Coarctation of the Aorta Flashcards
1
Q
What is CoAo of the Aorta?
A
- 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
2
Q
Common associated CHDs with CoAo?
A
- BAV (50% CoAo)
- Congenital AS (any level)
- VSD
- PDA
- Part of Shone syndrome
3
Q
Common associated syndromes with CoAo?
A
- Goldenhar syndrome
- Turner syndrome
4
Q
What are the two proposed mechanisms for the aetiology of CoAo?
A
- Ectopic Ductal Tissue Theory
- Reduced-Flow (Haemodynamic) Theory
5
Q
Mechanism for CoAo based on ectopic ductal tissue theory?
A
- 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
6
Q
Mechanism for CoAo based on reduced flow theory?
A
- 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
7
Q
Sites of CoAo?
A
- Pre-ductal (before ductus arteriosus)
- Juxta-ductal (at ligament arteriosum)
- Post-ductal (after ductus arteriosus)
8
Q
Types of CoAo?
A
- Discrete stenosis (most common)
- Tubular hypoplasia (associated with LVOTOB or VSD)
- Pseudo-coarct (non-obstructive kinking or buckling of aorta distal to origin of left subclavian artery; usually seen on CT or CMR)
9
Q
Diagnosing CoAo with echo?
A
- 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
10
Q
Assessing severity of CoAo?
A
- 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)
11
Q
Expanded Bernoulli Equation?
A
- Pressure gradient = 4(V2^2 - V1^2)
- Use when V1 ≥ 1.2m/s
12
Q
Limitation of CoAo Pressure Gradient: Collaterals?
A
- 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
13
Q
Limitation of CoAo Pressure Gradient: PDA?
A
- PDA: blood shunted from aorta to PA
- Therefore, blood flow across CoAo diminished
- Pressure gradient across CoAo reduced and severity may be underestimated
14
Q
False Negatives and False Positives: CoAo?
A
- 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
15
Q
Severe CoAo: CW Descending Aorta?
A
- 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
