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.