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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



  • 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


  • Spontaneous closure does not occur

  • Surgery is required

  • Complete correction in the first year of life, prior to ...

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