6 Atrioventricular Septal Defect

Echocardiographic Assessment

Background

Atrioventricular septal defects (AVSDs) are a collection of congenital cardiac defects all having a common atrioventricular (AV) junction and a lack of AV septation. Defects can be either complete or partial. A complete AVSD consists of an inlet ventricular septal defect (IVSD), a primum atrial septal defect (ASD), and a single AV valve (AVV). Partial AVSDs have a primum ASD, two separate AVV orifices, and cleft present in the left-sided AVV. AVSDs make up 2.9% to 6.2% of all congenital heart disease. A complete AVSD occurs in 30% to 50% of patients with trisomy 21.

Key Points

• Complete AVSDs are common in patients with trisomy 21. All patients diagnosed with trisomy 21 should undergo echocardiography (echo) to assess their cardiac anatomy shortly after the diagnosis is made.

• Various terms have been used to describe this defect including complete AVSD, complete atrioventricular canal (AVC) defect, common AVC defect, endocardial cushion defect, and atrioventricularis communis. For this chapter, AVSD is used.

• Complete AVSDs are commonly diagnosed in early childhood either as part of the evaluation for trisomy 21 or due to development of signs and symptoms of pulmonary overcirculation associated with shunting from the ventricular component. Partial AVSDs act similarly to ASDs and may be diagnosed later in life.

Anatomy

A complete AVSD has a common AV junction, a primum ASD, an IVSD, and a common AVV (Fig. 6-1). The primum ASD is anterior and inferior to the fossa ovalis, adjacent to the AVVs. The AVV consists of five leaflets: superior and inferior bridging leaflets, a left mural leaflet, a right mural leaflet, and a right anterosuperior leaflet (Fig. 6-2).

Figure 6-1 Apical four-chamber (4C) view of complete atrioventricular septal defect (AVSD). The primum atrial septal defect (ASD) can be seen above the common atrioventricular valve (AVV) and the inlet ventricular septal defect is seen below the level of the AVV.

Figure 6-2 The illustration shows the basic arrangement of the leaflets to be found in the valve guarding the common atrioventricular (AV) junction. The black dotted lines show the plane of the ventricular septum (VS), and the double-headed arrow shows the zone of apposition between the leaflets that bridge the VS. The valve is shown as seen from the cardiac apex, looking up the barrels of the ventricles.

(From Anderson RH, Baker EJ, Redington A, et al., eds. Paediatric Cardiology, 3rd edition, 2010, Philadelphia: Elsevier, Figure 27-11.)

A partial AVSD usually has a primum ASD and two separate AVVs, with a cleft in the anterior leaflet of the left-sided AVV (mitral valve [MV]) (Fig. 6-3). The cleft in the left-sided AVV usually results in some degree of regurgitation of the valve. There are rare instances of partial AVSDs with only an IVSD and no primum ASD.

Figure 6-3 Parasternal short axis view showing a cleft in the anterior leaflet of the left-sided AVV.

The term transitional AVSD has been used to refer to complete AVSDs in which the IVSD is predominantly occluded by chordal tissue from the AVV, resulting in minimal or no ventricular level shunting (Fig. 6-4). In transitional defects, there are two separate AVV orifices with a cleft in the left-sided AVV.

Figure 6-4 Apical 4C view of a transitional AVSD. The chordal attachments of the AVV to the crest of the VS are dense enough to have created only minimal shunting at the ventricular level.

Associated defects include left ventricular outflow tract obstruction (LVOTO), tetralogy of Fallot (TOF) (5%), dual-orifice left-sided AVV, and hypoplasia of one of the ventricles. Unbalanced AVSDs occur in 10% to 15% of patients, and, when present, two thirds are right ventricular dominant. When an unbalanced AVSD is present, there is the potential for hypoplasia of the nondominant chamber and outflow tract from that chamber. In right ventricular dominance, there can be hypoplasia of the left ventricle (LV) and aorta. In left ventricular dominance, there can be hypoplasia of the right ventricle (RV) and pulmonary artery (PA). Rarely, the AVSD can be severely unbalanced to give a double-inlet ventricle.

Key Points

• LVOTO may occur secondary to chordal attachments from the AVV that cross into the outflow tract.

• Anterior deviation of the infundibular septum may be seen causing right ventricular outflow tract (RVOT) obstruction (RVOTO) and would be consistent with TOF.

• The balance of a complete AVSD is extremely important to determine. If the defect is unbalanced, then attempting to septate the heart for a two-ventricle repair may not be successful and a single-ventricle (Fontan) approach may be needed.

Overview of the Echocardiographic Approach

The echocardiogram (echo) should fully evaluate all the components of the AVSD and assess for any associated abnormalities. Images should define the size of the atrial and ventricular components and demonstrate the direction of shunting. The AVV attachments need to be defined, and function of the AVV should be assessed by pulsed wave (PW) Doppler and color flow Doppler (CFD). The balance of the AVV above the ventricles should be evaluated along with flow across the valve to demonstrate the flow into both ventricles. Additional ASDs or ventricular septal defects (VSDs) can be present, and careful assessment of the atrial septum (AS) and ventricular septum (VS) should be performed. The outflow tracts should be interrogated, looking for any obstruction (Box 6-1).

Box 6-1

Goals of Echocardiographic Examination

• Atrial component (primum ASD)

• Size of the defect

• Direction of shunting

• Additional ASDs

• Ventricular component (VSD)

• Size of the defect

• Direction of shunting

• Additional VSDs

• Balance of the defect

• Distribution of the AVV over the ventricles

• Assess for ventricular hypoplasia

• Assess for outflow tract obstruction

• Left ventricular outflow

• Right ventricular outflow

• Hemodynamics.

• Flow across the AS and VS

• Peak velocity across the VSD

• Severity of AVV regurgitation

• Assess ventricular function

• Assess for associated lesions

• Patent ductus arteriosus (PDA)

• Coarctation of the aorta

• TOF

AVSDs are described by Rastelli classification, which is based on papillary muscle configuration, specifically attachments of the superior bridging leaflet (Box 6-2 and Fig. 6-5):

• Rastelli type A: the superior bridging leaflet has attachments to the crest of the VS.

• Rastelli type B: the attachments are to the right side of the VS.

• Rastelli type C: the superior bridging leaflet is free floating with no attachments to the VS.

Box 6-2

Rastelli Classification

• Based on papillary muscle configuration

• Type A: anterior bridging leaflet mostly in the LV with attachments to the crest of the VS

• Type B: Attachments of the anterior bridging leaflet to the right ventricular side of the septum

• Type C: No attachments of the anterior bridging leaflet to the VS (free-floating bridging leaflet)

Figure 6-5 The illustration shows the essence of the Rastelli classification of variability in the superior bridging leaflet. Although not included by Rastelli et al., it is now evident that the spectrum of malformation can be extended to include the ostium primum defect (top left). Then, depending on the commitment of the superior bridging leaflet to the right ventricle (RV) (wide double-headed arrow), there is a spectrum with reciprocal diminution in size of the anterosuperior leaflet of the left ventricle (LV) (narrow double-headed arrow), as shown in A through C, which represent the types designated alphabetically in the original description.

(From Anderson RH, Baker EJ, Redingtion A, et al., eds. Paediatric Cardiology, 3rd edition, 2010, Philadelphia: Elsevier, Figure 27-20.)

Anatomic Imaging

An apical four-chamber (4C) view is very useful in the evaluation of complete AVSDs, allowing visualization of the primum ASD, IVSD, and the common AVV. The AVV(s) will be noted to be at the same level as the primum ASD just above the AVV and the IVSD just below. From the apical 4C view, the balance of the AVV above the ventricles can be assessed and CFD can be used to assess for valve regurgitation.

Subcostal views allow evaluation of the primum ASD to determine size and direction of flow (Fig. 6-6). Subcostal short axis view allows an en face view of the AVV and can be used to assess the balance of the valve to the ventricles and look for attachments of the superior bridging leaflet to determine the Rastelli classification (Figs. 6-7 and 6-8).