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J Thorac Cardiovasc Surg 2002;124:541-552
© 2002 The American Association for Thoracic Surgery

Surgery for Acquired Cardiovascular Disease (ACD)

Hemodynamic performance of an unstented xenograft mitral valve substitute

From the Department of Cardiovascular and Thoracic Surgery^a and the Division of Cardiovascular Medicine,^c Stanford University School of Medicine, Stanford, Calif, and the Laboratory of Cardiovascular Physiology and Biophysics,^b Research Institute of the Palo Alto Medical Foundation, Palo Alto, Calif.

Supported by grants HL-29589 and HL-67025 from the National Heart, Lung, and Blood Institute and a contract from Medtronic Heart Valve Division, Minneapolis, Minn. Drs Timek, Tibayan, Dagum, and Lai are Carl and Leah McConnell Cardiovascular Surgical Research Fellows. Drs Timek and Dagum were supported by NHLBI Individual Research Service Awards HL-10452 and HL-10000. Dr Timek is also a recipient of the Thoracic Surgery Foundation Research Fellowship Award. Dr Lai was supported by a fellowship from the American Heart Association, Western States Affiliate.

Read at the Twenty-seventh Annual Meeting of The Western Thoracic Surgical Association, San Diego, Calif, June 20-23, 2001.

Received for publication June 28, 2001. Revisions requested Sept 19, 2001; revisions received Jan 4, 2002. Accepted for publication Feb 18, 2002. Address for reprints: D. Craig Miller, MD, Department of Cardiovascular Surgery, Falk Cardiovascular Research Center, Stanford University School of Medicine, Stanford, CA 94305-5247 (E-mail: dcm{at}stanford.edu).

Objective: Stentless mitral xenografts offer potential clinical benefits because they mimic the normal bileaflet mitral valve. How best to implant them and their hemodynamic performance and durability, however, remain unknown.
Methods: A stentless porcine mitral xenograft valve (Medtronic physiologic mitral valve) was implanted in 7 sheep with papillary muscle sewing tubes attached with transmural left ventricular sutures. Radiopaque markers were inserted on the leaflets, annular cuff, papillary tips, and left ventricle. After 10 ± 5 days, the animals were studied with biplane videofluoroscopy to determine 3-dimensional marker coordinates at baseline and during dobutamine infusion. Transesophageal echocardiography assessed mitral regurgitation and valvular gradients. Mitral annular area was calculated from the annular markers. Physiologic mitral valve leaflet and annular dynamics were compared with 8 native sheep valves.
Results: Average mitral regurgitation grade at baseline was 1.2 ± 1.0 (range, 0-4), and the mean transvalvular pressure gradients were 3.6 ± 1.3 and 6.2 ± 2.2 mm Hg during baseline and dobutamine infusion, respectively. Xenograft mitral annular area contraction throughout the cardiac cycle was reduced (6% ± 6% vs 13% ± 4% for physiologic mitral valve and control valve, respectively; P = .03). Physiologic mitral valve leaflet geometry during closure differed from the native valve, with the anterior leaflet being convex to the atrium and with little motion of the posterior leaflet. Three animals survived more than 3 months; good healing of the annular cuff and papillary muscle tubes was demonstrated.
Conclusion: This stentless xenograft mitral valve substitute had low gradients at baseline and during stress conditions early postoperatively, with mild mitral regurgitation. Preliminary analysis of healing characteristics appeared favorable at 3 months. Additional studies are needed to determine long-term xenograft mitral valve performance and resistance to calcification.

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