18-Fluoride PET: How Good for Evaluating Bioprosthetic Valve Function?

It is possible to monitor bioprosthetic valve degeneration noninvasively with PET-CT scanning, researchers found.

¹⁸F-fluoride uptake on PET-CT correlated with deterioration in all the conventional echocardiographic measures of valve function and was the sole independent predictor of future bioprosthetic dysfunction in the 78-person study, according to Marc Dweck, PhD, of the University of Edinburgh, and colleagues.

Moreover, patients with increased ¹⁸F-fluoride uptake showed faster deterioration in valve function, and all 10 patients who developed new bioprosthesis dysfunction during 2-year follow-up had evidence of ¹⁸F-fluoride uptake at baseline, they reported in the Journal of the American College of Cardiology.

“This technique holds major promise in the diagnosis of valvular degeneration and the surveillance of patients with bioprosthetic valves,” the authors asserted. “In this multimodality prospective imaging study, we have identified ¹⁸F-fluoride PET-CT as the first noninvasive technique capable of detecting early bioprosthetic valve degeneration and of predicting future valve dysfunction,” they said, though they acknowledged the need for external validation of their data.

Study participants were patients who had undergone surgical aortic valve replacement and were getting follow-up PET-CT imaging. They were divided into those with (n=6) or without (n=71) known bioprosthetic valve dysfunction.

The link between ¹⁸F-fluoride PET-CT and valve deterioration was supported by ex vivo experiments in 15 explanted valves showing tracer uptake colocalizing with tissue degeneration.

In an accompanying editorial, Zahi Fayad, PhD, and Claudia Calcagno, MD, PhD, both of the Icahn School of Medicine at Mount Sinai, New York City, stated that “there is still an unmet need for sensitive diagnostics that are able to quantify subclinical changes in valve tissue composition and structure, before the development of gross abnormalities that significantly impact valve hemodynamics and heart function.”

Transthoracic Doppler echocardiography is currently the modality of choice for bioprosthetic valve monitoring, followed by transesophageal echocardiography, CT, and MRI as other options, they said.

“Although international guidelines recommend serial echocardiography for the detection of bioprosthetic degeneration, visualization of the valve is often poor due to acoustic artefacts from the prosthesis, limiting its sensitivity. This means that valve degeneration is frequently well advanced before clinically overt valve dysfunction is apparent,” Dweck’s group said.

While the ¹⁸F-fluoride PET-CT data from the study authors “have important implications for the timely diagnosis and monitoring of subjects with subclinical valve degeneration,” another option is to combine PET with MRI instead, Fayad and Calcagno suggested.

“Combined PET/MRI effectively couples the molecular functional information from PET with the structural and quantitative functional assessment by MRI, while minimizing ionizing radiation compared with PET/CT,” they said. “In addition, PET/MRI offers new opportunities for motion correction, which may allow for the improved quantification of valvular ¹⁸F NaF signal in the future.”