Atrial Septal Defect

Slide 1 · Atrial Septal Defect

Development • morphology • hemodynamics • clinical significance

Dr Abu Suraih Sakhri

MBBS, MD (Pathology)

www.abusuraihsakhri.com

Slide 2 · What this lecture will explain

Distinguish a true atrial septal defect (ASD) from a patent foramen ovale (PFO).

Reconstruct atrial septation and localize three anatomical ASD types.

Connect abnormal atrial communication to pulmonary overcirculation, clinical presentation, and closure rationale.

Slide 3 · ASD belongs to congenital heart disease

Congenital heart disease (CHD) comprises structural abnormalities of the heart or great vessels present at birth.

Atrial defects belong to the septal-defect category, rather than outflow obstruction or great-vessel misrouting.

A circumscribed lesion may be compatible with live birth but become clinically relevant later.

Congenital heart disease

Septal defect

Atrial septal defect

Structural category — editable hierarchy

Slide 4 · Timing matters: Cardiac morphogenesis

Most CHD arises from errors in embryogenesis during gestational weeks 3–8.

Atrial development requires coordinated cell movement, tissue reshaping, and septation.

Disturbance of the septal program can leave an enduring interatrial opening.

Weeks 3–8

Cardiac structures form

Septation creates chambers

Developmental or clinical stages — schematic

Slide 5 · Building a four-chambered heart

Cardiac progenitors converge and form a beating heart tube by about day 20.

Chamber formation proceeds during the following days.

By about day 50, septation of atria, ventricles, and AV valves yields a four-chambered heart.

Day 20: Beating tube

~Day 28: Chamber formation

~Day 50: Four chambers

Developmental or clinical stages — schematic

Slide 6 · Heart-field contributions to the atria

First-wave progenitors contribute to the developing left ventricle.

The second heart field contributes to the outflow tract, right ventricle, and most atrial tissue.

Errors in spatially coordinated development can produce defects of discrete cardiac structures.

First heart field

Left ventricle

Second heart field

Right ventricle + most atria

Two cardiac progenitor lineages

Slide 7 · Etiology is heterogeneous, not deterministic

Genetic and environmental causes are established for CHD, but account for a minority of cases.

Examples of environmental associations include congenital rubella, teratogenic exposures, and gestational diabetes.

Most affected individuals have no identified single explanatory genetic lesion.

Contributors

Interpretation

Genetic variation

Can disrupt morphogenesis

Gestational exposures

Can alter development

Unexplained cases

Common in CHD

Native editable PowerPoint comparison table

Slide 8 · Septal development requires transcriptional coordination

Cardiac developmental programs use interacting transcription factors and signaling systems.

GATA4, TBX5, and NKX2.5 as interacting factors in septal development.

Variation in one component may disrupt their shared transcriptional targets.

GATA4

TBX5

NKX2.5

Interacting transcription factors

Textbook-described interaction; Not a quantitative network

Slide 9 · GATA4: Septal-defect association

GATA4 among genes associated with ASD or ventricular septal defect.

Its product is a transcription factor, not an anatomic structural component of the septum.

A gene–phenotype association does not imply that all ASDs carry this variant.

GATA4 variation

Developmental transcription altered

Septal defect can result

Conceptual mechanism — editable schematic

Slide 10 · NKX2.5: ASD and conduction phenotypes

NKX2.5 is linked in the Robbins gene table to nonsyndromic ASD or conduction defects.

The same developmental regulator may influence more than one cardiac phenotype.

The precise relationship between a variant and its clinical manifestation can vary.

Affected phenotype

Shared regulator

Atrial septal defect

NKX2.5

Conduction defect

NKX2.5

Native editable PowerPoint comparison table

Slide 11 · TBX5 and syndromic septal defects

TBX5 in Holt–Oram syndrome, with ASD, VSD, or conduction defects among cardiac features.

The gene product is a transcription factor.

Clinical association is not equivalent to a molecular diagnosis from cardiac anatomy alone.

TBX5 alteration

Cardiac developmental effects

ASD / VSD / conduction phenotypes

Conceptual mechanism — editable schematic

Slide 12 · Complex developmental causes explain heterogeneity

GATA4, TBX5, and NKX2.5 participate in common regulatory interactions.

Different alterations may yield overlapping phenotypes; One alteration can yield different manifestations.

That CHD pathogenesis remains incompletely understood.

GATA4

TBX5

NKX2.5

Interacting transcription factors

Textbook-described interaction; Not a quantitative network

Slide 13 · Three broad hemodynamic patterns in CHD

Shunts permit flow between chambers or blood vessels.

Left-to-right shunts usually increase pulmonary blood flow without initial cyanosis.

Right-to-left shunts bypass the lungs; Obstructive lesions impede passage through the cardiovascular circuit.

Pattern

Principal consequence

Left → right

Pulmonary overcirculation

Right → left

Systemic desaturation

Obstruction

Restricted forward flow

Native editable PowerPoint comparison table

Slide 14 · A true ASD is a fixed interatrial opening

The defect is an abnormal, persistent opening within the atrial septum.

It establishes direct communication between the right and left atria.

Its defining anatomy is distinct from the physiologic fetal foramen ovale.

RIGHT ATRIUM

LEFT ATRIUM

Central septal opening

Slide 15 · A patent foramen ovale is not a true ASD

PFO represents postnatal failure of the normal fetal atrial channel to seal.

The retained channel is flap-like and can open when right atrial pressure exceeds left atrial pressure.

A true ASD instead involves a fixed abnormal opening in septal tissue.

Atrial septal defect

Patent foramen ovale

Fixed tissue opening

Potential flap-like channel

Abnormal septal development

Incomplete postnatal sealing

Usually left → right

May open transiently right → left

Native editable PowerPoint comparison table

Slide 16 · Septation requires sequential, overlapping tissues

The septum primum develops first and only partially divides the common atrium.

New interatrial openings preserve fetal blood passage during septation.

The later septum secundum overlies the channel, leaving the foramen ovale.

Septum primum

Ostium secundum

Septum secundum → foramen ovale

Developmental or clinical stages — schematic

Slide 17 · Septum primum: Initial partial partition

The first septal ingrowth is crescent-shaped and membranous.

It develops posteriorly between the forming right and left atria.

Its growth begins separation without immediately eliminating fetal atrial communication.

Developing common atrium

Septum primum begins ingrowth

Original schematic of developmental sequence; Not an anatomic section

Slide 18 · Ostium primum: A transient opening

The gap remaining during early septum primum growth is termed ostium primum.

This opening allows interatrial blood movement during early development.

It is normally obliterated as development progresses.

Developing common atrium

Ostium primum: Transient gap

Original schematic of developmental sequence; Not an anatomic section

Slide 19 · Ostium secundum maintains interatrial transit

Before ostium primum is completely obliterated, another opening develops in the septum primum.

This second opening is the ostium secundum.

Its formation prevents premature elimination of fetal interatrial communication.

Developing common atrium

Ostium secundum: New opening

Original schematic of developmental sequence; Not an anatomic section

Slide 20 · Septum secundum creates an overlapping partition

A second septal ingrowth develops to the right and anterior of the septum primum.

It partially covers the ostium secundum.

The remaining channel is the foramen ovale, connected with the ostium secundum.

Developing common atrium

Overlapping septa → fetal channel

Original schematic of developmental sequence; Not an anatomic section

Slide 21 · The fetal foramen ovale is physiologic

During intrauterine life, interatrial right-to-left passage is normal.

Pulmonary vascular resistance is high while the lungs are not functioning for gas exchange.

This pressure setting favors right atrial pressure over left atrial pressure.

RIGHT ATRIUM

LEFT ATRIUM

Central septal opening

Slide 22 · The pressure gradient regulates fetal passage

Flow through the fetal atrial channel depends on right-versus-left atrial pressures.

When right atrial pressure is higher, fetal interatrial flow is right to left.

The channel is not equivalent to an irreversible tissue defect.

High fetal pulmonary resistance

Right atrial pressure relatively high

Right → left interatrial passage

Conceptual mechanism — editable schematic

Slide 23 · Birth reverses atrial pressure relationships

Lung expansion lowers pulmonary vascular pressure after birth.

Right atrial pressure falls below left atrial pressure.

The foramen ovale valve is pressed closed: Normal fetal communication is no longer required.

Lungs expand

Pulmonary pressure falls

LA pressure > RA pressure

Functional closure

Conceptual mechanism — editable schematic

Slide 24 · Functional closure and anatomic sealing differ

Pressure-driven apposition occurs with postnatal circulatory adaptation.

Permanent fusion of the atrial flap occurs subsequently in most individuals.

Failure of permanent fusion leaves PFO; Deficient septal tissue formation produces an ASD.

Transition

Structural result

Functional postnatal closure

Pressure-dependent apposition

Permanent anatomic fusion

Sealed normal channel

Failure of sealing

Patent foramen ovale

Native editable PowerPoint comparison table

Slide 25 · Atrial septation: Developmental checkpoints

First partition grows without immediately closing the atrial route.

A secondary perforation preserves passage as the first gap disappears.

Overlapping septa permit fetal flow and eventual postnatal closure.

Primum ingrowth

Primum closes + secundum forms

Secundum overlaps → fetal channel

Developmental or clinical stages — schematic

Slide 26 · Where development fails determines morphology

Deficient central septal development yields a secundum-type defect.

A defect near the atrioventricular valve region is termed a primum ASD.

A defect near the superior vena caval entry is termed sinus venosus ASD.

SECUNDUM

Center of septum

90%

PRIMUM

Near AV valves

5%

SINUS VENOSUS

Near SVC entry

5%

Robbins morphological classification

Slide 27 · Three anatomical ASD categories

Secundum: Central atrial septum.

Primum: Adjacent to the atrioventricular valves.

Sinus venosus: Near the entrance of the superior vena cava.

SECUNDUM

Center of septum

90%

PRIMUM

Near AV valves

5%

SINUS VENOSUS

Near SVC entry

5%

Robbins morphological classification

Slide 28 · Secundum ASD is the predominant type

Approximately 90% of ASDs to the secundum category.

These arise from deficient septum secundum formation near the septal center.

They are usually not associated with other congenital anomalies.

RIGHT ATRIUM

LEFT ATRIUM

Central septal opening

Slide 29 · Secundum ASD can vary markedly in geometry

A single defect may be small or large.

Multiple perforations may coexist in the same septum.

A fenestrated defect is therefore a recognized variation, not a separate main category.

RIGHT ATRIUM

LEFT ATRIUM

Multiple/fenestrated openings

Slide 30 · Secundum location determines its anatomy

The central atrial septum is the key anatomic landmark.

The fixed communication connects both atria rather than ventricles or major arteries.

Position is central; Multiplicity and size provide additional morphologic description.

RIGHT ATRIUM

LEFT ATRIUM

Central septal opening

Slide 31 · Primum ASD is a low septal defect

Approximately 5% of ASDs are described as primum anomalies.

They occur next to the atrioventricular valves.

Their location distinguishes them from a centrally situated secundum defect.

RIGHT ATRIUM

LEFT ATRIUM

Near AV valve plane

Slide 32 · Primum ASD often accompanies other lesions

Primum lesions with abnormalities of atrioventricular valves.

They may also occur together with a ventricular septal defect.

A primum finding warrants attention to nearby atrioventricular structures.

Low atrial septal defect

Adjacent AV valves

Look for AV valve anomaly ± VSD

Conceptual mechanism — editable schematic

Slide 33 · Sinus venosus ASD lies near the SVC

Approximately 5% of ASDs are sinus venosus defects.

The defect is located near entry of the superior vena cava.

Its anatomical position differs from central secundum and low primum defects.

RIGHT ATRIUM

LEFT ATRIUM

Near SVC entrance

Slide 34 · Sinus venosus defects: Venous association

Association with anomalous pulmonary venous return to the right atrium.

The septal defect and venous drainage pattern are therefore linked morphologic observations.

The association is not stated as obligatory for every sinus venosus defect.

Sinus venosus defect

Assess pulmonary venous connections

Possible return into RA

Conceptual mechanism — editable schematic

Slide 35 · Relative frequencies of ASD variants

Secundum dominates the distribution reported.

Primum and sinus venosus each comprise a small minority.

Percentages describe morphological categories, not severity or closure eligibility.

Secundum

90%

Primum

5%

Sinus venosus

5%

Proportions as, not population incidence

Slide 36 · Locate the defect before describing its consequences

Central defect: Secundum; Lower AV-valve region: Primum.

High septal region near SVC: Sinus venosus.

Record multiplicity and associated anomalies separately from type.

ASD type

Location

Key association

Secundum

Center

Usually isolated

Primum

Near AV valves

AV valve ± VSD

Sinus venosus

SVC entrance

Possible anomalous PV return

Native editable PowerPoint comparison table

Slide 37 · Postnatal ASD flow is usually left to right

The fixed opening permits blood to enter the right atrium from the left atrium.

Low-resistance pulmonary circulation facilitates this direction.

The resulting volume burden is largely on the right ventricle and pulmonary pathway.

RIGHT ATRIUM

LEFT ATRIUM

Central septal opening

Slide 38 · Pulmonary versus systemic vascular resistance

Pulmonary vascular resistance is much lower than systemic vascular resistance after birth.

A route from the left side to the right side of the circulation therefore permits recirculation through the lungs.

This is one major determinant of ASD shunting.

Low pulmonary resistance

LA → RA shunting

Pulmonary overcirculation

Conceptual mechanism — editable schematic

Slide 39 · Relative ventricular compliance matters

The right ventricle is more compliant (distensible) than the left ventricle.

This favors filling and accommodation of additional right-sided volume.

ASD shunt flow therefore reflects compliance as well as vascular resistance.

Physiologic feature

Effect on shunt

Lower PVR

Facilitates pulmonary recirculation

Higher RV compliance

Accommodates added volume

Fixed opening

Allows atrial communication

Native editable PowerPoint comparison table

Slide 40 · Trace the extra blood volume through the circuit

A portion of oxygenated left atrial blood returns to the right atrium.

The right ventricle ejects this additional volume into the pulmonary trunk.

The lungs receive more than the normal forward-flow volume.

Left atrium

Right atrium

Right ventricle

Pulmonary circuit

Recirculating pulmonary volume

Schematic excess flow loop; Systemic circuit omitted

Slide 41 · Right-ventricular volume load is characteristic

Robbins specifically distinguishes ASD from defects generating a strong right-ventricular pressure load.

ASD principally augments right-ventricular and pulmonary outflow volumes.

The remodeled right side may remain compensated for many years.

Left → right shunt

Extra RV filling

Increased RV outflow

Conceptual mechanism — editable schematic

Slide 42 · Pulmonary blood flow may rise substantially

Pulmonary flow volumes of two to eight times normal in ASD.

This is a possible range described by the source, not a patient-specific measurement.

High flow helps explain audible flow findings despite an initially well-tolerated lesion.

Atrial communication

Increased right-heart throughput

Pulmonary flow: 2–8× normal (textbook)

Conceptual mechanism — editable schematic

Slide 43 · Why the pulmonary valve can produce a murmur

Excess pulmonary outflow passes through an anatomically separate valve.

A murmur may reflect increased flow through the pulmonary valve and/or the atrial defect itself.

The sound is a hemodynamic clue, not a direct measure of defect diameter.

ASD shunt

Higher RV outflow

Flow-related murmur

Conceptual mechanism — editable schematic

Slide 44 · ASD differs from VSD and PDA hemodynamics

ASD primarily raises right-ventricular and pulmonary flow volumes.

VSD and PDA generally increase pulmonary blood flow and pressure.

These differences influence downstream pulmonary vascular stress.

Defect

Pulmonary volume

Pulmonary pressure

ASD

Increased

Less dominant early feature

VSD

Increased

Also increased

PDA

Increased

Also increased

Native editable PowerPoint comparison table

Slide 45 · Severity varies among left-to-right shunts

The hemodynamic consequences depend on anatomy, size, and location.

Left-to-right lesions may range from clinically silent to substantial hemodynamic disease.

ASD is often tolerated longer than major pressure-loading lesions.

Defect anatomy

Shunt magnitude

Cardiac / pulmonary burden

Clinical impact

Conceptual mechanism — editable schematic

Slide 46 · Why an uncomplicated ASD is acyanotic

An initially left-to-right shunt does not introduce systemic venous blood directly into systemic arterial outflow.

The additional circulating volume instead traverses the pulmonary circuit.

Cyanosis implies another mechanism, such as a significant right-to-left component.

Direction

Immediate consequence

Left → right

Pulmonary overcirculation

Right → left

Desaturated blood enters systemic circulation

Native editable PowerPoint comparison table

Slide 47 · Chronic shunt flow can remodel lung vessels

Sustained pulmonary circulatory overload may elicit arteriolar medial hypertrophy and vasoconstriction.

Longstanding exposure can generate obstructive intimal changes.

This general left-to-right shunt pathway explains concern about irreversible pulmonary vascular disease.

Prolonged pulmonary overload

Medial hypertrophy + vasoconstriction

Obstructive intimal remodeling

Conceptual mechanism — editable schematic

Slide 48 · Eisenmenger physiology is a late complication

In severe longstanding left-to-right CHD, pulmonary resistance may approach systemic resistance.

The shunt can reverse to right-to-left flow and produce hypoxemia and cyanosis.

That irreversible pulmonary hypertension is unusual in ASD specifically.

High pulmonary resistance

Shunt reversal

Systemic desaturation

Conceptual mechanism — editable schematic

Slide 49 · ASD is often clinically silent for decades

ASDs are usually asymptomatic until adulthood.

Symptoms commonly do not emerge before approximately age 30.

Clinical quiescence should not be confused with an absence of ongoing shunt flow.

Birth: Fixed opening

Childhood: Often tolerated

Adulthood: May manifest

Developmental or clinical stages — schematic

Slide 50 · Why ASDs commonly appear in adult practice

Ventricular septal defects are more common at birth, but many close spontaneously.

ASDs are less likely to close spontaneously in the comparison made by Robbins.

ASDs consequently constitute an important defect detected in adults.

VSD

ASD

More common initially

Less common initially

Many close spontaneously

Less likely to close

Fewer persist to adult diagnosis

Often diagnosed in adulthood

Native editable PowerPoint comparison table

Slide 51 · The clinical clue can be a flow murmur

A murmur may be present despite absent symptoms.

Increased pulmonary valve flow is a mechanism rather than proof that the valve is malformed.

An observed murmur alone does not establish defect subtype.

Pulmonary overcirculation

Audible flow phenomenon

Evaluate underlying shunt anatomy

Conceptual mechanism — editable schematic

Slide 52 · Why heart failure can eventually occur

The atrial communication perpetuates right-sided volume overload.

A chronically stressed cardiac circulation can eventually become unable to maintain compensation.

Preventing heart failure is one stated rationale for ASD closure.

Long-term shunt

Right-sided volume burden

Potential cardiac failure

Conceptual mechanism — editable schematic

Slide 53 · Paradoxical embolization requires a right-to-left route

Venous embolic material normally encounters the pulmonary circulation.

Interatrial right-to-left passage can provide access to systemic arterial blood.

Avoiding paradoxical embolization is an explicit rationale for ASD closure.

Venous embolus

Interatrial right → left passage

Systemic arterial embolus

Conceptual mechanism — editable schematic

Slide 54 · Pulmonary vascular disease is a preventable concern

Chronic abnormal pulmonary flow can produce structural vascular adaptation.

Late obstructive vascular remodeling may be irreversible.

Pulmonary hypertension as unusual in ASD but relevant to closure timing.

Abnormal pulmonary flow

Vascular remodeling

Risk of irreversible disease

Conceptual mechanism — editable schematic

Slide 55 · Closure targets future harm, not just current symptoms

ASD closure is undertaken to prevent later heart failure, embolic events, and permanent pulmonary vascular injury.

Surgical and intravascular closure approaches.

Clinical benefit is assessed in the context of the defect and its physiologic consequences.

Persistent defect

Prevent complications

Surgical or intravascular closure

Conceptual mechanism — editable schematic

Slide 56 · Two closure routes are described

Surgical repair and intravascular approaches both seek to eliminate the abnormal communication.

Anatomical type and associated lesions are relevant to procedural evaluation.

Robbins does not provide a detailed device-selection or procedural eligibility algorithm in this excerpt.

Approach

Textbook scope

Surgical closure

Named option

Intravascular closure

Named option

Patient selection

Not specified in excerpt

Native editable PowerPoint comparison table

Slide 57 · Reported outcome after closure is favorable

Robbins characterizes mortality after ASD closure as low.

Postoperative survival is reported as comparable to an unaffected population.

These are general textbook statements; Individual outcomes depend on clinical circumstances.

Closure of ASD

Prevention of sequelae

Generally favorable long-term survival

Conceptual mechanism — editable schematic

Slide 58 · PFO: Postnatal sealing is frequently incomplete

Permanent foramen ovale closure in approximately 80% by age two.

In about 20%, an unsealed flap-like channel persists.

This prevalence refers to PFO, not to the frequency of a true ASD.

Closed by age ~2

Unsealed channel persists

Approximately 80%

Approximately 20%

Normal completed fusion

Patent foramen ovale

Native editable PowerPoint comparison table

Slide 59 · PFO can open during transient pressure increases

Coughing, sneezing, or straining can raise right-sided pressure transiently.

A nonfused flap can open when right atrial pressure exceeds left atrial pressure.

Brief right-to-left shunting is then possible.

Transient RA pressure rise

PFO flap opens

Brief right → left flow

Conceptual mechanism — editable schematic

Slide 60 · PFO and ASD: Separate mechanisms for embolic risk

PFO creates an intermittent right-to-left channel under suitable pressure conditions.

ASD is a fixed opening with a usual left-to-right shunt, but paradoxical embolization remains a recognized concern.

The presence, direction, and hemodynamic context of an interatrial passage determine risk mechanisms.

PFO

ASD

Flap opens under RA pressure

Fixed abnormal defect

Transient right → left episodes

Usually left → right flow

May permit paradoxical embolus

Closure partly prevents embolic risk

Native editable PowerPoint comparison table

Slide 61 · Case: An adult with an incidental murmur

A person in early adulthood feels well but has a persistent flow murmur on examination.

The main question is whether a congenital left-to-right communication increases pulmonary output.

ASD can remain silent for decades; Lack of symptoms does not negate the possibility.

Why might a substantial ASD be detected only in adult life?

Interpretation

A compliant right ventricle tolerates additional volume, and irreversible pulmonary hypertension is uncommon early.

Slide 62 · Case: A low atrial septal opening

A fixed opening is seen near the atrioventricular valve plane.

This location favors a primum defect rather than a centrally placed secundum ASD.

The nearby valves and ventricular septum require careful assessment for associated anomalies.

Which structures are most relevant to inspect next?

Interpretation

Atrioventricular valves and the ventricular septum.

Slide 63 · Case: A high septal communication

A defect lies near the superior vena cava entrance.

This localizes to the sinus venosus category.

The possibility of pulmonary veins draining anomalously to the right atrium should be considered.

Which additional anatomical connection matters?

Interpretation

Pulmonary venous return.

Slide 64 · Case: Brief right-to-left passage during straining

The interatrial communication appears flap-like rather than a fixed septal tissue gap.

A transient pressure rise on the right opens the passage.

This is characteristic of PFO physiology, not evidence of secundum ASD.

What distinguishes this lesion from an ASD?

Interpretation

The channel is a nonfused fetal flap, not a fixed deficiency of septal tissue.

Slide 65 · Check understanding: Shunt reversal

A longstanding left-to-right lesion develops progressively elevated pulmonary vascular resistance.

When pulmonary resistance becomes sufficiently high, right-to-left passage may occur.

This defines the physiology of Eisenmenger syndrome; It is unusual in ASD.

Would this be an expected early ASD presentation?

Interpretation

No. ASD generally causes a tolerated left-to-right shunt; Irreversible pulmonary hypertension is unusual.

Slide 66 · Diagnostic interpretation: Read anatomy and physiology together

Location classifies the defect; Flow direction explains its immediate hemodynamic effects.

Associated atrioventricular or pulmonary venous anomalies can change the anatomical context.

Clinical manifestations cannot be inferred reliably from subtype alone.

Question

What it establishes

Where is the opening?

ASD morphological type

Which way does blood move?

Physiologic shunt direction

Which structures are associated?

Accompanying anomalies

Native editable PowerPoint comparison table

Slide 67 · ASD: Integrated mechanism in one sequence

A developmental septal deficiency produces a fixed communication between the atria.

Low pulmonary resistance and greater RV compliance favor left-to-right shunting.

Pulmonary overcirculation is initially tolerated but motivates preventive closure.

Septal deficiency

LA → RA shunt

RV volume load

Pulmonary overcirculation

Late-risk prevention

Conceptual mechanism — editable schematic

Slide 68 · High-yield anatomical synthesis

Secundum is central and represents about nine of ten ASDs.

Primum is adjacent to the AV valves and may accompany AV anomalies or VSD.

Sinus venosus is close to the SVC and may coexist with anomalous pulmonary venous return.

SECUNDUM

Center of septum

90%

PRIMUM

Near AV valves

5%

SINUS VENOSUS

Near SVC entry

5%

Robbins morphological classification

Slide 69 · High-yield clinical synthesis

Most ASDs are well tolerated until adult life; A flow murmur may be present.

Increased RV and pulmonary volumes are more characteristic than an early high-pressure shunt.

Closure aims to prevent failure, paradoxical embolization, and irreversible pulmonary vascular disease.

Often silent

RV volume overload + pulmonary flow

Prevent future complications

Conceptual mechanism — editable schematic

Slide 70 · Reference and further reading

Robbins, Cotran & Kumar: Pathologic Basis of Disease, 11th edition (2026).

Read the sections on congenital heart disease, atrial septal defect, and patent foramen ovale together.

Review the textbook diagrams and gene-association tables alongside the conceptual drawings in this lecture.