Disclosure Coarctation is a term derived from the Latin coarctation, meaning a drawing or pressing together. More precisely, coarctation refers to a narrowing of the lumen of a vessel producing an obstruction to flow. A localized segment of narrowing is called a coarctation, whereas a diffuse segment of narrowing is known as tubular hypoplasia. Coarctation was once described as infantile and adult; however, these descriptions were not accurate because both types can be observed in either age group. As our understanding of the pathophysiology of coarctation evolved, the terms preductal and postductal were often used to categorize coarctation in relation to the ductus arteriosus. Although this anatomic description remains true, the exact location usually does not change the presentation; this knowledge has, led to the unified description of most neonatal coarctation as juxtaductal. History of the Procedure: Meckel originally noted coarctation on autopsy in 1750, and Morgagni again noted it in 1760. Forty-four years after Paris provided the first accurate description of coarctation of the aorta in 1791, Legrand made the first diagnosis in a living patient in 1835. Bonnet was the first to categorize coarctation into infantile and adult forms, which were later revised to preductal and postductal forms. Blalock and Park proposed the first surgical repair in 1944, describing a bypass from the left subclavian artery to the aorta to circumvent the area of narrowing. Crafoord and Nylin performed the first resection with end-to-end reanastomosis in 1945, whereas Gross used homografts to replace the narrowed segments of aorta. In 1966, Waldhausen and Nahrwold performed the first subclavian-flap aortoplasty. More recently, advanced interventional cardiology techniques have led to an interest in percutaneous transluminal aortoplasty for both native coarctation and recoarctation. Problem: Coarctation is defined as a narrowing of the lumen of the aorta that obstructs flow. Variations of coarctation depend on the length of the involved segment. Typically located at the insertion of the ductus or ligamentum arteriosum, a localized coarctation may occur at any point along the length of the aorta. Coarctation rarely occurs at multiple sites, a phenomenon sometimes observed in Turner syndrome. Diffuse long-segment coarctation, also known as tubular hypoplasia, is typically found at the aortic isthmus (ie, the segment between the left subclavian artery and the insertion of the ductus). With extreme coarctation, the entire transverse arch may be hypoplastic. Pseudocoarctation Souders first described pseudocoarctation in 1951. Often discovered on simple chest radiography, the aorta has an abnormal contour. Aortography shows a tortuous, kinked aorta with no gradient. Kinking or buckling of the aorta changes the healthy conformation of the aorta but does not obstruct flow. Once thought benign, aneurysmal dilation can occur distal to the affected area, leading to the specter of rupture of the aorta. Current therapy requires close follow-up care. Aggressively pursue surgical repair after the aorta begins to demonstrate progressive dilation. Complete interruption of the aortic arch Complete interruption of the aorta, or interrupted aortic arch (IAA), is a fairly rare condition. First described in 1778 by Steidele, IAA accounts for less than 1.5% of all instances of congenital heart disease. Complete interruption of the aorta is usually associated with other anomalies, including DiGeorge syndrome (29% incidence) (Schreiber, 1997). In 1955, Samson performed the first known surgical correction of IAA. Sirak performed the first repair in a neonate in 1968. Defined as a complete absence of a segment of the aortic arch, the description of IAA is based on the absent segment. In 1959, Celoria and Patton developed the following classification of IAA; Schreiber et al provided the percentages in 1997:
Although the cause is unknown, IAA is associated with defects that decrease ascending aortic flow and increase ductal flow. As with coarctation, abnormal fetal blood-flow patterns are theorized to substantially contribute to the etiology of IAA. Previously uniformly fatal, the development of prostaglandin E1 (PGE1) therapy to maintain ductal patency has greatly improved surgical results by allowing time to optimize the patient's hemodynamic state before surgery. The prognosis of patients with IAA is poor if the condition is uncorrected. The mean age at death is 4-10 days, with 90% dying within the first year of life. After repair, the 10-year survival rate is approximately 47% (Sell, 1988). Whether a staged repair or a single operation should be used to repair IAA remains controversial. Median sternotomy is still preferred if correction of associated anomalies is to occur concomitantly. Methods of surgical correction are similar to those of coarctation repair and include end-to-end anastomosis of the remaining segments with or without patch augmentation, end-to-side anastomosis of the arch vessel with either the proximal or distal segment, or use of an interposition graft to take the place of the missing segment. Mortality Most data demonstrate that mortality rates decrease and outcomes improve with increasing experience. In their series, Schreiber et al demonstrated that early mortality rates decreased from 42% in 1975-1985 to only 17% in 1985-1995, which was a result of improved surgical techniques and advances in the preoperative and postoperative treatment of neonates. Immediate surgical intervention remains the only therapy. IAA is a difficult surgical problem, though the most recent results have been encouraging, with increased survival and decreased morbidity rates. Frequency: Observed in 1 in 3000 to 1 in 4000 autopsies, coarctation accounts for approximately 5-10% of cases of congenital heart disease. Isolated coarctation is more common in males than in females, whereas the incidence of complex lesions is equal in males and females. The birth prevalence of coarctation for patients in 1980-1994 was 0.32 case per 1000 live births (Grech, 1999). Etiology: Although the cause of coarctation remains controversial, 2 major theories are supported by the current literature. Muscular theory The muscular theory suggests that extension of tissue from the ductus arteriosus (a muscular artery) extends into the aorta (an elastic artery) during development. When the ductus contracts and fibroses at birth, it leads to a narrowing of the aortic lumen. Theory of abnormal fetal blood-flow patterns The second theory is related to abnormal fetal blood-flow patterns. During fetal development, the aortic isthmus is a watershed area, as the ascending aorta receives blood from the heart, sending it to the head, while the descending aorta receives ductal blood to send to the rest of the body. As a result, the initial diameter of the isthmus is small, and if the proper molecular cues are not present, it may not grow sufficiently. The incidence of coarctation is increased in disorders in which an obstruction of the left ventricular outflow tract reduces ascending aortic flow. In converse, the incidence is decreased in disorders in which decreased ductal flow is present, such as tetralogy of Fallot. Combination of theories Although both theories provide ample evidence, a combination probably best encompasses the likely etiology (Van Son, 1993). Common associated anomalies of coarctation of the aorta include bicuspid aortic valve, ventricular septal defect (VSD), patent ductus arteriosus, and various mitral-valve disorders. Congenital aortic stenosis, aortic atresia, and hypoplastic left-heart syndrome are less common. On occasion, coarctation to the aorta is observed in transposition of the great vessels, particularly when the right ventricular outflow tract is obstructed. Data suggest that more than 70% of VSDs that occur with coarctation may close spontaneously (Moene, 1987; Park, 1992). Coarctation is observed in as many as 50% of patients with the Taussig-Bing anomaly (Parr, 1983; Sadow, 1985). A genetic or familial basis may be involved because 15-36% of children with Turner syndrome may have coarctation. Pathophysiology: The pathophysiology of untreated coarctation revolves around the associated hypertension. A 3-pronged hypertensive response occurs in the presence of coarctation. Blood pressure is mechanically affected at all levels and at the level of the kidneys, and recent data suggest that hypertension evolves from an endothelial process as well. The natural history of coarctation depends on the age of the individual at presentation and on the associated anomalies. Symptomatic infants have a high mortality rate, and those who survival to adulthood still have greatly decreased life expectancy, even with surgical correction. The data have changed somewhat over the years with the introduction of antibiotics and improved neonatal care; however, untreated coarctation still results in a grave prognosis. In 1928, Abbott reviewed 200 cases with coarctation in patients older than 2 years and found that 34% died by the time they were aged 40 years, with an average age at death of 42 years. At that time, the 3 major causes of death were spontaneous rupture of the aorta, bacterial endocarditis, and cerebral hemorrhage. Neonates usually present with left ventricular failure as a result of severe and acute afterload, which is further exacerbated by acidosis. This acidosis results from diminished peripheral flow secondary to the coarct itself, in addition to the failing left ventricle. Twenty years later, in 1947, Reifenstein reviewed 104 cases and found little change, with an average age at death of 35 years. The 2 leading causes of death were unchanged. By 1970, the results had improved somewhat; however, the mortality rate was still 75% by the time a person with coarctation was aged 46 years (Campbell, 1970). In persons with untreated coarctation, the coronary arteries have intimal degeneration, medial thickening, and increased mineralization, all of which are secondary to the hypertension associated with untreated disease. Clinical: The clinical presentation of patients with coarctation depends on their age at presentation and on the presence and severity of any associated anomalies. The 2 clinically significant variants, preductal and postductal coarctation, can manifest in different ways. Preductal coarctation Preductal coarctation is associated with an increased incidence of cardiac defects, and the patient may present with congestive heart failure (CHF) if a VSD is present. A preductal defect does not change normal fetal blood-flow patterns. As a result, no collaterals form in utero. If blood flows through the patent ductus arteriosus, pulses are often palpable in the lower extremities. Symptoms develop as the ductus closes, leading to a clinically significant obstruction. On clinical examination, the infant often is irritable and disinterested in feeding. Tachycardia is often present. Few findings may be apparent on physical examination in a healthy-appearing infant. However, in the uncompensated patient, differential cyanosis may be observed between the upper body and the lower body. A systolic murmur may be present over the left precordium or between the scapulae on the patient's back. An infant who is compensating (ie, one with a left-to-right shunt through a patent foramen ovale) should have a substantial systolic blood-pressure gradient between the arms and the legs. Physical findings in a neonate who is decompensating and critically ill may differ substantially. The blood-pressure gradient is often absent secondary to diminished cardiac output. Hypotension, oliguria, and severe metabolic acidosis are concurrent with severe coarctation, as blood flow to the kidneys and all distal structures is drastically impaired. In severe obstruction or in IAA, diagnosis by physical examination can be obscured as long as the ductus remains patent because the pulmonary artery pulse is palpated in the femoral arteries. Paraductal and postductal anomalies Paraductal and postductal anomalies are often isolated defects, and the incidence of associated anomalies is low. Later in life, patients may present with headache, epistaxis, or visual disturbances. Exertional dyspnea and stroke are other presenting symptoms (Shearer, 1970). Coarctation can be clinically diagnosed depending on the available evidence, as described above. To summarize, hypertension or a systolic blood-pressure gradient between the arms and legs may be observed. Checking the patient's blood pressure in both arms is important because an anomalous origin of the right subclavian distal to the coarcted segment may be present. A systolic murmur over the left precordium or between the scapulae may be heard, and the femoral pulses may be absent or diminished with a delayed upstroke. In children older than 5 years, look for the signs of collateral circulation, ie, enlarged and palpable collateral vessels, audible bruits, and dilatation of the intercostals (rib notching).
The presence of coarctation alone is usually indication for surgery. Timing of the operation and the method of repair are decisions to be made. Symptomatic infants often require urgent surgery. However, the patient's condition must be stabilized with medical therapy before the coarctations is repaired. Neonates often present with profound acidosis and respiratory distress. An infusion of PGE1 may be administered within a month of birth, and it often opens a closed ductus.
Relevant Anatomy: The most relevant anatomy for understanding coarctation of the aorta is the aortic arch, the great vessels, and the insertion of the ductus. Because coarctation and IAA can occur anywhere along the arch, being able to recognize the origins of the great vessels, especially on aortography, is important. The ductus arteriosus is a remnant of the sixth left aortic arch; it connects the pulmonary trunk with the aorta in utero and attaches to the lower concave surface of the aortic arch directly opposite the left common carotid and left subclavian arteries. The left recurrent laryngeal nerve hooks around the lower border of this structure and can easily be damaged if care is not taken to avoid it. Contraindications: Generally considered a life-saving procedure, repair of coarctation has few absolute contraindications. Coexisting illnesses or anomalies in an infant (eg, necrotizing enterocolitis) make take initial precedence in treatment. Sepsis is likely the greatest relative contraindication to surgery. This condition is related to the overall inflammatory response and to edema formation observed with the septic immune response. Dissection into the periaortic space is made more difficult that is otherwise would be, and the crucial tension-free anastomoses are considerable more difficult to construct than they are in other situations. |
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In coarctation, ductal tissue often encircles the lumen of the aorta. As the ductus attempts to close soon after birth, ductal tissue encroaching on the aorta constricts as well, narrowing the aortic lumen. Of importance, this ectopic tissue growth is not present in all patients. This observation led to the proposal that coarctation is not a result of abnormal tissue growth, but rather, a result of abnormal fetal blood-flow patterns (Rudolph, 1972).
Medical therapy: The role of medical therapy in coarctation is limited. Medical therapy is confined to preoperative temporization to optimize the patient's hemodynamic status before surgery. Since 1984, medical therapy of coarctation has revolved around the introduction of PGE1 therapy. PGE1 allows for reopening of the ductus arteriosus and perfusion to the lower body. When PGE1 therapy is effective, the severe acidosis and oliguria, which are often present, are corrected by reestablishing blood flow to the lower body. Optimizing the patient's hemodynamic status and converting an otherwise emergency procedure into an elective one can substantially reduce the mortality risk. For additional information, please see Coarctation of the Aorta. Surgical therapy: Several techniques are currently used to repair coarctation of the aorta. The method of repair is usually tailored to each patient. To help determine the operative approach, consider the length of the segment involved and whether associated anomalies are present. Several surgical methods of repair are employed, including end-to-end reanastomosis, subclavian flap aortoplasty, prosthetic patch onlay grafts, and interposition grafts (see Intraoperative details). Many variations of the described procedures have been used throughout the years, including modification of the subclavian flap that include reimplantation, end-to-end anastomosis using the subclavian to enlarge the anastomosis, and ascending aorta–to–descending aorta bypass grafts. All of these techniques may be useful depending on the individual anatomy and associated anomalies. The repair of associated anomalies at the time of aortic coarctation repair remains controversial. Optimal management remains unclear. Current knowledge suggests ligation and division if a patent ductus is present. A bicuspid aortic valve can usually be left alone. Repair of VSDs remains somewhat clear; in the past, a band was often placed on the pulmonary artery. However, many VSDs associated with coarctation closed spontaneously. If preoperative CHF does not resolve, a second operation is required to close the VSD. In 1992, Park et al demonstrated that this suggestion was a feasible option in 23 infants younger than 3 months, 9 of whom required no further treatment. Six required early closure of the VSD, and 8 required late repair. Seven more were older than 3 months, and none required repair of the VSD. Although this approach is controversial, many surgeons prefer to repair a clinically significant VSD when the coarctation is repaired. If concurrent repair of associated anomalies is to be attempted at the time of coarctation repair, the best approach is by means of a median sternotomy (Ungerleider, 1987). Coarctation repair is then carried out in a manner to that used to repair and IAA.
Given the technical complexity of coarctation repair, the list of complications is remarkably short. Many of the complications are not specific to coarctation but are common with other cardiac procedures; these include hemorrhage, infection, chylothorax (from injuries to the thoracic duct), suture line thrombosis, and suboptimal repair or recurrence. A number of complications are unique to both aortic surgery and coarctation. A 2-phased phenomenon of paradoxic hypertension can occur after coarctation repair. During the first phase, systolic blood pressure rises throughout the first 24-36 hours after the operation. This rise is believed to result from activation of the sympathetic nervous system with elevation of serum catecholamine levels. A rise in diastolic blood pressure occurs later and is a result of activation of the renin-angiotensin system. Another complication unique to coarctation repair is the postcoarctectomy syndrome of abdominal pain and distension that Sealy first described in 1957. As many as 20% of patients have this complication, and laparotomy may be necessary. In 1985, Kawauchi et al noted that mesenteric ischemia secondary to acute necrotizing arteritis appeared to be the cause. Recent data suggest that aggressive control of postoperative hypertension usually prevents the full-blown syndrome. In addition, this phenomenon appears to be associated with coarctation in older patients, as this complication is rarely seen with infants and small children. The most worrisome complication after coarctation repair continues to be paraplegia, which occurring in 0.1-1% of neonates after coarctation repair. No definitive predisposing factors are known. Current data suggest that poor collaterals, anomalies of the origin of the right subclavian artery, distal hypertension during cross-clamp, reoperation, or relative hyperthermia during the operation may all contribute to the incidence of paraplegia. The incidence in the adult population undergoing coarctation repair rises proportionately with age and is as high as 2.6%. The tremendous variation in spinal-cord blood supply, including the elusive artery of Adamkiewicz, makes predicting adequate collateral flow extraordinarily difficult. Some theories suggest that maintaining a distal aortic pressure of >60 mm Hg may help to prevent cord ischemia (as measured by means of maintenance of somatosensory evoked potentials), and some have suggested using a shunt to achieve this if necessary. In 1987, Cunningham demonstrated that distal hypertension with loss of somatosensory evoked potentials for >30 minutes resulted in a >70% incidence of paraplegia. Other complications include temporary or permanent hoarseness from recurrent injury to the laryngeal nerve. The nerve can be injured directly by transection or indirectly by retraction. Careful identification of the anatomy and knowledge of the course of the recurrent laryngeal nerve is critical to avoid this complication.
Outcomes from coarctation repair depend on several factors, most notably the patient's age at the time of operation, the method of repair, and the presence of associated anomalies. The recoarctation rate with the end-to-end repair has historically approached 60%, with somewhat lower rates for subclavian-flap aortoplasty and prosthetic graft repair. However, recent studies have demonstrated that end-to-end repair favorably compares with other techniques, with recoarctation rates of only 5-10% (Van Son, 1999). Some suggested reasons for this dramatic change are improved neonatal intensive care units and advances in vascular surgical technique and suture materials. Improved preoperative conditioning and increased use of prostaglandins have also contributed to lowered mortality rates. Circumferential suture lines were initially blamed for high rates of recoarctation; however, since this technique was perfected with the arterial switch operation, they should likely prove effective for coarctation as well. At this time, the current authors know of no prospective randomized trials that are being conducted to compare the repair techniques. Overall mortality rates are still 2-10% in neonates, which includes those with intracardiac anomalies as well as those with coarctation. A 1998 retrospective study of 176 patients by Seirafi and associates demonstrated an overall mortality rate of 7.4%. Nine of 13 deaths were in patients with associated complex intracardiac anomalies. No mortality occurred in the 113 patients with isolated coarctation. A 15% incidence of residual or recurrent coarctation was reported, though neither the patient's age at operation nor the type of repair appeared to influence recurrence. The other major complication was persistent hypertension, which was associated with repair in patients older than 1 year (27% vs 4.2%). In 1998, Backer and associates reported a series of 55 infants who underwent repair by using extended resection with end-to-end reanastomosis. They reported a 5.4% mortality rate and a 3.6% rate of recurrence. The median age at surgery was 21 days. A total of 62% of surgeries performed through a left thoracotomy and the others through a median sternotomy with concurrent repair of associated anomalies. About 47% of patients had isolated coarctation, and 53% had at least 1 associated intracardiac anomaly, with VSD representing 69% of those anomalies. Total resection of all ductal tissue was achieved. In 2000, Allen and associates described a modified subclavian patch aortoplasty. They demonstrated excellent results in 53 infants with no mortality and only a 4% incidence of clinically significant recoarctation. Of these instances, 49% were associated with cardiac anomalies. As with all techniques, the key features to this technique are a tension-free repair and a long aortotomy to help prevent restenosis. Despite some excellent outcomes, controversy remains over the use of flap aortoplasty in infants younger than 3 months. Potential pitfalls are associated with early use of this technique, most notably concern over the loss of the major vascular supply to the left upper extremity. Complications are rare (the left subclavian was historically divided for pulmonary systemic shunts, with complications occurring rarely); however, decreased growth and rare reports of ischemia and gangrene have been documented (Sciolaro, 1991). In addition, neonates most often have associated arch hypoplasia, which is better addressed with resection and end-to-end anastomosis than with other methods. Complete hypoplasia of the aortic arch is best addressed by means of arch reconstruction performed through a median sternotomy. The prosthetic-path onlay technique has the advantages of a relatively short operating time, minimal dissection, maximal augmentation of the stenosed area, and maintenance of normal vascular anatomy. However, this technique has been associated with an aneurysmal-development rate of up to 35%, and repeat operation is required in almost 20% of patients (Aebert, 1993).
Balloon angioplasty has been performed for more than 20 years; however, its use in coarctation remains controversial because of the formation of pseudoaneurysms and concerns about long-term patency. The surgical literature shows a high restenosis rate for neonatal (<40 d) balloon angioplasty; 57% need surgical intervention. However, in the population with surgically treated restenosis (18%), secondary angioplasty is the treatment of choice, and no repeat interventions were necessary (Fiore, 2005). A recent long-term randomized study of angioplasty versus surgery in children (3-10 y) showed that only 50% of patients treated with balloon angioplasty remained free of both aneurysmal formation and repeat intervention compared with 87.5% of surgically treated subjects (Cowley, 2005). Stent placement has also been studied, though (to the authors' knowledge) no long-term results have been reported. A report published in 2000 by Thanopoulos et al suggests that stent implantation can be performed with low morbidity and mortality rates and that no recoarctation was noted in any of the 17 patients who were examined at the age of 33 months. Peak systolic gradients were reduced to just 2.1 mm Hg from 50 mm Hg. A report of retrospective study by Marshall et al in 2000 suggested that, though stent implantation was a feasible option for challenging cases, it was not without a risk of serious complications. At present, the optimal timing and mode of treatment for patients with coarctation remains controversial. In neonates and young children, surgical intervention remains the criterion standard. However, for patients with hemodynamic instability or for those who have undergone surgery for restenosis, angioplasty can be a palliative and potentially curative procedure. Stent placement is still under investigation in adolescents and adults, and long-term data is still being released. The future of aortic coarctation repair may include direct genetic intervention or in utero therapy, which may decrease the growth of ductal tissue into the main aorta or which may help alter neonatal blood flow in such a way to prevent coarctation completely. Until that time, surgical techniques will continue to improve, and the use of angioplasty should continue as we find the subset of patients in whom it will prove most useful.
Coarctation of the Aorta and Interrupted Aortic Arch: Surgical Perspective excerpt | |||||||||||||||||||||||||||||||||||||||||||
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