Potentially parachute mitral valve in common atrioventricular canal: pathological anatomy and surgical importance.

An essentially single focus of left ventricular chordal insertion was found in 23 of 164 autopsied cases of common atrioventricular canal (CAVC) with a normally formed spleen (14%). Suture closure of the cleft of the mitral valve in such cases results in the surgical creation of parachute mitral valve, often with fatal iatrogenic mitral stenosis. In such patients, the cleft of the mitral valve is its main orifice and must not be sutured closed. There are four anatomic types of potentially parachute mitral valve in CAVC: (1) with one papillary muscle group and one mitral orifice (type 1A), in 10 cases (43%); (2) with one papillary muscle group and two mitral orifices (type 1B), in one case (4%); (3) with two papillary muscle groups and one mitral orifice (type 2A), in five cases (22%); and (4) with two papillary muscle groups and two mitral orifices (type 2B), in seven cases (30%). Parachute mitral valve exists only when the AVC is divided, either naturally or surgically. The essence of parachute mitral valve is an essentially single focus of chordal insertion. One or both left ventricular papillary muscle groups may be present. The presence of only one focus of left ventricular chordal insertion contraindicates cleft closure.