Spatial relationship between the ventricular septal defect and the anomalous muscle bundle in a double-chambered right ventricle

Background. The hemodynamic profile and surgical approach to a double-chambered right ventricle (RV) are influenced by the position of a ventricular septal defect (VSD) in relation to the obstructing muscle bundle. This relationship, however, has not been systematically evaluated, with available literature yielding conflicting results. The objective of this study was to describe this relationship in a series of consecutive patients. Design. This is a retrospective study of patients with double-chambered RV at a single institution between 1999 and 2005. The location of the VSD in relation to the obstructing muscle bundle was established by a review of echocardiograms, cardiac catheterizations, and surgical notes. Results. Twenty-seven patients were identified, and 4 excluded because of inadequate data. There was no disagreement among the methods to determine the relationship between the VSD and the muscle bundle(s). The median age was 65 months (8-204 months). An associated VSD was seen in 21 patients (91%); 18 perimembranous (86%), 2 muscular (9%), and 1 supracristal (5%). The VSD was proximal to the obstructing muscle bundle in 13 (62%), and distal to the bundle in 9 (38%); the supracristal defect was distal, the 2 muscular were proximal, and 11 (61%) of the perimembranous defect were proximal to the muscle bundle. Conclusion. The position of the VSD in relation to the anomalous muscle bundle in a double-chambered RV is heterogeneous. The majority of defects communicate with the high-pressure chamber proximal to the muscle bundle(s).