AKT · Child health/Congenital heart

Atrial septal defect (ASD)

Acyanotic left-to-right shunt through a defect in the interatrial septum (ostium secundum/primum)

Overview

A defect in the interatrial septum (ostium secundum commonest; ostium primum associated with AVSD/Down). Left-to-right shunt, often asymptomatic in childhood and presenting in adulthood with arrhythmia, heart failure or a stroke (paradoxical embolism). The signature is an EJECTION SYSTOLIC murmur with a FIXED, widely-split second heart sound. Closed if significant.

Recognise

Often asymptomatic in childhood; ejection systolic murmur (pulmonary flow) at the upper left sternal edge with a FIXED widely-SPLIT S2
Adult presentation: exertional dyspnoea, palpitations/atrial arrhythmias, right heart failure, paradoxical embolism (stroke)
Ostium primum ASD associates with AVSD and Down syndrome

Red flags

Paradoxical embolic stroke (a venous clot crossing the defect)
Pulmonary hypertension/Eisenmenger if a large untreated shunt

Differentials & how to tell them apart

Innocent murmurno fixed split S2, normal echo

VSDpansystolic at the lower left sternal edge

Pulmonary stenosisejection systolic that varies with respiration; no fixed split

Investigations

Echocardiography (defect, shunt, right heart dilatation); ECG (RBBB, right axis [secundum] or left axis [primum]); CXR (cardiomegaly, pulmonary plethora).

Management

Close significant defects (transcatheter/surgical); often asymptomatic until adulthood

1Confirm on echo. Close haemodynamically significant defects (right heart dilatation), usually electively — often transcatheter for secundum defects.Gate: The FIXED widely-split S2 is the discriminator from a VSD/innocent murmur; an untreated large shunt risks pulmonary hypertension and paradoxical embolic stroke
2Transcatheter device (secundum) or surgical closure (primum/large); manage adult arrhythmia and stroke risk.

Transcatheter/surgical closure — for significant shunts (right heart dilatation) — often electively in childhood

Manage arrhythmia/anticoagulation — in adults presenting with AF/stroke

Key points

Ejection systolic murmur + FIXED widely-split S2 = ASD (often silent until adulthood — arrhythmia, paradoxical stroke). Ostium primum links to AVSD/Down. Fixed split is the exam giveaway.

Monitor & prognosis

Right heart size on echo; arrhythmia.

Good with closure; complications if large and untreated.

Source: RCPCH; paediatric cardiology