Coarctation of the aorta takes the form of an hour-glass shaped narrowing of varying length or of a membrane-type stenosis. It is located after the left subclavian artery root, just upstream of the ligamentum arteriosum (Video and Figures 14.71 and 14.72).


Video: Long-axis view (90°) of the descending aorta with a coarctation; colour flow shows a prestenotic acceleration zone (on the right of the screen) and a turbulent high-velocity flow distal to the stenosis (towards the left handside of the screen).

It occurs in 0.3% of births and in 5-7% of congenital heart disease cases [2]. In half of all cases involving young children, it is associated with a bicuspid aortic valve, VSD, AV canal defect, hypoplastic aortic arch, or patent ductus arteriosus. It is characterised by hypertension in the upper limbs and hypotension in the lower limbs.




Figure 14.71: Anatomical diagram showing coarctation of the aorta. PDA: patent ductus arteriosus (pink) LCA: left carotid artery. LSCA: left sub-clavian artery. The loop of the left recurrent laryngeal nerve is in the operating field.

If the coarctation is very narrow at birth, post-ductal perfusion is only possible via the patent ductus arteriosus (PDA) from the pulmonary blood flow (R-to-L shunt). A prostaglandin infusion is required to maintain sufficient flow through PDA (PGE1 0.01-0.05 mcg/kg/min). In such circumstances, the RV is connected to lower-body systemic pressure. The lower part of the body is hypoperfused and cyanotic. Splanchnic ischaemia and metabolic acidosis tend to creep in. Correction must be performed within days of birth before the LV becomes dysfunctional due to excessive afterload and before the patent ductus arteriosus closes.

In simple cases, the pressure gradient is over 35 mmHg. The coarctation imposes very high afterload on the LV, which hypertrophies concentrically as in aortic stenosis and may fail in the first years of life. An extensive collateral system of periscapular, internal mammary, cervical and intercostal arteries ensures perfusion below the lesion. This is visible on an angiogram from the age of 2 months. Dilated intercostal arteries create notches, which can be seen on the lower border of the ribs on a chest X-ray from the age of 5-8 years. A rough systolic murmur is audible along the left sternal border and in the back.



Figure 14.72: Coarctation of the aorta. A: membrane at the site of the isthmus. B: colour flow Doppler with a concentric acceleration zone (proximal isovelocity surface area PISA) upstream and turbulence downstream of the membrane (arrow). The aortic flow moves from right to left.

Surgery is indicated if the narrowing represents > 50% of the lumen or the pressure gradient is > 20 mmHg. Percutaneous dilation is the preferred treatment for children with suitable anatomy. It is less invasive and eliminates the risk of aortic clamping and medullary ischaemia [8]. However, in neonates, outcomes are improved by surgical resection [7]. The main risk of surgery is aortic clamping. Risk is dependent on the density of intercostal collaterals bypassing the stenosis. It increases if the pressure gradient between the right arm and the lower limbs is low, since in this case, there is little development of collateralisation. The stenosis is usually short and anastomosis can be performed end-to-end. A patch made from the subclavian artery or preferably from a synthetic fabric prevents residual stenosis. If the lesion is long, resection is advised and a tubular bypass graft is necessary, with CPB support in most cases. The risk of relapse is 5-8% irrespective of the technique used [7].

During clamping (< 20 minutes), upstream pressure is measured in the right arm (radial catheter) and downstream pressure is measured in a lower limb (pressure cuff or femoral catheter). Distal pressure below the clamp must be maintained ≥ 30 mmHg in neonates and ≥ 50 mmHg in children with arterial vasoconstrictors (norepinephrin, phenylephrine) to facilitate pressure-dependent flow through the collaterals and to limit the risk of medullary ischaemia. A hypertensive crisis above the clamp (160-200 mmHg) is less dangerous than distal hypotension. Postoperatively, a drop in diastolic pressure and a sudden rise in ETCO₂ are good indicators of the disappearance of the pressure gradient. The incidence of postoperative paraplegia secondary to medullary ischaemia is 0.1-0.4% of patients [3,7].

Anaesthesia

These cases are managed differently depending on whether they involve extreme coarctation in neonates or minimally symptomatic lesions in older children [4].

Surgery is performed through a left-sided thoracotomy. Monitoring comprises two SpO₂ sites (right arm and foot), an arterial catheter in the right radial artery and a pressure cuff or femoral catheter in the lower limb. The left radial artery cannot be used as the left subclavian artery is generally held in the proximal aortic clamp. Conventional balanced anaesthesia is applied (e.g. fentanyl-sevoflurane-rocuronium). If the child is of an appropriate age, a double-lumen tube is used to keep the left lung deflated. Intercostal infiltration of a local anaesthetic (bupivacaine 0.25%) is used to improve postoperative analgesia even though a thoracic epidural is more effective. An intrathoracic catheter for administering local anaesthetics is an elegant alternative. Having received effective pain relief, the child can be extubated on the operating table.

Numerous complications may occur.
 

 

Coarctation of the aorta

Characteristics:     - Narrow lesion in neonates: distal perfusion is provided by the patent ductus arteriosus     - Arterial hypertension in the upper limbs, arterial hypotension in the lower limbs (ΔP > 20 mmHg)     - Concentric LVH     - Thoracic collateral system Anaesthesia recommendations:     - SpO2 measurements in the right arm and lower limb     - Pre-ductal arterial pressure measured in the right arm (radial catheter), post-ductal pressure measured in the lower limb (pressure cuff or femoral         catheter)     - During clamping: maintain post-ductal pressure > 60 mmHg (alpha vasoconstrictor)     - Post-clamping: hypertensive crisis, mesenteric arteritis, risk of paraplegia

 

© BETTEX D, BOEGLI Y, CHASSOT PG, June 2008, last update May 2018
 

 

References