Background and aim of the study: Positioning of a mechanical prosthesis outside the native annulus facilitates mitral valve replacement, especially when the annulus is small and calcified, and preservation of the posterior leaflet (PML) is desired. Herein is described the authors’ initial experience with a new mechanical bileaflet prosthesis comprising a sheltered leaflet housing and a novel, modified asymmetrical sewing ring for an ‘atrialized’ implantation technique.
Methods: Forty-seven patients (24 males, 23 females; mean age 65.8 ± 10.9 years) were operated on for isolated mitral regurgitation or combined stenosis and insufficiency. Ten of the patients underwent valve replacement due to active endocarditis. Preoperative cardiac insufficiency was reflected by a mean NYHA class of 2.6 ± 0.7. The On-X Conform-X bileaflet mitral valve prosthesis (25/33 mm) was implanted in either an epiannular (43 patients) or intra-annular (four patients) fashion, and the PML and its chordae tendineae were preservable in 33 patients (70.2%). All patients were monitored intraoperatively by transesophageal echocardiography (TEE) and postoperatively by transthoracic echocardiography (TTE).
Results: TEE and TTE exhibited excellent function with low mean transvalvular gradients early after surgery (4.9 ± 2.7 mmHg) and after three months (4.8 ± 1.4

mmHg). Paravalvular leakage was not detected. Initialpostoperative left ventricular (LV) function was almost identical to preoperative findings (ejection fraction: preop. 55.1 ± 13.7%, early postop. 53.7 ± 13.6%) and improved slightly after three months (60.1 ± 6.4%). Clinically significant hemolysis was not apparent (LDH at postoperative day 7: 5.3 ± 0.8 µmol/l·s). Two patients died from multiorgan failure (4.2%) and four are currently in a reduced condition requiring long-term hospitalization (morbidity 8.5%). After three months all other patients were in an excellent clinical state (mean NYHA class 1.5 ± 0.6) and being followed up as outpatients.
Conclusion: Current designs of mechanical bileaflet valves require redundant space in the LV cavity for undisturbed leaflet movement. A small annulus, marked fibrosis and calcification of the valvular apparatus can lead to an impedance of prosthetic leaflet motion. Consequently, the native leaflets are often removed. The cylindrical housing of the On-X valve shelters almost the entire motion of the leaflets, allowing an undisturbed function and improved transvalvular flow pattern. The newly developed asymmetrical sewing ring facilitates anchoring of the ring in an ‘atrialized’ fashion, while the flexibility of the cuff adapts to all native ring diameters larger than 25 mm.
The Journal of Heart Valve Disease 2005;14:637-643