One of the most dramatic and tragic events associated with prosthetic heart valve replacement is sudden mechanical failure due to blockage or detachment from the surrounding tissues. The resulting heart failure is almost always fatal unless urgent replacement of the heart valve is undertaken. Equally dramatic, but less well recognised, is fracture or dislocation of the prosthetic valve disc.We report a fatal case of sudden mechanical failure of a current series Bjork-Shiley mitral valve prosthesis due to fracture of the minor disc support strut one year after the valve was inserted.Case report A 52 year old woman with rheumatic heart disease underwent replacement of the mitral valve with a Bjork-Shiley MBRC 29 mm prosthesis and of the aortic valve with an Omniscience 23 mm prosthesis in July 1982. She was well during the next 12 months and was taking warfarin, dipyridamole, and digoxin.In July 1983 she suddently became short of breath, which was associated with faintness and tightness in the chest. On physical examination she was agitated, restless, cyanosed, clammy, and severely dyspnoeic and was coughing up white frothy sputum. The pulse rate was irregular at 120 beats/min and the blood pressure unrecordable. Her from at least one valve were heard, with a moderately loud pansystolic murmur at the lower left sternal edge. The electrocardiogram indicated atrial fibrillation with salvoes of ventricular extrasystoles. A chest radiograph confirmed severe pulmonary oedema and showed that the minor strut and disc of the BjorkShiley prosthesis were in the apex of the left ventricle (Fig. 1).Despite vigorous medical treatment the patient lost consciousness and because her haemodynamic state rapidly deteriorated she was intubated and ventilated, and external cardiac massage was started.Cardiopulmonary bypass through femoral artery and vein cannulae was instituted three and a half hours after admission. After median sternotomy the 29 mm Bjork-Shiley valve ring (Fig. 2)

An investigation into the mechanisms of failure of current Bjork-Shiley cardiac valve prostheses is reported. Two failed valves, one apparently unfailed but defective valve, and one unused valve, were examined by scanning electron microscopy and metallographic section. In the first two valves (removed 12 and 23 months after implantation) fracture was associated with the welds joining the short strut to the valve ring. The fracture surfaces in all cases were heavily faceted and showed branching cracks. Extensive wear had occurred on one fracture surface in the first case, suggesting that one leg of the short strut had failed before the other, though this had been clinically undetectable. The third valve was removed owing to failure of the suturing (24 months after implantation) but one leg of the short strut was found to be completely fractured. The other leg showed extensive cracking and porosity in the weld region. A metallographic section taken through the weld region of the fourth (unused) valve illustrated several sizable defects directly attributable to the welding process. It is suggested that the valves failed by fatigue and that these problems could be overcome if the complete valve cage were machined as a single piece.

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