Internal Medicine Resident University of British Columbia Vancouver, British Columbia, Canada
Background: Degeneration is an inevitable outcome for bioprosthetic heart valves. In the setting of transcatheter aortic valve implantation (TAVI), calcification and leaflet thickening have implications for feasibility and outcomes of repeat interventions. We aimed to investigate the frequency and pattern of leaflet calcification and thickening in explanted transcatheter aortic valves (TAVs) to inform repeat interventions.
METHODS AND RESULTS: TAV explants were obtained from the EXPLANT THV registry and clinical institutions. Histology (hematoxylin & eosin) and micro-computed tomography (micro-CT) imaging (North Star Imaging X5000) with 3D reconstruction using Mimics software (Materialise) were utilized to evaluate TAV calcium volume, distribution, and leaflet thickening. Twenty TAV explants were analyzed: 11 self-expanding CoreValve/Evolut TAVs, 8 balloon-expandable SAPIEN 3 TAVs, and 1 mechanically-expandable Lotus TAV. Median patient age at explant was 73.0 (IQR: 63.0-81.0) years, with a median time to explant of 3 years and 3 months (IQR: 1 year and 10 months–4 years and 10 months). Eleven TAVs (55%) were found to have leaflet calcification (77.9 mm3; 24.7–336.1 mm3) and 9 TAVs (45%) had no calcium by micro-CT. Calcified TAVs had increased leaflet thickness compared to non-calcific samples (1.02 [0.81-1.59] mm vs 0.64 [0.47-0.89] mm; p=0.006). Increased leaflet thickness was correlated with implant duration on histology and micro-CT, with 60% of samples having the thickest region at the base of the leaflet on histology. All explants with more than mild calcification (>10mm3), had both intrinsic and extrinsic calcification on histology. From the base of the CoreValve/Evolut leaflets to nodes 4, 5, and 6 of the TAV frame, there was 16.8% (42.2 mm3), 44.0% (120.4 mm3), and 73.7% (230.7 mm3) of the calcium situated below these respective nodes, illustrating the extent to which this calcium may interact with an implanted SAPIEN 3 frame. In the central leaflet zone, the percentage of calcium in the top two-thirds (laceration zone), which is often lacerated during leaflet modification, was compared to the bottom one-third (traversal zone), which is typically targeted for leaflet traversal during modification. Calcium percentages for CoreValve/Evolut were 0.7-31.7% (traversal) and 20.5-32.1% (laceration), versus SAPIEN 3 with 0.4-22.0% (traversal) and 17.7-77.7% (laceration).
Conclusion: Explanted TAVs showed an association of thicker leaflets with increasing implant duration. There was heterogenous calcium distribution within individual leaflets and among leaflets of an individual TAV. Calcium pattern and location differed between TAV models. This may have important clinical implications for individualized planning when considering optimal THV devices during redo-TAVI and leaflet modification techniques.
