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Atrioventricular Septal Defect

(Atrioventricular Canal Defect; Endocardial Cushion Defect; Ostium Primum Atrial Septal Defect)

by Jeanne Marie Baffa, MD

Atrioventricular (AV) septal defect consists of an ostium primum type atrial septal defect and a common AV valve, with or without an associated inlet (AV septal type) ventricular septal defect (VSD). These defects result from maldevelopment of the endocardial cushions. Patients with no VSD component or a small VSD and good AV valve function may be asymptomatic. If there is a large VSD component or significant AV valve regurgitation, patients often have signs of heart failure, including dyspnea with feeding, poor growth, tachypnea, and diaphoresis. Heart murmurs, tachypnea, tachycardia, and hepatomegaly are common. Diagnosis is by echocardiography. Treatment is surgical repair for all but the smallest defects.

AV septal defect accounts for about 5% of congenital heart anomalies. An AV septal defect may be complete, transitional, or partial. In the complete form, the inlet VSD is large (nonrestrictive). In the transitional form, the VSD is small or moderate (restrictive). In the partial form, there is no VSD. The majority of patients with the complete form have Down syndrome. AV septal defect is also common among patients with asplenia or polysplenia (heterotaxy) syndromes.

Complete AV septal defect

A complete AV septal defect (see Figure: Atrioventricular septal defect (complete form).) consists of a large ostium primum atrial septal defect (ASD) in the anteroinferior aspect of the septum, a nonrestrictive inlet VSD, and a common AV valve orifice. This defect is also called a complete common AV canal defect. A left-to-right shunt occurs at the atrial and ventricular levels and is often large; AV valve regurgitation may be significant, sometimes causing a direct left ventricle-to-right atrial shunt. These abnormalities result in enlargement of all 4 cardiac chambers. Hemodynamic findings are similar to those of a large VSD. Over time, the increase in pulmonary blood flow, pulmonary artery pressure, and pulmonary vascular resistance may lead to reversal of shunt direction with cyanosis and Eisenmenger syndrome (see Eisenmenger Syndrome).

Atrioventricular septal defect (complete form).

Pulmonary blood flow, all chamber volumes, and often pulmonary vascular resistance are increased. Atrial pressures are mean pressures.

AO = aorta; IVC = inferior vena cava; LA = left atrium; LV =left ventricle; PA = pulmonary artery; PV = pulmonary veins; RA = right atrium; RV =right ventricle; SVC = superior vena cava.

Transitional AV septal defect

A transitional AV septal defect consists of an ostium primum ASD; a restrictive inlet VSD, which may be small or moderate in size; and a common AV valve. This defect is also called transitional AV canal defect. The shunt at the atrial level is usually large. The shunt at the ventricular level is smaller than in complete AVSD, and right ventricular pressure is lower than left ventricular pressure. The hemodynamics depend largely on the size of the VSD and whether there is significant AV valve regurgitation.

Partial AV septal defect

A partial AV septal defect consists of an ostium primum ASD and partitioning of the common AV valve into 2 separate AV orifices, resulting in a so-called cleft in the mitral valve (left AV orifice). The ventricular septum is intact. Hemodynamic abnormalities are similar to those of ostium secundum ASD (eg, left-to-right shunt at the atrial level, enlarged right heart chambers, increased pulmonary blood flow) with the additional finding of variable degrees of left AV valve regurgitation.

Symptoms and Signs

Complete AV septal defect with a large left-to-right shunt causes signs of heart failure (HF—eg, tachypnea, dyspnea with feeding, poor weight gain, diaphoresis) by age 4 to 6 wk. Pulmonary vascular obstructive disease (Eisenmenger syndrome) is usually a late complication but may occur earlier, especially in children with Down syndrome.

Partial AV septal defects are do not cause symptoms during childhood if mitral regurgitation is mild or absent. However, symptoms (eg, exercise intolerance, fatigue, palpitations) may develop during adolescence or early adulthood. Infants with moderate or severe mitral regurgitation often have signs of HF. Patients with transitional AV septal defects may have signs of HF if the VSD is only mildly restrictive or may be asymptomatic if the VSD is highly restrictive (small).

Physical examination in children with complete AV septal defects shows an active precordium due to volume and pressure overload of the right ventricle; a single, loud 2nd heart sound (S 2 ) due to pulmonary hypertension; a grade 3 to 4/6 systolic murmur; and sometimes a diastolic murmur at the apex and low left sternal border. Most children with a partial defect have wide splitting of the S 2 and a midsystolic (eg, ejection systolic) murmur audible at the upper left sternal border. A mid-diastolic rumble may be present at the lower left sternal border when the atrial shunt is large. A cleft in the left AV valve results in a blowing apical systolic murmur of mitral regurgitation. Thus, cardiac findings in children with the partial form are the same as those described for secundum ASD (see Atrial Septal Defect (ASD)); if mitral regurgitation coexists, there is also a high-pitched holosystolic murmur at the apex.

Diagnosis

  • Chest x-ray and ECG

  • Echocardiography

Diagnosis is suggested by clinical examination, supported by chest x-ray and ECG, and established by 2-dimensional echocardiography with color flow and Doppler studies.

Chest x-ray shows cardiomegaly with right atrial enlargement, biventricular enlargement, a prominent main pulmonary artery segment, and increased pulmonary vascular markings.

ECG shows a superiorly directed QRS axis (eg, left axis deviation or northwest axis), frequent 1st-degree AV block, left or right ventricular hypertrophy or both, and occasional right atrial enlargement and right bundle branch block.

Two-dimensional echocardiography with color flow and Doppler studies establishes the diagnosis and can provide important anatomic and hemodynamic information. Cardiac catheterization is not usually necessary unless hemodynamics must be further characterized before surgical repair (for example, to assess pulmonary vascular resistance in a patient presenting at an older age).

Treatment

  • Surgical repair

  • For HF, medical therapy (eg, diuretics, digoxin, ACE inhibitors) before surgery

Complete AV septal defect should be repaired by age 2 to 4 mo because most infants have HF and failure to thrive. Even if infants are growing well without significant symptoms, repair should be done before 6 mo to prevent development of pulmonary vascular disease, especially in infants with Down syndrome. In patients with 2 adequately sized ventricles and no additional defects, the large central defect (combination of the primum ASD and inlet VSD) is closed and the common AV valve is reconstructed into 2 separate valves. Surgical mortality rate was 5 to 10% in older series but more recently was as low as 3 to 4%. Surgical complications include complete heart block (3%), residual VSD, and/or left AV valve regurgitation. Pulmonary artery banding is no longer recommended unless associated abnormalities make complete repair in a small infant high risk. For asymptomatic patients with a partial defect, elective surgery is done at age 1 to 3 yr. Surgical mortality rate should be very low.

For patients with large shunts and HF, diuretics, digoxin, and ACE inhibitors may help to manage symptoms before surgery.

Endocarditis prophylaxis is not needed preoperatively and is required only for the first 6 mo after repair or if there is a residual defect adjacent to a surgical patch.

Key Points

  • An atrioventricular (AV) septal defect may be complete, transitional, or partial; the majority of patients with the complete form have Down syndrome.

  • A complete AV septal defect involves a large ostium primum atrial septal defect (ASD), a ventricular septal defect (VSD), and a common AV valve (often with significant regurgitation), all resulting in a large left-to-right shunt at both atrial and ventricular levels and enlargement of all 4 cardiac chambers.

  • A partial AV septal defect also involves an ASD, but the common AV valve is partitioned into 2 separate AV orifices and there is no VSD, resulting in enlargement of the right heart chambers because of a large atrial shunt but no ventricular shunt.

  • A transitional AV septal defect involves an ostium primum ASD, a common AV valve, and a small- or moderate-size VSD.

  • Complete AV septal defect with a large left-to-right shunt causes signs of heart failure (HF) by age 4 to 6 wk.

  • Symptoms in partial AV septal defects vary with the degree of mitral regurgitation; if mild or absent, symptoms may develop during adolescence or early adulthood, but infants with moderate or severe mitral regurgitation often have manifestations of HF.

  • Symptoms in transitional AV septal defect fall on a spectrum, depending on the size of the VSD.

  • Defects are repaired surgically between age 2 to 4 mo and 1 to 3 yr depending on the specific defect and severity of symptoms.

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