Pathology of Self-Expanding Transcatheter Aortic Bioprostheses and Hypoattenuated Leaflet Thickening

Courtesy of Dr. Juan Manuel Pérez.

Despite the available long term followup data on of transcatheter aortic valve replacement (TAVR), bioprosthesis durability continues under debate. One observed phenomenon is hypoattenuated leaflet thickening (HALT). This finding has been identified with CT and associated with subclinical valve thrombosis, characterized by valve density reduction. However, to date, there are no pathology studies confirming this link. 

This observational retrospective study carried out histological studies to identify thrombosis, pannus, inflammation, structural changes and calcification in percutaneously implanted aortic prosthesis. These findings were compared and correlated with HALT detection with microCT. 

The study looked at 123 valves from 11 clinical trials with CoreValve and Evolut obtained from autopsies (n=89) or surgical explant (n=34). Infective myocarditis (10/123) and valve-in-valve (3/123) cases were excluded. Mean implant duration was 66 days (range: 0-1958). Mean patient age was 80.3 ± 9.5, with 37% women. Most explanted valves were CoreValve (81.8%), followed by Evolut R (16.4%) and Evolut PRO (1.8%).

HALT was found in 43.4% of valves assessed by microCT, while histological analysis confirmed thickening in 40.6% of cases.

The main findings revealed that HALT corresponded to thrombi in different organization stages. <30 day implants (n=42) showed acute thrombosis in 36 cases. For 30 to 365 day implants, (n=35), 24 cases presented organizing thrombi. Finally, for implants over 365 days (n=33), 18 cases showed completely organized thrombi in pannus.

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Even though both methods have shown high correlation, microCT failed to differentiate between the different thrombi stages when histologically observed, i.e. organizing or completely organized (pannus).

Conclusion

In conclusion, histological analysis identified three kinds of thrombi; acute, organizing and organized (pannus) which could not be differentiated with microCT. Implants over 30 days presented signs of organization, while most year-old implanted valves showed completely organized thrombi. These findings highlight the importance of early detection of HALT, given its potential impact on antithrombotic strategy selection after TAVR.

Original Title: Pathology of Self-Expanding Transcatheter Aortic Bioprostheses and Hypoattenuated Leaflet Thickening.

Reference: Yu Sato et al. Circulation: Cardiovascular Interventions, Volumen 18, e014523, 2025.