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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. Defects may be asymptomatic if small. If large, they may cause heart failure with dyspnea with feeding, poor growth, tachypnea, diaphoresis, or arrhythmias. Heart murmurs 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. The defect may be complete or partial; 30% 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:
Complete AV septal defect (see Fig. 4: Congenital Cardiovascular Anomalies: Atrioventricular septal defect (complete form). ) consists of a large ostium primum atrial septal defect (ASD) in the anteroinferior aspect of the septum, an inlet ventricular septal defect (VSD), and a common AV valve orifice. A left-to-right shunt occurs at the atrial and ventricular levels; 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's syndrome (see Congenital Cardiovascular Anomalies: Eisenmenger's Syndrome).
Partial AV septal defect:
A partial defect consists of an ostium primum ASD, partitioning of the common AV valve into 2 separate AV orifices, and a cleft in the mitral valve (left AV orifice). The ventricular septum is intact, or there may be a small VSD. Hemodynamic abnormalities are similar to those of ostium secundum ASD with the additional finding of variable degrees of mitral 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's syndrome) is usually a late complication but may occur earlier, especially in children with Down syndrome.
Partial AV septal defects are asymptomatic 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.
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 (S2) 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 S2 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 Congenital Cardiovascular Anomalies: Atrial Septal Defect (ASD)); if mitral regurgitation coexists, there will also be a high-pitched holosystolic murmur at the apex.
Diagnosis
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.
Treatment
Complete AV septal defect should be repaired by age 2 to 4 mo, because most infants have HF and failure to thrive. However, 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. For a single-stage complete repair, 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%) and mitral 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 are indicated 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.
Last full review/revision March 2010 by Lee B. Beerman, MD
Content last modified February 2012
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