Truncus arteriosus

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Truncus arteriosus

  1. 1. Truncus Arteriosus Allison K. Cabalka MD William D. Edwards MD Joseph A. Dearani MD Persistent truncus arteriosus is an uncommon congenital cardiovascular malformation. There is not a striking gender difference in frequency, although most series contained more male than female subjects. Truncus arteriosus usually occurs as an isolated cardiovascular malformation, although on occasion it has been reported in association with anomalies of other systems, particularly the DiGeorge or velocardiofacial syndrome (microdeletion chromosome 22q11.2). Maternal diabetes has been implicated as a risk factor for truncus arteriosus. The anomaly has occurred in dizygotic twins and siblings, and there is an increased incidence of cardiac malformations in relatives of children with this lesion. Because corrective operation for this malformation was first performed more than 30 years ago, an ever-increasing number of postoperative patients is now reaching adolescence and adulthood. Patients who have had truncus arteriosus corrected need continued follow-up care throughout life. During the last 25 years, surgical correction of truncus arteriosus during infancy has become routine. Embryology The embryonic truncus arteriosus lies between the conus cordis proximally and the aortic sac and aortic arch system distally. Partitioning of the truncus arteriosus, which is intimately associated with conal and aortopulmonary septation, was reviewed by Van Mierop et al. and more recently by Bartelings and Gittenberger-de Groot. Truncus swellings, similar in appearance to endocardial cushions, divide the truncal lumen into two channels: The proximal ascending aorta and the pulmonary trunk. As the proximal portion of this truncal septum fuses with the developing conal septum (derived from conal swellings), the right ventricular origin of the pulmonary trunk and the left ventricular origin of the aorta are established. Valve swellings develop from truncal tissue at this line of fusion, and the excavation of these swellings leads to formation of the aortic and pulmonary valves in their respective sinuses. Along the aortic sac, the paired sixth aortic arches (primitive pulmonary arteries) migrate leftward, and the paired fourth aortic arches shift rightward. Invagination of the aortic sac roof thereby forms an aortopulmonary septum that eventually fuses with the distal extent of the truncal septum. Accordingly, the right and left pulmonary arteries originate from the
  2. 2. pulmonary trunk, and the aortic arch emanates from the ascending aorta. The spiral course of the truncoaortic partition produces the normal intertwinement of the great arteries. When conotruncal or truncoaortic septation does not proceed normally, various congenital ventriculoarterial anomalies may result. One of these anomalies is truncus arteriosus, in which a single arterial trunk exits from the heart. Also, either deficiency or absence of the conal (infundibular) septum produces a large ventricular septal defect. Because the conal septum also contributes to the development of the anterior tricuspid leaflet and the medial tricuspid papillary muscle, these structures may be malformed. The single truncal valve may be deformed and functionally insufficient or, less commonly, stenotic. If vestiges of distal truncoaortic septation develop, the pulmonary arteries may arise together from a short pulmonary trunk; otherwise, they arise separately from the truncal root. Pathology Truncus arteriosus is characterized by a single arterial vessel that arises from the base of the heart and gives origin to the coronary, pulmonary, and systemic arteries (Fig. 44.1). A single semilunar valve is found in truncus arteriosus, and this valve differentiates truncus arteriosus from aortic and pulmonary valve atresia, conditions in which a single arterial vessel also receives the entire output of both ventricles but in which a second atretic semilunar valve is present. Collett and Edwards recognized four types of truncus arteriosus on the basis of the anatomic origin of the pulmonary arteries. In type I, a short pulmonary trunk originating from the truncus arteriosus gives rise to both pulmonary arteries. When both pulmonary arteries separate from the truncus arteriosus, with no vestige of a main pulmonary artery, they may arise close to one another (type II) or at some distance from one another (type III). The type IV truncus arteriosus is now considered to represent a form of pulmonary atresia with ventricular septal defect and will not be discussed further in this chapter. Van Praagh and van Praagh have proposed an expanded classification system that also includes two commonly associated abnormalities of the great arteries. Their type A1 corresponds to type I of Collett and Edwards, and type A2 encompasses types II and III (Fig. 44.2). Type A3 includes cases with absence of truncal origin of one pulmonary artery, with blood supply to that lung from the ductus arteriosus or from a collateral artery. Last, type A4 is associated with underdevelopment of the aortic arch, including tubular hypoplasia, discrete coarctation, or complete interruption.
  3. 3. The ventricular septal defect in truncus arteriosus is generally large and results from either absence or pronounced deficiency of the infundibular septum. The defect is cradled between the two limbs of the septal band and is roofed by the truncal valve cusps (Fig, 44.1). In most instances, fusion of the inferior limb and the parietal band causes muscular discontinuity between the tricuspid valve and the truncal valve. Accordingly, the membranous septum is intact and the defect is of the infundibular type. When such fusion fails to occur, tricuspid-truncal valvular continuity is present, and the defect (which now involves the membranous septum) is of combined membranous and infundibular types. Rarely, the ventricular septal defect in truncus arteriosus may be small and restrictive or even absent. Among 400 cases of truncus arteriosus from four publications reviewed by Fuglestad et al., the truncal valve was tricuspid in 277 (69%), quadricuspid in 86 (22%), bicuspid in 35 (9%), pentacuspid in 1 (0.3%), and unicommissural in 1 (0.3%). The semilunar valve is in fibrous continuity with the mitral valve in all patients but is continuous with the tricuspid valve in only a minority. By overriding the ventricular septum, the truncus arteriosus has a biventricular origin in 68% to 83% of patients (15,18). In 11% to 29% of patients, the truncal valve arises entirely from the right ventricle, whereas in 4% to 6% of patients, it emanates entirely from the left ventricle. The anatomic cause for truncal valve insufficiency is variable and includes thickened and nodular dysplastic cusps, prolapse of unsupported cusps or of conjoined cusps with only a shallow raphe, inequality of cusp size, minor commissural abnormalities, and annular dilation. Truncal valve stenosis, when present, usually is associated with nodular and dysplastic cusps. The truncal root frequently is dilated, and the truncal sinuses often are poorly developed. A right aortic arch with mirror-image brachiocephalic branching is associated more commonly with truncus arteriosus, occurring in 21% to 36% of patients, than with any other congenital cardiac malformation except pulmonary atresia with ventricular septal defect. Rarely, a double aortic arch persists. Hypoplasia of the arch, either with or without coarctation of the aorta, occurs in 3% of patients. Interrupted aortic arch occurs relatively frequently (11% to 19% of patients) and is accompanied by ductal continuity of the descending thoracic aorta. It is frequently associated with the DiGeorge syndrome. The ductus arteriosus is absent in approximately half of patients with truncus arteriosus, but it remains patent postnatally in nearly two thirds of patients in whom it is present. The relative sizes of the aorta and the ductus arteriosus tend to vary inversely,
  4. 4. such that the ductus arteriosus is particularly large in patients with underdevelopment of the aortic arch (type A4 truncus). The pulmonary arteries most commonly arise from the left posterolateral aspect of the truncus arteriosus, a small distance above the truncal valve. Type I truncus arteriosus is observed in 48% to 68% of patients, type II in 29% to 48%, and type III in 6% to 10%. In type II, the left pulmonary artery ostium is generally somewhat higher than that of the right pulmonary artery. Rarely, in the setting of interrupted aortic arch, this ostium may arise to the right of the right pulmonary artery ostium and cause crossing of the pulmonary arteries posterior to the truncus arteriosus. Stenosis of the pulmonary artery ostia or arteries is uncommon. In rare instances, deformed truncal valvular tissue may obstruct the pulmonary ostia during ventricular systole. In general, however, unless pulmonary arterial banding is performed, the pulmonary vascular bed will be exposed to systemic arterial pressure. In rare instances, deformed truncal valvular tissue may obstruct the pulmonary ostia during ventricular systole. In truncus arteriosus, one pulmonary artery may be absent. Of the Mayo Clinic's previously published series of patients with truncus arteriosus, 16% (11 of 70) had only a single pulmonary artery. In 9 of the 11 patients, the pulmonary artery was absent on the side of the aortic arch. Thus, in truncus arteriosus, the pulmonary artery is most frequently absent on the side of the aortic arch, in contrast to tetralogy of Fallot, in which the pulmonary artery is more frequently absent on the side opposite the aortic arch. This chapter does not consider either so-called pseudotruncus arteriosus, which is actually a form of pulmonary valve atresia with ventricular septal defect, or hemitruncus, in which one pulmonary artery arises from the ascending aorta and the other emanates from the right ventricle and clearly has a well-developed pulmonary valve at its origin. The embryologic basis for these deformities appears to be different from that for true persistent truncus arteriosus. Knowledge of variations in coronary arterial origin and distribution, which are common in truncus arteriosus, is important to the surgeon. Because the left anterior descending coronary artery frequently is relatively small and displaced leftward, the conus branch of the right coronary artery, in a compensatory manner, is usually prominent and supplies several large branches to the right ventricular outflow tract. The posterior descending coronary artery arises from the left circumflex artery (left coronary dominance) in 27% of truncus arteriosus patients, which is about three times the frequency of this variation in the normal population. Anomalies of coronary ostial
  5. 5. origin, involving 37% to 49% of patients with truncus arteriosus, are common, regardless of the number of truncal valve cusps. In general, however, the left coronary artery tends to arise from the left posterolateral truncal surface and the right coronary artery from the right anterolateral surface. In the setting of a single coronary ostium, frequently associated with left coronary dominance, all three major epicardial branches originate from this common site, or the right coronary artery may be absent. When two ostia exist, both may arise from the same truncal sinus; one may take origin from the expected site of the noncoronary sinus, or both may arise normally. High ostial origin, above the truncal sinotubular junction, occurs often; but when the origin is at or slightly above a truncal valve commissure, the involved ostium (most commonly the left) may be slitlike and functionally stenotic. Conceivably, dysplastic valvular tissue also could obstruct an otherwise normal coronary ostium. Rarely, the left coronary artery originates from the pulmonary trunk. Combinations of the aforementioned coronary anomalies frequently are observed. The location of the conduction tissue in truncus arteriosus is also of surgical importance. The sinus node and the atrio-ventricular node are normal in location and structure. The atrioventricular bundle courses to the left of the central fibrous body, and the left bundle branch emanates along the left ventricular septal subendocardium, just beneath the membranous septum. The right bundle branch travels within the myocardium of the ventricular septal summit, attaining a subendocardial course at the level of the moderator band. In most instances in which the ventricular septal defect is truly infundibular and the membranous septum is intact, the atrio-ventricular conduction tissue is somewhat distant from the rim of the defect. In patients with combined membranous-infundibular ventricular septal defect, however, the conduction tissue passes along the left aspect of the posterior–inferior rim of the defect. The anomalies most commonly associated with truncus arteriosus (discussed above) are right aortic arch, interrupted aortic arch, absent ductus arteriosus, patent ductus arteriosus, unilateral absence of a pulmonary artery, coronary ostial anomalies, and an incompetent truncal valve. A secundum atrial septal defect has been noted in 9% to 20% of patients, an aberrant subclavian artery in 4% to 10%, a persistent left superior vena cava draining into the coronary sinus in 4% to 9%, and mild tricuspid stenosis in 6%. Total or partial anomalous pulmonary venous connection in association with truncus arteriosus also has been described. Rare associated anomalies that have been reported include tricuspid atresia, mitral atresia, ventricular inversion, and association with the asplenia complex. We have encountered one patient with both truncus
  6. 6. arteriosus and complete atrioventricular septal defect. Extracardiac anomalies, present in 21% to 30% of autopsy cases of truncus arteriosus, include skeletal deformities, hydroureter, bowel malrotation, and multiple complex anomalies. Among the secondary complications of truncus arteriosus, biventricular hypertrophy is frequent, and dilation of ventricular chambers is prominent when truncal valve insufficiency exists. If there is massive cardiac hypertrophy, chronic subendocardial myocardial ischemia may develop (even with normal epicardial coronary arteries). As a result of chronic exposure of the pulmonary vasculature to systemic arterial pressure, hypertensive pulmonary vascular disease (plexogenic pulmonary arteriopathy) may develop. The arteriolar lesions often develop more rapidly and to a more severe extent in truncus arteriosus than in isolated ventricular septal defect. With chronic truncal valve insufficiency, pulmonary venous hypertension also may develop. As patients with surgical repair survive into adulthood, progressive dilation of their aorta (original truncal artery) often occurs and may be associated with the development of ascending “aortic” aneurysms and an increased risk for “aortic” dissection or rupture, as well as “aortic” valve regurgitation. Manifestations Clinical Features In most patients with truncus arteriosus, congenital heart disease is recognized during early infancy, often during the neonatal period. During the 1990s, intrauterine diagnosis became possible with fetal echocardiography. The clinical features depend largely on the volume of pulmonary blood flow and whether associated significant truncal valve insufficiency is present. During the first weeks of life, persistence of increased pulmonary arteriolar resistance present during fetal life may cause mild cyanosis with little evidence of cardiac decompensation, unless severe truncal valve insufficiency is also present. As pulmonary resistance gradually decreases and flow through the lungs increases, the cyanosis may disappear. However, tachy-pnea, tachycardia, excessive sweating, poor feeding, and other signs of pulmonary overcirculation may appear. If truncal valve insufficiency is severe, the signs and symptoms of heart failure may appear shortly after birth. The additional volume load produced by this associated problem always adds to the increasing demands placed on the heart as pulmonary flow increases.
  7. 7. In the uncommon situation in which the infant has naturally occurring stenosis of the pulmonary arteries, obvious cyanosis may be present at birth and may intensify with increasing age. However, such stenosis protects the child from pulmonary overcirculation that would otherwise occur with falling pulmonary resistance. Severe cyanosis, in addition to the signs of heart failure, may be present early if the child has both naturally occurring stenosis of the pulmonary artery and severe insufficiency of the truncal valve. Physical Examination Physical findings are related primarily to the volume of pulmonary blood flow and the presence or absence of truncal valve insufficiency. Patients with increased pulmonary blood flow have little or no cyanosis. The peripheral pulses are accentuated and may be bounding. The pulse pressure usually is increased owing to runoff into the pulmonary vascular bed during diastole. A left precordial bulge may be noted, and a systolic thrill often is palpable along the left sternal border. The heart usually is overactive. The first heart sound is normal and frequently followed by an ejection click, which echocardiographic studies have shown to coincide with maximal opening of the truncal valve. The second heart sound usually is loud and single. The occasional auscultatory or phonocardiographic observation of a split second sound in these patients with a single semilunar valve may be caused by delayed closure of some of the cusps of the abnormal truncal valve. An apical third heart sound often is present. A loud pansystolic murmur maximal at the lower left sternal border and radiating to the entire precordium most often is heard. An apical diastolic low-pitched murmur caused by increased flow across the normal mitral valve frequently is audible. The patient with truncal valve insufficiency usually has a diastolic high-pitched murmur that is heard best along the left sternal border. A truly continuous murmur is uncommon in truncus arteriosus and, when present, is usually suggestive of pulmonary artery ostial stenosis. Continuous murmurs are common in patients with pulmonary valve atresia/ventricular septal defect, however, where either a patent ductus arteriosus or systemic collateral arteries provide pulmonary blood flow. Because the differential diagnosis of truncus arteriosus includes this lesion, a continuous murmur is strongly suggestive of pulmonary atresia rather than of truncus arteriosus. Patients in heart failure may exhibit the additional signs of tachypnea, crepitant rales, hepatomegaly, and neck-vein distension. Cyanosis is present, and clubbing of the fingers and toes may be seen in patients with decreased pulmonary blood flow caused by naturally occurring pulmonary artery
  8. 8. stenosis, pulmonary artery banding, or pulmonary vascular disease. If there is no associated truncal valve insufficiency, the peripheral pulses and pulse pressure are nearly normal. The apical diastolic murmur often is not present. These patients are less likely to have signs and symptoms of cardiac decompensation. Electrocardiographic Features The electrocardiogram normally shows a normal frontal plane QRS axis or minimal right-axis deviation. Generally, normal sinus rhythm is present, and the conduction times are not prolonged. Combined ventricular hypertrophy occurs frequently. Left ventricular forces are particularly prominent in patients with increased pulmonary blood flow. Left atrial enlargement also is common in this group. Patients with normal or decreased pulmonary flow may exhibit right ventricular hypertrophy only. Radiologic Features Typically, radiography of the chest shows moderate cardiomegaly and increased pulmonary vascular markings. The aortic arch is right-sided in approximately one third of patients, and the combination of a right aortic arch and increased pulmonary vascularity is strongly suggestive of truncus arteriosus. Type I truncus arteriosus frequently is associated with a relatively superiorly located proximal left pulmonary artery, which usually can be distinguished on a frontal chest radiograph (Fig, 44.3). A dilated truncal root is common. Although the pulmonary vascular markings typically are increased, variation in the pulmonary vascular pattern can be seen. In truncus arteriosus with absent pulmonary artery, the pulmonary vascular markings are markedly diminished on the side without the pulmonary artery (usually the left side). In addition, pulmonary vascular obstructive disease is common in patients with truncus arteriosus and is reflected in the chest radiograph by disproportionate enlargement of the central pulmonary arteries associated with accentuated tapering of the distal pulmonary arterial tree. Echocardiographic Features The use of two-dimensional, Doppler, and color Doppler echocardiography, has greatly increased the ability to determine accurately the cardiac anatomy and, in most cases, the hemodynamics in truncus arteriosus. Subcostal windows are used to document abdominal visceral situs and atrial situs, in addition to the position of the cardiac apex. A single great vessel arising from the heart is typically seen subcostally
  9. 9. (Fig. 44.4A), and assessment of the atrial septum is best performed from this location. Subcostal windows provide additional views for evaluation of the truncal valve function, truncal root and pulmonary artery branch anatomy. The parasternal long-axis view demonstrates the deficiency in the ventricular septum and the overriding great artery, with continuity between the truncal valve and the mitral valve. Slightly higher position in the parasternal long-axis view can be used to visualize the origin of the pulmonary trunk or branches (Fig. 44.4B). Further imaging is required to document the presence of a single arterial trunk and lack of a pulmonary outflow tract from the ventricle. High parasternal short-axis views will provide visualization of the pulmonary arteries arising directly from the posterolateral aspect of the truncal root, typically bifurcating into the right and left pulmonary arteries. Persistence of a short main pulmonary artery segment is seen in truncus arteriosus type I (Van Praagh type A1, Fig. 44.5), with separate origins of the pulmonary branches seen in type II (type A2). When only one pulmonary artery is present, as in type III truncus (type A3), the remaining pulmonary artery origin must be documented, typically originating from the aortic arch or ductus arteriosus. The short-axis view is also useful in evaluating the anatomy of the truncal valve leaflets (number and morphology), as well as visualization of the coronary arteries and their origins, and the location and extension of the ventricular septal defect. Suprasternal notch imaging is critical for evaluation of the aortic arch anatomy, as interruption of the aortic arch may be associated with truncus arteriosus (type A4). Right-sided aortic arch also is common in truncus arteriosus and can be determined from short axis imaging of the arch branching pattern. In addition, the pulmonary artery branches can also be visualized from the suprasternal notch, excluding any important branch stenoses. Aortopulmonary window is in the differential diagnosis of truncus arteriosus and angiocardiographically may be confused with truncus arteriosus. Echocardiographically, however, these two entities can be differentiated easily. Aortopulmonary window usually is not associated with a ventricular septal defect, and the right ventricular outflow tract and pulmonary valve are in the expected positions. These features usually are recognized easily by two-dimensional echocardiography. Moreover, in aortopulmonary window, use of a high parasternal short-axis view usually allows its direct visualization. In patients with truncal valve stenosis, Doppler echocardiography usually enables an estimation of this gradient. In patients with significant truncal valve insufficiency, the systolic Doppler gradient may overestimate the degree of valve stenosis owing to the volume of flow across the valve (two-dimensional morphology must be correlated with the Doppler findings). Truncal valve incompetence also can be
  10. 10. delineated and quantitated by Doppler technique; the color flow Doppler examination has been particularly helpful in this assessment. Doppler flow reversal in the abdominal descending aorta may be due to either pulmonary artery runoff, truncal valve insufficiency, or both. In the rare patient with a pulmonary artery band(s) in place, Doppler evaluation also permits assessment of the pressure gradient between the truncal root and the pulmonary arteries beyond the band. Truncus arteriosus also may be diagnosed in utero with fetal echocardiography. The echocardiographer must be certain to identify the central main pulmonary artery (MPA) origin or proximal branch origin from the ascending truncal root to differentiate this condition from pulmonary atresia/ ventricular septal defect. Severe truncal valve dysfunction (stenosis typically in combination with regurgitation) in utero may lead to fetal hydrops. Cardiac Catheterization and Angiocardiography With the introduction and advancement of accurate echo-Doppler techniques and the advent of surgical correction during early infancy before irreversible pulmonary vascular disease is a concern, diagnostic cardiac catheterization and angiography are now infrequently necessary in the patient with truncus arteriosus. Occasionally, the patient with truncus arteriosus with associated interruption at the aortic arch or single pulmonary artery will still need angiography to delineate aortic arch anatomy or the anatomy of the pulmonary arterial tree precisely. Even more uncommonly in this era, a patient with truncus arteriosus will still present initially beyond early infancy for consideration of surgical correction, and cardiac catheterization may be necessary to assess the status of the pulmonary vascular bed. An example of a truncal root angiogram is seen in Fig. 44.6. Patients with truncus arteriosus are at risk of having pulmonary vascular obstructive disease develop at an early age, and this has provided the major impetus for early surgical correction. For the occasional patient presenting beyond infancy, pulmonary vascular resistance must be assessed accurately to select the best treatment. Although direct measurement of pulmonary resistance is not possible, the calculated indirect value, obtained by dividing the mean driving pressure across the pulmonary bed (in mm Hg) by the total pulmonary flow index (in liters per minute per square meter), provides a reliable estimation of the status of the pulmonary arterioles. Patients with truncus arteriosus who have two pulmonary arteries and a pulmonary arteriolar resistance >8 units m2 are at higher operative risk than patients with resistances below that level. Among the group with resistances >8 units m2, late
  11. 11. deaths were due to progression of pulmonary vascular obstructive disease with secondary severe pulmonary hypertension and right ventricular failure. Among the survivors of operation in the group with preoperative resistance <8 units per m2, no late deaths occurred secondary to progressive pulmonary hypertension. Fortunately, the trend toward early corrective surgery has reduced the number of patients who are inoperable because of pulmonary vascular obstructive disease. Patients with truncus arteriosus who have significant elevation of pulmonary vascular resistance still occasionally are seen, however, and our current policy is not to offer corrective surgery to patients with truncus arteriosus who have two pulmonary arteries and whose pulmonary arteriolar resistance is >8 units m2. The exceptions are children younger than 2 years of age whose resistance decreases <8 units m2, when 100% oxygen is breathed or after administration of a pharmacologic vasodilator such as inhaled nitric oxide. In such young patients, surgery still may be offered if the parents are willing to accept a higher surgical risk because it is possible that the increased resistances may result from arteriolar or medial smooth muscle hypertrophy and vasoconstriction rather than advanced intimal occlusive disease. These changes, potentially, may be reversible. Different criteria must be used to assess the feasibility of operation in patients with unilateral absence of a pulmonary artery. Severe pulmonary vascular disease is particularly likely to develop at an early age in patients with a single pulmonary artery. To achieve good surgical results in this subgroup, corrective surgery should be performed in the neonatal period. Even in such patients who survive corrective operation, however, pulmonary vascular disease tends to progress postoperatively more often than it does in patients with corrected truncus arteriosus who have two pulmonary arteries. This difference may be related to the fact that the entire cardiac output still must pass through one lung so that the rate of flow through each arteriole remains approximately double. This may be a potential stimulus for the progression of pulmonary vascular changes. An accurate preoperative catheterization laboratory assessment of truncal valve insufficiency may be difficult because of contrast runoff into the pulmonary artery bed. Magnetic Resonance Imaging Cardiac magnetic resonance imaging (MRI) and angiography (MRA) can provide additional noninvasive anatomic and hemodynamic information in the patient with truncus arteriosus. Visualization of the conotruncus and pulmonary artery anatomy is accomplished by multiple techniques, including black blood and white blood imaging techniques with gating, and with the use of gadolinium contrast-enhanced MRA.
  12. 12. Differential Diagnosis In infants with truncus arteriosus and increased pulmonary blood flow, the differential diagnosis includes the other congenital cardiac conditions that cause early heart failure and are associated with either mild or no cyanosis. Such malformations include ventricular septal defect, patent ductus arteriosus, aorticopulmonary window, pulmonary atresia with ventricular septal defect, and patent ductus arteriosus, or large collateral arteries, double-outlet right ventricle, univentricular heart, and total anomalous pulmonary venous connection. In truncus arteriosus with decreased pulmonary flow, other conditions to be considered include pulmonary atresia, tricuspid atresia, tetralogy of Fallot, univentricular heart with pulmonary stenosis, and double- outlet right ventricle with pulmonary stenosis. Although certain physical findings, chest radiographic evidence, and electrocardiographic features may suggest the increased likelihood of a particular lesion, echocardiography is necessary to establish the diagnosis definitively. Natural History Although patients with truncus arteriosus occasionally survive to adulthood without surgery, the natural history of this condition is generally dismal. In one autopsy series, the mean age of death was 5 weeks. Another series reported a survival of only 15% beyond the age of 1 year. Death in infancy most commonly is caused by heart failure. In patients who survived the first 4 years, death may occur from heart failure, but more frequently it results from the complications of hypertensive pulmonary vascular disease and infective endocarditis. Once severe pulmonary vascular disease is present, deterioration often is rapid, with severe morbidity and death frequently occurring in late childhood or early adolescence. This dismal natural history was the main factor that gave rise to the approach of early surgical intervention that is now advocated for these patients. Treatment The diagnosis of truncus arteriosus in itself is an indication for operation. Diagnosis ideally is made prenatally or soon after birth. Medical stabilization is performed in the intensive care unit, and operation with complete repair is preferred in the first weeks of life. Delay of operation results in chronic ischemia of the hypertrophied ventricle, which is perfused by desaturated blood at a low diastolic perfusion pressure caused by runoff through the pulmonary arteries,
  13. 13. and, when present, “aortic” insufficiency. This hazard of ventricular dysfunction may explain in part the observation that repair of truncus at 6 to 12 months of age is associated with a mortality twice that for repair between 6 weeks and 6 months of age. Pulmonary vascular obstructive disease also can develop early, which provides additional impetus for correction in the first few months of life. Pulmonary vascular obstructive disease, no doubt, also is partly responsible for the increased surgical mortality in infants who undergo repair after 6 months of age. The preferred operation is complete repair during the neonatal period. Although pulmonary artery banding may provide palliation for young patients with truncus arteriosus, there are well-documented risks and potential complications of banding for this condition. In addition, successful banding has not guaranteed that these patients will be good candidates for later correction. During the past 15 years, improved surgical techniques and postoperative care have made correction of truncus arteriosus during infancy possible at an operative risk less than that previously reported for banding. Surgical Correction Successful definitive surgical correction in a patient with truncus arteriosus was first accomplished by McGoon et al. in 1967. In the original operation, based on the experimental work of Rastelli et al., continuity between the right ventricle and the pulmonary arteries was established with an aortic homograft. Cryopreserved homograft tissue continues to be the conduit of choice for repair of this defect in early infancy. The early and late results experienced by the initial 92 patients who had correction at the Mayo Clinic were reported in 1977. Although overall hospital mortality was 25%, the operative mortality decreased to 9% in the 33 patients operated on during the last 2 1/2 years of this early series. Since that time, an operative mortality of 5% was achieved in patients without severe associated abnormalities who subsequently have undergone correction of truncus arteriosus. In 1984, Ebert et al. (10) reported results of 100 infants repaired prior to 6 months of age, emphasizing the importance of early repair to prevent the development of pulmonary vascular obstructive disease. Early mortality was 11%. It also was emphasized at this time the importance of complete repair in early infancy to prevent the development of pulmonary vascular obstructive disease. During the last three decades, there as been great progress in the surgical management of infants. In the current era, excellent results have been obtained with corrective operation during infancy. In patients who undergo successful correction
  14. 14. during early infancy, the small conduit eventually must be replaced with a larger one, but reoperation for conduit replacement alone carries a low risk. A 1993 late follow-up of 137 patients with truncus arteriosus corrected at the Mayo Clinic between 1967 and May 1992 revealed no perioperative deaths in 39 patients who underwent subsequent reoperation for isolated conduit replacement. One death occurred in 15 patients who had isolated conduit replacement performed elsewhere. Although techniques of repair that do not include an extracardiac conduit have also been described, most prefer a valved conduit when complete repair is performed because of the presence of pulmonary hypertension. Techniques for conduit replacement have evolved over the last two decades. It is our current preference to use the autologous tissue reconstruction (“peel operation”) to reconstruct the right ventricular outflow tract when conduit replacement is required (Fig. 44.9). The technique includes placement of a prosthetic roof (usually bovine pericardium) over the fibrous bed of the explanted conduit with insertion of a prosthetic valve (usually bioprosthesis). Early mortality has been low for conduit replacement, in our experience, even after multiple conduit revisions. Early mortality was 2% but was 0% for isolated conduit replacement. Overall survivorship free of reoperation for the peel reconstruction at 10 and 15 years was 90.7% and 82%, respectively. The presence of a regurgitant truncal valve is almost always amenable to various repair techniques, and replacement is rarely if ever required in the neonatal period. Numerous authors have describe various truncal valvuloplasty techniques. Frequently used techniques include suturing of the prolapsing leaflet to adjacent leaflets; the prolapsing leaflet is usually thickened and adjacent leaflet edges are also thickened, which facilitates suture placement. The tops of the commissures often are splayed from dilation of the sinotubular junction. This can be corrected by wedge excisions of the aorta. If recurrent truncal valve incompetence occurs, our policy is to repair or replace the truncal valve at the time of reoperation for conduit replacement. Late results following complete repair are determined by the degree of truncal valve regurgitation and the need for conduit replacement. The need for truncal valve repair at the time of complete repair is low. If reoperation is required for truncal valve regurgitation, intermediate-term results favor repair of the truncal valve. Serial echocardiographic examinations are essential during lifelong follow-up. Recurrent truncal valve regurgitation may require repair or replacement at a subsequent operation (Fig. 44.10). In our follow-up of 137 patients with truncus arteriosus who were operative survivors in our initial 25-year experience, no one required truncal valve replacement when trivial or no truncal valve incompetence was present at the time of
  15. 15. correction. In patients who had mild, moderate, or severe truncal incompetence, the eventual need for truncal valve replacement was high. The difference between the two groups was highly significant (p <0.001, Fig. 44.11). The primary late problem related to extracardiac conduit operations is the need for conduit replacement because of patient somatic growth or progressive deterioration and calcification of the conduit (Fig. 44.12). Numerous reports have focused on issues of conduit size, valve degeneration, and conduit degeneration. Late outcome of homograft and prosthetic conduits has been reported with variable results. Our attempt to reduce the incidence of late conduit failure was the construction of an autologous tissue conduit, with or without a valve. Advantages of this technique include an autogenous floor with a pericardial roof that does not form obstructive peels, and the diameter of the pathway can be as large as desired, allowing a bioprosthesis to be inserted. We have examined the freedom from reoperation for conduit failure in an age- matched group of patients who have received a Hancock conduit, a homograft conduit, and a valved peel reconstruction (Fig. 44.13). The peel operation had statistically significant freedom from reoperation compared with the homograft (p = 0.001). Although the peel operation had more favorable durability than the Hancock conduit, this did not reach statistical significance (p = 0.19) owing to the small numbers in the peel operation group at late follow-up. The search continues for the ideal extracardiac conduit. Although the need for reoperation is inevitable for most patients, the risk of reoperation is low and most patients enjoy a good quality of life. At present, the peel operation provides the most favorable freedom from reoperation and is our procedure of choice when conduit replacement is required. Long-Term Issues In summary, the patient with repaired truncus arteriosus will need lifelong cardiovascular follow-up. Infective endocarditis precautions are warranted. Primary issues that will require attention, ongoing evaluation, and potentially further treatment after neonatal repair include truncal valve dysfunction (stenosis and/or insufficiency), function of the pulmonary homograft/conduit in the right ventricular outflow tract, and the development of branch pulmonary artery stenosis. Left and right ventricular function, both systolic and diastolic, must be evaluated in an ongoing fashion. Echocardiography and cardiac MRI/MRA are useful tools for ongoing noninvasive evaluation of the patient with repaired truncus arteriosus. Seamless transition from the
  16. 16. pediatric cardiologist to the adult congenital heart disease specialist is clearly warranted as this patient group ages.

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