AUTHOR AND EDITOR INFORMATION

Section 1 of 11  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Miscellaneous
• Multimedia
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INTRODUCTION

Section 2 of 11  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Miscellaneous
• Multimedia
• References

Background

Atrioventricular (AV) septal defects comprise a broad spectrum of lesions, from partial or intermediate forms with no shunting at the ventricular level to complete AV septal defects with large atrial septal defects, large ventricular septal defects, and a single common atrioventricular valve (AVV) orifice. Instead of separate mitral and tricuspid valve inlets, a common AVV has a single inlet (orifice) into the ventricular chambers. When this common AVV opens predominantly toward one ventricle or the other, an unbalanced AV canal (AVC) or AV septal defect forms.

If the common AVV opens predominantly into the morphologic left ventricle, the defect is termed a left ventricular (LV)–type or LV-dominant AV septal defect (canal). If the common AVV opens predominantly into the morphologic right ventricle, the defect is termed a right ventricular (RV)–type or RV-dominant AV septal defect (canal). The degree of unbalance varies from mildly unbalanced with 2 nearly normal-sized ventricles to severely unbalanced with a single dominant ventricle and a second hypoplastic ventricle. This results in essentially single-ventricle physiology. Importantly, the ventricles, not the common AVV, are unbalanced. The development of the ventricles is unbalanced with hypoplasia of the inlet and outlet septum, resulting in hypoplasia of the chamber with malalignment of the ventricular septum.

Embryology

AV septal defects occur at the embryonic age of 34-36 days when fusion of the endocardial cushions fails. This occurs when the endocardial cushion fibroblasts fail to migrate normally to form the septum of the AVC. As a result, a deficiency of the primum atrial septum, the ventricular septum, the septal leaflet of the tricuspid valve, and the anterior leaflet of the mitral valve occurs. The position of the AVVs becomes lower than normal. The anterior leaflet of the AVV extends across the ventricular septum and is shared between the left and right ventricles. If the leaflet opens preferentially toward either ventricle, blood flow is limited to the other ventricle, causing hypoplasia of that ventricle and creating unbalance between the 2 ventricles.

Anatomy

Please see Atrioventricular Septal Defect, Complete and Atrioventricular Septal Defect: Surgical Perspective for general anatomic principles common to all patients with AV septal defects.

As noted above, 2 major types of unbalanced AV septal defects (canals) exist (ie, LV-dominant, RV-dominant). Generally, concomitant hypoplasia of the left-sided structures (LV, aortic) or the right-sided structures (RV, pulmonary artery [PA]) also occurs. Although a considerable spectrum of ventricular dominance occurs, the term unbalanced AV septal defect generally implies hypoplasia of one ventricle and its associated outflow tract with essentially single-ventricle physiology. RV-dominant AV septal defects occur more commonly than LV-dominant AV septal defects. The LV or RV is severely hypoplastic in approximately 7% of patients born with complete AVC defects.

Pathophysiology

The physiology of the lesion depends on the degree of ventricular unbalance, size of AV septal defects, AVV competence, degree of right or left sided outflow obstruction, and pulmonary vascular resistance. As with balanced AV septal defects, in the absence of significant left- or right-sided outflow obstruction, the physiology and clinical presentation of partially unbalanced AV septal defects are generally those of pulmonary overcirculation. Infants typically present with congestive heart failure (CHF) in the first month of life. Infants may present in extremis with acidosis if severe hypoplasia of left-sided structures with ductal-dependent systemic circulation is present, or they may present with severe cyanosis if severe hypoplasia of the right-sided structures with ductal-dependent pulmonary circulation is present.

When a large ventricular septal defect (VSD) is present, the risk of pulmonary vascular disease is high. If the patient is deemed a poor candidate for 2-ventricle repair, effort should be made early to protect the pulmonary vascular bed to optimize a single-ventricle repair. Pulmonary artery banding in this situation allows additional time before a decision must be made about proceeding with either a univentricular or biventricular repair. If the VSD is small in the presence of LV hypoplasia, this may bode well for a possible biventricular repair because most cardiac output still is being carried by the small LV.

Frequency

United States

AV septal defects are relatively common forms of congenital heart disease, representing approximately 3% of all congenital heart disease; the estimated incidence is 0.19 per 1000 live births (one half of patients have Down syndrome). AV septal defects are present in 45-62% of infants with Down syndrome.

Unbalanced forms occur in approximately 7% of patients with AV septal defects. The vast majority of these do not occur in patients who have Down syndrome.

Unbalanced AV septal defects are observed frequently in patients with heterotaxy syndromes. They occur much more frequently in patients with asplenia than in those with polysplenia.

Mortality/Morbidity

• Long-term morbidity and mortality rates are related to the development of pulmonary vascular obstructive disease. As many as 30% of patients with complete AV septal defects develop pulmonary vascular obstructive disease by age 7-12 months, and 90% develop it by age 3-5 years.
• The true natural history is difficult to accurately determine because no group of infants born with this lesion has been monitored without surgical intervention.
• Patients with unrepaired complete AV septal defects have an overall poor prognosis. Approximately 80% of patients with complete AV septal defects die by age 2 years. In 1979, in a study of autopsied patients, Berger et al reported that only 54% of infants survived 6 months, 35% survived 1 year, and 4% survived 5 years. In 1981, Somerville et al found that 55% of patients died or had significant medical problems in the first year of life. In 1985, Bull et al found that this outlook was not as dismal for patients with Down syndrome and that only 4 late deaths occurred over a 27-year period in patients aged 1 year with unoperated AV septal defects.

Race

No known racial predilection exists.

Sex

No known sexual predilection exists.

Age

AV septal defects are present at birth; most patients present within the first month of life.

CLINICAL

Section 3 of 11  

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• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Miscellaneous
• Multimedia
• References

History

• If no significant right- or left-sided obstruction is present, infants generally present within the first month of life with CHF with tachypnea and failure to thrive due to pulmonary overcirculation.
• If pulmonary outflow tract obstruction is present, infants may present with cyanosis or an audible murmur.
• Occasionally, neonates may present in extremis with acidosis in the presence of ductal-dependent systemic circulation or cyanosis in the presence of ductal-dependent pulmonary circulation.
• Patients with abdominal heterotaxy may present with situs inversus noted incidentally on a routine chest radiograph.

Physical

• Most children appear healthy, except the rare patient with features of Down syndrome.
• This lesion is associated with a variety of auscultatory findings, depending on the underlying physiology.
• Murmurs of pulmonary stenosis, LV outflow tract obstruction, or AVV regurgitation may be appreciated.
• Cyanosis may be present.
• Reduced lower extremity pulses may suggest coarctation of the aorta, which may coexist with RV-dominant AVC.

Causes

• The genetic basis for this lesion has not been elucidated; however it can be associated with trisomy 21.
• Unbalanced AV septal defect may be observed in patients with abdominal heterotaxy. The presence of complete AV septal defect is more than twice as frequent in patients with asplenia than in those with polysplenia.

DIFFERENTIALS

Section 4 of 11  

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Other Problems to be Considered

In the setting of abdominal heterotaxy, other abnormalities may include intestinal malrotation, renal anomalies, and asplenia.

WORKUP

Section 5 of 11  

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Lab Studies

• A CBC count with special attention to the peripheral smear to exclude Howell-Jolly bodies should be obtained in patients with heterotaxy syndrome. Howell-Jolly bodies may be noted in patients with functional asplenia.
• Chromosome testing may be performed, although findings are usually normal unless the patient has Down syndrome.

Imaging Studies

• Chest radiography
• • The chest radiograph may reveal abdominal situs inversus with heterotaxy. Abnormalities of bronchial anatomy may be evident in the setting of asplenia or polysplenia.
  • Generally, the chest radiograph depicts cardiomegaly with increased pulmonary vascular markings.
  • If significant subpulmonic obstruction is present, pulmonary markings may be normal.
• Two-dimensional echocardiography and Doppler analysis
• • Doppler-echocardiography is definitive and is the method of choice in making the diagnosis of unbalanced AV septal defect. Cardiac anatomy, hemodynamics, and ventricular function can be assessed in detail noninvasively. Doppler-echocardiography alone generally can provide sufficient anatomic and functional information before repair and/or palliation.
  • The initial Doppler-echocardiogram should focus on the following:
    • Atrial and visceral situs
    • Presence and size of atrial-level defect and shunt (Common atria may be observed.)
    • Presence and size of ventricular-level defect and shunt
    • Anatomy of the AVV, including annulus size, leaflet morphology, chordal attachments, and papillary muscle architecture (Assess the proportion of the AVV overlying each ventricle from the subcostal short-axis view as well as the degree of AVV regurgitation.)
    • Relative chamber sizes and functions
    • Relationship and sizes of the great arteries
    • Detailed attention to the anatomy of the LV and RV outflow tracts and the presence of obstruction
    • Systemic and pulmonary venous connections
    • Hypoplasia of aortic arch and/or status of ductus arteriosus
    • Presence or absence of RV/PA hypertension
  • The greatest clinical challenge for the cardiologist is to determine the feasibility of the 2-ventricular repair in borderline cases. This depends on relative ventricular sizes, AVV structure and function, size of the VSD, size of the LV outflow tract, and aortic arch hypoplasia.
    • No strict quantitative guidelines exist; qualitative and/or clinical impressions often provide accurate guidance in the feasibility of a 2-ventricular repair.
    • PA banding in infancy protects the pulmonary vascular bed and allows additional time before a commitment needs to be made for either a univentricular or biventricular repair. Additionally, many perform primary repair if a biventricular approach is considered, again to avoid the deleterious hypertrophy that can occur after PA banding.
• MRI can be useful in delineating the intracardiac, pulmonary artery, systemic and pulmonary venosum, and abdominal anatomy in patients with heterotaxy syndrome. In the future, 3-D echocardiography and MRI may be useful in providing more detailed quantitative information about ventricular potential in borderline cases.
• Abdominal ultrasonography: This study helps detect presence or absence of the spleen.

Other Tests

• The electrocardiogram often depicts left axis deviation, initial counterclockwise frontal loop, and RV hypertrophy. In patients with heterotaxy, P wave axis may assist in determining the location of the sinus node.

Procedures

• Cardiac catheterization and angiography
• • Invasive studies are not always needed before surgical repair and/or palliation if all the anatomic and functional data can be obtained by means of echocardiography.
  • Catheterization may be helpful in borderline cases to assist with decision making about whether to proceed with univentricular or biventricular repair.
  • Catheterization may assist with defining systemic venous and pulmonary venous anatomy more completely.
  • If single-ventricular repair is chosen, catheterization is often used prior to creation of the bidirectional Glenn anastomosis to assess the pulmonary artery architecture and pressures. Catheterization may also be obtained prior to completion of a Fontan repair to assess systemic and pulmonary artery structure and hemodynamics.

TREATMENT

Section 6 of 11  

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Medical Care

• Generally, treat CHF with digoxin, diuretics, and angiotensin-converting enzyme (ACE) inhibitors as needed before surgical palliation and/or repair.
• The most important prerepair medical care involves the decision-making process regarding univentricular versus biventricular repair. A successful biventricular repair requires creation of 2 competent AVVs, and both ventricles must be large enough to carry a full cardiac output.
• • Preoperative LV volume calculations can greatly underestimate the potential volume of the LV once the RV is unloaded.
  • In 1997, Van Son and colleagues predicted postoperative LV volumes based on preoperative echocardiograms in patients with RV-dominant unbalanced AV septal defects. They found that a preoperative indexed volume of greater than 15 mL/m² was sufficient for a biventricular repair. They also noted that the commonly held notion that the LV should be apex forming is misleading; this is not essential for a successful biventricular repair.
  • Cohen et al suggested an approach using an echocardiographically derived AVV index. The advantage to this approach is that it is less affected by volume load differences than ventricular cavity volumes. They suggest that a left-to-right AVV area ratio of less than 0.67 in the presence of a large VSD or ductal-dependent circulation precludes biventricular repair.
  • Neither of these strategies takes into account potential for growth, particularly in small infants.

Surgical Care

• Surgical techniques for the treatment of patients with AV septal defects have evolved considerably since Lillehei first reported successful repair of an AVC defect using cross-circulation in 1956. Results have improved remarkably in the past 20 years.
• Most patients who are eligible for a biventricular repair undergo repair before age 6 months (as with other patients with balanced AV septal defects). Most institutions are comfortable performing a biventricular repair in symptomatic patients aged 3-4 months or younger and can do so with a mortality rate of less than 3%.
• The following 2 surgical approaches commonly are used with excellent results to repair balanced AV septal defects:
• • The 2-patch technique using a synthetic (eg, Dacron, Gore-Tex) ventricular patch and a separate pericardial atrial patch
  • The 1-patch technique, usually pericardial, which covers both the ventricular and atrial components
• In patients with severe hypoplasia of one ventricle, the single-ventricle pathway offers the best long-term results, although it is palliative at best. Drinkwater and Laks reported on 34 patients with unbalanced AV septal defects who underwent cavopulmonary shunt procedures between 1988 and 1996. Of these patients, 25 (73%) were RV-dominant. The hospital mortality rate was 9% (3 of 34 patients). Of 31 survivors, 3 late deaths occurred (9.6% of patients). Of the 16 patients who underwent completion of the Fontan operation, 1 died in the hospital and 5 late deaths occurred.
• In the early postoperative period, nitric oxide may be beneficial for those patients who have elevated pulmonary vascular resistance.

Consultations

• Pediatric cardiologist
• Pediatric cardiothoracic surgeon
• Geneticist if indicated

Diet

No specific diet is needed. Maximizing nutrition and caloric intake is important in every child with CHF symptoms and before surgical repair and/or palliation. Increased caloric density of formula is often required for growth.

Activity

Activity restrictions must be determined on a patient-by-patient basis and vary considerably depending on whether a 1- or 2-ventricle repair is achieved. In addition, residual defects such as AVV regurgitation or LV outflow tract obstruction may influence exercise performance. After staged completion, patients who underwent single-ventricle repair may experience up to 80% of normal exercise tolerance.

MEDICATION

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No specific or recommended drug therapy exists for unbalanced AV septal defects. If evidence of pulmonary overcirculation is present, management of CHF with digoxin, diuretics, and ACE inhibitors may be indicated. ACE inhibitors may also be indicated for AVV regurgitation.

Drug Category: Cardiac glycosides

These agents theoretically provide a positive inotropic effect. They are used to treat acute and chronic CHF.

Drug Category: Loop diuretics

These agents inhibit electrolyte reabsorption in the ascending loop of Henle, thereby promoting diuresis. They are used to treat heart failure or hepatic, renal, or pulmonary disease when sodium and water retention has resulted in edema or ascites.

Drug Category: ACE inhibitors

ACE inhibitors are beneficial in all stages of chronic heart failure. Pharmacologic effects result in decreased systemic vascular resistance, reducing blood pressure, preload, and afterload.

FOLLOW-UP

Section 8 of 11  

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Further Inpatient Care

• Admit for testing and surgical intervention.
• Optimize management of CHF before surgical repair and/or palliation.

Further Outpatient Care

• Give careful attention to AVV function and development of LV outflow obstruction on follow-up visits if a biventricular repair was accomplished.
• If a single-ventricle repair was performed, follow-up care and complications occur as with other patients with a single ventricle. See Single Ventricle for a comprehensive list of postoperative complications and medical management.

In/Out Patient Meds

• If a successful biventricular repair is accomplished, long-term cardiac medications generally are not needed after surgical convalescence.
• In patients who underwent single-ventricle palliation, aspirin with or without Coumadin may be used to reduce the risk of thrombus formation within the Fontan circuit. Additionally, an ACE inhibitor may be prescribed to optimize ventricular function or for the treatment of AVV regurgitation. Antiarrhythmic medications are used as indicated for the treatment of specific arrhythmias.

Transfer

• After diagnosis is made, or to ensure an accurate diagnosis, transfer the patient to a tertiary facility where pediatric cardiologists and/or cardiovascular surgeons are available.

Complications

• Postoperative complications following biventricular repair include AV block, pulmonary hypertension, residual AVV regurgitation, AVV stenosis, and residual LV outflow tract obstruction.
• Postoperative complications following univentricular repair include the following:
• • Pleural effusions, pericardial effusions, ascites
  • Atrial flutter and other atrial or, less commonly, ventricular arrhythmias
  • Pulmonary thromboembolism, stroke
  • Protein-losing enteropathy
  • Residual pulmonary branch stenosis
  • Formation of systemic venous collaterals resulting in a right-to-left shunt or the development of pulmonary arteriovenous fistulae
  • Low exercise capacity
  • Growth failure
  • Formation of systemic-to-pulmonary arterial collaterals that may result in a residual left-to-right shunt and excessive volume load on the systemic ventricle

Prognosis

• Prognosis following biventricular repair generally is good. The operative mortality rate generally is less than 3%. Most patients remain asymptomatic with a normal functional status. Less than 10-15% of patients require reoperation for residual AVV insufficiency or LV outflow tract obstruction.
• Prognosis following univentricular repair is reasonable and improving as surgical techniques and medical management improve. However, the true long-term function of a single ventricle, especially a single right ventricle, remains unknown.
• Emanuel et al reported that 14% of offspring of mothers with AV septal defects have congenital heart disease.

MISCELLANEOUS

Section 9 of 11  

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• Miscellaneous
• Multimedia
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Medical/Legal Pitfalls

• Failure to recognize potential for early pulmonary vascular obstructive disease and initiating surgical therapy accordingly

MULTIMEDIA

Section 10 of 11  

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• Follow-up
• Miscellaneous
• Multimedia
• References

Media file 1:  Echocardiogram image demonstrating a left ventricular dominant AV canal defect.
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Media type:  Echo

Media file 2:  Catheterization in a patient with a LV dominant AV canal defect. The catheter is positioned in the pulmonary artery demonstrating pulmonary artery band and branch pulmonary arteries.
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Media type:  Image

Media file 3:  ECG of a 3 month old female with an LV dominant AV canal. The ECG demonstrates left axis deviation with an initial counterclockwise frontal loop.
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Media type:  ECG

Media file 4:  Echocardiogram clip demonstrating common AV valve regurgitation in a patient with an LV dominant AV canal defect.
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Media type:  Video

REFERENCES

Section 11 of 11

• Authors and Editors
• Introduction
• Clinical
• Differentials
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• Anderson RH, Mccartney FJ, Shinebourne EA. Atrioventricular septal defects. Pediatr Cardiol. 1987;1:571-609.
• Apfel HD, Gersony WM. Clinical evaluation, medical management and outcome of atrioventricular canal defects. Prog Pediatr Cardiol. 1999;10:129-136.
• Berger TJ, Blackstone EH, Kirklin JW, et al. Survival and probability of cure without and with operation in complete atrioventricular canal. Ann Thorac Surg. Feb 1979;27(2):104-11. [Medline].
• Bricker J, McNamara D, Garson A. Defects of the atrial septum including the atrioventricular canal. In: Science and Practice of Pediatric Cardiology. Lippincott Williams & Wilkins;1990:1036-1051.
• Bull C, Rigby ML, Shinebourne EA. Should management of complete atrioventricular canal defect be influenced by coexistent Down syndrome?. Lancet. May 18 1985;1(8438):1147-9. [Medline].
• Cohen MS, Jacobs ML, Weinberg PM, Rychik J. Morphometric analysis of unbalanced common atrioventricular canal using two-dimensional echocardiography. J Am Coll Cardiol. Oct 1996;28(4):1017-23. [Medline].
• Daebritz S, del Nido PJ. Surgical management of common atrioventricular canal. Prog Pediatr Cardiol. 1999;10:161-171.
• Drinkwater DC, Laks H. Unbalanced atrioventricular septal defects. Semin Thorac Cardiovasc Surg. Jan 1997;9(1):21-5. [Medline].
• Emanuel R, Somerville J, Inns A, Withers R. Evidence of congenital heart disease in the offspring of parents with atrioventricular defects. Br Heart J. Feb 1983;49(2):144-7. [Medline].
• Foker JE, Berry J, Steinberger J. Ventricular growth stimulation to achieve two-ventricle repair in unbalanced common atrioventricular canal. Prog Pediatr Cardiol. 1999;10:173-186.
• Journois D, Baufreton C, Mauriat P, et al. Effects of inhaled nitric oxide administration on early postoperative mortality in patients operated for correction of atrioventricular canal defects. Chest. Nov 2005;128(5):3537-44. [Medline].
• Kirklin JW, Barratt-Boyes BG. Atrioventricular canal defect. In: Cardiac Surgery. 2nd ed. Churchill Livingstone Inc;1993:693-747.
• Levine JC, Geva T. Echocardiographic assessment of common atrioventricular canal. Prog Pediatr Cardiol. 1999;10:137-151.
• Nadas, AS. Endocardial cushion defects. In: Flyer DC, ed. Nadas' Pediatric Cardiology. Hanley & Belfus Inc;1992:577-586.
• Somerville J, Revel-Chion R, Van Der Cammen T. Atrioventricular canal defects - natural and unnatural history. Pediatr Cardiol. 1981;404-416.
• VanPraagh R, Litovsky S. Pathology and embryology of common atrioventricular canal. Prog Pediatr Cardiol. 1999;10:115-127.
• van Son JA, Phoon CK, Silverman NH, Haas GS. Predicting feasibility of biventricular repair of right-dominant unbalanced atrioventricular canal. Ann Thorac Surg. Jun 1997;63(6):1657-63. [Medline].

Article Last Updated: Jun 26, 2006