Atrial septal defect and patent foramen ovale

01OverviewDefinition, clinical context and the essential points that orientate the chapter.

ASD presentation ranges from an incidental murmur to exertional limitation, atrial arrhythmia, right-heart failure or pulmonary hypertension. Primum, sinus venosus and coronary-sinus defects need careful anatomical definition and usually surgical rather than device treatment.

PFO closure is a secondary-stroke-prevention decision, not treatment for an incidental bubble-study finding. Neurology and interventional cardiology should agree that the infarct is embolic and no more likely cause is present.

Key points

A secundum ASD is a true deficiency of atrial septal tissue; a PFO is a flap-like persistence of fetal communication and usually has no resting shunt.
A significant ASD produces right-atrial and right-ventricular volume loading, often with a wide fixed split second heart sound and pulmonary flow murmur.
A PFO is common and usually incidental; do not assume causality after stroke until alternative mechanisms have been excluded.
TTE is first line for ASD; contrast echocardiography and TOE refine PFO shunt and septal anatomy when results will change management.
Close a haemodynamically significant ASD before irreversible pulmonary vascular disease develops; device closure is preferred for suitable secundum anatomy.
Do not close an ASD in established Eisenmenger physiology or when pulmonary vascular resistance makes closure unsafe.
NHS England commissions selected PFO closure after otherwise unexplained embolic ischaemic stroke in adults around age 60 or younger after multidisciplinary assessment.

02AetiologyUnderlying causes, associations and risk factors, with why each one matters.

Secundum atrial septal defect

Incomplete formation of septum secundum or excessive resorption of septum primum leaves a true tissue deficiency at the fossa ovalis and permits persistent interatrial flow.

Other congenital septal defects

Primum, sinus venosus and coronary-sinus defects reflect different embryological abnormalities and often coexist with AV-valve or anomalous pulmonary-venous anatomy, affecting whether surgery rather than device closure is needed.

Patent foramen ovale

A PFO results when septum primum and septum secundum fail to fuse after birth. It is a flap-like potential channel, not missing septal tissue, and is commonly incidental.

03PathophysiologyThe causal sequence from the underlying abnormality to symptoms and harm.

1
ASD branch: left-to-right shunting
Because left-atrial pressure usually exceeds right-atrial pressure, blood crosses a true ASD into the right heart. Shunt size depends on defect anatomy and ventricular compliance.
2
ASD branch: right-heart volume loading
Chronic excess flow dilates the right atrium and ventricle and increases pulmonary blood flow, producing the pulmonary flow murmur and relatively fixed splitting of the second heart sound.
3
ASD branch: possible pulmonary vascular disease
In a susceptible minority, a large longstanding shunt can remodel pulmonary arterioles and raise pulmonary vascular resistance. Advanced disease may reverse or make the shunt bidirectional, causing cyanosis and potentially making closure unsafe.
4
ASD branch: atrial and embolic consequences
Atrial dilatation and remodelling promote flutter or AF. Transient right-to-left flow across an ASD can also permit venous thrombus to bypass the lungs and enter systemic arteries.
5
PFO branch: intermittent or redirected flow
A PFO does not usually cause haemodynamically important resting volume loading. Transiently raised right-atrial pressure, or favourable anatomical streaming in selected patients, can direct blood through the flap and permit paradoxical embolism or positional hypoxaemia.

04Clinical features and red flagsSymptoms, examination findings, patterns of presentation and time-critical warnings.

Secundum ASD examination

Right-ventricular heave, ejection systolic murmur at the upper left sternal edge and a wide fixed split S2 reflect increased pulmonary flow.

Late ASD presentation

Exertional dyspnoea, reduced exercise capacity, atrial flutter/fibrillation, right-heart failure or pulmonary hypertension may appear in adulthood.

PFO-related embolism

A cortical embolic infarct plus a large right-to-left shunt, atrial septal aneurysm or temporally related venous thrombosis raises causal likelihood only after other sources are excluded.

Platypnoea-orthodeoxia

Dyspnoea and desaturation when upright that improve supine can occur with positional right-to-left shunting through a PFO.

Shunt reversalRed flag

Cyanosis, clubbing and advanced pulmonary hypertension suggest right-to-left shunting and make routine closure dangerous.

05InvestigationsWhat to request, why it matters and how to interpret it.

Investigation order

Read from the initial assessment onwards. Tests may run in parallel in urgent care; first-line, preferred, confirmatory, definitive and gold-standard labels appear only when the chapter explicitly states them.

01
12-lead ECGFirst step
Why
Identify right-heart effects and atrial arrhythmia.
Interpretation and limitations
Secundum ASD may show right-axis deviation and incomplete RBBB; primum ASD more often has left-axis deviation.
02
Transthoracic echocardiography
Why
Define defect, shunt direction, right-heart size, pulmonary pressure estimate and associated lesions.
Interpretation and limitations
Right-ventricular volume overload is more important than defect diameter alone when judging haemodynamic significance.
03
Agitated-saline contrast study
Why
Demonstrate an interatrial right-to-left shunt when PFO is suspected.
Interpretation and limitations
Early left-sided bubbles with an effective Valsalva support intracardiac shunt; late bubbles suggest an intrapulmonary source.
04
TOE or cardiac MRI
Why
Define rims, pulmonary venous anatomy, shunt volume and suitability for closure.
Interpretation and limitations
Sinus venosus ASD with anomalous pulmonary veins is not a routine secundum device-closure lesion.
05
Stroke and pulmonary-hypertension work-up
Why
Exclude AF, arterial disease, thrombophilia when appropriate and unsafe pulmonary vascular disease.
Interpretation and limitations
Right-heart catheterisation is required when non-invasive findings suggest pulmonary hypertension and closure is being considered.

06Differential diagnosisRealistic alternatives and the features that help distinguish them.

PFO rather than ASD

A PFO has a flap tunnel, usually no haemodynamically important resting left-to-right shunt and no chronic RV volume overload. TOE defines septal anatomy, while contrast imaging demonstrates right-to-left passage.

Pulmonary arteriovenous malformation

This also permits right-to-left passage. Bubbles typically appear in the left heart later than with an intracardiac shunt, but timing alone is imperfect; pulmonary-vein observation and chest imaging can localise the connection.

Partial anomalous pulmonary venous return

Anomalous venous return can cause unexplained RV volume overload and commonly accompanies sinus venosus ASD. TOE, CT or CMR maps pulmonary-vein connections missed on routine TTE.

Pulmonary stenosis or an innocent flow murmur

Both may cause an upper-left sternal ejection murmur, but pulmonary stenosis has an outflow gradient and innocent murmurs lack fixed S2 splitting and RV volume overload.

Alternative stroke mechanism

AF, carotid or intracranial arterial disease and small-vessel disease may better explain an infarct than an incidental PFO. Stroke pattern and comprehensive vascular and rhythm assessment discriminate.

07ManagementImmediate care, first-line treatment, alternatives and escalation.

01FirstNew atrial-level shuntFirst stepMurmur, right-heart dilatation, unexplained hypoxaemia or incidental septal communication.

1Confirm anatomy and physiology with expert echocardiography rather than labelling every communication a PFO.
2Assess symptoms, oxygen saturation, rhythm, right-heart size, pulmonary pressure and associated anomalous veins or valves.
3Refer a true ASD with right-heart volume overload or symptoms to an adult congenital heart disease service.
4If pulmonary hypertension is suspected, obtain specialist haemodynamic assessment before any closure decision.

02NextASD closure decisionSignificant left-to-right shunt with right-ventricular volume overload and no prohibitive pulmonary vascular disease.

1Use TOE/CMR and, when needed, catheter haemodynamics to define anatomy and operability.
2Prefer transcatheter closure for a suitable secundum ASD; refer other anatomical types for congenital surgical assessment.
3Do not close when Eisenmenger physiology or irreversible pulmonary vascular disease makes the shunt protective.
4After closure, arrange rhythm, residual-shunt, right-heart and device surveillance through the ACHD service.

03EscalationPFO after embolic strokeEscalationIschaemic stroke with a PFO and no immediately established cause.

1Complete brain and vascular imaging and an age-appropriate search for AF and other embolic sources.
2Confirm PFO anatomy and shunt using contrast echo/TOE and assess venous-thromboembolism history.
3Discuss adults around 60 years or younger in a stroke-interventional cardiology MDT under the NHS England policy.
4If closure is selected, give the agreed post-device antithrombotic course and monitor for new AF and recurrent neurological events.

08ComplicationsImportant consequences, why they occur and why they matter clinically.

Right-heart failure

A significant ASD chronically overloads the RV and can eventually cause dilatation, functional tricuspid regurgitation, reduced exercise capacity and systemic venous congestion. A PFO alone does not cause this volume load.

Pulmonary hypertension and Eisenmenger physiology

In a minority with a large longstanding ASD, high pulmonary flow can contribute to irreversible pulmonary vascular disease, bidirectional or reversed shunting and cyanosis. Closing the defect when pulmonary vascular disease is advanced may precipitate right-heart failure.

Atrial flutter or fibrillation

Atrial dilatation and remodelling create arrhythmic substrate, to which surgical scar may contribute after repair. Arrhythmia may first reveal an adult ASD and can persist or appear even after late repair.

Paradoxical embolism and hypoxaemia

A venous clot can cross an ASD or PFO during right-to-left flow and cause stroke or systemic infarction. Positional shunting can rarely produce platypnoea-orthodeoxia.

09Monitoring and follow-upTreatment response, safety checks and longer-term review.

For unrepaired or repaired ASD, monitor symptoms, oxygen saturation, ECG/rhythm, right-heart size and pulmonary pressure at ACHD-defined intervals.
After device closure, confirm device position, residual shunt and pericardial effusion, then follow the device and ACHD plan.
Look for atrial flutter/fibrillation, which may persist or develop even after late ASD closure.
After PFO closure, monitor for early new atrial fibrillation and ensure the antithrombotic stop date is explicit.
Reassess urgently for new cyanosis, haemoptysis, syncope, stroke/TIA or right-heart failure.

10Special situationsVariants, exceptions and circumstances that change the usual approach.

Fixed splitting mechanism

Chronic RV volume loading blunts respiratory variation in pulmonary valve closure, producing the classic fixed split S2.

Defect size is not enough

Right-ventricular volume overload and pulmonary vascular state drive ASD closure decisions more than a single measured diameter.

PFO is not an ASD

A probe-patent flap may allow transient right-to-left passage without the chronic volume load of an ASD.

Bubble timing matters

An intracardiac shunt generally opacifies the left atrium early; delayed appearance should raise intrapulmonary shunting.

Closure can create harm

In advanced pulmonary vascular disease an ASD may decompress the right heart; closing it can precipitate failure.

11Common pitfallsFrequent interpretation and management errors.

01
Calling an incidental PFO the cause of stroke before excluding AF and arterial disease.
02
Offering PFO closure for primary prevention in an asymptomatic person.
03
Using defect diameter alone to judge ASD significance.
04
Closing an interatrial shunt without assessing pulmonary vascular resistance when PH is suspected.
05
Discharging an adult after childhood ASD repair with no plan for arrhythmia or residual-lesion review.