THE CONTEXT
Investigation of an atrial septal defect demonstrates the defect itself and the effects of left-to-right shunting on the right ventricle and pulmonary circulation.
Echocardiographic findings
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Echocardiography is diagnostic and directly demonstrates the defect.
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Typical findings include right ventricular dilatation, right ventricular hypertrophy and pulmonary artery dilatation.
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The precise size and location of the defect are best defined by TOE.
Chest X-ray and electrocardiogram
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Chest X-ray typically shows enlargement of the heart and pulmonary artery, together with pulmonary plethora.
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The ECG usually shows incomplete right bundle branch block because ventricular dilatation delays right ventricular depolarisation.
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A primum defect is also associated with left axis deviation.
Shunt and murmur mechanism
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Blood flows across the atrial septum from left to right.
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The murmur results from increased flow velocity across the pulmonary valve due to left-to-right shunting and a large stroke volume.