Introduction

• Uncommon, often associated with other defects. Rare as isolated defect.
• Cause: congenital defect due to failure of normal development.
• Signs: may be asymptomatic, congestive heart failure in severe cases.
• Diagnosis: clinical examination, radiography, electrocardiography, 2-D and Doppler echocardiography.
• Treatment: medical treatment of congestive heart failure or surgery to close defect.
• Prognosis: good in mild cases, fair for congestive heart failure.

Pathogenesis

Etiology

• Embryological failure of normal development of the interatrial septum. Can involve septum primum or septum secondum.

Specific

• Hereditary?

Pathophysiology

• Defect in interatrial septum → communication between left atrium and right atrium → degree of bidirectional shunting occurs, depending on size of the defect and relative compliance of the ventricles → left atrial systolic pressure greater than right atrial pressure and right ventricular compliance is higher than left → normally net left-to-right systolic shunt → volume overload of right atrium, right ventricle, pulmonary circulation.

• Primum ASD - defect low in atrial septum adjacent to atrioventricular valves. May involve defects of atrioventricular valves.
• Secundum ASD - defect in mid atrial septum in region of fossa ovalis.
• Sinus venosus ASD - high in atrial septum adjacent to cranial or caudal vena cava.
• Coronary sinus ASD - defect between coronary sinus and left atrium (very rare).
• Allows shunting of blood predominantly from left-to-right atrium, although mild bidirectional shunting occurs in most cases.
• Rarely a clinical problem as driving pressure from left-to-right atrium is low; low pressure gradient across the defect.
• Flow across ASD rarely causes murmur, but increased blood flow through the normal pulmonary valve may cause a murmur called a 'murmur of relative pulmonic stenosis'.

Severe

• Left-to-right atrial shunt → overloads right atrium and ventricle → pulmonary hypertension → increased right atrial and right ventricular pressures → possibly right-sided CHF.
• If pulmonary overcirculation is sufficient → vascular changes → pulmonary hypertension → right ventricular hypertrophy (but rarely right-sided CHF) → right-to-left atrial shunt results and may lead to cyanosis.
• Atrial stretch → dysrhythmias (especially atrial).

Timecourse

• From birth.

Diagnosis

Treatment

Prevention

Outcomes