AUTHOR AND EDITOR INFORMATION

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INTRODUCTION

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Background

Atrioventricular septal defects (AVSDs), characterized by a deficiency of the atrioventricular septum, are a broad spectrum of malformations presumed to result from abnormal or inadequate fusion of the superior and inferior endocardial cushions with the mid portion of the atrial septum and the muscular (trabecular) portion of the ventricular septum.

Several methods of classification and nomenclature exist, causing considerable confusion. The term partial AVSD (also called partial common atrioventricular canal) generally refers to endocardial cushion defects, which have an interatrial communication but lack an interventricular communication. In these types of defects the mitral and tricuspid annuli are separate. In addition, certain anatomic features should be present, alone or in combination: primum atrial septal defect (ASD), inlet ventricular septal defect (VSD), cleft of the anterior mitral valve leaflet, and wide anteroseptal tricuspid valve commissure or cleft septal tricuspid leaflet (See Image 1). The most frequently encountered abnormality in patients with partial AVSD is the combination of primum ASD and cleft of the anterior mitral valve leaflet.

The term intermediate AVSD (also called transitional common atrioventricular canal) is variably defined; however, it most commonly refers to the combination of a partial AVSD with a small interventricular communication. This is an infrequent form of AVSD. There is usually a single valvar annulus where the anterior and posterior bridging leaflets fuse overlying the ventricular septum. Because of the leaflets' fusion there are two distinct valvar components (See Image 2).

A thorough description of associated atrioventricular valve abnormalities should be included when classifying these defects.

This article considers AVSDs that demonstrate minimal or no shunting through an interventricular communication.

Pathophysiology

In the absence of obstruction of the right ventricular outflow tract, such as in pulmonary stenosis or pulmonary vascular obstructive disease, predominant left-to-right shunting occurs. The clinical presentation is determined by the degree of interatrial shunting, atrioventricular regurgitation, or both. The most inferior portion of the atrial septum is deficient. The resulting ostium primum defect varies in size and may occur in association with more superior ostium secundum–type ASDs. In some of the latter cases, only a small strand of the atrial septum remains, leading to the appearance of a common atrium. Some observers reserve the term common atrium for those cases with an additional sinus venosus deficiency.

The degree of left-to-right shunting through the atrial defect is determined by the size of the communication and the relative compliance of the 2 atria and ventricles. Ventricular compliance is affected by the level of pulmonary vascular resistance (PVR). In the newborn with a less compliant right ventricle (RV) and relatively high PVR, little left-to-right shunting occurs. If the defect is extremely large, obligatory mixing in a common, or near-common, atrium creates a component of right-to-left shunting. Left-to-right shunting increases with age as PVR decreases and RV compliance increases. This results in progressive RV enlargement and pulmonary vascular engorgement.

The atrioventricular valves are abnormal, even in a partial AVSD. Fusion failure of the endocardial cushions usually results in a separation or cleft in the anterior mitral valve leaflet. The degree of regurgitation through the cleft depends on its size and, occasionally, on the coexistence of left ventricular outflow tract (LVOT) obstruction or coarctation of the aorta. Typically, the cleft directs regurgitant blood through the atrial defect, creating an LV-to-RA (right atrium) shunt. RA enlargement, rather than left atrial (LA) enlargement, may occur. In addition, mitral regurgitation (MR) contributes to LA and LV enlargement.

Frequency

United States

Prevalence estimates of cardiovascular malformations in large cohorts vary from 4-8 per 1000 births. AVSD constitutes 5-8% of these defects. Incidence of AVSD in fetuses is 17%; however, occurrence of partial AVSD has not been separated from this general classification.

Studies report the incidence of congenital heart defect (CHD) in children with Down syndrome (trisomy 21) to be 42-48%. Of those CHDs, 45% are AVSDs.

In general, AVSDs, when not associated with heterotaxia syndrome, occur commonly in Down syndrome.

Partial AVSD, as opposed to complete AVSD, of the ostium primum type is more common in patients without Down syndrome.

International

International frequency of cardiovascular malformations is similar to US figures.

Mortality/Morbidity

Left-to-right shunting through the atrial communication is generally well tolerated through the first decade of life. Patients are asymptomatic if MR is mild or absent. Symptoms of left-to-right shunting may develop in adolescence and are exacerbated by atrial arrhythmia. Sinus node dysfunction may occur and contributes to exercise intolerance if the defect is not repaired.

Moderate to severe MR may lead to morbidity in infancy and early childhood. Severe MR causes congestive heart failure (CHF) and failure to thrive in infants; it may result in death if left untreated.

A large left-to-right shunt from the LV to the RA through a cleft mitral valve causes volume overload in both ventricles, with CHF early in life.

CLINICAL

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History

In the absence of moderate to severe MR and other associated CHD, partial AVSD is often discovered later in childhood when the patient is referred for evaluation of a heart murmur. Also, partial AVSD is less common in Down syndrome than in complete AVSD.

• The clinical presentation of patients with partial AVSD depends on the degree of MR and on the associated cardiac defects.
• Other cardiac anomalies that may be associated with partial AVSD are secundum ASD, persistent left superior vena cava draining to the coronary sinus, pulmonary stenosis, discrete subaortic stenosis, tricuspid stenosis, tricuspid atresia, coarctation of the aorta, patent ductus arteriosus (PDA), perimembranous VSD, and hypoplastic LV.
• Children with atrioventricular valve competence usually exhibit no significant symptoms. They are usually referred to a pediatric cardiologist if a heart murmur is detected during routine examination.
• Substantial left-to-right shunting may exacerbate pulmonary disease and cause frequent lower respiratory infections in some patients. These patients may present with tachypnea, respiratory distress, and inadequate weight gain.
• Infants with severe MR often demonstrate poor feeding, tachypnea, and labored breathing. Rarely, respiratory distress may be so severe as to require mechanical ventilation.
• Progressive cardiac enlargement and LV dysfunction cause shocklike symptoms and eventually lead to mortality.
• Adolescents and young adults may note progressive exercise intolerance.
• Palpitations caused by atrial arrhythmia become more common in young adulthood, and sustained supraventricular tachycardia, atrial flutter, or atrial fibrillation may trigger the onset of CHF in older patients with AVSD.
• Hypervolemia of pregnancy may trigger CHF symptoms and complicate pregnancy.

Physical

• General appearance
• • Most children with partial AVSD and minimal MR appear healthy. Patients who have Down syndrome exhibit features typical of the condition.
  • Patients with severe MR in infancy can manifest tachypnea, retractions, and diaphoresis, especially during and immediately after feeding. Poor caloric intake and excessive metabolic demands lead to growth failure. Older children and adolescents with severe MR may display a prominent left chest as well as a slim (asthenic) build.
• Pulmonary and cardiovascular examination
• • Palpation and auscultatory findings depend on the severity of the left-to-right shunt, the presence of MR, and associated defects (eg, LV outflow obstruction, PDA).
  • Fine rales or rhonchi, or both, may be heard in the lung fields of older patients with severe MR but are rare in infants.
  • The partial AVSD provides auscultatory findings that are indistinguishable from those created by any other large ASD. A prominent impulse along the right sternal border, consistent with an RV lift, may be present. Alternatively, severe MR can cause a prominent apical impulse or thrill.
  • The classic auscultatory finding associated with an ASD is a constant or fixed splitting of the second heart sound (S₂), frequently accompanied by a pulmonary ejection murmur audible at the upper left sternal border.
  • A large AVSD with substantial left-to-right shunting creates a mid-diastolic rumbling murmur, audible along the lower left sternal border. This often occurs in association with a prominent third heart sound (S₃) in that location. These sounds are attributed to an abnormally high flow across the tricuspid component of the atrioventricular valve.
  • The apical murmur of MR occurs even with a small cleft in the atrioventricular valve. This murmur has a blowing quality and must be differentiated from the murmur caused by a VSD. However, when it occurs with a fixed split S₂, this murmur is helpful in differentiating a partial AVSD from a secundum ASD.
  • Severe MR can also cause a diastolic murmur audible over the apical area, which, in association with the systolic murmur, produces a to-and-fro quality.

Causes

For CHD, experimental and epidemiologic data suggest that a single mechanism may cause a range of anatomic malformations.

Specifically, AVSDs are presumed to occur secondary to extracellular matrix abnormalities that produce faulty development of the endocardial cushions and the atrioventricular septum.

Normal development of the human heart requires an orderly coordination of transcriptional programs. One of the most important factors for the differentiation of mesodermal progenitor cells is the homeobox protein Nkx-2.5. For example, the lack of Nkx-2.5 in mice arrests heart development prior to looping, which is lethal. In humans, 28 germline Nkx-2.5 mutations have been associated with CHD. Recent studies have shown that mutations in the gene Nkx-2.5 are associated specifically with AVSD and VSD.

DIFFERENTIALS

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Other Problems to be Considered

Cleft mitral valve
Common atrium (usually associated with complex CHD)

WORKUP

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Imaging Studies

• Chest roentgenography usually shows the following:
• • Prominent pulmonary artery segment and abnormally dense pulmonary vascular markings
  • Cardiac enlargement, especially RA and RV enlargement
• Echocardiography is the diagnostic method of choice:
• • Ostium primum defect is seen as an echo dropout in the lower portion of the septum at the crux of the heart.
  • Abnormal morphology of the AV valves can be studied in detail, including small inferior and mural leaflets, lack of coaptation of leaflets, and a cleft in the anterior mitral valve leaflet.
  • The attachments of the AV valves may extend into the LVOT and may create obstruction. AV valve tissue may extend to the crest of the ventricular septum.
  • Apical 4-chamber view will show the tricuspid and mitral valve components at the same level without the normal apical displacement of the tricuspid valve.
  • Anterior and superior displacement of the aorta, with elongation and narrowing of the LVOT, is seen in the long parasternal axis.
• Doppler and color Doppler studies are used for the following:
• • Demonstration of left-to-right shunting through the ASD and detection of presence and severity of MR (shunting from the LV to the RA may also be identified).
  • If tricuspid regurgitation is present, RV pressure may be estimated. Care is needed to interrogate tricuspid regurgitation rather than the LV-to-RA jet; otherwise, a falsely high ventricular pressure estimate results.
  • LVOT obstruction may be identified and quantitated.
  • Three dimensional (3-D) echocardiography has been shown to provide excellent quality images of the AV valve morphology and relationships with the rest of the cardiac structures.
  • It is also being used in centers to assess the dynamic morphology of the left-sided AV valve and LVOT anatomy after AVSD repair.
• Magnetic resonance imaging (MRI) is being more frequently used because more precise delineation of anatomy and evaluation of function may be obtained with this noninvasive method than with either echocardiography or angiography alone.
• • MRI can be used to help define morphologic abnormalities in AV septal defect as well as important anatomic variations.
  • MRI is particularly useful for evaluating shunt severity, expressed quantitatively as the ratio of pulmonary flow to systemic flow (Qp/Qs).

Other Tests

• Electrocardiography
• • Classic anatomic studies of the conduction tissue have shown that the AV node is usually displaced posteriorly, originating in the posterior wall of the RA.
  • The bundle of His is displaced posteriorly and skirts the lower margin of the VSD (the right bundle may give off several branches instead of continuing as a single trunk through the RV).
  • This unusually long course and peculiar orientation of the conduction tissue creates a different advancing front of depolarization, resulting in the following characteristic electrocardiographic (ECG) features:
    • The superior-oriented, counterclockwise vector loop in the frontal plane occurs commonly in AVSD.
    • The mean QRS axis ranges from -30 to -120° (mostly between -30 and -90°).
    • On the standard 12-lead ECG, the small R wave is followed by a prominent S wave in lead aVF; in aVL, a small Q wave is followed by a prominent R wave. This pattern is caused by abnormal septal depolarization in AVSD, including PR-interval prolongation and RV hypertrophy, particularly an rSR' or RSR' pattern.
    • P wave enlargement concordant with RA, LA, or biatrial enlargement is seen in approximately half of patients with AVSDs.
    • Indications of LV hypertrophy occur with severe MR and include prominent R wave voltage in left precordial leads and a deep S wave in right precordial leads.

Procedures

• Cardiac catheterization and angiography
• • This test is no longer needed to confirm the diagnosis of partial AVSD.
  • This procedure might be performed if echocardiography is not sufficient to delineate anatomy and if pulmonary hypertension is suspected. The shunt can be measured, and the response of the pulmonary arterial pressure and resistance to pulmonary vasodilators can be assessed. If present, LVOT obstruction can be quantified or other associated lesions evaluated.

TREATMENT

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Medical Care

Treatment for CHF is occasionally required if MR cannot be adequately reduced surgically.

Surgical Care

Management is primarily surgical, and repair includes patch closure of the atrial septal defect, mitral valve annuloplasty, or cleft closure. Other defects (eg, LVOT obstruction, PDA) may require repair during the same operation.

• Repair is usually performed electively in children aged 2-5 years, unless significant MR is present, in which case earlier repair is indicated. However, in the current era, repair of AVSD can be done successfully in patients weighing less than 5 kg (Prifti, 2004).
• Surgical morbidity
• • Severe MR develops in a significant number of patients after correction of ASD. As a matter of fact, MR is the most common indication for reoperation in patients after repair of both partial and complete AVSD (Ten Harkel, 2005).
  • Preoperative severe left-sided AV valve regurgitation and associated valve malformations are important risk factors for postoperative development of MR (Abbruzzese, 1990), (Ten Harkel, 2005).
  • According to another study, predictors for reoperation include postoperative MR of 2 or more, presence of major associated cardiac malformations, associated left AV valve malformations, non– or partial left AV valve cleft closure and weight < 5 kg (Prifti, 2004).
  • It has been shown that when the left-sided AV valve requires replacement because of unacceptable degrees of regurgitation, higher mortality and complete AV block should be expected (Aubert,2005).
  • One study showed that spontaneous regression of left-sided AV valve regurgitation after the immediate postoperative period can occur thus, avoiding the need for reoperation (Ten Harkel, 2005).
  • LVOT obstruction may not be evident for years after the initial repair.
• Surgical mortality
• • Depending on the surgical series, early postoperative mortality rate is less than 3% in patients with mostly uncomplicated partial AVSD (Najm, 1998; Ten Harkel, 2005).
  • However, poorer survival is seen in patients with major associated cardiac malformations and pulmonary hypertension, with an early postoperative mortality of 8% (Prifti, 2004).

Consultations

• Pediatric cardiologist
• Cardiovascular surgeon
• Geneticist if an abnormality is suspected (eg, Down syndrome)

MEDICATION

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Medical treatment is indicated in patients with CHF usually before surgical repair. However, it may also be needed in patients in whom MR persists postoperatively. The treatment outlined below is usually indicated for outpatient management.

Drug Category: Angiotensin-converting enzyme inhibitors (ACE inhibitors)

These medications are used to decrease the afterload to the LV produced by the MR. This effect is achieved by producing peripheral vasodilatation, which in turn, reduces systemic blood pressure (ie, reduces afterload). Reduction in systemic blood pressure decreases the amount of blood pumped by the LV with each systolic contraction (ie, stroke volume), and it also reduces the pressure at which the blood is being ejected. This, in turn, diminishes the amount of blood regurgitated by the mitral valve from the LV into the LA during systole, which decreases pulmonary venous pressure and, thus, decreases pulmonary congestion. By decreasing the afterload to the LV, the ACE inhibitors reduce the left-to-right shunt through the AVSD (the ASD in the case of partial AVSD).

Drug Category: Diuretics

These agents help decrease pulmonary congestion.

Drug Category: Inotropic, Antiarrhythmic

It is used because of its direct inotropic effects in addition to indirect effects on the cardiovascular system.

Its indirect actions result in increased carotid sinus activity and enhanced sympathetic withdrawal for any given increase in mean arterial pressure. These effects help reduce the heart rate response to CHF, rendering a more effective stroke volume with each ventricular systole.

FOLLOW-UP

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Further Inpatient Care

• Follow-up is determined on an individual basis, and the frequency depends on the persistence and severity of AV valve regurgitation or other abnormalities. Chest radiographs, ECGs, and echocardiograms should be obtained if the physical examination warrants.

MISCELLANEOUS

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Medical/Legal Pitfalls

• Delay in diagnosis of these defects may lead to morbidity and mortality.
• Failure to counsel for adequate dental care or antibiotic prophylaxis when a potential risk exists for bacteremia may lead to endocarditis, especially in patients with MR.

Special Concerns

• Genetic counseling for possible risk factors, especially in families with CHD, must be sought.
• • Defects of the extracellular matrix have been associated with a higher incidence of extracardiac anomalies, such as gastrointestinal (Hirschsprung disease, intestinal obstruction, annular pancreas, imperforate anus, biliary atresia) and facial (facial cleft).
  • In patients with CHARGE association (Colobomata, Heart defects [in 50%], choanal Atresia, Retardation of growth or development, Genital hypoplasia, Ear anomalies), AVSD may be seen, as well as other CHDs.
  • Patients with Ellis–van Creveld syndrome may have AVSD or a common atrium.

MULTIMEDIA

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Media file 1:  Partial atrioventricular septal defect (AVSD): The mitral and tricuspid annuli are separate.The cleft in the mitral leaflet is in the anterior position. This type of anatomy is usually associated with a primum atrial septal defect (ASD). Partial AVSD is more common than intermediate AVSD.
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Media type:  Image

Media file 2:  Intermediate atrioventricular septal defect (AVSD): There is a single valve annulus. The anterior and posterior bridging leaflets are fused (whereas in complete AVSD the anterior and posterior bridging leaflets are not fused). Therefore, the atrioventricular valve has a tricuspid and a mitral component. Intermediate AVSD is the least common type of AVSD.
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Media type:  Image

Media file 3:  Echocardiogram of the apical 4-chamber view demonstrating a partial atrioventricular septal defect (AVSD). Chambers are denoted by RA, right atrium; RV, right ventricle; and LV, left ventricle.
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Media type:  Image

Media file 4:  Echocardiogram with subcostal view demonstrates an atrioventricular septal defect (AVSD). A portion of the ostium secundum atrial septum is also missing, just superior to the ostium primum defect.
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Media type:  Image

Media file 5:  Color Doppler demonstrates left-to-right shunting through the partial atrioventricular septal defect (AVSD) shown in Images 1-2.
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Media type:  Image

Media file 6:  Left superior axis deviation in the frontal plane and rR' pattern in right precordial leads.
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Media type:  ECG

REFERENCES

Section 11 of 11

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• Neufeld HN, Titus JL, Dushane JW. Isolated ventricular septal defect of the persistent common atrioventricular canal type. Circulation. May 1961;23:685-96. [Medline].
• Parsons JM, Baker EJ, Anderson RH. Morphological evaluation of atrioventricular septal defects by magnetic resonance imaging. Br Heart J. Aug 1990;64(2):138-45. [Medline].
• Piccoli GP, Gerlis LM, Wilkinson JL. Morphology and classification of atrioventricular defects. Br Heart J. Dec 1979;42(6):621-32. [Medline].
• Portman MA, Beder SD, Cohen MH. Conduction abnormalities detected by electrophysiologic testing following repair of ostium primum atrioventricular septal defect. Int J Cardiol. Apr 1986;11(1):111-9. [Medline].
• Portman MA, Beder SD, Ankeney JL. A 20-year review of ostium primum defect repair in children. Am Heart J. Nov 1985;110(5):1054-8. [Medline].
• Pretre R, Dave H, Kadner A. Direct closure of the septum primum in atrioventricular canal defects. J Thorac Cardiovasc Surg. Jun 2004;127(6):1678-81.
• Prifti E, Bonacchi M, Bernabei M. Repair of complete atrioventricular septal defects in patients weighing less than 5 kg. Ann Thorac Surg. May 2004;77(5):1717-26. [Medline].
• Sadeghi AM, Laks H, Pearl JM. Primum atrial septal defect. Semin Thorac Cardiovasc Surg. Jan 1997;9(1):2-7. [Medline].
• Ten Harkel AD, Cromme-Dijkhuis AH, Heinerman BC. Development of left atrioventricular valve regurgitation after correction of atrioventricular septal defect. Ann Thorac Surg. Feb 2005;79(2):607-12. [Medline].
• Wang ZJ, Reddy GP, Gotway MB. Cardiovascular shunts: MR imaging evaluation. Radiographics. Oct 2003;23 Spec No:S181-94. [Medline].
• van den Bosch AE, van Dijk VF, McGhie JS. Real-time transthoracic three-dimensional echocardiography provides additional information of left-sided AV valve morphology after AVSD repair. Int J Cardiol. Jan 26 2006;106(3):360-4. [Medline].

Article Last Updated: Sep 14, 2006