Stenting for relief of stenosis in narrowed vessels is now common practice both in interventional cardiology and interventional radiology, with many options to choose from as to delivery systems, balloons, and types of stent. When dealing with coarctation of the aorta, these choices are limited due to the special considerations that need to be taken into account, and this chapter provides a practical framework for the interventionalist to approach this straightforward but challenging lesion (Figure 39-1).

Coarctation of the aorta occurs in approximately 7% of live births with congenital heart disease, and although there are many variants of the anatomy and associated lesions, the effects of the narrowing of the aortic lumen have the common denominator of increased left ventricular afterload, upper body hypertension, flow disturbance in the thoracic aorta, and decreased perfusion to the lower body.^1,2 Presentation is dependent on the balance between the degree of flow disturbance and the compensatory mechanisms available to overcome it, and therefore, if survived in infancy, coarctation is often discovered in adolescence or adulthood when undergoing a workup for hypertension (Figure 39-2).

Untreated coarctation has a poor prognosis, with most patients suffering from significant morbidities associated with hypertension including premature death due to heart failure, cerebovascular accidents, and premature coronary artery disease.³ Surgery, balloon angioplasty, or stent implantation usually provides relief of the obstruction; however, recoarctation from scarring, failure to match somatic growth and tissue ingrowth,^4–7 and acute and late aortic wall injury are ongoing issues.

Surgery has been in practice since 1944⁸ and is still the preferred treatment for infants with native coarctation; however, in older patients, surgical complications are more common and occasionally can be severe, particularly when an adequate collateral circulation has not developed, and spinal cord damage can ensue.⁹ Balloon angioplasty was an acceptable technique for the relief of coarctation^10–12 and is particularly effective in cases of recoarctation¹³ following surgical repair in infants. However, the use of this technique in native coarctations at all ages remains controversial due to the disruption of the intima and media of the aortic wall predisposing to a high incidence for future aneurysm formation.^10–12 It is important to note that the aortic wall in coarctation is primarily abnormal, and this is compounded by the flow disturbance over time, so that in the adolescent and adult patient, tortuousity, thinning, cystic medial necrosis, and calcification may be present, further increasing the predisposition to dissection, aneurysm formation, or even rupture.¹⁴

For these reasons, stent implantation for relief of aortic coarctation has gained popularity since its initiation in 1991 with the rationale that overdilation, dissection, and elastic recoil of the aorta are avoided with this technique. In addition, the stent pins the intimal flaps to the aortic wall after tearing of the intima and media and promotes healing^15–20 and can also reinforce weakened areas within the aortic wall and provide a framework for neointima formation to cover the tear.

These features of stenting result in less aortic injury than with balloon angioplasty (Figure 39-3),²⁰ but dissection and aneurysm formation still remain important issues. Covered stents provide an internal material cover to supplement the advantages of bare stent implantation, affording additional protection to the acutely disrupted aortic wall and the downstream area of poststenotic dilation (Figure 39-4). For these reasons, the use of covered stents has broadened to be the primary treatment for coarctation in some centers.^21–27 However, both covered and bare stents can require relatively large delivery systems, restricting their use to patients with adequate vascular access, which is typically greater than 8 Fr for stents that can achieve an adult size of at least 18 mm. The implantation of stents of narrower maximal diameters may allow for smaller delivery systems and the treatment of infants and young children; however, the need for repeated reintervention to further dilate the stent to match somatic growth and the limited maximal diameter restrict the use of stents in this group of patients.^17–19

Coarctation of the aorta, native or recurrent, is typically diagnosed^23,28–31 when a systolic blood pressure gradient of 20 mm Hg between the upper and lower limbs is present. The echocardiographic findings include 2-dimensional imaging of a narrowing in the descending aorta, a Doppler gradient with turbulence of color Doppler and persistence of the gradient into diastole, and an abnormal Doppler tracing with “damping” of the signal in the abdominal descending aorta. Noninvasive imaging by computed tomography (CT) or magnetic resonance imaging (MRI) is useful to demonstrate a significant narrowing and wall abnormalities in the descending thoracic aorta. At cardiac catheterization, a peak-to-peak pressure gradient greater than 20 mm Hg is often cited as an indication for intervention; however, this can be influenced by the use of general anesthesia, a large collateral circulation, or ventricular dysfunction.²⁸ Relief of milder obstructions can be beneficial in preserving systolic and diastolic ventricular function in the long term,^32,33 especially in patients with hypertension at rest, abnormal blood pressure response during exercise, and complex heart disease, particularly Fontan palliations.

Stenting reduces the gradient at the coarctation site more effectively than balloon dilation,^7,34,35 and therefore, we consider this technique in all patients in whom vascular access appropriate for the required delivery system is available. Exception is made in very small children due to the need for repeated reinterventions to match somatic growth. We routinely stent patients with coarctation and a weight greater than 20 kg.

Covered stent implantation is indicated in patients with coarctation^21–27 associated with aneurysm or degenerative changes of the aortic wall suggested by the presence of an aneurysmal ascending aorta or significant aortic tortuosity; with associated with a patent ductus arteriosus; with critical or atretic obstructions; with age over 18 years; with aortitis; with Turner syndrome; with Williams syndrome; in the presence of aortic wall injury (aneurysm, dissection, or rupture) following balloon dilation; with bare stent implantation or surgery; or in the presence of circumferential fractures within a previously implanted stent in the aorta. Due to improvements in balloon and stent technologies that afford lower profile systems and the encouraging results from recent reports, we now use covered stents as our first choice for the treatment of coarctation of the aorta in suitable patients (Figure 39-5).

The ideal stent for coarctation is a covered stent, premounted on a high-pressure balloon, with a very low profile that is both flexible with considerable radial strength and achieves a diameter of 25 mm without foreshortening. Unfortunately, such stents are currently unavailable, and therefore, familiarity with particular features and disadvantages of the stents that are available is necessary to choose the most appropriate stent for the particular patient at hand.

Balloon-expandable bare metal stents^5,6,17 are the most commonly used and are made from stainless steel, platinum-iridium alloy,¹⁸ or a chromium-cobalt alloy.³⁶ The chromium-cobalt alloy is stronger than stainless steel, and therefore, thinner struts will allow for a lower crimped profile without compromising radial strength. Closed-cell stents are strong and rigid and will markedly foreshorten, whereas open-cell stents, although weaker, will foreshorten less, conform to the anatomy, and allow access to side branches. Balloon-expandable expanded polytetrafluoroethylene (ePTFE)-covered stents are available in a closed-cell design (Cheatham Platinum [CP] Stent; NuMED, Cross Roads, TX) and open-cell design (Advanta V12 LD; Maquet Getinge, Rastatt, Germany). Self-expanding bare nitinol stents have been reported in the treatment of coarctation of the aorta, although their use is uncommon.^27,37 Self-expandable stent grafts, which are commonly used for the endovascular treatment of thoracic aortic aneurysms, have been used in special circumstances, usually when the degree of coarctation is mild and there is an aortic-bronchial fistula or large aneurysm for which a balloon-expandable covered stent would be inadequate and in which case they are the safest choice.^27,37

The most commonly used bare stents in our catheterization lab are the Palmaz Genesis XD and Palmaz XL 14-series stents (Cordis, Milpitas, CA). The latter can be dilated up to 25 mm and are available in 30- to 50-mm lengths. They are laser-cut from a rigid stainless steel tube and shorten significantly when expanded to their full diameter. Palmaz stents, with their closed-cell design, have little to no flexibility and will not conform to the contour of the aortic arch. The Palmaz Genesis XD stent is also laser-cut from stainless steel, and the closed-cell design is modified by a “sigma hinge” interposed between the cells, which affords some flexibility around curves and also reduces the degree of shortening on expansion. The Genesis stents are available in multiple lengths but cannot be expanded further than 18 mm. This limitation makes the use of this stent inappropriate for larger aortas and patients. Unless the aorta is expected to reach a diameter significantly greater than 18 mm, the radial strength and flexibility of the Genesis stent make it a good option for treatment of lesions that lie across the curve between the transverse arch and the descending aorta. However, concerns have been raised with regard to fracturing when expanded to large diameters.^38,39

The CP stent is composed of a 90% platinum and 10% iridium alloy, with the metal wires arranged in a “zig” pattern.¹⁸ Earlier versions of the stent were prone to fracture, and refinements in the welding process using gold have been successfully employed to minimize this problem.¹⁸ CP stents with 8 “zigs” can be expanded up to 25 mm and shorten less than the Palmaz stents, with the 39- and 45-mm lengths usually being appropriate.^23,25

The Andrastent XL and XXL stents (Andramed, Reutlingen, Germany) are hybrid open-closed cell cobalt-chromium stents that can be dilated up to 25 and 32 mm, respectively, and are available in a variety of lengths. This combination of high radial strength and lower profile, conformability, and minimized shortening makes it a good candidate for the treatment of coarctation of the aorta, particularly in curved anatomy. Because this stent is relatively new, the reported experience is encouraging but limited.³⁶

There are 2 ePTFE balloon-expandable covered stents currently available. The covered CP stent is the standard CP stent covered with an ultrathin stretchable ePTFE membrane applied to the stent using biodegradable adhesives^18,23; this stent is also available crimped and premounted on a BIB balloon.

The Advanta V12 LD Stent is a stainless steel, open-cell stent encapsulated by a covering of ePTFE on the interior and exterior aspects (Figure 39-6). It is available in 3 lengths (29, 41, and 61 mm) and is premounted on high-pressure balloons of 12-, 14-, and 16-mm diameters. The stent can be incrementally dilated by 4 mm at a time to avoid tearing of the ePTFE, up to a maximal diameter of 22 mm.²⁶ In countries, such as the United States, where the availability of covered stents is limited, interventionalists have reported on the use of self-fabricated covered stents^40,41 for high-risk patients or during acute aortic wall complications.

The major concern with the implantation of covered stents in the aorta is the risk of side branch occlusion, particularly of the left subclavian artery or the spinal artery, resulting in paraplegia.^42,43 The latter complication is usually avoided by not implanting a covered stent below the ninth thoracic vertebra. An additional concern with the use of covered stents is when distal migration occurs because the stent cannot be easily “parked” without occluding side branches and the origins of the renal and mesenteric arteries must be avoided.

Balloon-expandable stents are available premounted, as described earlier, or need to be crimped onto a balloon for deployment. Although there are many types of balloons available, we commonly use Powerflex (6-12 mm) and MaxiLD (14-25 mm; Cordis). Single large-diameter balloons tend to expand first at their ends, which may predispose to stent movement if one end inflates before the other or balloon rupture if the stent has sharp edges. The BIB (“balloon-in-balloon”; NuMED) catheter is made from an inner balloon and a 1-cm longer outer balloon that is twice the diameter of the inner balloon, and it is available in outer balloon sizes of 8 to 24 mm. The BIB catheters offer the important advantage of initially opening the stent more uniformly along its length, resulting in more control over its precise placement and preventing stent flaring and migration; however, they are bulkier than their single-balloon counterparts. The choice of balloon depends on the coarctation anatomy and dimensions, the stent to be implanted, and operator preference and experience. Single-balloon catheters are preferable in smaller patients to reduce risk to the femoral artery at the access site, whereas the BIB balloon is helpful in precise positioning in transverse arch stenting. On occasion, high-pressure balloons, such as the Mullins balloons (NuMED) and Atlas (Bard Peripheral Vascular, Tempe, AZ) balloons, may be needed to dilate up a residual waist, particularly in postsurgical coarctations (Figure 39-7). Generally, a balloon that is slightly longer (~1 cm) than the stent is used for implantation.