The atrioventricular septal defects (AVSDs), also referred to as atrioventricular canal defects or endocardial cushion defects, encompass a wide spectrum of anatomic findings. The pathognomonic feature of this group of hearts is a common atrioventricular junction [1]. The complete AVSD consists of a large ventricular septal defect beneath the plane of the atrioventricular (AV) valves, an atrial septal defect immediately superior to the plane of the AV valves, and, instead of two AV valve orifices, a single or common AV valve orifice. AVSDs account for 4% of all congenital cardiac malformations and over half of the cardiac defects seen in children with trisomy 21 [2, 3]. There can be varying degrees of incomplete development of the septal tissue surrounding the AV valve, along with varying degrees of abnormalities of the AV valves themselves, leading to the broad classification of partial, intermediate, and complete AV septal defects [4].

The first successful repair of a complete AVSD was reported by Lillehei and colleagues in 1955, using cross‐circulation and direct suture of the atrial rim of the septal defect to the crest of the ventricular septum [5]. The early experience with surgical correction of complete AVSD had a high mortality and a high incidence of complications such as complete AV block, residual AV valve insufficiency, and subaortic stenosis. Developments in the understanding of the precise anatomic details of this lesion and refinements in operative technique have led to substantial improvement in patient outcome (Figure 17.1) [6]. A significant advance occurred in 1958 when Maurice Lev described the location of the bundle of His in patients with complete AV septal defect [7]. This understanding resulted in a significant reduction in the incidence of postoperative heart block. In 1962, James Maloney and Frank Gerbode independently described a single‐patch technique suspending the AV valve tissue to a single patch that closed both the atrial and ventricular septal defects [8, 9]. Giancarlo Rastelli and colleagues at the Mayo Clinic described a classification system of complete AVSD in 1966 that emphasized the heterogeneity of this lesion and the different approaches required by different anatomic findings [10]. The two‐patch technique was first reported by George Trusler in 1975 [11]. This technique employed a Dacron patch to close the ventricular septal defect component, suturing the valve leaflets to the crest of the ventricular septal defect patch, closing the left AV valve zone of apposition, and using a pericardial patch to close the atrial septal defect component. More recently, Ben Wilcox from the University of North Carolina at Chapel Hill [12] and Graham Nunn from Sydney Children’s Hospital [13] have reported a technique of repair that does not use a patch for the ventricular septal defect closure. Congenital heart surgeons should be familiar with all techniques and, in point of fact, different anatomic morphology in different patients often lends itself to one of these three techniques. A recent review of over 800 patients from Australia demonstrated essentially equivalent outcomes comparing the modified single‐patch to the classic two‐patch repairs [14].

Pulmonary artery banding in infants with complete AV septal defect is used to limit pulmonary overcirculation in patients for whom a complete biventricular repair is either not feasible or high risk. In a Congenital Heart Surgeons’ Society 28‐institution study, pulmonary artery banding was found to be a successful strategy in patients with common AVSD to bridge to biventricular repair, and was associated with similar post‐biventricular repair survival to primary biventricular repair [15]. Improvements in neonatal and infant techniques of cardiopulmonary bypass, anesthesia, and postoperative intensive care unit medical management have allowed earlier repair of AVSDs, with, in nearly all instances, improvement in outcome by earlier date of operation. Most centers currently recommend repair of complete AVSDs at the age of 3–6 months (Figure 17.2).

Pathology and Anatomy

AVSD represents a spectrum of cardiac anomalies subdivided into partial, intermediate, and complete AVSDs [4]. Partial AVSD (also referred to as partial atrioventricular canal) has an atrial septal defect adjacent to the AV valves along with a trifoliate left AV valve, leading to varying degrees of left AV valve insufficiency (Figure 17.3). The atrial septal defect is a crescent‐shaped defect in the inferior portion of the atrial septum immediately adjacent to the AV valves. This defect has also been called an ostium primum atrial septal defect, which is a misnomer, as it has nothing to do with the septum primum (Figure 17.4).

Intermediate AVSD (also known as transitional atrioventricular canal) is “intermediate” between the partial and complete lesions: there are two distinct left and right AV valve orifices, an atrial septal defect adjacent to the AV valves, and a ventricular septal defect below the AV valves [16]. The ventricular septal defect in these patients is usually in the inlet septum, and there is no “bare area” at the crest of the ventricular septal defect.

Complete AVSD (also known as complete atrioventricular canal) has both an atrial septal defect and a defect in the ventricular septum below the common AV valve (Figure 17.5). In complete AVSD there is a common AV valve that bridges both the right and left sides of the heart, creating superior (anterior) and inferior (posterior) bridging leaflets. These patients always have a “bare area” at the crest of the ventricular septum. These anatomic variations (partial, intermediate, complete) are merely different phenotypic expressions of the same underlying genotype [17].

The Rastelli classification (Figure 17.6) [4] describes three types of complete AVSD based on the morphology of the anterior (superior) bridging leaflet, its degree of bridging, and its chordal attachments [10]. The Rastelli classification does not relate to the anatomy of the posterior common leaflet or inferior bridging leaflet. In a Rastelli type A defect, the common superior (anterior) bridging leaflet is effectively divided into two leaflets. The left superior leaflet is entirely over the left ventricle and the right superior leaflet is entirely over the right ventricle. This division of the common anterior leaflet into left and right components is accompanied by extensive attachment of the superior bridging leaflet to the crest of the ventricular septum by chordae tendineae. This morphologic finding effectively divides the anterior common AV valve into right and left components for the surgeon at the time of reconstruction. The anterior common leaflet is “divided and attached.” Rastelli type B is quite rare and describes an anomalous papillary muscle attachment from the right side of the ventricular septum to the left side of the common anterior bridging leaflet. In Rastelli type C defects, there is marked bridging of the ventricular septum by the anterior (superior) bridging leaflet. The anterior (superior) bridging leaflet is not divided and floats freely over the ventricular septum without chordal attachment to the crest of the ventricular septum. The anterior common leaflet is “not divided and not attached.” In our series of AV septal defect patients, the Rastelli classification breakdown in 110 patients was Rastelli A, 76 patients (69%), Rastelli B, 10 patients (9%), and Rastelli C, 24 patients (22%) [18].

There is a definite association of complete AVSD and other conotruncal anomalies, particularly tetralogy of Fallot, double‐outlet right ventricle, and transposition of the great arteries. The most common conotruncal anomaly associated with AVSD is tetralogy of Fallot. It is encountered in 6% of cases of AVSD [19]. The pathophysiology in these patients is dictated by the degree of right ventricular outflow tract obstruction, which causes varying degrees of cyanosis. Congestive heart failure is infrequent in these patients because of the restricted pulmonary blood flow. Double‐outlet right ventricle in association with complete AVSD is also rare (34 of 507 pathology specimens, 6%), and transposition of the great arteries is even rarer (17 of 507 specimens, 3%) [19]. Other anomalies associated with complete AVSD are patent arterial duct (10%), persistent left superior caval vein (3%), and left ventricular outflow tract obstruction (3%) from discrete subaortic stenosis or redundant AV valve tissue.

Deficiencies in the atrioventricular septum in patients with AV septal defects result in displacement of the atrioventricular conduction tissue (Figure 17.7) [7, 20]. The AV node is more posterior and inferior (near the coronary sinus ostium) than normal. The bundle of His usually courses along the inferior rim of the ventricular septal defect and therefore the bundle branches arise more inferiorly. It is this displacement of the AV node that causes the northwest axis on electrocardiogram.

Hemodynamics/Natural History

Patients with an AVSD initially have excessive pulmonary blood flow resulting from left‐to‐right shunting at the atrial and ventricular levels. If there is no interventricular communication, the hemodynamics are similar to those of a large atrial septal defect, with increased right ventricular stroke volume. As the AV valve insufficiency through the left AV valve increases over time, these patients may develop a larger left‐to‐right shunt. In some cases, the regurgitation from the left AV valve proceeds directly into the right atrium. These patients develop progressive cardiomegaly and congestive heart failure that is definitely more significant than in a patient with an atrial septal defect without left AV valve insufficiency.

In patients with a complete AVSD, the nonrestrictive ventricular component causes right ventricular and pulmonary artery pressures to be the same as the systemic (left ventricle) pressure. These patients have significant pulmonary hypertension from birth, which is unrelenting until they have complete intracardiac repair. They can have a relatively rapid progression of their pulmonary vascular disease [21]. Trisomy 21 appears to be associated with accelerated development of pulmonary hypertension [22]. Within a few months of birth, the pulmonary vascular resistance is frequently significantly elevated. In our series of AV septal defect patients, the mean pulmonary vascular resistance (PVR; u/m²) at 0–3 months was 2.1 ± 0.9, at 4–6 months was 4.0 ± 2.6, and at 7–17 months was 5.7 ± 3.0 [18]. The pulmonary hypertension and congestive heart failure are compounded by the presence of AV valve insufficiency, which increases the ventricular volume overload. It is the rapid elevation of pulmonary vascular resistance and progression of pulmonary vascular obstructive disease that makes early repair of complete AVSDs so important.

Diagnosis

Patients with a complete AVSD typically have all the classic symptoms of congestive heart failure in infants. This includes frequent upper respiratory tract infections, poor feeding and inadequate weight gain, and sweating with feeds. On physical examination, these patients will have tachycardia, tachypnea, dyspnea, and hepatomegaly. On cardiac examination, the precordium is hyperactive and if there is significant AV valve insufficiency a loud systolic murmur will be present. Chest x‐ray will demonstrate cardiomegaly with biventricular enlargement and increased pulmonary vascular markings. Electrocardiographic findings include biventricular hypertrophy, a prolonged P‐R interval, and a characteristic northwest or leftward and superior axis. Of note is that the appearance of left axis deviation on the electrocardiogram in a patient with an atrial septal defect should alert the surgeon to the possible presence of a partial AVSD type of defect.

Two‐dimensional echocardiography with Doppler color interrogation has become the standard for diagnosis and surgical preparation of patients with AVSDs [23, 24]. Two‐dimensional echocardiography can identify and characterize valvular abnormalities, atrial and ventricular septal defect morphology, and associated anomalies (e.g., left superior caval vein, patent arterial duct, left ventricular outflow tract obstruction). Color flow Doppler imaging provides accurate information regarding the degree of interatrial and interventricular shunting and assessment of AV valve insufficiency. For patients with a partial AVSD, the degree of left AV valve insufficiency and evaluation of the left AV valve “cleft” can be obtained with color Doppler examination. It is more and more frequent now for the diagnosis of complete AV valve defect to be made on a prenatal ultrasound [25]. Cardiac catheterization was previously frequently used to evaluate patients with complete AVSDs. However, because most of these patients are known to have systemic pulmonary artery pressures, the use of cardiac catheterization is now more frequently limited to those patients presenting late in life, where there can be a question as to whether or not the pulmonary vascular resistance has elevated to a point where repair is no longer indicated. In our practice, the most common indication for cardiac catheterization is as noted above or to evaluate other associated defects such as tetralogy of Fallot and double‐outlet right ventricle. The characteristic “goose neck” deformity is seen in both the partial and complete forms of AVSD (Figure 17.8) [26]. This is caused by the “unwedging” of the aorta [1].

Indications and Timing of Operation

In patients with a partial AVSD, surgical repair is usually performed electively between 1 and 2 years of age [27, 28]. Exceptions to this may occur if there is significant left AV valve regurgitation or hypoplastic left‐sided cardiac structures (coarctation of the aorta, abnormal mitral valve, subaortic stenosis) [29]. Patients with complete AVSD usually present with congestive heart failure within the first 1–3 months of infancy. These children should be operated on between the ages of 3 and 6 months [6, 14]. Failure to perform the operation until after 6–9 months of age can be associated with the risk of developing elevated pulmonary vascular resistance that is not reversible. Although in earlier surgical series patients with associated tetralogy of Fallot and significant right ventricular outflow tract stenosis were often initially palliated with a preliminary modified Blalock–Taussig–Thomas shunt, in the current era most surgeons recommend early primary repair [30, 31]. However, recent long‐term analysis demonstrates no difference in outcomes between staged and primary repairs, most likely because of careful selection bias [32, 33].

Operative Management and Results

Partial Atrioventricular Septal Defect

The steps of partial AVSD repair are illustrated in Figure 17.9. After antegrade cardioplegia has been administered and the right atrium opened, the vent is removed from the orifice of the left AV valve and left ventricle and placed in the posterior left atrium. The left AV valve can then be irrigated with cold saline to assess the patient for insufficiency and to evaluate the area of the zone of apposition. The zone of apposition is closed with simple interrupted polypropylene sutures. This repair is facilitated by placing the first suture at the leading edge of the left AV valve at the junction of the chordae tendineae, with the edge of the left AV valve on either side. This then splays out the zone of apposition and it can be closed with simple interrupted polypropylene sutures. We do not like to use a running suture technique because of the risk of foreshortening the valve when the suture is tied. Some surgeons have elected not to repair this zone of apposition in those patients who do not have left AV valve regurgitation. In our experience, we have had several patients with this type of repair performed elsewhere; these patients have then been referred with moderate or severe left AV valve insufficiency and sometimes with elevated pulmonary artery pressures. It is our opinion that all patients with a partial AVSD and a trifoliate valve should have the zone of apposition closed at the time of atrial septal defect closure. The pericardial patch is then brought onto the field and secured to the leaflet tissue that bridges the crest of the ventricular septum between the left and right AV valves. As the surgeon progresses with the suturing in a clockwise fashion and gets close to the coronary sinus, superficial bites must be taken to avoid the atrioventricular node. Injury to the atrioventricular node can be minimized by carrying this suture line almost into the left ventricle, very close to the mitral valve. Once one passes the area of the coronary sinus, firmer bites can be taken. The suture line is completed by bringing a second suture line counterclockwise, again along the area of bridging leaflet tissue and up to the edge of the atrial septal defect. The remainder of the closure and de‐airing are similar to those for an ostium secundum defect. Some surgeons prefer to carry the suture line on the right side of the coronary sinus, allowing the coronary sinus to drain to the left side to the left atrium. We have not found this necessary to prevent creation of atrioventricular heart block. After completing the zone of apposition repair, the vent can be replaced across the left AV valve and into the left ventricle. The vent can then be used as part of the de‐airing process.

We currently employ intraoperative transesophageal echocardiography in all patients with a partial, intermediate, or complete AVSD. Transesophageal echocardiography is used to evaluate the preoperative anatomy, the right and left ventricular sizes, the anatomy of the AV valves, straddling or other unusual chordal issues, and the extent of preoperative AV valve insufficiency. Postoperatively, the transesophageal echocardiography can be used to evaluate for residual ventricular septal defect, residual atrial septal defect, subaortic stenosis, and right and left AV valve insufficiency or stenosis. All of these can be potential indications for an immediate re‐repair of the noted abnormality.

Complete Atrioventricular Septal Defect

All centers have now adopted early primary repair as the procedure of choice for patients with complete AVSD [34]. Pulmonary artery banding is only used now in exceptional cases where the use of cardiopulmonary bypass must be avoided (cerebrovascular accident, sepsis, etc.) and for select patients undergoing neonatal coarctation repair [15, 35].

The principles of operative management of complete AVSD include closure of the atrial septal defect, closure of the ventricular septal defect, creation of two nonstenotic competent AV valves, and avoidance of damage to the AV node and bundle of His. Repair of complete AVSDs has been described using single‐patch, two‐patch, and modified single‐patch techniques (Figure 17.10). The method of cardiopulmonary bypass is similar for the three different techniques. We have routinely used continuous cardiopulmonary bypass with moderate hypothermia (28–32 °C) and intermittent antegrade cold‐blood (del Nido) cardioplegia for myocardial protection. In some cases we cannulate the superior caval vein directly with a right‐angle cannula to improve exposure within the right atrium. We have used a vent placed in the right superior pulmonary vein after beginning cardiopulmonary bypass. This vent can be pulled back into the atrium during the time of the left‐sided AV valve repair. It is then reinserted into the left ventricle as the atrial septal defect is closed and the right‐sided AV valve repair is performed. We have emphasized a long, medial atriotomy (parallel to the right coronary artery) that extends to a point medial to the inferior caval vein. This offers excellent exposure of the defect to facilitate the repair (Figure 17.11). Some surgeons use both antegrade and retrograde cardioplegia [36]. Very few, if any, centers now use deep hypothermia and circulatory arrest [34]. We and others use transesophageal echocardiographic assessment for all cases of AVSD [37].

One of the keys to successful repair of AVSDs using any technique is a careful inspection of the intracardiac anatomy. This includes an assessment of the right and left ventricular size, the size and shape of the atrial and ventricular septal defect components, the number and location of papillary muscles, and the arrangement of the chordal structures, including their attachment to the ventricular septum. The ventricular chambers should be gently filled with cold saline prior to the procedure to float the AV valve leaflets to their closed position. Floating the valvar leaflets with saline helps to identify the line of apposition between the superior and inferior bridging leaflets (Figure 17.7) [20]. Careful inspection of the leaflet tissue then identifies the imaginary line that divides the valves into the right and left components.

Single‐Patch Technique

The single‐patch technique has been described using a pericardial, polytetrafluoroethylene (PTFE), or Dacron patch [36]. The pericardial patch is most commonly used, especially for smaller infants, but carries some risk of aneurysm development at the ventricular level [38]. This can be avoided by fixing the patch in glutaraldehyde. The Dacron patch runs the risk of postoperative hemolysis should the jet of mitral or tricuspid valve insufficiency strike the Dacron. The patch dimensions are determined by the size and shape of the ventricular septal defect, the distance between the anterior and posterior margins of the AV valve annulus, and the dimensions of the atrial septal defect. This repair is started by floating the AV valve leaflets into the closed position. The line of apposition of the superior and inferior bridging leaflets is noted and an imaginary line demarcating the right and left AV valve components is created by marking the coaptation of the leaflets with a horizontal mattress suture (Figure 17.12). The crest of the ventricular septum is then sutured to the inferior aspect of the patch with multiple interrupted horizontal mattress sutures (Figure 17.13

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