Catheter Management of Coarctation

Anatomy and Physiology

Coarctation of the aorta is characterized by a distinct region of obstructive narrowing involving the descending aortic arch. It is typically present at the juxtaductal position, which is the insertion site of the ductus arteriosus and just distal to the takeoff of the left subclavian artery. Other positions of aortic coarctation include the abdominal aorta or transverse portion of the aortic arch. This narrowed region can also exist as part of a long segment of arch hypoplasia associated with obstructive left-sided abnormalities, including hypoplastic left heart syndrome. Coarctation of the aorta is commonly found in conjunction with other congenital defects, including ventricular septal defect, bicuspid aortic valve, patent ductus arteriosus, and left-sided obstructive circulatory lesions.[1]

Coarctation anatomy plays a significant role in the decision of transcatheter vs. surgical management. Lesions favorable for transcatheter management include native, juxtaductal, or simple coarctation that are found in older children or adolescents/adult patients. The employment of surgical techniques is favored in patients with more complex anatomical considerations. These complexities include transverse aortic arch obstructive lesion, significant tortuous regions of re-coarctation, or deformation of nearby arterial branches. When associated congenital defects require repair, surgical intervention is also given precedence.[2]

Indications

The American Heart Association (AHA) provides a class 1 recommendation of catheter-based stenting in adults who have the finding of significant coarctation in the native aorta or in recurrent coarctation that was previously intervened. Aortic coarctation is defined as significant if there is a peak to peak resting gradient or mean doppler gradient of greater than or equal to 20 mmHg between the upper and lower extremities. Additionally, a significant coarctation is an upper extremity to lower extremity peak to peak gradient or mean doppler gradient of greater than or equal to 10 mmHg with decreased left ventricular systolic function, aortic regurgitation, or demonstration of collateral flow around the coarcted segment. The AHA adds that this physiologic data should be accompanied by advanced imaging, including computed tomography angiography or cardiac magnetic resonance imaging. The strongest indication for intervention includes a patient with systemic hypertension, a mean doppler or peak-to-peak gradient of greater than or equal to 20 mmHg between the upper and lower extremities, and anatomically significant coarctation as confirmed by advanced imaging.[3]

The spectrum of symptoms and exam findings that formulate the indications for the procedure vary among infants vs. children and adults. Older adults typically display manifestations of a 20 mmHg systolic gradient between the upper and lower extremities, systolic hypertension, and headaches. Uncommonly this group has associated ventricular dysfunction and diastolic component hypertension. Children and young adults typically are asymptomatic with elevated systolic blood pressure with less frequently associated headaches.

In addition to the pathophysiologic gradients and confirmation of coarctation by advanced imaging, other considerations need to be understood in the decision-making process of surgical vs. transcatheter management. These parameters include age at presentation, if the coarcted segment is native or recurrent, and the complexity of the lesion. Transcatheter management is favored as a temporizing measure in infants too unstable for eventual surgical management. In the younger adult, transcatheter stent implantation has been deemed the preferred approach for native and recurrent coarctation.[4] The recommendation is supported by the Coarctation of the Aorta Stent Trial (COAST), which involved 105 children (median age of 16 years) and adults in a single-arm prospective multicenter trial. In this trial, the treatment of native or recurrent coarctation with stent placement has deemed a success in 99 percent of trial participants. Importantly, no trial patients suffered deaths or serious adverse events and sustained reduction in upper to lower extremity gradients for two years.[5] Preference for stent placement in these patients is predicated upon the stent being able to be dilated to adult size parameters.[2]

Contraindications

Balloon dilatation and angioplasty are not advised for infants that are less than four months old.[6] In addition, balloon dilatation should not be pursued in patients with aortic arch hypoplasia. Balloon dilatation of coarctation in the setting of aortic arch hypoplasia has a high incidence of re-coarctation with repeat interventions needed in as short an interval as 5 to 12 weeks after the initial procedure.[7] The necessity to repair multiple congenital heart defects, including coarctation of the aorta, would prompt favorability of surgical intervention over transcatheter management.

Given the concern for femoral arterial injury with large sheath placement, stent utilization is typically not advised in patients weighing less than 25 kg. In addition, placing a stent in patients less than 30 kg necessitates repeated stent dilatations as they grow. Thus, it has been recommended that stent implantation is only pursued in patients who are able to receive a stent that can be further dilated to adult size.

Equipment

Three types of stents are commonly utilized in the treatment of coarctation, including closed-cell, open-cell, and hybrid designs. The closed-cell design is more rigid with the creation of fixed points formed by the connection of the internal inflection points of the stent material. Open-cell type offers more flexibility of the stent with the lack of connection of all of the structural components of the stent. The ability to offer more flexibility makes the open-cell design desirable in the placement of a stent in the transverse aortic arch position. Hybrid designs utilize a combination of open and closed-cell stents. Another structural difference is the utilization of welding together of single wires or the use of a uniform tube lacking junctions between the components. The welding points, however, mark weak points in stent architecture. The more modern CP stents have undergone soldering with gold to strengthen these welded points. The stents are further differentiated based upon the metal from which they are composed. The common types include platinum-iridium alloy, chromium-cobalt alloy, and stainless steel. Stents are then classified as covered and bare stents.

Polytetrafluoroethylene (PTFE) is the most common inorganic compound used for cover. Covered stents are preferred in the treatment of coarctation of the aorta in patients with genetic aortopathies, tortuous aortas, narrow coarcted segments, or with aneurysms that all carry an increased risk of aortic wall complications with the intervention.[8] There is a platinum-Iridium stent with an outer cover composed of polytetrafluoroethylene. It is the most commonly utilized stent in the treatment of coarctation of the aorta and the only stent that has received Food and Drug Administration indication for use in coarctation intervention.

Personnel

The healthcare team involved in transcatheter management of coarctation of the aorta is multidisciplinary in approach. It involves personnel, including those involved with appropriate diagnosis and detailed imaging of the coarcted segment with interpretation by imaging specialties. Echocardiographers provide detailed anatomy allowing parameters such as mean doppler gradients to be recorded so indications for intervention may be fulfilled.

The interventional cardiologist planning intervention must collaborate with cardiothoracic surgery to determine if the best outcomes for specific patients are achieved with a surgical or transcatheter approach. Cardiac anesthesiologists provide intraprocedural close hemodynamic monitoring and can provide imaging such as transesophageal echocardiography if required. Registered Cardiovascular Invasive Specialists (RCIS) provide additional intraoperative monitoring of hemodynamics and electrocardiographic data in the control area.[9]

Preparation

Prior to catheterization, common preprocedural testing is comprised of a complete blood count, chest x-ray, and electrocardiogram. On some occasions, stress testing is ordered to examine for the provocation of systemic hypertension and worsening of arm and leg pressure gradients.[10] Echocardiogram is also obtained prior to intervention and provides the location of coarctation, aortic arch anatomy, and severity of the lesion. The suprasternal and subcostal views are utilized to determine the site and the severity of the coarcted segment.

Doppler at the stenotic region demonstrates increased velocity with the characteristic "diastolic runoff pattern." Additionally, transthoracic echocardiography provides assessment for other accompanying congenital heart abnormalities, including ventricular septal defect, bicuspid aortic valve, mitral valve abnormalities, and left ventricular hypoplasia.[4] However, commonly in adolescent and adult patients, echocardiography does not completely visualize the complete aortic arch. Thus, the utilization of cardiac MRI or computed tomography of the chest is helpful in the preprocedural planning stages. These advanced imaging modalities allow for determination of the exact size of the lesion, evaluation for the presence of transverse arch hypoplasia, sizing of the aorta proximal and distal to the lesion, and for the localization of adjacent structures. The imaging allows for sizing balloons and stents and identifying fluoroscopic angles and nearby landmarks.[10]

Technique or Treatment

Published discussions of procedural techniques recommend that balloon angioplasty or stent placement in the treatment of coarctation of the aorta be performed under general anesthesia. The rationale for this preference is that dilatation of the coarcted segment elicits pain in the patient leading to patient movement adding additional challenges to the procedure. Access is via the femoral artery with a retrograde approach. The arterial puncture site is localized at the level of the compressible site of the femoral head, and an angiogram is obtained afterward to confirm appropriate positioning. The preclosure device is then placed. If the coarcted segment is unable to be crossed in a retrograde fashion, radial or brachial access can be used to facilitate anterograde catheterization.

Femoral venous access is also performed in a complete right heart catheterization and allows for placement of a transvenous pacemaker to be used if necessary during stent placement for rapid right ventricular pacing. Intravenous heparin is then administered to achieve an activated clotting time (ACT) of greater than 250 ms. A multipurpose or Judkins right catheter is advanced over the guidewire to the descending aorta, and a soft-tipped wire is crossed through the coarcted segment. Peak to peak systolic pressures are recorded across this stenotic region. After the lesion is crossed from the retrograde approach, the catheter is exchanged for a pigtail catheter, and it is positioned just proximal to the proximal coarcted segment. At this point, biplane angiography is performed. This angiogram allows for the visualization of the coarctated region, whole transverse aortic arch anatomy with the location of the brachiocephalic vessel, and the diameter with dimensions of the descending aorta down the level of the diaphragm.

After angiography, measurements are made to appropriately size the balloon or stent. Stent sizing is according to the diameter of the proximal arch and does not exceed the diameter of the diaphragmatic descending aorta. In addition, the ratio of final stent diameter to the most stenotic region of the coarcted segment should measure less than 3.5.

After performing angiography with the pigtail catheter, a wire (typically J-tipped Amplatzer guide wire) stiffer than the soft-tipped wire is used to exchange the pigtail catheter. The tip of the guidewire is left positioned in the right subclavian artery. A long blue Cook or Mullins sheath is advanced over the guidewire across the coarcted segment of the aorta. The sizing of the sheath when using ballon in ballon (BIB) catheters is one French greater than what is needed by the BIB catheter. BIB catheters are preferred by most centers as they allow for controlled stent expansion and most often prevent complications, including balloon rupture and stent migration. The dilator is then removed after the tip of the sheath is placed proximal to the site of the lesion. The appropriately sized stent is hand-crimped onto the balloon with the additional support of umbilical tape. This apparatus, including the BIB catheter and the crimped stent, is advanced through the valve of the introducer sheath. The stent is placed across the coarcted segment with position confirmed by angiography. When the position is confirmed and is appropriate, the proximal balloon is covered by the delivery sheath, and the distal segment of the stent is dilated to its complete size. The sheath is subsequently removed from the balloon catheter, and the rest of the stent is placed across the stenotic lesion. A pigtail catheter is advanced over the guidewire to obtain simultaneous pressures across the stent. A successful intervention is confirmed with a gradient of less than 10 mmHg across the implanted stent.[8][11]

Complications

Endovascular stenting has minimized the invasiveness in the repair of coarctation of the aorta but does carry documented complications. The most feared and serious complication is the rupture of the aorta. Based on a large multicenter trial, it was calculated to occur in 1.6% of cases. Noted risk factors for aortic rupture include pre-dilatation balloon angioplasty, abdominal aortic location of the coarctation, and age over forty years of age. The creation of aneurysms has been reported post stent intervention with an estimated incidence of around 5 to 9%. Etiologies of aneurysmal formation are attributed to overstretching with balloon dilatation of the vessel wall and diminished quantity of elastin fibers with an increased collagen component.[12] The contribution of stretching of the vessel wall leading to wall trauma and the above-described sequelae has been shown to be minimized with the use of covered stents in the COAST II trial.[13]

Complications can involve the stent itself. Embolization and migration of the stent can occur. There is a tendency for migration in situations where an oversized balloon or an undersized balloon catheter has been used. The stent may become lodged into the aorta or femoral artery, requiring the utilization of a lasso device, which can assist in its retrieval back into the sheath.

Restenosis has been documented to occur in 13 to 31% of cases with balloon angioplasty. This occurrence was found to be reduced to around 2.7% in one study with the employment of stenting. One of the etiologies of this process is a neo-intimal proliferation in the stent. Additional complications arise from femoral access, including limb ischemia and hematoma. These complications have been reduced by the utilization of vascular closure devices.[12]

Clinical Significance

Endovascular repair of aortic coarctation and the timing of this intervention is an important factor in the overall outcome of the patient. Early intervention, especially in the younger population, is associated with a diminished risk for the development of late hypertension and improved survival. Even though there are diminished survival and higher prevalence of development of late hypertension with individuals repaired later on in life, there is still benefit in these cases with endovascular repair. Coarctation repair improves the feasibility of medical management of blood pressure and allows for a decreased amount of pharmacotherapy to control hypertension. On account of the known benefits of repair and improved technologies facilitating endovascular repair, early intervention in childhood has become the common practice. The downside of this is the extensive follow-up and further re-intervention in the future.[14]

Enhancing Healthcare Team Outcomes

The process of deciding which patients are appropriate for endovascular repair of aortic coarctation is challenging. This requires numerous factors, including the patient's age, presence of concomitant congenital heart defects, and the specific anatomy of the coarcted segment. As such, appropriate patient selection for intervention involves collaboration among adult congenital heart disease cardiologists, congenital heart disease cardiothoracic surgeons, and interventionalists. The multi-team approach to intervention management is referenced in the 2008 American Heart Association and American College of Cardiology (ACC/AHA) guidelines. This is a class 1 level of evidence C recommendation. This coordination of care extends past the periprocedural time frame and includes the lifelong follow-up period. ACC and AHA provide a class 1 recommendation of life long follow up with a cardiologist that has specialization in adult congenital heart disease.[15]

Nursing, Allied Health, and Interprofessional Team Interventions

Patients with congenital heart disease, including coarctation of the aorta, have better outcomes when a multidisciplinary collaborative approach is undertaken. This collaborative effort must target the cardiac sequelae that can possibly manifest in the course of treatment of coarctation. This enlists the required support of the following:

• Advanced cardiac imaging services to interpret anatomy pre and post-procedure
• Interventional cardiologists to plan and execute an intervention
• Cardiac anesthesiologists to titrate appropriate anesthetic and monitor hemodynamics intraoperative
• Pediatric or general adult cardiologists with expertise in congenital heart disease

An effort to refine care for congenital heart disease including coarctation of the aorta has led to the American Board of Medical Specialties to approve Adult Congenital Heart Disease (ACHD) as a subspecialty that encompasses adult cardiology and pediatric cardiology. Additionally, there exist ACHD specialists who are not board-certified but have gained a considerable amount of experience and expertise prior to the inception of board certification bodies in this field.

In general, patients with complex congenital heart disease and those undergoing invasive management have better outcomes, including survival when they are managed at specialized centers.[16]

Nursing, Allied Health, and Interprofessional Team Monitoring

Given the documented risks of aneurysm formation, restenosis, and late hypertension, clinical evaluation is recommended at approximately 4 to 6 weeks after the procedure. In this evaluation, clinical history and physical examination can elicit the recurrence of symptoms such as lower extremity claudication and potential physical exam findings of hypertension and radio femoral delay. Additionally, clinical monitoring after the procedure involves the measurement of ambulatory or exercise blood pressures. This is recommended as some patients are normotensive at rest but become hypertensive upon provocation with exercise.

Abnormalities found on these postoperative surveillance measures prompt follow up imaging such as the preferred multiple detector computed tomography (MDCT) or MRI. MDCT is given preference in instances of the indwelling stent resulting in susceptibility artifact. Repeat angiography was once the preferred method of initial follow up imaging, but its not the case anymore with the advent of advanced imaging modalities.[14]