What is the ideal orientation of a mitral disc prosthesis? An in vivo haemodynamic study based on colour flow imaging and continuous wave Doppler

Doppler colour flow imaging demonstrates normal laminar flowto enter the left ventricle in diastole through the mitral inflowtract located posteriorly in the left ventricle. Laminar flowthen passes around the left ventricular apex to the anteriorlylocated outflow tract. As this is the normal physiologic flowpattern, it would seem appropriate that in the surgical implantationof a mitral tilting disc prosthesis the greater orifice shouldbe directed posteriorly to mimic the normal native valve flowpattern. To determine whether variable positioning of the greater orificehad any significant haemodynamic conse–quences, intracavitaryblood flow patterns were studied in 30 patients with mitralBjörk-Shiley prostheses variously orientated in the mitralorifice. The orientation of the greater orifice (OGO) of theprosthesis was determined by fluoroscopy and the pattern ofthe left ventricular inflow from Doppler colour flow imaging.Twelve patients had their OGO and inflow directed towards theinflow tract (orientation I): nine patients had their OGO andinflow directed anteriorly towards the outflow tract (orientationII) and nine patients had their prosthesis with OGO and inflowin an intermediate position (orientation III). The mean prostheticdiastolic gradient, calculated using continuous wave Doppler,averaged 2.8 mmHg (±0.5mmHg) for the 25-mm prosthesisin orientation I, but 6.0 mmHg (±0.7mmHg) for the samesize prosthesis in orientation II and 5.8 mmHg (±0.9mmHg) with a 25-mm prosthesis in orientation III. Similarly,for prostheses of 27 mm and 29–31 mm the lowest mean diastolicgradient was found in orientation I (2.7 mmHg ± 0.8 and2.8 mmHg ± 0.5, respectively). However, the differencein mean gradient between orientations I, II (5.6 mmHg±0.2and 3.6 mmHg) and III (5.1 mmHg ±0.7 and 3.8 mmHg ±0.4)was less pronounced for the larger prostheses. From these results,it was concluded that the best haemodynamic result is obtainedby a mitral disc prosthesis when its greater orifice is orientatedposteriorly. This would appear to be especially important forthe smaller disc prosthesis.