Coarctation of the Aorta

Question 1

What is CoAo of the Aorta?

Answer 1

• Characterised by discrete narrowing in descending aorta, just distal to left subclavian artery and adjacent to ligament arteriosum
• Accounts for around 6-8% of CHD
• Anatomic variation include location and type of narrowing
• CoAo may occur a a long segment stenosis or diffuse hypoplasia, and rarely may occur in ascending or abdominal aorta

Question 2

Common associated CHDs with CoAo?

Answer 2

• BAV (50% CoAo)
• Congenital AS (any level)
• VSD
• PDA
• Part of Shone syndrome

Question 3

Common associated syndromes with CoAo?

Answer 3

• Goldenhar syndrome
• Turner syndrome

Question 4

What are the two proposed mechanisms for the aetiology of CoAo?

Answer 4

1. Ectopic Ductal Tissue Theory
2. Reduced-Flow (Haemodynamic) Theory

Question 5

Mechanism for CoAo based on ectopic ductal tissue theory?

Answer 5

• Muscle tissue of ductus arteriosus ‘invades’ wall of aorta just distal to aortic isthmus
• When DA contracts after birth, ductal muscle in aorta also contracts, forming a shelf or indentation in descending thoracic aorta

Question 6

Mechanism for CoAo based on reduced flow theory?

Answer 6

• CoAo occurs due to reduced flow in aortic isthmus during foetal circulation
• Failure or aortic isthmus to enlarge after birth = narrowing persists as a coarctation
• Following closure of PDA, isthmus normally enlarges until it is the same diameter as aorta on either side of it, however, if this enlargement doesn’t occur –> narrowing persists as a coarctation

Question 7

Sites of CoAo?

Answer 7

1. Pre-ductal (before ductus arteriosus)
2. Juxta-ductal (at ligament arteriosum)
3. Post-ductal (after ductus arteriosus)

Question 8

Types of CoAo?

Answer 8

1. Discrete stenosis (most common)
2. Tubular hypoplasia (associated with LVOTOB or VSD)
3. Pseudo-coarct (non-obstructive kinking or buckling of aorta distal to origin of left subclavian artery; usually seen on CT or CMR)

Question 9

Diagnosing CoAo with echo?

Answer 9

• CoAo diagnosis base on visualisation of shelf-like narrowing of aorta or tissue ridge extending into aortic lumen
• Best visualised from suprasternal window
• CFI confirms CoAo; turbulent flow through region of narrowing

Question 10

Assessing severity of CoAo?

Answer 10

• Measure peak velocity and maximum PG across narrowing using CW
• Simplified Bernoulli equation: PG = 4V^2 (can only use when velocity of flow proximal to the narrowing, V1, is < 1.2m/s)

Question 11

Expanded Bernoulli Equation?

Answer 11

• Pressure gradient = 4(V2^2 - V1^2)
• Use when V1 ≥ 1.2m/s

Question 12

Limitation of CoAo Pressure Gradient: Collaterals?

Answer 12

• Collateral circulation: blood flow diverted to internal thoracic and intercostal arteries
• Therefore, blood flow effectively bypasses CoAo
• Pressure gradient across CoAo reduced and severity may be underestimated

Question 13

Limitation of CoAo Pressure Gradient: PDA?

Answer 13

• PDA: blood shunted from aorta to PA
• Therefore, blood flow across CoAo diminished
• Pressure gradient across CoAo reduced and severity may be underestimated

Question 14

False Negatives and False Positives: CoAo?

Answer 14

• False positive: aorta images from oblique plane - ‘pseudo shelf’
• False negative: inability to image distal descending thoracic aorta (CoAo site missed)
• Incidence of false +/-ives reduced by using CW Doppler and CFI to interrogate descending aorta

Question 15

Severe CoAo: CW Descending Aorta?

Answer 15

• Persistent PG across narrowing over both systole and diastole
• Diastolic tail/saw-tooth pattern suggests severe stenosis and collateral circulation which is clinically significant irrespective of peak velocity

Question 16

Normal vs Severe CoAo: PW Abdominal Aorta?

Answer 16

• Normal: rapid upstroke in early systole with flow terminating at end T-wave on ECG
• Severe CoAo: forward flow velocity blunted, slow upstroke, so time to peak systolic velocity is delayed, and persistent forward flow throughout diastole
• Note: diastolic flow can also be seen with CFI

Question 17

CoAo is significant when?

Answer 17

Mean Doppler systolic gradient:
- > 20mmHg
- > 10mmHg + either deceased LV systolic function or AR
- > 10mmHg with collateral flow

• These findings in conjunction with systemic HTN, upper extremity to lower extremity BP differences and anatomic evidence of CoAo provide best evidence for intervention and surgery

Question 18

Percutaneous repair of CoAo?

Answer 18

• Stent
• Balloon angioplasty

Question 19

Surgical repair of CoAo?

Answer 19

• End to end anastomosis
• Patch repair

Question 20

Post repair CoAo echo needs to assess?

Answer 20

• LV size, systolic function, wall thickness and evaluation of repair site
• Identify potential post-op complications such as re-coarctation, and formation of an aortic aneurysm (best evaluated by CMR)
• Consider aortic arch remodelling

Question 21

Types of aortic arch remodelling?

Answer 21

1. Gothic arch: angular geometry (Doppler assessment difficult due to acute angle of arch - parallel alignment not possible)
2. Crenel arch: rectangular shape
3. Romanesque arch: smooth round shape similar to normal arch anatomy