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Bioprosthetic Aortic Valve Degeneration
Study Questions:
Can 18F-fluoride, a molecular imaging agent that binds to areas of nascent microcalcification, detect bioprosthetic aortic valve degeneration via positron emission tomography (PET)-computed tomography (CT) and predict valve dysfunction?
Methods:
1) Ex vivo micro PET-CT was performed on explanted degenerated aortic valve bioprostheses, obtained from patients undergoing repeat surgical aortic valve replacement.
2) Patients with surgical bioprosthetic aortic valves were prospectively recruited into a single-center cohort study and followed over 2 years with in vivo contrast-enhanced CT angiography, 18F-fluoride PET, and serial echocardiography.
Results:
1) Fifteen failed explanted bioprosthetic aortic valves were obtained. While ex vivo micro-CT detected leaflet calcification in 13 valves, all 15 valves demonstrated 18F-fluoride leaflet uptake. 18F-imaging correlated with a range of histological markers of bioprosthetic tissue degeneration such as leaflet thickening, fluid inundation, and disrupted collagen architecture.
2) The clinical cohort had 78 patients, 75 ± 7 years of age, with a range of bioprosthetic valve models, valve ages (1 month to >10 years), and a high prevalence of coronary artery disease. Of this cohort, seven had suspected bioprosthetic valve failure at baseline. Both CT and 18F-fluoride PET imaging were abnormal in six of these patients, with target-to-background (TBR) ratios nearly 3 times higher than in patients without known valvular dysfunction (TBR 2.91 vs. 1.12; p < 0.001). The patient without CT abnormalities or 18F-fluoride uptake had severe patient-prosthesis mismatch.
3) CT revealed abnormal leaflet pathology in 14 of the 71 patients without known bioprosthetic valve dysfunction, whereas 18F-fluoride PET uptake was increased in 24 of these patients. Patients with abnormal 18F-fluoride PET exhibited more rapid deterioration in valve function, as measured by echocardiography, with a change in annualized peak transvalvular velocity (0.30 vs. 0.01; p < 0.001). On multivariable analysis, 18F-fluoride uptake was the only independent predictor of future bioprosthetic dysfunction.
Conclusions:
Both CT and 18F-fluoride uptake identified abnormalities in patients with suspected bioprosthetic valve failure. However, 18F-fluoride PET-CT was superior in detecting subclinical bioprosthetic valve degeneration, predicting subsequent deterioration in valve performance and identifying patients at high risk for valve failure.
Perspective:
Studies to date have focused on the use of 18F-fluoride PET in the assessment of coronary artery disease. This is the first multimodality prospective imaging study using 18F-fluoride PET-CT to detect early bioprosthetic valve degeneration. Future studies need to investigate whether 18F-fluoride activity is equally useful in aortic and mitral transcatheter valves, as well as whether 18F-fluoride signal can be used to monitor for the effect of therapies aimed at decreasing valve failure.
Clinical Topics: Cardiac Surgery, Geriatric Cardiology, Invasive Cardiovascular Angiography and Intervention, Noninvasive Imaging, Valvular Heart Disease, Cardiac Surgery and VHD, Interventions and Imaging, Interventions and Structural Heart Disease, Angiography, Computed Tomography, Echocardiography/Ultrasound, Nuclear Imaging
Keywords: Bioprosthesis, Calcification, Physiologic, Calcinosis, Cardiac Surgical Procedures, Coronary Angiography, Diagnostic Imaging, Echocardiography, Fluorides, Geriatrics, Heart Valve Diseases, Heart Valve Prosthesis, Molecular Imaging, Multimodal Imaging, Positron-Emission Tomography, Tomography, X-Ray Computed, Transcatheter Aortic Valve Replacement
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