CardiologyTier 2Disease (DEADMAN)

Congenital heart disease - transposition of the great arteries

Description

d-TGA (complete / dextro-TGA)

Ventriculo-arterial discordance with atrioventricular concordance
- RA -> RV -> aorta; LA -> LV -> pulmonary artery
-> two circulations in parallel, not in series
- -> deoxygenated blood recirculates systemically; oxygenated blood recirculates pulmonary
- -> *incompatible with life unless the circulations mix* (PFO/ASD, VSD, PDA)
Aorta lies anterior and to the right of the pulmonary artery

ccTGA (congenitally corrected / levo-TGA)

Double discordance: AV and ventriculo-arterial
- RA -> morphological LV -> pulmonary artery; LA -> morphological RV -> aorta
-> physiologically "corrected" - circulation is in series, patient is acyanotic
-> but the morphological RV is the systemic ventricle for life - eventual systemic ventricular failure and systemic (tricuspid) AV valve regurgitation
Often presents in adulthood with heart failure or complete heart block

d-TGA ~5% of congenital heart disease, ~1 in 3,500 live births
M>F (~2:1)
ccTGA ~0.5% of congenital heart disease - rare
Risk factors: maternal diabetes, maternal rubella, maternal age
Recurrence risk in siblings ~2%
Nearly all Australian adults with d-TGA now had an arterial switch in infancy; patients over ~40 had an atrial switch**

Failure of normal spiralling of the aorticopulmonary septum during conotruncal development
- -> straight rather than spiral septation -> aorta arises from the RV
Associated with abnormal neural crest cell migration
Usually sporadic; associated with laterality/heterotaxy genes (ZIC3, NODAL, CFC1) and maternal diabetes

Associated lesions (d-TGA)

ccTGA associations

VSD (~70%), pulmonary stenosis (~40%), Ebstein-like malformation of the systemic (tricuspid) valve (~90%)
Complete heart block - 2%/yr cumulative (abnormal AV node and elongated His bundle)

d-TGA - neonatal presentation

Profound cyanosis within hours of birth, worsening as the duct closes
Cyanosis without respiratory distress; hyperoxia test fails (PaO2 stays <100 mmHg on 100% O2)
Single loud S2, often no murmur (a murmur suggests VSD or LVOT obstruction)
CXR: "egg on a string" - narrow mediastinum from the anteroposterior great vessel relationship, increased pulmonary vascularity
Echocardiography is diagnostic - parallel great arteries, ventriculo-arterial discordance, coronary anatomy

ccTGA - adult presentation

Often incidental: abnormal ECG, murmur, or cardiomegaly
ECG: reversed septal activation -> Q waves in the right precordial leads (V1-V3) and absent in V5-V6; varying degrees of AV block
Systemic AV valve (tricuspid) regurgitation murmur
Cardiac MRI to define ventricular morphology, systemic RV function and volumes

Adult follow-up imaging

TTE - systemic ventricular function, AV valve regurgitation, baffle/conduit assessment
CMR - gold standard for systemic RV volumes and function, baffle anatomy, fibrosis
CT - stents, coronary assessment post-arterial switch
CPET - objective functional capacity, serial trend
Ambulatory ECG - atrial arrhythmia and sinus node dysfunction post-atrial switch

A. Neonatal stabilisation (d-TGA)

Prostaglandin E1 infusion - keep the duct open -> mixing
- Watch for apnoea; be ready to intubate
Balloon atrial septostomy (Rashkind) - tears the atrial septum to create mixing
Correct acidosis; avoid excess oxygen (constricts the duct)

B. Definitive surgery - arterial switch (Jatene), within the first 1-2 weeks of life

Great arteries transected and swapped; the coronary arteries must be re-implanted into the neo-aorta
- Coronary transfer is the technically demanding, prognosis-determining step
Must be done before the LV "deconditions" against low pulmonary resistance (after ~2-3 weeks the LV cannot support systemic pressure without banding/staged repair)
Operative survival now >95%; excellent long-term outcome

C. Historical - atrial switch (Mustard or Senning)

An intra-atrial baffle redirects venous return at atrial level
- Systemic venous blood -> LV -> pulmonary artery; pulmonary venous blood -> RV -> aorta
Leaves the morphological RV supporting the systemic circulation for life
Still the operation in adults born before the late 1980s - recognise them by the sternotomy scar, age and complication profile

D. ccTGA

Anatomical repair ("double switch") in selected children: atrial switch + arterial switch, restoring the LV to the systemic circulation
Otherwise: treat the systemic RV failure and systemic AV valve regurgitation
Pacemaker for AV block (and take care at any surgery - the conduction system is in an abnormal position)

E. Adult congenital management - lifelong specialist ACHD care

Systemic RV failure (post-atrial switch or ccTGA)
- Conventional HFrEF therapy has weak evidence in a systemic RV - beta blockers, ACEi/ARB and MRA are used but trial data are limited; SGLT2 inhibitors are increasingly used
- CRT and transplantation in advanced disease
Arrhythmia - atrial tachycardia/intra-atrial re-entry is common post-atrial switch and poorly tolerated; ablation is complex (access to the pulmonary venous atrium is through the baffle)
Anticoagulation for atrial arrhythmia
Endocarditis prophylaxis for prosthetic material/conduits
Pregnancy - high risk with a systemic RV or moderate-severe dysfunction; pre-conception counselling, ACHD-led care
Exercise: encourage; restrict competitive/isometric sport if significant dysfunction or arrhythmia

Post-atrial switch (Mustard/Senning) - late problems
- Systemic RV failure and systemic (tricuspid) AV valve regurgitation
- Sinus node dysfunction (~50% lose sinus rhythm) and atrial tachyarrhythmia -> pacing often needed
- Sudden cardiac death (arrhythmic, in the context of systemic RV dysfunction)
- Baffle obstruction (SVC or IVC limb -> venous congestion) or baffle leak (-> shunt, paradoxical embolus)
- Pulmonary hypertension
Post-arterial switch (Jatene) - late problems
- Coronary compromise at the re-implantation sites -> ischaemia, silent infarction, sudden death
- Neo-aortic (formerly pulmonary) valve regurgitation and root dilatation
- Neo-pulmonary (supravalvular) stenosis and branch pulmonary artery stenosis - at the LeCompte manoeuvre site
- Arrhythmia less common than after atrial switch
ccTGA - progressive complete heart block (2%/yr), systemic RV failure, Ebstein-like tricuspid regurgitation

Untreated d-TGA: ~90% mortality in the first year
Arterial switch: survival >90% at 20-25 years, most in NYHA I with normal exercise capacity
- The morphological LV is the systemic ventricle - this is why it is the superior operation
Atrial switch: survival ~75-80% at 25 years; progressive systemic RV failure dominates
ccTGA: systemic RV failure in most by the 5th-6th decade; worse if there is significant tricuspid regurgitation or an associated VSD

Surveillance

Lifelong ACHD review, at least annually in complex or symptomatic patients
Echo +/- CMR, ambulatory ECG, CPET (serial peak VO2 trend is a good early marker of decline)
Ischaemia assessment post-arterial switch - coronary imaging at transition to adult care and if symptoms
The commonest error in adult practice is managing these patients as though the anatomy were normal - always establish which operation they had

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