Atrioventricular Septal Defects (AVSD)
Primum ASD | Atrioventricular canal | Cleft mitral valve | AV canal | Common AV junction
Components of the common atrioventricular (AV) valve: The common AV valve in AVSD is composed of 2 bridging leaflets and a left and right Atrioventricular valve components. The left AV valve has the two bridging leaflets variably extending into it and mural leaflet guarding the left ventricle . The right AV valve is composed of two bridging leaflet extensions and 2 resident leaflets (anterior and mural/posterior) guarding the right ventricle.
There may be significant variation in the development of individual leaflets. The bridging leaflets vary in their position, development and extention to the right or left vetricle. These variations can be recognised by RT3DE and has significant implications in the surgical repair.
Role of 3Dechocardiography in atrioventricular septal defects
Role of RT3DE in defining the morphology of Atrioventricular Septal Defects
Morphology of Left AV valve
In AVSD, the Left Atrioventricular valve is morphologically different from the mitral valve. Even when there are two seperate AV valve orifices, the left AV valve is formed of a posterior or mural leaflet and two bridging leaflets opposing each other. These leafflets together form the anterio-superior leaflet. The so called 'cleft' is the point of apposition between the two bridging leaflets as shown on the 3D echocardiographic picture in the adjacent panel. The mural leaflet guards only 50% of the Left AV valve as opposed to 2/3rd of that of the mitral valve. In congenital 'cleft' mitral valve the morphology of the mitral valve is different. The cleft is eccentric and the mitral leaflet retains its normal extent of 2/3rd of the artioventricular junction as shown in the image below.
The clear differentiation between a cleft mitral valve and the point of apposition of bridging leaflets are shown in the movie. Here the cleft in the left AV valve is located eccentrically between 1 and 3O'clock position giving rise to a trifoliate Left AV valve. In AVSD the point of apposition is towards septum (between 11 and 12 O'clock position).
Plane of the AV Valve
Mltiplane Review (MPR) has given exciting and very important insight into the orientation of the valve components at the atrioventricular junction.
This is an illustration of the technique of MPR in defining the functional morphology of the atrioventricular septal defect. Here, by aligning the plane of dissection in anatomical planes in an attitudinally appropriate manner, one can demonstrate the plane of the common valve in relation to the plane of the septum. Note the orientation of inter- atrial septum and the plane of the interventricular septum. Deviation of the atrial septum in a different plane to that of the interventricular septum can be well visualized here. This is a clear demonstration of double outlet right atrium, a concept often disputed (as often it is difficult to demonstrate).
Double orfice Left AV valve
Another abnormality of the left AV valve seen in association with atrioventricular septal defect is double orifice left AV valve. As illustrated in the video, the papillary muscles and subcordal apparatus are abnormally oriented in this condition leading to abnormal planes of coapation and division of left atrioventricular valve
Surgeons view of a double orifice left atrioventricular valve: Ao=Aorta, O1= orifice 1, O2 =Orifice 2. This patient had complete atrioventricular septal dfects with balanced ventricles. Both the orifices were competent and was left as such during surgical repair.
AVSD (post surgical repair without suturing the zone of apposition)
Post Surgical repair: Severe Left AV Valve regurgitation resulting from non closure of the zone of apposition between the two bridging leaflets
Fig1. The view frfom the LA with aorta anterior and Tricuspid valve to the right.
The trifoliate closure of the left AV valve well seen from the left atrium. Note the zone of apposition between the two bridging leaflets labelled SBL and IBL. The Mural Leaflet (ML) only forms the posterior 1/3rd of the circumference of the left AV valve as opposed to the noraml mitral valve where it covers more than 2/3 rd.
Fig2. View from the LV apex. This also demonstrates the unwedged position of the aorta from the commom AV valve ring.
Fig3. In this video, the mural leaflet is cut off to bring to view the coaptation between the two bridging leaflets to expose the zone of apposition. Here you can clearly visualize the SBL sliding over the IBL as the systole progresses. This prolapse of the SBL is mainly due to the fact that the IBL is held down by secondary chordae to the LV wall. There is severe AV valve regurgitation and the patient awaits surgical repair
Atiro Ventricular Septal Defect (AVSD) with intact atrial and ventricular septum
A healthy 12 year old with previously documented normal heart develops progressive mitral regurgitation. Remains asymptomatic. On 3D TEE, he has an AVSD with intact septum, a dimple at the region of the septum primum above the bridging leaf lets of the common AV valves, Moderate Left AV valve regurgitation on 3D colour imaging. There is also a true cleft in the posterior leaflet. Note the posterior leaf let is small and covers only 50% of the Left AV valve annulus.
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