defects in the apical muscular septum are those least likely to be visualized without the aid of color-flow mapping Such mapping is usually required to differentiate multiple defects from a single muscular defect crossed by right ventricular trabeculations FIG 32.26 Two-dimensional image (A) and corresponding color Doppler echocardiographic image in a posterior and inferiorly tilted apical plane (B) demonstrate two small apical muscular ventricular septal defects (VSD) located inferior to the moderator band (star) LV, Left ventricle; RV, right ventricle FIG 32.27 Two-dimensional image (A) and corresponding color Doppler echocardiographic image in the parasternal short-axis plane (B) demonstrating a muscular outlet ventricular septal defect (VSD) located at approximately the 12 o'clock position relative to the left ventricular outflow tract The defect is completely surrounded by muscle, including being bordered by the posteroinferior limb of the septomarginal trabeculation (star), which separates the aortic valve (AoV) from the tricuspid valve PV, Pulmonary valve Doubly committed juxtaarterial defects are recognized because of the fibrous continuity in the roofs of the leaflets of the aortic and pulmonary valves These features are seen in long-axis, short-axis (Fig 32.28; Videos 32.13 and 32.14), and subcostal right oblique views (Fig 32.29) If present, prolapse of the aortic valvar leaflets will be visualized (Fig 32.30; Video 32.15) When the focus is also on the leaflets of the tricuspid valve, it is possible to show whether a doubly committed juxtaarterial defect is perimembranous or is separated from the central fibrous body by a muscular rim This feature will best be appreciated from the parasternal short-axis section across the aortic valve This cut demonstrates the defect extending from the perimembranous region at approximately the 9 o'clock position to the pulmonary root at approximately 12 o'clock (see Fig 32.28B; Video 32.14) Note, however, that due to the developmental aberration producing the doubly committed defect, namely failure of muscularization of the proximal outflow cushions, there is a poorly formed subpulmonary infundibulum It is a mistake, therefore, strictly to use this “clock face” when defining the borders of the various outlet defects It is the fibrous continuity between the leaflets of the arterial valves that defines the doubly committed defect Due to the poorly formed subpulmonary infundibulum, nonetheless, the geographical location can appear similar to the other outlet defects when viewed in the short axis FIG 32.28 Echocardiographic images demonstrating the doubly committed juxtaarterial ventricular septal defect (VSD) (A) and the doubly committed juxtaarterial defect with perimembranous extension (B) In both defects, there is fibrous continuity from the aortic valve (AoV) to the pulmonary valve (PV), the phenotypic feature of the doubly committed defect (A) The posterior margin of the defect is composed of muscle formed by the posteroinferior limb of the septomarginal trabeculation (star) (B) The posterior margin of the defect extends to the perimembranous region with additional fibrous continuity from the aortic valve to the tricuspid valve Therefore the defect in panel B is both doubly committed and perimembranous S, Septal leaflet of the tricuspid valve