Foundation Centre for Cardiovascular Science in Edinburgh, United Kingdom, said in a press release. “For the first time, we have shown that this is possible, and given the ability of this new, noninvasive imaging technique to identify high-risk or ruptured coronary plaques, it has the potential to transform how we identify, manage and treat patients with stable and unstable heart disease.”

In a related editorial, Gregory S. Thomas, MD, MPH, and Reka A. Haraszti, MD, from Long Beach Memorial Medical Center, Long Beach, Calif., and University of California in Irvine, wrote that the use of 18F-sodium fluoride is promising for patients with MI and ACS, and the best way to use information collected via 18F-sodium fluoride and 18F-fluorodeoxyglucose must be determined.

“How do Joshi and colleagues’ findings apply to women, in whom plaque erosion is a much more common mechanism of MI than in men?” Thomas and Haraszti wrote. “How do the findings apply to patients with diabetes? Does coronary artery bypass graft biology differ with respect to [18F-sodium fluoride] activity? … Joshi and colleagues and earlier pioneers have identified a new and hopefully fruitful frontier in nuclear cardiology and atherosclerotic imaging.”

For more information:

Joshi NV. Lancet. 2013;doi:10.1016/S0140-6736(13)61754-7.

Thomas GS. Lancet. 2013;doi:10.1016/S0140-6736(13)61911-X.

Disclosure: See the study for a list of the researchers’ relevant financial disclosures.