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Atrial Septal Defects

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Overview

Atrial septal defects (ASDs) describe holes in the atrial septum, allowing blood flow between the right and left atria. Most ASDs occur sporadically with no family history. The two main types of ASDs are ostium secundum and ostium primium.

Atrial septal defects vs. patent foramen ovale

Some blood flow between them is normal pre-birth and immediately after birth via the foramen ovale. If the foramen ovale does not close spontaneously, this is known as a patent foramen ovale.

This is different to ASD as this is not clinically significant in most patients, unlike ASDs. In some rare circumstances, a patent foramen ovale can lead to paradoxical emboli and stroke.

Epidemiology

  • Ostium secundum ASDs are the most common
  • ASDs often present for the first time in adulthood

Presentation

ASDs often present for the first time in adults. Most patients are asymptomatic and evaluated due to the presence of a heart murmur. Features include:

  • An ejection systolic murmur with fixed splitting of the second heart sound:
    • The second heart sound does not become a single heart sound with expiration
  • Infants may rarely present with:
  • Paradoxical emboli leading to stroke, see Complications below
  • Features of Eisenmenger syndrome

Investigations

Investigations include:

  • ECG:
    • Provides evidence of heart chamber hypertrophy
  • Chest x-ray:
    • May show cardiomegaly
  • Echocardiography – diagnostic test of choice:
    • Visualises ASD

Differential Diagnoses

Ventricular septal defect

  • The murmur heard tends to be a pansystolic murmur

Patent ductus arteriosus

  • The murmur tends to be a continuous systolic and diastolic ‘machinery-like’ murmur
  • A left subclavian thrill may be felt

Management

Overview

Management may involve observation, corrective closure via surgery, or heart-lung transplantation if Eisenmenger syndrome develops.

Complications

Paradoxical emboli

Venous thrombi dislodge and generally cause a pulmonary embolism, however in people with ASDs, they can cross from the right to the left side and enter the arterial system leading to stroke.

Congestive heart failure

This generally presents in people aged 40-50 years. Shunting of blood between the atria leads to increased strain and hypertrophy, negatively impacting the heart’s function as a pump.

Arrhythmia

Shunting of blood between atria can lead to increased strain and hypertrophy, which can lead to arrhythmia including atrial fibrillation.

Eisenmenger syndrome

Left-to-right shunting increases the pressure in the pulmonary vasculature resulting in pulmonary hypertension. This puts more strain on the right ventricle, which results in right ventricular hypertrophy and increased pressure on the right side of the heart.

Eventually, this exceeds the pressure on the left side of the heart, and the shunt is reversed, resulting in deoxygenated blood flowing from the right to the left side and entering the systemic circulation, bypassing the lungs. This leads to cyanosis and clubbing.

The development of Eisenmenger syndrome is an indication for a heart-lung transplant.

Prognosis

  • Isolated ASDs that are repaired early in infancy or childhood have a good prognosis and survival similar to that of the general population

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