PET/CT imaging can help distinguish between active infection of a cardiac electronic device and normal residual post-implant inflammation, a small study found.

In 42 patients with suspected device infection, PET/CT was positive for 32, with only one of these being a false positive, reported Jean-François Sarrazin, MD, from the Institut Universitaire de Cardiologie et de Pneumologie in Quebec, and colleagues.

In a control group of 12 patients whose devices had been implanted for longer than 6 months and who were imaged for other reasons, the PET/CT scans showed no abnormal uptake of the radiotracer around the implanted devices, according to the study published in the May 1 edition of the Journal of the American College of Cardiology.

Although PET/CT imaging with the tracer FDG is validated for cancer imaging, myocardial viability, and detection of infection in orthopedic prostheses, the data are limited regarding its use for distinguishing infection in cardiovascular implantable electronic devices.

Sarrazin and colleagues noted that PET/CT could help “determine the systemic extension of the infectious process, and justify an invasive procedure.”

For the study, they evaluated a group of 42 patients (28 men, mean age 62) who were suspected of infection. The mean time since implant was 11 months.

The researchers defined infection by the presence of at least one of the following: pocket infection (26), device erosion (six), lead endocarditis (seven), and persistent or recurrent bacteremia in the absence of another identifiable source (three).

The researchers also imaged a second group of 12 controls (11 men, mean age 65) whose devices had been implanted between 4 and 8 weeks prior. They wanted to get a sense of background residual inflammation at this more acute phase.

The third group to undergo PET/CT imaging was another control group of 12 patients (nine men, mean age 70) whose devices had been implanted a mean 24 months prior and who underwent scanning for other indications such as lung nodules.

The electronic devices included pacemakers and defibrillators, with some biventricular devices.

In the group suspected of device infection, PET/CT scans were positive for 32 of the 42. Sarrazin and colleagues pointed out that abnormal FDG uptake was seen around the generators in 18 patients, over the leads in 18, in the superficial skin tissue in 13 (six of which had no direct contact with the generator or leads), in the subcutaneous tissue in 13, and within the heart in two.

For 24 of the patients, the devices were extracted with excellent correlation between the FDG uptake and localization of infection, the researchers said. They saw clinical resolution in six of the remaining seven patients who were treated as having superficial infection. “One patient with positive PET/CT but negative leukocyte scan was considered false positive due to Dacron pouch,” which surrounds the device and is used to help mitigate movement.

The 10 patients with negative PET/CT scans were treated with antibiotics. None of them had relapsed at a mean of 12 months. Overall, 35 patients had confirmed infections associated with the electronic devices.

The acute phase controls exhibited no or mild uptake, and only at the level of the connector, while those with other indications for imaging had no FDG uptake associated with their devices.

The sensitivity and specificity of PET/CT was 88% and 85%, respectively.

Sarrazin and colleagues said that a positive PET scan combined with the CT anatomic distribution information “had a significant impact on the final management of these patients.”

Conversely, a negative scan also had an effect on patient management as it allowed conservative treatment with antibiotics, they added.

The authors cautioned that they did not evaluate PET/CT’s sensitivity and specificity within the first month post-implant, but said it is likely lower. They also said that a longer follow-up is needed to determine the incidence of late infection recurrence.

They also noted that the cost-effectiveness of this approach has not been evaluated. However, if a PET/CT scan (cost $2,500 in Canada) can help avoid a device extraction (cost in Canada between $30,000 and $60,000), this approach “could be acceptable,” they said.

The inhospital charges in the U.S. for a device infection are in excess of $140,000, according to Jeffrey Brinker, MD, from Johns Hopkins University.

In an accompanying editorial, Brinker noted that any delay in extraction increases the risk of adverse outcomes. However, more evidence regarding PET/CT imaging in this setting, particularly around false negatives and false positives, is needed before it becomes part of the routine evaluation, he said.

Primary source: Journal of the American College of Cardiology
Source reference: Sarrazin J, 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: 1616–1625.

Additional source: Journal of the American College of Cardiology
Source reference: Brinker J “Imaging for infected cardiac implantable electronic devices: A new trick for your pet” J Am Coll Cardiol 2012; 59: 1626-1628.