Coarctation derives from the Latin term coartatio , which translated literally means a drawing together. Aortic coarctation, therefore, indicates a narrowing at some point along the course of the aorta. When used in the context of the congenitally malformed heart, coarctation most usually described an area of narrowing of the thoracic aorta in the region of the insertion of the arterial duct, with or without additional abnormalities of the aortic arch. Obstructive lesions can be found more proximally, involving the ascending aorta. These are considered, along with lesions of the aortic valve, in Chapter 44 . Those distal to the thoracic aorta, together with acquired lesions, are beyond the remit of this chapter. Within this chapter, however, we will include consideration of patients with interruption of the aortic arch. This condition exists when there is discontinuity between two adjacent segments of the aortic arch, and in haemodynamic terms includes cases with a fibrous cord between the discontinuous segments. In this respect, interruption can be interpreted as the extreme end of the spectrum of obstruction of the aorta ( Fig. 46-1 ).
HISTORICAL CONSIDERATIONS
The first description of aortic coarctation is generally attributed to Johann Freidrich Meckel, the famous Prussian anatomist, who presented the case of an 18-year-old female to the Royal Academy of Sciences of Berlin in 1750. At postmortem, she was found to have an aorta that was ‘so narrow that its diameter was smaller by half than that of the pulmonary artery, which it should have exceeded or at least have equalled in calibre’. Some argue, however, that it was Morgagni who should be given priority. 1 As pointed out by Craigie, 2 nonetheless, a more recognisable description was published in Desault’s Journal de Chirurgie in 1791. According to Craigie, Monsieur Paris, the Prosector of the Amphitheatre at the Hotel-Dieu described, in the winter of 1789, the postmortem of ‘a very emaciated woman about 50 years old’. As well as recognising that the thoracic arteries were thicker and more tortuous than normal, he gave the following description: ‘The part of the aorta which is beyond the arch, between the ligamentum arteriosum and the first inferior intercostal, was so greatly narrowed that it had at most the thickness of a goosequill. Hence in taking apart its walls, which had not decreased in this place, there remained only a small lumen. The part of the vessel which was above the constriction was slightly dilated; the distal part was of normal calibre. The most careful dissection did not reveal either in the aorta or in its vicinity any cause to which this extraordinary condition could be attributed’. With regard to interruption of the aortic arch, as discussed above, this can be considered as the severest end of the spectrum of aortic coarctation (see Fig. 46-1 ). It was Celoria and Patton 3 who classified this lesion into types A, B and C ( Fig. 46-2 ). Interruption at the aortic isthmus had been the first pattern described, being recognised in 1778 by Stiedele in Vienna. 4 The more common variety, with interruption between the left common carotid and left subclavian arteries, was described some 40 years later by Siedel. 5 The least frequent variant, with interruption between the brachiocephalic and left common carotid arteries, was not seen until 1948. 6
PREVALENCE AND AETIOLOGY
Aortic coarctation accounts for 7% of liveborn children with congenitally malformed hearts, 7 with a higher incidence in stillborn infants. 8 The overall incidence is in the region of 1 in 12,000, with a slight increased occurrence in males. 9 Coarctation is generally said to show multi-factorial inheritance, although genetic factors are clearly important in certain groups. The lesion was found in one-tenth of a large Danish series of patients with Turner’s syndrome, albeit with a lower incidence in patients with mosaicism, or those with structural anomalies of the X chromosome. 10 Inheritance has also been reported as an autosomal dominant trait. 11 It is now known that cells migrating from the neural crest populate the aortic arches, and 22q11 deletion is well recognised as being associated with interruption between the left common carotid and subclavian arteries. 12 The finding of coarctation in an infant with this deletion, therefore, prompted suggestions of a similar association. 13 There is a reported seasonal incidence, with paucity of males born between April and August, but without any identification of an exogenous aetiological agent. 14
Interruption of the aortic arch accounts for just over 1% of cases of so-called critical congenital cardiac disease. 9 As already emphasised, there is a known association between deletion of chromosome 22q11, or Di George syndrome, and interruption between the left common carotid and subclavian arteries. This is known to be due to abnormal migration of cells from the neural crest. 12 As many as one third of those with Di George phenotype have interruption of this type, and, conversely, two-thirds of those with interruption between the left common carotid and subclavian arteries have Di George syndrome. 15 Taking those with interruption as a group, interruption between the left common carotid and subclavian arteries is held to account for between half and three-quarters of cases, interruption at the isthmus for two-fifth, and interruption between the carotid arteries is rare. 16,17 Interruption as an isolated lesion is also rare. 18 The combination of congenital absence of the aortic isthmus, patency of the arterial duct, and ventricular septal defect is very common and reported to occur in three-quarters of patients with interruption. 19 The incidence is equal between the genders. 16
MORPHOLOGY
The lesions to be considered in this chapter all occur in proximity to the junction of the aortic arch and the arterial duct. This junction is clearly of fundamental importance to their evolution and morphology, although isolated coarctation can also exist proximal to the brachiocephalic arteries, or in the descending thoracic aorta. Aortic coarctation, however, is not a uniform entity. Rather, it represents a spectrum of lesions, generally encompassing variable degrees of hypoplasia, along with additionally stenotic areas, within the aortic arch. The extreme end of the spectrum is interruption of the aortic arch (see Fig. 46-1 ). Less severe is the presence of a fibrous cord between the interrupted segments of the arch, so that there is haemodynamic interruption but anatomic continuity. This is also known as atresia of the arch ( Fig. 46-3 ). Tubular hypoplasia is present when there is a uniform narrowing of part of the arch ( Fig. 46-4 ), whereas discrete coarctation is produced by a localised shelf-like lesion within the lumen of the arch, often with a degree of proximal tapering of the arch itself towards the obstructive shelf ( Fig. 46-5 ).
The Obstructive Lesions
Presence of a discrete obstructive shelf within the lumen of the arch is much commoner than tubular hypoplasia, and has been the subject of manifold classifications. The most systematic approach was suggested by Edwards, 20 who emphasised the need to describe precisely the site of coarctation, irrespective of whether the arterial duct is patent, closed or ligamentous, and irrespective of the presence of additional anomalies. These other features, of course, also require description. In terms of location, nonetheless, when the arterial duct is patent, then the obstructing lesion can be preductal, paraductal, or postductal ( Fig. 46-6 ). The most common site for discrete coarctation is at the junction of the aortic isthmus, the arterial duct or ligament, and the descending aorta. When the duct is open, there is usually a degree of isthmal hypoplasia, with the isthmus tapering down towards the junction with the duct, and the obstruction is preductal ( Fig. 46-7 ). The obstructive lesion itself takes the form of a discrete waist, associated with infolding of the aortic wall ( Fig. 46-8 ). In the majority of cases, the shelf is formed by ductal tissue, which completely encircles the lumen of the isthmus (see Fig. 46-5 ). The ductal shelf produces the major obstruction to flow, being the most important factor in coarctation. The waisting of the aortic wall usually accompanies the ductal shelf, but can occur in isolation. 21 When the arterial duct is closed, then the ductal shelf becomes converted to a fibrous diaphragm, often with a pinhole meatus ( Fig. 46-9 ). Paraductal coarctation occurs directly opposite the mouth of the duct at its insertion to the aorta, and is found in one-tenth of cases ( Fig. 46-10 ). Postductal obstruction is seen distal to the aortic origin of the arterial duct, and again accounts for about one-tenth of cases seen in infancy. The most important consequence of this variant is the lack of improvement of such critically ill infants despite maintenance of ductal patency with prostaglandin. Such postductal coarctation is the norm in adults, although then occurring in postligamental, rather than postductal, position.
Tubular hypoplasia, describing the presence of a uniformly narrow segment of the aortic arch, frequently co-exists with discrete coarctation, but can exist in isolation (see Fig. 46-4 ). It is distinct from the gradual tapering of the isthmus characteristically seen with discrete coarctation (see Fig. 46-7 ). Histologically, the wall of an affected segment is normal, in contrast to the ductal and fibrous nature of discrete coarctation. The most frequent sites for tubular hypoplasia are either at the isthmus, or between the common carotid and the left subclavian arteries (see Fig. 46-4 ). It is rare for the segment between the brachiocephalic and left common carotid arteries to be affected. Atresia of the aortic arch exists when the arch itself is anatomically continuous, but there is no patency within one of its segments. The commonest site for such atresia is the aortic isthmus (see Fig. 46-3 ), but atresia can also be found between brachiocephalic and left common carotid arteries. Interruption exists when there is anatomic, as well as haemodynamic, discontinuity between segments of the aortic arch (see Fig. 46-2 ). The commonest site for interruption, accounting for about three-quarters of cases, is between the left common carotid and subclavian arteries ( Fig. 46-11 ), the so-called Type B pattern of Celoria and Patton. 3 Most of the remaining cases show interruption at the isthmus, the so-called Type A ( Fig. 46-12 ). As we have already emphasised, interruption between the brachiocephalic and left common carotid arteries, so-called Type C, is extremely rare.
Associated Malformations
The presence of associated cardiovascular lesions was one of the criterions commonly used to differentiate coarctation found in patients presenting in infancy from those presenting, often in isolation, in later childhood and adulthood. In this respect, the association of aortic coarctation, hypoplasia of the isthmus, patency of the arterial duct, and the presence of an interatrial communication or patency of the oval foramen, is so common as to be referred to sometimes as part of a coarctation complex in neonates. The typical associated anomalies are those that tend preferentially to potentiate flow to the pulmonary rather then systemic arterial pathway. Such lesions lead to reduced flow through the aortic isthmus in fetal life. This can be produced first by defects that produce left-to-right flow at either the level of the ventricles or the great arteries. The most common of these lesions is a ventricular septal defect. When found in the presence of coarctation, the ventricular septal defect is similar to the archetypical pattern found in hearts from patients with interruption of the aortic arch, with posterior deviation of the muscular outlet septum, or its fibrous remnant, into the subaortic area, the deviation leading to subaortic obstruction 22 ( Figs. 46-13 and 46-14 ). In the setting of coarctation, however, the defects are more frequently perimembranous, and associated with postero-inferior overriding of the aortic valve 22 ( Fig. 46-15 ). Interruption of the aortic arch can be found with an aortopulmonary window rather than a ventricular septal defect (see Fig. 46-12 ). It, and coarctation, of course, can be found in the setting of discordant ventriculo-arterial connections, or double outlet ventricle, or common arterial trunk. The coarctation or interruption is then considered the associated lesion, and these are dealt with in the appropriate chapters of our book. Very rarely, interruption can be found in the absence of associated lesions, and with a closed arterial duct. 18,22 The supply to the lower half of the body is then dependent on collateral circulation.
The second mechanism underscoring the existence of associated lesions is one producing obstruction to the outflow from the left ventricle both pre- and postnatally. Lesions falling into this second category include valvar and subvalvar aortic stenosis, and potentially the aortic valve with two leaflets. Congenital stenotic lesions of the mitral valve will also lead to decreased flow through the aortic arch, as will supravalvar mitral shelf, stenosing left atrial ring, and divided left atrium. The presence of several such lesions in combination presents a particularly poor prognosis, with the heart itself in such settings overlapping with the hypoplastic left heart syndrome. The best known combination involves co-existence of parachute mitral valve, supravalvar left atrial ring, subaortic stenosis, and aortic coarctation. It is known as Shone’s syndrome. 23
The aortic valve with two leaflets is usually haemodynamically insignificant in early postnatal life. It is, nonetheless, a common finding in patients with aortic coarctation. In later life, the malformation of the aortic valve predisposes to calcific stenosis, regurgitation, and infective endocarditis. When found in association with coarctation, however, the morphology of the bifoliate valve is significantly different from that seen as an isolated lesion. 20 When found in patients with coarctation, the valve typically has two equally sized leaflets, whereas bifoliate aortic valves seen in isolation usually have leaflets of unequal size. Irrespective of the valvar morphology, there is a known association between the bifoliate valve and weakness in the aortic wall, this accounting for the long-term incidence of dilation, and subsequent dissection of the aortic root and ascending aorta. 24 Whether this association will produce problems in the long-term follow-up of patients with coarctation has still to be established.
Anomalies of the subclavian arteries can accompany either discrete coarctation or interruption of the aortic arch. They are important both clinically and surgically, being seen more frequently in association with interruption. The most common anomaly is origin of the right subclavian from the aorta distal to the site of the ductal insertion (see Fig. 46-11 ). The anomalous artery then pursues a retro-oesophageal course, often arising from the expanded segment of aorta called the diverticulum of Kommerrell. The left subclavian artery can also be anomalous, arising paraductally (see Fig. 46-4 ). In this setting, the isthmus itself is exceedingly short or non-existent. The mouth of the subclavian artery can be incorporated in the ductal sling, and has a tendency to be stenosed at its origin.
As might be anticipated, coarctation, atresia, or interruption can also occur when the aortic arch is right sided. Coarctation can also be found in the setting of a double aortic arch, while interruption of part or parts of the hypothetical double aortic arch is an essential part of the understanding of vascular rings (see Chapter 47 ). Abnormal ventriculo-arterial connections are also described with interruption, including discordant ones, double outlet right ventricle with subpulmonary defect, or the Taussig–Bing malformation, 25 aortopulmonary window with intact septum, 26,27 and congenitally corrected transposition. 28
Collateral Circulation
Although rarely present in infants, collateral circulation gradually develops throughout childhood in those with subcritical coarctation. Such collateral arteries bypass the obstruction and augment perfusion to the lower body. The most common pattern involves a large aberrant artery arising from the right subclavian artery, and supplying the aorta below the coarctation, together with various branches of the left subclavian artery, including the thyrocervical trunk, the left intercostal arteries via the left internal thoracic artery, this leading to notching of the ribs, and the anterior spinal artery through the left vertebral artery. One particular vessel in this circulation has achieved recognition as the artery of Abbott. This anomalous vessel ( Fig. 46-16 ) arises from the posterior aspect of the isthmus, and passes medially behind the carotid artery and transverse arch. 29
Secondary Pathology
Secondary pathology can be divided into local effects, effects on the myocardium and distant effects, the last in general caused by hypertension. The local changes tend to be characteristic. In older children and adults, fibrous intimal thickening is superimposed on the site of coarctation. The thickened layer is composed of concentric layers of collagen, with varying degrees of elastin and smooth muscle cells. The characteristic depletion and disarray of elastic tissue seen with cystic medial necrosis have also been observed. 30 The intimal proliferation, together with superimposed thrombus, can lead to near or complete obliteration of the lumen. In such instances, all distal perfusion becomes dependent on the collateral circulation. The distal aortic wall often shows post-stenotic dilatation and is somewhat thinner than normal. The abdominal aorta may, however, be somewhat hypoplastic owing to diminished flow. The combination of these local changes accounts for the occasional development of aortic dissection in patients with advanced disease without treatment. Pregnancy imposes an increased haemodynamic strain on the aortic wall owing to the physiological changes that occur, particularly in the last trimester and peripartum. Aortic dissection, and even rupture, can initially be misdiagnosed as pre-eclampsia. Such complications can also follow an apparently successful repair. Whether earlier surgical intervention decreases the occurrence of the changes in the aortic wall is not yet known.
The direct effect on the myocardium of obstruction to the left ventricular ejection depends on the rapidity of the onset, as well as the degree of the increase in afterload, the left ventricle having numerous compensatory mechanisms. In the neonate undergoing rapid decompensation with ductal closure, left ventricular systolic and diastolic dysfunction rapidly lead to congestive hear failure. Diastolic flow in the coronary arteries decreases as left ventricular wall stress increases. This leads to ischaemia, especially of the subendocardium. The resultant decrease in cardiac output causes, and then perpetuates, a metabolic acidosis, which further depresses the left ventricular contractility. In part, in infancy, this is a consequence of the inability of the myocardium to mount the usual adaptive responses to increased impedance to outflow. These will be discussed below under pathophysiology. Unless intervention is performed, death can be rapid. Of those who survive the initial insult, some develop marked subendocardial fibrosis. If the onset of obstruction is less abrupt, compensatory adaptations can occur, primarily in the form of left ventricular hypertrophy. Ischaemic heart disease eventually occurs in many, even in the absence of proximal coronary arterial occlusion. Distant complications include the well-recognised and classic berry, or saccular, aneurysm of the circle of Willis. All the organs in the upper body can sustain pathology secondary to hypertension. These changes are not entirely ameliorated by the initial relief of obstruction. This will also be discussed at greater length in the sections to follow.
Morphogenesis
There are three main aberrations in embryological development proposed to explain abnormalities of the aortic arch. The first, abnormal embryogenesis of the vessels of the arch, and the second, abnormal development of the arterial duct, are closely interlinked. The third implicates changes in the ratio of flow between the pulmonary and systemic arterial pathways.
In the usual situation, with a left-sided arch, it is the left fourth branchial arch that becomes the definitive aortic arch. The arterial duct is the persisting artery of the left sixth branchial arch, connecting to the dorsal aorta. The left subclavian artery, in contrast, forms from the seventh segmental artery. This must undergo a cephalad migration through differential growth before it assumes its definitive position proximal to the aortic isthmus. In its migration, it must cross many structures. Derangements in this process are suggested to be of importance in the pathogenesis of coarctation. The hypothesis implicating the arterial duct is based on the presence of the ductal sling around the entire circumference of the aortic isthmus in the setting of coarctation. Unequivocal evidence of such a ductal sling ( Fig. 46-17 ) was provided initially by Wielenga and Dankmeijer, 31 and subsequently confirmed by others. 32,33
The third proposal is that the patterns of flow of blood in the fetal circulation influences embryogenesis, specifically that a reduction in the volume of blood passing through the ascending aorta in fetal life leads postnatally to the development of coarctation. 34 Such a hypothesis is strongly supported by the common association of coarctation with other obstructive lesions in the left side of the heart, along with those malformations that result in decreased flow in the fetal ascending aorta.
No single hypothesis can explain the morphogenesis of all obstructive lesions in the aortic arch. It is most likely that there is interplay between the various mechanisms. It is highly likely, for example, that decreased flow to the aorta in some way influences the distribution of ductal tissue in the aortic arch. These basis mechanisms certainly help in the understanding of the clinical presentation, early management, and even successful treatment of the various obstructive lesions to be described below.
Presentation and Clinical Symptomatology
Neonates and Infants
Most infants with coarctation or interruption present with varying degrees of heart failure in infancy. When seen immediately, this is manifested by collapse, or later by poor feeding, sweating, breathlessness and failure to thrive. The group that survives infancy without symptoms will be discussed below. The onset of cardiac failure is commonly within the first 3 months of life, but a significant number present within the first week of life, who uniformly will have critical narrowing of the aorta. They present when the supplementary effect of blood flow through the duct from the right ventricle to the descending aorta is interrupted by its closure, critically limiting the blood flow to the lower body. The situation, therefore, is often described as a duct-dependent systemic circulation. This process causes them to become acutely unwell with metabolic acidosis, shock, renal failure and necrotising enterocolitis. Similarly, interrupted aortic arch tends to present with cardiac heart failure of acute onset occurring simultaneously with closure of the arterial duct within the first few days of life. Four-fifths are admitted to a specialist hospital within 2 weeks. 35
The secondary effects of acidosis on the myocardium, will then lead to additional global reduction in cardiac output. The coarctation itself may only be recognised as the infant is resuscitated. With the introduction of prostaglandin E 1 in the 1970s, it was possible to temporarily maintain ductal patency, and this revolutionised the management of these infants. This will be discussed below.
In the most common situation, where interruption is associated with a patent arterial duct and ventricular septal defect, the infant will initially be well because the pulmonary vascular resistance is high and blood will, therefore, pass through the arterial duct to the systemic circulation. One of two events will precipitate collapse in these infants. First, ductal closure will lead to a critical reduction in lower body perfusion and rapid development of acidosis and shock. Second, a falling pulmonary vascular resistance in the presence of a widely patent duct will lead to preferential flow of blood to the pulmonary circulation to the detriment of the systemic circulation. More slowly progressive, but potentially equally important, tissue acidosis leading to collapse may also occur. In those with the rarer variant of interruption occurring in isolation, there must be a collateral circulation, usually via the head and neck vessels, which can develop very rapidly. 36
Physical Findings
The signs on presentation in infancy include tachypnea, with intercostal recession. If markedly low cardiac output is present, they will often show profound skin mottling, slow capillary refill, and peripheral cyanosis. Central cyanosis will occur only in the presence of an associated cyanotic congenital cardiac lesion, or when there is persistence of the fetal circulation. The presence of palpable femoral pulses in the first day or two of life does not exclude the diagnosis of coarctation or interruption, since flow of blood to the lower body may be maintained antegradely through the persistently patent arterial duct. Once symptoms occur, the femoral pulses are usually weaker, or absent. If the patient has severe low output and no pulses are felt, resuscitation usually causes the pulses in the right arm to return. The praecordium is often active, unless myocardial function is depressed. On auscultation, there is usually a summation gallop rhythm. There is often a systolic murmur found along the left sternal edge, from the site of coarctation, and this may also be audible posteriorly. The continuous murmur classically ascribed to coarctation is unusual in infancy. Associated cardiac or central vascular defects, such as the persistently patent arterial duct, can produce additional murmurs. An ejection systolic murmur may indicate an associated bicuspid aortic valve. Signs of congestive heart failure, such as hepatomegaly and crepitations on auscultation, are commonly found. Auscultation in patients with interrupted aortic arch is usually unhelpful. Often a gallop rhythm is present, and the heart sounds are usually easily audible, the second being split. An ejection click may indicate the presence of associated bicuspid aortic valve, but this is non-specific. If a murmur is present, it is often pan- or mid-systolic and of low intensity, indicating the non-restrictive nature of the ventricular septal defect.
Measurements of the blood pressure in all four limbs reveal a gradient between the upper and lower limbs irrespective of the method used to measure it, although Doppler appears preferable. 37 It should be remembered that differences in pressure of up to 20 mm Hg may be revealed by Doppler interrogation in the normal neonate, presumably owing to the isthmal narrowing that is normal at this stage. 38 It is sometimes necessary to measure blood pressures serially if the diagnosis remains unclear. Paradoxically, the diagnosis of coarctation can be made more difficult by the administration of prostaglandin. Although greatly improving the physical condition, the manoeuvre leads to the pressure difference between the arms and legs becoming significantly diminished, making the clinical diagnostic process less clear. Indeed, in the presence of a marked run-off between the right subclavian and the iliac arteries as occurs with a large arterial duct or a cerebral arterio-venous malformation, for example, it may be possible to detect a large difference between systolic blood pressures measured in the arms and legs and yet the femoral pulses will remain easily palpable. The combination of weak or absent femoral pulses together with a gradient in pressure between the limbs is therefore virtually pathognomonic of aortic coarctation.
Older Children and Adults
Frequently patients with coarctation go beyond infancy without detection, either because initially the coarctation was not severe enough to become critical following closure of the arterial duct, or because of a significant early collateral circulation. The diagnosis then usually follows a routine medical examination, where the murmur is discovered, femoral pulses are found to be weak, or unexplained systemic hypertension is found. Headaches, nosebleeds, cold feet, or calf pain on exercise are often experienced. 39 Sometimes patients present with end-stage systemic hypertensive disease, such as subarachnoid haemorrhage or hypertensive retinopathy. Very occasionally, the lesion is detected during investigations for coronary arterial disease in later life.
Physical Findings
The physical findings in older patients usually rest upon the appreciation of diminished or delayed femoral pulses compared with the pulses in either arm. The femoral pulse is normally fractionally earlier than the radial, with a similar character, waveform and volume. If this is not the case, then the patient should be further investigated. More reliable than the delay of the femoral pulse to exclude coarctation is measurement of blood pressures in all limbs. 40 Further signs include a normal jugular venous pressure, and normal sized liver. Indirect signs of left ventricular hypertrophy, such as a displaced apical beat and heave, are often found on palpation of the praecordium. On auscultation, the first and second heart sounds are usually normal, but may be accompanied by an apical fourth heart sound if the left ventricle is becoming non-compliant. The murmur of coarctation is best heard in the left infraclavicular fossa and radiates to the back over the left scapula. It is continuous, peaks late in systole, and continues into early diastole, corresponding with the diastolic tail seen on Doppler echocardiography. Additional continuous murmurs may be generated by larger collateral arteries, which can restore adequate flow of blood to the lower body, resulting in palpable femoral pulses, albeit usually reduced and delayed. If surgery is considered, this feature will be crucial, as it determines if partial cardiopulmonary bypass is required or not to maintain adequate perfusion of the lower body and spinal cord whilst the coarcted segment is excluded with clamps for the repair. In the patients beyond infancy, the physical findings of associated abnormalities, such as an ejection click with bicuspid aortic valve, or a murmur owing to a small ventricular septal defect, will be typical of those lesions. A search for disease caused by hypertension is often unrewarding in childhood, although fundoscopic changes with a unique corkscrew appearance to the retinal arteries has been described. These changes are different from the usual hypertensive change. 41
Investigations
Chest Radiography
In infants, cardiomegaly and increased pulmonary vascular markings can be seen on the radiograph. In older children, the heart size is often normal, but if cardiomegaly is present, it is usually caused by left ventricular enlargement. There are two pathognomonic signs on the plain chest radiograph in older children. The first is the figure 3 sign, which appears to the left of the mediastinum and is caused by pre- and post-stenotic dilation of the aorta ( Fig. 46-18 ). The second sign is rib notching, which is usually not seen until 4 years of age, although appearance in the first year has been described. 42 By adulthood, around three-quarters of untreated patients have rib notching. It is best seen posteriorly in the medial third of the lower borders of the fourth to eighth ribs, where the intercostal artery crosses the rib (see Fig. 46-18 ). The notching in coarctation is classically bilateral, to be differentiated from the unilateral notching seen after a classical Blalock–Taussig shunt, although unilateral notching can also occur with coarctation when a subclavian artery arises aberrantly distal to the site of obstruction.
In those with interruption the heart is usually left sided with normal abdominal and bronchial arrangement. Cardiomegaly, particularly enlargement of the left atrium, is present in nine-tenths of neonates. 43 Increased pulmonary vascular markings with pulmonary oedema are also the norm. In the rare patients who survive infancy untreated, more specific signs can be seen, 44 including absence of the aortic knob, a midline trachea, absence of an aortic impression on the barium swallow, and termination of the descending aorta at the level of the pulmonary trunk. Rib notching can also be seen on the side of the subclavian arteries arising from the ascending aorta in the presence of a restrictive or closed arterial duct. A narrow mediastinum may suggest absence of the thymus gland, a feature of Di George syndrome.
Electrocardiography
The majority of young infants presenting with coarctation will have normal right ventricular dominance, with extreme right-axis deviation. Later, left ventricular hypertrophy supervenes. There are early electrocardiographic signs of left ventricular dominance and strain in some infants. This has been linked to subendocardial ischaemia 45 or co-existing aortic stenosis. There are no specific features that are diagnostic for interruption. As with coarctation the findings are strongly influenced by associated abnormalities, the tracings may show any combination of ventricular hypertrophy, right, left or both, or they may be normal. Occasionally, a prolonged QT interval may be seen secondary to the hypocalcaemia of Di George syndrome.
Magnetic Resonance Imaging
Although echocardiography is a superior modality for the diagnosis of congenital cardiac disease in infants and young children, and magnetic resonance imaging is limited in smaller children because of the need for sedation or anaesthesia, the latter technique combined with phase velocity mapping can be used as a complete diagnostic tool in obtaining both morphological and physiological information in coarctation. 46 It is also an excellent tool in the assessment of postoperative repair. It can reveal not only the primary pathology and the collateral flow, but also assess secondary pathology, for example, the aortic root for dilation if a bicuspid aortic valve is present, aortic valvar incompetence and stenosis, and provide details of left ventricular mass and function. Magnetic resonance, therefore, is rapidly establishing itself as the method of choice in the evaluation of treatment and complications of aortic coarctation, most notably of aortic gradients and recoarctation. The gradient in blood pressure between the arms and legs is not a reliable indicator of haemodynamic significance of restenosis in patients with prior repair of coarctation. Direct visualisation of collateral vessels by magnetic resonance angiography, and proportional increases in flow from proximal to distal descending thoracic aorta, in contrast, are reliable indicators of haemodynamic significance. 47 Changes in the collateral circulation after stenting of coarctation segments have also been successfully demonstrated using phase-contrast magnetic resonance. 48 The combination of anatomic and flow data obtained by magnetic resonance provides a sensitive and specific test for predicting catheterisation gradient greater than 20 mm Hg in native and recurrent coarctations. 49 Contrast-enhanced magnetic resonance angiography provides additional diagnostic information compared to fast-spin echo magnetic resonance. 50
When magnetic resonance, magnetic resonance angiography, and Doppler echocardiography are compared in relation to surgical repair of coarctation, it has been shown that magnetic resonance is superior to Doppler echocardiography in the evaluation of the aorta, and that the internal measurement of the narrowing does not correspond to the external aspect of the surgical narrowing. 51 Helical computer tomography and magnetic resonance do not seem to differ when used for follow-up assessment of adults with treated coarctations. There can be a substantial variation in two subsequent measurements, without an overall substantial bias towards larger diameter in one of the two methods. 52 In those with interruption of the arch, magnetic resonance can also be a useful tool to assess the length of the interruption and any associated anomalies, most notably with three-dimensional gadolinium-enhanced magnetic resonance angiography. 53
Echocardiography
Echocardiography has become the diagnostic method of choice in infancy. The aortic arch is best visualised from the suprasternal notch in the superior paracoronal view, revealing details of the entire arch ( Fig. 46-19 ). In those with coarctation, there is most commonly a short narrowed segment just distal to the left subclavian artery caused by the obstructive shelf projecting into the aorta posteriorly. More rarely, there is a longer segment of narrowing involving the isthmus ( Fig. 46-20 ). It must be remembered that the apparent anterior shelf often seen on the anterior wall of the aorta is not part of the coarctation, but the overlapping point of entry of the duct. 54 It is important, especially in infants, to assess the size of the transverse aortic arch. It can often be hypoplastic ( Fig. 46-21 ) or stenotic, and can result in residual obstruction after distal repair. In the absence of an arterial duct, the haemodynamic severity of coarctation can readily be assessed by Doppler echocardiography.
The spectral recording shows an extension of antegrade flow, and a persisting gradient into diastole, the so-called diastolic tail. There is rarely any doubt to its significance, but if uncertainty does exist, the spectral recording can be analysed further 55 according to the peak velocity and the half-time of diastolic velocity decay. This predicts accurately the severity of anatomical coarctation ( Fig. 46-22 ).Another useful feature is the carotid-subclavian arterial index, which is the ratio of the diameter of the aortic arch at the left subclavian artery to the distance between the left carotid artery and the left subclavian artery, with a ratio of less than 1.5 being both sensitive and specific for coarctation in infants and neonates. 56 In neonates with a patent arterial duct, measurements of ratio of diameters of the isthmus and descending aorta, along with the delineation of the posterior shelf and a discrepancy in blood pressure between the limbs, has been shown satisfactorily to identify those with coarctation. 57 In isolated coarctation, the peak instantaneous pressure drop across the obstruction can be calculated from the peak velocity of the jet by using the simplified Bernoulli equation. In the presence of a significant associated obstructive lesion in the left heart, it is necessary to quantify the peak velocity of the jet proximal to the site of coarctation. This can often be significantly raised and, if not taken into account by using the expanded Bernoulli equation, there can be a significant overestimation of the gradient. 58 The remaining examination must be focused on the potential associated malformations, with care taken to assess the mitral and aortic valves accurately. Left ventricular mass should be measured and an M-mode assessment of left ventricular shortening fraction should be made. It must always be remembered that, in the presence of coarctation severe enough to cause low cardiac output, the severity of associated obstructive lesions in the left heart can be underestimated. All of these observations must be modified in the presence of an arterial duct. When large, any gradient across the site of coarctation will be obviated, and the pattern of flow altered. Under these circumstances, much more reliance is placed upon adequate imaging of the stenotic area. In experienced hands, the diagnosis of coarctation using echo Doppler can be made with 95% sensitivity and 99% specificity. 59
When the arch is interrupted in patients with Di George syndrome, echocardiography is more difficult because of absence of the thymic window. The examination must focus on the intracardiac anatomy, as well as on the aortic arch. Subcostal views will demonstrate the discrepancy in size between aorta and pulmonary arteries. Suprasternally, a relatively small ascending aortic arch is seen to follow an obviously straight course, leading to at least one arterial branch, while the much larger pulmonary trunk leads, via the arterial duct, to the proximal end of a much larger descending aorta. 60 If approached in this fashion, it is possible to show the entirety of the aorta, despite the interruption, permitting accurate diagnosis in almost all neonates ( Fig. 46-23 ). The parasternal long-axis view will demonstrate the ventricular septal defect, along with the degree of obstruction of the left ventricular outflow tract. Particular care is needed to exclude an aberrant right subclavian artery, or right-sided arterial duct, in the usual setting of a left-sided aortic arch.
Fetal Echocardiography
Significant advantages accrue when congenitally malformed hearts are diagnosed accurately during fetal life, especially those lesions that can be deemed duct dependent, as intervention electively with prostaglandin can prevent shock and acidosis. For those with coarctation, antenatal diagnosis has been shown to permit presentation in a better condition, with less consequent mortality. 61 There are difficulties, nonetheless, in prenatal diagnosis of coarctation. Although a certain combination of features is strongly suggestive of abnormalities in the aortic arch, there is a significant rate of false-positive diagnosis, particularly in late pregnancy. 62,63 Severe coarctation is certainly associated with relative hypoplasia of the components of the left heart when compared with the right, and this is visible in early pregnancy, but this can also be a feature of the normal fetus later in pregnancy. Milder forms of coarctation, furthermore, are compatible with an entirely normal fetal echocardiogram, especially in the last trimester.
Cardiac Catheterisation and Angiography
In most cases, sufficient information can be obtained from clinical and non-invasive examination to decide on an appropriate plan for management. Cardiac catheterisation is of limited value in delineating further the anatomy in the neonate, and it is associated with significant morbidity. It is rarely necessary for the assessment of associated anomalies. Indeed, even if significant mitral obstruction, mitral regurgitation or aortic stenosis is present, the baby is often better assessed after repair of the coarctation, when cardiac output, the effects of the arterial duct and other abnormalities of ventricular performance, have resolved. One potential indication for invasive assessment, nonetheless, is for intervention in the setting of coarctation. Controversy has surrounded the use of balloon angioplasty as the primary treatment for patients of various ages with coarctation since its first use in 1982. 64 This will be discussed in more detail below.
On the rare occasion that aortography is performed in the setting of interrupted arch, an injection into the ascending aorta will demonstrate, in three-fifths of cases, the classic V sign as seen in the frontal projection of the brachiocephalic and left common carotid arteries, as also seen in the echocardiogram ( Fig. 46-24) . 43 Occasionally, the V more resembles a U or W if all three arteries take origin proximal to the interruption. The appearance is still characteristic in that the aortic arch continues smoothly into its most distal branch proximal to the interruption, regardless of whether this is the brachiocephalic, left common carotid, or subclavian artery. If the aortic arch continues beyond its last branch, and appears to taper down to apparent complete obstruction, the diagnosis is either aortic atresia, or else severe coarctation with distal wash-in from the arterial duct and not interruption. 65
COURSE AND PROGNOSIS
The quoted mean length of survival is 31 years for those with coarctation surviving the first year without an operation, three-quarters being dead by the age of 46 years. This information was derived from clinical records and postmortem studies. 66 In a natural history study in which infants who died in their first year of life were excluded, 66 it was suggested that those presenting with congestive heart failure might have had a survival rate at 1 year as low as 16%, this figure taking no account of associated lesions. In older patients, the cause of death was often related to systemic hypertension, the two most common findings being congestive cardiac failure and aortic dissection or rupture. Bacterial endocarditis was also common. An additional significant group died as a result of ruptured berry or saccular aneurysms causing intracranial bleeding, a feature more commonly found in coarctation. 67 Hypertension secondary to coarctation is not, however, thought to be the only pathogenetic factor. Abnormalities of the vessel wall are important, certainly in intracerebral catastrophes, but also with the other causes of death such as aortic dissection or rupture. Cystic medial necrosis and new structural abnormalities are seen in areas remote from the coarcted segment itself and may be unrelated to the type and age at surgery.
When considering interruption of the arch, the natural history is poor. Without surgery, three-quarters die in the first month of life, the majority in the first 10 days. Less than one-tenth survive without correction beyond the first year of life if there is co-existing ductal patency. 16,68,69 With the evolution of prostaglandin therapy and surgical intervention over the past decades, the impact of the associated cardiac and extracardiac defects has become of greater relevance in interruption, although little long-term follow up is available.
The mortality from bacterial endocarditis has fallen markedly in recent years through improved diagnostic techniques, especially cross sectional echocardiography, and aggressive early treatment with antibiotics. If present, the site of endocarditis is often in the aorta, distal to the site of coarctation or interruption, or on an associated bicuspid aortic valve. At present, nonetheless, it is usually recommended that children with coarctation or interruption receive prophylactic antibiotics against endocarditis, even after definitive surgical repair, during dental, colonic and genitourinary procedures.
MANAGEMENT
Stabilisation of Neonates and Infants
Clinical management of infants with coarctation and interruption was dramatically changed in the 1980s by the advent of pharmacological means to maintain patency and reopen the arterial duct. This now enables the majority of infants with either preductal coarctation or interruption, who present with heart failure, shock and deteriorating renal function, to perfuse their lower body, albeit with systemic venous blood. This will, nonetheless, reverse the tissue ischaemia as long as ductal patency and flow is maintained. The beneficial effects of prostaglandin E 1 in maintaining ductal patency under both aerobic and anaerobic conditions 70 did not lead immediately to its use, but a decade later it was commonly used in patients with obstructive lesions such as coarctation and interruption. 71 Prostaglandin E 1 is given initially at a dose of 0.05 to 0.1 μg/min/kg body weight. This can be increased to 0.4 μg/min/kg if required, although lower initial doses have been shown to be equally therapeutic and less likely to cause apnoea. 72 The maximal response occurs between 15 minutes and 4 hours. 73 Occasional improvement has been documented in infants as old as 5 weeks, but treatment is generally less impressive in older neonates, and in those whose ducts are closed at presentation. 73,74 Positive effects have also been found on the diameter of the coarcted segment of the aorta without any reopening of the arterial duct, suggesting the presence of reactive ductal tissue in the aorta. 75,76 Side effects can include a decreased respiratory drive leading to apnoea, occasionally requiring ventilation. There can also be hypotension with cutaneous vasodilation; jitteriness, which can lead to seizures; fever; susceptibility to infections; diarrhoea; and, more rarely, coagulopathy. For the neonates, management depends on timing of diagnosis. If the diagnosis has been made, or is strongly suspected, antenatally, then there is little to be lost from starting prostaglandin E 1 at birth. Certain centres advocate antenatal transfer and delivery in or close to the cardiac centre. If a neonate is found to have weak or absent femoral pulses, and remains well, it is justifiable to arrange transfer to a tertiary centre, having commenced prostaglandin E 1 to avoid the catastrophe of an acute closure of the duct during transfer.
In any infant becoming shocked within the first few weeks of life in the absence of pulses in the lower limbs, it should be mandatory to start prostaglandin along with the normal resuscitatory manoeuvres while expert assistance is sought. Ventilation with positive pressure will reduce the systemic demand for oxygen, and may improve cardiac failure. During ventilation, manoeuvres to increase pulmonary vascular resistance, and hence reduce the ratio of pulmonary to systemic blood flow, will lead to increased right-to-left flow through the arterial duct, thus improving perfusion of the lower body. The management is similar to that adopted in the pre- and post-operative care of the infant with hypoplastic left heart syndrome (see Chapter 29 ). This will include minimising the fraction of inspired oxygen, maintaining arterial partial pressure of carbon dioxide at 6 kPa or more, and the judicious use of volume and ionotropes. The outcome in these children with multiorgan failure is much more favourable if time is taken medically to stabilise them before carrying out definitive intervention. 77 If prostaglandin E 1 produces no effect of augmenting distal aortic flow, which occurs in a small proportion of patients, then immediate definitive treatment is required. 78
During the preoperative workup, patients require chromosomal analysis for 22q11 deletion using fluorescent in situ hybridisation. Levels of calcium need to be measured to exclude hypocalcaemia, and to anticipate it before clinical sequels, such as convulsions, develop. Infusions of calcium are useful in the acute phase. Subsequently, the management is identical to that of isolated hypoparathyroidism, involving oral supplementation of calcium and administration of vitamin D. Documentation of decreased levels of parathormone in the setting of low levels of calcium are diagnostically important before embarking on treatment, which should ideally be conducted with advice from a paediatric endocrinologist. Abnormalities can occur in the function of the T cells, and it is important to assay their number and function. In the acute phase, infants with interruption should be presumed to have defects of the T cells. Transfusion, including cardiopulmonary bypass, should be performed using irradiated blood to avoid the possibility of transfused lymphocytes causing graft-versus-host disease. Later on, the susceptibility to infection may lead to the need for rotational antibiotics or other immune manipulation. These children often have developmental delay and problems with feeding, both of which need a significant amount of medical input after repair.
Definitive Treatment
As yet, there is no single cost-effective technique with clearly demonstrable superior outcomes in the short-term and long-term, and without significant side-effects, for all types of coarctation and interruption. The pursuit of a single ideal form of therapy for all forms of coarctation is almost certainly misguided, as the obstructive lesions show great variability in their morphology, even before ductal patency and associated intracardiac lesions are considered. 79 Furthermore, a significant proportion of the literature is now of only historical value, as over the past 50 years both surgical and cardiological techniques and medical resuscitation have improved greatly, and prostaglandin has been introduced. Many studies exist, but are based on different groups of patients from different periods of time, and treated with different techniques. 79 Large multi-centric randomised controlled trials of the various forms of surgical and interventional cardiological techniques for various types of coarctation, therefore, are long overdue.
Non-elective Surgical Repair
The majority of infants with duct-dependent circulations can be stabilised medically, and will benefit from an interlude before definitive treatment while metabolic derangements are corrected. These infants, nonetheless, will need relief of their aortic obstruction within 1 or 2 days of presentation. There have been reports that minimally symptomatic infants with isolated coarctation can be managed medically for a period of time. 80,81 Nowadays, even those born with coarctation and very low weight, less than 2 kg, can undergo corrective surgery with a low mortality, but will be at a higher risk of recoarctation. 82 The majority of symptomatic infants undergo surgery with little delay. There is a subgroup of patients who present in cardiogenic shock and cannot easily be stabilised medically. Timely intervention, with the therapeutic strategy individualised to the anatomy, has been shown to give excellent outcomes in neonates with coarctation. 83 There is ongoing debate, nonetheless, about the procedure of choice, and whether the associated defects should be addressed at the same time as resection of the coarctation, or at a second procedure.
The major concern remains the significant incidence of recoarctation. Difficulties arise in the interpretation of the data, as some papers cite residual gradients from arm to leg, others measure differences between the arms, whereas still others measure the difference in the pressure between the arms and legs as exposed by exercise. Furthermore, many cases that are termed recoarctation represent residual coarctations. In order to try to standardise these features, four patterns of gradients have been described between the arms and legs after initial surgery. 84 The first pattern results in complete and permanent abolition of the gradient after surgery, the second leads to an initial abolition followed by late recurrence. The third group has initial residual obstruction followed by late resolution, whereas the last group has persistent residual obstruction. Defining rates of recoarctation as the percentage of patients undergoing surgery who are known to have recoarctation at the time of reporting, is very dependent on the period over which progress has been monitored, and therefore actuarial rates of recoarctation should be used. 85,86
Management of Associated Lesions in Infancy
The management of associated lesions is tailored according to clinical needs and pathology. An arterial duct, if patent, should be ligated during surgery. Controversy surrounds the management of concomitant ventricular septal defects when treating coarctation in neonates and infants. Some opt for repair of the coarctation through a lateral thoracotomy, with subsequent assessment of progress. In this approach, inability to wean from the ventilator, or failure to thrive, would indicate the need for surgical closure of the ventricular septal defect. Its advantages include allowing improvement in ventricular performance, pulmonary oedema, and the general condition of the infant. It may even buy time for spontaneous closure of small defects. More frequently, especially if there is a single defect and the child is not small, the option nowadays is to proceed with complete repair in one stage. This involves closing the defect, together with repair of coarctation, via a midline sternotomy. In earlier times, this was associated with higher mortalities, but contemporary reviews suggest this is no longer the case. 87 Another alternative is to use only one operation, but to repair the coarctation through a left thoracotomy, using a subsequent sternotomy to correct the intracardiac defect. 88 This approach has the downside of multiple incisions but will lead to shorter periods on bypass, and avoids any circulatory arrest. It also reportedly decreases the time spent in both intensive care and hospital. 88 The least fashionable option nowadays is to repair the coarctation and band the pulmonary trunk. This option remains valid for those with multiple ventricular septal defects, or for those in whom the defects are judged inaccessible. It is rarely recommended for the management of single large defects. The presence of a left-to-right shunt prior to repair of the coarctation, and extension of the defect into the right ventricular inlet or outlet, nonetheless, are two situations in which the ventricular septal defect is less likely to close spontaneously. 89 In addition more complicated associated defects, such as transposition, double outlet right ventricle, tricuspid atresia or double inlet ventricle, also need to be taken into consideration and addressed at the time of repair of coarctation.
In those infants at the extreme end of the spectrum with multiple obstructive lesions in the left heart, such as Shone’s complex, the prognosis is more guarded with a significant early mortality, although there possibly is some benefit from aggressive reconstructive surgery with early attention paid to the mitral valve. 90,91 The late functional outcome can be favourable compared with more conservative approaches. 91
Elective Repair
There has also been much debate regarding optimal age for surgical treatment in asymptomatic patients with coarctation. Various issues need to be considered. Generally, overall operative mortality is greatest in those under 1 year of age for most conditions, although this has improved greatly in recent years through a combination of improved medical and intensive care management and better surgical techniques. Furthermore, the likelihood of recoarctation is related not only to the type of repair, but also to the timing of repair, being more common in those undergoing surgery under 1 year of age. 92,93 Age at operation is also important with regard to the incidence of late hypertension. This was reported in one-tenth of patients after neonatal and early repair, but increased mortality was found in children undergoing repair over the age of 5 years. 92 It had already been demonstrated that patients undergoing repair of coarctation in their late teens had an excessively high mortality from cardiovascular causes in later life. 94 There is an age, therefore, beyond which operative repair may not change the natural history of the disease. 94 These findings were subsequently confirmed by others, who also showed that residual hypertension was a poor prognostic factor. 95 Still others have since shown that hypertension can occur late after repair, 96 while a much higher incidence of permanent hypertension not caused by recoarctation is found in patients undergoing surgery above 4 years of age. 97 The break-point in another cohort was 1 year of age, with this group making recommendation some time ago for elective repair during the second 6 months of life. 98 Since then, scattered reports have appeared of permanent hypertension occurring in patients undergoing repair of coarctation in infancy, or even the neonatal period. 99–101 The problem should, nonetheless, be kept in perspective, since one analysis found no patient with permanent hypertension without recoarctation among 118 survivors of repair of coarctation in infancy. 102 In young asymptomatic children without duct dependent circulations, a more recent report has suggested that the timing of surgical repair does not seem to be a predictor of morbidity or mortality. It also does not predict residual hypertension, any residual gradient, persistent cardiomegaly, post-operative neurological sequels, the requirement for a second surgery, or the need for balloon dilation for residual post-operative coarctation and the need for antihypertensive medications within five years after surgery within a follow-up of up to 20 years. 103 In hypertensive adults with coarctation, the hypertension was abolished without requirement for medication in two-thirds of the patients, although one-third of these were hypertensive on exercise. 104 Most adults with significant coarctation that has not been treated die before the age of 50 years from cardiovascular complications. A subset of patients can survive beyond this age, and for these the benefits of surgery are unclear. Surgery for such hypertensive patients can be undertaken with low morbidity and mortality, and most are symptomatically improved, with some normotensive at rest, although a majority remains hypertensive on exercise. 105 Some patients are found, nonetheless, in whom permanent hypertension will ensue irrespective of the age of repair. To some extent, all of this discussion has become irrelevant to contemporary management. Elective surgery is performed nowadays in most centres at, or shortly after, presentation at any age. The above discussion serves as a reminder of the potential long-term implications for those with the disease, no matter when, or how, it is repaired.
The risk of paraplegia is important. Pre-operative evaluation by magnetic resonance imaging to show the presence or absence of collateral circulation is now considered to be valuable in identifying the need for pre-emptive protective actions. Options include using a temporary bypass with a polytetrafluoroethylene tube from the ascending to the descending aorta, 106 or partial bypass from the left atrium to the descending aorta. 107
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