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Atrioventricular Septal Defect

Atrioventricular (AV) septal defect consists of primum type atrial septal defect with AV valve malformation, with or without a ventricular septal defect. These defects result from maldevelopment of the endocardial cushions.

image 179 Defects may be asymptomatic if small. If large, they may cause heart failure, with dyspnea with feeding, poor growth, tachypnea, diaphoresis, or arrhythmias. A single loud S2 and heart murmur are common. Diagnosis is by echocardiography or cardiac catheterization. Treatment is surgical repair for moderate to severe cases. Endocarditis prophylaxis is recommended.

AV septal defect accounts for about 5% of congenital heart anomalies. It may be complete or partial; 30% of patients with the complete form have Down syndrome. AV septal defect is also common in patients with asplenia or polysplenia syndrome.

Complete AV septal defect consists of a large ostium primum atrial septal defect (ASD, in which the defect is in the anteroinferior aspect of the septum), an inlet ventricular septal defect (VSD), and a common AV valve orifice with regurgitation. A left-to-right shunt occurs at the atrial and ventricular levels; AV valve regurgitation may be significant, sometimes producing a direct left ventricle-to-right atrial shunt. These abnormalities result in enlargement of all 4 cardiac chambers. 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's syndrome

Partial AV septal defect consists of an ostium primum ASD, 2 separate AV valve openings, and a cleft in the mitral valve. The ventricular septum is intact. Hemodynamic abnormalities are similar to those of ostium secundum ASD.

Symptoms and Signs
Complete AV septal defect with a large left-to-right shunt produces signs of heart failure (HF—tachypnea, dyspnea with feeding, poor weight gain, diaphoresis) by age 4 to 6 wk. Pulmonary vascular obstructive disease (Eisenmenger's syndrome) may begin to develop before age 1 yr, especially in children with Down syndrome. Smaller defects with little or no AV valve regurgitation may be asymptomatic during childhood.

Partial AV septal defect is asymptomatic during childhood if mitral regurgitation is mild or absent. However, symptoms (eg, exercise intolerance, fatigue, palpitations) may develop during adolescence. Infants with moderate or severe mitral regurgitation often have signs of HF.
Physical examination in children with complete AV septal defect detects an active precordium because of volume and pressure overload. A single loud S2 and a grade 3 to 4/6 holosystolic murmur are audible.

Most children with a partial defect have wide splitting of the S2 and a midsystolic (or 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 AV valve produces the blowing apical murmur of mitral regurgitation.
Cardiac findings in children with the partial form are the same as those described for secundum ASD; if mitral regurgitation coexists, there will also be an early systolic murmur at the apex.

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, a counterclockwise QRS loop in the vectorcardiogram, frequent 1st-degree AV block, left or right ventricular hypertrophy or both, occasional right atrial hypertrophy, and right bundle branch block.
Cardiac catheterization is not usually necessary unless anatomy must be further characterized before surgical repair.

Complete AV septal defect should be repaired before age 1 yr (in many centers as early as age 3 to 4 mo) to prevent development of Eisenmenger's syndrome, especially in infants with Down syndrome. In patients with 2 suitably sized ventricles and no additional defects, the primum ASD and inlet VSD are closed and the AV valve is reconstructed into 2 trileaflet valves. For a single-stage complete repair, mortality rate is 5 to 10%. Surgical complications include complete heart block (3%) and mitral regurgitation (7%). Pulmonary artery banding is no longer recommended unless associated abnormalities make complete repair high risk. For asymptomatic patients with a partial defect, elective surgery is done at age 1 to 2 yr. Surgical mortality rate is about 3%.

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