Pediatric Unbalanced Atrioventricular Septal Defects 

Updated: Jan 04, 2016
Author: Mark A Law, MD; Chief Editor: Howard S Weber, MD, FSCAI 



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 (VSDs), 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, as shown below.

Echocardiogram image revealing a left ventricular Echocardiogram image revealing a left ventricular dominant atrioventricular (AV) canal defect.

If the common AVV predominantly opens 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.


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.[1, 2, 3]


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) are recognized (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.


The physiology of the lesion depends on the degree of ventricular unbalance, the size of AV septal defects, AVV competence, the degree of right-sided or left-sided outflow obstruction, and pulmonary vascular resistance. As with balanced AV septal defects, in the absence of significant left-sided 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 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. PA 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.



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 frequently observed in patients with heterotaxy syndromes. They occur much more frequently in patients with asplenia than in those with polysplenia.



The prognosis following biventricular repair is generally good. The operative mortality rate is generally 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.[4]

The 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.

In 1983, Emanuel et al reported that 14% of offspring of mothers with AV septal defects have congenital heart disease.[5]


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 a poor overall prognosis. Approximately 80% of patients with complete AV septal defects die by age 2 years. In 1979, a study of autopsied patients reported that only 54% of infants survived 6 months, 35% survived 1 year, and 4% survived 5 years.[6] In 1981, Somerville et al found that 55% of patients died or had significant medical problems in the first year of life.[7] 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.[8]


Postoperative complications following biventricular repair include atrioventricular (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


No racial predilection is known.


No sex predilection is known.


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




Infants with unbalanced atrioventricular (AV) septal defects generally present in the first month of life with congestive heart failure (CHF) with tachypnea and failure to thrive due to pulmonary overcirculation, if no significant right-sided or left-sided obstruction is present.

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 incidentally noted on routine chest radiography.


Note the following:

  • Most children appear healthy, except the rare patient with features of Down syndrome.

  • This lesion is associated with various auscultatory findings, depending on the underlying physiology.

  • Murmurs of pulmonary stenosis, left ventricular (LV) outflow tract obstruction, or atrioventricular valve (AVV) regurgitation may be appreciated.[9]

  • Cyanosis may be present.

  • Reduced lower extremity pulses may suggest coarctation of the aorta, which may coexist with right ventricle (RV)–dominant atrioventricular canal (AVC).


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.



Diagnostic Considerations

It is important to recognize the potential for early pulmonary vascular obstructive disease and, thus, to initiate surgical therapy accordingly.

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

Differential Diagnoses



Laboratory 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.


Electrocardiography often reveals left axis deviation, initial counterclockwise frontal loop, and RV hypertrophy, as depicted below.

ECG of a 3-month-old female with a left ventricula ECG of a 3-month-old female with a left ventricular (LV)–dominant atrioventricular (AV) canal. The ECG reveals left axis deviation with an initial counterclockwise frontal loop.

In patients with heterotaxy, P-wave axis may assist in determining the location of the sinus node.

Imaging Studies

Chest radiography

Chest radiography may reveal abdominal situs inversus with heterotaxy. Abnormalities of bronchial anatomy may be evident in the setting of asplenia or polysplenia.

Generally, chest radiography reveals cardiomegaly with increased pulmonary vascular markings. If significant subpulmonic obstruction is present, pulmonary markings may be decreased.

Two-dimensional echocardiography and Doppler analysis

Doppler-echocardiography is definitive and is the method of choice in making the diagnosis of unbalanced atrioventricular (AV) septal defect (see image below). Cardiac anatomy, hemodynamics, and ventricular function can be noninvasively assessed in detail. Doppler-echocardiography alone can generally provide sufficient anatomic and functional information before repair and/or palliation.[3, 10, 11, 12]

Echocardiogram image revealing a left ventricular Echocardiogram image revealing a left ventricular dominant atrioventricular (AV) canal defect.

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 atrioventricular valve (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.) See video below.[13]

    Echocardiogram clip demonstrating common atrioventricular (AV) valve regurgitation in a patient with a left-ventricular (LV)–dominant AV canal defect.
  • Relative chamber sizes and functions

  • Relationship and sizes of the great arteries

  • Detailed attention to the anatomy of the left ventricular (LV) and right ventricular (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 and/or pulmonary artery (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 ventricular septal defect (VSD), size of the LV outflow tract, and aortic arch hypoplasia. Note the following:

  • 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.

  • Three-dimensional echocardiography may be useful in providing more detailed information about ventricular potential in borderline cases and has been described in evaluating the anatomy in AV septal defects and AVV regurgitation.[14, 15]

Abdominal ultrasonography

This study helps detect presence or absence of the spleen.

Magnetic resonance imaging

MRI can be useful in delineating the intracardiac, PA, systemic and pulmonary venosum, and abdominal anatomy in patients with heterotaxy syndrome. MRI may also be useful in providing more detailed quantitative information about ventricular potential in borderline cases.


Cardiac catheterization and angiography

Note the following:

  • Invasive studies are not always needed before surgical repair and/or palliation if all the anatomic and functional data can be obtained using 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 (see image below). Catheterization may also be obtained prior to completion of a Fontan repair to assess systemic and PA structure and hemodynamics.

    Catheterization in a patient with a left ventricul Catheterization in a patient with a left ventricular (LV)–dominant atrioventricular (AV) canal defect. The catheter is positioned in the pulmonary artery demonstrating pulmonary artery band and branch pulmonary arteries.


Medical Care

Admit patients for testing and surgical intervention.

Optimize management of congestive heart failure (CHF) before surgical repair and/or palliation. Generally, treat congestive heart failure (CHF) with digoxin, diuretics, and 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 atrioventricular valves (AVVs), and both ventricles must be large enough to carry a full cardiac output. Note the following:

  • Preoperative left ventricular (LV) volume calculations can greatly underestimate the potential volume of the LV once the right ventricle (RV) is unloaded.

  • In 1997, Van Son and colleagues predicted postoperative LV volumes based on preoperative echocardiography in patients with RV-dominant unbalanced atrioventricular (AV) septal defects.[16] 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.

  • The use of echocardiography to derive an AVV index has been described. 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 ventricular septal defect (VSD) or ductal-dependent circulation precludes biventricular repair.[17]

  • Neither of these strategies takes into account potential for growth, particularly in small infants.[18]


Consult with a pediatric cardiologist and a pediatric cardiothoracic surgeon. Consult with a geneticist, if indicated.


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.

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 1955.[19] Results have remarkably improved over the past 20 years.[11]

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%.[4]

The following 2 surgical approaches are commonly used with excellent results to repair balanced AV septal defects:

  • The 2-patch technique uses a synthetic (eg, Dacron, Gore-Tex) ventricular patch and a separate pericardial atrial patch.

  • The 1-patch technique, usually pericardial, covers both the ventricular and atrial components.

In one study that compared the 2-patch technique with a modified 1-patch technique, the outcomes were similar.[20] The modified 1-patch technique was performed with shorter cross-clamp and cardiopulmonary bypass times.

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.[21] 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.[22]


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 restrictions must be determined on a patient-by-patient basis and vary considerably, depending on whether a 1-ventricle 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 as much as 80% of normal exercise tolerance.



Medication Summary

No specific or recommended drug therapy is available for unbalanced atrioventricular (AV) septal defects. If evidence of pulmonary overcirculation is present, management of congestive heart failure (CHF) with digoxin, diuretics, and ACE inhibitors may be indicated. ACE inhibitors may also be indicated for atrioventricular valve (AVV) regurgitation.

Cardiac glycosides

Class Summary

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

Digoxin (Lanoxin)

Frequently used cardiac glycoside that inhibits the sarcolemmal sodium-potassium ATPase, leading to an increase in intracellular calcium concentration and increased myocardial contractility.

Loop diuretics

Class Summary

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.

Furosemide (Lasix)

Increases excretion of water by interfering with chloride-binding cotransport system that inhibits sodium and chloride reabsorption in the ascending loop of Henle and distal tubule.

ACE inhibitors

Class Summary

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.

Captopril (Capoten)

Inhibits activity of ACE, thereby preventing conversion of angiotensin I to angiotensin II (a potent vasoconstrictor). Decreased levels of angiotensin II lead to increased plasma renin levels and decreased aldosterone levels.

Enalapril (Vasotec)

Prevents conversion of angiotensin I to angiotensin II, a potent vasoconstrictor, resulting in increased levels of plasma renin and a reduction in aldosterone secretion.

Helps control blood pressure and proteinuria. Decreases pulmonary-to-systemic flow ratio in the catheterization laboratory and increases systemic blood flow in patients with relatively low pulmonary vascular resistance. Has favorable clinical effect when administered over a long period. Helps prevent potassium loss in distal tubules. The body conserves potassium; thus, less oral potassium supplementation needed.

Patients who develop a cough, angioedema, bronchospasm, or other hypersensitivity reactions after starting ACEIs should be switched to an angiotensin-receptor blocker.



Further Outpatient Care

Give careful attention to atrioventricular valve (AVV) function and development of left ventricular (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.

Inpatient & Outpatient Medications

If a successful biventricular repair is accomplished, long-term cardiac medications are generally not needed after surgical convalescence.

In patients who underwent single-ventricle palliation, aspirin with or without warfarin (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.