Characteristics of calcium deposition on expanded polytetrafluoroethylene membrane as a valve substitute in the pulmonary position

An expanded polytetrafluoroethylene membrane has been widely used off-label as a substitute for a pulmonary valve leaflet. However, details regarding the calcification of the membrane in human samples have not been fully described. This report observed the precise extent and distribution of calcification in the membrane. Two samples of calcified expanded polytetrafluoroethylene membranes used as pulmonary valve substitutes were taken at replacement surgery 10 and 15 years after implantation into a valved conduit or transannular patch, respectively. In addition to general histological examination, 3D micro-computed tomography imaging and scanning electron microscopy-backscattered electron imaging were performed to reveal the precise location and extent of calcium deposition in the excised valve leaflets. Along with mineralization across the immobile membrane embedded in calcified pseudointimal tissue, calcium deposits were also detected in micro-interstices of the membrane in areas not covered by calcified fibrous tissue in both specimens. Fluorine properties and specific membrane interstices structure may cause unique calcium deposition independent of the foreign body reactions, leading to transmural calcification with thick pseudointimal embedding.