Optimal orientation of the 60 degrees and the 70 degrees Björk-Shiley tilting disc valves.

The free movement of the disc is the most important factor for optimal function of the Björk-Shiley tilting disc valve prosthesis. A thin chorda remaining after excision of the mitral valve or an excessively long suture after aortic valve replacement may be caught between the disc and the valve ring and firmly lock the disc in the closed position. Immediate exploration of the valve prosthesis is then a life-saving measure. During closure, approximation to the valve ring is closer with the convexo-concave disc than with the flat disc, and therefore the surgeon must be especially careful with chordae and sutures. In aortic valve replacement, the large opening of the Björk-Shiley valve should be oriented towards the convexity or outer wall of the aortic curvature, i.e. anteriorly and slightly to the right. In pulse duplicator studies with an acrylic model of the human aorta, this orientation decreased the transvalvular pressure gradient by 1.3 mmHg at a pulse rate of 72 beats per minute and by 2 mmHg at 150 beats per minute, using a 23 mm Björk-Shiley aortic valve with a 60 degrees opening angle. The corresponding decreases with opening angle 70 degrees were 0.4 and 1.7 mmHg. In mitral valve replacement, clinical experience has shown that the transvalvular pressure gradient is lower when the large opening of Björk-Shiley prosthesis is oriented against the posterior wall of the left ventricle, away from the septum. No significant reduction in this gradient was obtained in resting patients, but during an exercise test with cardiac output 10 liters per minute, the gradient over a 29 mm mitral valve was 5 mmHg lower with posterior orientation of the large opening as compared with anterior orientation against septum or aorta.