homograft There is certainly a potential for growth of the pulmonary autograft However, this advantage is often lost for the pediatric population because the technique requires the insertion of the autograft in a synthetic conduit for its stabilization (“top hat procedure”)102,103 and also for the build-up of a tight circular fibrous deposit around the intra-atrial portion of the latter conduit Aortic, pulmonary, and mitral homografts are today no longer used because of their poor durability Complications Historically, the postoperative results were poor, especially for patients younger than 2 years The early mortality rate was 20% in most reports and can potentially double in patients younger than 2 years.33,94,104–106 A complete heart block occurs in around 15% of patients, requiring insertion of a permanent pacemaker.33,94,107 Detailed analysis demonstrated that the risk of death is associated with the insertion of an oversized prosthesis Placement of an adequately sized prosthesis in an intraannular position does not carry this associated mortality probability (Fig 34.42).33 FIG 34.42 Mitral valve protheses and their z-scores to evaluate their size relative to the normal mitral valve annulus size for the recipient's body surface area at the time of implantation Patients receiving a prosthesis matching exactly the normal annular size have a probability of survival at 1 year of 100% (From Caldarone CA, Raghuveer G, Hills CB, et al Longterm survival after mitral valve replacement in children aged