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Aortic Coarctation and Interrupted Aortic Arch
Coarctation of the Aorta
Definition and Morphology
Coarctation of the aorta (CoA) is a complex cardiovascular disorder, and, as part of a generalized arteriopathy, a lifelong disease that persists after treatment.
It was Morgagni who, in 1760, first described CoA, during the autopsy of a monk. More detailed pathoanatomic descriptions came from Jordan (1827) and Reynaud (1828).
In the adult, CoA is almost always located at the junction of the distal aortic arch and the descending aorta just below the origin of the left subclavian artery ( Fig. 40.1 ). In atypical cases, coarctation may occur in the ascending aorta, in the aortic arch, the descending thoracic aorta, or the abdominal aorta.
The cause of CoA is likely multifactorial. Theories include postnatal constriction of aberrant ductal tissue, intrauterine alterations of blood flow through the aortic arch, and genetic causes.
In view of the pathogenesis, all typical types of CoA can be called juxtaductal .
CoA can be either a localized stenosis or a longer hypoplastic segment. The localized form is caused by a shelf-like folding of the posterior aortic wall into the aortic lumen, opposite, proximal, and/or distal to the ductus arteriosus. The shelf, which is always in continuity with the muscular tissue of the ductus arteriosus, is located opposite the ductus arteriosus and consists of thickened aortic media and intima. At the time of ductal closure, anomalous fibroductal tissue surrounding the aorta partially or circumferentially tracks the shelf toward the ductal orifice, causing luminal obstruction. The more diffuse form of CoA is characterized by a tubular hypoplasia involving the aortic arch or the aorta distal to the origin of the left subclavian artery and the ductus area.
CoA may occur as an isolated defect. “Simple CoA” refers to coarctation in the absence of other relevant lesions. “Complex CoA” is used to describe coarctation in the presence of other important intracardiac and/or extracardiac lesions, mainly a bicuspid aortic valve, ventricular septal defects, mitral valve abnormalities, intracranial aneurysms (most commonly berry aneurysm of the circle of Willis) and Turner, Williams-Beuren, or Noonan syndromes. CoA may complicate complex heart defects, such as transposition of the great arteries, Taussig-Bing anomaly, double-inlet left ventricle, tricuspid atresia, and hypoplastic left heart syndrome, but only rarely is it associated with severe right ventricular outflow tract obstructions.
In the paracoarctation aorta and in the ascending aorta (in patients with associated bicuspid aortic valve), aortic medial abnormalities may be present. Early elastic fiber fragmentation, fibrosis, and so-called cystic medial necrosis could be uncovered in the wall of the ascending and descending aorta. These wall abnormalities result in increased stiffness of the aorta and of the carotid arteries, in a blunted baroreceptor reflex, and in an increased brachial pulse wave velocity, and may be related to late aneurysm formation or aortic dissection.
Aortic stiffness and increased pulse wave velocity are also present long after CoA repair. Furthermore, an increased carotid intimal-medial thickness was found in young adults and children with CoA, as well as a diminished endothelium-dependent and independent vasodilation in the right brachial artery.
With the passage of time, arterial hypertension, endothelial dysfunction, and increased aortic stiffness may contribute to the development of diastolic and systolic heart failure.
Genetics and Epidemiology
CoA is a common type of congenital heart defect. The overall prevalence is not precisely known because of an occasionally delayed diagnosis. Estimates range from 5% to 9% of all congenital cardiac anomalies and an incidence of 1 in 2500 live births. Series from Southeast Asian countries show different numbers. Besides sporadic cases, a genetic basis is possible, and mutations in the NOTCH1 gene have been identified. CoA is more common in white males than in white females, with a male-to-female ratio of 1.3 to 2.0:1.
Early Presentation
Severe CoA commonly causes heart failure in early infancy and is called “critical CoA,” while milder forms can remain undetected throughout many decades of life. Unrepaired CoA after the second or third decade of life may cause problems as a consequence of the heart defects associated with it.
Depending on the degree of stenosis and associated cardiovascular defects, 60% of untreated patients with symptomatic high-grade CoA and 90% of those with complicated CoA die during the first year of life. In a historic study of those who survived the first 2 years, 25% died before 20 years, 50% before age 32 years, 75% before age 46 years, and 92% before age 60 years. Although the natural history of untreated CoA carries a mean life expectancy of approximately 35 years, there have been anecdotal reports of patients living to 78, 85, or indeed 92 years.
Major problems later in life and possible causes of death include left ventricular failure (28%), intracranial hemorrhage (12%), infective endocarditis (18%), aortic rupture/dissection (21%), premature coronary artery disease, and associated heart defects.
Untreated patients surviving into adulthood typically have either mild postductal CoA or extreme collateral vessels. They may remain asymptomatic or undiagnosed for a long time. A murmur and arterial hypertension are usually present, but may not be discovered or may remain unrecognized as the expression of the disease, thus delaying diagnosis until adolescence or adulthood.
Typical symptoms attributed to upper-body arterial hypertension may include headache, nosebleeds, dizziness, tinnitus, cold feet, abdominal angina, exertional leg fatigue, and even intracranial hemorrhage. True leg claudication may suggest the presence of abdominal aortic coarctation.
Management
The treatment of choice in adults is catheter intervention, preferably by the implantation of covered stents. In comparison to surgery, the procedure is less invasive and has equivalent results. The individual treatment options depend on the degree of stenosis, the presence or absence of arterial hypertension, the morphology of the stenosis, and on associated cardiac defects.
Treatment is indicated whenever symptoms are present—mainly arterial hypertension. While a systolic gradient of at least 20 mm Hg across the stenosis is required by some authors, there is the tendency to treat even milder gradients whenever arterial hypertension is present and stent therapy is possible.
Surgical Treatment
Since the early 1940s, several different surgical techniques ( Table 40.1 ) have been designed; the most important are depicted in Fig. 40.2 .
TABLE 40.1
Surgical Management of Aortic Coarctation
| Operative Technique | Comment |
|---|---|
| Resection and end-to-end anastomosis | Procedure of choice in patients older than 1 year |
| Resection and extended end-to-end anastomosis | Advantage: excision of all abnormal aortic tissue; enlargement of hypoplastic aortic arch |
| Prosthetic patch aortoplasty (arch augmentation) | Seldom used for primary repair because of the high incidence of late aneurysm, especially, if Dacron is used |
| Subclavian flap aortoplasty | Primarily used in patients younger than 1 year |
| Interposition (tube) graft | If a long segment of coarctation is present |
| Bypass tube (jump) graft | Especially in older patients with fragile aortic tissue or in long-segment coarctation |
| Extraanatomic bypass graft (ascending to descending aorta | If very complex re-coarctation repair or in combination with other cardiac surgery |
Operative treatment aims to remove the stenosis and the stress and strain across the aorta and to maintain aortic patency. All surgical techniques have specific advantages, disadvantages, and long-term problems, which have to be considered at follow-up.
The choice of procedure depends on the nature, site, and extent of the coarctation and on the patient’s age. Today, early repair is usually preferred. There is a tendency to operate as early as possible after diagnosis to minimize late mortality and morbidity. However, the age-related risk and the rate of complications have to be taken into account.
A survey of 11 major studies published between 1989 and 1996, which include 2355 patients operated on between 1946 and 1994, shows an operative mortality rate of 3% to 32%. Death was strongly correlated with the complexity of associated lesions. Today, the surgical risk is less than 1% in patients with simple CoA.
The best age for elective operation has proved to be 2 to 5 years because surgical risk is low in this age group. Beyond the age of 6 years, there is the additional risk that arterial hypertension will persist in 25% to 50% of patients.
If indicated, older children and adults are operated on soon after making the diagnosis. Beyond 30 or 40 years of age, the intraoperative mortality rate increases as a consequence of degenerative aortic wall changes. Additional surgical risk factors in this age group include a coexisting bicuspid aortic valve, mitral valve abnormalities, coronary artery disease, and end-organ damage from systemic arterial hypertension.
Interventional Treatment
While surgical repair of CoA is still preferred in infants and complex lesions, angioplasty, in the majority of cases with stent implantation, has become an established and safe alternative treatment in older children, and is the treatment of choice in adolescents and adults. The interventions result in an immediate increase of the coarctation diameter and reduction of the gradient across the coarctation. Stent implantation provides better hemodynamic results than balloon angioplasty alone and reduces the incidence of aneurysm formation.
Late Outcome
Survival and Functional Status
Unfortunately, satisfactory results are by no means achieved in all patients who undergo operation or catheter interventions. Operation improves clinical symptoms and the blood pressure situation, at least in the short term, and also increases survival. Long-term survival after operation, however, continues to be lower than in the general population because of cardiovascular complications and arterial hypertension.
In the largest follow-up study of 646 patients who underwent simple CoA repair at the Mayo Clinic between 1946 and 1981, the postoperative 10-year survival rate was 91%, the 20-year rate was 84%, and the 30-year rate was 72%. For patients operated on before the age of 14 years, the 20-year survival rate was 91%, compared with 79% for those operated on after 14 years of age. Among 571 patients with long-term follow-up, there were 87 late deaths. The mean age at death of these patients was 38 years. The most common cause of postsurgical death was coronary artery disease, followed by sudden cardiac death, left ventricular failure, stroke, and ruptured aortic aneurysm. Despite all improvements in medical and surgical care, a study by the same institution found in 2013 a very similar postoperative survival rate of 93% after 10 years, 86% after 20 years, and 74% after 30 years. In addition, an Australian research group recently reported an actuarial survival of 98% after 40, 98% after 50, and 89% after 60 years of age.
Late Complications
Long-term problems may occur after all forms of treatment ( Table 40.2 and Box 40.1 ). The most important residua, sequelae, and complications are arterial hypertension, restenosis, or residual stenosis in the region of the previous treatment, and aneurysms of the ascending aorta or at the site of intervention. Further problems may develop due to coronary artery disease, bicuspid aortic valves, mitral valve anomalies, infective endocarditis, or cerebral aneurysms.
TABLE 40.2
Follow-Up Issues and Investigations After Repair of Aortic Coarctation
| Problem | Follow-Up Procedures |
|---|---|
| Arterial hypertension | Blood pressure monitoring Exercise testing Ambulatory blood pressure monitoring |
| Bicuspid aortic valve | Clinical monitoring Echocardiography |
| Re-coarctation or residual stenosis | Clinical monitoring Blood pressure monitoring Echocardiography Magnetic resonance imaging Computed tomography Cardiac catheterization study |
| Distention or aneurysm of the ascending aorta | Echocardiography Magnetic resonance imaging Computed tomography |
| Dilation or aneurysm of the descending aorta | Echocardiography Magnetic resonance imaging Computed tomography Cardiac catheterization |
| Coronary artery disease | Clinical monitoring Stress scintigraphy (myocardial perfusion imaging) Coronary angiography |
| New or different quality headache (should raise alarm to possible cerebral aneurysm) | Neurologic evaluation Magnetic resonance imaging Computed tomography |
BOX 40.1
Complications After Surgical Repair of Aortic Coarctation
-
Persistent or new arterial hypertension at rest or during exercise
-
Distention and/or aneurysm of the ascending and/or descending aorta
-
Re-coarctation or residual stenosis in the region of the aortic isthmus and/or aortic arch
-
Coronary artery disease
-
Aortic stenosis (in patients with a bicuspid aortic valve)
-
Aortic insufficiency (in patients with a bicuspid aortic valve)
-
Mitral valve defects (mitral valve prolapse)
-
Infective endocarditis or endarteritis
-
Rupture of aortic or cerebral aneurysm
Arterial Hypertension
Arterial hypertension, either at rest or during exercise, is common, even after successful treatment of aortic coarctation. The estimated prevalence ranges from 25% to 68%.
Hypertension associated with CoA is probably related to re-coarctation, structural changes in the wall of peripheral and central vessels with abnormal aortic distensibility, reduced baroreceptor sensitivity, alterations in the renin-angiotensin system, raised plasma concentrations of epinephrine and norepinephrine, or the coexistence of essential hypertension. Another significant factor may be a hypoplastic aortic arch that was not corrected. Compared with the general population, arterial hypertension is an important risk factor for increased mortality and morbidity.
As with other forms of uncontrolled hypertension, affected patients are considered to be at risk of ventricular dysfunction, rupture of aortic or cerebral aneurysms, and perhaps premature coronary artery disease. Such complications mainly occur in the third and fourth decades of life.
Patients who underwent surgical correction a long time ago or at an older age are at greater risk of abnormal blood pressure responses after operation than those operated on in childhood.
The previously mentioned Mayo Clinic study showed a direct correlation between cardiac death and raised blood pressure after surgery. The higher the systolic pressure after operation, the greater the probability of early cardiac death. Some studies provide evidence that patients operated on in early childhood (between the ages of 2 and 9 years) have a higher rate of normal blood pressure postoperatively. Several studies also suggest an increase in the prevalence of systemic hypertension with increasing length of follow-up after CoA repair: 13% at 8 years, 49% at 17 years, and 68% at 30 years. In a recent large cross-sectional study, more than 50% of patients were hypertensive after CoA repair, and even 30% of those without restenosis and without noncompliant prosthetic material were hypertensive.
The authors believe that, after CoA repair, systemic hypertension is frequently exacerbated by exercise or occurs only during exercise. The impact of isolated, exercise-induced hypertension is still a matter of debate, but in the follow-up of these patients, regular blood pressure checks, supplemented by selective exercise tests, are necessary.
Re-coarctation or Residual Coarctation
Residual coarctation or restenosis at the site of coarctation is an important cause of morbidity after coarctation treatment because re-coarctation may induce or aggravate systemic arterial hypertension, left ventricular wall mass, coronary artery disease, or diastolic or systolic heart failure. After operation, the reported rate of re-coarctation was found to be between 3% and 15% (−41%).
In 2015, Choudhary et al. reported a re-coarctation rate of 34%.
Re-coarctation or residual stenosis may occur with all known surgical techniques: no single technique appears to be superior to the others. However, in a recent study, adults with end-to-end repair had lower rates of significant re-coarctation.
Re-coarctation is associated with smaller patient size, younger age at operation, and the presence of associated transverse arch hypoplasia. The era in which the operation was performed, the surgical technique used, and the duration of follow-up further influence the risk.
Children who are operated on in infancy or early childhood are at particular risk. After operation in infancy or early childhood, the incidence of residual coarctation and restenosis is high in past studies: 20% to 38%. In patients older than 3 years, it is only about 1.5%.
Re-coarctation is an important issue after operation and after angioplasty, mostly due to an aortic recoil mechanism or scar tissue formation after injury of the aortic intima and/or media. Unfortunately, comparison of the different study results is difficult since comparability is hardly given because of different study design, different patient cohorts, and demographical data.
In earlier studies, restenosis within 20 years is reported in up to 20% of patients with native CoA.
Adults with native coarctation developed a restenosis in 8% to 11%. With respect to re-coarctation after previous surgical repair, the results of several large series involving angioplasty showed an early success rate (pressure gradient less than 20 mm Hg) of 65% to 100%. An early multicenter report of 548 patients showed a complication rate of 13%. In the 1997 pediatric balloon angioplasty study by Yetman et al. 72% of patients with optimal immediate results did not require reintervention within a 12-year follow-up.
Angioplasty of CoA may be unsuccessful because of immediate elastic recoil, long-segment narrowing, or multiple serial obstructions. In such situations, balloon-expandable stents were found to be effective and safe, at least in the short and medium term. Recent studies using uncovered and/or covered endovascular stents have shown low complication and restenosis rates. Therefore, balloon intervention without stenting is no longer recommended in adults with significant coarctation.
Aneurysms of the Ascending Aorta or in the Region of the Aortic Isthmus
Aneurysms of the ascending aorta or in the region of the aortic isthmus carry the risk of life-threatening rupture. The cause of an aneurysm in the ascending aorta has not yet been fully explained ( Fig. 40.3 ). Current consensus is that bicuspid aortic valve, independent aortic wall changes, and/or arterial hypertension may together be largely responsible for aneurysm formation in this area.
Several postoperative follow-up studies comprise cases of late death related to dissection of the aorta, particularly in the ascending aorta. As a consequence, supervision with serial assessment of size and morphology of these ascending aortic aneurysms is mandatory.
Practically all surgical techniques carry the risk of postoperative aneurysms ( Fig. 40.4 ). Their occurrence depends to some extent on the era of the operation, the patient’s age at the time of surgery, the postoperative interval, and the surgical technique employed.
Contemporary studies show postoperative aortic aneurysms in only 5% to 9% of patients. The lowest incidence is reported after end-to-end anastomosis or after extraanatomic tube grafts. In older studies, the reported frequency of aneurysm after Dacron patch aortoplasty was 33% to 51%. The most recent series of adults with CoA describes aneurysms in the descending aorta in 18% of cases. These aneurysms might be detected less often after end-to-end repair than in other methods.
Whether and when postoperative aneurysms arise cannot be predicted with certainty. Some anastomotic aneurysms have been found after a postoperative interval of more than 30 years. In many patients, aneurysms are detected as an incidental finding because their development seldom produces symptoms.
An aneurysm may also occur after balloon angioplasty of native coarctation or postoperative obstruction. The reported frequency of aneurysms after angioplasty in native adult coarctation varies from 3% to 20%.
This situation may be causally connected to the injury to the endovascular layers and to the presence of histologic medial changes in the precoarctation and postcoarctation segments. This complication has been documented despite the presumption that surgical scar tissue after a previous surgical repair may protect against aneurysm and aortic dissection or rupture. Aneurysms may develop immediately after angioplasty or after a period of several months. However, even major tears caused by angioplasty may decrease in size and disappear without aneurysm formation.
Because the incidence of aneurysm after surgery or catheter intervention appears to increase with longer follow-up periods, all patients need careful follow-up after angioplasty or stenting for CoA.
In addition to the problems just specified, there are certain additional issues that have to be considered during follow-up.
Infective Endocarditis or Endarteritis
Patients with coarctation, particularly if untreated, may have an increased risk of infective endocarditis or endarteritis. Altered arterial wall structure and the effect of abnormal blood flow and pressure associated with aortic and mitral valve anomalies or persistent obstruction at the CoA site may predispose the patient to infective endocarditis. Therefore, until recently, lifelong endocarditis prophylaxis was recommended after surgical or interventional treatment of CoA. According to newer international guidelines, endocarditis prophylaxis is no longer recommended, but this guideline is controversial.
Personally, we are more liberal and still recommend endocarditis prophylaxis in certain circumstances, based on careful consideration of the clinical situation, the entire health status, and potential contraindications.
Bicuspid Aortic Valve
Three research groups found that up to 85% (45 of 62) of patients with aortic coarctation have a bicuspid aortic valve. The complication rate of bicuspid aortic valves increases with age. Fibrosis, calcification, or myxomatous degeneration may lead to aortic valve stenosis in 59% to 81% and to aortic valve regurgitation in 13% to 22% of patients.
Besides those valvular lesions, 11% to 15% will develop ectasia of the ascending aorta, which may progress to aortic aneurysm and even to aortic dissection and rupture. A recent Mayo Clinic study reported that acute aortic dissection occurred in 2.5% of patients with bicuspid aortic valves.
Therefore, in addition to valve dysfunction and endocarditis, attention must be paid to the development of an ascending aortic aneurysm.
Aneurysms of the Circle of Willis
Berry aneurysms of the circle of Willis or other vessels occur in up to 11% of patients with CoA ( Fig. 40.5 ). Aneurysm size and the likelihood of rupture increase with age. Uncontrolled hypertension promotes their growth and increases the risk of rupture.
Most patients are asymptomatic until rupture occurs, although some aneurysms may leak prior to rupture, resulting in headache, photophobia, weakness, or other warning symptoms.
Because rupture of a cerebral aneurysm is associated with a high mortality rate, this anomaly should be considered for treatment, at least in symptomatic patients.
The wisdom of screening for cerebrovascular aneurysms is still a matter of debate because of the complex mix of benefits and risks associated with various-sized aneurysms and their possible treatment. However, in the era of newer minimally invasive techniques with coils or exclusion devices, the threshold for treatment has decreased considerably.
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