Atrioventricular septal defects
Formerly known as "canal defects" or "endocardial cushion defects"
atrioventricular septal defects (AVSD) are present when any abnormality
exists of the shared septum between the left ventricle and the
right atrium (the atrioventricular septum). As previously discussed,
ostium primum atrial septal defects extend into this common septal
area and are really a mild form of an atrioventricular septal
defect.
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| Fig.18 |
In its most severe form (Fig. 18) the primum septum is absent
with the defect extending to the muscular septum leaving the entire
central portion of the heart without dividing septal tissue, either
atrial or ventricular. In this setting, a common atrioventricular
valve orifice is present with a double-committed single atrioventricular
valve (i.e., the single atrioventricular valve enters into both
ventricles). In this case the AVSD is referred to as a complete
defect.
Those inexperienced with congenital heart disease frequently have
difficulty understanding these defects. This is principally brought
about because of the failure to recognize that AVSDs are comprised
of a family of defects with ostium primum as a mild form and a
complete AVSDs as the most severe. Many possibilities exist between
the two extremes.
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| Fig.19 |
Fig. 19 shows a parasternal diastolic four-chamber view of an
infant with a complete AVSD. Only a small portion of the interatrial
septum is present. There is total communication and mixing through
the primum defect, ventricular septal defect, and common atrioventricular
orifice. Fig. 7 demonstrated the other extreme of a primum defect
alone.
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| Fig.20 |
Fig.
20 shows the diastolic and systolic appearance of a patient
with a complete AVSD and common atrium. Note the insertion of
some of the chordal structures onto the crest of the ventricular
septum. AVSDs include a broad spectrum of atrioventricular junction
abnormalities, all of which have two common features: an absent
atrioventricular septum and abnormally formed atrioventricular
valves.
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| Fig.21 |
Fig. 21 shows an unusual subcostal short-axis view through the
common atrioventricular valve orifice from a patient with a total
AVSD. It is important to identify all the leaflets present and
trace their insertion into the left or right ventricle. Occasionally,
an atrioventricular leaflet may bridge the central defect and
have chordal insertion into both ventricles. In such cases, the
leaflet is known as a "bridging leaflet" and must be surgically
divided into left and right portions. It then is resuspended from
a central patch to create separate atrioventricular orifices at
the time of correction.
Certain "transitional" forms of AVSD exist. In these, a primum
defect is seen in the atrial septum and a small ventricular septal
defect is noted near the atrioventricular junction. Two separate
atrioventricular valve orifices may be seen. Notably, patients
thought to have merely a primum defect may, indeed, have a ventricular
component.
2004