Functional evaluation of the medtronic stentless porcine xenograft mitral valve in sheep

Background-Recently, renewed interest in allograft and stentless "freehand" bileaflet xenograft mitral valve replacement has arisen. The variability o f human papillary tip anatomy and scarcity of donors limit allograft availa bility, making xenograft mitral valves an attractive alternative; however, these valves require new surgical implantation techniques, and assessment o f their hemodynamics and functional geometry is lacking. Methods-Seven sheep underwent implantation of a new stentless, glutraraldeh yde-preserved porcine mitral valve (Physiological Mitral Valve [PMV], Medtr onic) and were studied acutely under open-chest conditions. a new method of retrograde cardioplegia was developed. Hemodynamic valve function was asse ssed by epicardial Doppler echocardiography. 3D motion of miniature radiopa que markers sutured to the valve leaflets, annulus, and papillary tips was measured. Six other sheep with implanted markers served as controls. Results-Both papillary muscle tips avulsed in the first animal, leaving 6 o ther animals. Mitral regurgitation was not observed in any xenograft valve. The peak and mean transvalvular gradients were 4.6+/-1.8 mm Hg and 2.6+/-1 .5 mm Hg, respectively. The average mitral valve area was 5.7+/-1.6 cm(2). Valve closure in the xenograft group occurred later (30+/-11 ms, P<0.015) a nd at higher left-ventricular pressure (61+/-9 mm Hg, P<0.001) than in the control group; furthermore, leaflet coaptation was displaced more apically (5.6+/-2.2 mm, P<0.001) and septally (5.8+/-1.5 mm, P<0.001), and the anter olateral papillary tip underwent greater septal-lateral displacement (2.7+/ -1.5 mm. P<0.001). Annular contraction during the cardiac cycle was similar in the 2 groups (xenograft 9.2+/-4.5) versus control 10.6+/-4.5% [mean+/-S D; 2-factor ANOVA model]). Conclusions-Successful freehand stentless porcine mitral valve implantation is feasible in sheep and was associated with excellent early postoperative hemodynamics. Physiological mitral valve annular contraction and functiona l leaflet closure mechanics were preserved. Long-term valve durability, cal cification, and hemodynamic performance remain to be determined in models.