Atrial Septal Defect in Adults

Overview

Atrial septal defect (ASD) is a congenital cardiac anomaly characterised by an abnormal communication between the left and right atria, resulting in left-to-right shunting of blood. While traditionally considered a paediatric condition, ASD represents the most common congenital heart lesion diagnosed in adulthood, accounting for 20-40% of all congenital heart disease detected after age 40 years. [1,2] The condition demonstrates a marked female predominance with a 2:1 to 3:1 female-to-male ratio across all ASD subtypes. [3]

The clinical significance of ASD in adults extends beyond the anatomical defect itself. The chronic volume overload imposed on the right heart chambers leads to progressive right ventricular dilatation, pulmonary vascular remodelling, and eventually irreversible pulmonary arterial hypertension if left untreated. [1] Adults with unrepaired ASD face substantial morbidity including atrial arrhythmias (particularly atrial fibrillation and flutter), paradoxical embolism with cryptogenic stroke, exercise intolerance, and right heart failure. [2,4] However, timely closure—whether surgical or transcatheter—can reverse many pathophysiological changes and significantly improve long-term outcomes even in older adults.

The diagnosis of ASD in adults often occurs incidentally during investigation of unexplained dyspnoea, atrial arrhythmias, or stroke in young patients, or may be detected on routine imaging. [1] Contemporary management has been revolutionised by transcatheter device closure, which has largely replaced open-heart surgery for secundum defects and offers excellent outcomes with minimal morbidity. [5,6] Understanding the natural history, diagnostic approach, and treatment indications for adult ASD is essential for all physicians, as delayed diagnosis and inappropriate management can result in preventable cardiovascular complications.

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Epidemiology

Prevalence and Incidence

Demographics and Risk Factors

ASD demonstrates clear epidemiological patterns that influence clinical presentation and outcomes. The female preponderance is observed across all ASD subtypes and becomes more pronounced in older age groups, with women comprising up to 75% of adults diagnosed over age 60. [1] This sex difference may relate to hormonal influences on cardiac remodelling and differential survival rates.

Genetic and familial factors play an important role in ASD pathogenesis. Approximately 5-10% of ASDs occur as part of recognised genetic syndromes, including Holt-Oram syndrome (TBX5 mutations), Noonan syndrome, and 22q11.2 deletion syndrome. [16] Familial clustering occurs in 10-15% of cases, with first-degree relatives having a 3-fold increased risk of congenital heart defects. [3,16] Recent genetic studies have identified multiple susceptibility loci including mutations in NKX2.5, GATA4, and TBX5 genes that regulate cardiac septation during embryogenesis. [16]

Environmental risk factors during pregnancy include:

• Maternal diabetes mellitus (2-3 fold increased risk)
• First-trimester exposure to teratogens (phenytoin, lithium, retinoic acid)
• Maternal rubella infection
• Advanced maternal age (> 35 years)
• Assisted reproductive technology

Trends Over Time

The epidemiology of adult ASD has evolved significantly over recent decades. [1] Improved prenatal and neonatal screening has reduced the proportion of large defects presenting in adulthood, as these are increasingly identified and repaired in childhood. Conversely, the population of adults living with repaired ASD continues to grow, creating a cohort requiring lifelong surveillance for late complications including arrhythmias, residual shunts, and pulmonary hypertension. [1,2]

The advent of transcatheter closure devices in the 1990s has transformed treatment paradigms, with device closure now representing 70-80% of all ASD closures in developed countries for suitable secundum defects. [5,6,8] This shift has lowered the threshold for intervention and enabled treatment of patients previously considered too high-risk for surgical repair.

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Aetiology and Pathophysiology

Embryological Basis

Normal atrial septation is a complex developmental process occurring between the 4th and 7th weeks of gestation. The process involves the sequential formation and fusion of the septum primum and septum secundum, with coordinated remodelling to create a competent interatrial septum with physiological closure of the foramen ovale at birth. [3]

ASDs result from failure of this septation process:

1. Ostium secundum ASD (75% of cases): Deficiency of the septum primum or excessive resorption of the septum secundum in the region of the fossa ovalis. This is the "classic" ASD amenable to transcatheter closure. [2,3]

2. Ostium primum ASD (15-20% of cases): Failure of fusion between the septum primum and the endocardial cushions. This is part of the spectrum of atrioventricular septal defects (AVSD) and invariably involves abnormalities of the AV valves, particularly a "cleft" in the anterior mitral leaflet. [3,7]

3. Sinus venosus ASD (5-10% of cases): Located outside the true atrial septum, near the junction of the superior (most common) or inferior vena cava with the right atrium. These defects are almost always associated with partial anomalous pulmonary venous return (PAPVR), where one or more pulmonary veins drain to the right atrium or vena cava. [2,15]

4. Coronary sinus ASD (less than 1% of cases): Unroofing of the coronary sinus creating communication between the left atrium and coronary sinus, often associated with a persistent left superior vena cava.

Exam Detail: ### Molecular Pathophysiology

The genetic basis of ASD involves disruption of transcription factors governing cardiac development. Key pathways include:

Transcription Factor Networks:

• NKX2.5: Homeobox transcription factor essential for septal formation. Mutations cause secundum ASD with progressive AV conduction disease.
• GATA4: Zinc-finger transcription factor regulating cardiac morphogenesis. Mutations associated with secundum ASD and pulmonary stenosis.
• TBX5: T-box transcription factor; mutations cause Holt-Oram syndrome (ASD + upper limb defects + conduction disease).

Signalling Pathways:

• Bone morphogenetic protein (BMP) signalling defects impair endocardial cushion formation
• Notch pathway dysregulation affects septum primum development
• VEGF pathway abnormalities contribute to PAPVR in sinus venosus defects

Epigenetic Factors: Recent evidence suggests environmental exposures during pregnancy can induce epigenetic modifications (DNA methylation, histone acetylation) affecting expression of septal development genes, potentially explaining sporadic cases without identifiable mutations. [16]

Haemodynamic Consequences

The pathophysiological impact of ASD is determined by three principal factors:

1. Magnitude of left-to-right shunt (quantified as Qp:Qs ratio)
2. Duration of exposure to volume overload
3. Compliance characteristics of right vs left ventricle

Shunt Direction and Magnitude

In normal physiology, left atrial pressure slightly exceeds right atrial pressure throughout the cardiac cycle, creating a left-to-right pressure gradient across any atrial communication. The magnitude of shunting depends on:

• Defect size: Larger defects permit greater flow
• Relative ventricular compliance: The more compliant right ventricle preferentially accepts shunted blood
• Relative ventricular afterload: Lower pulmonary vascular resistance favours right ventricular filling
• Atrial pressures: Influenced by ventricular function, valve disease, and respiratory cycle

Shunt quantification:

• Qp:Qs less than 1.5:1 = Small shunt (usually asymptomatic)
• Qp:Qs 1.5-2.0:1 = Moderate shunt (may be symptomatic)
• Qp:Qs > 2.0:1 = Large shunt (typically symptomatic, requires closure)

The shunt is predominantly left-to-right during ventricular diastole, when blood flows from left atrium to right atrium and then preferentially into the more compliant right ventricle rather than the stiffer left ventricle.

Right Heart Volume Overload

Chronic left-to-right shunting imposes sustained volume overload on the right atrium, right ventricle, and pulmonary circulation:

Right Atrial Changes:

• Progressive dilatation accommodating increased venous return
• Atrial wall stress triggers fibrosis and remodelling
• Substrate for atrial arrhythmias (particularly atrial flutter and fibrillation)

Right Ventricular Changes:

• Eccentric hypertrophy and dilatation to accommodate 1.5-3 times normal stroke volume
• Initially preserved systolic function due to enhanced preload (Frank-Starling mechanism)
• Progressive myocardial fibrosis and dysfunction with decades of volume overload
• Eventual development of restrictive physiology reducing compliance

Pulmonary Circulation Changes:

• Increased pulmonary blood flow (high-output state)
• Initially normal pulmonary vascular resistance with increased flow
• Progressive endothelial dysfunction and vascular remodelling
• Development of pulmonary arterial hypertension in 5-10% of adults
• Risk of Eisenmenger physiology (shunt reversal) if pulmonary vascular resistance exceeds systemic resistance

Exam Detail: ### Pulmonary Vascular Remodelling in ASD

The pulmonary vasculature undergoes distinct histopathological changes in response to chronic high-flow states:

Stage 1 - Adaptive (reversible):

• Endothelial activation with increased NO production
• Recruitment and dilatation of pulmonary capillaries
• Maintained normal pulmonary vascular resistance despite increased flow
• Responsive to pulmonary vasodilators

Stage 2 - Intermediate (potentially reversible):

• Medial hypertrophy of small pulmonary arteries
• Intimal proliferation
• Progressive increase in pulmonary vascular resistance
• Reduced vasodilator responsiveness

Stage 3 - Eisenmenger (irreversible):

• Severe obliterative arteriopathy with plexiform lesions
• Necrotising arteritis and arterial thrombosis
• Pulmonary vascular resistance exceeds systemic resistance
• Shunt reversal causing cyanosis (right-to-left shunt)
• Contraindication to defect closure

The time course of pulmonary vascular disease varies enormously between individuals. Unlike ventricular septal defects where pulmonary vascular disease develops in infancy, ASD rarely causes Eisenmenger syndrome before the 3rd-4th decade, and most adults with ASD never develop irreversible pulmonary hypertension. [14] Factors accelerating pulmonary vascular disease include Down syndrome, altitude residence, and genetic susceptibility.

Left Heart Considerations

While ASD primarily affects the right heart, important left-sided consequences occur:

• Left ventricular underfilling: Reduced preload may cause relative LV hypotrophy
• Diastolic dysfunction: Septal flattening and ventricular interdependence impair LV filling
• Atrial fibrillation: Biatrial enlargement provides substrate for AF
• Paradoxical embolism: Right-to-left shunting (even transient) can allow venous thrombi to bypass pulmonary filtration and cause systemic embolisation

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Clinical Presentation

The clinical presentation of ASD in adults is highly variable, ranging from complete absence of symptoms to severe heart failure and cyanosis. The timing and nature of symptoms relate to defect size, patient age, and development of complications.

Asymptomatic Presentation

Approximately 20-30% of adults with ASD are completely asymptomatic at initial diagnosis, with detection occurring incidentally during investigation of:

• Heart murmur detected on routine examination
• Abnormal chest radiograph (cardiomegaly, increased pulmonary vascular markings)
• Echocardiogram performed for another indication
• Pre-operative cardiac assessment
• Family screening after diagnosis of congenital heart disease in a relative

Even in asymptomatic individuals, objective evidence of right heart volume overload is typically present (RA/RV dilatation on echo, ECG changes), and many patients retrospectively report limited exercise tolerance once compared to post-closure status. [1]

Symptomatic Presentation

Dyspnoea and Exercise Intolerance

The cardinal symptom of significant ASD is exertional dyspnoea, reported by 60-70% of adults at diagnosis. [1,2] The mechanism is multifactorial:

• Reduced cardiac output reserve due to "stealing" of LV preload
• Pulmonary congestion from increased pulmonary blood flow
• Right ventricular dysfunction limiting augmentation of stroke volume
• Coexistent pulmonary hypertension (in advanced cases)
• Chronotropic incompetence (unable to increase heart rate appropriately)

Symptom progression is typically insidious over years to decades. Patients often unconsciously reduce activity levels and may not recognise limitation until questioned specifically. Formal exercise testing frequently reveals marked reduction in peak VO2 and anaerobic threshold even in those reporting minimal symptoms.

Palpitations and Arrhythmias

Atrial arrhythmias are a major source of morbidity in adult ASD, with incidence increasing sharply after age 40. [10] The mechanism involves:

• Atrial dilatation creating arrhythmogenic substrate
• Atrial wall fibrosis disrupting normal conduction
• Increased atrial wall stress
• Sinus node dysfunction (particularly with sinus venosus ASD)

Common arrhythmias:

• Atrial fibrillation: 10-15% at age 40, increasing to 30-40% by age 60 [1,10]
• Atrial flutter: Often typical counterclockwise cavotricuspid isthmus-dependent flutter
• Sinus node dysfunction: Bradycardia, sinus pauses (especially sinus venosus defects)
• Supraventricular tachycardia: Less common than AF/flutter

Importantly, atrial arrhythmias frequently persist or develop de novo even after successful ASD closure if repair is delayed beyond the 4th decade, highlighting the importance of timely intervention. [1,10]

Stroke and Systemic Embolisation

Paradoxical embolism through ASD is an important cause of cryptogenic stroke in young adults. [19] The mechanism involves:

1. Venous thromboembolism (often occult DVT or pelvic vein thrombosis)
2. Right-to-left shunting across ASD (may be transient, occurring only with Valsalva or coughing)
3. Thrombus bypasses pulmonary filtration and embolises to systemic (cerebral) circulation

Risk factors for paradoxical embolism:

• Provocation of right-to-left shunt (cough, Valsalva, pregnancy)
• Coexistent atrial septal aneurysm (highly mobile interatrial septum)
• Hypercoagulable states
• Prolonged immobility or air travel
• Presence of atrial fibrillation (LA thrombus + right-to-left shunt)

ASD should be considered in any patient less than 60 years with cryptogenic stroke, particularly if echocardiography demonstrates right heart dilatation or if transcranial Doppler shows large right-to-left shunt. [19]

Cyanosis and Eisenmenger Syndrome

Central cyanosis in ASD indicates shunt reversal (right-to-left shunting) due to suprasystemic pulmonary vascular resistance—Eisenmenger syndrome. [14] This represents end-stage disease and occurs in approximately 5-10% of adults with longstanding unrepaired ASD, typically not before the 3rd-4th decade.

Clinical features of Eisenmenger syndrome:

• Central cyanosis (may be differential—affecting toes more than fingers in some cases)
• Clubbing of fingers and toes
• Polycythaemia (haematocrit often > 55%)
• Hyperviscosity symptoms (headache, visual disturbance)
• Haemoptysis (pulmonary vascular dilatation and rupture)
• Right heart failure
• Cerebral abscess (loss of pulmonary filtration of bacteraemia)

Once Eisenmenger physiology develops, ASD closure is contraindicated as the defect serves as a "pop-off" valve preventing acute right heart failure. [14] Management is palliative, focused on pulmonary vasodilator therapy and symptom control.

Pregnancy-Related Presentation

Pregnancy causes significant haemodynamic stress in women with ASD due to:

• 40-50% increase in blood volume augmenting left-to-right shunt
• Increased venous return during labour and delivery
• Decreased systemic vascular resistance (favouring shunt)
• Hypercoagulable state increasing paradoxical embolism risk

Most women with simple ASD tolerate pregnancy well if pulmonary pressures are normal. [12,18] However, complications include:

• New-onset or worsened atrial arrhythmias (15-20%)
• Right heart failure (5-10% in large defects)
• Paradoxical embolism
• Eisenmenger syndrome (maternal mortality 30-50%, contraindication to pregnancy)

Women should undergo full cardiac assessment including echocardiography and consideration of ASD closure prior to conception if Qp:Qs > 1.5:1. [12,18]

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Physical Examination Findings

The classical examination findings in ASD are subtle and easily missed, contributing to delayed diagnosis. Findings relate to right heart volume overload and increased pulmonary blood flow.

General Inspection

• Normal appearance in most cases (no cyanosis, no dysmorphic features in isolated ASD)
• Cyanosis if Eisenmenger syndrome (bluish discolouration of lips, tongue, nail beds)
• Clubbing in longstanding Eisenmenger syndrome
• Dysmorphic features if syndromic (Holt-Oram: absent/hypoplastic thumb; Down syndrome)

Cardiovascular Examination

Precordial Palpation

• Right ventricular heave along left sternal border (parasternal lift) indicating RV volume overload—present in most moderate-large ASDs
• Palpable P2 in 2nd left intercostal space if pulmonary hypertension
• Apex beat often non-palpable or laterally displaced by dilated right ventricle

Auscultation

The pathognomonic finding in ASD is wide fixed splitting of the second heart sound (S2):

• Wide splitting: Due to prolonged RV ejection time (increased stroke volume) delaying P2
• Fixed splitting: Split does not vary with respiration, as both left and right heart filling increase during inspiration (equalization)
• Present in 90% of moderate-large ASDs but easily overlooked without careful auscultation

Additional auscultatory findings:

Important negative findings:

• No cyanosis in simple ASD (unless Eisenmenger)
• No thrill (unlike VSD)
• No S3 gallop (preserved RV systolic function initially)

Exam Detail: ### Examination Technique for Wide Fixed Split S2

Correct technique is essential:

1. Patient supine, quiet room
2. Use diaphragm of stethoscope (high-frequency sounds)
3. Position at 2nd left intercostal space (pulmonary area)
4. Listen during normal respiration—S2 split throughout respiratory cycle
5. Ask patient to take deep breath and hold—split persists (fixed)
6. Compare to aortic area (S2 single) and mitral area (split not audible)

Common errors:

• Confusing S2 split with S3 or S4 gallop
• Not appreciating that S2 normally splits physiologically during inspiration
• Failure to listen throughout respiratory cycle to confirm "fixed" nature

The sensitivity of fixed split S2 for ASD is approximately 85-90% for defects with Qp:Qs > 1.5:1, but may be absent in small defects, elderly patients, or those with pulmonary hypertension (where P2 becomes markedly delayed and loud). [2,3]

Primum ASD-Specific Findings

Ostium primum ASD (AVSD type) presents with additional examination features due to associated AV valve abnormalities:

• Pansystolic murmur of mitral regurgitation (apex radiating to axilla)
• Left parasternal heave (volume-loaded LV as well as RV)
• S3 gallop if significant MR
• Superior QRS axis on ECG (leftward axis deviation)

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Differential Diagnosis

The presentation of ASD overlaps with numerous cardiovascular and respiratory conditions. Key differentials include:

Structural Cardiac Lesions

Functional Mimics

Important "Must Not Miss" Differentials

When RV dilatation is detected, always exclude:

1. Pulmonary embolism (acute or chronic): May cause acute RV dilatation; check D-dimer, CTPA
2. Arrhythmogenic RV cardiomyopathy (ARVC): Family history of SCD; T-wave inversion V1-V3; fatty infiltration on MRI
3. Ebstein's anomaly: Apical displacement of tricuspid valve; giant RA; cyanosis if ASD/PFO
4. LV systolic dysfunction with secondary TR: Elevated JVP; pulmonary oedema; dilated LV on echo

Clinical Pearl: Diagnostic pitfall: Right heart dilatation detected on routine echocardiography is often labelled as "pulmonary hypertension" or "right heart failure of unknown cause" without systematically excluding ASD. Always carefully interrogate the interatrial septum with colour Doppler and consider bubble study if image quality is suboptimal. Missing an ASD condemns the patient to progressive symptoms and potentially preventable complications.

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Investigations

The diagnostic workup of suspected ASD follows a structured approach, moving from non-invasive screening to definitive imaging and occasionally invasive haemodynamic assessment.

First-Line Investigations

Electrocardiography (ECG)

The ECG in ASD is rarely normal if the defect is haemodynamically significant. Typical findings reflect right heart volume overload and conduction abnormalities:

Common findings (Secundum ASD):

• Right axis deviation (+90° to +180°): Present in 70-80% of cases
• Incomplete right bundle branch block (RBBB): rSR' pattern in V1, QRS less than 120ms—present in 90% of moderate-large defects
• Right atrial enlargement: Peaked P waves in II, III, aVF (P pulmonale)
• Right ventricular hypertrophy: R>S in V1; deep S in V5-V6
• Prolonged PR interval: First-degree AV block in 10-15% (particularly sinus venosus type)
• Atrial fibrillation/flutter: Increasingly common > 40 years

Primum ASD-specific findings:

• Superior (leftward) QRS axis: −30° to −90°—pathognomonic for AVSD
• Prolonged PR interval (> 200ms): Due to AV node displacement
• RBBB pattern: Similar to secundum

ECG in pulmonary hypertension:

• Right axis deviation becoming more marked
• Tall R wave in V1 (> 7mm)
• Right ventricular strain pattern: ST depression and T-wave inversion V1-V4
• Right atrial enlargement: Tall peaked P waves

Exam Detail: Why does ASD cause incomplete RBBB?

The rSR' pattern (incomplete RBBB) in ASD results from:

1. RV volume overload: Prolonged RV ejection time delays completion of right ventricular depolarisation
2. RV dilatation: Increased muscle mass requires longer to depolarise
3. Septal depolarisation abnormality: Altered septal geometry and activation sequence

This is "volume overload RBBB" and differs from true RBBB (QRS > 120ms) which indicates conduction system disease. The distinction is important—volume overload RBBB often normalises after ASD closure, while true RBBB does not.

Chest Radiography

CXR findings correlate with shunt magnitude and chronicity:

Typical appearances (moderate-large ASD):

Eisenmenger syndrome findings:

• Markedly dilated central pulmonary arteries
• "Pruning" of peripheral vessels (sudden vessel cutoff)
• Normal or even small cardiac silhouette (paradoxically)

CXR may be normal in:

• Small ASDs with Qp:Qs less than 1.5:1
• Early stages before significant RV dilatation
• Young patients with compliant chest wall masking cardiomegaly

Second-Line Investigations

Transthoracic Echocardiography (TTE)

TTE is the primary diagnostic modality for ASD, providing both diagnosis and haemodynamic assessment. [4,9]

Standard views for ASD assessment:

1. Subcostal views: Best for imaging interatrial septum perpendicular to ultrasound beam

   • Subcostal four-chamber: Identifies defect location
   • Subcostal short-axis: Sweeps through septum to characterise defect
   • Subcostal bicaval view: Identifies sinus venosus defects

2. Apical four-chamber: Assesses chamber sizes and shunt direction with colour Doppler

3. Parasternal views: Evaluates RV size, PA pressure, valve function

Key TTE measurements:

Shunt quantification methods:

1. Qp:Qs calculation:

   • Qp (pulmonary flow) = RVOT VTI × RVOT area × HR
   • Qs (systemic flow) = LVOT VTI × LVOT area × HR
   • Ratio > 1.5:1 indicates significant shunt

2. Volumetric method: RV stroke volume / LV stroke volume

3. Colour Doppler: Direct visualisation of shunt jet (qualitative)

Echo-defined criteria for intervention:

• Qp:Qs ≥1.5:1 AND evidence of RV volume overload (RA/RV dilatation)
• Paradoxical septal motion (septal flattening from RV overload)
• Unexplained stroke with demonstrated shunt

Limitations of TTE:

• Poor image quality in 10-15% (obesity, lung disease, chest wall deformity)
• Sinus venosus defects frequently missed (outside standard imaging planes)
• PAPVR not reliably detected
• Secundum rims difficult to measure accurately

Transoesophageal Echocardiography (TOE)

TOE provides superior visualisation of atrial structures and is essential for:

1. Pre-procedure planning for transcatheter closure: [9,13]

   • Accurate defect sizing (often 20-30% larger than TTE measurement)
   • Rim assessment (needs ≥5mm rim in most directions except anterosuperior)
   • Exclusion of multiple defects
   • Detection of interatrial septal aneurysm
   • Identification of anomalous pulmonary venous drainage

2. Intraoperative guidance during device deployment

3. Problem-solving when TTE non-diagnostic

ASE Guidelines on ASD assessment recommend TOE for: [4]

• All patients being considered for transcatheter closure
• Suspected sinus venosus or coronary sinus ASD
• Suspected PAPVR
• Cryptogenic stroke (bubble study for PFO/ASD)

Exam Detail: ### Advanced Imaging: Cardiac CT and MRI

Cardiac CT:

CT angiography (CTA) is particularly valuable for:

• Sinus venosus ASD with PAPVR: Gold standard for defining pulmonary venous anatomy [15]
• 3D reconstruction: Anatomical planning for complex defects
• Coronary assessment: In older patients (> 40 years) before surgical repair

Typical protocol: ECG-gated cardiac CTA with late-phase imaging to enhance pulmonary veins.

Cardiac MRI:

MRI offers comprehensive assessment including:

• Accurate shunt quantification: Phase-contrast velocity mapping directly measures Qp and Qs
• Ventricular volumes and function: Precise RV volumes (gold standard)
• PAPVR detection: Non-invasive pulmonary vein mapping
• Late gadolinium enhancement: Detects myocardial fibrosis (prognostic information)
• No radiation exposure: Preferred in young patients

Indications for CT/MRI:

• Sinus venosus ASD (to map pulmonary veins)
• Discordant TTE and TOE findings
• Unexplained RV dilatation with non-diagnostic echo
• Pre-operative planning for complex repairs
• Post-repair surveillance for residual shunts

Bubble Contrast Study

Agitated saline contrast ("bubble study") detects right-to-left shunting:

Technique:

1. Inject agitated saline into peripheral vein during echo imaging
2. Normal: Bubbles opacify RA/RV, then disappear (trapped in pulmonary capillaries)
3. Positive: Bubbles appear in LA/LV within 3-5 cardiac cycles (shunt present)

Interpretation:

• Positive at rest: Large ASD or significant RV dysfunction/pulmonary hypertension
• Positive with Valsalva only: Smaller ASD or PFO (RA pressure transiently exceeds LA pressure)
• Timing: less than 3 beats = cardiac shunt (ASD/PFO); > 5 beats = pulmonary AV malformation

Clinical use:

• Screening for PFO/ASD in cryptogenic stroke
• Detecting right-to-left shunt in suspected Eisenmenger
• Monitoring for shunt closure post-device/surgery

Invasive Investigations

Right Heart Catheterisation

Cardiac catheterisation is reserved for specific indications:

1. Pulmonary hypertension assessment: [14]

   • Measure PA pressures directly
   • Calculate pulmonary vascular resistance (PVR)
   • Vasodilator challenge if PVR elevated
   • Determine suitability for defect closure

2. Shunt quantification when non-invasive methods inconclusive:

   • Oximetry run (O2 saturation step-up at RA level confirms shunt)
   • Fick or thermodilution Qp:Qs calculation

3. Coronary angiography: In patients > 40 years before surgical repair

Contraindication to ASD closure:

• PVR > 5 Wood units (approximately > 400 dynes·s·cm⁻⁵)
• Irreversible pulmonary hypertension despite vasodilator challenge
• Net right-to-left shunt at rest

Typical catheterisation findings in ASD:

• O2 saturation step-up ≥7% at RA level (confirms left-to-right shunt)
• RA pressure mildly elevated (6-10mmHg)
• RV systolic pressure variable (normal to moderately elevated)
• PA pressure normal or mildly elevated in simple ASD (less than 40/20mmHg)
• PCWP normal (unless LV dysfunction)
• Qp:Qs > 1.5:1 in haemodynamically significant defects

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Classification and Subtypes

ASD classification is based on anatomical location within the interatrial septum, with important implications for associated anomalies, closure technique, and prognosis.

Anatomical Classification

Secundum ASD Subtypes

Secundum defects are further classified by rim adequacy for device closure:

Rim requirements for transcatheter closure: [9,13]

• Anterosuperior (aortic) rim: May be deficient (not essential)
• Anteroinferior (AV valve) rim: ≥5mm required
• Posteroinferior (IVC) rim: ≥5mm required
• Posterosuperior (SVC) rim: ≥5mm required
• Tissue rim around entire defect: ≥38mm total septal length

Secundum ASD categories:

1. Simple: Single, central defect with adequate rims—ideal for device closure
2. Complex: Multiple defects (fenestrated septum), deficient rims, or very large defects (> 35-40mm)—may require surgical repair
3. Interatrial septal aneurysm: Hypermobile septum primum (> 10mm excursion)—associated with higher stroke risk

Primum ASD (Partial AVSD)

Primum defects represent the lower end of the AVSD spectrum:

Anatomical features:

• Located immediately above AV valves (not in fossa ovalis)
• Invariably associated with cleft anterior mitral leaflet
• Common AV valve annulus (though two separate valve orifices)
• ECG shows superior QRS axis (pathognomonic)

Goose-neck deformity: Characteristic LV outflow tract elongation and angulation seen on ventriculography

Surgical considerations:

• Direct closure with patch
• Cleft repair mandatory (prevent progressive MR)
• Risk of heart block 1-2% (conduction tissue displaced)

Sinus Venosus ASD

Superior sinus venosus defect (90% of SV-ASD):

• Located at SVC-RA junction
• Invariably associated with anomalous drainage of right upper or middle pulmonary vein to SVC or high RA
• Not a "true" septal defect (deficiency of SVC wall)
• Requires baffling procedure (Warden or caval division)

Inferior sinus venosus defect (10% of SV-ASD):

• Located at IVC-RA junction
• Associated with right lower pulmonary vein draining to IVC or low RA
• Requires surgical baffle repair

Clinical Pearl: Why sinus venosus ASDs are often missed:

1. Located outside fossa ovalis, often missed on standard TTE apical views
2. Subcostal bicaval view required but frequently not obtained
3. PAPVR is the dominant haemodynamic lesion but pulmonary veins not routinely assessed
4. Often incorrectly diagnosed as "secundum ASD" without careful anatomical delineation

Any patient with RV volume overload and "ASD" should have pulmonary venous anatomy defined by TOE, CT, or MRI to exclude sinus venosus defect with PAPVR before planning transcatheter closure—which is contraindicated in SV-ASD.

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Management

Contemporary ASD management integrates patient symptoms, shunt magnitude, right heart impact, and procedural risk to individualise treatment. The fundamental decision is between closure (transcatheter or surgical) versus conservative management with surveillance.

Indications for Closure

Class I indications (should be performed): [1,2,6]

1. Significant left-to-right shunt:

   • Qp:Qs ≥1.5:1 AND
   • Evidence of RV volume overload (RA/RV dilatation)
   • Regardless of symptoms

2. Paradoxical embolism:

   • Documented stroke/TIA with no other identified source AND
   • Demonstrable ASD with right-to-left shunt
   • Even if Qp:Qs less than 1.5:1

Class IIa indications (reasonable to perform):

1. Orthodeoxia-platypnoea syndrome (positional hypoxaemia due to right-to-left shunt)
2. Documented platypnoea (dyspnoea improved by lying flat)

Contraindications to closure: [1,14]

1. Eisenmenger syndrome: PVR > 5 Wood units with net right-to-left shunt
2. Severe irreversible pulmonary hypertension: PVR remains > 5 WU despite vasodilator therapy
3. Active endocarditis
4. Severe LV systolic dysfunction (closure may precipitate LV failure)

Relative contraindications:

• Small shunt (Qp:Qs less than 1.5) without symptoms or stroke
• Very advanced age (> 80 years) with comorbidities
• Severe diastolic dysfunction (closure may worsen pulmonary oedema)

Exam Detail: ### Haemodynamic Assessment for Closure in Pulmonary Hypertension

When PA pressures are elevated (PASP > 40mmHg), careful assessment is required to determine if ASD closure is safe:

Step 1: Right heart catheterisation

• Measure baseline PA pressure, PCWP, cardiac output
• Calculate PVR = (mean PA pressure − PCWP) / cardiac output
• Perform oximetry run to confirm shunt

Step 2: Vasodilator challenge

• Administer inhaled NO, prostacyclin, or IV adenosine
• Reassess PA pressure and PVR
• Positive response: ≥20% decrease in PVR

Step 3: Trial balloon occlusion (if PVR elevated but less than 5 WU):

• Inflate balloon in ASD to temporarily occlude shunt
• Monitor haemodynamics for 10-15 minutes
• Safety criteria:
  • PA pressure does not rise excessively
  • PCWP remains less than 18mmHg
  • Cardiac output maintained
  • Patient tolerates without dyspnoea

Decision algorithm:

• PVR less than 3 WU: Safe to close
• PVR 3-5 WU + positive vasodilator test + tolerates balloon occlusion: Consider closure with close monitoring
• PVR > 5 WU or negative tests: Contraindicated; medical therapy only
• Consider fenestrated device (allows pop-off) in borderline cases [11]

Transcatheter Device Closure

Device closure has become the first-line therapy for suitable secundum ASDs, accounting for 70-80% of all closures. [5,6,8]

Patient selection criteria: [6,8,9,13]

1. Anatomical suitability:

   • Secundum ASD (not primum or sinus venosus)
   • Maximum diameter typically ≤38-40mm (device-dependent)
   • Adequate rims (≥5mm except anterosuperior)
   • Total septal length ≥38mm
   • Sufficient distance from AV valves, pulmonary veins, coronary sinus

2. Clinical suitability:

   • Qp:Qs ≥1.5:1 or paradoxical embolism indication
   • No contraindications (see above)
   • Suitable vascular access (femoral vein)
   • Patient accepts device and follow-up

Available devices:

Multiple devices are approved with similar efficacy:

• Amplatzer Septal Occluder: Most widely used; dual-disc nitinol device
• GORE Cardioform: Soft conformable Gore-Tex material
• Occlutech Figulla: Nitinol mesh with enhanced rim stability
• Others: Lifetech CeraFlex, Cocoon devices

Device sizing typically 1.3-2× the balloon-stretched diameter of the defect.

Procedural approach:

1. Pre-procedure: TOE for anatomical confirmation; antibiotic prophylaxis
2. Vascular access: Femoral vein cannulation under local anaesthetic ± sedation
3. Imaging guidance: Fluoroscopy + TOE or ICE (intracardiac echo)
4. Defect crossing: Catheter advanced from IVC → RA → across ASD to LA
5. Sizing balloon: Balloon inflation to measure stretched diameter
6. Device deployment: Left disc deployed in LA, right disc in RA, connecting waist spans defect
7. Position verification: TOE/ICE confirms stable position, no valve interference, no residual shunt
8. Release: Device released from delivery cable
9. Post-procedure: Antiplatelet therapy; echo at 1, 6, 12 months

Outcomes: [5,6,8]

Post-procedure management:

• Dual antiplatelet therapy: Aspirin + clopidogrel for 3-6 months (device endothelialisation)
• Endocarditis prophylaxis: For 6 months post-device (until endothelialised)
• Activity restriction: Avoid contact sports for 1 month
• Follow-up echo: At 1, 6, and 12 months, then annually
• Surveillance: Arrhythmia monitoring (increased AF risk persists)

Surgical Closure

Surgical repair remains the treatment of choice for: [5,7]

1. Primum ASD (requires cleft closure and possible valve repair)
2. Sinus venosus ASD (requires baffle to redirect pulmonary veins)
3. Coronary sinus ASD (requires unroofing repair)
4. Large secundum ASD unsuitable for device (> 38-40mm, deficient rims)
5. Multiple defects (fenestrated septum)
6. Concomitant procedures (valve surgery, CABG, arrhythmia surgery)

Surgical approaches:

Median sternotomy (traditional):

• Full cardiopulmonary bypass (CPB)
• Direct visualisation of defect
• Primary closure (small defects) or patch repair (larger defects)
• Allows concomitant procedures

Minimally invasive (right thoracotomy):

• Smaller incision (5-7cm at right 4th intercostal space)
• CPB via femoral vessels
• Cosmetically superior, faster recovery
• Suitable for isolated ASD

Robotic-assisted:

• Emerging technique in specialist centres
• Excellent cosmetic results
• Requires robotic infrastructure

Surgical outcomes: [5,7]

Primum-specific outcomes:

• Residual mitral regurgitation: 10-15% (may require reoperation)
• Subaortic stenosis: 5% (LVOT obstruction from "goose-neck" deformity)

Conservative Management and Surveillance

Small ASDs (Qp:Qs less than 1.5:1) without symptoms or RV dilatation may be managed conservatively:

Surveillance protocol:

• Clinical review annually
• TTE every 2-3 years (monitor for progressive RV dilatation, rising PA pressures)
• ECG annually (detect arrhythmias, conduction disease)
• Exercise testing if symptoms develop

General measures:

• Endocarditis prophylaxis: Not required for isolated ASD (unlike VSD)
• Air filter on IV lines: To prevent paradoxical air embolism
• Pregnancy counselling: Usually well-tolerated if PA pressures normal [12,18]
• Arrhythmia management: Standard AF/flutter treatment; consider closure if recurrent
• Thromboprophylaxis: Consider if AF develops

Criteria to re-evaluate for closure:

• Development of symptoms
• Progressive RV dilatation on serial echo
• New-onset atrial arrhythmias
• Embolic event (stroke/TIA)
• Increase in Qp:Qs or PA pressures

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Special Populations

Pregnancy and ASD

Pre-pregnancy counselling: [12,18]

Women of childbearing age with ASD should be counselled regarding:

1. Pregnancy risk stratification (WHO classification):

   • WHO Class I: Small ASD, normal PA pressure → low risk
   • WHO Class II: Moderate ASD, mildly elevated PA pressure → moderate risk
   • WHO Class III: Large ASD, moderate PAH → high risk
   • WHO Class IV: Eisenmenger syndrome → contraindication (maternal mortality 30-50%)

2. Pre-pregnancy closure recommendation:

   • Consider closure if Qp:Qs > 1.5:1 prior to conception
   • Allows medication-free pregnancy and reduced maternal risk
   • Wait 6 months post-device before conception (endothelialisation, stop antiplatelet therapy)

3. Pregnancy management if ASD unclosed:

   • Multidisciplinary care (cardiology, obstetrics, anaesthetics)
   • Monthly cardiology review; echo each trimester
   • Avoid Valsalva (increases right-to-left shunt risk)
   • Vaginal delivery preferred; Caesarean only for obstetric indications
   • Air filter on all IV lines (prevent paradoxical air embolism)
   • LMWH thromboprophylaxis postpartum
   • Avoid ergometrine (increases PA pressure)

Pregnancy complications:

• Atrial arrhythmias: 15-20%
• Paradoxical embolism: 1-2%
• Right heart failure: 5-10% (large defects)
• Pregnancy usually well-tolerated if PA pressures normal

Elderly Patients (> 60 years)

Considerations for closure in older adults: [1]

Benefits of ASD closure persist even in patients > 60 years:

• Symptomatic improvement in 70-80%
• Reduction in arrhythmia burden
• Prevention of progressive RV dysfunction
• Reduced mortality compared to untreated

However:

• Higher procedural risk (comorbidities, vascular access issues)
• Atrial arrhythmias may persist post-closure if longstanding atrial remodelling
• LV diastolic dysfunction more prevalent → risk of pulmonary oedema post-closure
• Careful patient selection essential

Age alone should not preclude closure if: [1]

• Symptomatic with clear attributable symptoms
• Favourable anatomy for device closure
• Acceptable procedural risk
• Adequate life expectancy to benefit

ASD and Eisenmenger Syndrome

Management principles: [14]

Once Eisenmenger physiology develops (PVR > 5 WU, net right-to-left shunt), ASD closure is contraindicated. Management becomes palliative:

1. Pulmonary vasodilator therapy:

   • Endothelin receptor antagonists (bosentan, ambrisentan)
   • Phosphodiesterase-5 inhibitors (sildenafil, tadalafil)
   • Prostacyclin analogues (treprostinil, epoprostenol)
   • Aims to reduce PVR, improve symptoms, slow progression

2. Supportive care:

   • Oxygen if hypoxaemic (though may increase PVR)
   • Avoid dehydration (increases haematocrit)
   • Judicious phlebotomy if haematocrit > 65% with symptoms
   • Iron supplementation if iron-deficient

3. Complication management:

   • Anticoagulation controversial (bleeding vs thrombosis risk)
   • Haemoptysis: usually conservative; rarely requires embolisation
   • Arrhythmias: rate/rhythm control; avoid excessive bradycardia
   • Heart failure: gentle diuresis; avoid over-diuresis

4. Advanced therapies:

   • Heart-lung transplantation: Curative but limited donor availability
   • Lung transplant + ASD repair: Alternative option

5. Avoid:

   • Pregnancy (contraindicated—maternal mortality 30-50%)
   • Anaesthesia and surgery (high-risk—seek specialist advice)
   • Dehydration and high altitude
   • Non-selective vasodilators (systemic hypotension worsens shunt)

Athletes and Exercise

Exercise recommendations: [1]

• Pre-closure: Avoid competitive sports if significant shunt (Qp:Qs > 1.5) or elevated PA pressures
• Post-closure: Return to full activity after 3-6 months if:
  • Complete/trivial residual shunt
  • Normal PA pressures
  • Normal RV size and function
  • No significant arrhythmias

Sports participation after device closure:

• Avoid contact sports for 1-3 months (risk of device displacement)
• Scuba diving controversial (theoretical gas embolism risk if residual shunt)

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Complications and Long-term Sequelae

Untreated ASD Complications

Natural history of untreated ASD: [1,2]

• Age 20-30: Usually asymptomatic
• Age 30-40: Exertional dyspnoea develops
• Age 40-50: Atrial arrhythmias emerge
• Age 50-60: Right heart failure, significant functional limitation
• Survival: Reduced life expectancy by 20-30 years if moderate-large shunt untreated

Post-Closure Complications

Early complications (less than 30 days):

Late complications (> 30 days):

Exam Detail: Device erosion—a rare but serious complication:

Erosion of device through atrial wall is rare (less than 0.1% incidence) but potentially catastrophic:

Risk factors:

• Deficient anterosuperior rim (less than 5mm to aorta)
• Oversized device (> 1.5× defect diameter)
• Rigid devices in thin patients
• Vigorous CPR post-procedure

Presentation:

• Acute: Cardiac tamponade, haemodynamic collapse
• Subacute: Pericardial effusion, chest pain, device migration

Management:

• Emergency pericardiocentesis if tamponade
• Urgent surgical device removal and ASD repair
• High mortality if not promptly recognised

Prevention:

• Careful rim assessment on TOE
• Appropriate device sizing
• Avoid excessive manipulation during deployment
• Post-procedure echo surveillance

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Prognosis

Natural History (Untreated)

Prognosis of untreated ASD depends on shunt magnitude and development of complications:

Small ASD (Qp:Qs less than 1.5:1):

• Often asymptomatic lifelong
• Minimal impact on life expectancy
• Low risk of complications

Moderate-Large ASD (Qp:Qs > 1.5:1):

• Progressive symptoms from 3rd-4th decade
• Reduced life expectancy by 20-30 years
• 50% mortality by age 50 if untreated [1,2]

Survival data (untreated moderate-large ASD): [1,2]

• 10-year survival: 85%
• 20-year survival: 70%
• 30-year survival: 50%
• 40-year survival: 30%

Cause of death (untreated ASD):

• Heart failure: 40%
• Pulmonary hypertension/Eisenmenger: 15%
• Stroke/systemic embolism: 10%
• Arrhythmias/sudden death: 10%
• Other cardiovascular: 10%
• Non-cardiovascular: 15%

Outcomes After Closure

Survival benefit: [1,5,6]

ASD closure significantly improves survival, particularly if performed before age 40:

Symptomatic improvement: [1,5,6]

• Dyspnoea: Improves in 70-80% of patients
• Exercise capacity: Increases by 20-30% on formal testing
• Quality of life: Significant improvement across all domains

Structural reverse remodelling:

Arrhythmia outcomes: [10]

• Pre-existing AF: Persists in 60-70% if closure after age 40
• New-onset AF: Risk reduced but not eliminated
• Sinus node dysfunction: May improve (sinus venosus) or persist

Optimal timing for closure:

To maximize benefit and minimize late complications:

• Ideal: Childhood/adolescence (before structural changes)
• Good: Young adulthood (less than 40 years)
• Acceptable: Middle age (40-60 years)—still benefit but higher residual arrhythmia risk
• Selective: Older adults (> 60 years)—individualised assessment

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Prevention and Screening

Primary Prevention

There are no established primary prevention strategies for congenital ASD, as the condition results from embryological developmental abnormalities. However, general measures to reduce congenital heart disease risk include:

• Pre-pregnancy counselling: Optimisation of maternal diabetes control
• Folic acid supplementation: Reduces neural tube defects; possible cardiovascular benefit
• Avoidance of teratogens: Phenytoin, lithium, retinoic acid, alcohol in pregnancy
• Rubella vaccination: Prevents congenital rubella syndrome

Genetic Counselling

Indications for genetic evaluation: [16]

• Syndromic features (Holt-Oram, Noonan, Down syndrome)
• Family history of congenital heart disease
• Multiple extracardiac anomalies
• Recurrent pregnancy loss with CHD

Recurrence risk:

• Isolated ASD (sporadic): 2-3% risk in future pregnancies
• Familial ASD: 10-15% risk in first-degree relatives
• Syndromic ASD: Depends on syndrome (may be 50% for autosomal dominant)

Screening Recommendations

Fetal screening:

• Routine fetal anomaly ultrasound at 20 weeks detects major cardiac defects
• Secundum ASD is difficult to diagnose prenatally (foramen ovale normally patent in fetus)
• Primum AVSD can be detected on fetal echo

Family screening:

First-degree relatives of patients with ASD have 3-fold increased risk of congenital heart disease: [3,16]

• Recommendation: Clinical exam and TTE for first-degree relatives if:
  • Multiple family members with CHD
  • Syndromic ASD
  • Other congenital anomalies present

Screening in cryptogenic stroke:

Consider screening for PFO/ASD in patients with cryptogenic stroke less than 60 years:

• TTE with bubble study
• TOE if TTE non-diagnostic
• Consider closure if large shunt or associated atrial septal aneurysm [19]

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Key Guidelines

International Society Guidelines

European Society of Cardiology (ESC) 2020 Guidelines on Adult Congenital Heart Disease:

• ASD closure indicated if Qp:Qs ≥1.5:1 with RV volume overload (Class I)
• Device closure preferred for suitable secundum defects (Class I)
• Consider closure for paradoxical embolism even if Qp:Qs less than 1.5:1 (Class IIa)
• Contraindicated if PVR > 5 Wood units (Class III)

American College of Cardiology/American Heart Association (ACC/AHA) 2018 Guidelines:

• Closure recommended for secundum ASD with RV enlargement regardless of symptoms (Class I)
• Device closure preferred when anatomically suitable (Class I)
• Surgical closure for primum, sinus venosus, or unsuitable secundum defects (Class I)

American Society of Echocardiography (ASE) 2015 Guidelines on ASD/PFO Assessment: [4]

• TOE recommended for all patients considered for transcatheter closure (Class I)
• Bubble study indicated for cryptogenic stroke evaluation (Class I)
• Detailed rim assessment essential for device selection (Class I)

European Stroke Organisation (ESO) 2024 Guidelines: [19]

• PFO/ASD closure reduces recurrent stroke risk in cryptogenic stroke less than 60 years (Class I)
• Antiplatelet therapy alone insufficient if large shunt present

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Common Exam Questions

1. "What are the causes of wide fixed splitting of the second heart sound?"

   • Primarily ASD (left-to-right shunt)
   • Differential: RBBB, pulmonary stenosis (wide but not fixed)
   • Explanation: RV volume overload delays P2; fixed because both ventricles fill more in inspiration

2. "How would you investigate a 30-year-old with unexplained exertional dyspnoea and a systolic murmur?"

   • History: Exercise tolerance, palpitations, stroke/TIA, family history
   • Examination: Wide split S2, RV heave, pulmonary flow murmur
   • ECG: RAD, incomplete RBBB
   • CXR: Cardiomegaly, pulmonary plethora
   • TTE: Confirms ASD, quantifies shunt, assesses RV size/function

3. "What is your management approach to an adult with secundum ASD and Qp:Qs 2.5:1?"

   • Meets criteria for closure (Qp:Qs > 1.5:1, RV volume overload)
   • TOE to confirm anatomy and assess suitability for device closure
   • If suitable rims: transcatheter device closure
   • If unsuitable: surgical closure
   • Post-closure: antiplatelet therapy, echo surveillance, arrhythmia monitoring

4. "A 35-year-old woman with known ASD is planning pregnancy. What advice do you give?"

   • Assess PA pressures and shunt magnitude
   • Recommend pre-pregnancy closure if Qp:Qs > 1.5:1
   • If Eisenmenger: pregnancy absolutely contraindicated
   • If closes device: wait 6 months before conception
   • If unclosed: multidisciplinary pregnancy care, monthly cardiology review

5. "What are the complications of untreated ASD?"

   • Atrial arrhythmias (AF/flutter): 30-40% by age 60
   • Right heart failure: progressive RV dysfunction
   • Pulmonary hypertension: 10-15%
   • Eisenmenger syndrome: 5-10%
   • Paradoxical embolism/stroke: 5-10%
   • Reduced life expectancy: 20-30 years if moderate-large shunt

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Viva Points

Viva Point: Opening statement:

"Atrial septal defect is an abnormal communication between the left and right atria, resulting in left-to-right shunting and right heart volume overload. It is the most common congenital heart lesion diagnosed in adulthood, accounting for 20-40% of adult congenital heart disease, with a marked female predominance."

Classification (know this cold):

"There are four anatomical types:

1. Secundum (75%)—located in the fossa ovalis, amenable to transcatheter closure
2. Primum (15-20%)—part of AVSD spectrum, involves AV valves, requires surgery
3. Sinus venosus (5-10%)—at SVC or IVC junction, associated with anomalous pulmonary veins, requires surgery
4. Coronary sinus (less than 1%)—unroofed coronary sinus, requires surgery"

Pathophysiology pearl:

"The direction and magnitude of shunting depend on the relative compliance of the ventricles. The right ventricle is more compliant than the left, so blood preferentially shunts left-to-right across the ASD during diastole. The shunt is quantified as Qp:Qs—the ratio of pulmonary to systemic blood flow. A ratio > 1.5:1 is significant."

Examination finding you must mention:

"The pathognomonic sign is wide fixed splitting of S2—the split is wide due to prolonged RV ejection from volume overload, and fixed because it doesn't vary with respiration. An ejection systolic murmur at the left sternal border represents increased flow across the pulmonary valve."

Management decision-making:

"The fundamental question is: does this ASD require closure? Indications are:

• Qp:Qs ≥1.5:1 with RV volume overload (even if asymptomatic)—Class I
• Paradoxical embolism—Class I
• Contraindicated if PVR > 5 Wood units or Eisenmenger syndrome

For secundum defects with suitable anatomy, transcatheter device closure is preferred. Primum and sinus venosus defects require surgery."

Complication you must not miss:

"Eisenmenger syndrome—irreversible pulmonary vascular disease causing shunt reversal and cyanosis. It occurs in 5-10% of adults with longstanding untreated ASD, typically in the 4th-5th decade. Once established, ASD closure is contraindicated. Management is palliative with pulmonary vasodilators."

Prognosis statement:

"Timely closure significantly improves outcomes. If closed before age 40, patients have near-normal life expectancy. However, atrial arrhythmias may persist if closure is delayed, as atrial remodelling is often irreversible."

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Common Mistakes

❌ Mistakes that fail candidates:

1. Missing the diagnosis entirely:

   • Attributing RV dilatation on echo to "pulmonary hypertension" without carefully interrogating the interatrial septum
   • Failing to examine for wide fixed split S2 on clinical exam
   • Not considering ASD in young patients with cryptogenic stroke

2. Incorrect classification:

   • Calling all ASDs "secundum" without anatomical confirmation
   • Missing sinus venosus ASD (requires subcostal bicaval view, pulmonary vein assessment)
   • Not recognising primum ASD (look for superior QRS axis, cleft mitral leaflet)

3. Wrong treatment approach:

   • Attempting device closure in primum or sinus venosus ASD (contraindicated—requires surgery)
   • Closing ASD in Eisenmenger syndrome (contraindicated—will cause acute RV failure)
   • Conservative management of large shunt (Qp:Qs > 2:1) in young patient—should close

4. Incorrect investigation strategy:

   • Relying on TTE alone for pre-device assessment (TOE mandatory to assess rims)
   • Not defining pulmonary vein anatomy in suspected sinus venosus defect
   • Failing to measure PA pressures and PVR if elevated pressures suspected

5. Wrong prognostic information:

   • Telling patient "ASD is benign and doesn't need treatment" (untrue for moderate-large defects)
   • Stating arrhythmias will resolve after closure (they often persist if closure delayed)
   • Advising against pregnancy in simple ASD with normal PA pressures (usually well-tolerated)

6. Endocarditis prophylaxis error:

   • Prescribing routine endocarditis prophylaxis for isolated ASD (not required)
   • Forgetting prophylaxis for first 6 months post-device (required during endothelialisation)

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Model Answers

Q: Describe your approach to a 45-year-old woman with exertional dyspnoea found to have a systolic murmur and wide split S2 on examination.

A: "This presentation suggests a left-to-right shunt lesion, most likely atrial septal defect given the wide fixed split S2. I would approach this systematically.

History: I would quantify the dyspnoea—exercise tolerance, NYHA class, progression over time. I'd ask about palpitations (atrial arrhythmias are common), previous stroke or TIA (paradoxical embolism), and family history of congenital heart disease.

Examination: I would confirm the wide fixed split S2—it should not vary with respiration, distinguishing it from physiological splitting. I'd assess for signs of RV volume overload including a right ventricular heave, and auscultate for an ejection systolic murmur at the left sternal border from increased pulmonary flow. I would check for cyanosis (would indicate Eisenmenger syndrome) and signs of right heart failure.

Investigations:

• ECG would likely show right axis deviation and incomplete RBBB (rSR' in V1), both indicating RV volume overload.
• Chest X-ray would show cardiomegaly from RA and RV enlargement, pulmonary plethora from increased pulmonary blood flow, and a prominent pulmonary artery.
• Transthoracic echo is the key diagnostic test—it would confirm the ASD, quantify the shunt (Qp:Qs ratio), assess the magnitude of RV dilatation, estimate PA pressures, and look for associated anomalies.

Management decision: If the Qp:Qs is ≥1.5:1 with evidence of RV volume overload, closure is indicated according to guidelines. For a secundum defect, I would arrange TOE to assess suitability for transcatheter device closure—this requires adequate rims and defect size typically less than 38-40mm. If anatomy is suitable, device closure is preferred. If unsuitable, or if it's a primum or sinus venosus defect, surgical closure would be required.

Follow-up: Post-closure, she would need antiplatelet therapy for 3-6 months, echo surveillance to confirm closure, and long-term monitoring for atrial arrhythmias which may persist given her age at closure."

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References

1. Baumgartner H, et al. Atrial septal defect in adulthood: a new paradigm for congenital heart disease. Eur Heart J. 2022;43(28):2660-2671. doi:10.1093/eurheartj/ehab735

2. Geva T, et al. Atrial Septal Defect. StatPearls. 2025. PMID:30571061

3. Webb G, et al. Atrial septal defects. Circulation. 2014;129(21):2090-2093. doi:10.1161/CIRCULATIONAHA.113.005124

4. Silvestry FE, et al. Guidelines for the Echocardiographic Assessment of Atrial Septal Defect and Patent Foramen Ovale. J Am Soc Echocardiogr. 2015;28(8):910-958. doi:10.1016/j.echo.2015.05.015

5. Butera G, et al. Surgical or interventional treatment for adult patients with atrial septal defect. Cochrane Database Syst Rev. 2022;7:CD013796. doi:10.1002/14651858.CD013796.pub2

6. Rao PS, et al. Recent review of transcatheter closure of atrial septal defect. World J Cardiol. 2018;10(6):43-59. doi:10.4330/wjc.v10.i6.43

7. Hoffman JI, et al. Atrial septal defects. Pediatr Clin North Am. 2014;61(4):655-673. doi:10.1016/j.pcl.2014.04.003

8. Jalal Z, et al. Transcatheter Closure of Atrial Septal Defect: A Review of Currently Used Devices. Arch Cardiovasc Dis. 2023;116(6-7):368-377. doi:10.1016/j.acvd.2023.04.004

9. Johri AM, et al. Transcatheter Closure of PFO and ASD: Multimodality Imaging for Patient Selection and Procedural Guidance. JACC Cardiovasc Imaging. 2021;14(9):1801-1816. doi:10.1016/j.jcmg.2021.02.033

10. Silversides CK, et al. Arrhythmias and conduction disorders associated with atrial septal defects. Prog Cardiovasc Dis. 2018;61(3-4):275-281. doi:10.1016/j.pcad.2018.08.004

11. Kijima Y, et al. Fenestrated Transcatheter ASD Closure in Adults with Diastolic Dysfunction and/or Pulmonary Hypertension. JACC Cardiovasc Interv. 2016;9(11):1150-1157. doi:10.1016/j.jcin.2016.02.039

12. Ruys TP, et al. Shunt Lesions. Cardiol Clin. 2015;33(4):575-586. doi:10.1016/j.ccl.2015.07.011

13. Bharucha T, et al. Atrial Septal Defect Sizing and Transcatheter Closure. Cardiol Clin. 2019;37(3):299-315. doi:10.1016/j.ccl.2019.04.003

14. D'Alto M, et al. Eisenmenger syndrome and atrial septal defect: nature or nurture? Int J Cardiol. 2006;108(3):302-303. doi:10.1016/j.ijcard.2005.05.020

15. Haramati LB, et al. An adult with a sinus venosus atrial septal defect and dilated cardiomyopathy. J Cardiovasc Comput Tomogr. 2014;8(3):246-249. doi:10.1016/j.jcct.2014.04.003

16. Blue GM, et al. Human Genetics of Atrial Septal Defect. Circ Genom Precis Med. 2024;17(3):e004203. doi:10.1161/CIRCGEN.123.004203

17. Egbe A, et al. Catheter Management of Atrial Septal Defect. Interv Cardiol Clin. 2019;8(2):163-175. PMID:30725593

18. De Backer J, et al. Quality of life in pregnancy after percutaneous closure of atrial septal defect or patent foramen ovale. Int J Cardiol. 2023;371:472-478. doi:10.1016/j.ijcard.2022.11.028

19. Dawson J, et al. European Stroke Organisation (ESO) Guidelines on the diagnosis and management of patent foramen ovale in stroke. Eur Stroke J. 2024;9(2):277-303. doi:10.1177/23969873241248934

20. Backer CL, et al. Atrial septal defect closure. Semin Thorac Cardiovasc Surg Pediatr Card Surg Annu. 2013;16(1):46-52. doi:10.1053/j.pcsu.2013.01.006

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Last updated: 2025-01-06 Evidence Level: High (20 PubMed citations, systematic review-based)