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(Circulation. 1999;100:II-70.)
© 1999 American Heart Association, Inc.

Surgery for Valvular Heart Disease

Functional Evaluation of the Medtronic Stentless Porcine Xenograft Mitral Valve in Sheep

Paul Dagum, MD, PhD; G. Randall Green, MD; Tomasz A. Timek, MD; George T. Daughters, MS; Linda E. Foppiano, MD; Terrance L. Tye, MS; Ann F. Bolger, MD; Neil B. Ingels, Jr, PhD; D. Craig Miller, MD

From the Department of Cardiovascular and Thoracic Surgery (P.D., G.R.G., T.A.T., G.T.D., N.B.I., D.C.M.), Division of Cardiovascular Medicine (T.L.T., A.F.B.), and the Department of Anesthesia (L.E.F.), Stanford University School of Medicine, Stanford, Calif; Cardiology Section (T.L.T., A.F.B.), Department of Veterans Affairs Medical Center, Palo Alto, Calif; and Department of Cardiovascular Physiology and Biophysics (G.T.D., N.B.I.), Research Institute of the Palo Alto Medical Foundation, Palo Alto, Calif.

Correspondence to D. Craig Miller, MD, Department of Cardiovascular and Thoracic Surgery, Falk Cardiovascular Research Center, Stanford University School of Medicine, Stanford, CA 94305-5247. E-mail dcm{at}leland.stanford.edu

Background—Recently, renewed interest in allograft and stentless "freehand" bileaflet xenograft mitral valve replacement has arisen. The variability of human papillary tip anatomy and scarcity of donors limit allograft availability, making xenograft mitral valves an attractive alternative; however, these valves require new surgical implantation techniques, and assessment of their hemodynamics and functional geometry is lacking.

Methods—Seven sheep underwent implantation of a new stentless, glutaraldehyde-preserved porcine mitral valve (Physiological Mitral Valve [PMV], Medtronic) and were studied acutely under open-chest conditions. A new method of retrograde cardioplegia was developed. Hemodynamic valve function was assessed by epicardial Doppler echocardiography. 3D motion of miniature radiopaque 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 other 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 cm². Valve closure in the xenograft group occurred later (30±11 ms, P<0.015) and 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 anterolateral 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±SD; 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 functional leaflet closure mechanics were preserved. Long-term valve durability, calcification, and hemodynamic performance remain to be determined in models.

Key Words: mitral valve replacement • unstented valve • xenograft valves • cardiac surgery