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Splitting the anterior mitral leaflet impairs left ventricular function in an ovine model.

OBJECTIVES
During mitral valve replacement the anterior mitral leaflet is usually resected or modified. Anterior leaflet splitting seems the least disruptive modification. Reattachment of the modified leaflet to the annulus reduces 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
In six adult sheep a wire was placed around the anterior leaflet and exteriorized through the left ventricular wall to enable splitting the leaflet in the beating heart. Releasable snares to reduce annulo-papillary distance were likewise positioned and exteriorized. A mechanical mitral prosthesis was inserted to prevent mitral incompetence during external manipulations of the native valve. Instantaneous changes in left ventricular function were recorded before and after shortening the annulo-papillary distance, then before and after splitting the anterior leaflet.


RESULTS
After splitting the anterior leaflet, Preload Recruitable Stroke Work, Stroke Work, Stroke Volume, Cardiac Output, Left Ventricular End Systolic Pressure and Mean Pressure were significantly decreased by 26%, 23%, 12%, 9%, 15% and 11% respectively. Shortening the annulo-papillary distance was associated with significant decrease in End Systolic Pressure Volume Relationship, Preload Recruitable Stroke Work, Stroke Work and Left Ventricular End Systolic Pressure by 67%, 33%, 15% and 13% respectively. Shortening the annulo-papillary distance after splitting the leaflet had no significant effect.


CONCLUSIONS
Splitting the anterior mitral leaflet acutely impaired left ventricular contractility and haemodynamics in an ovine model. Shortening the annulo-papillary distance after leaflet splitting did not further impair left ventricular function.