Splitting The Anterior Mitral Leaflet Impairs Left Ventricular Function In An Ovine Model
Laurencie M. Brunel1, Zoe A. Williams1, Konstantin Yastrebov2, Benjamin M. Robinson1, Innes K. Wise1, Hugh S. Paterson1, Christopher S. Burrows1, Paul G. Bannon1.
1The University of Sydney, Sydney, Australia, 2The University of New South Wales, Sydney, Australia.
OBJECTIVE: Preservation of the subvalvular apparatus is paramount in ischemic mitral valve replacement. To prevent left ventricular outflow tract obstruction, the anterior mitral leaflet is often split in the middle and its edges folded and re-attached at the annular level, therefore reducing the annulo-papillary distance. This study quantifies the acute effects of splitting the anterior mitral leaflet and shortening the annulo-papillary distance on left ventricular function.
METHODS: Six adult sheep (mean body weight 48.5 ± 3.7 kg) underwent a mechanical mitral valve insertion on normothermic beating-heart cardiopulmonary bypass, with retention of the native mitral valve and placement of releasable snares to reduce the papillary-commissural distance. The anterior mitral leaflet was split using a wire pre-placed around the leaflet and exteriorized through the left ventricular wall. Instantaneous changes of cardiac mechano-energetics were analysed before and after shortening the papillary-commissural distance, then before and after splitting the anterior mitral leaflet.
RESULTS: Shortening the papillary-commissural distance was associated with a significant decrease in End Systolic Pressure Volume Relationship and Preload Recruitable Stroke Work by 51% and 33% respectively. Stroke Work and Left Ventricular End Systolic Pressure were reduced by 12% and 10% respectively. After splitting the anterior mitral leaflet, Preload Recruitable Stroke Work, Stroke Work, Stroke Volume, Cardiac Output, Left Ventricular End Systolic Pressure and Mean Pressure were significantly decreased by 27%, 23%, 13%, 10%, 14% and 11% respectively. Reducing the papillary-commissural distance after splitting the anterior leaflet did not further alter left ventricular function.
CONCLUSIONS: Splitting the anterior mitral leaflet and shortening the papillary-commissural distance both individually acutely impaired left ventricular function but the effects were not additive. In patients with already severe left ventricular systolic dysfunction, future mitral prosthetic designs and surgical techniques should focus on preventing further damage of the ventricle.
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