Atrial Septal Defect

Defect in the interatrial septum causing left to right shunting. Types: secundum (about 75%), primum (about 15 to 20%, part of an atrioventricular septal defect), sinus venosus (about 5 to 10%, with anomalous drainage of right pulmonary veins), coronary sinus (less than 1%).

• About 7% of congenital heart disease; female to male about 2:1 in adults.
• Mechanism: the more compliant right ventricle receives the shunt, giving right atrial and ventricular volume overload and pulmonary overcirculation. Pulmonary arterial hypertension develops in about 5 to 10%, and Eisenmenger syndrome is rare.
• Secundum defects less than 3 mm usually close spontaneously by 1 to 2 years; those greater than 8 mm rarely close.

• Children are usually asymptomatic. Adults: exertional dyspnoea, fatigue, palpitations (atrial flutter or fibrillation), recurrent chest infections, right heart failure, stroke from paradoxical embolism, cyanosis in Eisenmenger syndrome.
• Examination: fixed wide splitting of the second heart sound, ejection systolic murmur at the left upper sternal edge, mid-diastolic tricuspid flow murmur with a large shunt, right ventricular heave.
• Differential diagnosis: patent foramen ovale, pulmonary stenosis, partial anomalous pulmonary venous return, innocent flow murmur, ventricular septal defect, Ebstein anomaly, primary pulmonary hypertension.
• Complications: device erosion (rare, about 0.1%), embolisation, residual shunt, pericardial effusion, atrial arrhythmias, thrombus on the device.

• ECG: incomplete or complete right bundle branch block with right axis deviation (secundum), left axis deviation (primum), prolonged PR interval, atrial arrhythmia.
• Chest X-ray: cardiomegaly, enlarged pulmonary arteries, pulmonary plethora.
• Transthoracic echocardiography with colour Doppler and agitated saline contrast; transoesophageal echocardiography for sinus venosus defects and to size devices (rims of 5 mm or more needed, except the aortic rim).
• Cardiac MRI quantifies shunt and shows anomalous veins. A pulmonary to systemic flow ratio (Qp:Qs) of 1.5 or more with right heart enlargement is significant.
• Right heart catheterisation if pulmonary hypertension is suspected: closure is reasonable with pulmonary vascular resistance less than 3 Wood units; at 3 to 5 Wood units close if Qp:Qs is greater than 1.5; with 5 Wood units or more do not close, treat the pulmonary hypertension, and close only if resistance falls to less than 5 Wood units with a net left to right shunt.

• Closure indications: significant shunt (right ventricular dilatation, Qp:Qs 1.5 or more), symptoms, paradoxical embolism, with pulmonary vascular resistance less than 3 Wood units, or 3 to 5 Wood units with Qp:Qs greater than 1.5. Elective closure at ages 3 to 5 years in children; adults benefit at any age, including after 60 years, with better exercise capacity.
• Percutaneous device closure for secundum defects with adequate rims and a stretched diameter up to about 38 mm. Surgical closure for primum, sinus venosus (with rerouting of anomalous veins), coronary sinus, very large secundum or inadequate rims.
• After device closure: aspirin 75 to 100 mg daily for 6 months, with clopidogrel 75 mg daily for 1 to 3 months in many centres (practice varies); antibiotic prophylaxis for dental procedures for 6 months (amoxicillin 2 g orally 30 to 60 minutes before).
• Atrial flutter or fibrillation: rate control with bisoprolol 2.5 to 10 mg daily. Anticoagulate regardless of risk score in unrepaired defects, because of paradoxical embolism: warfarin to INR 2.0 to 3.0, or apixaban 5 mg twice daily (2.5 mg twice daily if two of: age 80 or more, weight 60 kg or less, creatinine 133 micromol/L or more). Ablation of flutter (cavotricuspid isthmus), with a surgical maze procedure at the time of surgical closure in selected patients.
• Heart failure: furosemide 20 to 40 mg daily, with closure when criteria are met.
• Pulmonary hypertension with high resistance or Eisenmenger syndrome: do not close; give specialist led targeted therapy, for example sildenafil 20 mg three times daily or bosentan 62.5 mg twice daily for 4 weeks then 125 mg twice daily (check liver function monthly).
• Special groups: pregnancy (tolerated well without pulmonary hypertension; thromboprophylaxis because of paradoxical embolism risk; maternal mortality is about 30 to 50% with pulmonary hypertension, so advise against pregnancy); children (observe small defects); elderly (closure still improves symptoms, but new atrial arrhythmia risk persists).
• Red flags: stroke or transient ischaemic attack, cyanosis, syncope, right heart failure, sustained arrhythmia.
• Follow up after closure at 1 to 3 months, 6 months and 12 months with echocardiography, then every 2 to 5 years. Unrepaired small defects: review every 3 to 5 years. Arrhythmia risk persists for life, particularly when closure is after age 40.