Endocardial Cushion Defects (Atrioventricular Canal Defects, Atrioventricular Septal Defects)

Updated: Dec 28, 2020
Author: Mary C Mancini, MD, PhD, MMM; Chief Editor: Yasmine S Ali, MD, MSCI, FACC, FACP 



Endocardial cushion defects, more commonly known as atrioventricular (AV) canal or septal defects, include a range of defects characterized by involvement of the atrial septum, the ventricular septum, and one or both of the AV valves.

These defects can be classified by several methods. A distinction generally is made between partial and complete defects. A complete AV septal defect indicates the presence of both atrial and ventricular septal defects with a common AV valve (see image below). A partial defect indicates atrial septal involvement with separate mitral and tricuspid valve orifices.

Endocardial Cushion Defects (Atrioventricular Cana Endocardial Cushion Defects (Atrioventricular Canal Defects, Atrioventricular Septal Defects). Anatomy of the endocardial cushion defect (ie, complete form); note the common atrioventricular valve straddling the atrial septal and ventricular septal defects.

AV canal defects arise from abnormal development of the endocardial cushions. In these patients, the superior and inferior cushions do not close completely. An interatrial communication is left at the lower portion of the atrial septum. This is called an ostium primum defect. The failure of the endocardial cushions to fuse results in an abnormally low position of the AV valves and an abnormally high position of the aortic valve. A portion of the AV valves originates from the endocardial cushions, and their improper fusion results in anterior and posterior components to the mitral valve leaflet.[1]

Patient education

Parents must be instructed to ensure that antibiotic prophylaxis for dental procedures is instituted for the child. Good dental hygiene for the child is imperative.


Predominant left-to-right shunting of blood through the heart occurs in patients with endocardial cushion defects (atrioventricular [AV] canal or septal defects). In patients with partial defects, this occurs through the ostium primum atrial septal defect. When a complete endocardial cushion defect is present, a large ventricular septal defect as well as valvular insufficiency may develop, resulting in volume overload of both the left and right ventricles associated with heart failure in early life. In patients with long-standing pulmonary overload, pulmonary vascular disease may develop and congestive heart failure (CHF) symptoms may improve. This improvement is a poor prognostic indicator because it heralds the development of right-to-left shunting and irreversible pulmonary hypertension (ie, Eisenmenger syndrome).[2]



The characteristic pattern of the endocardial cushion defect (atrioventricular [AV] canal or septal defect) has been attributed to trisomy 21 and Down syndrome in some cases. Some evidence exists that a critical region of chromosome band 21q22 may contribute particularly to the cardiac malformation in this syndrome.

Other chromosomal abnormalities also can result in AV septal defects, in particular, deletion of 8p, partial 10q monosomy, partial 13q monosomy, ring 22 14 q+, and 1p+3p-.

In most cases of significant chromosomal aberration, AV septal defects are associated with other noncardiac congenital defects. However, isolated AV septal defects can be transmitted in families as an autosomal dominant trait.

Linkage analyses have suggested a locus for autosomal dominant AV septal defects on chromosome 1p but no specific gene defect has yet been identified.

Growth factor aberrations

In the developing fetus, cardiac tissue formation is dependent upon appropriate growth factor stimulation including transforming growth factor beta and platelet-derived growth factor. Alterations in the concentration or efficacy of these factors during embryogenesis can contribute to the cardiac malformations.


United States data

The frequency rate of endocardial cushion defect (atrioventricular [AV] canal or septal defects) is about 3% of children with congenital heart disease. Sixty to seventy percent of these defects are of the complete form. More than half of those affected with the complete form have Down syndrome.

International data

The frequency rate is about 3% of children who have congenital heart disease. Data from a Canadian study indicated that by 2010, adults accounted for two thirds of patients with congenital heart disease in the general population.[3]

Race-, sex-, and age-related demographics

No racial predilection is apparent. Girls are affected slightly more frequently than boys.

Endocardial cushion defect is a congenital defect present at birth. The severity of the symptom complex and presentation is dependent directly upon the severity of the defect and the presence of mitral insufficiency.


The long-term results of surgical correction for endocardial cushion defect  (atrioventricular [AV] canal or septal defect) depend upon the degree of preoperative pulmonary vascular disease and upon the amount of residual AV valve regurgitation. If the pulmonary vasculature is protected and the amount of valvular regurgitation is reduced substantially, prognosis is good. When severe pulmonary vascular disease is present preoperatively, morbidity and mortality rates are high. Complete heart block and arrhythmias may occur after correction, and their incidence increases with age. As the patient grows older, mitral valve replacement may be needed.

The surgical mortality rate in patients with partial endocardial cushion defects is 0-6%, while that for the complete defect ranges from 3-10%.


Patients with only ostium primum atrial septal defect and minimal insufficiency of the left AV valve (ie, mitral valve) do well without treatment during infancy, childhood, and adolescence. During adulthood, these patients develop symptoms of CHF and atrial arrhythmia.

Patients with septal defects and mitral valve insufficiency develop CHF early in life, with high rates of morbidity and mortality if the valvular insufficiency is pronounced. Patients with a complete defect develop CHF in infancy, with frequent respiratory infections and poor weight gain.

The American Heart Association issued recommendations intended to optimize the neurodevelopmental outcomes of children with congenital heart disease.[4]  The recommendations included (1) using the medical home model of care to manage children with chronic conditions (eg, congenital heart disease) and to stratify them by risk (low and high) for neurodevelopmental disorder/disability at every medical home visit; (2) following the AAP guidelines for screening/surveillance, evaluation, and intervention in children with congenital heart disease; and (3) referral for patients at high risk of neurodevelopmental disorder/disability to formal developmental and medical evaluation as well as early intervention/childhood special education services.[4]


Since synthetic material is used to repair the atrial and ventricular septal defect, the child is at risk of infection. Other potential complications include complete heart block, ventricular arrhythmia, and AV valve stenosis and/or insufficiency.




An infant with endocardial cushion defect (atrioventricular [AV] canal or septal defect) may be relatively asymptomatic. In severe cases, patients have a history of poor feeding, chronic upper respiratory tract infections, pneumonia, and poor growth. The mother may notice difficulty with crying, frequent pauses during feeding, and nasal flaring. As the child grows older, the more common manifestations of congestive heart failure (CHF) may develop, including aversion to activity and play, easy fatigability, dyspnea, and edema.

Physical Examination

Partial endocardial cushion defects (atrioventricular [AV] canal or septal defects) present with the physical findings common to atrial septal defects (ASDs).

  • The second heart sound is widely split without respiratory variations.

  • A systolic ejection murmur may be heart at the upper left sternal border.

  • A low-pitched early diastolic rumble may be heart at the lower left sternal border and is related to increased tricuspid valve flow.

  • A murmur of mitral insufficiency may or may not be present.

Additional findings in complete endocardial cushion defects relate to the ventricular septal defect (VSD) and valvular insufficiency.

  • Poor physical development, hyperinflated thorax, bulging precordium, Harrison grooves, mild or intermittent cyanosis, and stigmata of Down syndrome (eg, oblique palpebral fissures, large protuberant tongue, short and broad hands, simian crease, inner epicanthic skin fold)

  • Arterial and jugular venous pulse: Water hammer pulse, dominant v wave in the jugular venous pulse

  • Precordial movement and palpation: Systolic thrill, palpable impulse in the second and third intercostal space representing a dilated pulmonary artery, prominent heave at the left sternal border

  • Auscultation: (1) A single first heart sound is heard, which may be a relatively soft fixed splitting of the second heart sound. (2) A systolic murmur of a ventricular septal defect can be heard as well as the systolic murmur of mitral insufficiency. (3) Pulmonary hypertension is associated with a loud pulmonic component of the second heart sound.




Laboratory Studies

Laboratory testing for patients with suspected endocardial cushion defect (atrioventricular [AV] canal or septal defects) include the following

  • Complete blood cell (CBC) count: Blood tests determine the presence of polycythemia in a potentially cyanotic condition.

  • Prothrombin time/activated partial thromboplastin time (PT/aPTT): In children with cyanotic heart disease, the coagulation profile may be abnormal because of associated polycythemia.

  • Electrolytes: This test detects any abnormalities incurred with treatment of congestive heart failure (CHF).

Imaging Studies

Electrocardiography (ECG)

The typical ECG in patients with partial atrioventricular (AV) septal defects (AVSDs) shows first-degree AV block and left-axis deviation (because of late left anterior fascicular depolarization). Patients with right ventricular (RV) dilatation usually have partial or complete right bundle-branch block. Complete AV block and atrial fibrillation commonly occur in older patients.

A prolonged PR interval accompanied by biventricular or left ventricular (LV) hypertrophy also may be seen. 

Chest radiography

Chest radiography is a good general screening study that shows cardiac enlargement, particularly of the right atrium and ventricle.

The main pulmonary artery usually is prominent with increased pulmonary vascular markings. After pulmonary hypertension develops, a reduction in pulmonary vascular markings is observed.


M-mode echocardiography shows diastolic movement of the mitral valve with enlarged RV and paradoxical motion of the interventricular septum.

Two-dimensional echocardiography is highly reliable in identification of septal defects. Echocardiography identifies the absence of the interventricular septum. Findings may include RV dilatation and paradoxical motion of the interventricular septum. The extent of septal defects as well as the left-to-right shunting and degree of valvular insufficiency can be determined as well as an estimate of pulmonary artery pressure. Lack of displacement of the left and right AV valves is a characteristic finding in this condition. Prolonged diastolic contact between the anterior mitral leaflet and the interventricular septum also may be noted. Associated defects that may require attention also can be detected.

Abnormalities in the AV valves can be identified reliably. Transesophageal echocardiography (TEE) clearly identifies AV valve morphology.[5, 6, 7]

Magnetic resonance imaging (MRI)

MRI readily visualizes the deficiency in the ventricular septum as well as AV valve morphology.[8, 9]


Cardiac catheterization

Cardiac catherization is indicated when clinically significant questions remain unanswered after a comprehensive noninvasive evaluation. If other lesions are suspected or if operative planning cannot be performed adequately after noninvasive testing, then catheterization should be undertaken. Left ventricular angiography in the frontal plane shows an elongated left ventricular outflow tract, called a "gooseneck deformity," which is characteristic of this condition. Catheterization should involve quantitation of the shunts and valvular insufficiency and calculation of pulmonary vascular resistance. Aortography may be performed to determine whether a patent ductus arteriosus is present.



Medical Care

Medical treatment for endocardial cushion defect (atrioventricular [AV] canal or septal defect) is designed to relieve the symptoms of congestive heart failure (CHF) until operative correction is feasible. The objective of therapy is to avoid development of pulmonary vascular obstructive disease. When heart failure and associated pulmonary congestion are present, diuretics and digoxin are indicated.

Postoperative recovery requires 5-10 days of hospitalization, depending upon the condition of the child prior to surgery and whether palliative or complete correction is undertaken. With palliation (ie, pulmonary artery banding), the presurgical condition of volume overload still must be regulated. With complete correction, recovery generally is uneventful.

Diet and activity

For infants in CHF, discretion with fluid intake and salt use is encouraged.

Rest during feeding is encouraged, because one manifestation of dyspnea in these infants is the inability to feed. Generally, the child limits activity without encouragement.

Outpatient care

Continued observation is needed with regularly scheduled echocardiography in order to assess the integrity of the AV valvular reconstruction. This area is prone to development of valvular insufficiency that may require further intervention as the child grows older.

Surgical Care

See also the Guidelines section for American Heart Association/American College of Cardiology (2018)[10] and European Society of Cardiology (2020)[11, 12] ​ recommendations.

Infants with partial endocardial cushion defect (atrioventricular [AV] canal or septal defect [AVSDs]) that are symptomatic are referred for corrective surgery, which includes mitral valvuloplasty and closure of the atrial septal defect. Asymptomatic patients with an ostium primum defect are referred for elective repair after infancy.

Patients with complete AVSDs who do not have associated right ventricular (RT) outflow obstruction (OTO) generally have pulmonary artery pressures near systemic levels. These patients will develop pulmonary vascular disease after the first year of life and usually are referred for corrective surgery in infancy.

Historically, children were treated with pulmonary artery banding in infancy to protect the pulmonary vasculature from excessive blood flow and development of pulmonary vascular disease. Patients were referred for corrective surgery when older than 3-4 years.

Corrective surgery can be performed even in early infancy, in several ways. A single Dacron patch can be used to close the atrial and ventricular septal defect (see image below). The right and left portions of the common AV valve are then resuspended from the patch. A two-patch technique also may be used.

Endocardial Cushion Defects (Atrioventricular Cana Endocardial Cushion Defects (Atrioventricular Canal Defects, Atrioventricular Septal Defects). Repair of the endocardial cushion defect. The patch is covering the ostium primum atrial septal defect.

Severe and irreversible pulmonary vascular disease is a contraindication to corrective surgery, and these children may be referred for cardiopulmonary transplantation.[13, 14, 15, 16]

In a study that evaluated trans-left AV valve (LAVV) blood flow in patients after AVSD correction and in healthy controls, 25 patients after AVSD correction and 25 controls underwent 4DFlow magnetic resonance imaging (MRI).[17] Streamline visualization of 4DFlow MRI data showed dynamic trans-LAVV inflow and increased lateral flow after AVSD correction.

Ginde and colleagues examined the outcomes of complete AVSD (CAVSD) repair in 198 patients who underwent surgical repair for CAVSD at their institution between 1974 and 2000.[18] Overall perioperative mortality was 10.1%, with a significant decrease to 2.9% in the surgical era of 1991 to 2000. For the entire cohort, the overall estimated survival was 85% at 10 years, 82% at 20 years, and 71% at 30 years after initial CAVSD repair.[18]


The current limited knowledge of the genetic abnormalities that predispose to the formation of the endocardial cushion defect can be expanded greatly with current advances in the Human Genome Project. As the knowledge base expands, prenatal detection and possibly treatment may be possible in the future.



Guidelines Summary

2018 American Heart Association/American College of Cardiology (AHA/ACC) guidelines

The 2018 ACC guidelines published in 2019 recommend the following for atrioventricular (AV) septal defect (AVSD).[10]

Cardiac catheterization should be used to assess for the presence of pulmonary hypertension and to assess pulmonary vasoreactivity.

Left AV valve repair or replacement should be undertaken for stenosis and/or regurgitation if it causes symptoms, atrial or ventricular arrhythmia, progressive increase in left ventricular (LV) dimensions or deterioration in LV function. Care should be taken to be sure that pulmonary systolic pressures are less than 50% systemic.

Surgical repair should be undertaken for LV outflow tract obstruction (OTO) with a mean gradient of at least 50 mmHg or peak instantaneous gradient above 70 mmHg or a gradient below 50 mmHg associated with significant mitral regurgitation (MR) or aortic regurgitation (AR).

Surgical repair should be undertaken for residual or recurrent atrial septal defect (ASD) or ventricular septal defect (VSD) with a significant left-to-right shunt. Repair should not be attempted in the face of a right-to-left shunt.

Primary operation is recommended in adults with a left-to-right shunt and pulmonary artery systolic pressures less than 50% systemic and pulmonary vascular resistance (PVR) ess than one third systemic. 

2020 ESC guidelines

The European Society of Cardiology (ESC) updated their 2010 guidelines on the management of adult congenital heart disease (ACHD) in 2020.[11, 12]  Their class I and III recommendations for ASVD are outlined below.

Surgical repair is not recommended in those with Eisenmenger physiology and patients with pulmonary arterial hypertension (PAH) (PVR ≥5 Wood units) who present with exercise desaturation.

Surgical closure performed by a congenital cardiac surgeon is recommended in patients with significant right ventricular (RV) volume overload. Valve surgery, preferably AV valve repair, performed by a congenital cardiac surgeon is recommended in symptomatic patients with moderate to severe AV valve regurgitation.

In asymptomatic patients with severe left-sided AV valve regurgitation, valve surgery is recommended when LV end systolic diameter (ESD) is ≥45 mm and/or LV ejection fraction (EF) is ≤60% after ruling out other causes of LV dysfunction.



Medication Summary

Digitalis and diuretics are used to control the volume overload encountered in these patients until palliative or corrective surgery can be undertaken.

Digitalis provides myocardial support during the postoperative period and can be discontinued after 2-3 years.

Generally, the diuretic furosemide is prescribed for several months after repair in order to correct volume overload; it is discontinued once euvolemia is reached.


Class Summary

These agents are used to decrease volume overload.

Furosemide (Lasix)

Increases excretion of water by interfering with chloride-binding co-transport system, which in turn results inhibits sodium and chloride reabsorption in ascending loop of Henle and distal renal tubule.

Inotropic agents

Class Summary

These agents provide myocardial support in the perioperative period for patients with heart failure. The more restrictive the connection between the proximal and distal chambers, the more likely inotropic support will be required. A number of agents are available in this category.

Digoxin (Lanoxin)

Acts directly on cardiac muscle, increasing myocardial systolic contractions. Its indirect actions result in increased carotid sinus nerve activity and enhanced sympathetic withdrawal for any given increase in mean arterial pressure.