Transposition of the Great Arteries

Slide 1 · Transposition of the Great Arteries

Anatomical discordance • parallel circulation • mixing • systemic ventricular adaptation

Congenital cardiac pathology

Dr Abu Suraih Sakhri

MBBS, MD (Pathology)

www.abusuraihsakhri.com

Slide 2 · Learning objectives

Trace normal and discordant atrioventricular and ventriculoarterial connections.

Explain why d-TGA forms parallel circulations and why mixing permits survival.

Relate shunt closure and systemic ventricular workload to clinical outcomes.

Differentiate d-TGA from congenitally corrected l-TGA and key congenital comparators.

Slide 3 · Congenital heart disease: A structural framework

Congenital heart disease (CHD) changes chamber, valve, or great-vessel connections.

Robbins organizes functional disturbances as shunts, outflow obstruction, or their combination.

TGA is distinguished by the destination of ventricular outflow, not simply a hole between chambers.

Structural lesion

Altered blood pathway

Hypoxemia or overload

Clinical course

Slide 4 · Normal circulation depends on two ventricular outflows

Right atrium → right ventricle → pulmonary artery → lungs.

Systemic veins

RA

RV

Pulmonary trunk

Lungs

Body

Aorta

LV

LA

Pulmonary veins

Single series circuit: Systemic return → lungs → pulmonary venous return → aorta → tissues

Slide 5 · Atrioventricular concordance: Atrium to expected ventricle

Right atrium communicates with the morphologic right ventricle.

RA

RV

LA

LV

Slide 6 · Ventriculoarterial concordance: Expected arterial origins

Morphologic right ventricle gives rise to pulmonary trunk.

RV

Pulmonary trunk

LV

Aorta

Slide 7 · Discordance describes connections, not chamber position

AV discordance: An atrium connects to a ventricle of unexpected morphology.

Level

Concordant

Discordant

Atrioventricular

RA → RV; LA → LV

RA → morphologic LV; LA → morphologic RV

Ventriculoarterial

RV → PT; LV → aorta

RV → aorta; LV → PT

Slide 8 · TGA is a ventriculoarterial connection abnormality

Transposition of the great arteries produces ventriculoarterial discordance.

Variant

AV connection

VA connection

d-TGA

Concordant

Discordant

l-TGA

Discordant

Discordant

Slide 9 · How common is TGA in the Robbins CHD table?

Robbins Table 12.2 lists TGA at 388 per million live births.

Malformation

Per million live births

Share in source table

Ventricular septal defect

4,482

42%

Tetralogy of Fallot

577

5%

Transposition of great arteries

388

4%

Slide 10 · Right-to-left shunt: Why cyanosis develops

Systemic venous blood can bypass pulmonary oxygenation and enter the systemic arterial supply.

Arterial hypoxemia produces cyanosis of skin and mucous membranes.

D-TGA creates a different arrangement—parallel circuits—which likewise threatens systemic oxygen delivery.

Poorly oxygenated blood

Systemic arterial entry

Arterial hypoxemia

Cyanosis

Slide 11 · A shunt and a transposition are not synonyms

Shunt: An abnormal communication permitting flow between compartments.

Feature

Shunt

d-TGA

Primary anatomical problem

Communication across compartments

Discordant great-artery origins

Hemodynamic consequence

Flow along pressure gradient

Parallel systemic/pulmonary loops

Role of interconnection

Part of defect

Permits essential mixing

Slide 12 · Cardiac outflow development requires coordinated septation

Second-heart-field cells contribute to the cardiac outflow tract and right ventricle.

Neural crest–derived cells participate in aortic and pulmonary outflow tract septation.

This developmental context localizes d-TGA to great-vessel partitioning.

Cardiac progenitors

Outflow tract formation

Neural crest contribution

Separated arterial outlets

Slide 13 · Normal separation depends on spiraling septa

Formation of spiraling truncal and aortopulmonary septa.

RV

Pulmonary trunk

LV

Aorta

Slide 14 · D-TGA: Abnormal outflow septation changes arterial alignment

Abnormal development of the spiraling outflow septa is the textbook mechanism.

RV

Aorta

LV

Pulmonary trunk

Slide 15 · Embryologic explanation is not a genetic diagnosis

The d-TGA section attributes the defect to abnormal outflow septation.

Supported by the source

Not specified for TGA

• Disordered spiraling outflow septation

• Resultant VA discordance

• A disease-defining mutation

• A TGA-specific inheritance probability

Slide 16 · From arterial malposition to circulation in parallel

Aorta arising from RV returns systemic venous blood directly to systemic tissues.

Systemic loop — poorly oxygenated return

Pulmonary loop — oxygenated venous return

Systemic veins

Pulm. Veins

RA

LA

RV

LV

Aorta

PT

Body

Lungs

Parallel-loop schematic • PT = pulmonary trunk; Dashed arrows indicate recirculation

Slide 17 · D-TGA preserves both atrium–ventricle connections

Right atrium still enters morphologic right ventricle.

RA

RV

LA

LV

Slide 18 · D-TGA reverses the expected great-artery outlets

Aorta originates from the morphologic right ventricle.

RV

Aorta

LV

Pulmonary trunk

Slide 19 · Trace the systemic venous pathway in d-TGA

Systemic veins deliver poorly oxygenated blood to RA.

RA → RV remains anatomically concordant.

RV ejects into aorta: Blood can return to body without passage through lungs.

Systemic veins

Right atrium

Right ventricle

Aorta

Body

Slide 20 · Trace the pulmonary venous pathway in d-TGA

Oxygenated pulmonary venous blood enters LA.

LA → LV remains anatomically concordant.

LV ejects into the pulmonary trunk, sending blood toward lungs again.

Pulmonary veins

Left atrium

Left ventricle

Pulmonary trunk

Lungs

Slide 21 · D-TGA produces two circulations in parallel

Systemic circuit loops through RA–RV–aorta–body.

Systemic loop — poorly oxygenated return

Pulmonary loop — oxygenated venous return

Systemic veins

Pulm. Veins

RA

LA

RV

LV

Aorta

PT

Body

Lungs

Parallel-loop schematic • PT = pulmonary trunk; Dashed arrows indicate recirculation

Slide 22 · The systemic circuit recirculates venous blood

Oxygen-poor systemic return enters RA and RV.

Systemic veins

RA

RV

Aorta

Systemic tissues

Slide 23 · The pulmonary circuit recirculates oxygenated blood

Pulmonary veins deliver oxygenated blood to LA and LV.

Pulmonary veins

LA

LV

Pulmonary trunk

Lungs

Slide 24 · Why the two circuits cannot independently sustain life

Anatomical continuity from lungs to systemic aorta is absent in uncommunicating d-TGA.

Systemic loop — poorly oxygenated return

Pulmonary loop — oxygenated venous return

Systemic veins

Pulm. Veins

RA

LA

RV

LV

Aorta

PT

Body

Lungs

Parallel-loop schematic • PT = pulmonary trunk; Dashed arrows indicate recirculation

Slide 25 · Mixing is the determinant of immediate viability

Robbins explicitly relates survival to the degree of mixing between circuits.

Communication between loops

Systemic circuit

Systemic veins → RA → RV

→ aorta → body → systemic veins

Pulmonary circuit

Pulmonary veins → LA → LV

→ PT → lungs → pulmonary veins

Schematic mixing between circuits; The label identifies the communicating anatomical level.

Slide 26 · Three important sites for communicating flow

Atrial level: Patent foramen ovale (PFO), or an atrial communication.

Atrial level

PFO / ASD

Right ↔ left atrium

Ventricular level

VSD

Right ↔ left ventricle

Great-vessel level

PDA

Pulmonary artery ↔ aorta

Slide 27 · VSD permits interventricular mixing

A VSD connects the ventricles otherwise serving separated circuits.

VSD — ventricular level

Systemic circuit

Systemic veins → RA → RV

→ aorta → body → systemic veins

Pulmonary circuit

Pulmonary veins → LA → LV

→ PT → lungs → pulmonary veins

Schematic mixing between circuits; The label identifies the communicating anatomical level.

Slide 28 · PFO permits interatrial mixing

The patent foramen ovale is an opening between the atria.

PFO — atrial level

Systemic circuit

Systemic veins → RA → RV

→ aorta → body → systemic veins

Pulmonary circuit

Pulmonary veins → LA → LV

→ PT → lungs → pulmonary veins

Schematic mixing between circuits; The label identifies the communicating anatomical level.

Slide 29 · PDA permits great-vessel mixing

The ductus arteriosus joins pulmonary artery and aorta.

PDA — great-vessel level

Systemic circuit

Systemic veins → RA → RV

→ aorta → body → systemic veins

Pulmonary circuit

Pulmonary veins → LA → LV

→ PT → lungs → pulmonary veins

Schematic mixing between circuits; The label identifies the communicating anatomical level.

Slide 30 · Shunt anatomy predicts stability of blood mixing

Patients with VSD against those dependent on PFO or PDA.

Mixing pathway

Clinical implication in d-TGA

VSD

Often a relatively stable shunt

PFO

Communication vulnerable to functional closure

PDA

Communication vulnerable to physiological closure

Slide 31 · Do not mistake mixing proportions for survival probabilities

The source cites VSD in approximately 35% of d-TGA patients.

Reported arrangement

Approximate share

Meaning

d-TGA with VSD

35%

Ventricular mixing pathway

PFO/PDA-dependent mixing

65%

Vulnerable postnatal pathways

Slide 32 · Postnatal transition can close a vital shunt

In term infants, the ductus normally constricts within 1–2 days of birth.

At birth, lower pulmonary vascular pressure contributes to foramen ovale closure.

These normal events can sharply reduce mixing in d-TGA.

Birth and lung expansion

Falling pulmonary resistance

Atrial/ductal closure

Less mixing

Severe hypoxemia

Slide 33 · Why closure of the ductus is dangerous in d-TGA

Ductus patency allows connection between aorta and pulmonary trunk.

Functional closure removes that communication.

If other mixing sites are inadequate, systemic oxygenation deteriorates rapidly.

PDA open

Great-vessel communication

PDA closes

Communication lost

Oxygen delivery falls

Slide 34 · A closing foramen ovale creates a similar risk

The fetal foramen ovale normally permits right-to-left atrial passage.

Postnatal changes in atrial pressures favor flap closure.

A d-TGA infant dependent on this pathway can lose crucial interatrial mixing.

Atrial communication

Postnatal pressure change

Flap closes

Mixing falls

Hypoxia worsens

Slide 35 · Hypoxemia is a circuit problem, not merely poor lung function

Pulmonary blood can still become oxygenated in the lung circuit.

Systemic loop — poorly oxygenated return

Pulmonary loop — oxygenated venous return

Systemic veins

Pulm. Veins

RA

LA

RV

LV

Aorta

PT

Body

Lungs

Parallel-loop schematic • PT = pulmonary trunk; Dashed arrows indicate recirculation

Slide 36 · Three determinants of outcome in d-TGA

Extent of blood mixing between parallel circulations.

Severity of tissue hypoxia from inadequate systemic oxygen delivery.

Ability of the morphologic right ventricle to sustain systemic circulation.

Mixing adequacy

Tissue oxygenation

Systemic RV performance

Clinical outcome

Slide 37 · Early cyanosis reflects inadequate oxygenated systemic flow

TGA is grouped with cyanotic congenital heart lesions.

Mixing failure allows poorly oxygenated blood to supply systemic arteries.

Presentation may become critical as transitional interconnections close.

Parallel loops

Inadequate mixing

Arterial hypoxemia

Cyanosis

Slide 38 · A VSD can stabilize the newborn circulation

A persistent interventricular opening connects the two pathways.

Persistent VSD: Stable mixing

Systemic circuit

Systemic veins → RA → RV

→ aorta → body → systemic veins

Pulmonary circuit

Pulmonary veins → LA → LV

→ PT → lungs → pulmonary veins

Schematic mixing between circuits; The label identifies the communicating anatomical level.

Slide 39 · PFO/PDA dependence creates a narrow intervention window

The source describes closure of these communications early after birth.

Loss of mixing poses an immediate physiological threat.

An intervention to establish communication may be required in the first days of life.

PFO / PDA mixing

Postnatal closure

Mixing failure

Urgent communication

Slide 40 · Balloon atrial septostomy: Physiological objective

Balloon atrial septostomy as an early intervention.

Created atrial communication

Systemic circuit

Systemic veins → RA → RV

→ aorta → body → systemic veins

Pulmonary circuit

Pulmonary veins → LA → LV

→ PT → lungs → pulmonary veins

Schematic mixing between circuits; The label identifies the communicating anatomical level.

Slide 41 · The morphologic right ventricle becomes systemic

In d-TGA, RV pumps directly into the aorta.

RV

Systemic aorta

LV

Pulmonary trunk

Slide 42 · Systemic loading produces right ventricular hypertrophy

The source states that RV hypertrophy becomes prominent over time.

This is a response to maintaining the high-pressure systemic circulation.

The hypertrophy is an acquired hemodynamic consequence, not an additional connection anomaly.

RV → aorta

Systemic pressure load

Myocyte enlargement

RV hypertrophy

Slide 43 · Pulmonary loading produces left ventricular thinning

The morphologic LV supplies the lower-resistance pulmonary circuit.

Over time, a thin-walled, atrophic LV.

The remodeling direction is opposite to that of the systemic RV.

LV → pulmonary trunk

Low-resistance circuit

Lower workload

LV thinning / atrophy

Slide 44 · D-TGA ventricular remodeling is asymmetric

Right ventricle: Systemic pressure work → hypertrophy.

Morphologic RV

Morphologic LV

• Ejects into aorta

• Maintains systemic circulation

• Progressive hypertrophy

• Ejects into pulmonary trunk

• Supports lower-resistance circuit

• Progressive thinning / atrophy

Slide 45 · Without surgical correction, natural history is severe

Most infants with untreated d-TGA die within months.

Critical limitations are systemic hypoxia and sustaining systemic output.

A transiently successful shunt is not definitive anatomical correction.

Discordant arteries

Mixing dependence

Persistent systemic hazard

Early mortality

Slide 46 · Definitive surgery restores the arterial pathway

Early surgery that repositions the aorta and pulmonary artery.

RV

Pulmonary trunk

LV

Aorta

Slide 47 · Interim mixing and definitive correction solve different problems

Balloon atrial septostomy increases communication between parallel streams.

Approach in source

Immediate objective

Changes great-artery origins?

Balloon atrial septostomy

Improve intercirculatory mixing

No

Great-artery repositioning

Correct outlet alignment

Yes

Slide 48 · Why survival into adulthood is now possible

Untreated d-TGA has a very poor natural history in the source.

Earlier stabilization and surgical correction alter that course.

Many operated patients now reach adulthood.

Early recognition of mixing need

Stabilization / communication

Surgical correction

Adult survival possible

Slide 49 · L-TGA adds atrioventricular discordance

Less common l-TGA is also called congenitally corrected transposition.

Connection level

l-TGA arrangement

Right atrial inflow

RA → morphologic LV

Left atrial inflow

LA → morphologic RV

Ventricular arterial outlets

Morphologic LV → PT; morphologic RV → aorta

Slide 50 · Right atrium drains into the morphologic left ventricle

In l-TGA, the right atrium connects to an LV by internal morphology.

RA

Morphologic LV

Morphologic LV

Pulmonary trunk

Slide 51 · Left atrium drains into the morphologic right ventricle

The left atrium connects to a morphologic right ventricle.

LA

Morphologic RV

Morphologic RV

Aorta

Slide 52 · Double discordance produces physiological correction

AV discordance sends venous blood into the morphologic LV and oxygenated blood into RV.

Systemic veins

RA

Morphologic LV

Pulmonary trunk

Lungs

Body

Aorta

Morphologic RV

LA

Pulmonary veins

Physiological series pathway persists despite two discordant connection levels

Slide 53 · Why uncomplicated l-TGA need not cause cyanosis

The right atrial stream reaches lungs through a morphologic LV.

Systemic veins

RA

Morphologic LV

Pulmonary trunk

Lungs

Body

Aorta

Morphologic RV

LA

Pulmonary veins

Physiological series pathway persists despite two discordant connection levels

Slide 54 · Congenital correction does not mean a normal heart

Physiologically useful blood flow masks two anatomical discordances.

Physiological benefit

Anatomical liability

• Oxygenated blood reaches aorta

• No intrinsic cyanosis from discordance alone

• Systemic morphologic RV

• Potential progressive heart failure

Slide 55 · Congenitally corrected TGA may remain asymptomatic

Some people have no early symptoms.

The diagnosis may be made during evaluation for another cardiac concern in adulthood.

Absence of cyanosis must not be taken as proof of normal cardiac connections.

Double discordance

Physiologically adequate flow

Silent childhood possible

Adult recognition

Slide 56 · The morphologic RV is exposed to systemic loading

The morphologic RV empties into the aorta in l-TGA.

Longstanding systemic loading produces ventricular hypertrophy.

The same chamber is the long-term vulnerable systemic pump.

Morphologic RV → aorta

Chronic systemic workload

RV hypertrophy

Risk of failure

Slide 57 · Systemic RV failure is a late clinical consequence

L-TGA can eventually cause heart failure.

The consequence follows long-term reliance on the morphologic RV for systemic output.

Early clinical quiescence and late ventricular dysfunction are compatible.

Functioning circulation

Systemic RV overload

Hypertrophy

Possible heart failure

Slide 58 · Other congenital defects frequently coexist with l-TGA

The source explicitly lists ventricular septal defect (VSD).

Associated defect

Anatomical level

VSD

Interventricular communication

ASD

Atrial septal communication

PFO

Persistent fetal interatrial flap channel

Slide 59 · Morphologic identity—not ventricular side—sets the terminology

In l-TGA, the ventricle connected to RA has left-ventricular morphology.

RA

Morphologic LV

LA

Morphologic RV

Slide 60 · D-TGA versus l-TGA: Anatomic logic

D-TGA has one discordant connection level: Ventriculoarterial.

Anatomical level

d-TGA

l-TGA

Atrioventricular

Concordant

Discordant

Ventriculoarterial

Discordant

Discordant

Net arrangement

Parallel circuits

Physiological series circulation

Slide 61 · D-TGA versus l-TGA: Clinical and ventricular consequences

D-TGA: Urgent mixing dependence and early cyanosis.

Feature

d-TGA

l-TGA

Immediate oxygenation

Mixing needed

Usually maintained

Typical source-described course

Critical infancy untreated

Can be silent until adulthood

Morphologic RV

Systemic pump; hypertrophy

Systemic pump; hypertrophy/failure

Slide 62 · TGA and tetralogy of Fallot: Different mechanisms of cyanosis

TOF combines VSD, RV outflow obstruction, overriding aorta, and RV hypertrophy.

Disease

Primary anatomy

Why hypoxemia occurs

Tetralogy of Fallot

VSD plus RV outflow obstruction and overriding aorta

Right-to-left shunt across VSD when obstruction severe

d-TGA

RA→RV→aorta; LA→LV→PT

Inadequate mixing of parallel loops

Slide 63 · PDA: A lesion by itself, a lifeline in d-TGA

Isolated PDA ordinarily creates abnormal flow between aorta and pulmonary artery.

Isolated PDA context

D-TGA context

• Persistent great-vessel connection

• Often left-to-right flow initially

• Bridge between parallel loops

• Closure can sharply impair oxygenation

Slide 64 · Read a congenital cardiac diagram in four checks

Identify atrial return: Which atrium receives systemic versus pulmonary veins?

Trace atrium-to-morphologic-ventricle connections.

Trace each ventricle to pulmonary trunk or aorta.

Venous inflows

AV identity

Great-artery origins

Series vs parallel

Mixing sites

Slide 65 · Case: Neonatal cyanosis with closing ductus

A newborn has d-TGA without an appreciable VSD; Ductal mixing has been maintaining systemic oxygenation.

PDA closing: Mixing threatened

Systemic circuit

Systemic veins → RA → RV

→ aorta → body → systemic veins

Pulmonary circuit

Pulmonary veins → LA → LV

→ PT → lungs → pulmonary veins

Schematic mixing between circuits; The label identifies the communicating anatomical level.

Slide 66 · Case interpretation: Ductal closure eliminates a bridge

D-TGA circuits remain parallel; Lung oxygenation does not by itself supply aorta.

Closure of the PDA reduces cross-circuit communication.

The source supports urgent creation of another mixing route, e.g., atrial septostomy.

PDA closes

Communication lost

Systemic hypoxemia

Atrial mixing intervention

Slide 67 · Case: Adult without cyanosis but a systemic morphologic RV

An adult evaluated for another cardiac concern has RA → morphologic LV and LA → morphologic RV.

Systemic veins

RA

Morphologic LV

Pulmonary trunk

Lungs

Body

Aorta

Morphologic RV

LA

Pulmonary veins

Physiological series pathway persists despite two discordant connection levels

Slide 68 · Case interpretation: L-TGA with systemic RV vulnerability

The two discordant connection levels establish congenitally corrected l-TGA.

Effective series flow explains the absence of intrinsic cyanosis.

The systemic morphologic RV may hypertrophy and eventually fail.

AV discordance

VA discordance

Physiological correction

Systemic RV failure risk

Slide 69 · Case: Communication present despite abnormal outflow

A d-TGA newborn has a VSD providing stable intercirculatory mixing.

VSD permits mixing; Arteries remain discordant

Systemic circuit

Systemic veins → RA → RV

→ aorta → body → systemic veins

Pulmonary circuit

Pulmonary veins → LA → LV

→ PT → lungs → pulmonary veins

Schematic mixing between circuits; The label identifies the communicating anatomical level.

Slide 70 · Case interpretation: Physiological bridge is not repair

A VSD can improve mixing without changing RV–aorta and LV–pulmonary artery origins.

Observed feature

Interpretation

VSD mixing

Acute physiological benefit

Persistent VA discordance

Uncorrected anatomical lesion

Arterial repositioning

Definitive anatomic correction in source

Slide 71 · Integrate anatomy, physiology and outcome

D-TGA: VA discordance with AV concordance → parallel loops → mixing-dependent neonatal survival.

Variant

Anatomy

Physiology

Dominant risk

d-TGA

AV concordant; VA discordant

Parallel circuits

Critical hypoxemia without mixing

l-TGA

AV and VA discordant

Physiological series flow

Systemic RV failure over time

Slide 72 · Primary reading

Robbins, Cotran & Kumar

Pathologic Basis of Disease • 11th edition (2026)

The Heart — Congenital Heart Disease

Review the sections on right-to-left shunts, transposition, and related congenital lesions.