Atrioventricular Septal Defects

Abstract

Atrioventricular septal defects (AVSD) are a group of malformations involving the atrioventricular (AV) septum and common AV junction. They are divided into complete, partial, intermediate and transitional AVSD. It is most commonly associated with Down Syndrome. All of them share a few common features. Complete AVSDs are also classified as balanced and unbalanced. Echocardiography is the primary imaging tool to diagnose these defects. Patients with complete and intermediate forms clinically present early and require surgical correction during infancy, whereas partial, and transitional forms become symptomatic in early childhood. Patients who are ineligible for complete surgical repair initially undergo palliative pulmonary artery banding. The surgical management of unbalanced AVSDs is complex. Most of these patients fall into either single ventricle, one and a half or bi-ventricular repair. Overall surgical outcomes for AVSDs are excellent. Left atrioventricular valve regurgitation is the most common reason for reoperation.

1. Introduction

Atrioventricular septal defects are a group of malformations involving the atrioventricular (AV) septum and common atrioventricular junction (Figure 1). Previously, referred to as atrioventricular canal or endocardial cushion defects, is now called AV septal defect (AVSD). For the purpose of this chapter, we will use the term AV septal defects. They are divided into complete, partial and variations of both of them based on the orifices and septal communications which will be discussed in detail in this chapter.

Figure 1.

Atrioventricular septum in the normal heart. The atrioventricular septum (AVS) lies between the right atrium (RA) and the left ventricle (LV). LA, left atrium; RV, right ventricle; MV, mitral valve; TV, tricuspid valve. “From: Cetta F, Truong D, Minich LL, Maleszewski JJ, O’Leary PW, Dearani JA & Burkhart HM. Chapter 29: Atrioventricular Septal Defects. In: Allen HD, editor. Moss & Adams’ Heart Disease in Infants, Children, and Adolescents, Including the Fetus and Young Adult, 9th Edition. Philadelphia: Lippincott Williams & Wilkins, 2016; used with permission of Mayo Foundation for Medical Education and Research, all rights reserved.”

2. Prevalence

Congenital heart disease (CHD) accounts for around 1–1.2% of live births both in the United States and globally [1, 2]. AVSDs account for around 4–5% of all CHDs, with 5.38 cases per 10,000 live births, an increase from prior reports [1, 3]. It is the most common fetal cardiac anomaly detected on prenatal screening (Figure 2). Around half of the patients with AVSD have Down syndrome. However, approximately 45% of CHD patients with Down syndrome have AVSD [4, 5]. Most of these cases are isolated, although some may have pulmonary stenosis or atresia. There is an association with other anomalies like heterotaxy and Ellis-Van Creveld syndrome [6].

Figure 2.

Fetal echocardiogram four-chamber view: Complete AVSD. RA, right atrium; LA, left atrium; RV, right ventricle; LV, left ventricle. *Primum atrial septal defect and inlet ventricular septal defect.

3. Pathology

In a normal heart, tricuspid and mitral valve annuli are positioned at different levels because of the atrioventricular septum. In AV septal defects, tricuspid valve annulus is located more apically in relation to mitral valve. The portion of the offset between tricuspid and mitral valve is the location of atrioventricular septum. It has overlapping atrial and ventricular walls [7]. Aortic valve is located anterior and superior between tricuspid and mitral valve, what is referred to as wedged between these valves. This makes the subaortic outflow region placed in between tricuspid and mitral valves. The papillary muscles in the left ventricle are located antero-superior and postero-inferior region. Another feature of importance to this topic, the distance from mitral valve to apex of left ventricle is same as the distance from left ventricular apex to aortic valve (Figure 3).

Figure 3.

2D echocardiogram parasternal long axis view: A. In normal cardiac anatomy, distance from the mitral valve to left ventricular (LV) apex and from LV apex to aortic valve is same. B. In AVSD, LVOT is elongated and distance from LV apex to left AV valve annulus is shorter. LA, left atrium; RV, right ventricle; Ao, aorta.

In patients with AV septal defect, the fundamental abnormality is absence of the atrioventricular septum or having a common atrioventricular junction. This results in a cascade of features that are different from normal hearts. The common features shared by all forms of atrioventricular septal defects are:

1. Presence of common atrioventricular valve

2. Elongation of the left ventricular outflow tract

3. Clockwise rotation of papillary muscles

4. Cleft in the left AV valve

4. Classification

There are two major types of AV septal defects: complete and partial AVSDs. Two sub-types are described: intermediate and transitional, which are variations of complete and partial AV septal defects, respectively (Figure 4). It is preferable to describe the features of these subtypes rather than identifying them as an entity. Different combinations of shunting across atria and ventricles could happen based on the attachments and relationship of the bridging leaflets to septal structures. In general, we would see ostium primum defect and ventricular septal defect (VSD). If the bridging leaflets are attached to the atrial septum, there could be only a ventricular level shunt (Figure 5). When the bridging leaflets are attached to the crest of ventricular septum, it results in an atrial level shunt with an ostium primum defect. In rare instances, where the bridging leaflets close the septal defect(s), we will still see features of the common atrioventricular valve [8, 9, 10]. Complete AVSDs are classified further into three types based on the morphology of anterior bridging leaflet and is named after Giancarlo Rastelli who made significant contributions in his short career and life span:

1. Type A: In this type, anterior bridging leaflet (ABL) is divided and attached to the crest of the interventricular septum. It is the most common defect and is associated with Down syndrome.

2. Type B: ABL is partly divided and is not attached to the crest of the septum. Chordae attach usually to papillary muscle in the right ventricle (RV), on the septal surface. It is the least common of all types.

3. Type C: ABL is not attached or divided and is termed “free-floating”. There are chordal attachments to RV free wall. This type is seen in Down syndrome patients with Tetralogy of Fallot; double outlet right ventricle, complete transposition of the great arteries, and heterotaxy syndromes.

Figure 4.

Summary of AVSD. Anatomic and physiologic similarities between the different forms of atrioventricular septal defect (AVSD) are illustrated. Complete AVSDs have one orifice with large interatrial and interventricular communications. Intermediate defects (two orifices) are a subtype of complete AVSD. Complete AVSDs have physiology of VSDs and atrial septal defects (ASDs). In contrast, partial AVSDs have physiology of ASDs. Transitional defects are a form of partial AVSD in which a small inlet VSD is present or the ventricular level shunt has been obliterated by chordal tissue. Partial AVSDs and the intermediate form of complete AVSD share a similar anatomic feature: A tongue of tissue divides the common atrioventricular valve into distinct right and left orifices. LA, left atrium; LPV, left pulmonary vein; LV, left ventricle; RA, right atrium; RPV, right pulmonary vein; RV, right ventricle. “From: Cetta F, Truong D, Minich LL, Maleszewski JJ, O’Leary PW, Dearani JA & Burkhart HM. Chapter 29: Atrioventricular Septal Defects. In: Allen HD, editor. Moss & Adams’ Heart Disease in Infants, Children, and Adolescents, Including the Fetus and Young Adult, 9th Edition. Philadelphia: Lippincott Williams & Wilkins, 2016; used with permission of Mayo Foundation for Medical Education and Research, all rights reserved.”

Figure 5.

2D echocardiogram apical four-chamber view: A rare form of AVSD with large inlet ventricular septal defect (*) without a primum atrial septal defect. Note that AV valves are at same level. RA, right atrium; RV, right ventricle; LA, left atrium; LV, left ventricle.

5. Other features

5.1 Left AV valve

In normal hearts, mitral valve has two leaflets, anterior and posterior with a zone of opposition in one plane. In hearts with AV septal defects, the left AV valve closes in tri-foliate fashion with zones of opposition between posterior, superior and inferior bridging leaflets. This characteristic feature of the left AV valve in AV septal defects will never achieve a mitral valve as in normal hearts. Usually, jet of LAVV cleft is directed to the ventricular septum when compared to isolated mitral valve clefts which are directed anteriorly towards the aortic valve [11]. Rarely, a fusion of the leaflets within the left AV valve (bridging and posterior leaflet) would lead to a double orifice valve. The combined area of the double orifice valve is always less than the single left AV valve area.

5.2 Left ventricular outflow tract (LVOT)

As described earlier, LVOT is wedged anteriorly and is narrow when compared to the aortic valve, irrespective of the type of AV septal defect. In partial form, where the superior bridging leaflet is attached to the crest of the septum, it is markedly narrow (Figure 6). This abnormality has been described as goose-neck deformity.

Figure 6.

A. Diagram in a normal heart showing aortic valve (AoV) wedged between tricuspid valve (TV) and mitral valve (MV). B. In AVSD, aorta is not wedged between these valves, termed “sprung aortic valve”. PV, pulmonary valve; RAVV/LAVV, right and left atrioventricular valve. A. by Dr. Johannes Sobotta - Sobotta's atlas and text-book of human anatomy 1906, public domain, https://commons.wikimedia.org/w/index.php?curid=29901804.

5.3 Chamber dominance

Depending on the overall flow from the atrioventricular orifices to respective ventricles, the chambers are usually the same size which is termed as ‘balanced AVSD’. When a common AV valve opens more into the right ventricle or to the left ventricle, it would cause decreased growth of the contralateral ventricle and its great artery, leading to the term ‘unbalanced AVSD’. In right ventricle dominant atrioventricular septal defect, left ventricle and aorta are hypoplastic depending on the amount of blood flow, but usually, the atrial and ventricular septal alignment is maintained. In left ventricular dominance, there will be hypoplasia of the right ventricle and pulmonary artery, typically with septal malalignment. This chamber dominance when it involves the atrium would give rise to double outlet atrium (Figure 7).

Figure 7.

2D echocardiogram showing right ventricle (RV) dominant AVSD with severely hypoplastic left AV valve and ventricle (LV). Moderately dilated right atrium (RA) and RV with large primum ASD. LA, left atrium.

5.4 Associated malformations

In partial atrioventricular septal defects, the most common associated malformation includes secundum ASD, patent ductus arteriosus and persistent left superior vena cava to coronary sinus [12].

Tetralogy of Fallot with pulmonary stenosis is found in one-tenth of the patients with common atrioventricular septal defect and in these patients, Rastelli type C is common. Among others, common atrium, double outlet right atrium, double inlet ventricle with discordant ventriculoarterial connections can be seen.

5.5 Atrioventricular conduction tissues

In normal hearts, AV node is located in the triangle of Koch which is formed by Tendon of Todaro, coronary sinus ostium and septal leaflet of the tricuspid valve [13, 14, 15]. In patients with AVSDs, because of deficient AV septum, the atria will meet the ventricle at the crux of the heart, shifting the AV node more posteriorly and inferiorly.

6. Embryology

In the past, failure of the fusion of endocardial cushions was thought to be the only reason for AV septal defects [16]. It could be the first step in the formation of these hearts, but not in entirety. Delamination of valve leaflets occurs late in development, with its formation occurring by undermining of the ventricular myocardium [17]. When the endocardial cushions fail to meet, subaortic outflow tract will not be normally wedged and there will be abnormal development of ventricular mass. Additionally, mesenchymal tissues surrounding the primum ostial foramen play a role in these defects [18, 19].

7. Pathophysiology

In patients with complete AVSD, there is one common AV valve with large atrial and inlet VSD (Figure 8). In intermediate form, there are two AV valve orifices, which are formed by a tongue of tissue between superior and inferior bridging leaflets. It has similar physiology as the complete form with large ASD and VSD. In partial AV septal defects, where there are two AV valve orifices with the bridging leaflet attached to ventricular septal crest, giving rise to only interatrial communication (Figure 9A). In some instances, there could be communication at the ventricular level from the chordal attachments which is described as a transitional type (Figure 9B). In all forms of AV septal defects, the left AV valve invariably has a cleft. Rarely there will be no septal communications seen with other common features of AVSD [8].

Figure 8.

2D echocardiogram apical 4-chamber view: Complete balanced AVSD. A. When AV valve is closed, there is large primum atrial septal defect (ASD, *) and large inlet ventricular septal defect (VSD, +). Common AV valve and single orifice. B. with valve open. RA, right atrium; LA, left atrium; RV, right ventricle; LV, left ventricle.

Figure 9.

Transesophageal echocardiogram, four-chamber view. A. Partial AVSD with large primum atrial septal defect (ASD) (*). Note the valvar attachments to crest of the septum. B. Transitional AVSD with small primum ASD and inlet ventricular septal defect (+) covered by right AVV chordal attachments to the crest of ventricular septum. RA, right atrium; LA, left atrium; RV, right ventricle; LV, left ventricle.

8. Clinical features

8.1 Partial AVSD

Usually, patients with partial AV septal defect (also called primum ASD) remain asymptomatic until early childhood. They rarely present early with failure to thrive depending on the size of the defect and severity of AV valve regurgitation. Patients with primum ASDs usually present earlier and with symptoms when compared with secundum ASDs. Auscultatory findings include widely split and fixed second heart sound, crescendo- decrescendo systolic ejection murmur at the left upper sternal border from the increased flow across pulmonary valve, and holosystolic murmur at the apex from LAVV regurgitation. A mid-diastolic murmur may be heard at the apex if there is significant mitral regurgitation or at the left lower sternal border if there is a large atrial shunt.

8.2 Complete AVSD

Patients with complete AV septal defects present in the neonatal period after first few days/weeks of life when pulmonary vascular resistance falls. This is attributed to the large atrial and ventricular level shunts leading to pulmonary over circulation. There will be tachypnea, increased work of breathing, failure to gain weight. More often, they would require high-calorie nutrition, diuretics to decrease the preload. On exam, there will be accentuated first heart sound, with S1- coincident holosystolic murmur from LAVV regurgitation, widely split and fixed S2, crescendo- decrescendo systolic ejection murmur at the left upper sternal border from the increased flow across pulmonary valve and sometimes mid-diastolic murmur at apex.

9. Investigations

9.1 Electrocardiogram

As previously described, AV node is displaced posteriorly and inferiorly in these defects; this may result in prolongation of the PR interval. There will be a left superior deviation of the mean frontal plane vector. Biventricular hypertrophy is seen in complete and intermediate forms. Right ventricular hypertrophy is seen in the partial form. If there is moderate to severe mitral insufficiency, left ventricular hypertrophy may be seen. Other abnormalities which might be seen are prolongation of PR interval (Figure 10) [20].

Figure 10.

12-lead EKG in patient with CAVSD showing left superior axis deviation and right ventricular hypertrophy.

9.2 Chest roentgenogram

Chest roentgenogram shows cardiomegaly with increased pulmonary vascular markings. Features of pulmonary edema may be seen in subjects with congestive heart failure.

9.3 Echocardiography

Echocardiography is the primary diagnostic modality for the evaluation of atrioventricular septal AV defects [21]. Assessment of the ASD can be best done from a subcostal coronal and sagittal view. VSD could be best evaluated in the parasternal short axis. En-face view of the common AV valves is best achieved with a modified subcostal left anterior oblique view (Figure 11). This view also demonstrates the bridging leaflets, their attachments and helps with the Rastelli classification in patients with complete AVSDs. Subcostal short axis view would assess atrial or ventricular level unbalance. An Apical four-chamber view would augment the information on previously mentioned variables along with AV valve inflow and regurgitation. Overall, all the views complement each other to get comprehensive information, as in any other heart. Associated malformations like tetralogy of Fallot, coarctation, patent ductus arteriosus, arch sidedness should be evaluated using modified subcostal right anterior oblique/parasternal long axis and high parasternal/suprasternal views [22]. 3D echocardiography demonstrates a comprehensive and accurate assessment of the size and extent of the septal defects, size, number, and abnormalities of AV valve leaflets and their attachment sites, as well as the relation of the valvular structures to the great vessels [23]. Other findings such as double orifice left AV-valve, single papillary muscle should be evaluated.

Figure 11.

Echocardiogam left anterior oblique (LAO) view. 1. Rastelli type a with attachments of the anterior/superior bridging leaflet (SBL) to crest of venticular septum; B. when valve is closed, notice the cleft in LAVV valve; C. Rastelli type C with “free floating” anterior bridging leaflet (<−>) and chordal attachments to right ventricular (RV) free wall (−>); D. 3D image showing tri-foliate cleft LAVV. IBL, inferior bridging leaflet; ML, mural leaflet; RAL, right anterior leaflet; RPL, right posterior leaflet; ML, left mural leaflet; LV, left ventricle.

In determining the balance of ventricles, a quantitative approach was proposed by Cohen et al. [24] using a subcostal sagittal view. In this view, they measured the area of AV valve over each ventricle and calculated a left/right ventricular ratio, also known as AV valve index (AVVI). Based on the index, patients were stratified either to single-ventricle or bi-ventricular repair pathways. Patients with an AVVI <0.67 and a large VSD would be considered for the single-ventricle pathway. This was modified to the left AV valve area/total area. An AVVI >0.6 is considered left ventricular dominant whereas AVVI <0.4 was considered right ventricular dominant. It is important after surgical repair to assess for residual defects, progressive LVOT obstruction, AVV stenosis and regurgitation, systolic function.

9.4 Cardiac catheterization

Cardiac catheterization is not frequently performed in AVSDs. However, it is helpful in assessing the hemodynamic information like the degree of shunting, pulmonary vascular resistance. One would see the characteristic “gooseneck appearance” from elongated LVOT on angiography. Patients with severely elevated PVR are poor candidates for full repair and may eventually be candidates for lung transplantation [25].

9.5 Advanced cardiac imaging

Cardiac computed tomography (CT) is particularly helpful to assess for any extracardiac defects or associated anomalies in these patients. Retrospective gated approach is useful for the evaluation of ventricular function and ventricular sizes, allows volumetric measurements, and also allows evaluation of ventricular function and wall motion. This may be of particular relevance in patients with hypoplastic ventricles and unbalanced AVSDs [26]. Cardiac magnetic resonance imaging (MRI) is an important tool to assess the degree of unbalance and guide for future surgical planning. These modalities have proven to decrease the amount of radiation exposure during cardiac catheterization [27].

10. Management

10.1 Medical management

Patients with complete defects present early with signs and symptoms of pulmonary over circulation such as tachypnea, increased work of breathing. In the neonatal period, when the pulmonary vascular resistance decreases, they require diuretics to help with pulmonary congestion and control heart failure along with optimizing nutrition. Occasionally they require afterload reducing agents if there is significant AV valve regurgitation and rarely inotropes. If heart failure or failure to thrive persists despite maximizing medical management, they would be referred for surgery. Based on the corrected gestational age, weight, type of atrioventricular septal defect and associated anomalies, surgical options vary which will be discussed below. As mentioned earlier, patients with partial atrioventricular septal defects usually show symptoms in childhood.

10.2 Surgical management

The goals of the surgery are to close the septal defect(s), repair the AV valve, construct two separate and competent AV valves, and avoid injury to conduction tissue.

1. 1. Balanced atrioventricular septal defects

• Surgical Palliation

Palliation with main pulmonary artery band (PAB) is performed in babies less than 5 Kg who failed medical management. In the recent era, complete repair is done even in this weight range. Palliation is considered in patients who are premature, those deemed ineligible for definitive repair or with other co-morbidities. A recent study showed that PAB in complete AVSDs as a bridge to biventricular repair has similar survival as those for primary biventricular repair [28].

• Surgical Correction

Patients with complete AVSDs frequently require surgical repair in early infancy with a median age of 3.6 months at the time of repair [29]. Surgical repair is achieved by singe-patch, modified single-patch (Australian/Nunn) or two-patch techniques. A meta-analysis, which compared modified single-patch and two patch techniques showed no significant difference between two groups, but modified single-patch performed when there is small VSD had shorter cardiopulmonary bypass and aortic cross-clamp time [30]. Several other studies showed similar findings [31, 32, 33, 34, 35]. The main advantages of the two-patch technique are maintaining planar alignment of AV valves, lower chances of narrowing of LVOT, not compromising ventricular volumes and preserving the integrity of bridging leaflets [36]. In the Pediatric Heart Network (PHN) study, earlier complete repair showed increased resource utilization with longer intensive care unit stay but no association with incidence of residual VSD or significant left AV valve regurgitation at six months of age (Figure 12). Moderate or greater left AV valve regurgitation was found in 22% at six months with the strongest predictor being moderate or greater left AV valve regurgitation at one month [32]. In the majority of the cases, cleft was closed, 93% in this study [37], it was partially closed, or left open in remaining cases.

Figure 12.

A, B: Intra-operative transesophageal echocardiogram, color compare deep transgastric view of left AV valve. A. Pre-operative image showing moderate regurgitation. B. Postoperative after left AVV repair. Note cleft is completely closed without any regurgitation. C. Transthoracic apical 4-chamber view of another patient with severe left AVV regurgitation in multiple jets.

Associated anomalies like patent ductus arteriosus, double orifice left AV valve parachute left AV valve should be addressed. Patients with complete AVSDs and tetralogy of Fallot associated with Down syndrome may need initial palliation with systemic to pulmonary artery shunt or right ventricular outflow tract (RVOT) stent placement and full repair at a later age. In a retrospective study [38], RVOT stenting showed a significant increase in median Z-score for both branch pulmonary arteries at a median follow-up of 255 days. Four patients out of 26 patients died during follow- up period, but none after the initial intervention. Another meta-analysis found no significant difference in the 6-year survival between staged palliation and primary repair, with higher rate of reintervention for RVOT who underwent staged repair [39].

In patients with partial and transitional AVSDs, there has been controversy regarding the age of surgical correction. A PHN study in 2010, showed good results at a median age of 1.8 years, with left AV valve regurgitation being most common and more frequently in children repaired after 4 years of age [12, 40, 41]. One patient out of 87 died in the hospital. Another review showed excellent results at median age of 1.5 years with LV outflow tract obstruction being most common reason for reoperation at their center [42]. Several other studies showed good long-term outcomes with 30-day and 5-, 10-, 20-, and 40-year survivals at 98%, 94%, 93%, 87%, and 76%, respectively. Approximately 3% of the patients in the Mayo group required permanent pacemaker [40, 41]. A minimally invasive right axillary approach has also been performed with good results in partial AVSD patients [43].

1. 2. Unbalanced atrioventricular septal defects

Surgical techniques in patients with unbalanced AVSDs include single ventricle palliation, biventricular repair and 1.5 ventricular repair.

• Single Ventricle Palliation

Patients with severely hypoplastic right/left ventricle would be managed using staged single ventricle palliation. Initially, they are palliated with PAB and later undergo bidirectional Glenn around four to six months of age, if the pulmonary artery pressures are favorable. Around 2 to 3 years of age, extracardiac Fontan completion with or without fenestration is performed [44].

• One and half or bi-ventricular repair (BVR)

There are no clear selection criteria to stratify patients into either single or bi-ventricular pathways. Several factors are taken into consideration such as hypoplastic ventricle end-diastolic volume (EDV) of >30 mL/m², normal ventricular function, adequate AV valve size and function, and low end-diastolic pressures on cardiac catheterization [45].

In select patients with right ventricular dominant AVSD, a staged left ventricular recruitment approach is considered, especially in patients with trisomy 21. It includes ASD closure or restriction, without VSD closure, septation of the common AV valve and banding of the main pulmonary artery [45, 46]. This strategy allows rehabilitation of the left ventricle. With this approach, patient would not be committed at an early age to either a single or bi-ventricular approach and it would give an opportunity to monitor for LV growth [45].

On the other hand, in patients with LV dominant AVSD with inadequate RV size, one and a half ventricular repair has been proposed with primary AVSD repair along with a bidirectional Glenn procedure [47]. This would allow growth of the hypoplastic right ventricle for future biventricular conversion. In some institutions, routine 3-D printing is done for all complex AVSD for pre-surgical planning which permitted biventricular repair in some patients who were previously deemed to be candidates for single ventricle palliation [48, 49].

11. Surgical outcomes

Even though the outcomes for partial AVSDs are excellent, approximately 10–15% of patients require additional operations. It is well known that pre-operative left AV valve regurgitation predicts the post-operative severity of regurgitation. Other factors are severely dysplastic valve, failure to close the cleft, age of initial surgery, left AV valve stenosis and LVOT obstruction [41]. A technical performance score (TPS) was proposed to grade residual lesions after partial and transitional AVSD repair. In that study, left AV valve regurgitation was the strongest predictor of in-hospital outcomes and unplanned reinterventions after discharge [50]. When compared to complete AVSD, LVOT obstruction occurs more frequently after repair of partial AVSD. Several technical strategies were proposed to decrease the likelihood of subaortic stenosis [51, 52, 53].

In complete AVSDs, late reoperation occurs in around 11–20% of patients with most common reason being left AV valve regurgitation [54, 55]. In these studies, freedom from further reoperation after the first reoperation was 63%, 48%, and 42% at 5, 10, and 15 years, respectively. On later follow-up (median 10.7 years, maximum 30 years), actuarial overall survival was 91%, 91%, and 86% at 5, 10, and 15 years, respectively [55]. A recent study showed improved outcomes with overall survival at 10, 15 and 20 years was 91.7%, 90.7% and 88.7%, respectively and freedom from reoperation was 82.7%, 81.1% and 77%, respectively [56].

12. Down syndrome

Around 36.5–66% of Down patients have pulmonary hypertension with congenital heart disease less than six months of age [5, 57]. There has been controversy about the extent of pulmonary vascular changes with Down and non-Down syndrome patients. There are studies which showed earlier development of pulmonary parenchymal hypoplasia and pulmonary vascular obstructive disease (PVOD) in this patient population [58, 59, 60]. In children with Down syndrome, Rastelli type A is most common. But when associated with tetralogy of Fallot, Rastelli type C is common. In unbalanced AVSDs, left ventricular dominance is more common [6]. It’s known that this patient population tolerates single ventricle physiology poorly [61]. Nevertheless, surgical outcomes are not different for biventricular repair when compared with non-Down syndrome patients. Survival at 30 years was 85.6% for complete AVSD, in patients with trisomy 21 [62].

13. Conclusions

AVSDs are a group of disorders with deficient AV septum and abnormal AV valve morphology. It is the most common defect in Down syndrome. The definitive surgical repair has excellent outcomes in balanced AVSDs. For unbalanced AVSDs, it is a complex decision-making process and their repairs are usually categorized to single, one and half or bi- ventricular repair. For a select subset of patients, ventricular recruitment procedures improve the candidacy for future bi-ventricular circulation. Patients with Down syndrome should have similar surgical strategies as that of non-Down syndrome patients. The most common reason for reoperation is left AV valve regurgitation.

Conflict of interest

The authors declare no conflict of interest.