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Atrioventricular Defect (AVSD)

AVSD occurs in 2% of all CHD and is more prevalent in patients with Down Syndrome. Forty percent of children with Down Syndrome have CHD, and 40 % of the defects are forms of AVSD.

Anatomy

Atrioventricular septal defect is also known as endocardial cushion defect (ECD) and atrioventricular canal (AVC). It consists of a variety of defects in the endocardial cushions which form the lower part of the atrial septum, upper part of the ventricular septum, and the medial parts of the tricuspid and mitral valves.

The defect may be incomplete or complete.

  • Incomplete AVSD (primum ASD) consists of a defect in the lower part of the atrial septum and is usually associated with a cleft in the anterior mitral leaflet causing mitral insufficiency.
  • Complete AVSD has a defect that extends from the lower part of the atrial septum to the upper part (inlet) of the ventricular septum. The mitral and tricuspid valves lose their anchor points in the ventricular septum and are instead attached to each other, forming a common AV valve that overhangs the ventricular septum.

Pathophysiology

There is a left to right shunt at the atrial level due to increased relative right ventricular compliance leading to right atrial enlargement. Left atrial enlargement occurs because of mitral insufficiency secondary to the mitral valve cleft. There is varying degree of pulmonary hypertension as the pulmonary vasculature is exposed to excess blood volume at higher pressure. The pulmonary hypertension may develop at about one to two years in normal patients and at about six months to one year in patients with Down Syndrome.

Clinical presentation

The clinical presentation of AVSD is variable and depends on the size of the defect and the degree of the left to right shunt. Patients with complete AVSD usually present with congestive heart failure in the first few weeks of life, while those with incomplete AVSD (primum ASD) may be completely asymptomatic.

Symptoms of CHF include poor feeding, shortness of breath, diaphoresis during feeding, and poor weight gain. Mild cyanosis may be present because of right to left shunt due to excessive pulmonary over circulation or due to preferential streaming of the venous blood from the IVC to the left atrium.

Making the diagnosis

  • Physical findings are variable and depend on the presence or the absence of congestive heart failure. The precordium may be hyperdynamic and the cardiac apex might be displaced inferiorly and to the left.
  • The auscultatory findings are also variable and may include a systolic ejection murmur due to increased flow through the pulmonary valve with wide and fixed splitting of S2 as in ASD. A loud, single S2 indicates pulmonary hypertension.
  • Additional auscultatory findings include a mid-diastolic murmur at the lower left sternal border due to increased flow through the tricuspid valve, apical holosystolic murmur radiating to the left axilla due to mitral insufficieny, apical mid-diastolic murmur of severe mitral insufficiency and a holosystolic murmur of VSD.
  • EKG is characterized by left axis deviation, right atrial enlargement, bi-ventricular hypertrophy and an incomplete right bundle branch block (rSR in V1 indicating right ventricular volume overload). A prolonged PR interval (first degree heart block) probably due to abnormal AV node may be present.
  • Chest radiograph shows varying degrees of cardiomegaly and increased pulmonary vascularity.
  • Echocardiography is useful in demonstrating the anatomical lesions and associated abnormalities. It is essential to assess the integrity of the AV valves.

Management

Congestive cardiac failure is managed with diuretics, ACE inhibitors, and digoxin. A high caloric-density formula should be used with no fluid restriction.

Almost all patients with AVSD will need surgery. The timing of surgery depends on the size of the patient, the presence of CHF, response to medical management, and the presence or absence of pulmonary hypertension. In asymptomatic patients with partial AVSD, surgery may be delayed to preschool age. Corrective surgery is usually performed in symptomatic patients with intractable CHF in the first three months of life. Even in patients who respond to medical management, the presence of Down Syndrome necessitates early surgery to prevent development of pulmonary hypertension. If corrective surgery can not be performed in a symptomatic patient, pulmonary arterial banding may help limit the pulmonary blood flow until corrective surgery is possible.

More info: AVSD from American Heart Association