JACC: PET/CT may guide therapy for infections with CV implantable devices
While the incidence of CIED infections is still low, at 1.9 cases by 1,000 implants per year, the study authors noted that the total number of CIED infections is “increasing, mainly with new clinical indications and the growing number of implants worldwide.” They also pointed out that definitive CIED infection diagnosis is “often challenging.” And, because lead extraction is associated with significant morbidity and mortality, the researchers suggested that new imaging modalities to confirm the infection and its dissemination would be of clinical value.
To assess the value of PET/CT in these patients, Jean-François Sarrazin, MD, of the division of cardiology at the Institut Universitaire de Cardiologie et de Pneumologie de Québec in Quebec City, Quebec, and colleagues compared three groups. In Group A, 42 patients with suspected CIED infection underwent 18F-FDG PET/CT. The researchers defined a positive PET/CT as abnormal uptake along cardiac devices.
Group B included 12 patients without infection who underwent PET/CT four to eight weeks post-implant. Group C included 12 patients implanted for more than six months without infection who underwent PET/CT for another indication.
The researchers also obtained a semi-quantitative ratio (SQR) from the ratio between maximal uptake and lung parenchyma uptake.
In Group A, Sarrazin et al found that 32 of 42 patients with suspected CIED infection had positive PET/CT. Twenty-four patients with positive PET/CT underwent extraction with excellent correlation. In seven patients with positive PET/CT, six were treated as superficial infection with clinical resolution. One patient with positive PET/CT, but a negative leukocyte scan, was considered false positive due to Dacron pouch. Ten patients with negative-PET/CT were treated with antibiotics and none has relapsed at 12.9 months.
In Group B, patients had mild uptake seen at the level of the connector. There was no abnormal uptake in Group C patients. Also, the median SQR was significantly higher in Group A (A at 2.02 vs. B at 1.08 vs. C at 0.57).
Based on these findings, the study found that 18F-FDG PET/CT is helpful to differentiate between an active cardiac device infection and residual normal post-operative inflammation sometimes present four to eight weeks after the operation, and thus, to assess the extension of the infectious process.
“The ratio between maximal device count and normal lung parenchyma allows adequate differentiation between post-operative inflammation and active infection,” the authors wrote.
“In addition, patients with absence of 18F-FDG uptakes despite an initial suspicion of CIED infection had a good outcome with initial antibiotic therapy alone, suggesting that 18F-FDG PET/CT could help in risk stratification and decision management of these patients.”
In the accompanying editorial, Jeffrey A. Brinker, MD, of the division of cardiology at Johns Hopkins University in Baltimore, wrote that there is increasing evidence that 18F-FDG PET/CT is useful for the detection and localization of infection, including infective endocarditis. He wrote that this study makes an additional important contribution regarding the utility of 18F-FDG-PET/CT for suspected CIED infection.
“Like other imaging options including TEE [transesophageal echocardiogram], 18F-FDG-PET does not identify infection per se; rather, it localizes in metabolically active cells be they malignant growths or leukocytes responding to inflammation or infection,” wrote Brinker. “It is not clear, then, whether this modality can be relied upon in the presence of marked leukopenia, although some recent data suggests that it might.”
Although no data are available on the cost-effectiveness of this approach, it could be acceptable if it avoids unnecessary lead extractions and device re-implantations (estimated costs in Canada for a pacemaker are 30,000 CAD and for a defibrillator are 60,000 to 80,000 CAD, while the initial 18F-FDG PET/CT cost is less than 2,500 CAD in Canada), according to Sarrazin et al. Brinker said that the scan is “relatively expensive (at least three times that of a TEE at my institution).”
Given all these considerations, Brinker questioned whether 18F-FDG-PET should become part of the routine evaluation of CIED infection. “Favorable experience derived from prospective employment of the diagnostic algorithms proposed by Sarrazin et al would go far in determining whether this PET will indeed become the extractionists' best friend,” he wrote.