Arterial hypertension is a slow killer. A severe coarctation presenting in the neonatal period is frequently associated with hypoplasia of the aortic arch, which is proof of earlier poor foetal flow. Many hypoplastic segments after coarctation repair will show good outgrowth, probably due to enhanced flow through the arch. Early repair during infancy optimises arch growth, while late repair increases the risk of residual hypoplasia and late arterial hypertension.1 The incidence of re-coarctation or arch hypoplasia after surgical repair is related to the age at repair, type of repair and the definition of re-coarctation used.2 Neonatal surgical repair now aims to treat hypoplastic segments by extended end-to-end repair. However, even after a successful coarctectomy some gradient over the arch may persist during growth in about one-third of patients: a narrowed arch segment, a high cervical arch, an abnormal winding or an acute-angled cross may persist.3 Such a gradient over the arch will predispose to and enhance arterial hypertension,4 exposing these patients to increased cardiovascular risk with ‘premature’ morbidity and mortality beyond the fourth decade.5,6 Coronary artery disease and cerebral bleeding are the most common causes of ‘premature’ late death after ‘successful’ coarctation repair, and late systemic hypertension is largely held responsible for this. Therefore, the clinician should aim for an aortic arch free of any gradient.
Treatment Options – Medical, Surgical, Interventional
Recent guidelines define significant residual or re-coarctation in adults as “resting or exercise-induced hypertension and a resting arm/leg blood pressure gradient ≥30mmHg”.7 Patients with mild residual gradients at rest would not be considered for re-intervention based on these guidelines, but still have elevated blood pressures that require attention. Medical treatment alone can decrease blood pressure, but when an anatomical lesion is present often very high doses of antihypertensive drugs are needed, not infrequently associated with significant side effects during long-term follow-up. Surgical options to treat residual hypoplasia of the aortic cross and/or isthmus consist of extensive aortic arch reconstruction under complex cardiopulmonary bypass, an ascending aorta to thoracic aorta crossover or placement of an ascending aorta to abdominal aorta conduit. These surgical procedures have some morbidity and mortality, including a long hospitalisation, a significant rehabilitation period and a relatively high cost. Suggesting such major operations for only mild residual aortic arch narrowing could be considered ‘overkill’. Balloon angioplasty alone can be efficient in some narrowed vessels by making a controlled non-transmural tear in the vessel wall.
However, this technique is usually unsuccessful in these aortic lesions. It is nearly impossible to make a safe, satisfactory non-transmural tear with lasting result because of elastic recoil or unfavourable anatomy, such as long tubular narrowing, hypoplasia, angulation or only mild obstruction that requires large balloons.8 In contrast, expansion of small segments with a stent can address these concerns appropriately.
Stenting a Hypoplastic Aortic Segment – Technique9
The stent procedure is preferably delayed until the stent can be deployed up to a near-adult size. An angiogram perpendicular to the hypoplastic segment is made (mostly mid-left anterior oblique view), and a long and stiff guidewire is advanced into the ascending aorta or the left ventricle. The diameter of the balloon is chosen to be between the aortic diameter proximal to the hypoplastic segment and the diameter of the descending aorta at the level of the diaphragm. Stent delivery occurs through a long 11 or 12 French Mullins sheath on a BIB (Balloon-In-Balloon®, Numed, NY, US). This balloon allows sequential inflation–expansion of the stent, thereby preventing slipping of the stent from the balloon during initial inflation, and allows repositioning of the stent before full deployment. The stent is manually crimped onto a vacuumised balloon. It is important to choose a stent that is able to reach adult-size aorta (18–20mm) without significant shortening, which may cause dislocation or distal vessel tear. Stent length is determined by the length of the desired segment to stent, taking shortening during expansion into consideration. If the ends of the stent might protrude over the origin of a neck vessel, we prefer to use the Cheatham Platinum stent (Numed, NY, US). Due to the structure of this stent, the distal end struts can be opened or flared separately as required. Covered stents can be considered if no neck vessel is at risk of exclusion.
The origin of the left subclavian artery can electively be crossed with the stent, but no late redilation should be required compared with infra (see below on redilation). The left carotid artery can partially be crossed, but then additional opening and flaring is preferred. All stents are inflated manually, thereby limiting the pressure to 3–5 atmospheres and leaving full control to the operator during expansion as to whether or not to dilate pressure-resistant waists. The systolic gradient across the aortic arch should decrease to nearly 0mmHg. Overdistention of pressure-resistant hypoplastic segments may lead to severe vessel wall damage, with a higher risk of transmural aortic tear or vessel rupture.
Those segments that are treated with stent expansion are usually free of post-surgical scars or adhesions, and therefore even a small tear may be catastrophic, which is unacceptable, especially when a procedure is performed for prognostic reasons. In many patients, emergency deployment of a covered stent as a back-up is not safely applicable because of the proximity of the origin of the neck vessels. Such a strategy of stent expansion limited by operator pressure may result in some residual narrowing with minimal gradient in some patients. We feel that the potential late benefits of complete gradient relief do not outweigh the possible early risks. Additional experience is required to determine whether or not these pressure-resistant waists can be dilated at the initial or later catheter intervention, if indicated.
Post-procedure haemostasis of the femoral artery is obtained with local compression or, preferably, with an occlusion device. Heparin sulphate is neutralised only when activated clotting time (ACT) exceeds 250msec. Patients are discharged the day after the procedure following a transthoracic echocardiogram and a chest roentgenogram. No chronic medication (anticoagulation nor anti-aggregation) is given, except antihypertensives when indicated.
Results of Stent Implantation and Follow-up
We recently reported our early experience of stent expansion of hypoplastic aortic segments in 20 patients with arterial hypertension, mostly after previous coarctectomy.9 All patients demonstrated significant and relevant gradient reduction, and normalisation of upper-limb blood pressure occurred in half of the patients. Many patients still needed antihypertensive treatment, but with better control or at a significantly lower dose than before the intervention. However, it is known that many patients, even without a residual gradient across the aortic arch, will develop arterial hypertension during follow-up.10 Life-long follow-up therefore remains mandatory. No major complications were seen at stent placement and during follow-up (currently 5.1 years). Late aneurysm formation occurring unexpectedly and silently after stent implantation has been described.11 Routine imaging techniques other than transthoracic echocardiography have been advocated after stent implantation for treatment of re-coarctation to avoid ‘silent’ complications. The stent in the cross or isthmus can be adequately evaluated by transthoracic echo (short distance, stent more perpendicular to echo beam).
Crossing a vessel with a stent may theoretically lead to thromboembolism, vessel narrowing and branch occlusion;12 we did not observe this in these large vessels. Increased stiffness and altered vascular relaxation reserve in the upper-body vessels have been implicated in the aetiology of hypertension at rest and during exercise after coarctation repair.13,14 Following stent placement, patients may theoretically develop exercise-induced gradients across the stent as it is a rigid, metallic structure. However, preserved overall aortic compliance has been documented in animal models after stent implantation in the aorta.15
Timing of Stenting – Adult Size or Accept Redilation?
We chose to stent the mild residual hypoplasia only at an age where a near-adult-sized stent could be implanted, thereby avoiding the necessity of later redilation. Late redilation may be associated with aortic dissection at the distal end of the stent, dehiscence of endothelium or in-stent peel embolisation into a side branch. Other complications may be: the risk of embolic events if crossing any head vessel (in this situation to the carotid artery or from the subclavian into the vertebral artery);16 clot formation within the stent; pediculated tissue within the stent; distal embolisation of peel; vessel rupture along the stent;17 dissection or vascular rupture at the edge of the stent; stent fracture; and vessel tear at a distance.
Dissection or vascular rupture at the edges of the stent can occur by pulling the vascular wall from the stent.18 It needs to be determined whether this complication can be avoided by utilising the following methods: better stent design without sharp edges or a circular wire; technique of redilation with inflation of a short balloon first within the stent using several balloons with progressively wider diameter, thereby avoiding too much tension at the end of the stent; or restenting the distal edge of the first stent as a dissection may be progressive at this end.
Some stents will significantly shorten when overdilated,19 which may cause a vessel tear at a distance or sidebranch occlusion within or near the stent. Therefore, if clinically possible, deployment of a stent is best postponed until a near-adult size can be implanted.
Stenting Mild Hypoplasia of the Aortic Arch – Everywhere but in the US
In most parts of the world, vascular stents can be used anywhere in the circulatory system where a responsible clinician sees a clear advantage for the patient. Balloon-expandable stents are not released for general use in children in the US. An aortic stent can be applied in children only in “exceptional life-threatening situations”. Therefore, the overall experience of ‘simple’ aortic stenting is limited, which makes the possibility of more complex stenting between the carotid arteries more remote. Moreover, covered stents are not available in the US. However, it is a general recommendation that a covered stent should be to hand as a back-up should an accident occur during aortic stenting. At the time of writing this article, aortic stenting is the number one reason for lawsuits against interventional congenital cardiologists in the US. Before stenting of hypoplastic segments for prognostic reasons can be applied in the US, significant changes of legislation and of US Food and Drug Administration (FDA) regulations will be required.
The Place of Stent Deployment in the Management of Hypertension with Hypoplastic Segments
The final goal of these procedures is to prolong survival without vascular complications in patients with aortic arch abnormalities. Pressure loss due to hypoplastic aortic segments can effectively and safely be treated with stent implantation. Only long-term follow-up will determine in a few decades whether this objective will be met. The observation that arterial hypertension regresses or becomes easier to treat suggests a favourable outcome.