Atrial septal defect and patent foramen ovale

Definition

An atrial septal defect (ASD) is an opening in the interatrial septum causing a left-to-right shunt and volume overload of the right atrium and right ventricle. A patent (persistent) foramen ovale (PFO) is an interatrial communication that has not closed after birth; blood can intermittently pass through it from right to left.

Classification

• Ostium secundum defect: defect in the fossa ovalis in the central part of the atrial septum.
• Sinus venosus defect: in the posterior septum near the superior or inferior vena cava, frequently with anomalous return of the right upper or lower pulmonary veins to the right atrium or vena cava.
• Ostium primum defect: in the anteroinferior septum, a form of atrioventricular septal defect (endocardial cushion defect).
• Small defects often represent a stretched patent foramen ovale.

Occurrence & epidemiology

Atrial septal defects account for about 6–10 % of congenital heart disease. A patent foramen ovale is found in about one quarter of adults.

Aetiopathogenesis

• Causes: mostly isolated and sporadic; sometimes part of a genetic syndrome (e.g. Holt-Oram syndrome). The combination of ASD and AV conduction disturbance may be associated with mutations in the homeobox gene NKX2-5.
• ASD pathophysiology: the shunt is initially left to right. Moderate to large defects cause volume overload of the right atrium and ventricle; with a long-standing defect, pulmonary arterial hypertension, raised pulmonary vascular resistance and right ventricular hypertrophy may develop by the 30s or 40s. A late consequence may be shunt reversal with cyanosis (Eisenmenger syndrome), mostly after the age of 40.
• Paradoxical embolism: even with a predominantly left-to-right shunt, a transient right-to-left shunt can allow emboli into the systemic circulation.
• PFO: right-to-left shunting through a PFO can facilitate paradoxical thromboembolism, cryptogenic stroke, paradoxical gas embolism (decompression sickness in divers), arterial hypoxemia and migraine with aura. The risk of disease mainly affects people with a large shunt and a large PFO.

Clinical features

• Small to moderate ASDs are usually asymptomatic, as are even large defects in young children.
• Larger shunts: slow weight gain in early childhood; in older patients exercise intolerance, exertional dyspnea, fatigue and palpitations.
• Atrial arrhythmias (supraventricular tachycardia, atrial flutter, atrial fibrillation); paradoxical emboli with stroke.
• Auscultation: midsystolic ejection murmur (grade 2–3/6) and widely, fixed split second heart sound at the upper left sternal border; with a large shunt a low-pitched diastolic murmur due to increased tricuspid flow; parasternal right ventricular heave.

Diagnosis

• ECG with a relevant shunt: right axis deviation, right ventricular hypertrophy or right ventricular conduction delay (rSR' pattern in V1 with a tall R').
• Chest X-ray: cardiomegaly with dilatation of the right atrium and ventricle, prominent main pulmonary artery segment, increased pulmonary vascular markings.
• Echocardiography with color flow and Doppler: confirms the location and size of the defect and the degree of right heart volume overload.
• Detection of a PFO or right-to-left shunt: ultrasound with bubble contrast given via a venous cannula at rest and after release of a Valsalva maneuver; shunt size is graded by the number of bubbles crossing. Transcranial Doppler detects the shunt but does not distinguish atrial from pulmonary shunts; transesophageal echocardiography may miss a PFO if the Valsalva maneuver cannot be performed with the probe in place.

Keep learning in the app

Further reading (open access)

1. MSD Manual Professional: Atrial Septal Defect (ASD)
2. Persistent (patent) foramen ovale assessment and closure for the general physician, Clin Med 2026
3. StatPearls: Atrial Septal Defect
4. StatPearls: Patent Foramen Ovale

Cross-references