Morphologic and histologic findings in bioprosthetic valves explanted from the mitral position in children younger than 5 years of age

Background: Mitral valve replacement (MVR) in very young children is challenging. This study investigates the mechanisms for early bioprosthetic valve failure in very young patients through review of the macroscopic and microscopic findings in explanted bioprosthetic valves. Methods: Patients who underwent MVR with a bioprosthetic valve at Boston Children's Hospital between January 2010 to April 2016 at <5 years of age were the subjects of this study. Valve failure was defined as prosthetic mitral valve explantation with mitral valve re-replacement. Results: Bioprosthetic valves were used in 31 of 77 MVRs during the study period. Valve failure occurred in 10 patients (32%). Freedom from valve failure was 80% at 1 year and was associated with older age at implantation. On gross and microscopic evaluation, valve failure (predominantly stenosis) was found to be due to pannus deposition and intrinsic leaflet calcification. Conclusions: Successful long-term use of bioprosthetic valves in the mitral position in very young children continues to be a challenge. In addition to intrinsic calcification, excessive pannus deposition can lead to early bioprosthetic valve failure in this population. Early exuberant pannus growth appears due to thrombus deposition on the valves themselves and to the host's reaction to foreign material.