DISCUSSION
Bioprosthetic valves have good durability and a predictable mode of failure, with gradual degeneration of the leaflet tissue being the norm (1-3). As a result, when a re-operation is required, is usually done in a controlled and safe manner (1-3). Nevertheless, some patients do experience sudden valve dysfunction due to acute structural valve deterioration, needing urgent attention (1,2,3,6,7).
In a cohort of 836 patients who had a porcine bioprosthetic valve replacement, 28 required a re-operation with 18 of them having a leaflet tear of the explanted valve. Of these 18 patients, 12 had a previous MVR and 6 had AVR (3). Thus, the proportion of bioprosthetic valve leaflet tear leading to a re-operation was 2.1.% (3). Cusp rupture or detachment in a mitral bioprosthesis may cause massive MR with serious consequences (3-7). Amongst the 12 patients who had a leaflet tear in a mitral bioprosthesis in Pomar’s series, 6 presented in NYHA III and 6 in NYHA IV (3).
The initial diagnosis in our patient was cardiogenic pulmonary oedema, which suggests that the cuspal tear of the bioprosthesis and the ensuing massive MR was
the primary event. Subsequent clinical, radiological, laboratory and echocardiographical findings made right lobar pneumonia and/or infective endocarditis (IE) a likely diagnosis, even though serial blood cultures were negative. It is well known that approximately 1/3 of patients with IE have sterile cultures (8). In either case, considering the major hemodynamic burden caused by the massive MR, urgent surgical intervention was in our patient imperative (8). Notably, all 6 patients who had cuspal tear of a bioprosthetic MV went on to have redo MVR in the elegant study by Pomar (3).
Single or multiple cuspal tears, leaflet perforations, free-edge tears and basal tears have all been described with the later (also seen in our patient) being the commonest (3-7). Some torn leaflets are calcified whereas in others calcification is visible only under light microscopy (3). In our patient, leaflet tear occurred at the base across its attachment onto the frame of the prosthetic valve (Figure 4) bearing no calcium, vegetations or other sign suggestive of infection, and valve culture was negative. These implies that the detachment of leaflet from the frame of the valve was a purely mechanical event (9).
Leaflet detachment occurred 4 years after surgery in our patient, which is in keeping with an average time for cuspal tears of around 4-6 years quoted by Pomar (3). However, following implantation of a mitral bioprosthesis, Miura (6) reported a cusp detachment occurring only 10 months after surgery and Ha et al (7) 12 years after surgery.