assessment of the various leaflets and supporting valvar apparatus to be considered in presurgical planning The papillary muscles supporting the left atrioventricular valve are also profiled well in this plane, often positioned in a counterclockwise rotated orientation as compared with the normal heart (Video 31.2) In practice, full sweeps in addition to still planes will reveal all the features necessary for the diagnosis, with emphasis on the subcostal views in delineating the atrioventricular valve and its relationship to the ventricular mass (Fig 31.17) Because patients with atrioventricular septal defects frequently have isomerism of the atrial appendages, it is important precisely to determine the atrial arrangement, as well as the ventricular topology FIG 31.17 Subcostal scan from a patient with an atrioventricular septal defect with exclusively atrial-level shunting and separate atrioventricular orifices Imaging starts in a subcostal four-chamber plane (A), a small atrial component of the defect with lack of offsetting of the atrioventricular valves The transducer is tilted to show the aortic valve, which appears only when the left atrium (la) is no longer in the imaging plane, indicating the unwedged position of the aortic root (B) Slight additional tilting (C) shows the gooseneck deformity of the left ventricular outflow tract (lvot), the superior (sbl) and inferior (ibl) bridging leaflets both firmly attached to the crest of the muscular ventricular septum, and the tongue of tissue (asterisk) connecting the bridging leaflets and separating the two orifices Additional tilting (D) demonstrates the right ventricular outflow tract (rvot) and the pulmonary trunk (pa) All images were taken at the end of diastole Ao, Aorta; lv, left ventricle; ra, right atrium; rv, right ventricle Color-flow Doppler interrogation complements the anatomic investigation by demonstrating the sites of intracardiac shunting and the presence or absence of atrioventricular valvar regurgitation or stenosis as well as localizing any obstructions within the ventricular outflow tracts Pulsed and continuous-wave Doppler is used for quantitative measurements, including assessment of atrioventricular or outflow tract stenosis or for the presence of pulmonary hypertension Interventricular shunting at very low velocity readily establishes any elevation of right ventricular pressures, but pulsed or continuous-wave Doppler interrogation is needed to calculate the difference in pressures between the ventricles As in patients with isolated ventricular septal defects, it is usually possible to estimate both the flow of blood to the lungs and pulmonary vascular resistance A regurgitant jet across the right atrioventricular valve with high velocity may be the result of left ventricular to right atrial shunting and should be interpreted with caution (Fig 31.18; Video 31.3) This type of shunting is relatively common, and although it is readily appreciated in the presence of a ventricular septal defect, it may lead to the erroneous conclusion of right ventricular hypertension in those patients with shunting exclusively at the atrial level or after surgical closure of the defect FIG 31.18 Systolic frame from an apical four-chamber image with colorflow mapping demonstrating a central regurgitant jet, which probably represents shunting from left ventricle (lv) to right atrium (ra) The color flow jet may be misinterpreted as right atrioventricular valvar regurgitation la, Left atrium; rv, right ventricle Separate Atrioventricular Valvar Orifices Separate valvar orifices within a common junction are the consequence of a tongue of valvar tissue joining together the facing surfaces of the bridging valvar leaflets (see Fig 31.17) Almost always there is an interatrial communication between the leading edge of the atrial septum and the crest of the ventricular septum, to which the bridging leaflets are usually connected Consequently there is absence of the normal offsetting of the leaflets and no potential for ventricular shunting Historically such a lesion was called an ostium primum atrial septal defect, but since the shunting is across an atrioventricular septal defect, the inaccuracies of this usage are obvious Standard four-chamber sections readily demonstrate the atrioventricular septal defect (Fig 31.19; Videos 31.4 to 31.6), limited on one side by the atrioventricular valvar apparatus and on the other side by the leading edge of the atrial septum (Fig 31.19A; Video 31.4); see also Fig 31.17A) The atrial component of the defect as well as any additional secundum atrial septal defect will best be profiled in the subcostal planes positioned perpendicular to the atrial septum and atrial component of the atrioventricular septum and parallel to resulting flow from the defect, assuring interrogation at the level of the atrioventricular valve or valves positioned anterior to the coronary sinus (Fig 31.20; Video 31.7) The other key diagnostic features are the trifoliate configuration of the left atrioventricular valve, well seen in the subcostal or parasternal short-axis sections of the left ventricular inlet (Figs 31.21 and 31.22; Video 31.8), and the gooseneck-like elongation of the left ventricular outflow tract This last feature is best seen in parasternal and subcostal long-axis sections of the left ventricle (see Fig 31.16) It is more prominent in hearts with separate right and left atrioventricular valves, where the attachment of the superior bridging leaflet to the ventricular septum accentuates the nature of the body of the goose (Fig 31.23) When there is complete absence of any interatrial communication and four-chamber sections demonstrate an interventricular communication opening to the inlet of the right ventricle, it is lack of offsetting between left and right atrioventricular orifices and, again, the trifoliate arrangement of the left atrioventricular valve that give the diagnostic clues (see