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.

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.

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

• Assess anatomy of the common AVV

• Rastelli classification (type A, B, or C)

• Presence and degree of valve regurgitation.

• Note whether on the right or left side of the AVV

• Additional valve abnormalities

• Dual-orifice left AVV

• 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).

Figure 6-6 Subcostal long axis view shows the primum ASD above the common AVV.

Figure 6-7 Subcostal short axis view of the common AVV. There are attachments of the superior bridging leaflet to the crest of the VS consistent with a Rastelli type A defect.

Figure 6-8 Subcostal short axis view of the common AVV. There are no attachments to the crest of the VS consistent with a Rastelli type C defect.

The parasternal long axis view allows for assessment of the VS and AVV regurgitation (AVVR). In the parasternal short axis view, the VSD can be evaluated.

The aortic valve, which is usually wedged between the MV and tricuspid valve (TV) annuli, is anteriorly displaced or “unwedged” in AVSDs, resulting in elongation of the left ventricular outflow tract (LVOT). LVOTO may occur in all types of AVSDs but is more common in the partial defects. An apical five-chamber (5C) view allows assessment of the LVOT for possible obstruction (Boxes 6-3 and 6-4).

Box 6-3

Anatomic Imaging

• Diagnostic imaging overview

• AVVs are at the same level

• Absence of the AV septum

• Unwedging and anterior displacement of the aortic valve

• Elongated LVOT

• Counterclockwise rotation of left ventricular papillary muscles

• Cleft of left AVV component directed toward the septum

• Complete AVSD

• Primum ASD (interatrial communication anteroinferior to fossa ovalis and adjacent to the AVV)

• VSD (posterior portion of VS at the level of the AVV)

• Common (single) AVV

• Partial AVSD

• Primum ASD

• No VSD

• Common AVV with two separate orifices (cleft in left-sided AVV)

• Transitional AVSD

• Chordal attachments of the AVV to the crest of the septum resulting in restrictive VSD

• Primum ASD

Box 6-4

Overview of Imaging Windows

Complete AVSD

• Subcostal long axis view

• AS (primum ASD and additional ASDs)

• Unwedging of the aortic valve

• Elongation of the LVOT (“goose-neck” deformity)

• Subcostal short axis view

• Anatomy of the common AVV

• Chordal attachments of the superior bridging leaflet

• En face view of the AVV to assess balance

• Apical 4C view

• IVSD

• Balance of common AVV to ventricles

• Valve regurgitation

• Apical 5C view

• LVOT

• Parasternal long axis view

• AVVR

• VS

• LVOT

• Parasternal short axis view

• VSD

Partial and Transitional AVSD

• Subcostal long axis view

• AS (primum ASD and additional ASDs)

• “Unwedging” of the aortic valve

• Elongation of the LVOT (“goose-neck” deformity)

• Subcostal short axis view

• AVVs

• Cleft in left-sided AVV

• Two separate valve orifices

• Apical 4C view

• AVVs in relation to the septum

• AVVs at the same level

• Valve regurgitation

• Ventricular level shunting

• Parasternal short axis view

• VSD

• Cleft in the left AVV

Partial AVSDs will have two separate AVVs noted to be at the same level. A cleft in the anterior leaflet of the left-sided AVV usually results in AVVR. There is also a primum ASD. Rarely a partial AVSD will have no primum ASD, but will have only an IVSD. The best views for evaluation include the subcostal long axis and short axis views to look at the AS and the AVV, the apical 4C view for the AVVs and ventricular shunting, and the parasternal short axis for the VS and the cleft in the MV (see Box 6-3).

A transitional AVSD refers to a complete AVSD in which there are chordal attachments of the AVV to the crest of the VS, resulting in a restrictive VSD or no shunting at the ventricular level. There is a single AVV and a primum ASD. Imaging views are the same as for complete AVSDs (see Box 6-3).

Key Points

• Full definition of the AVSD is needed to assist with surgical planning. The surgeon will use the information from the echo to determine which approach to use in septation of the heart and creating two separate AVVs from the single AVV.

• The atrial component of an AVSD may be quite large, resulting in a “common atrium.” In this situation, drainage of the systemic and pulmonary veins should be clearly defined before surgical intervention.

• The VSD may appear to be small in the apical 4C view, at least in a single plane. It is important to sweep the plane of the transducer from posterior to anterior in the heart to determine the extent of the defect.

• The primum ASD is usually moderate to large in size. Occasionally a patient may have a very small primum ASD of a size that is hemodynamically insignificant.

• Transitional AVSDs will often appear to have a significant ventricular component on two-dimensional imaging. There will be prominent chordal attachments to the VS, and when the defect is interrogated with CFD, minimal or no shunting will be detected.

Acquisition

Complete and Transitional Atrioventricular Septal Defect

Step 1: Assess the Atrioventricular Valve

• In the subcostal short axis view, look for attachments of the anterior bridging leaflet to the crest of the septum, to the right of the septum, or if the leaflet is free floating (Rastelli classification type A, B, or C).

• CFD assessment for AVVR. If present, quantify the degree and whether from the right or left side of the AVV (Fig. 6-9).

• Balance of the valve above the ventricles can be determined from the apical 4C view and subcostal short axis view.

• By drawing an imaginary line from the AS to the VS, does the valve look like it is equally committed to both ventricles?

• With CFD, determine whether there is flow across the valve into both ventricles (part of the assessment of “balance” of the valve).

Figure 6-9 Apical 4C color compare image of complete AVSD showing mild right- and left-sided AVVR.

Step 2: Assess the Inlet Ventricular Septal Defect

• Determine the presence and size of an IVSD.

• Determine direction of flow by CFD and spectral Doppler.

• Assess the remainder of the VS for additional VSDs.

• Apical 4C and parasternal long axis and short axis views allow for good imaging of the VS.

Step 3: Assess the Primum Atrial Septal Defect

• The primum ASD will be at the level of the AVV(s) and can be seen best in the subcostal long axis view but may also be seen in the apical 4C view.

• Determine the size of the defect.

• Determine the direction of flow by spectral Doppler and CFD.

• Assess for additional atrial level shunts.

Step 4: Assess for the Presence of Associated Defects

• LVOTO using the parasternal long axis view and apical 5C view.

• If LVOTO is present, need to assess the aortic arch for possible coarctation of the aorta.

• RVOTO, in particular TOF.

• A dilated coronary sinus (CS) suggests the presence of a left superior vena cava to the CS.

• Hypoplasia of one ventricle (Figs. 6-10 and 6-11).

• Coarctation of the aorta may be present in a right ventricular dominant AVSD.

• Pulmonary stenosis or RVOTO may be present in the left ventricular dominant AVSD.

• Patent ductus arteriosus (PDA).

Figure 6-10 Two images from an apical 4C view of a right ventricular dominant complete AVSD. A, During systole with the common AVV closed. The valve appears to be predominantly above the RV; also note the small LV. B, During diastole showing that the AVV opens predominantly into the RV.

Figure 6-11 Apical 4C view of a left ventricular dominant AVSD with the common AVV predominantly above the LV.

Step 5: Assess the Chamber Size and Function

• Shunting across the primum ASD may cause dilation of the right atrium (RA), RV, and PAs.

• Shunting across the VSD may cause dilation of the LV.

• When there is a large VSD present, the interventricular septal position is flattened.

Partial Atrioventricular Septal Defect

Step 1: Assess the Atrioventricular Valves

• The AVVs will be at the same level in the apical 4C view (Fig. 6-12).

• A cleft will be present in the left-sided (mitral) AVV and is best seen in the parasternal short axis or subcostal short axis view (Fig. 6-13).

• CFD and spectral Doppler evaluation for regurgitation and stenosis. If present, quantify the degree.

Figure 6-12 Apical 4C view of a partial AVSD. There is a large primum ASD above the AVVs, and the AVVs are at the same level.

Figure 6-13 Subcostal short axis view of the left-sided AVV showing a cleft in the anterior leaflet.

Step 2: Assess the Atrial Septum

• The primum ASD will be at the level of the AVV(s) and can be seen best in the subcostal long axis view but may also be seen in the apical 4C view.

• Determine the size of the defect.

• Determine the direction of flow by spectral and CFD.

• Assess for additional atrial level shunts.

Step 3: Assess the Ventricular Septum

• Partial AVSDs rarely have ventricle-level shunting.

• Assess for any ventricular shunting.

• Parasternal long axis and short axis views are best.

Step 4: Assess for Associated Defects

• LVOTO from the apical 5C view.

Step 5: Assess the Chamber Size and Function

• Shunting across the primum ASD may cause dilation of right heart structures.

• If there is significant left-sided AVVR, the LV and left atrium may become dilated.

Physiologic Data

Step 1: Atrioventricular Valves

• Assess severity of AVVR by CFD.

• Severity is a qualitative assessment.

• If there is a restrictive VSD, the right ventricular systolic pressure should be estimated from the TV regurgitation jet velocity by continuous wave (CW) Doppler.

Step 2: Atrial Septal Defect

• Assess the direction of the shunt with CFD.

• Assess the direction of the shunt with spectral Doppler.

• Spectral Doppler may make it easier to determine whether shunting is bidirectional.

Step 3: Ventricular Septal Defect

• Assess the direction of the shunt with CFD.

• Assess the direction of the shunt with spectral Doppler.

• Record the peak velocity by spectral Doppler.

Step 4: Outflow Tract Obstruction

• Peak velocity across the LVOT by pulsed and CW Doppler.

• Peak velocity across the RVOT by pulsed and CW Doppler.

Step 5: Hemodynamic Load on Ventricles

• Dilation of the RV.

• Dilation of the LV.

• Increased flow across the pulmonary valve.

• Increased left AVV inflow.

Pitfalls

• The IVSDs in complete AVSDs are usually large and nonrestrictive. A low spectral Doppler velocity may be present due to the large defect and should not be interpreted as evidence of pulmonary hypertension (PHTN).

• Right-sided AVVR Doppler velocity is increased if the VSD is nonrestrictive as the pressure from the LV is transmitted to the LV. The increased right heart pressures signifies the expected presence of elevated right ventricular pressure due to the large VSD. However, elevated right ventricular pressure (expected) does not equate to increased pulmonary vascular resistance (PVR), which is typically a late finding associated with pathologic changes in the pulmonary vasculature.

• The balance of an AVSD is often best determined on the initial study done in the newborn period. Later studies may be difficult to interpret due to dilation of chambers that occurs secondary to shunting at the atrial or ventricular level.

• LVOTO may develop after surgical repair and not be evident on preoperative studies.

• AVV regurgitation may be progressive over time before surgery, so follow-up ECGs are needed before surgical intervention.

In older patients with complete AVSDs with no previous surgery, elevation of PVR (also termed Eisenmenger syndrome) will develop. The anatomic findings are the same as those seen before surgery, but with the increased right heart pressures, the shunting at the VSD may be right to left. In unoperated-on patients, significant AVVR may also develop.

Intraoperative imaging by transesophageal echocardiography (TEE) can assist with identifying AVV morphology, AVVR, and other associated defects at the time of the initial surgery. Immediate postoperative assessment of the surgery can be done after cardiopulmonary bypass and should include looking for residual VSDs, ASDs, AVV stenosis or insufficiency, and LVOTO or RVOTO. The finding of a left ventricular-to-right atrial shunt is termed a Gerbode defect. This will be of high velocity due to the pressure difference between these two chambers. This can be confused with residual tricuspid regurgitation jetting into the RA, which will be of low velocity postoperatively if the right ventricular pressure has appropriately decreased.

After surgery, patients will require lifelong follow-up. Echocardiography can be helpful in assessing for residual atrial or ventricular level shunting. The right- and left-sided AVVs should be assessed not only for regurgitation, but also for stenosis. Severe left AVVR may occur in as many as 20% immediately postoperatively, and 10% to 15% of patients will require reoperation. LVOTO may occur in 10% to 15% of patients after repair and is more common in partial AVSDs. Reoperation is required in 5% to 10% of patients to relieve the obstruction. If the repair was performed later in life, patients may be at risk of the development of PHTN and should be assessed for this possibility (Box 6-5).

Box 6-5

Postoperative Assessment

• AVVR

• Residual ASD

• Residual VSD

• LVOT

• PHTN

• Ventricular dysfunction

• Stenosis of AVV

Alternative Approaches

• Transthoracic echocardiography (TTE) is often the only imaging needed to determine the cardiac anatomy. Older patients may need to undergo TEE to define the anatomy.

• Usually echocardiography will fully define the anatomy to determine a treatment plan. Occasionally patients may require cardiac catheterization to evaluate PA pressures if there is concern about the presence of PHTN.

Suggested Reading

1 Backer CL, Stewart RD, Mavroudis C. Overview: History, anatomy, timing, and results of complete atrioventricular canal. Semin Thorac Cardiovasc Surg Pediatr Card Surg Annu. 2007:3-10.

A review of the history of surgical repair of AVSD, timing of repair, and recent outcomes.

2 Bakhtiary F, Takacs J, Cho MY, et al. Long-term results after repair of complete atrioventricular septal defect with two-patch technique. Ann Thorac Surg. 2010;89:1239-1243.

A study looking at 121 consecutive patients from 1975 to 1995 with regard to mortality and need for reoperation.

3 Cohen MS. Common atrioventricular canal defects. In: Lai WW, Mertens LL, Cohen MS, Geva T, editors. Echocardiography in Pediatric and Congenital Heart Disease: From Fetus to Adult. Hoboken, NJ: Wiley-Blackwell; 2009:230-248.

A chapter with a discussion of echocardiographic findings in AVSDs.

4 Cohen GA, Stevenson JG. Intraoperative echocardiography for atrioventricular canal: Decision-making for surgeons. Semin Thorac Cardiovasc Surg Pediatr Card Surg Annu. 2007:47-50.

Discussion of the use of pre- and postoperative TEE to assist with surgical planning and evaluation of surgical results.

5 Craig B. Atrioventricular septal defect: from fetus to adult. Heart. 2006;92:1879-1885.

Review of AVSDs including fetal diagnosis.

6 Ebels T, Elzenga N, Anderson RH. Atrioventricular septal defects. In: Anderson RH, Baker EJ, Redington A, et al, editors. Paediatric Cardiology. 3rd ed. Philadelphia: Elsevier; 2010:553-589.

A chapter with a thorough review of anatomy, pathophysiology, evaluation, and treatment discussions.

7 Espinola-Zavaleta N, Munoz-Castellanos L, Kuri-Nivon M, Keirns C. Understanding atrioventricular septal defect: Anatomoechocardiographic correlation. Cardiovasc Ultrasound. 2008;6:33.

Echocardiographic images compared with pathology specimens with similar findings with the conclusion of good correlation between echocardiographic findings and anatomy.

8 Lim DS, Ensing GJ, Ludomirsky A, et al. Echocardiographic predictors for the development of subaortic stenosis after repair of atrioventricular septal defect. Am J Cardiol. 2003;91:900-903.

This article looks at 448 patients with AVSDs, finding 10 with subaortic stenosis. Findings suggest that displacement of the AVV into the LV may be a marker of potential subaortic stenosis. In evaluating the LVOT look for displacement of the AVV into the LV as potential indication of development of LVOT after repair.

9 Mahle WT, Shirali GS, Anderson RH. Echo-morphological correlates in patients with atrioventricular septal defect and common atrioventricular junction. Cardiol Young. 2006;16:43-51.

A good review of echocardiographic imaging of AVSDs and the limitations of imaging.

10 Sittiwangkul R, Ma RY, McCrindle BW, et al. Echocardiographic assessment of obstructive lesions in atrioventricular septal defects. J Am Coll Cardiol. 2001;38:253-261.

This article looks at 549 patients with AVSDs for left-sided inflow or outflow obstruction with the conclusion that echocardiography provides accurate preoperative information.