An arterio-venous fistula is an abnormal connection between an artery and a vein in the absence of any intervening capillary bed. As a result of the low resistance in the veins, a large shunt can occur through such fistulas. The shunting occurs throughout the cardiac cycle, thus producing a continuous flow murmur. Arterio-venous fistulas can involve either the pulmonary or systemic circulations. These are separate entities, and will be considered separately.
EXTRACARDIAC SYSTEMIC ARTERIO-VENOUS MALFORMATIONS
Arterio-venous malformations and fistulas can affect any part of the body. They have a wide range of pathologies, ranging from malformations consisting of abnormal capillaries and dilated venous spaces to direct fistulous communications between major arteries and veins.
Systemic arterio-venous malformations and fistulas can be subdivided into those within and those outside the heart. Extracardiac systemic arterio-venous malformations are of importance to the paediatric cardiologist only when they are haemodynamically significant, and are associated with a large left-to-right shunt. This is a rare situation. Abnormalities with such features are usually congenital in origin. Any large systemic malformation may present with high-output cardiac failure in later life, but rarely in childhood. When a neonate or infant presents with high-output cardiac failure, the most likely extracardiac cause is an aneurysm of the vein of Galen.
Aneurysm of the Vein of Galen
The aneurysmal vein of Galen is an intracerebral arterio-venous malformation. It is the most frequent haemodynamically significant extracardiac arterio-venous shunt encountered in neonates and infants, and affects males three times more frequently than females. It is an uncommon cause of severe cardiac failure in infancy. Affected neonates and infants may present with congestive cardiac failure that suggests a cardiac cause, and this can give rise to diagnostic difficulties. The abnormality consists of multiple feeding arteries, principally the anterior and posterior choroidal arteries and the anterior cerebral artery, which drain directly into an enlarged venous sump. The abnormal vein is considered to be the precursor of the vein of Galen, hence the name of the malformation. The aneurysmal vein drains directly into the straight sinus, and then into the superior sagittal sinus.
Clinical Presentation
The malformations are uncommon. Over a period of almost 20 years, 16 patients with the lesion were encountered at Great Ormond Street Hospital in London, 1 while 29 patients were seen at the Hospital for Sick Children in Toronto over a period of 30 years. 2 Review of the English literature from 1937 to 1981 found only 128 cases. It has been estimated that, in a population of 3 million, it might be expected that one new patient would be seen each year. 3 The cause of these aneurysms is unknown, but they probably result from an early embryonic somatic mutation.
Antenatal scans using ultrasound may occasionally detect the aneurysms in late pregnancy. Colour flow Doppler studies will show the vascular abnormality. Antenatal magnetic resonance imaging will confirm the diagnosis and assess any cerebral damage. Prenatal diagnosis will enable referral to a specialist centre, with all the requisite skills needed to deal with these complex patients.
The majority of cases are diagnosed after birth. Amongst the patients collected from the literature review, about one-third presented in the neonatal period, one-quarter were seen between 3 weeks and 11 months, and the remainder were encountered as older children and adults. Of the neonates, all but two presented with cardiac failure, these patients presenting with subarachnoid haemorrhage and hydrocephalus, respectively. In addition to cardiac failure, which is often refractory to treatment, the neonates showed features of pulmonary hypertension and myocardial ischaemia, as well as cerebral ischaemia resulting from the cerebral steal effect. Compared with the neonates, only two of those presenting as infants had cardiac failure. The majority had hydrocephalus, although one patient presented with a subarachnoid haemorrhage. In the older children and adults, only one had cardiac failure. At these ages, the most common presentation was with subarachnoid haemorrhage, seen in almost half. About one-third developed hydrocephalus, with venous hypertension resulting in epistaxis and distended veins, seen in one-sixth, and generalised neurological deterioration in another sixth thought to be caused by the steal effect of the fistula. In those with the aneurysms, the initial days of life are often unremarkable. If the pulmonary vascular resistance remains high, right-to-left shunting and cyanosis can occur as a result of the grossly increased systemic return. As the run-off from the arterial to venous circulations is of low resistance, there may be bounding pulses, particularly in the carotid arteries, as well as tachycardia. The veins in the neck may be engorged, and a continuous murmur is typically heard over the vault of the skull.
Diagnosis
When the fistula is large, the chest radiograph usually shows cardiac enlargement with marked pulmonary plethora ( Fig. 50-1 ). If there is significant right-to-left shunting as a result of an elevated pulmonary vascular resistance, then pulmonary oligaemia may also be present. The electrocardiogram usually shows biventricular hypertrophy. Echocardiography demonstrates enlargement of all four chambers, and excludes a cardiac cause for heart failure. Prior to the availability of ultrasound, the diagnosis was often difficult, and angiography was usually necessary. Angiography should now be performed only with a view to proceeding with embolising the abnormal connection. Ultrasonic scanning of the head across the anterior fontanelle will demonstrate the centrally situated aneurysmal vein. It also often shows the presence of the feeding arteries ( Fig. 50-2 ). Doppler interrogation, and in particular colour Doppler, more readily demonstrates the direction of flow of blood. Where the ultrasound findings are not clear, or when more information is required in older patients, magnetic resonance imaging is indicated. This is now preferred to using computed tomographic (CT) scanning with contrast.
Management
The therapeutic options are embolisation or endovascular treatment. This involves very specialised neuro-interventional techniques, and very few specialised centres achieve the level of expertise and experience required to provide consistent treatment.
The outlook for neonates treated medically is grim. 4 In the series reported from Toronto, 2 all but one of the children treated medically died. Surgery has little or no role nowadays, as the surgical approach also carried a very high mortality, and resulted in significant morbidity. If possible, treatment is initially conservative, as arteriography and embolisation in the neonate is technically very difficult. 5 If the cardiac failure can be managed medically, the therapeutic options are much more encouraging at the age of about 6 months.
Arteriography is performed at the same time as embolisation. Different patterns have been described. In neonates, multiple arteries arise from the internal carotid arterial branches and feed the aneurysm at its antero-superior border ( Fig. 50-3 ). The aneurysm then drains by very large straight and lateral sinuses ( Fig. 50-4 ). Most commonly in infants, the feeding artery is situated inferiorly and laterally and consists of a single posterior choroidal artery. In infants and older children, the feeding arteries are usually located anteriorly and superiorly, and consist of one or two posterior choroidal arteries, as well as anterior cerebral arteries. In older children, most commonly the feeding vessels consist of a network of branches arising from the posterior choroidal and thalamic perforating arteries.
The transtorcular venous approach was used at one time directly to access the venous aneurysm, 6–8 but has now largely been superseded by the transarterial route. This involves transfemoral approach and selectively catheterising the small feeding branches to the aneurysm. Embolisation is best performed with liquid embolic agents, such as cyanoacrylate glue. The outlook, if treatment is performed before the onset of cerebral damage, is good. 9 In this the largest series of endovascular treatment, neonates presenting early with severe cardiac failure had the worst prognosis. When there is associated cerebral damage, known as the melting brain syndrome, death or survival with severe cerebral damage is likely. There is often a restriction on the amount of embolisation that can be performed at any one session, particularly in neonates and infants, so multiple embolisations may be necessary. Sometimes these cases may be complicated by stenoses in the jugular bulbs, and stenting has been described in this situation. 10
CORONARY ARTERIO-VENOUS FISTULAS
These lesions, also known as coronary arterial fistulas or malformations, are connections between one or more of the coronary arteries and a cardiac chamber or great vessel, having bypassed the myocardial capillary bed. They are rare, and usually occur in isolation. The exact incidence is unknown, although they are the most common haemodynamically significant coronary arterial anomaly. 11–13 A majority of the fistulas have a congenital origin, but some may occasionally be detected after cardiac surgery, such as valvar replacement, coronary arterial bypass grafting, and after repeated myocardial biopsies in cardiac transplantation. 14–17 The lesions were discovered in 0.1% of more than 33,000 patients undergoing coronary angiography. 18
Morphology
It is difficult to provide accurate data on the distribution of the origins and sites of drainage of the fistulas, because reports vary depending on the analysed populations. Patients undergoing interventional or surgical treatment are likely to represent the severe end of the spectrum, whilst information will be unavailable in those with asymptomatic fistulas.
The artery feeding the fistula may be a main coronary artery or one of its branches. The vessel may be dilated and tortuous, and terminates in one of the cardiac chambers or another vessel. The more proximal its origin from the feeding artery, the more dilated the fistula is likely to be. If the fistula drains to the right atrium, and arises proximally from a main artery, it tends to be considerably dilated and less tortuous ( Fig. 50-5 ). When the origin is more distal, and in particular when it arises from the left coronary artery and the drainage is to the right ventricle, the feeding artery may be very tortuous and present a challenge for interventional catheter closure ( Fig. 50-6 ). Multiple arteries can feed into a single coronary arterio-venous fistula, or alternatively the fistula can have multiple sites of drainage. 16,19 The fistulas originate from the right coronary artery in about half the cases, the left anterior interventricular artery being the next most frequently involved, in approximately one-third, and the circumflex artery in about one-fifth. 20 Over nine-tenths of the fistulas, irrespective of their origin, drain to the right side of the heart. 21 In those draining to the right heart, the fistulas open most frequently to the right ventricle, in about two-fifths, followed by the right atrium, coronary sinus, and pulmonary trunk. Multiple fistulas between the three major coronary arteries and the left ventricle have also been reported. 22–24 In adults, fistulas may occasionally be encountered which originate from both the coronary arteries and drain into the pulmonary trunk. These fistulas may cause angina even in the absence of coronary arterial disease ( Fig. 50-7 ). They require closure.
Pathophysiology
When the fistula drains to the right side of the heart, the volume load is increased to the right heart, as well as to the pulmonary vascular bed, the left atrium, and the left ventricle. This results in a left-to-right shunt similar to that produced by an atrial or ventricular septal defect, or patency of the arterial duct. When the fistula drains into the left atrium or the left ventricle, there is volume overloading of these chambers but no increase in the pulmonary blood flow. The situation then mimics mitral regurgitation. When the fistula drains into the left ventricle, the haemodynamic effect is similar to that produced by aortic regurgitation. Thus, there may be different echocardiographic appearances, with dilation of different cardiac chambers depending on the sites of the shunts. The size of the shunt is determined by the size of the fistula, and the difference in pressure between the coronary artery and the chamber into which the fistula drains. Occasionally, there may be congestive cardiac failure, while in adults, myocardial ischaemia may rarely occur due to a coronary arterial steal.
Clinical Features
The fistulas are usually asymptomatic in the first two decades, especially when they are haemodynamically small. Indeed a small number may close spontaneously. 25 After the second decade, there is an increase in the frequency of symptoms and complications. 26 Complications include steal from the adjacent myocardium causing myocardial ischaemia, thrombosis and embolism, cardiac failure, atrial fibrillation, rupture, endocarditis or endarteritis, and arrhythmias. 13,20,27–31 Thrombosis within the fistula, although rare, may cause acute myocardial infarction and atrial and ventricular arrhythmias. 32–34 Spontaneous rupture of an aneurysmal fistula has been reported to produce haemopericardium. 35 Recurrent septic pulmonary embolism may occur as a complication of endocarditis of the tricuspid valve if associated with a coronary arterial fistula. 36 Jet lesions may be found on the wall of the coronary sinus opposite the site of entry of the fistula, on the tricuspid valve, or at the orifice of the coronary artery. 36–38
The fistulas may increase in size over time, although some may be large in the newborn period, and may even be detected prenatally. 39 They may form a short and direct connection with a chamber or a large vessel or form complex long tortuous and aneurysmal cavities. The aneurysmal section of the fistula may dilate progressively, and the feeding artery may become more tortuous. 40 The largest shunts occur when the coronary artery connects to the right rather than the left heart chambers. Even then, the left-to-right shunt is rarely more than 3 to 1.
The presentation varies between finding an asymptomatic continuous murmur, to presentation with congestive cardiac failure or exercise-induced angina. 18 The majority of the patients are asymptomatic, with normal exercise tolerance. Patients with large left-to-right shunts may have symptoms of congestive cardiac failure, especially in infancy, and occasionally in the neonatal period. 41,42 Congestive cardiac failure may also occur in the elderly. 43 Some adult patients may have angina and electrocardiographic evidence of myocardial ischaemia. 16 The mechanism of the angina is presumed to be a steal phenomenon. 28,44,45 Exercise-stress thallium scintigraphy has shown the presence of reversible ischaemia supporting such a phenomenon. 46
Some patients may be referred because of an asymptomatic murmur, which will be continuous, and heard over the praecordium. Whilst the murmur may sound similar to that of a patent arterial duct, it must be differentiated from the latter. The murmur of a coronary arterial fistula is heard over the mid-chest, rather than below the left clavicle. It may even be audible to the right of the sternal border, and typically peaks in mid-diastole rather than systole, as is the case when the murmur originates from the persistently patent arterial duct. Such findings should alert the physician to the possibility of a coronary arterio-venous fistula. If the fistula connects to the left ventricle, only an early diastolic murmur may be heard. The patient is then referred for echocardiographic assessment.
The differential diagnoses include persistent patency of the arterial duct, ruptured aneurysm of a sinus of Valsalva, ventricular septal defect with aortic regurgitation, venous hums, and other systemic and pulmonary arterio-venous fistulas. Indeed, when it became possible to close patent arterial ducts surgically, the similarities in physical findings led, on occasion, to unintentional surgical exploration of patients with coronary arterial fistulas.
Investigations
The electrocardiogram and chest X-ray are usually unhelpful in the diagnosis and assessment. The electrocardiogram may show the effects of left ventricular volume overload and ischaemic changes. If it is normal, and the patient is old enough to exercise either on the treadmill or a bicycle, changes in the ST segments indicative of ischaemia may become apparent. The chest X-ray is usually normal, but occasionally moderate cardiomegaly may be present when there is a large left-to-right shunt.
When the fistula and the resulting shunt are small, colour Doppler echocardiography may be helpful, demonstrating the chamber or the vessel into which the fistula drains. Conventional pulsed and continuous wave Doppler can then confirm the high velocity of the flow through the fistula. Cross sectional and colour Doppler echocardiography are helpful in demonstrating dilation of the affected coronary artery. As indicated, colour flow mapping may show the site of drainage, but it is difficult to define the detailed anatomy of the fistula with this technique. 47,48 Additional clues may be present when the coronary artery feeding the fistula is enlarged, ectatic or tortuous, or when there is a large shunt. If a dilated coronary artery can be traced from its aortic origin into the fistula, the diagnosis can be confirmed with certainty by conventional Doppler, and in particular by colour flow mapping. Transoesophageal echocardiography has also been used for better definition of the fistulas. 48–51 On colour Doppler interrogation, significant flow may be seen at the origin, or even along the length, of the vessel. It may also be possible to see flow into the chambers of the right heart. Magnetic resonance imaging can confirm, permitting recognition of the proximal coronary arteries, or even the whole length of the fistula.
In patients who are able to exercise, and especially those who complain of angina or dyspnoea, myocardial perfusion or stress thallium scanning may demonstrate reversible ischaemia. It may also determine the size of the territory under threat of ischaemia. 46 In older patients, other areas of acquired coronary arterial disease may be discovered that influence the subsequent management. In these older patients, if a coronary arterial fistula is discovered, even if the coronary arteries are free of atheromatous disease, closure of such a fistula may relieve the symptoms. 52
The main diagnostic technique remains cardiac catheterisation and angiography, the investigation also helping in planning the appropriate treatment. Initial diagnostic catheterisation is used to assess the haemodynamic significance of the fistula, and to provide details of its anatomy, in particular its size, origin, course, presence of any stenoses, and its site of drainage. Selective angiography of the coronary arteries allows confirmation of the diagnosis, and demonstrates the detailed anatomy of the fistula ( Fig. 50-8 ). Selective injections, however, should be performed only when definitive treatment is planned, such as an interventional procedure or surgery. They should rarely be required nowadays to make the diagnosis. A preliminary aortogram taken in the root helps to determine which coronary artery should be catheterised selectively, but it is usually good practice to perform selective angiography of both the coronary arteries. Visualisation of the fistula may be improved by using the so-called laid-back aortogram. 53 This is obtained by adding caudal angulation at 45 degrees to the frontal view, with slight left or right anterior oblique orientation. A more important reason for detailed selective coronary angiographic assessment is to investigate the possibility of multiple arteries feeding the fistula ( Fig. 50-9 ). Coronary angiography in several planes then assumes great importance. It should be performed as in adults. These views include right anterior oblique, straight antero-posterior, left anterior oblique, left anterior oblique with caudocranial angulation, and left lateral projections.
Management
The options include closure at surgery, or by use of devices inserted through a catheter. The goal of treatment is to occlude the fistula whilst preserving normal coronary arterial flow. The options can be optimised by careful identification of the number of fistulous connections, the nature of the feeding vessel or vessels, the sites of drainage, and quantification of myocardium at risk for injury or loss. The indications for treatment include the presence of a large or increasing left-to-right shunt, left ventricular volume overload, myocardial ischaemia, left ventricular dysfunction, congestive cardiac failure, and prevention of endocarditis or endarteritis.
As techniques for accurately diagnosing coronary arterio-venous fistulas have improved, open heart surgery has become safer, making it even more unlikely that the natural history will ever be clearly defined. In the past, most authors have advocated surgical closure of the fistulas in view of the low operative mortality. 54–57
Even as long ago as 1979, it had been noted that symptomatic patients over the age of 20 years suffered more problems, as well as more post-operative complications, than did younger patients. 26 This prompted the suggestion that all haemodynamically significant fistulas should be closed, even in the absence of symptoms, to prevent potential complications, such as endarteritis, progressive enlargement of the fistula, secondary atherosclerotic involvement with rupture, and thrombo-embolism. Early surgery also avoids the post-operative problems that can complicate operations performed in later life. The policy of closure, however, has to be balanced against the reports of spontaneous regression or closure, in some younger children with relatively small fistulas draining in particular into the right ventricle. 25, 26, 58–62
The aim of surgery is to close the fistula while preserving the flow of blood through the normal coronary arterial branches. Different surgical techniques have been used, and all of them appear to be adequate. The fistula is closed at the point of entry into the heart, without interrupting the continuity of the more proximal artery. When the lesion is clearly visible, closure can be achieved, without extracorporeal circulation, by clamping and suturing the fistulous channels on the outside of the heart. This approach does not require opening the fistula, the cardiac chambers, or the coronary arteries, and may be performed with the heart beating. More frequently, however, cardiopulmonary bypass is needed. This may be essential if it becomes necessary to enter a chamber to close the fistula from within, or if insertion of a bypass graft is necessary to maintain viability of the myocardium distal to the ligated artery. A small proportion of patients may develop complications post-operatively. These include ischaemia or infarction downstream from the point of ligation. This may be especially significant when a fistula from the right coronary artery drains to the right atrium or the superior caval vein. Ligation of such a vessel may interrupt the supply to the artery of the sinus node.
Surgical treatment is associated with morbidity, but low mortality rate, which ranges in reported series from zero to 6%. 13,56,57,63–68 Mortality rate, as expected, was higher in the historically older series. Myocardial infarction has been reported in less than one-twentieth of patients, 64 albeit that there is a low, but significant, risk of persistence or recurrence of the fistula. 63–66,69 The true incidence of recurrence, however, is unknown. The reason for the recurrence may be the presence of multiple fistulas, which are difficult to deal with by surgery. Median sternotomy and cardiopulmonary bypass also have their own associated morbidity. 68 Little has been said about the possibility of developing arteriosclerosis in the region of the fistula either subsequent to or prior to surgical treatment.
Until recently, surgery was the only available definitive treatment. In the last two decades, percutaneous transcatheter embolisation has emerged as an effective and safe alternative. When available, it should now be considered the treatment of choice. 16,70–77 The aim of closure by catheterisation is to occlude the artery feeding the fistula as distally, and close to its point of termination, as is possible to avoid occlusion of branches feeding normal myocardium. If the feeding artery is occluded too distally, and if there is no significant stenosis within the artery, then the possibility exists for inadvertent embolisation into the pulmonary circulation. Occlusion should be performed at a precise point, using various materials which include detachable balloons, stainless steel coils, or platinum microcoils. 16,74–79 It is rare nowadays to use detachable balloons, although they proved useful in the past. A large variety of equipment should be available in the catheterisation laboratory to achieve successful closure, because different techniques may be required should the fistula have unusual morphology. It is also necessary to have access to devices of different shapes and sizes, such as the conventional Gianturco coils, controlled-release coils, and a variety of devices normally used to close atrial or ventricular septal defects, persistently patent arterial ducts, or other abnormal vessels.
The choice of the equipment, and the technique to be used, is determined by the morphology of the fistulas. Other important determinants include the age and size of the patient, the size of the catheter that can be used in the patient, the size of the vessel to be occluded, and the tortuosity of the course required to reach the intended point of occlusion. For example, if the route to the target vessel is tortuous, then superfloppy guide wires combined with Tracker or Micro-ferret infusion catheters are recommended. In the presence of high flow, a stop-flow technique with a balloon is recommended during deployment of a coil or a device. Because of the need for precise occlusion, it is always preferable to use a potentially reversible technique.
For many years, stainless steel coils of 0.038-inch calibre have been widely used for embolisation elsewhere in the vascular system. They can be delivered through standard non-tapered catheters of 5 or 6 French size to occlude coronary arterial fistulas. Positioning such catheters satisfactorily in a distal location in a tortuous fistula, however, may be both difficult and hazardous. In such circumstances,it is safer to insert platinum microcoils, with calibre of 0.018 inch, which are delivered through a co-axial 3 French catheter. Such catheters, used with steerable guidewires, can be manipulated safely through tortuous arteries into very distal locations ( Fig. 50-10 ). Moreover, the high flow that is often encountered in large fistulas makes them difficult to occlude. A mass of platinum coils is frequently necessary. In the last 10 years or so, new interlocking detachable coils have been used, the delivery of which can be controlled. 78,80 Use of such coils makes closure much safer, with the added advantage that they can be retrieved into the catheter if the final position is deemed unsatisfactory. Such coils offer very little resistance to passage through the microcatheters. Even if they embolise inadvertently, they are easy to retrieve with snares. Fistulous arteries permitting very high flow present a particular problem, but temporary occlusion of the proximal portion with a balloon permits safe insertion of an occluding mass of coils ( Figs. 50-11 and 50-12 ). 80,81
Preliminary arteriography will usually have demonstrated the anatomy of the fistula prior to embolisation. Further detailed, and more selective, coronary angiography is essential to obtain details of the normal coronary arterial branches, which may be small but are at risk during occlusion. The steal from a fistula permitting high flow usually results in poor opacification of the normal branches and possible underestimation of their size. With all the current techniques, occlusion or near occlusion should be achieved soon after the embolisation. Sometimes, a small second feeding branch to the fistula may only become opacified when the main artery has been occluded ( Figs. 50-13 and 50-14 ). The key to success is to select a technique for embolisation that is suitable for the size and the location of the fistula.
Some fistulas may be more easily closed from the right side of the heart. These fistulas tend to be large, less tortuous, and have a short course to their point of drainage to the right heart ( Fig. 50-15 ). Depending on their size, they may be suitable for occlusion with a vascular plug, a ductal occluder ( Fig. 50-16 ), or an occluder usually used to close atrial or ventricular septal defects. 42,82–86 Fistulas closed in this fashion should be large, and should permit relatively easy and straight access from the right heart. If needed, occlusion can be achieved with the help of an arterio-venous guide wire circuit, using either femoral venous or internal jugular venous access.
After occluding the main fistulous vessel, repeat selective coronary angiography in both the coronary arteries should be performed in order to see if there is a second branch feeding the fistula, which may also need occlusion at the same procedure. When closing fistulas through a catheter, complete occlusion is expected in well over nine-tenths of procedures. The main complications include inadvertent embolisation of coils, transient electrocardiographic T-wave changes, transient bundle branch block, and myocardial infarction. All these complications are rare, apart from inadvertent embolisation, which may result from high flow in the large fistulas, or use of undersized coils. 80 As already discussed, should the coils migrate, they can easily be retrieved with snares.
AORTO–LEFT VENTRICULAR TUNNEL
The aorto–left ventricular tunnel is a rare defect, consisting of an endothelialised communication between the aorta and the left ventricle which bypasses the line of attachment of one of the aortic valvar leaflets. The abnormal channel originates in the ascending aorta, and terminates in the left ventricle ( Fig. 50-17 ). 86 The lesion is found more frequently in males than females, with a ratio of 2:1 to 3:1. 87,88 Although it was originally believed that the lesion was acquired after birth, it is now generally agreed that the entity is congenital, 87,89 having been detected prenatally by echocardiography. 90,91 Detected as early as 19 weeks of gestation, the most important clue to presence of the lesion was colour Doppler evidence of marked aortic regurgitation.
The tunnel usually originates above the right aortic sinus of Valsalva, and can involve the orifice of the right coronary artery. The tunnel courses in the tissue plane between the free-standing muscular right ventricular infundibulum and the aortic sinus, and usually enters the left ventricle through the fibrous triangle between the right and left coronary leaflets of the aortic valve. 92 Occasionally, the tunnel may originate above the origin of the left coronary artery ( Fig. 50-18 ). 93 The tunnel itself may be dilated aneurysmally through part or the entirety of its course. Associated cardiac defects include aortic valves with two leaflets, with aortic stenosis or regurgitation present in the majority of patients. Other defects include patency of the arterial duct, ventricular septal defect, pulmonary stenosis, infundibular right ventricular obstruction, aneurysm of the membranous septum, and critical aortic stenosis. 94,95 Distortion of the aortic valve occurs because of the lack of support of the afflicted leaflet, producing severe regurgitation.
Clinical Features
The symptoms and signs depend on the size of the tunnel and the severity of aortic regurgitation. Patients with severe regurgitation usually present with symptoms of congestive cardiac failure, with presentation at any point from birth to adult life. 88,96 The signs may include a wide pulse pressure, and loud systolic and diastolic to-and-fro murmurs at the base of the heart, usually with a short interval separating them. The anomaly should be considered in the differential diagnosis of any neonate or infant with systolic and diastolic murmurs along with the signs of aortic regurgitation. The abnormal haemodynamics may produce congestive cardiac failure in the neonate or infant, often with associated left ventricular enlargement and overactivity, with a dilated ascending aorta on a chest radiograph. As emphasised already, the key to diagnosis in fetal life is aortic regurgitation, sometimes with left ventricular dysfunction and hydrops. 90,91
Investigations
The electrocardiogram shows left ventricular hypertrophy in the majority of patients. Cross sectional and colour Doppler echocardiography usually confirms the diagnosis. In the occasional patient in whom the diagnosis is difficult, magnetic resonance imaging or cardiac catheterisation may be helpful. 97 Angiography in the aortic root usually confirms the diagnosis, although this should be rarely required nowadays. There may be gross dilation and distortion of the aortic sinus, ascending aorta, and the left ventricle. Angiography may also show normal origin of the coronary arteries, thus differentiating the tunnel from a fistula from the coronary artery to the left ventricle. The anterior location of the abnormal tunnel, and the demonstration of a normal aortic sinus of Valsalva, distinguishes the tunnel from ruptured aneurysm of a sinus of Valsalva into the left ventricle.
Management
Surgical closure in early life was first reported over 45 years ago. 87 Presentation with severe regurgitation is at or soon after birth, with early congestive cardiac failure. 88,98 Symptoms of congestive cardiac failure may also appear later, in the second or third decade of life. 87,96 Some patients may die despite medical treatment, 87 but others survive to undergo successful surgical repair. In presence of congestive cardiac failure, surgery is clearly indicated. In asymptomatic neonates, or in those patients in whom cardiac failure is well controlled, surgery can be delayed for a few weeks or months. Early intervention can prevent progressive damage to the aortic valvar leaflets or deformity of the aortic root, 99,100 and early surgery is also required should there be severe aortic stenosis rather than regurgitation. 101
The technique of repair depends on the type of tunnel. For those with a small aortic opening, closure of the orifice in two layers is advocated. 87 In the setting of larger openings, the aortic end is closed with a patch, while both the aortic and left ventricular ends of the tunnel can be closed. 102 In all the techniques, it is imperative to avoid distortion of the aortic valve and damage to the right coronary artery or the conduction system. The reported operative mortality ranges between zero and 20%. 91,100,102,103 Late complications after repair include aortic regurgitation in up to three-quarters of patients. 100,103 This may necessitate reoperation on the aortic valve. Occasionally, should it be severely stenotic, it may not be possible to preserve the native aortic valve. Replacement with an aortic homograft may then be required to repair both the tunnel and the stenotic valve. 101
ANEURYSMS OF THE SINUSES OF VALSALVA
Aneurysm of one of the aortic sinuses of Valsalva is a rare defect, which may be congenital or acquired. The incidence varies from 0.14% to 0.35%. 104 Its prevalence appears to be increased in the Asian countries when compared to Western populations. 105 Congenital aneurysms are the result of sinusal mural weakness, which produces downward prolapse of the leaflet. The dilated sinus may bulge into an atrium or ventricle, and may rupture. It is rare in infancy and childhood, being more commonly seen in adults. Aneurysms may be acquired through bacterial endocarditis, albeit that the endocarditis may have occurred on a congenital aneurysm. It can be difficult, therefore, to distinguish between congenital and acquired aneurysms, although frequently the congenital ones are associated with a ventricular septal defect and aortic coarctation. Most aneurysms are single, and most commonly affect the right coronary aortic sinus. Less commonly, the non-coronary aortic sinus is involved. The left coronary aortic sinus is rarely involved. Aneurysms of the right coronary aortic sinus usually prolapse into the right ventricle or right atrium, and those from the non-coronary sinus into the right atrium. Aneurysms of the left coronary aortic sinus prolapse into the left ventricle. The most common aneurysm, from the right coronary aortic sinus prolapsing into the right ventricle, may be associated with a ventricular septal defect.
As indicated, the aneurysms may rupture, this occurring during childhood or adolescence, and most frequently into the right rather than the left chambers. As expected from their position, aneurysm of the right sinus of Valsalva may rupture into the right ventricle or the right atrium, while those involving the non-coronary sinus tend to rupture into the right or left atrium, and those involving the left coronary aortic sinus rupturing into the left ventricle or the left atrium ( Fig. 50-19 ). 106–108 Rupture can also occur through the septal leaflet of the tricuspid valve, producing an acquired atrioventricular septal defect. 109 There is an increased incidence of rupture when an aneurysm occurs in the presence of a doubly committed subarterial ventricular septal defect. Rupture in these cases may occur into the right ventricular outflow tract. 110 Aneurysms occurring in the setting of Marfan’s syndrome are considered as a separate entity. Other associated lesions include an aortic valve with two leaflets, and aortic coarctation. Rupture has also been reported in a patient with Behçet’s disease, 111 and as a late complication after repair of dissection of the ascending aorta. 112
Clinical Features
When the aneurysm has not ruptured, it usually produces no symptoms. It may only be discovered as a chance finding on echocardiography, or angiography, performed during interrogation of another lesion, such as ventricular septal defect. The natural history of unruptured aneurysms is not known. Although rupture has been reported in the neonatal period, 113 it occurs more frequently in the third or fourth decade of life. When the aneurysm ruptures, the majority of the patients become symptomatic. Rupture may produce central precordial chest pain, along with sudden dyspnoea, because of a large left-to-right shunt combined with aortic regurgitation. Very occasionally, rupture may not produce any symptoms. Even rarer still is rupture into the pericardial cavity. 114 Unruptured aneurysms may cause angina, which may be intractable, especially when the aneurysm causes distortion of the origins of the coronary arteries. 115 Myocardial infarction may be the consequence of compression of the coronary arteries, and may occasionally be fatal. 116,117 Other possible complications include transient ischaemic attacks and cerebral embolism. 118–120 Physical examination may reveal a wide pulse pressure and left or right ventricular overactivity. The murmurs vary, with ejection systolic combined with early but long diastolic murmurs, or continuous murmurs heard at the right or left lower sternal borders. Obstruction of the right ventricular outflow tract has occasionally been reported, with or without the presence of a ventricular septal defect. 121,122
Investigations
The electrocardiogram usually shows left ventricular hypertrophy, occasionally with biventricular hypertrophy. Cross sectional combined with colour Doppler echocardiography is helpful in making the diagnosis, 123 and frequently shows dilation of the aortic root and left ventricular volume overload. A ruptured right coronary aortic sinus may protrude anteriorly, caudally, and leftwards. Severe aortic regurgitation may be present, with turbulent flow into the right ventricle or right atrium seen on colour Doppler. 107 Echocardiography will also show the presence or absence of a ventricular septal defect. Transoesophageal echocardiography shows the anatomy in more detail, and is perhaps superior to the transthoracic approach. 124 Frequently, surgery can be performed without the need for cardiac catheterisation. 119,125 Cardiac catheterisation and angiography merely confirm the echocardiographuc findings, albeit often showing the deformity of the aortic sinus more convincingly. Although filling of the right heart chambers, into which the aneurysm may have ruptured, is frequently seen, occasionally the rapid heart rate and the high cardiac output prevent their opacification. Apart from conventional echocardiography, contrast imaging has also been used for non-invasive diagnosis. 126,127
Management
The conventional treatment is surgical, although transcatheter approaches have increasingly been used in recent years. 128–130 If the surgical approach is chosen, it is performed on cardiopulmonary bypass. Direct closure can be carried out through an aortotomy, through the right ventricle, or via the right atrium. Sometimes both the aorta and the chamber of entry need to be explored to achieve effective repair. 131,132 Surgical repair may then involve closure of both ends of the aneurysm with patches. If a ventricular septal defect is present, it too should be closed. The aortic valvar leaflets may need resuspension in order to reduce the severity of aortic regurgitation, which may determine the outcome. Even after successful surgical repair, the prognosis is guarded. Recurrence, or an increase, of aortic regurgitation may be seen, and require further surgery. It is debatable whether an aneurysm discovered incidentally in an asymptomatic child should be surgically repaired. Surgical repair can now be achieved without mortality, even though it may be necessary to replace the aortic valve. 133 A more recent surgical experience 134 reported overall survival of 95% at 20 years. In the latter series, reoperation was needed in one-sixth of the patients for replacement of the aortic valve, recurrence of the fistula, or recurrence of a ventricular septal defect.
Transcatheter closure of a ruptured aneurysm of the sinus of Valsalva was first reported in 1994, using a Rashkind umbrella to close the defect. 128 Since then, different devices have been used, and the transcatheter experience has increased. 129, 135 To achieve success, the point of origin of the ruptured sinus needs to be clear of an orifice of a coronary artery by at least half a centimeter. The procedure is usually performed under general anaesthesia, using femoral venous and arterial access, and incorporating selective coronary angiography and an aortogram to delineate the anatomy. Having established an arterio-venous circuit, it is important to size the defect. When the size is uncertain, a balloon can be passed over the guidewire to provide increased accuracy. As discussed, a variety of devices, such as Amplatzer ductal occluder or the device designed for closure of muscular ventricular septal defects, have been used to occlude the ruptured sinus ( Figs. 50-20 and 50-21 ). Having inserted the device, selective coronary angiography is performed to ensure that the aortic end of the device has not encroached on the origin of the coronary arteries. Insertion of the device should produce complete occlusion of the defect. Haemolysis can occur if there is a significant residual flow, so selection of the most appropriate device is crucial. Reported results have thus far been good. 128–130
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