Pathological findings in explanted prosthetic heart valves from ventricular assist devices.

AIMS: Ventricular assist devices (VADs) are now a mainstay in the management of patients with end-stage heart failure. An important consideration in the long-term durability of these devices is the structural integrity of the prosthetic valves. Herein, we report the morphological findings in inflow and outflow explanted bioprostheses from seven such devices.

METHODS: The porcine bioprostheses (n = 7; HeartMate, Novacor) were examined from inflow and outflow valve conduits. Cusp tears were assessed on gross examination. Tissues were then processed for histology and graded for pannus, thrombus, and calcification. Immunohistochemistry was performed using anti-CD68 (macrophages), CD45 (leukocytes) and CD31 (endothelial cells) antibodies to assess inflammation.

RESULTS: There was no evidence of infection, host tissue growth, or calcification in either the inflow or the outflow valves in any case. A mild-to-moderate mononuclear cell 'deposit' was present on all porcine bioprostheses, largely on the non-flow surface of the valve cusps. In the case of the longest implant (HeartMate, duration 567 days), a significant mononuclear cell infiltrate was seen on the flow surface, the non-flow surface, as well as the base of the cusp tissue. Variably sized cusp tears were found in all inflow porcine bioprostheses at and beyond 3 months post-implantation, with the longest duration implant showing multiple tears. No tears were identified in the outflow valves. Histology revealed thrombus deposition in all inflow and outflow porcine valves. In addition, inflow valve cusps were characterised by the presence of longitudinally running 'cystic' spaces, which seem to increase in size with increasing implant duration.

CONCLUSION: Bioprosthetic heart valves in VADs show significant changes which appear to correlate with duration post-implantation. These changes suggest that haemodynamic forces and the inflammatory reaction may play a significant role in the long-term durability of the porcine bioprostheses in these devices.