Late incompetence of the left atrioventricular valve after repair of atrioventricular septal defects: The morphologic perspective

Objective: The mortality following repair of atrioventricular septal defects has fallen dramatically in the last 4 decades, but reoperation for late regurgitation across the left atrioventricular valve has remained disconcertingly stagnant. Seeking potential structural causes, we compared the morphology of the surgically created septal leaflet of the left valve following repair of atrioventricular septal defects to the aortic leaflet of the normal mitral valve. Methods: We compared the mitral valves of 92 normal hearts to the left ventricular components of the bridging leaflets of hearts with atrioventricular septal defect with common atrioventricular junction, determining the shape of the leaflets and the arrangement of the subvalvar apparatus. Results: The aortic leaflet of the mitral valve is triangular compared with its rectangular septal counterpart after repair of atrioventricular septal defect. The cordal arrangement in the mitral valve is well organized, compared with the deficient cordal arrangement of the abnormal valve. A greater proportion of cords in the mitral valve divide to 3 generations (55.5% compared with 8.7%; P < .001), and a higher percentage of cords remain undivided in atrioventricular septal defects (60.8% compared with 25%; P < .001). Conclusions: Not only is the annular component in the left atrioventricular valve abnormal, but the subvalvar apparatus is characterized by deficiency and disarray. Furthermore, the axis of cordal insertion may potentiate to separation over the long term of the leaflets joined surgically. Valvar repair in this setting will never restore the arrangement of the normal mitral valve.