Role of Transcatheter Therapy in the Treatment of Coarctation of the Aorta

ABSTRACT: Coarctation of the aorta is one of the most common congenital heart defects. Transcatheter therapy for treatment of coarctation is effective, with low morbidity and mortality rates. The current trend is toward primary stent implantation for treatment, however, the results of balloon angioplasty in children and young adults are equivalent to the results following primary stent placement. Judicious use of stents is recommended in infants and children. J INVASIVE CARDIOL 2008;20:660–663 Coarctation of the aorta is a simple yet heterogeneous defect which occurs in 5.1–8.1% of patients with congenital heart defects.1 Coarctation of the aorta was the first congenital heart defect to be repaired surgically in 1945 by Crafoord,2 followed by transcatheter balloon angioplasty in the early 1980s.3,4 Coarctation of the aorta can occur as an isolated defect or in association with a patent ductus arteriosus, ventricular septal defect, or aortic stenosis. It can also be a part of a complex congenital heart defect such as the Taussig-Bing anomaly or Shone’s complex. The segment of coarctation presents as a stricture in the juxtaductal region. It can be a discrete or long segment associated with varying degrees of hypoplasia of the isthmus or the transverse arch. In rare instances, isolated abdominal coarctation may be present. In the large majority of patients, there is post stenotic dilation of the aorta. Collateral vessels may be present, which decompress the segment proximal to the stenosis. Pathologically, the stricture occurs because of medial thickening and infolding of the media with superimposed neointimal tissue. The majority of patients with coarctation present prior to 1 year of age with congestive heart failure or decreased cardiac output. Children and adults are usually asymptomatic and present with murmur, hypertension and occasionally with leg pain and weakness. The indications for balloon angioplasty for coarctation of the aorta are: 1) native or recurrent arch obstruction with a gradient > 20 mmHg; 2) coarctation where there is left ventricular hypertrophy or systemic hypertension proximal to the site of coarctation. In neonates and infants 1 year of age with a well-developed isthmus. Technique of Balloon Angioplasty At our center the procedure is performed under general anesthesia. The femoral artery and vein are cannulated and heparin is administered to maintain an activated clotting time > 250 seconds. A complete hemodynamic study including a pressure gradient across the coarctation segment is performed. Biplane angiography is performed to profile the area of coarctation and measure the diameter of the coarctation site, the transverse arch, the aorta at the diaphragm and the length of the coarctation segment (Figure 1A). A balloon catheter 2–3 times the diameter of the coarctation segment, but not exceeding the diameter of the adjacent arch proximal to the narrowed segment is selected and inflated across the coarctation site. Repeat aortography and pressure pullback across the site of coarctation are performed (Figure 1B). In patients with native coarctation of the aorta, use of a low-pressure balloon is preferred to minimize the risk of aortic wall trauma. Technique of Stent Implantation After hemodynamic evaluation and angiography have been performed, a transseptal sheath is positioned across the coarctation site. A balloon catheter that is twice the diameter of the narrowed segment is selected and a stent is crimped onto it. The wire is positioned in the right or left subclavian artery. The stent struts are flared proximally and distally to approximate the vessel wall, especially in the area of the post stenotic dilation to allow for endothelialization of the vessel wall. We do not routinely perform balloon angioplasty prior to stent placement except with low-pressure balloons at Results of Balloon Angioplasty Published reports of balloon angioplasty demonstrate that this procedure results in short-term effective relief of a gradient in 75–79% of patients and a low mortality rate of 0.7–2.5%.5,6 Long-term follow up revealed a restenosis rate ranging from 25–36%.5–11 McCrindle,5 in the VACA registry data, reported the acute results in 970 procedures from 25 centers following balloon angioplasty of coarctation of the aorta. There were 422 native and 548 recurrent lesions. In patients with native coarctation, there was a greater reduction in gradient and a larger increase in the coarctation diameter. Suboptimal outcomes occurred in 19% of native and 25% of recurrent lesions (p = 0.04). There was a 0.7% mortality rate for native and recurrent coarctations. Fletcher et al8 reported their results of 102 patients with native coarctation. The patients ranged in age from 3 days to 29 years (mean 4.6 years of age). Immediate relief of the gradient occurred in 91.2% of the patients, with restenosis occurring in 21/71 patients. They concluded that recoarctation was more likely to occur in neonates and should be considered palliative in children 5 months of age, the procedure was effective and provided sustained benefits. The major drawback of angioplasty alone is recoil of the vessel wall with recurrence of stenosis. Balloon angioplasty of the aorta can cause intimal and medial tears resulting in aortic wall dissection in 1–4% of patients, and aneurysm formation in 4–11.5%.5,9–13 Shaddy et al14 compared the results of angioplasty with surgery in 36 patients. They concluded that the immediate gradient reduction was similar in both modalities. However, there was an increased incidence of aneurysm formation and restenosis after balloon angioplasty. Results of “Bare” Stent Implantation Stent placement is a viable alternative in patients with elastic vascular stenosis.15–19 With the current array of stents available, we do not advocate stent placement in infants and children where future redilation will be necessary. Mullins20 has advocated and even “preached” that stent placement in infants and children may be problematic because the stent may not effectively dilate up to an adult-size vessel. Forbes et al17 reported the results and complications of a 17-center multi-institutional study. There were 565 stent procedures in 555 patients with a total of 627 stents being placed; 52.3% of the patients had native coarctation, and in 81.4% of the patients, this was located at the isthmus, with 74.7% of the patients having a discrete coarctation. The patients ranged in age from 4–49 years (median age, 15 years). Success as defined as a stent coarctation systolic gradient 3.5 and the performance of pre-stent angioplasty. Reintervention occurred in 9/41(22%) patients. Results of “Covered” Stent Implantation Covered stents have been extensively used outside the United States in order to address the problems associated with aortic wall injury by balloon angioplasty and “bare” stent placement. Covered stents are preferentially placed in: a) patients where an aortic wall aneurysm exits;21 b) where a tight native coarctation is present and balloon or “bare” stent dilatation can be associated with the risk of dissection or rupture;22,23 c) where there is an associated arterial duct;24 and d) in older patients in whom the vessel wall is relatively less compliant.25,26 The limitations of using a covered stent are the larger sheath size and occlusion of the branches of the aorta. Occlusion of the left subclavian artery is well tolerated, however, an intact vertebrobasilar system should be documented prior to the procedure.27,28 The covered stents are balloon-expandable or self-expanding. The balloon-expandable covered Cheatham-Platinum stent (NuMED) and the Palmaz Genesis™ covered stent (Cordis) are covered with expanded PTFE. The Jostent peripheral stent graft (Jomed International AB, Helsingborg, Sweden) consists of expandable PTFE graft material placed between 2 flexible stainless steel stents. The Valiant™ endoprosthesis (Medtronic Inc., Minneapolis, Minnesota) is a self-expanding stent graft composed of a mono-filament polyester graft sewn to a self-expanding nitinol wire stent and is designed to limit flaring at the proximal and distal ends. The stent is delivered with the XCelerant™ delivery system, which has a 22–25 Fr outer diameter and is designed to track over a 0.035 inch guidewire. Kenny et al29 reported their results in 37 patients who underwent placement of covered stents. The patients ranged in age from 9–65 years( median 29.6 years of age). There were 13 native coarctations, 11 recurrent coarctations following surgical treatment, 7 with an aneurysm associated with previous coarctation surgery, 2 each with an aorto-bronchial fistula leading to acute hemoptysis and patent ductus arteriosus, and 1 with a stent fracture. The major complication in 1 patient was an aortic rupture requiring surgery. Self-expanding stent grafts may be preferable to balloon-expandable stents when there is aneurysmal formation in the setting of aortopathy. Redilatation of covered stents is effective.25–30 Tzifa et al25 reported their results in 30 patients who underwent Cheatham-Platinum stent placement, with the only complication being stent fracture in 2 patients. Conclusion Transcatheter therapy for native and recurrent coarctation is effective, with good immediate and intermediate follow-up results. The current trend is toward primary stent implantation15–17,30 for treatment, however, the results of balloon angioplasty in children and young adults are equivalent to those with primary stent placement.The judicious use of stents is recommended in infants and children. Biodegradable33 and “open-ring” stents would be useful additions for smaller patients. Despite adequate gradient relief, patients continue to present with systemic hypertension and elevated blood pressure response to exercise, therefore, the optimal treatment modality for this defect continues to evolve.34,35 Coarctation of the aorta is a heterogenous disease with a significant incidence of late complications at and remote from the coarcatation site, and therefore frequent imaging at follow up is recommended.

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