Atrial septal defect !
An atrial septal defect is a hole, present from birth, in the wall between the heart's upper chambers; it may cause few symptoms for years.
Updated 2026-10-29
Structures involved
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- Interatrial septum
- Right atrium
- Left atrium
- Right ventricle
- Pulmonary trunk
- Pulmonary arteries
- Superior vena cava
- Pulmonary veins
- Coronary sinus
In embryology
- Fetal circulation and the changes at birth
- Atrial septation: septum primum, septum secundum and foramen ovale
- Embryonic heart structures and their adult derivatives (the table to know)
- Atrial septal defect and patent foramen ovale
- Atrioventricular septal defect (endocardial cushion defect)
In the clinical exam
In physiology
- Heart sounds and where they come from
- Physiology of congenital shunts
- Fetal circulation and the transition at birth
Why it happens
What it is
An opening in the interatrial septum that lets blood pass between the atria, usually from left to right. It is one of the commonest congenital heart defects and is often found late, because symptoms can be mild for years.
Who gets it
One of the most frequent congenital heart defects, diagnosed more often in females. Many cases are first recognised in adolescents or adults after a murmur, an abnormal ECG or an echocardiogram done for another reason.
Causes
- Incomplete formation or overlap of the septum primum and septum secundum during fetal development
- Genetic syndromes, such as Down syndrome (primum defects) and Holt-Oram syndrome
- Familial forms linked to cardiac transcription factor genes; most cases have no single cause
Risk factors
- Family history of congenital heart disease
- Maternal rubella, diabetes or alcohol use in pregnancy
- Exposure to some teratogenic drugs in pregnancy
- Chromosomal syndromes
Pathophysiology
Left atrial pressure is slightly higher than right, so blood crosses the defect from left to right and overloads the right atrium, right ventricle and lungs. Over years the right heart dilates and atrial arrhythmias and pulmonary hypertension can appear. Rarely, pulmonary vascular disease reverses the shunt to right-to-left (Eisenmenger syndrome) and causes cyanosis.
Classification
- Ostium secundum: the commonest type, in the region of the fossa ovalis
- Ostium primum: low in the septum, part of the atrioventricular septal defect spectrum, often with a cleft mitral valve
- Sinus venosus: near the superior or inferior vena cava, often with anomalous pulmonary venous return
- Coronary sinus (unroofed) defect: rare
Symptoms and signs
- Often no symptoms in childhood
- Exercise intolerance, tiredness and breathlessness, mostly in adults
- Palpitations from atrial flutter or fibrillation
- Recurrent chest infections in some children
- Wide, fixed split second heart sound and a soft ejection murmur at the upper left sternal border from extra flow across the pulmonary valve
Diagnosis
- Clinical
- Wide, fixed split S2 that does not vary with breathing, a pulmonary flow murmur and signs of right ventricular volume overload.
- Tests
- ECG: right axis deviation and incomplete right bundle branch block in secundum defects; left axis deviation suggests a primum defect. Pulse oximetry is usually normal.
- Imaging
- Transthoracic echocardiography with Doppler shows the defect and shunt. Transoesophageal echo, cardiac MRI or CT define sinus venosus defects and the rims for device closure. Chest X-ray may show a large right heart.
Differential diagnosis
- Patent foramen ovale
- Ventricular septal defect
- Pulmonary valve stenosis
- Partial anomalous pulmonary venous return
- Pulmonary hypertension from another cause
Goal of treatment
Close significant shunts before right heart enlargement, arrhythmias or pulmonary vascular disease develop, and treat complications.
Treatment
- Follow-up
- Small secundum defects in infants are followed with echocardiography, because many close on their own.
- Procedure
- Transcatheter device closure is used for suitable secundum defects with adequate rims.
- Surgical
- Surgical patch or direct closure is used for primum, sinus venosus, coronary sinus and large defects unsuitable for a device.
- Medical
- Diuretics for heart failure symptoms, rate or rhythm control and anticoagulants for atrial arrhythmias. Closure is not done once Eisenmenger syndrome is established.
Complications
- Atrial flutter and atrial fibrillation
- Right heart failure
- Tricuspid regurgitation
- Pulmonary arterial hypertension and Eisenmenger syndrome
- Paradoxical embolism and stroke
Prognosis
Small defects often close or cause no problems. Closure in childhood gives a near-normal life expectancy; closure in adults still improves symptoms, but the risk of atrial arrhythmias remains.
Test yourself
Think of the answer, then tap the question to see it.
Which heart sound finding is classic for an atrial septal defect?
A wide, fixed split S2 that does not change with breathing.
What is the commonest type of atrial septal defect?
The ostium secundum defect.
Which atrial septal defect is linked to Down syndrome and left axis deviation on the ECG?
The ostium primum defect, part of the atrioventricular septal defect spectrum.
Where does the systolic murmur of an atrial septal defect come from?
From increased flow across the pulmonary valve, not from blood crossing the defect.
What is Eisenmenger syndrome?
Reversal of a left-to-right shunt to right-to-left after pulmonary vascular disease develops, causing cyanosis; the defect is then no longer closed.
Related conditions
- Ventricular septal defect
- Patent ductus arteriosus
- Atrial fibrillation
- Heart failure
- Ischaemic stroke
- Tetralogy of Fallot
Educational information, not medical advice. For any symptom, see a health professional.
Sources: Atrial Septal Defect (StatPearls (NCBI Bookshelf), 2025).
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