Atrioventricular Septal Defect (AVSD)

Key Features

Essentials of Diagnosis

• Murmur often inaudible in neonates

• Loud pulmonary component of S₂

• Common in infants with Down syndrome

• ECG with extreme left axis deviation

General Considerations

• Results from incomplete fusion of the embryonic endocardial cushions

• Accounts for about 4% of all congenital heart disease

• Defined as partial or complete

• Partial AVSD

  • There is a low insertion of the AV valves, resulting in a primum atrial septal defect (ASD) without a ventricular defect component.

  • There are two separate AV valve orifices and usually a cleft in the left-sided valve

  • Behaves like an isolated ASD with variable amounts of regurgitation through the cleft in the left AV valve

• Complete AVSD

  • Causes large left-to-right shunts at both the ventricular and atrial levels with variable degrees of AV valve regurgitation

  • If there is increased pulmonary vascular resistance (PVR), the shunts may be bidirectional

  • Bidirectional shunting is more common in Down syndrome or in older children who have not undergone repair

Clinical Findings

Symptoms and Signs

• Partial AVSD may produce symptoms similar to ostium secundum ASD

• Complete AVSD

  • Failure to thrive

  • Tachypnea

  • Diaphoresis with feeding

  • Recurrent bouts of pneumonia

  • In the neonate, the murmur may be inaudible due to relatively equal systemic vascular resistance and PVR

• After 4–6 weeks, as PVR drops, a nonspecific systolic murmur develops

• S₂ is loud, and a pronounced diastolic flow murmur may be heard at the apex and the lower left sternal border

• If a right-to-left shunt is present, cyanosis will be evident

Diagnosis

Imaging

• Cardiac enlargement is always present in the complete form and pulmonary vascular markings are increased

• Often, only the right heart size may be increased in the partial form, although a severe mitral valve cleft can rarely lead to left heart enlargement as well

• Echocardiography

  • Diagnostic test of choice

  • The anatomy can be well visualized by two-dimensional echocardiography

  • AV valve regurgitation can be detected

  • The LV outflow tract is elongated (gooseneck appearance)

Diagnostic Procedures

• Electrocardiography

  • Extreme left axis deviation with a counterclockwise loop in the frontal plane

  • Right, left, or combined ventricular hypertrophy is present depending on the particular defect and the presence or absence of pulmonary hypertension

• Cardiac catheterization and angiocardiography

  • Cardiac catheterization is not routinely used to evaluate AVSD but may be used to assess pulmonary artery pressures and resistance in the older infant with Down syndrome

  • Increased oxygen saturation in the RV or the right atrium identifies the level of the shunt

  • Angiocardiography reveals the characteristic gooseneck deformity of the LV outflow tract in complete AVSD

Treatment

• Spontaneous closure does not occur

• Surgery is required

• Complete correction in the first year of life, prior to the onset of irreversible pulmonary hypertension, is obligatory