The mitral valve replacement by the new-type bioprostheses (features of design and long-term results).

The BAKS bioprostheses were created in our centre and they have the following features: (1) to reduce immunogenicity they underwent a combined fermentochemical treatment which resulted in the native xenovalve consisting of collagen and elastic fibres only; (2) in cutting out the valve the natural aortic sinuses were preserved; and (3) the xenovalve was fixed on a functional frame of an original design. From 1979, BAKS have been implanted in 243 patients with the isolated mitral valve reumatic injury. The patients age varied from 11 to 59 years; 91 patients (37.5%) were under 35 years. The 12-year survival rate (without hospital lethality) was 65.5 +/- 5.3%. The most serious longterm complications were: infectious endocarditis (3.14 patients/years); spontaneous degeneration of bioprosthetic cusps (2.24% patients/years); thromboembolism (0.6% patients/years). The morphological examination of bioprostheses removed in reoperations from 10 days to 10 years after implantation was performed in 51 cases. Most often, collagen degeneration occurred in patients under 35. The pathologic structural changes originated because of the localized saturation of bioprosthetic cusps with the recipient plasma proteins, gradual disintegration of collagen fibres, and further calcification of that area. The indications to the mitral valve replacement by BAKS were: the left atrium thrombosis, thromboembolytic syndrome, contraindications to anticoagulation therapy, and the age over 35 years.