Pulmonary valve-moderator band distance and association with development of double-chambered right ventricle

Double-chambered right ventricle (DCRV), a form of right ventricular outflow obstruction that sometimes accompanies a ventricular septal defect (VSD), is associated with superior and rightward displacement of the septal insertion of the moderator band. It was hypothesized that this superior displacement is present and identifiable by echocardiography in patients with a VSD even before right ventricular outflow tract obstruction develops. Eight patients who had a previous echocardiographic study showing a VSD alone were echocardiographically diagnosed as having DCRV. Their initial echocardiographic studies were reviewed, and superior displacement of the moderator band was quantified by measuring the distance between the pulmonary valve and moderator band, normalized to tricuspid anulus diameter. These measurements were compared with those from the initial studies of the following 3 other groups: (1) an age-matched group of 10 patients with no structural heart disease; (2) an age-matched group of 10 patients with a VSD who did not develop DCRV; and (3) a group (not age-matched) of 10 patients with VSD and DCRV in whom subpulmonary obstruction was present on the initial study. The 8 patients who eventually developed subpulmonary obstruction had significant superior displacement of the moderator band at the time of their initial echocardiogram compared with that of the 2 age-matched control groups (p < 0.01). In contrast, there was no significant difference in moderator band displacement between these patients and the 10 with DCRV who already had right ventricular outflow obstruction at their initial study (p = not significant). Superior displacement of the moderator band is quantifiable by 2-dimensional echocardiography and may help to predict which infants with a VSD are at risk to develop subpulmonary obstruction.