用FDG PET/CT區別implanted device infections

FDG PET/CT Can Identify Infections Around Implanted Device

Reed Miller

April 23, 2012 (Quebec City, Quebec City) — Combined fluorodeoxyglucose marked by fluorine-18 (¹⁸F-FDG) positron-emission tomography (PET) and computed tomography (CT) distinguish between an active infection around a cardiovascular implantable electronic device and normal postoperative inflammation, a new study in the May 1, 2012 issue of the Journal of the American College of Cardiology shows [1].

It's always difficult to know for sure if there's infection when there's local inflammation, Dr Jean-Francois Sarrazin (Institut universitaire de cardiologie et pneumologie de Quebec, Quebec City) told heartwire. And if it is infected, it is not certain whether it's deeply infected, in which case the physician may need to remove everything, or if the infection is superficial and the site can be treated with antibiotics. Lead extraction is associated with significant morbidity (1.5% to 2% complication rate) and a mortality rate of about 0.8%, so accurately identifying patients whose only good option is lead extraction could prevent many complications and save the costs associated with extraction and device replacement, Sarrazin said. "Another difficult situation is when people get bacteremia and they have a device. Is the device infected? Is that the cause of infection?"

The value of ¹⁸F-FDG-PET/CT is already established in oncology for cancer diagnosis and staging and in cardiology to assess myocardial viability because it allows 3-D measurement of metabolic activity within an organ by measuring disintegration of the injected ¹⁸F-FDG, according to Sarrazin and colleagues. A few case reports and small studies suggest that ¹⁸F-FDG PET/CT can help diagnose device infections by highlighting cells with higher metabolic activity, so the authors expect this technique may show the extent of an infection to allow the physician to determine whether device extraction is worth the risks.

The study included three patient groups. Group A included 42 patients with suspected device infection based on normal symptoms of an infection. To compare the ¹⁸F-FDG PET/CT images of infection in that group with that of normal postimplant inflammation, Group B included 12 patients without signs of infection who had received a device within the past four to eight weeks, and Group C included 12 patients without signs of infection who received their devices at least six months prior to thoracic ¹⁸F-FDG PET/CT imaging for some other indication.

In Group A, all patients underwent ¹⁸F-FDG PET/CT for risk stratification, and 22 patients also had a transesophageal echocardiogram (TEE). The most common presenting symptom was local wound infection (n=16), followed by erosion of the pocket caused by the device (n=13), bacteremia (n=10), fever of unknown origin (n=1), local persistent swelling (n=1), and chronic wound discomfort (n=1). Eight patients without local signs of device infection showed signs of infective endocarditis. In Group A, 24 patients underwent extraction and 18 patients were treated with antibiotics only. After complete evaluation, 35 patients were confirmed to have device-related infections. Of the remaining seven patients, five patients were treated successfully for an infection unrelated to the cardiac device, one patient with a fever was finally diagnosed with reactive arthritis, and one patient previously treated for superficial infection followed by chronic local discomfort had no evidence of recurrent infection.

In Group B, patients showed mild uptake of the ¹⁸F-FDG seen at the level of the device connector, indicating inflammation. There was no such abnormal uptake in Group C.

The difference in the images between the infected and noninfected patients shows that this PET/CT method can distinguish between postoperative inflammation and active infection. Further, the patients with no ¹⁸F-FDG uptake despite some symptoms of infection had a good outcome with antibiotic therapy alone, suggesting that ¹⁸F-FDG PET/CT could help risk-stratify these patients and guide their treatment.

Counting the Cost

Sarrazin told heartwire said that his institution is now routinely using ¹⁸F-FDG-PET/CT to identify device infection, but he expects future research to better clarify the patient population for which ¹⁸F-FDG-PET/CT imaging of possible device infection is cost-effective. "People don't like to do extraction because of the risk of rupture and perforation, and people can die as well. So if you can validate that it's really infected, it may save costs, because if you do the extraction and have to reimplant, it can be very expensive."

Sarrazin's group is currently studying ¹⁸F-FDG-PET/CT in patients with no definitive sign of local infection but with infection in their bloodstream and some signs of possible vegetation around the device leads. "Most people would say that you should take out the device from those patients," he said. But studies show that what appears to be infection vegetation on TEEs are often clots, fibrin, or other inflammatory tissue that isn't infected. If the false-negative rate of the ¹⁸F-FDG-PET test is not unacceptably high, this method may be able to pick out patients in this group that do not require immediate extraction and can instead be safely treated more conservatively, he said.

In an accompanying editorial [2], Dr Jeffrey Brinker (Johns Hopkins University, Baltimore, MD) writes that the evidence supporting routine ¹⁸F-FDG-PET/T imaging of suspected implanted device infection is "encouraging," but "wider experience is needed before such a recommendation can be made.

"The scan is relatively expensive (at least three times that of a TEE at my institution), and it exposes the patient to radiation, which admittedly is modest considering the importance of establishing a diagnosis. While its use at this time is justified in diagnostic dilemmas, a better appreciation of the incidence of false-negative and false-positive scans as well as the possible causes of such would be necessary before it is widely embraced."

Subcutaneous ICD Designed to Prevent Device Infections

On April 26, FDA's Circulatory System Devices Panel will review Cameron Health's premarket approval application for the S-ICD, a completely subcutaneous implantable defibrillator that does not require an electrode to be placed either on or in the heart and, unlike most ICD systems, does not require leads to be passed through the venous system. As reported by heartwire, an advantage of the S-ICD touted by Cameron is its lack of a transvenous pathway by which microorganisms can reach the endocardium.

In the 321-patient pivotal trial supporting Cameron's application, there were 18 total infections reported, four of which were system infections requiring explant. The rest were superficial. Overall, over 97% of patients in the trial were complication-free at 180 days postimplant, which easily met the prespecified safety performance goal for the trial of a 79% complication-free rate.

All authors have reported that they have no relationships relevant to this paper to disclose.

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References

1. Sarrazin JF, Philippon F, Tessier M, et al. Usefulness of fluorine-18 positron emission tomography/computed tomography for identification of cardiovascular implantable electronic device infections. J Am Coll Cardiol 2012; 59:1616–25.
2. Brinker J. Imaging for infected cardiac implantable electronic devices: A new trick for your Pet. J Am Cardiol 2012: 59:1626-1628.