Polyurethane: material for the next generation of heart valve prostheses?

Objectives: The prospects for a durable, athrombogenic, synthetic, flexible leaflet heart valve are enhanced by the recent availability of novel, bios table polyurethanes. As a forerunner to evaluation of such biostable valves , a prototype trileaflet polyurethane valve (utilising conventional materia l of known in vitro behaviour) was compared with mechanical and bioprosthet ic valves for assessment of in vivo function, durability, thromboembolic po tential and calcification. Methods: Polyurethane (PU), ATS bileaflet mechan ical, and Carpentier-Edwards porcine (CE) valves were implanted in the mitr al position of growing sheep. Counting of high-intensity transient signals (HITS) in the carotid arteries, echocardiographic assessment of valve funct ion, and examination of blood smears for platelet aggregates were undertake n during the 6-month anticoagulant-free survival period. Valve structure an d hydrodynamic performance were assessed following elective sacrifice. Resu lts: Twenty-eight animals survived surgery (ten ATS; ten CE; eight PU). At 6 months the mechanical valve group (n = 9) showed highest numbers of HITS (mean 40/h, P = 0.01 cf. porcine valves), and platelet aggregates (mean 62. 22/standard field), but no thromboembolism, and no structural or functional change. The bioprosthetic group (n = 6) showed low HITS (Ik) and fewer agg regates (41.67, P = 1.00, not significant), calcification and severe pannus overgrowth with progressive stenosis. The PU valves (n = 8) showed a small degree of fibrin attachment to leaflet surfaces, no pannus overgrowth, lit tle change in haemodynamic performance, low levels of HITS (5/h) and platel et aggregates (17.50, P < 0.01 cf. mechanical valves, P = 0.23 cf. porcine valves), and no evidence of thromboembolism. Conclusions: In the absence of valve-related death and morbidity, and retention of good haemodynamic func tion, the PU valve was superior to the bioprosthesis; lower HITS and aggreg ate counts in the PU valve imply lower thrombogenicity compared with the me chanical valve. A biostable polyurethane valve could offer clinical advanta ge with the promise of improved durability (cf. bioprostheses) and low thro mbogenicity (cf. mechanical valves). (C) 2000 Elsevier Science B.V. All rig hts reserved.