Background: Cleft mitral valve without an ostium primum defect, referred to as isolated cleft mitral valve, has been the subject of many reports; yet its morphology and operability remain incompletely understood.
Methods: The anatomic findings in 36 postmortem cases, five explanted hearts, and relevant clinical data constitute the material basis of this report. Cardiac catheterization data were available in 29 cases and two-dimensional echocardiograms in 13 cases.
Results: Twenty cases had normally related great arteries with subpulmonary conus. Of these cases 4 (20%) had tetralogy of Fallot and 1 had tricuspid atresia. Twenty-one cases had abnormal ventriculoarterial relationships with subaortic or bilateral conus resulting in transposition in 16 (76%) and double-outlet right ventricle in 5 (24%). In the cases with normally related great arteries, the morphology of the ventricular septal defect and the mitral cleft were similar to those of the more complete forms of atrioventricular canal defects. The mitral cleft usually resulted in progressive mitral regurgitation, which can be treated by surgical closure of the cleft. In the cases with abnormal conus, the morphology of the ventricular septal defect and the mitral cleft did not resemble atrioventricular canal defects. The attachment of the cleft usually produced obstruction of the left ventricular pulmonary outflow tract. Surgical repair of the cleft cannot eliminate this obstruction.
Conclusions: There are two different anatomic types of isolated cleft mitral valve: the canal type, and abnormal conus type. Diagnosis of the associated ventriculoarterial relationships helps to guide their surgical treatment.