Echocardiography in Pediatric and Adult Congenital Heart Disease, 2nd Ed.

7. Atrioventricular Septal Defects

INTRODUCTION AND SURGICAL HISTORY

Atrioventricular septal defects (AVSDs) comprise a spectrum of lesions characterized by deficient atrioventricular (AV) septation and a variety of AV valve anomalies. AVSDs occur due to failure of fusion of the embryonic endocardial cushions. AVSDs represent 4% to 5% of congenital heart defects. Other terms have been used to describe this group of defects, including “AV canal defect,” “persistent common AV canal,” “atrioventricular defect,” and “endocardial cushion defect.” For the purposes of this chapter, the term “AVSD” will be used. The severity of AVSD is determined by many factors, including the size of atrial and ventricular level shunts, the extent of AV valve abnormalities, the presence of associated cardiac anomalies, and discrepancy in ventricular sizes.

The first surgery for AVSD was performed by Clarence Dennis in 1951 at the University of Minnesota and was the world’s first use of a cardiopulmonary bypass machine. The case involved a 6-year-old girl who was intraoperatively discovered to have an AVSD. She unfortunately died; her defect was deemed “unrepairable.” At that time, the lack of understanding of surgical anatomy made repair extremely challenging. Gian Carlo Rastelli, an Italian born research surgical associate at Mayo Clinic, recognized the important need for better understanding of surgical anatomy. In 1966, Rastelli and John Kirklin at Mayo Clinic published a detailed anatomic review of AVSD resulting in the “Rastelli” Classification for AVSD. In 1968, Rastelli reported the surgical outcomes of AVSD and described novel reparative techniques. This study revealed a 40% reduction in hospital mortality. His novel surgical techniques revolutionized operative management of AVSD. Rastelli later went on to describe the “Rastelli procedure” for relief of pulmonary outlet obstruction in patients with transposition, VSD, and pulmonary stenosis. Despite his enormous contributions to the field, he was diagnosed with Hodgkin lymphoma at age 31 years and eventually died at age 36. Strikingly, Rastelli kept the severity of his illness secret from his peers and it was during this time when he produced these immense contributions to the understanding of AVSD. Thanks in large part to the foundation of knowledge that Rastelli established, long-term survival after surgical repair for AVSD has improved and 20-year survival of 95% is now reported. However, reoperation awaits 15% to 25% of patients because of progressive left AV valve regurgitation or development of left ventricular outflow tract (LVOT) obstruction. Therefore, long-term postoperative echocardiographic surveillance is required in all patients with AVSD.

TERMINOLOGY AND CLASSIFICATION

Many classification schemes have been used to describe AVSDs, resulting in confused terminology (Figs. 7.1 and 7.2). There is general agreement that AVSDs can be subdivided into two forms: complete and partial. Complete AVSDis characterized by a primum atrial septal defect (ASD) that is contiguous with an inlet ventricular septal defect (VSD), and the presence of a common AV valve. The common AV valve is composed of five leaflets: anterior and posterior bridging leaflets, an anterior leaflet (present on the right side), and right and left lateral leaflets.

The typical partial AVSD is distinguished from complete forms of the malformation by the absence of an inlet VSD. The anatomic hallmarks of partial AVSD are the primum ASD and a cleft in the anterior mitral valve leaflet. A valvular “cleft” differs from a commissure in that a cleft has no cords arising from the edges and is without subjacent papillary muscle tissue. This type of AVSD has distinct mitral and tricuspid valves, each with a complete and separate annulus.

Two other subtypes, the intermediate and transitional forms, have been described. Intermediate AVSD is considered a variant of complete AVSD and is characterized by a single AV valve annulus that is divided by a tongue of tissue into right and left orifices. Because of the single annulus, it is preferred to use the terms “right and left components of the common AV valve” in complete and intermediate AVSDs rather than “tricuspid” and “mitral” valves.

transitional AVSD has two separate AV valve annuli and is considered a variant of partial AVSD. In addition to a primum ASD and a cleft mitral valve, there is a small inlet VSD that is often restricted or obliterated by dense chordal attachments of the AV valves to the crest of the ventricular septum. Complete and intermediate AVSDs have the physiology and clinical features of an ASD and a VSD. In contrast, partial and transitional AVSDs have the clinical picture of a large ASD (Table 7.1).

Figure 7.1. Summary of atrioventricular septal defects (AVSDs). Anatomic and physiologic similarities between the different forms of AVSD are illustrated. Complete AVSD has one annulus with a large atrial septal defect (ASD) and a large ventricular septal defect (VSD). Intermediate defects (one annulus, two orifices) are a subtype of complete AVSD. Complete AVSD has physiology of a VSD and an ASD. Partial AVSD has physiology of an ASD. Transitional defects are a subtype of partial AVSD in which a small inlet VSD is also present. Partial defects and the intermediate form of complete AVSD share a similar anatomic feature: a tongue of tissue divides the common AV valve into distinct right and left orifices. AV, atrioventricular; LA, left atrium; LPV, left pulmonary vein; LV, left ventricle; RA, right atrium; RPV, right pulmonary vein; RV, right ventricle.

Figure 7.2. Spectrum of atrioventricular septal defects (AVSD). The diagrams on the upper row illustrate the spectrum of AVSDs. Partial (upper left), transitional (upper middle), and intermediate (upper right) forms of AVSD. The spectrum of complete AVSD can be subclassified into Rastelli types A, B, and C, illustrated in the lower row of diagrams. A, anterior leaflet; AB, anterior bridging leaflet; I, inferior leaflet; LML, left mural leaflet; P, posterior leaflet; PBL, posterior bridging leaflet; RML, right mural leaflet; S, septal leaflet (with permission of Mayo Foundation).

CHARACTERISTIC ANATOMIC FEATURES OF AVSDS

A number of characteristics are shared by all forms of AVSDs. These features aid in making the echocardiographic diagnosis of AVSD and have important clinical implications (Table 7.2).

Level of Atrioventricular Valve Insertion

In normal hearts, the tricuspid valve inserts onto the ventricular septum more apically than the mitral valve. With this “offset” in the level of insertion, a portion of septum, called the AV septum (Fig. 7.3A), separates the right atrium (RA) and the left ventricle. In AVSDs, both right and left AV valve components insert at the same level, and this is best appreciated from an apical four-chamber view. Apical four-chamber imaging demonstrates the crux of the heart, which has been referred to as the most reliable and consistent intracardiac landmark. A unifying feature of all forms of AVSDs is the complete absence of the AV septum (Fig.7.3B).

Unwedging of the Aortic Valve

In normal hearts, the aortic valve is “wedged” between the mitral and tricuspid valves (Fig. 7.4). In AVSDs, the aortic valve is “sprung” and displaced anteriorly. This contributes to elongation of the LVOT. This is best appreciated from the parasternal long-axis and subcostal outflow views.

Figure 7.3. Atrioventricular septum (AVS). A: Diagram of the AVS (shaded area) in the normal heart (four-chamber view). The AVS lies between the right atrium and the left ventricle. The interatrial septum is above and the interventricular septum is below the AVS. The septal tricuspid leaflet normally inserts at a lower (more apical) level than the anterior mitral leaflet. B: Line drawing demonstrating the deficiency of the AVS in all forms of AVSD (with permission of Mayo Foundation).

Figure 7.4. Unwedged aortic valve. Left: Normal pathologic specimen cut in short-axis at the base demonstrating where the atrioventricular junction has a “figure eight” configuration. Right: Similar projection in a heart with an atrioventricular septal defect (AVSD) where the atrioventricular junction is “unwedged.” The aortic valve between the atrioventricular valve annuli is anteriorly displaced (instead of being wedged). This elongates the left ventricular outflow tract (LVOT) in AVSDs.

Elongation of the Left Ventricular Outflow Tract

In normal hearts, the distance from the left ventricular (LV) apex to the aortic annulus is equal to the distance from the LV apex to the mitral annulus (Fig. 7.5). The inlet and outlet portions of the left ventricle are approximately equal in length. In contrast, the deficiency of the AV septum and apical displacement of the left AV valve insertion in AVSDs lends a scooped-out appearance to the ventricular septum and results in a shorter inlet portion. In addition, the anterior displacement of the unwedged aortic valve leads to an elongated and narrowed LVOT. The narrow, long LVOT has been classically described as having a “goose neck” appearance. This can be identified on angiographic and echocardiographic long-axis views of the left ventricle. This anatomic feature is clinically important since it provides the substrate for development of LVOT obstruction, especially when present with other findings such as aberrant left AV valve chordal insertions or displacement of a papillary muscle anteriorly into the LVOT.

Figure 7.5. Left ventricular outflow elongation in atrioventricular septal defects (AVSD). The two diagrams in the upper left illustrate the LV inlet and outlet lengths in the normal heart (left) and in one with an AVSD (right). In patients with AVSD, the LV outlet is much longer than the inlet. Due to deficiency of the ventricular component of the atrioventricular septum and the “unwedged” aortic valve, the distance from the LV apex to the posterior left atrioventricular valve annulus is 20–25% shorter than the distance from the apex to the aortic annulus. Upper right: Pathologic specimens cut in long-axis projection in (A) a normal heart and (B) a heart with AVSD. These images demonstrate the changes in relative inlet/outlet length that were outlined by the diagrams. As a result, the distance from the LV apex to the aortic annulus is notably longer than the distance from the apex to the mitral annulus in AVSD, as opposed to nearly equal distances in the normal heart. Lower left: Apical five-chamber view demonstrating the elongated LVOT typical of AVSD. It has been described as a “goose neck.” Lower right: Springtime in Rochester, MN with pediatric and adult “goose necks.” (Upper left image with permission from Robert Anderson, MD.)

Figure 7.6. Cleft left atrioventricular valve. A: Left: In atrioventricular septal defect (AVSD), the cleft in the anterior leaflet of the left atrioventricular valve is typically oriented toward the mid-portion of the ventricular septum (arrow) along the anterior-inferior rim of the septal defect. Right: Subcostal sagittal image demonstrating the septal orientation of the cleft. B: The cleft (arrow) in the anterior leaflet gives the valve a trileaflet appearance as seen in this parasternal short-axis image.

Cleft of the Left Atrioventricular Valve

In partial AVSDs, the anterior mitral leaflet inserts onto the crest of the ventricular septum (Fig. 7.6). A cleft is invariably present in the anterior mitral leaflet and it is directed toward the mid-portion of the ventricular septum. In complete AVSDs, the common AV valve consists of five leaflets, and the two that span across the ventricular septum are known as the anterior and posterior bridging leaflets. Conceptually, the anterior bridging leaflet corresponds to the superior half of the anterior mitral leaflet, and the posterior bridging leaflet represents fusion of the septal tricuspid leaflet and the inferior portion of the anterior mitral leaflet. No tongue of tissue separates the AV valve into right and left components, and the space between the anterior and posterior bridging leaflets is analogous to the cleft in the anterior mitral leaflet in partial AVSDs.

Counterclockwise Rotation of the Left Ventricular Papillary Muscles

In all forms of AVSD, the LV papillary muscles are rotated counterclockwise compared with normal. In the parasternal short-axis projection, normal mitral papillary muscles are located at the “4 o’clock” and “8 o’clock” positions. In AVSD, LV papillary muscles are rotated toward the “3 o’clock” and “7 o’clock” positions. This causes the anterior mitral leaflet (or anterior bridging leaflet) to be more anteriorly located and contributes to narrowing of the LVOT.

ECHO EVALUATION OF AVSDS

Primum Atrial Septal Defects

Echocardiography is the diagnostic modality of choice for delineation of all anatomic features of AVSDs (Figs. 7.7 to 7.10). The best transducer position to define the number and size of ASDs is the subcostal view, as the plane of sound is perpendicular to the atrial septum. Both the subcostal four-chamber and sagittal (bicaval) views are helpful in that regard. Color Doppler delineates the shunt. The primum ASD in partial AVSD is typically large and easily visualized in the subcostal, parasternal, and apical four-chamber projections. The TEE four-chamber view readily demonstrates a primum ASD and the insertion of the tricuspid and mitral valves onto the crest of the septum.

Figure 7.7. Partial atrioventricular septal defect (AVSD): Anatomic specimen. This heart has been cut in a plane simulating the apical four-chamber view and demonstrates the classic anatomy of a partial AVSD. The large primum atrial septal defect is highlighted by the arrow. Right atrial and right ventricular dilation are present. LA, left atrium; LV, left ventricle; RA, right atrium; RV, right ventricle.

Figure 7.8. Partial atrioventricular septal defect (AVSD): Echocardiographic anatomy. Top/right: The four-chamber echocardiographic images in the two upper panels correspond to the anatomic plane shown in Figure 7.7. The upper left image was captured in systole and illustrates how the septal components of the two atrioventricular (AV) valves are at the same level. The potential VSD has been sealed by chordal attachments (arrow). The upper right panel was captured in diastole; it more clearly demonstrates the presence of a large primum ASD (asterisk) and the distinctly separate right and left AV valve orifices. The two color Doppler images in the bottom panels are paired with the two-dimensional images above them. The systolic frame on the left demonstrates regurgitation of both AV valves. The diastolic frame on the right shows a low velocity, but large, left atrial–to–right atrial/ventricular shunt crossing the ASD. LA, left atrium; LV, left ventricle; RA, right atrium; RV, right ventricle.

Figure 7.9. Cleft Mitral Valve associated with partial atrioventricular septal defect (AVSD). These two parasternal short-axis scans are focused on the anterior mitral valve leaflet in the left ventricular inflow tract. The image on the left is taken in diastole and demonstrates the division of the anterior leaflet into two separate components. This division creates a triangular (three-leaflet) appearance to the diastolic orifice of the mitral valve. The gap between the two components is referred to as the “cleft” (asterisk). The image on the right is a systolic color Doppler map demonstrating mitral regurgitation associated with the cleft. LV, left ventricle. RV, right ventricle.

Figure 7.10. Partial atrioventricular septal defect (AVSD): Transesophageal Echocardiographic (TEE) anatomy. This diastolic four-chamber TEE image demonstrates a large primum ASD (asterisk) with insertion of both tricuspid and mitral valve leaflets to the crest of the ventricular septum. Marked RA and RV dilation are also evident, consistent with a large left-to-right shunt. LA, left atrium; LV, left ventricle; RA, right atrium; RV, right ventricle.

Figure 7.11. Cleft mitral valve (MV) and double-orifice atrioventricular valve. Left: Cleft MV. The anterior leaflet of the MV has a characteristic break (asterisk) that represents a cleft in the anterior leaflet. This feature is common to both partial and complete forms of atrioventricular septal defects (AVSDs). Right: Double-orifice atrioventricular valve. Each papillary muscle receives a separate atrioventricular valve orifice (arrows). The combined mitral orifice is less than the sum of both orifices and results in mitral stenosis. LV, left ventricle; RV, right ventricle; VS, ventricular septum. (Modified from Seward JB, Tajik AI, Edwards WD, et al. Two-Dimensional Echocardiographic Atlas. Vol. 1. Congenital Heart Disease. New York: Springer-Verlag, 1987:270–292.)

Mitral Valve Abnormalities

The cleft of the anterior mitral leaflet is best appreciated from subcostal and parasternal short-axis views (Fig. 7.11A). The cleft changes the appearance of the mitral valve from the usual “fish-mouth” to a triangular configuration. In patients with AVSD, the mitral valve cleft is directed toward the ventricular septum; in contrast, in patients with “isolated cleft of the mitral valve,” it is directed toward the LVOT. The cleft causes mitral regurgitation due to improper leaflet coaptation in that area. This regurgitation is usually progressive as the patient ages. The cleft is closed at the time of repair.

Several other abnormalities may occur in the mitral valve or the left component of the common AV valve. Left AV valve abnormalities occur much more commonly in partial than in complete AVSD. A tongue of tissue may divide the mitral valve into two orifices, creating what is known as a “double-orifice” mitral valve. This has been described in approximately 3% to 5% of AVSDs. The effective combined area of the two orifices is always smaller than the total area of the undivided orifice (Fig. 7.11B). Therefore, a double-orifice mitral valve is generally associated with stenosis. The leaflets are thickened and exhibit limited diastolic excursion.

Parachute deformity of the mitral valve has also been described in AVSDs. As the name suggests, mitral chordae attach to only one papillary muscle, creating the appearance of a parachute. The single dominant papillary muscle may restrict the left-sided orifice, causing functional stenosis. The parasternal short-axis view is best to assess the number of papillary muscles and it determines the presence of a two-orifice mitral valve. The mitral inflow gradient typically is evaluated by spectral Doppler from the apical four-chamber projection. However, in the setting of a large ASD, this measurement underestimates the severity of the stenosis because the ASD “decompresses” the left atrium.

Left Ventricular Outflow Tract Obstruction

In AVSD, the LVOT is elongate and narrow (Fig. 7.12). LVOT obstruction may be present preoperatively but more commonly develops postoperatively. LVOT obstruction is more common in partial AVSD than in complete AVSD. An explanation for this may be the fixation of the mitral valve leaflets to the crest of the ventricular septum. Other factors that contribute to LVOT obstruction are accessory chordal attachments to the septum and anterior displacement of the papillary muscles.

THE CONCEPT OF BALANCE

Both partial and complete AVSD can be either “balanced” or “unbalanced” based on how the AV junction is shared by the ventricles. If the AV inlet is equally shared by the two ventricular chambers, then this is consistent with a balanced AVSD. In an unbalanced AVSD, one ventricle is hypoplastic compared with the other. The larger ventricle is termed the “dominant” ventricle. For example, unbalanced AVSD with right ventricular (RV) dominance has a hypoplastic left ventricle with more than half of the AV junction committed to the right ventricle. RV dominance is associated with coarctation of the aorta and other arch anomalies. In contrast, unbalanced AVSD with LV dominance has a hypoplastic right ventricle and is associated with pulmonary stenosis or atresia. Unbalanced AVSD occurs in 10% to 15% of all AVSDs and two-thirds are RV dominant (Fig. 7.13A).

Figure 7.12. Left ventricular outflow tract (LVOT). A: Accessory mitral chordal attachments to the LVOT demonstrated on apical long-axis view. Note the relationship of the aortic valve (asterisk) and accessory chordal attachments (arrow), which can potentially contribute to LVOT obstruction. B: Parasternal long-axis view in a neonate with complete atrioventricular septal defect (AVSD) demonstrating tunnel-like LVOT obstruction and a discrete subaortic ridge (arrows). C: Parasternal long-axis view demonstrating LVOT obstruction in a 17-year-old after repair of partial AVSD at age 15 months. LVOT obstruction (arrow) is usually progressive and may be undetected at time of initial repair. Ten percent of patients with AVSD may require reoperation to relieve LVOT obstruction. Progressive LVOT obstruction is more common in partial than in complete AVSD. Mechanisms of LVOT obstruction include attachments of superior bridging leaflet to ventricular septum, extension of the anterolateral papillary muscle into the LVOT, discrete fibrous subaortic stenosis, and tissue from an aneurysm of the membranous septum bowing into the LVOT.

The relative sizes of the ventricles are best appreciated from the apical four-chamber view. This view also allows visualization of malalignment between the atrial and ventricular septa in complete AVSD. Malalignment of the atrial septum and the ventricular septum is another clue to an unbalanced AVSD. The subcostal en face view of the AV valves gives an estimate of the proportion of AV valve area committed to each ventricle. Determining balance in AVSD is important since it forms the basis for deciding on a single-ventricle versus biventricular surgical approach. Modest degrees of RV hypoplasia may also be addressed with a 1.5-ventricle strategy in which shunts are closed and a bidirectional cavo-pulmonary connection is formed.

Cohen and colleagues (Fig. 7.13B) proposed a quantitative approach using the en face subcostal view to delineate cases with LV hypoplasia that may be better palliated with a single-ventricle approach. These authors measured the area of the AV valve apportioned over each ventricle and calculated an AV valve index (AVVI) as a left/right valve area ratio. The AVVI may be used as the basis for an algorithm to stratify patients into a single-ventricle or biventricular pathway. Those with AVVI less than 0.67 who have a large VSD would be considered for a single-ventricle path. A retrospective study by Walter and colleagues suggested that outcome was improved in patients with small left ventricles undergoing biventricular repair if the long-axis ratio of LV to RV measured by angiography was greater than 0.65.

One has to be aware of several caveats that may make interpretation of balance less straightforward. For example, the severity of valve malalignment may not necessarily correlate with the degree of ventricular hypoplasia. Moreover, pulmonary venous blood preferentially flows across the ASD, causing underfilling of the left ventricle. Finally, the presence of a large left-to-right shunt may cause severe RV enlargement with bowing of the septum to the left, lending a hypoplastic appearance to the LV. van Son et al. attempted to estimate the “potential volume” of the LV preoperatively by using a theoretical model that calculates the relative areas of the LV and RV in short-axis after assuming normal septal configuration (Fig. 7.13C).

RASTELLI CLASSIFICATION OF THE COMMON ATRIOVENTRICULAR VALVE

Evaluation of common AV valve morphology is crucial to identify mechanism of regurgitation, commitment to the RV and LV masses, attachments of the valvular/subvalvular apparatus, and the existence of possible anomalies such as double-orifice left AV valve (Figs. 7.14 and 7.15). The best view that visualizes the anatomy of the valve is the “en face” view obtained from the subcostal window by rotating the transducer clockwise from the four-chamber view. Once the valve is seen “en face,” the transducer is then tilted slowly inferiorly and superiorly to obtain multiple short-axis views of the valve from the inferior margin of the atrial septum to the superior margin of the ventricular septum. Classifying the common AV valve into Rastelli Type A, B, or C is often made from this plane (see Fig. 7.2 and Table 7.3).

Figure 7.13. A: The four upper panels show examples of complete unbalanced atrioventricular septal defect (AVSD) with right ventricular (RV) dominance and left ventricular (LV) dominance. The plane of the ventricular septum is indicated with the dashed line. In the LV dominant form, the common atrioventricular (AV) valve opens predominantly into the LV, as opposed to the RV dominant form where the AV valve opens predominantly into the RV. B: Subcostal sagittal images demonstrating a variety of relative AV valve areas for use in evaluating ventricular dominance in AVSD. C: Diagram illustrating the concept of septal displacement in AVSD and its relative effect on ventricular dominance in AVSD. (A, with permission of Mayo Foundation. B, technique described by Cohen MS, Jacobs ML, Weinberg PM, et al. Morphometric analysis of unbalanced common atrioventricular canal using two-dimensional echocardiography. J Am Coll Cardiol. 1996;28:1017–1023. C, as described by van Son JA, Phoon CK, Silverman NH, et al. Predicting feasibility of biventricular repair of right-dominant unbalanced atrioventricular canal. Ann Thorac Surg 1997;63:1657–1663.)

Figure 7.14. Rastelli classification of common atrioventricular valves in complete atrioventricular septal defects. A (left upper and lower panels): Rastelli Type A defects are characterized by insertion of the atrioventricular valves to the crest of the ventricular septum (VS). B (central upper and lower panels): Type B defects are characterized by dominant insertion of the anterior leaflets into papillary muscles in the right ventricle (RV). In this example, the anterior bridging leaflet inserts onto the crest of the ventricular septum, as well as onto a large ventricular papillary muscle (P). C (right upper and lower panels): Type C. The anterior leaflet is unattached (small arrows) and overrides the crest of the ventricular septum. The undivided, free-floating anterior leaflet does not insert onto the ventricular septum. I, inferior; L, left; LA, left atrium; LV, left ventricle; RA, right atrium; S, superior (modified from Seward JB, Tajik AJ, Edwards WD, et al. Two-Dimensional Echocardiographic Atlas. Vol. 1. Congenital Heart Disease. New York: Springer-Verlag, 1987:270–292.)

The Rastelli classification of the common AV valve is applicable only to complete forms of AVSD. The three types of common AV valve described by Rastelli and his colleagues are illustrated in Figures 7.2and 7.14. The classification originally had prognostic implications and is based on the attachment and degree of bridging of the anterior bridging leaflet. While the Rastelli classification is helpful when communicating with surgeons, a descriptive approach of valve morphology should be the primary focus of the echocardiographer rather than condensing the features into an imperfect scheme. The spectrum of common AV valve anatomy seen in complete AVSD is illustrated in Figs. 7.14 and 7.15Type A complete AVSD has an anterior bridging leaflet that is evenly divided between the two ventricular inlets. Chordae anchor the center of the right and left components of the anterior bridging leaflet to the anterosuperior ventricular septum. The commissure between these components overlies the septum and VSD. In cases with Type B morphology, the anterior bridging leaflet is unevenly divided and its commissure and papillary muscle attachments lie within the RV. The anterior bridging leaflet in patients with Type Cmorphology is completely undivided with no central commissure. The chordal/papillary muscle attachments are evenly divided between the two ventricular cavities, but there are no attachments to the anterosuperior septum. As a result, this undivided anterior bridging leaflet has been described as “free-floating.”

Figure 7.15. Anatomic and echocardiographic examples of common atrioventricular valves: The image in the upper left panel is an anatomic specimen, dissected in a plane simulating a short-axis view of the ventricles and common atrioventricular valve. This valve has Type A morphology with an evenly divided anterior bridging leaflet and central attachments to the ventricular septum (arrow). The echocardiographic (subcostal) image on the upper right shows similar findings in a different patient. The middle panels show a common AV valve with Type C morphology. The systolic (left) and diastolic (right) subcostal sagittal frames demonstrate a “free-floating,” unattached anterior bridging leaflet (arrow). Imaging note: The subcostal sagittal view is the most helpful for the determination of the Rastelli classification of AVSD. The bottom panels show apical four-chamber echocardiographs from a patient with complete AVSD in systole (left) and diastole (right). Imaging note: The apical four-chamber scanning plane is posterior to the anterior bridging leaflet and does not adequately evaluate its attachments. The posterior bridging leaflet can be seen and typically appears “attached” to the septum in all forms of AVSD. LA, left atrium; LV, left ventricle; RA, right atrium; RV, right ventricle; VS, ventricular septum.

LESIONS ASSOCIATED WITH AVSD

Left AV valve abnormalities and LVOT obstruction comprise the majority of associated issues with all forms of AVSD. In addition, partial AVSD has been associated with secundum ASD and connection of a left superior vena cava to the coronary sinus. RV outflow tract abnormalities are most common in Type C complete AVSD. Other associated anomalies are: pulmonary valve atresia, double-outlet right ventricle, and anomalous pulmonary venous connections. All of these occur more commonly with complete AVSD.

Unbalanced AVSD with LV dominance is associated with defects resulting from anterior malalignment of the ventricular septum such as pulmonary stenosis, pulmonary atresia, and tetralogy of Fallot. Unbalanced AVSD with RV dominance is associated with defects resulting from posterior malalignment of the ventricular septum including subaortic stenosis, coarctation of the aorta, and interrupted aortic arch.

Abnormalities of sidedness (situs) can also occur in association with AVSDs. Most cases of right atrial isomerism are associated with complex forms of AVSD, typically with a common atrium and unbalanced ventricles (see Fig. 7.13). There is also a reported association of complete AVSD with double-outlet right ventricle in the setting of left atrial isomerism syndrome.

DOWN SYNDROME AND AVSD

A clear association exists between AVSD and Down syndrome. About 40% of individuals with Down syndrome have an underlying congenital heart disease, and approximately 40% of those have an AVSD. Conversely, approximately half the patients afflicted with an AVSD have Down syndrome. Type A is the most common subtype of complete AVSD seen in Down syndrome. The combination of tetralogy of Fallot with AVSD occurs more commonly in patients with Down syndrome than in patients with normal karyotype. Heterotaxy is rare in those with Down syndrome. Also, patients with Down syndrome are less likely to have associated LVOT obstruction, LV hypoplasia, coarctation of the aorta, or additional muscular VSDs. In the 1960s–1970s, patients with Down syndrome reportedly had a worse prognosis after surgical repair of AVSD than did patients with normal karyotype. Currently, surgical outcome is excellent for all patients with AVSD. However, duration of postoperative hospitalization may be longer for patients with Down syndrome.

FETAL ECHO

AVSD is readily identified with fetal echocardiography, and is often detected during routine obstetrical four-chamber ultrasonography (Fig. 7.16). In a population-based study, Allen and colleagues from the United Kingdom found that AVSD was one of the most common forms of congenital heart disease detected by fetal echocardiography. The ratio of the atrial-to-ventricular septal length (AVL) may assist in evaluation of fetal AVSD. This is based on the fact that the length of the atrial septum is not affected in AVSD. However, the “scooped-out” ventricular septum (measured from the level of AV valve insertion to LV apex in four-chamber view) is much shorter than normal. The mean AVL was found to be 0.47 in normal fetuses, versus 0.77 in AVSD. A cutoff value of AVL ratio of 0.6 is characteristic of AVSD. If used routinely, this measurement may be useful to increase the yield of obstetrical ultrasonography in detecting AVSD.

Antenatal detection of AVSD should also prompt the search for other associated cardiac anomalies as well as fetal karyotype testing. Up to 45% of cases of prenatally detected AVSD have heterotaxy syndromes; most have left atrial isomerism. Heart block has been described in 10% to 15% of fetal cases of AVSD and is more common in those with left atrial isomerism. An association of trisomy 21, AVSD, and complete heart block has also been described. Prognosis for fetuses with structural cardiac disease and complete heart block remains poor.

Figure 7.16. Prenatal common atrioventricular valve regurgitation: these images were taken during an examination of a 31-week gestation fetus. They revealed severe common atrioventricular valve regurgitation. The upper right panel was taken in diastole, the upper left in systole, and the lower panel in a systolic image with color Doppler. All demonstrate a common atrium, common atrioventricular valve, and common ventricle. Color flow outlined a broad regurgitant jet in this case.

SURGICAL REPAIR AND POSTOPERATIVE ECHO

Partial AVSD

Major advancements have been made in the surgical management of partial AVSD, with significant reduction in morbidity and mortality over the past few decades. The aim of surgery in partial AVSD is to close the interatrial communication and restore mitral valve competence while avoiding creation of a stenotic valve and inadvertent damage to conduction tissue. The mitral valve cleft is usually closed. Sometimes the tricuspid valve also requires repair. Currently, surgery for repair of partial AVSD is performed at 18–24 months of age. However, recent data from our institution show that if repair of partial AVSD is delayed until later in childhood (5–8 years old) the incidence of moderate or greater mitral regurgitation is much lower than in those repaired in infancy. Transcatheter device closure of the primum ASD is not an option because of the proximity of the defect to the AV valves and AV node; the latter is displaced inferiorly and is positioned between the coronary sinus ostium and the ventricular crest. In the current era, surgical mortality is <3% and complete heart block is rare.

Complete AVSD

Complete AVSD is repaired between 3 and 6 months of age. Early repair is desirable to avoid the development of pulmonary vascular disease. Operative mortality is usually less than 3%. Despite these advancements, the need for reoperation remains a problem: 10% to 15% of patients require reoperation for left AV valve issues or development of progressive LVOT obstruction.

The aim of surgical repair in uncomplicated complete AVSD is to close any intracardiac shunts and divide the common AV valve into competent right and left orifices. In complete AVSD, the primum ASD and inlet VSD are contiguous, so they can be closed using a single-patch or a double-patch technique. The former technique has been modified from its original “classic” description and currently involves direct suturing of the common AV valve leaflets to the crest of the ventricular septum, then using a single patch for closing the defect above the AV valve and separating it into two orifices. The classic single-patch technique consists of dividing the AV valve into right and left components, placement of a single patch across the ASD and VSD, and then reattaching the two “halves” of the AV valve to the mid-portion of the patch. As the name implies, a double-patch technique uses two patches: a pericardial patch for closure of the ASD and a synthetic patch to close the VSD. The modified single patch or “Australian technique” is a third pathway for repair. It involves “tucking” the bridging leaflets onto the crest of the ventricular septum while leaving the leaflets intact rather than dividing them. One then attaches the two “halves” of the AV valve onto the septum.

These techniques have been used in clinical practice, each with its own advocates and opponents. Theoretical concerns with the single-patch technique include crowding of the LVOT, providing a substrate for obstruction, higher incidence of residual VSD, and increased AV valve regurgitation due to shifting of the AV valve hinge-point to a “nonphysiologic” height. In contrast, the two-patch technique is thought to result in more normal anatomy. In that technique, one of the patches serves to reconstruct the deficient portion of the inlet septum. The Australian technique may have an advantage over the single- and two-patch repairs because the bridging leaflet anatomy remains intact. Subsequently, this has been shown to result in decreased reoperation for left AV valve dysfunction. Nevertheless, further studies are needed to elucidate these differences.

Patients with AVSD with associated tetralogy of Fallot (so called “Tet canal”) were traditionally repaired using a two-stage approach with a systemic-to-pulmonary artery shunt in infancy followed by complete repair later in childhood. More recently, multiple centers have reported primary repair of this lesion in infancy with good results.

Transesophageal echocardiography (TEE) is a useful tool in the operating room during the repair of AVSD. The TEE prior to initiation of cardiopulmonary bypass often provides incremental information regarding the exact anatomy of the AV valves. After cessation of cardiopulmonary bypass, assessment of ventricular function, residual intracardiac shunts, and AV valve stenosis and regurgitation can be assessed prior to chest closure.

Postoperative Echo Follow-up

Postoperative echocardiography is used to assess AV valve regurgitation or stenosis, residual atrial or ventricular septal defects, LVOT obstruction, pulmonary hypertension, and ventricular dysfunction (Fig. 7.17).

Left AV valve regurgitation is the most common problem encountered after the repair of AVSD, and it is the most common reason for reoperation. Severe left AV regurgitation is present in approximately 20% of patients immediately postoperatively. However, approximately 25% of those patients show normalization of their left AV valve competence over time. Ultimately, 10% to 15% of all patients require reoperation for left AV valve regurgitation. Traditionally, an important predictor of postoperative severe left AV valve regurgitation was the presence of severe regurgitation preoperatively. However, several recent studies have drawn that into question. Other risk factors for severe postoperative left AV valve regurgitation include: significant intraoperative valve regurgitation, left AV valve dysplasia, and failure to close the cleft. Stenosis is more likely to develop in the hypoplastic, dysplastic, double-orifice, or parachute mitral valves and is further “unmasked” postoperatively once the ASD is closed.

Figure 7.17. Patient with partial atrioventricular septal defect (AVSD) after patch closure of a primum atrial septal defect (ASD) and repair of a cleft mitral valve. Left: Four-chamber anatomic specimen. The patch (arrow) is attached to the right side of the atrial septum and the right AV valve to avoid damage to the conduction tissue and left AV valve. Right: Corresponding apical four-chamber echocardiograph.

In a recent review, Stulak and colleagues described the Mayo Clinic’s 35-year experience with reoperation for patients with complete AVSD. Fifty patients had reoperation after previous successful repair of AVSD at a median age of 1 year. Forty of the 50 patients (80%) required reoperation due to left AV valve regurgitation. Half of these patients had left AV valve re-repair and half had valve replacement. These results are encouraging because traditionally, most patients have anticipated left AV valve replacement during the reintervention. Fifteen-year survival after reoperation for complete AVSD was 86%.

Doppler interrogation of right and left AV valve stenosis or regurgitation is warranted. A search for residual shunts should also be performed. Doppler evaluation of the velocity profiles across a ventricular level shunt and right AV valve regurgitation can provide accurate determination of RV systolic pressure. However, in the setting of a residual VSD, the VSD jet may contaminate the right AV valve regurgitation signal and preclude accurate quantification of RV systolic pressure. In that setting, the echocardiographer needs to use indirect techniques such as assessment of ventricular septal flattening or bowing, RV size and function, and Doppler interrogation of the pulmonary regurgitation velocity to assess pulmonary artery diastolic pressure.

Progressive LVOT obstruction occurs in up to 15% of patients after repair of partial AVSD. It is more frequent in partial than complete AVSD. The “goose neck deformity” described earlier serves as the substrate for the development of obstruction. The rate of reoperation for LVOT obstruction is about 5% to 10% and appears higher for patients with partial AVSD. One approach to repair LVOT obstruction is resection of any discrete areas of obstruction due to muscle ridges or accessory chordal tissue and, when necessary, peeling of fibrous tissue from the anterior surface of the mitral valve. A septal myectomy may also decrease the likelihood of recurrence. Because of the persistent risk for the development or progression of LVOT obstruction years after the repair, lifelong follow-up of these patients is warranted.

SUMMARY

Echocardiography is the imaging modality of choice for diagnosis and management of all forms of AVSDs. Meticulous assessment of progressive left AV valve regurgitation or stenosis and progression of LVOT obstruction is required during serial evaluations. Despite the need for reoperation in a subset of these patients, long-term survival is excellent.

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Questions

1.Which of the following is the correct description of the anterior bridging leaflet (ABL) and chordal attachments in complete AVSD Rastelli Type B?

A.ABL is divided and attached to the crest of the ventricular septum.

B.ABL is partly divided into two components, but not attached to the crest of the septum. Instead, chordae attach to a papillary muscle in the LV.

C.ABL is undivided and unattached to the ventricular septal crest (“free-floating”); chordal attachments are to a papillary muscle on the RV free wall.

D.ABL is partly divided into two components, but not attached to the crest of the septum. Chordae are attached to a papillary muscle in the RV.

2.Which imaging plane is optimal for distinguishing the Rastelli class of the common AV valve in complete AVSD?

A.Parasternal long-axis

B.Parasternal short-axis

C.Subcostal sagittal

D.Suprasternal notch

3.Which of the following distinguishes intermediate AVSD from complete AVSD?

A.Inlet VSD

B.Common AV valve annulus

C.Two orifices within the common AV valve separated by a tongue of leaflet tissue

D.Primum ASD

4.An anatomic feature shared by all forms of AVSD is?

A.septal insertion of the right AV valve inferior to the level of the left AV valve.

B.unwedged and anterior displacement of the aortic valve.

C.shortened LVOT.

D.clockwise rotation of the LV papillary muscles.

5.Which is the most common type of AVSD in patients with Down Syndrome?

A.Partial AVSD

B.Complete AVSD Rastelli Type A

C.Complete AVSD Rastelli Type B

D.Complete AVSD Rastelli Type C

6.What is the most common problem encountered after AVSD repair?

A.Right AV valve regurgitation

B.LVOT obstruction

C.Left AV valve stenosis

D.Left AV valve regurgitation

7.What percentage of patients with Down Syndrome and congenital heart disease have AVSD?

A.20%

B.40%

C.60%

D.80%

8.The AV valve index (AVVI) is a ratio of left/right valve area and is used as a basis for an algorithm to stratify patients for single or biventricular repair in unbalanced AVSD. An AVVI less than ___ would be considered for single-ventricle pathway?

A.0.9

B.0.67

C.0.5

D.0.33

9.Which of the following has the physiology of a VSD + ASD?

A.Intermediate AVSD

B.Partial AVSD

C.Transitional AVSD

D.None of the above

10.Parachute mitral valve deformity in AVSD is associated with which anatomic abnormality?

A.Double orifice left AV valve

B.Accessory mitral chordal attachments to the LVOT

C.Supravalve mitral ring

D.Single dominant LV papillary muscle

Answers

1.Answer: D. In complete Type B AVSD, the chordal attachments of the anterior bridging leaflet are to an anomalous papillary muscle within the RV on the septomarginal trabeculation.

2.Answer: C. The subcostal sagittal view delineates the relationship between the anterior bridging leaflet and the anterior crest of the ventricular septum.

3.Answer: C. Intermediate AVSD can be thought of as a form of complete AVSD, with the exception of the existence of a tongue leaflet tissue connecting the anterior and posterior bridging leaflets to form two separate orifices within one common annulus.

4.Answer: B. Due to the failure of fusion of the superior and inferior endocardial cushions, the aortic valve is not able to descend to its normal position between the AV valves and is instead unwedged or “sprung” superiorly, resulting in an elongated or “stretched” LVOT.

5.Answer: B. AVSD Type A is the most common AVSD in Down Syndrome and, coincidently, is the most common AVSD in patients with normal karyotype.

6.Answer: D. Left AV valve regurgitation is the most common problem after surgical repair of AVSD, with 10-15% of patients requiring additional surgery.

7.Answer: B. Approximately 40% of individuals with Down Syndrome have congenital heart disease, and approximately 40% of those have an AVSD.

8.Answer: B. Patients with an AVVI ratio < 0.67 are better suited for single-ventricle palliation.

9.Answer: A. Intermediate and complete AVSD have physiology of VSD + ASD; partial and transitional AVSD have ASD physiology only.

10.Answer: D. In parachute deformity of the mitral valve, mitral chordae attach only to a single predominant LV papillary muscle, creating the appearance of a parachute. In this case, the left mural leaflet is often underdeveloped or absent.