eMedicine Specialties > Pediatrics: Cardiac Disease and Critical Care Medicine > Cardiology

Atrioventricular Septal Defect, Complete

Author: Michael Pettersen, MD, Director of Echocardiography, Division of Cardiology, Children's Hospital of Michigan; Associate Professor of Pediatrics, Wayne State University School of Medicine
Contributor Information and Disclosures

Updated: Nov 10, 2009

Introduction

Background

Atrioventricular septal defects (AVSDs) are anatomic defects that arise from faulty development of the embryonic endocardial cushions. This spectrum ranges from a primum atrial septal defect and cleft mitral valve, known as a partial atrioventricular septal defect (partial AVSD), to defects of both the primum atrial septum and inlet ventricular septum and the presence of a common atrioventricular valve, referred to as complete atrioventricular septal defect (complete AVSD). The terms atrioventricular canal defect and endocardial cushion defect are used in reference to this group of defects; however, atrioventricular septal defect is now the preferred terminology. These defects, particularly the complete form, typically present in the fetal or neonatal period and are an important source of cardiac morbidity and mortality in this age group.

This article focuses on the complete form. Partial, intermediate, and unbalanced forms are reviewed in other chapters (see Atrioventricular Septal Defect, Partial and Intermediate and Atrioventricular Septal Defect, Unbalanced).

Embryology

 Faulty development of the endocardial cushions, which represent the primordia of the atrioventricular septum and atrioventricular valves, plays a central role in the development of atrioventricular septal defects.1,2 The superior and inferior endocardial cushions appear at 4-5 weeks' gestation. During this time, the common atrioventricular canal is positioned over the primitive left ventricle.

Mesenchymal cells invade these masses of tissue, and, during the fifth week of gestation, the cushions approach each other and fuse. This divides the common atrioventricular canal into right and left canals.3 The right and left lateral endocardial cushions develop shortly after the appearance of the superior and inferior cushions, followed by the dextrodorsal conus cushion. These structures are involved in the development of the mitral and tricuspid valves and their support apparatus (see Media file 1).

Atrioventricular (A-V) valve leaflets viewed from...

Atrioventricular (A-V) valve leaflets viewed from the cardiac apex in normal valves (A) and in the Rastelli type A complete form of common A-V canal (B).

In A, the normal tricuspid valve (TV) has anterior (AL), septal (SL), and posterior (PL) leaflets. A normal mitral valve (MV) has ALs and PLs.

In B, the superior cushion–derived leaflet bridges the ventricular septum and attaches to the papillary muscle of the conus at its rightmost extent.

A right superior leaflet (RSL) typically attaches to the papillary muscle of the conus and to the anterior papillary muscle of the right ventricle (RV), and a right lateral leaflet (RLL) attaches to the anterior papillary muscle of the RV and to the posterior papillary muscle of the RV. The inferior cushion–derived bridging leaflet is usually cleft, giving the appearance of a right inferior leaflet (RIL) and a left inferior leaflet (LIL).

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Atrioventricular (A-V) valve leaflets viewed from...

Atrioventricular (A-V) valve leaflets viewed from the cardiac apex in normal valves (A) and in the Rastelli type A complete form of common A-V canal (B).

In A, the normal tricuspid valve (TV) has anterior (AL), septal (SL), and posterior (PL) leaflets. A normal mitral valve (MV) has ALs and PLs.

In B, the superior cushion–derived leaflet bridges the ventricular septum and attaches to the papillary muscle of the conus at its rightmost extent.

A right superior leaflet (RSL) typically attaches to the papillary muscle of the conus and to the anterior papillary muscle of the right ventricle (RV), and a right lateral leaflet (RLL) attaches to the anterior papillary muscle of the RV and to the posterior papillary muscle of the RV. The inferior cushion–derived bridging leaflet is usually cleft, giving the appearance of a right inferior leaflet (RIL) and a left inferior leaflet (LIL).


The endocardial cushions do not directly form the valve components but play an essential role in the process by which undermining and delamination of the myocardium forms the valve leaflets and chordal attachments.4 Complete failure of fusion of the endocardial cushions results in deficiency of the inlet portion of the interventricular septum, a common atrioventricular valve annulus and common AV valve, as well as deficiency of the inferior (primum) portion of the atrial septum. This constellation of features results in a large defect in communication with all 4 chambers of the heart.

Anatomy

In complete atrioventricular septal defect, a single atrioventricular valve annulus, a common atrioventricular valve, and a defect of the inlet ventricular septum are observed. The deficiency of the atrioventricular septum also results in the presence of a large primum atrial septal defect. Details of the anatomy, particularly the morphology of the atrioventricular valve are crucial in planning surgical repair of this lesion. The common AV valve consists of at least 4 leaflets. These include the anterior and posterior bridging leaflets and 2 lateral leaflets. The anterior leaflet may be further subdivided to produce a total of 5 leaflets. The classification system initially described by Rastelli et al is used to describe the morphology of the atrioventricular valve.5

With the Rastelli type A valve, the anterior leaflet is divided into 2 portions of approximately equal size. The lateral portions of this leaflet attach to the anterior papillary muscles in each ventricle. Chordae tendineae attach the medial portion of this leaflet to the crest of the ventricular septum or slightly to the right ventricular side. Interventricular communication may occur between the anterior and posterior bridging leaflets and underneath the anterior leaflet in the interchordal spaces.

In type B valves, the rarest type, the anterior bridging leaflet is divided but overhangs the ventricular septum more so than in type A valves. The chordae from the medial portion of the divided anterior leaflet have no direct insertion to the ventricular septum but rather insert onto an anomalous papillary muscle positioned in the right ventricle near the ventricular septum. Because of the lack of chordal insertions to the septum, free interventricular communication occurs beneath the anterior leaflet.

In a Rastelli type C valve, the anterior bridging leaflet is larger and overhangs the septum more so than with a type A and type B valves. It is not attached in its mid portion to the ventricular septum or elsewhere and is referred to as being “free floating." Free interventricular communication also occurs underneath this valve leaflet.

Because of the deficient atrioventricular septum, the atrioventricular valves are displaced apically. As a result, the left ventricular inlet distance (distance from mitral valve annulus to apex) is shorter than the outlet distance (apex to aortic valve annulus). In the normal heart, these distances are nearly equal. In addition, the left ventricular outflow tract is displaced anteriorly, as opposed to wedged between the 2 atrioventricular valves. These features lead to the characteristic "gooseneck" deformity seen on anteroposterior angiography. Although this leads to a left ventricular outflow tract (LVOT) diameter that is smaller than normal, it usually does not cause clinically significant obstruction by itself. However, contribute to an LVOT obstruction when associated with a subaortic membrane or accessory atrioventricular valve tissue.

Defects commonly seen in association with complete atrioventricular septal defect include patent ductus arteriosus, coarctation of the aorta, atrial septal defects, absent atrial septum, and anomalous pulmonary venous return.6 Abnormalities of the mitral valve also commonly occur, including single papillary muscle (“parachute mitral valve”) and double orifice mitral valve. Tetralogy of Fallot is also present in about 2.7-10% of cases. At least 75% of patients with tetralogy of Fallot and complete atrioventricular septal defect have Down syndrome.7

Pathophysiology

The pathophysiology of complete atrioventricular septal defect depends on the magnitude of blood flow through the ventricular septal defect (VSD) and the amount of atrioventricular valve regurgitation. Patients with little atrioventricular valve regurgitation and high pulmonary vascular resistance (PVR) are asymptomatic early in life, and their condition may be difficult to diagnose.

These patients occasionally remain relatively asymptomatic until their second or third decade, when they develop increasing cyanosis from advanced pulmonary vascular disease. In most cases, the PVR decreases normally over the first 6 weeks of life, and the patient develops a large left-to-right shunt through both the atrial and ventricular defects, resulting in congestive heart failure (CHF). Patients with clinically significant atrioventricular valve regurgitation may also have signs of CHF, such as tachypnea, excessive sweating, and failure to appropriately gain weight.

Frequency

United States

Atrioventricular septal defects account for 2-9% of congenital heart disease in various series. Most investigators report a prevalence rate in the range of 3-5%.8 The male-to-female distribution of atrioventricular septal defect is approximately equal.9 The incidence of atrioventricular septal defect is higher among stillborn infants, likely due to the higher number of chromosomal and other genetic anomalies in this group. The pooled frequency of atrioventricular septal defects from several series of congenital heart disease in stillborn infants was about 7%.10

Freeman et al reported a prevalence of 9.6 cases of Down syndrome per 10,000 live births.11 Congenital heart disease is present in 44% of affected infants, and atrioventricular canal defects are present in 45% of infants with Down syndrome and congenital heart disease.

Familial clustering may occur with atrioventricular canal defects. About 14% of women with common atrioventricular canal pass on congenital heart disease to their children. In a pedigree analysis, 11.7% of probands had a family history of congenital heart disease.12

Mortality/Morbidity

Patients with complete atrioventricular septal defect typically develop tachypnea and failure to thrive in the first few months of life. Tachypnea hampers normal feeding. In addition, respiratory tract infections, such as those due to respiratory syncytial virus (RSV), are poorly tolerated.

Patients may survive past the first few years of life without surgical intervention if the PVR remains elevated, although they may develop irreversible pulmonary vascular obstructive disease (PVOD) at a rapid rate. Surgical morbidity and mortality rates associated with this defect have dramatically improved over the years. Some centers report a surgical survival rate of 94% and an overall survival rate of 91% in patients with the balanced form of complete common atrioventricular canal repaired by age 4-6 months. About 3% of patients with a surgical heart block require a pacemaker, and about 7% may require repeat operation for residual defects or surgically induced mitral insufficiency. Actuarial survival at 13 years is 81%.

In patients with a nonrestrictive VSD component, pulmonary vascular disease (Eisenmenger syndrome) eventually occurs unless the VSD component is surgically closed. Rare cases have occurred even when surgical repair is successfully accomplished in infants younger than 6 months. Cyanosis occurs when patients develop some degree of right-to-left shunt at either atrial or ventricular levels. Although patients' quality of life may be impaired at this point, their life expectancy may be 20-50 years.

Treatment for the complete atrioventricular septal defect is primarily surgical. Operative morbidity and mortality for this procedure has dramatically improved over the past 20 years. Tweddell et al identified risk factors for surgical and late mortality and morbidity; these are the era of operation, patient's age at operation, severity of left atrioventricular valve regurgitation, magnitude of preoperative heart failure, presence of accessory atrioventricular valve orifices, other congenital heart disease, and Down syndrome.13

In infants, the published mortality rate for complete atrioventricular septal defect repair is 3.6% with minimal long-term morbidity; the 10-year survival rate is 81%. Bando et al found similar results while identifying risk factors for early death and the need for repeat operation.14 Risk factors included postoperative pulmonary hypertensive crisis, immediate postoperative severe left atrioventricular valve regurgitation, and a double-orifice left atrioventricular valve. McElhinney et al described an occasional anomalous attachment or tissue of the atrioventricular valve, which may complicate operative repair.15

Race

The occurrence does not appear to vary on the basis of race. Advanced maternal age is a risk factor for Down syndrome. Because at least two thirds of patients with uncomplicated complete atrioventricular septal defect have trisomy 21, ethnic groups in which advanced maternal age is common may have an increased incidence of complete atrioventricular septal defect.

Sex

The male-to-female ratio for complete atrioventricular septal defect is 1:1.

Age

Patients with complete atrioventricular septal defect often present with symptoms early in life. CHF usually develops by 6 weeks as PVR decreases and pulmonary blood flow increases. A rare case of survival to the eighth decade with untreated complete atrioventricular septal defect was reported. In some patients, PVR never decreases, and symptoms of CHF do not develop. In these rare cases, patients may remain asymptomatic as their pulmonary vascular obstructive changes worsen until cyanosis develops because of a right-to-left shunt.

Clinical

History

  • Tachypnea, repeated respiratory infections, poor feeding, and failure to thrive are frequent symptoms in patients with complete atrioventricular septal defect (AVSD) and large left-to-right shunts. These symptoms are usually present by 6-8 weeks and due to blood flow through the large interventricular communication with or without incompetence of the common atrioventricular valve.
  • Pulmonary vascular disease results from damage caused by excessive pulmonary flow and elevated pulmonary artery pressure due to the large ventricular septal defect (VSD). Irreversible pulmonary vascular disease may be present by age 2 years or, in rare cases, earlier.

Physical

  • General physical examination may show characteristics of Down syndrome, including flat facial profile, upslanting palpebral fissures, prominent inner epicanthal folds, Brushfield spots, protuberant tongue, abnormal palmar creases, and fifth finger clinobrachydactyly. Inspection may reveal pallor or Harrison grooves (horizontal depression along lower border of chest at diaphragm insertion site due to chronic tachypnea).16 Failure to thrive is common due to excessive metabolic cardiovascular requirements and poor caloric intake (due to tachypnea) is common.
  • The cardiac examination is remarkable for and overactive precordium. The volume and pressure overload on the right ventricle result in a prominent systolic heave along the left sternal border and subxiphoid regions. The pulmonary component of the second heart sound may be palpable at the left second intercostal space. Regurgitation of the atrioventricular valve may uncommonly result in a palpable apical thrill.
  • The first heart sound is single and often accentuated. The second heart sound is narrowly split, with an accentuated pulmonary component. A crescendo-decrescendo murmur may be audible at the upper left sternal border due to increased blood flow through a normal pulmonary valve. A mid diastolic rumble may be audible at the lower left sternal border and apex due to the increased flow across the common atrioventricular valve. A holosystolic murmur is often appreciated at the apex due to atrioventricular valve insufficiency. Because the VSD in complete atrioventricular septal defect is large and unrestrictive, it is not associated with a murmur.
  • When pulmonary vascular resistance (PVR) is elevated, the systolic murmur may not be prominent, and the diastolic rumble may disappear, reflecting less left-to-right shunt. This finding can occur in the infant in whom PVR has never fallen or in the older child with developing pulmonary vascular obstructive disease (PVOD), for whom the improvement in congestive heart failure (CHF) symptoms is an ominous finding.
  • In patients with advanced PVOD, the left parasternal impulse is prominent, S2 may be palpable, and the systolic murmur may be soft and short. A high-pitched decrescendo diastolic murmur of pulmonary insufficiency (Graham Steell murmur) may be detected at the left upper sternal border, reflecting severely elevated PVR.
  • Factors that can influence hemodynamics in Down syndrome include chronic nasopharyngeal obstruction, relative hypoventilation, carbon dioxide retention, and sleep apnea. Nonspecific CHF signs that may be seen include hepatosplenomegaly, pulmonary rales, and tachypnea. Skull erosion and striations have been noted from venous distension and increased blood volume.

Causes

  • Trisomy 21 (Down syndrome) is the most frequently associated genetic abnormality with complete atrioventricular septal defect, although it may also occur in association with trisomy 13 and trisomy 18. In patients without trisomy 21 who have common atrioventricular canal (CAVC) defects, a genetic locus on chromosome 1 can account for the disorder in some families.17
  • Interstitial deletion on chromosome 16 can be associated with atrioventricular septal defect. Endocardial cushion tissue seems to function as an adhesive for myocardial structures. Fibroblasts of endocardial cushions in trisomy 21 tend to be more adhesive, possibly leading to cardiac malformations. Atrioventricular septal defect may be seen with other less common syndromes, such as Dandy-Walker malformation, Joubert syndrome, and Ritscher-Schintal (craniocerebellocardiac) syndrome. An orocardiodigital syndrome consisting of tongue hamartomas, polysyndactyly, and atrioventricular septal defect has been described.
  • Atrioventricular septal defect is one of several cardiac abnormalities commonly seen with heterotaxy syndromes (asplenia and occasionally with polysplenia). Other rare combinations include atrioventricular septal defect with total anomalous pulmonary venous return and atrioventricular septal defect with Ebstein anomaly. Uncommon associations with atrioventricular septal defect include DiGeorge syndrome and coloboma of the eye, heart defects, atresia of the choanae, renal anomalies and retardation of growth and/or development, genital anomalies in males such as micropenis or cryptorchidism, and ear abnormalities or deafness (CHARGE) syndrome.
  • Recently, the presence of vascular endothelial growth factor (VEGF) gene mutations has been associated with atrioventricular septal defect.18 The prevalence of the VEGF +405C allele was higher in patients with CHD than in control subjects (0.42 vs 0.21; P <.05). The presence of VEGF +405C presented increased risk for CHD (odds ratio [OR], 1.72; 95% CI, 1.32–2.26).
  • Advanced maternal age is a risk factor for Down syndrome, and at least two thirds of patients with uncomplicated atrioventricular septal defect have trisomy 21.

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References
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Further Reading

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Keywords

complete atrioventricular septal defect, complete AVSD, endocardial cushion defect, ECD, common AV canal defect, AVC defect, CAVC, congestive heart failure, CHF, treatment, diagnosis

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Contributor Information and Disclosures

Author

Michael Pettersen, MD, Director of Echocardiography, Division of Cardiology, Children's Hospital of Michigan; Associate Professor of Pediatrics, Wayne State University School of Medicine
Michael Pettersen, MD is a member of the following medical societies: American Academy of Pediatrics, American College of Cardiology, American Heart Association, and American Society of Echocardiography
Disclosure: Nothing to disclose.

Medical Editor

Paul M Seib, MD, Associate Professor of Pediatrics, University of Arkansas for Medical Sciences; Medical Director, Cardiac Catheterization Laboratory, Co-Medical Director, Cardiovascular Intensive Care Unit, Arkansas Children's Hospital
Paul M Seib, MD is a member of the following medical societies: American Academy of Pediatrics, American College of Cardiology, American Heart Association, Arkansas Medical Society, International Society for Heart and Lung Transplantation, and Society for Cardiac Angiography and Interventions
Disclosure: Nothing to disclose.

Pharmacy Editor

Mary L Windle, PharmD, Adjunct Assistant Professor, University of Nebraska Medical Center College of Pharmacy, Pharmacy Editor, eMedicine
Disclosure: Pfizer Inc Stock Investment from financial planner; Avanir Pharma Stock Investment from financial planner ; WebMD Salary and stock Employment and investment from financial planner

Managing Editor

Alvin J Chin, MD, Professor of Pediatrics, Division of Cardiology, The Children's Hospital of Philadelphia, University of Pennsylvania School of Medicine
Alvin J Chin, MD is a member of the following medical societies: American Association for the Advancement of Science and American Heart Association
Disclosure: Nothing to disclose.

CME Editor

Gilbert Z Herzberg, MD, Assistant Professor, Department of Pediatrics, Section of Pediatric Cardiology, New York Medical College; Consulting Staff, Department of Pediatrics, Sound Shore Medical Center
Gilbert Z Herzberg, MD is a member of the following medical societies: American Academy of Pediatrics
Disclosure: Nothing to disclose.

Chief Editor

Steven R Neish, MD, SM, Director of Pediatric Cardiology Fellowship Program, Associate Professor, Department of Pediatrics, Baylor College of Medicine
Steven R Neish, MD, SM is a member of the following medical societies: American Academy of Pediatrics, American College of Cardiology, and American Heart Association
Disclosure: Nothing to disclose.

 
 
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