Congenital Heart Disease
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Tetralogy of Fallot
William W. Pinsky, MD,* and Eduardo Arciniegas, MDt
Although tetralogy of Fallot is well known by name to those involved in pediatric medicine, it is not necessarily well known by its detailed anatomy and physiology. It will be the purpose of this article to highlight those aspects of tetralogy of Fallot to allow those involved in the care of children to have an up-to-date understanding of this entity.
HISTORICAL PERSPECTIVE AND INCIDENCE Although this syndrome carries the name of Dr. Fallot, the first description of this constellation of anatomic defects initially was described by Stensen in 1671. 1 Sandifort in 17772 described some of the clinical manifestations that we now consider part of this syndrome; in 1784 Hunter3 expanded on these. It was Fallot's publication in 18884 that correlated the previously described clinical findings and attached his name to the syndrome with the now well-known tetrad of right ventricular outflow tract obstruction, dextroposition and overriding of the aorta, ventricular septal defect, and hypertrophy of the right ventricle. As a single entity, tetralogy of Fallot is the most common malformation of children born with cyanotic heart disease, with an incidence of approximately 10 per cent of congenital heart disease. 5 There is no known definite genetic/environmental pattern giving rise to tetralogy of Fallot. However, it has been described in various syndromes and associated with various teratogens such as thrombocytopenia and absent radius, APERTs, DiGeorge's, trimethadione, sex hormones, tha-
From the Children's Hospital of Michigan, Wayne State University School of Medicine, Detroit, Michigan
* Professor
of Pediatrics and Vice Chairman, Department of Pediatrics; and Chief, Division of Pediatric Cardiology t Clinical Professor of Surgery and Chief, Pediatric Cardiovascular Surgery Pediatric Clinics of North America-Vol. 37, No.1, February 1990
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lidomide, and phenylketonuria. 6 Risk within a family ranges from 2.5 per cent with an affected sibling, to 4 per cent with an affected parent. 7
ANATOMIC PATHOLOGY Although there can be a wide spectrum as to the severity of the anatomic defects, there is the association of a ventricular septal defect (VSD), aortic override, right ventricular outHow tract obstruction, and right ventricular hypertrophy.8 This can range from mild right ventricular outHow tract obstruction to complete atresia of the pulmonary valve and hypoplasia of the pulmonary arteries. Aortic override can be minimal or as much as 75 per cent. 9 Although the ventricular septal defect is generally large and nonrestrictive, there have been reports of restrictive ventricular septal defects.lO For the purpose of discussion, we will not inc! ude patients with complete atresia of the right ventricu1ar outHow tract. The degree of obstruction to blood How through the right ventricular outHow tract is considered to be the determining factor of the degree and type of dysfunction exhibited by patients. It is universally accepted that patients will have at least some minor abnormality of the pulmonary valve, although the valve orifice usually is at least the same size or larger than the smallest diameter of the infundibular opening. 11 The valves, therefore, may have abnormalities in terms of the number of cusps or the degree of stenosis. l l The infundibulum is rotated cephalad and this position is instrumental in developing obstruction at this level. 12 The normally nonprominent crista supraventricularis is displaced and hypertrophied, infringing on the outHow tract both in systole and diastole. The parietal band is displaced superiorly and more towards the septum obstructing blood How during ejection. Distal to the crista may be a more normal outHow tract that is generally described as the "infundibular chamber." It is thought that the ventricular septal defect in tetralogy of Fallot is perimembranous. In a review of 53 specimens, Anderson found three different types of defects. 12 In 41 specimens, the defect extended cephalad and anteriorly and was limited by the infundibular septum. Caudally the defects were limited by aspects of the trabecular septa marginalis. These perimembranous defects were in association with the malalignment of the trabecular and infundibular muscular components of the ventricular septum. Eleven specimens contained defects that had a complete muscular rim. The remaining defect was categorized as subarterial as it was roofed over by the aortic and pulmonary valve rings. Anderson described this as being a "doubly committed subarterial defect with absence of the infundibular septum." The aortic override can range from a small degree to 75 per cent. This occurs by an abnormal anterior extension of the aortic root relative to the ventricular septum, resulting from maldevelopment of the conal region. 13 There may be coronary artery anomalies associated with tetralogy of Fallot. These anomalies generally have no functional significance
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but they have a great deal of significance to the surgeon repairing the defect.14 It is believed that 2 to 9 per cent of patients will have the most common anomaly, which is origin of the left anterior descending coronary artery arising from the right coronary artery. 15, 16 This means that the anomalous artery will cross the right ventricular outflow tract in the area where a ventriculotomy incision frequently is made during repair of tetralogy of Fallot. Other abnormalities are found in tetralogy including the presence of a single right coronary artery that gives off a left branch that goes anterior to the pulmonary trunk, and a left coronary artery that originates normally and then crosses anteriorly between the aorta and pulmonary arteries and then laterally across the pulmonary trunk. In almost all cases with tetralogy of Fallot, the infundibular branch of the right coronary artery is very prominentY . Twenty-five p,er cent of patients with tetralogy of Fallot have a right aortic arch. 1 This may occur in association with anomalous origin of the left subclavian artery arising from the distal aorta. 19 It is important to note the situs of the arch as well as the origin of the arch vessels when planning operative palliation of these patients.
PHYSIOLOGY The consequence of the large ventricular septal defect, overriding aorta, and right ventricular outflow tract obstruction is generally that of a right-to-Ieft shunt. Based on the degree of override and right ventricular outflow tract obstruction, right-to-Ieft shunting may vary from mild to severe. Consequences to the myocardium are that the right ventricle hypertrophies secondary to contraction against the fixed obstruction at the outflow tract, as well as pumping blood through the ventricular septal defect against systemic resistance. Iflarge collateral vessels are present, then the left ventricle may enlarge and hypertrophy. Longstanding hypertrophy will result in some degree of diastolic stiffness in the right ventricle, although it is thought not to be clinically significant in most circumstances. With prolonged arterial desaturation, polycythemia will develop. The increased viscosity secondary to polycythemia will increase effective pulmonary and systemic resistance causing more strain on the respective ventricles. 20
CARDIAC EXAMINATION Patients with tetralogy of Fallot have an active precordium. The point of maximal impulse will generally be the right ventricle with the left ventricle being the apical impulse. Generally there are no thrills felt. The first heart sound is normal; the second heart sound is single and increased in intensity representing the sound of the anteriorly located aortic closure. The murmur is that of obstruction to the right ventricular outflow tract. It is a harsh systolic ejection murmur heard
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maximally over the pulmonary area. The murmur radiates across the chest anteriorly and to both sides of the back. Even with some left-toright shunting, the murmur of the ventricular septal defect is overshadowed by the right ventricular outflow tract obstruction murmur.
CLINICAL MANIFESTATION Newborns may present with cyanosis and murmur or just a loud murmur. Any young infant with a harsh systolic ejection murmur that radiates to both sides of the back with a single second heart sound should be suspected of having tetralogy of Fallot. Most infants with cyanosis, other than those with pulmonary valve atresia, will be diagnosed outside of the newborn period. These infants may be mildly cyanotic at rest or noted to have cyanosis with crying or feeding. Growth patterns in the first few months oflife are normal. Occasionally an older infant will present with tetralogy of Fallot. These are infants that have a net left-to-right shunt and are referred to as having "pink" tetralogy of Fallot. As they become older and develop more infundibular narrowing, these patients will demonstrate cyanosis at rest or be prone to hypercyanotic episodes. Hypercyanotic episodes occur most frequently at a time when systemic vascular resistance is at its lowest. For young infants, these times are soon after awakening or after feeding. 21 Crying and defecating also may precipitate the events. 21 Increased rate and depth of respiration (hyperpnea) are the hallmarks of the initiation of a spell. As the pulmonary blood flow decreases, the patient becomes more hypoxic and hypercarbic with lowering of the pH. This causes increasing pulmonary and decreasing systemic vascular resistances which contribute to the promotion of decreased pulmonary blood flow. This cycle can be broken only by increasing the amount of blood flow to the lungs. This is accomplished by decreasing oxygen demands through sedation, and by augmenting blood flow to the lungs by increasing systemic venous return using the "knee-chest position." It has been suggested that "infundibular spasm" is the initiator of spells. 22 Although this concept might be attractive, this does not answer the question as to why spells may occur with pulmonary atresia. Spells occur most frequently in infants and occur less frequently in older children.
LABORATORY STUDIES Electrocardiogram The electrocardiogram is not specific for tetralogy of Fallot. There is right-axis deviation and right ventricular hypertrophy such as is seen in many other forms of congenital heart disease. On occasion there may be right atrial enlargement. In patients with large bronchial circulation
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Figure 1. AP radiograph depicting an uptilted apex, diminished MPA prominence, and a right aortic arch.
or patients who have had an aorta to pulmonary anastomosis created to palliate cyanosis, there may be associated left atrial enlargement and left ventricular hypertrophy.23 Chest Radiograph The classic chest radiograph shows a "boot-shaped" heart. This results from right ventricular hypertrophy and a decreased main pulmonary artery segment. A right aortic arch may be noted on radiographs and, as previously stated, has a high association with tetralogy of Fallot (Fig. 1). In patients with significantly decreased blood flow, pulmonary vascular markings are decreased as well. Echocardiography In a patient with suspected congenital heart disease, echocardiography is a very important screening tool as well as a definitive diagnostic modality. As seen in Figure 2, typical findings of tetralogy of Fallot can be documented by echocardiogram, including large ventricular septal defect, overriding aorta, and ventricular hypertrophy. The status of the pulmonary valve and pulmonary arteries can also be determined. Other forms of congenital heart disease with similar features need to be distinguished from tetralogy, including persistent truncus arteriosus and double outlet right ventricle. Doppler recordings identify the direction of shunting through the ventricular septal defect, as well as the turbulence through the right ventricular outflow tract. Gradient estimation can be performed. Left-to-right shunt to the pulmonary circulation via a ductus, aorta-to-pulmonary anastomosis, or collateral blood vessels can also be identified.
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4
;, Figure 2. A, Long-axis view demonstrating overriding aorta and large VSD. B, Short-axis view with hypertrophy of the LV and RV.
Cardiac Catheterization Physiologic measurements will determine the direction and amount of shunting, as well as the pressure gradient from the right ventricles to the pulmonary circulation. Young patients who are cyanotic with tetralogy of Fallot generally will have some degree ofleft-toright shunting, however, with a net right-to-Ieft shunt. Pressures demonstrate the amount of gradient from the right ventricle to the pulmonary arteries. Angiography gives definitive information as to the location and number of the ventricular septal defects, the degree and location of the right ventricular outflow tract obstruction, and any collateral circulation to the lungs. Associated defects such as atrial septal defect and anomalies of venous and systemic return also can be identified. Figure 3 demonstrates the spectrum of size of pulmonary arteries seen in tetralogy of Fallot. The best views to determine pulmonary artery anatomy are cranial RAO and LAO views. 24 The LAO cranial view also allows optimal visualization of the size and site of the VSD. The lateral view gives more information about infundibular involvement. It is important to identify coronary artery anatomy so that any anomalies of the course of the left coronary artery will be discovered. MANAGEMENT OF PATIENTS Newborns Newborns who are cyanotic with tetralogy of Fallot generally have severe obstruction of right ventricular outflow as well as small pulmonary arteries. These patients should be started on a prostaglandin El infusion to stabilize them for further diagnosis. After the diagnosis
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Figure 3. Cranial LAO views: A, Relatively large pulmonary arteries with moderate right-to-left shunting, with significant infundibular obstruction. B, Normal pulmonary arteries with minimal right to left shunting. PV is thickened and domes. C, Large amount of right-to-left shunting with severe hypoplasia of pulmonary arteries and outflow tract.
is established by echocardiography, it is our practice to proceed with cardiac catheterization to identify collateral vessels and pulmonary and coronary artery anatomy. At the time of initial cardiac catheterization, as much detailed anatomy is identified as possible so that any subsequent studies will be directed to document any change in anatomy secondary to palliation. Infants who are not cyanotic and are identified as having tetralogy of Fallot by echocardiography are not catheterized on an emergency basis. The parents are cautioned about signs and symptoms of hypercyanotic episodes. These patients are electively catheterized sometime between 3 and 6 months of age to determine the details of their anatomy.
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SURGICAL APPROACH Infants with classic tetralogy of Fallot and favorable anatomy should undergo primary complete intracardiac repair early after the onset of symptoms. Patients with hypoplastic pulmonary arteries, multiple ventricular septal defects or associated coronary artery anomalies are best treated initially by a systemic-pulmonary artery shunt, followed by elective complete repair at 18 to 24 months of age. 25- 28 Palliation by Shunt The classic Blalock-Taussig (BT) shunt29 provides excellent initial palliation and remains the shunt of choice in our service. It can be performed successfully in most patients regardless of early age or small size. Exceptions include the occasional infant with a retroesophageal subclavian artery (which results in an unfavorable anastomotic angle) and patients with a right aortic arch with mirror-image branching and origin of the ductus arteriosus from the bifurcation of the left innominate artery (in whom the left subclavian artery is frequently small during infancy). The BT shunt carries a very low postoperative morbidity and mortality (1 per cent), only 2 patients having died among 158 of those with tetralogy of Fallot who underwent a preliminary BT shunt in our unit. It also has a high probability of early and late patency without complicating or compromising the subsequent intracardiac repair and late hemodynamic result. The Waterston shunt30 also can be constructed with a similarly low mortality. It may be associated with a higher probability of early pulmonary edema, early and late congestive heart failure, pulmonary artery hypertension, and varying degrees of obstruction of the right pulmonary artery. Additionally, it adds technical difficulty to and often compromises the excellence of the late postoperative result. A modified subclavian artery-pulmonary artery shunt31 using a 5-mm segment of polytetrafluoroethylene tube offers an excellent alternative to the Waterston shunt for those patients in whom a classic Blalock-Taussig anatomosis cannot be constructed adequately. Patching the right ventricular outflow tract without closure of the ventricular septal defect also has been recommended as a palliative operation32 in patients with hypoplastic pulmonary arteries. This may improve systemic oxygen saturation and promote pulmonary artery growth. However, a higher early operative mortality (12 per cent) and the frequent development of late pulmonary artery stenosis at the end of the patch makes this procedure less appealing than the conventional systemic-pulmonary artery shunts. The Potts anastomosis 33 seldom is used today because it frequently leads to pulmonary vascular obstructive disease, in addition to the added technical difficulty of its take down at the time of intracardiac repair. Total Repair Early primary repair of tetralogy of Fallot in infants and young children formerly carried a significant risk of early postoperative
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deaths. However, more recent refinements in surgical technique, extracorporeal perfusion methods, and perioperative care have resulted in lower postoperative death rates in all patient groupS.25-28,34 The objectives of intracardiac repair are to completely and permanently close the ventricular septal defect, to relieve the right ventricular outflow tract obstruction, to interrupt pre-existing shunts, and to correct any associated cardiac defects.
OPERATIVE TECHNIQUE The heart is exposed through a midsternotomy.34 The coronary artery anatomy is noted. Pre-existing shunts are dissected out. Standard cardiopulmonary bypass is established by direct aortic cannulation and insertion of caval cannulae through the right atrium. Hemodilution (hematocrit: 25 per cent) and moderate systemic hypothermia (25°C esophageal) are routinely used. The left ventricle is vented through the left atrium from the right pulmonary veins. The aorta is cross-clamped to obtain a quiet, bloodless field, and ischemic myocardial injury is minimized by multidose injection of a crystalloid or oxygenated blood cardioplegic solution, immersing the heart in ice slush, and reducing the pump flow. The myocardial temperature is measured continuously during the period of aortic cross-clamping, and is kept below 18°C. Deep hypothermic arrest may be employed to facilitate extensive reconstruction of the right and left pulmonary arteries when bronchopulmonary blood flow is abundant. Previous palliative shunts are interrupted or dismantled. The right ventricle is opened vertically through an avascular area, but in the presence of a large conal coronary artery branch, a transverse incision or trans atrial approach is used. Recently, to maximally preserve early and late right ventricular function, the trans atrial approach for relief of the right ventricular outflow tract obstruction has been advocated. 35- 37 The obstructing parietal and septal bands are resected, with care taken to avoid injury to the aortic valve, perforating the interventricular septum, injuring the papillary muscles of the tricuspid valve, or ,excessively thinning out the right ventricular free wall. The VSD is closed with a prosthetic patch which may be anchored either with interrupted horizontal mattress sutures buttressed with small Teflon pledgets or with a continuous suture. In the posteroinferior margin of the defect the stitches are placed to the right and below its edge to minimize the possibility of injury to the conduction system. The remainder of the ventricular septum is inspected for additional defects and, if any are found, they are closed with prosthetic patches to minimize the possibility of dehiscence. The atrial septum is inspected routinely through the tricuspid valve, and small defects are closed easily through this approach. Larger defects require closure through a separate right atriotomy. The pulmonary valve is exposed through the right ventriculotomy
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and, if stenotic, a commissurotomy is performed from below or through a separate incision in the pulmonary artery. The pulmonary valve annulus is sized with Hegar dilators; when it is small, the ventriculotomy is extended across the valve ring into the pulmonary artery and trans annular patch, and either pericardium or Dacron is inserted. It is likely that the type of patch used is less important in the prevention of aneurysm formation than avoidance of residual outflow tract obstruction or intracardiac shunt. The need for transannular patching is based on a comparison of the patient's annular size with sizes listed in tables prepared by Pacifico et a1. 38 It is directed at avoiding significant residual obstruction with a postrepair right ventricular to left ventricular pressure ratio greater than 0.65. A high ratio increases the probability of low cardiac output and early postoperative death. When the right ventricular outflow tract cannot be relieved adequately by resection and valvulotomy, or if an anomalous left anterior descending coronary artery is present, it is necessary to insert a right ventricular-pulmonary artery conduit. If the distal pulmonary arteries are of adequate size the conduit may be valveless. If they are not of optimal caliber, then a valved pulmonary artery homograft is used. When a transannular patch is used, no effort is routinely made to restore pulmonary vascular competence. However, insertion of a valved homograft is recommended in patients with moderate hypoplasia of the pulmonary arteries, in congenital absence of the left pulmonary artery, and sometimes in congenital absence of the pulmonary valve since preservation of pulmonary valve function in these patients may result in improved early postoperative survival and better late hemodynamic performance. In the presence of stenosis of the origin of the left pulmonary artery, the transannular patch is extended well beyond the narrowed area. Stenosis of the right pulmonary artery, whether congenital or shunt related, requires a separate patch. This can be either pericardial or prosthetic and can be inserted without transection of the ascending aorta. On discontinuation of cardiopulmonary bypass and after hemodynamic stabilization has been achieved, the intracardiac pressures are measured. When indicated, bypass is resumed to relieve any remaining significant obstruction. Measurement of systemic, right atrial, and pulmonary artery oxygen saturation also may be performed to detect the presence of any residual left to right shunt. A small plastic catheter is left in the right and left atria for pressure monitoring, and a thermister probe is placed in the pulmonary artery through the right ventricular infundibulum for postoperative determination of cardiac output. Myocardial pacing wires are inserted prophylactically in all patients.
POSTOPERATIVE RESULTS Currently, the overall 30-day "hospital mortality" after complete repair of tetralogy of Fallot is approximately 3 to 5 per cent. There were 16 early postoperative deaths among 467 patients (3.4 per cent) who
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have undergone intracardiac repair since 1971 at Children's Hospital of Michigan. Similar results have been reported by other groups.27, 39, 40 Although the adverse influence of young age on early postoperative survival currently appears to be a decreasing risk factor,26,28 a somewhat higher postoperative death rate may be anticipated in patients below 6 months, especially among those under the age of 3 months. 27 Surgically induced complete heart block now occurs in less than 1 per cent of patients of all ages because of increased awareness of the location of the conduction system. Similarly, the incidence of residual or recurrent VSD is currently less than 4 per cent. lO
LATE POSTOPERATIVE RESULTS The majority of patients (87 per cent) surviving total correction of tetralogy of Fallot have an excellent late clinical and hemodynamic result without functional disability, need for cardiac medication, or significant residual intracardiac defects. Fair and poor results (5 and 7 per cent, respectively) are related to the presence of residual right ventricular outflow tract obstruction, VSD, ventricular arrhythmias, and late development of conduction disturbances. 39, 40 Residual right ventricular outflow tract obstruction is most commonly due to inadequately relieved stenosis at the origin of one or both main pulmonary artery branches. This obstruction tends to be progressive, is associated with significant persistent cardiomegaly, and is probably (as is significant residual VSD) an important etiologic factor in the development of outflow tract patch aneurysms. Late residual stenosis at the pulmonary valve annulus is rare and tends to decrease with time in patients who are managed by trans annular patching. This is in contrast to the tendency for significant residual stenosis to worsen in patients treated by infundibulectomy and valvulotomy alone. 39 Pulmonary valvular insufficiency generally is well tolerated in the absence of distal pulmonary artery obstruction or pulmonary vascular obstructive disease. Although it may be associated with a somewhat higher incidence of persistent cardiomegaly, it causes cardiac disability in less than 1 per cent of patients. 39, 40 Consequently, routine insertion of a homograft valve, bioprosthesis, or a monocusp at the initial operation in patients receiving a transannular patch probably is not justified. Exercise-induced ventricular ectopy, which has been demonstrated in approximately 25 per cent of postoperative patients, and late complete heart block, which develops in approximately 1 per cent of patients, probably account for the majority of the sudden unexplained deaths (3 per cent) occurring during the late postoperative period.4l Complete right bundle branch block is present postoperatively in the majority of patients and is associated with left anterior hemiblock in 3 to 7 per cent of cases. 40, 41 This type of bifascicular block has been considered by some 42 to result in late complete heart block and sudden
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death. However, it seems that the combination of right bundle branch block and left anterior hemiblock may carry an unfavorable prognosis only in patients with temporary intraoperative complete heart block, in whom the latter indicates more extensive and important surgical injury to the conduction system. 43 Postoperative cardiomegaly (cardiothoracic ratio;::: 0.55) is present in approximately 25 per cent of patients and is more common in those who are symptomatic or have a poor result. 41 The mean cardiothoracic ratio tends to be somewhat higher in patients who received a transannular patch than in those treated by infundibulectomyalone. In patients with a residual defect44 ,45 and in those operated on after early childhood,46 late hemodynamic evaluation has demonstrated abnormalities of right ventricular volume and function as well as reduced cardiac performance during exercise. Cardiac catheterization studies also have documented the frequent occurrence of residual abnormalities in clinically asymptomatic patients. 47
BE-OPERATIONS Re-operation is required during the late postoperative period for residual intracardiac abnormalities in 4 per cent of patients and usually can be performed with a surgical risk no greater than that from the original operation. 48,49 Residual or recurrent VSD with a pulmonarysystemic flow ratio greater than 1.5 generally is tolerated poorly, is associated with congestive heart failure, and requires surgical closure. Residual right ventricular outflow tract obstruction with a systolic pressure above 60 mm Hg should be surgically corrected by transannular patching when located at the infundibulum or at the annulus, or by extensive angioplasty when located at the origin of the main pulmonary artery branches. Isolated pulmonary valvular insufficiency requires insertion of a pulmonary valve when associated with persistent cardiomegaly, poor ventricular function, exercise intolerance, or persistent right-sided heart failure. True aneurysm of the outflow patch occurs in less than 3 per cent of patients. 34 , 40 It develops only when unreinforced pericardium is used and when the patch is large. It should be resected to prevent rupture and to prevent recurrent pulmonary embolization from the frequently associated mural thrombus. False aneurysms are rare and occur mainly after the use of prosthetic outflow patches. False aneurysms constitute a more serious problem when they occur at the ventricular suture lines. They are secondary to residual obstruction and excessive surgical thinning of the infundibular myocardium or infection. Re-operation also is needed occasionally to repair or replace an incompetent tricuspid valve, to insert a permanent pacemaker in a patient with late development of complete heart block, or to obliterate an incompletely closed systemic-pulmonary artery shunt.
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27. Kirklin JW, Blackstone EH, Colvin EV, et al: Early primary correction of tetralogy of Fallot. Ann Thorac Surg 45:231, 1988 28. Gustafson RA, Murray GF, Warden HE, et al: Early primary repair of tetralogy of Fallot. Ann Thorac Surg 45:235, 1988 29. Blalock A, Taussig HB: The surgical treatment of malformation of the heart in which there is pulmonary stenosis or pulmonary atresia. JAMA 128:189, 1945 30. Waterston DJ: Treatment of Fallot's tetralogy in children under one year of age. Rozh Chir 41:181, 1962 31. McKay R, DeLeval MR, Rees P, et al: Post-operative angiographic assessment of modified Blalock-Taussig shunts using expanded polytetrafluoroethylene (GoreTex). Ann Thorac Surg 30:137,1980 32. Tucker WY, Turley K, Ullyot DJ, et al: Management of symptomatic tetralogy of Fallot in the first year of life. J Thorac Cardiovasc Surg 78:494, 1979 33. Potts WJ, Smith S, Gibson S: Anastomosis of the aorta to a pulmonary artery. JAMA 132:627, 1946 34. Arciniegas E: Tetralogy of Fallot. In Arciniegas E (ed): Pediatric Cardiac Surgery. Chicago, Year Book Medical, 1985, pp 208-215 35. Pacifico AD, Sand ME, Margeron LM Jr, et al: Transatrial-transpulmonary repair of tetralogy of Fallot. J Thorac Cardiovasc Surg 93:919, 1987 36. Binet JP: Correction of tetralogy of Fallot with combined transatrial and pulmonary approach. Surg Rounds 9:33, 1986 37. McGrath LB, Gonzalez-Lavin L: Determination of the need for a ventriculotomy in the repair of tetralogy of Fallot. J Thorac Cardiovasc Surg 96:947, 1988 38. Pacifico AD, Kirklin JW, Blackstone EH: Surgical management of pulmonary stenosis in tetralogy of Fallot. J Thorac Cardiovasc Surg 74:382, 1977 39. Poirier RA, McGoon DC, Danielson GE, et al: Late results after repair of tetralogy of Fallot. J Thorac Cardiovasc Surg 73:900, 1977 40. Arciniegas E, Farooki ZQ, Hakimi M, et al: Early and late results of total correction of tetralogy of Fallot. J Thorac Cardiovasc Surg 80:770, 1980 41. Fuster V, McGoon DC, Kennedy MA, et al: Long-term evaluation (12-22 years) of open heart surgery for tetralogy of Fallot. Am J CardioI46:635, 1980 42. WolffGS, Towland TW, Ellison RC: Surgically induced right bundle branch block with left anterior hemiblock: An ominous sign in post-operative tetralogy ofFallot. Circulation 46:587, 1972 43. Godman MJ, Roberts NK, Izukawa T: His bundle analysis of conduction disturbances following repair of ventricular septal defect and tetralogy of Fallot. Circulation 46 (suppl II):37, 1972 44. Wessel HU, Cunningham WJ, Paul MH, et al: Exercise performance in tetralogy of Fallot after intracardiac repair. J Thorac Cardiovasc Surg 80:582:1980 45. Graham TP Jr, Cordell D, Atwood GF, et al: Right ventricular volume characteristics before and after palliative and reparative operation in tetralogy of Fallot. Circulation 54:417, 1976 46. Rocchini AP: Hemodynamic abnormalities in response to supine exercise in patients after operative correction of tetralogy of Fallot after early childhood. Am J Cardiol 48:325, 1981 47. Joransen JA, Lucas RV Jr, Moller JH: Post-operative hemodynamics in tetralogy of Fallot: A study of 132 children. Br Heart J 41:33, 1979 48. Castaneda AR, Sade RM, Lamberti J, et al: Re-operation for residual defects after repair of tetralogy of Fallot. Surgery 76: 10 10, 1974 49. Miller DC, Rossiter SJ, Stinson EB, et al: Late right heart reconstruction following repair of tetralogy of Fallot. Ann Thorac Surg 28:239, 1979 Department of Cardiology Children's Hospital of Michigan 3901 Beaubien Street Detroit, MI 48201
0031-3955/90 $0.00 + .20
Tetralogy of Fallot
William W. Pinsky, MD,* and Eduardo Arciniegas, MDt
Although tetralogy of Fallot is well known by name to those involved in pediatric medicine, it is not necessarily well known by its detailed anatomy and physiology. It will be the purpose of this article to highlight those aspects of tetralogy of Fallot to allow those involved in the care of children to have an up-to-date understanding of this entity.
HISTORICAL PERSPECTIVE AND INCIDENCE Although this syndrome carries the name of Dr. Fallot, the first description of this constellation of anatomic defects initially was described by Stensen in 1671. 1 Sandifort in 17772 described some of the clinical manifestations that we now consider part of this syndrome; in 1784 Hunter3 expanded on these. It was Fallot's publication in 18884 that correlated the previously described clinical findings and attached his name to the syndrome with the now well-known tetrad of right ventricular outflow tract obstruction, dextroposition and overriding of the aorta, ventricular septal defect, and hypertrophy of the right ventricle. As a single entity, tetralogy of Fallot is the most common malformation of children born with cyanotic heart disease, with an incidence of approximately 10 per cent of congenital heart disease. 5 There is no known definite genetic/environmental pattern giving rise to tetralogy of Fallot. However, it has been described in various syndromes and associated with various teratogens such as thrombocytopenia and absent radius, APERTs, DiGeorge's, trimethadione, sex hormones, tha-
From the Children's Hospital of Michigan, Wayne State University School of Medicine, Detroit, Michigan
* Professor
of Pediatrics and Vice Chairman, Department of Pediatrics; and Chief, Division of Pediatric Cardiology t Clinical Professor of Surgery and Chief, Pediatric Cardiovascular Surgery Pediatric Clinics of North America-Vol. 37, No.1, February 1990
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lidomide, and phenylketonuria. 6 Risk within a family ranges from 2.5 per cent with an affected sibling, to 4 per cent with an affected parent. 7
ANATOMIC PATHOLOGY Although there can be a wide spectrum as to the severity of the anatomic defects, there is the association of a ventricular septal defect (VSD), aortic override, right ventricular outHow tract obstruction, and right ventricular hypertrophy.8 This can range from mild right ventricular outHow tract obstruction to complete atresia of the pulmonary valve and hypoplasia of the pulmonary arteries. Aortic override can be minimal or as much as 75 per cent. 9 Although the ventricular septal defect is generally large and nonrestrictive, there have been reports of restrictive ventricular septal defects.lO For the purpose of discussion, we will not inc! ude patients with complete atresia of the right ventricu1ar outHow tract. The degree of obstruction to blood How through the right ventricular outHow tract is considered to be the determining factor of the degree and type of dysfunction exhibited by patients. It is universally accepted that patients will have at least some minor abnormality of the pulmonary valve, although the valve orifice usually is at least the same size or larger than the smallest diameter of the infundibular opening. 11 The valves, therefore, may have abnormalities in terms of the number of cusps or the degree of stenosis. l l The infundibulum is rotated cephalad and this position is instrumental in developing obstruction at this level. 12 The normally nonprominent crista supraventricularis is displaced and hypertrophied, infringing on the outHow tract both in systole and diastole. The parietal band is displaced superiorly and more towards the septum obstructing blood How during ejection. Distal to the crista may be a more normal outHow tract that is generally described as the "infundibular chamber." It is thought that the ventricular septal defect in tetralogy of Fallot is perimembranous. In a review of 53 specimens, Anderson found three different types of defects. 12 In 41 specimens, the defect extended cephalad and anteriorly and was limited by the infundibular septum. Caudally the defects were limited by aspects of the trabecular septa marginalis. These perimembranous defects were in association with the malalignment of the trabecular and infundibular muscular components of the ventricular septum. Eleven specimens contained defects that had a complete muscular rim. The remaining defect was categorized as subarterial as it was roofed over by the aortic and pulmonary valve rings. Anderson described this as being a "doubly committed subarterial defect with absence of the infundibular septum." The aortic override can range from a small degree to 75 per cent. This occurs by an abnormal anterior extension of the aortic root relative to the ventricular septum, resulting from maldevelopment of the conal region. 13 There may be coronary artery anomalies associated with tetralogy of Fallot. These anomalies generally have no functional significance
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but they have a great deal of significance to the surgeon repairing the defect.14 It is believed that 2 to 9 per cent of patients will have the most common anomaly, which is origin of the left anterior descending coronary artery arising from the right coronary artery. 15, 16 This means that the anomalous artery will cross the right ventricular outflow tract in the area where a ventriculotomy incision frequently is made during repair of tetralogy of Fallot. Other abnormalities are found in tetralogy including the presence of a single right coronary artery that gives off a left branch that goes anterior to the pulmonary trunk, and a left coronary artery that originates normally and then crosses anteriorly between the aorta and pulmonary arteries and then laterally across the pulmonary trunk. In almost all cases with tetralogy of Fallot, the infundibular branch of the right coronary artery is very prominentY . Twenty-five p,er cent of patients with tetralogy of Fallot have a right aortic arch. 1 This may occur in association with anomalous origin of the left subclavian artery arising from the distal aorta. 19 It is important to note the situs of the arch as well as the origin of the arch vessels when planning operative palliation of these patients.
PHYSIOLOGY The consequence of the large ventricular septal defect, overriding aorta, and right ventricular outflow tract obstruction is generally that of a right-to-Ieft shunt. Based on the degree of override and right ventricular outflow tract obstruction, right-to-Ieft shunting may vary from mild to severe. Consequences to the myocardium are that the right ventricle hypertrophies secondary to contraction against the fixed obstruction at the outflow tract, as well as pumping blood through the ventricular septal defect against systemic resistance. Iflarge collateral vessels are present, then the left ventricle may enlarge and hypertrophy. Longstanding hypertrophy will result in some degree of diastolic stiffness in the right ventricle, although it is thought not to be clinically significant in most circumstances. With prolonged arterial desaturation, polycythemia will develop. The increased viscosity secondary to polycythemia will increase effective pulmonary and systemic resistance causing more strain on the respective ventricles. 20
CARDIAC EXAMINATION Patients with tetralogy of Fallot have an active precordium. The point of maximal impulse will generally be the right ventricle with the left ventricle being the apical impulse. Generally there are no thrills felt. The first heart sound is normal; the second heart sound is single and increased in intensity representing the sound of the anteriorly located aortic closure. The murmur is that of obstruction to the right ventricular outflow tract. It is a harsh systolic ejection murmur heard
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maximally over the pulmonary area. The murmur radiates across the chest anteriorly and to both sides of the back. Even with some left-toright shunting, the murmur of the ventricular septal defect is overshadowed by the right ventricular outflow tract obstruction murmur.
CLINICAL MANIFESTATION Newborns may present with cyanosis and murmur or just a loud murmur. Any young infant with a harsh systolic ejection murmur that radiates to both sides of the back with a single second heart sound should be suspected of having tetralogy of Fallot. Most infants with cyanosis, other than those with pulmonary valve atresia, will be diagnosed outside of the newborn period. These infants may be mildly cyanotic at rest or noted to have cyanosis with crying or feeding. Growth patterns in the first few months oflife are normal. Occasionally an older infant will present with tetralogy of Fallot. These are infants that have a net left-to-right shunt and are referred to as having "pink" tetralogy of Fallot. As they become older and develop more infundibular narrowing, these patients will demonstrate cyanosis at rest or be prone to hypercyanotic episodes. Hypercyanotic episodes occur most frequently at a time when systemic vascular resistance is at its lowest. For young infants, these times are soon after awakening or after feeding. 21 Crying and defecating also may precipitate the events. 21 Increased rate and depth of respiration (hyperpnea) are the hallmarks of the initiation of a spell. As the pulmonary blood flow decreases, the patient becomes more hypoxic and hypercarbic with lowering of the pH. This causes increasing pulmonary and decreasing systemic vascular resistances which contribute to the promotion of decreased pulmonary blood flow. This cycle can be broken only by increasing the amount of blood flow to the lungs. This is accomplished by decreasing oxygen demands through sedation, and by augmenting blood flow to the lungs by increasing systemic venous return using the "knee-chest position." It has been suggested that "infundibular spasm" is the initiator of spells. 22 Although this concept might be attractive, this does not answer the question as to why spells may occur with pulmonary atresia. Spells occur most frequently in infants and occur less frequently in older children.
LABORATORY STUDIES Electrocardiogram The electrocardiogram is not specific for tetralogy of Fallot. There is right-axis deviation and right ventricular hypertrophy such as is seen in many other forms of congenital heart disease. On occasion there may be right atrial enlargement. In patients with large bronchial circulation
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Figure 1. AP radiograph depicting an uptilted apex, diminished MPA prominence, and a right aortic arch.
or patients who have had an aorta to pulmonary anastomosis created to palliate cyanosis, there may be associated left atrial enlargement and left ventricular hypertrophy.23 Chest Radiograph The classic chest radiograph shows a "boot-shaped" heart. This results from right ventricular hypertrophy and a decreased main pulmonary artery segment. A right aortic arch may be noted on radiographs and, as previously stated, has a high association with tetralogy of Fallot (Fig. 1). In patients with significantly decreased blood flow, pulmonary vascular markings are decreased as well. Echocardiography In a patient with suspected congenital heart disease, echocardiography is a very important screening tool as well as a definitive diagnostic modality. As seen in Figure 2, typical findings of tetralogy of Fallot can be documented by echocardiogram, including large ventricular septal defect, overriding aorta, and ventricular hypertrophy. The status of the pulmonary valve and pulmonary arteries can also be determined. Other forms of congenital heart disease with similar features need to be distinguished from tetralogy, including persistent truncus arteriosus and double outlet right ventricle. Doppler recordings identify the direction of shunting through the ventricular septal defect, as well as the turbulence through the right ventricular outflow tract. Gradient estimation can be performed. Left-to-right shunt to the pulmonary circulation via a ductus, aorta-to-pulmonary anastomosis, or collateral blood vessels can also be identified.
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4
;, Figure 2. A, Long-axis view demonstrating overriding aorta and large VSD. B, Short-axis view with hypertrophy of the LV and RV.
Cardiac Catheterization Physiologic measurements will determine the direction and amount of shunting, as well as the pressure gradient from the right ventricles to the pulmonary circulation. Young patients who are cyanotic with tetralogy of Fallot generally will have some degree ofleft-toright shunting, however, with a net right-to-Ieft shunt. Pressures demonstrate the amount of gradient from the right ventricle to the pulmonary arteries. Angiography gives definitive information as to the location and number of the ventricular septal defects, the degree and location of the right ventricular outflow tract obstruction, and any collateral circulation to the lungs. Associated defects such as atrial septal defect and anomalies of venous and systemic return also can be identified. Figure 3 demonstrates the spectrum of size of pulmonary arteries seen in tetralogy of Fallot. The best views to determine pulmonary artery anatomy are cranial RAO and LAO views. 24 The LAO cranial view also allows optimal visualization of the size and site of the VSD. The lateral view gives more information about infundibular involvement. It is important to identify coronary artery anatomy so that any anomalies of the course of the left coronary artery will be discovered. MANAGEMENT OF PATIENTS Newborns Newborns who are cyanotic with tetralogy of Fallot generally have severe obstruction of right ventricular outflow as well as small pulmonary arteries. These patients should be started on a prostaglandin El infusion to stabilize them for further diagnosis. After the diagnosis
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Figure 3. Cranial LAO views: A, Relatively large pulmonary arteries with moderate right-to-left shunting, with significant infundibular obstruction. B, Normal pulmonary arteries with minimal right to left shunting. PV is thickened and domes. C, Large amount of right-to-left shunting with severe hypoplasia of pulmonary arteries and outflow tract.
is established by echocardiography, it is our practice to proceed with cardiac catheterization to identify collateral vessels and pulmonary and coronary artery anatomy. At the time of initial cardiac catheterization, as much detailed anatomy is identified as possible so that any subsequent studies will be directed to document any change in anatomy secondary to palliation. Infants who are not cyanotic and are identified as having tetralogy of Fallot by echocardiography are not catheterized on an emergency basis. The parents are cautioned about signs and symptoms of hypercyanotic episodes. These patients are electively catheterized sometime between 3 and 6 months of age to determine the details of their anatomy.
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SURGICAL APPROACH Infants with classic tetralogy of Fallot and favorable anatomy should undergo primary complete intracardiac repair early after the onset of symptoms. Patients with hypoplastic pulmonary arteries, multiple ventricular septal defects or associated coronary artery anomalies are best treated initially by a systemic-pulmonary artery shunt, followed by elective complete repair at 18 to 24 months of age. 25- 28 Palliation by Shunt The classic Blalock-Taussig (BT) shunt29 provides excellent initial palliation and remains the shunt of choice in our service. It can be performed successfully in most patients regardless of early age or small size. Exceptions include the occasional infant with a retroesophageal subclavian artery (which results in an unfavorable anastomotic angle) and patients with a right aortic arch with mirror-image branching and origin of the ductus arteriosus from the bifurcation of the left innominate artery (in whom the left subclavian artery is frequently small during infancy). The BT shunt carries a very low postoperative morbidity and mortality (1 per cent), only 2 patients having died among 158 of those with tetralogy of Fallot who underwent a preliminary BT shunt in our unit. It also has a high probability of early and late patency without complicating or compromising the subsequent intracardiac repair and late hemodynamic result. The Waterston shunt30 also can be constructed with a similarly low mortality. It may be associated with a higher probability of early pulmonary edema, early and late congestive heart failure, pulmonary artery hypertension, and varying degrees of obstruction of the right pulmonary artery. Additionally, it adds technical difficulty to and often compromises the excellence of the late postoperative result. A modified subclavian artery-pulmonary artery shunt31 using a 5-mm segment of polytetrafluoroethylene tube offers an excellent alternative to the Waterston shunt for those patients in whom a classic Blalock-Taussig anatomosis cannot be constructed adequately. Patching the right ventricular outflow tract without closure of the ventricular septal defect also has been recommended as a palliative operation32 in patients with hypoplastic pulmonary arteries. This may improve systemic oxygen saturation and promote pulmonary artery growth. However, a higher early operative mortality (12 per cent) and the frequent development of late pulmonary artery stenosis at the end of the patch makes this procedure less appealing than the conventional systemic-pulmonary artery shunts. The Potts anastomosis 33 seldom is used today because it frequently leads to pulmonary vascular obstructive disease, in addition to the added technical difficulty of its take down at the time of intracardiac repair. Total Repair Early primary repair of tetralogy of Fallot in infants and young children formerly carried a significant risk of early postoperative
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deaths. However, more recent refinements in surgical technique, extracorporeal perfusion methods, and perioperative care have resulted in lower postoperative death rates in all patient groupS.25-28,34 The objectives of intracardiac repair are to completely and permanently close the ventricular septal defect, to relieve the right ventricular outflow tract obstruction, to interrupt pre-existing shunts, and to correct any associated cardiac defects.
OPERATIVE TECHNIQUE The heart is exposed through a midsternotomy.34 The coronary artery anatomy is noted. Pre-existing shunts are dissected out. Standard cardiopulmonary bypass is established by direct aortic cannulation and insertion of caval cannulae through the right atrium. Hemodilution (hematocrit: 25 per cent) and moderate systemic hypothermia (25°C esophageal) are routinely used. The left ventricle is vented through the left atrium from the right pulmonary veins. The aorta is cross-clamped to obtain a quiet, bloodless field, and ischemic myocardial injury is minimized by multidose injection of a crystalloid or oxygenated blood cardioplegic solution, immersing the heart in ice slush, and reducing the pump flow. The myocardial temperature is measured continuously during the period of aortic cross-clamping, and is kept below 18°C. Deep hypothermic arrest may be employed to facilitate extensive reconstruction of the right and left pulmonary arteries when bronchopulmonary blood flow is abundant. Previous palliative shunts are interrupted or dismantled. The right ventricle is opened vertically through an avascular area, but in the presence of a large conal coronary artery branch, a transverse incision or trans atrial approach is used. Recently, to maximally preserve early and late right ventricular function, the trans atrial approach for relief of the right ventricular outflow tract obstruction has been advocated. 35- 37 The obstructing parietal and septal bands are resected, with care taken to avoid injury to the aortic valve, perforating the interventricular septum, injuring the papillary muscles of the tricuspid valve, or ,excessively thinning out the right ventricular free wall. The VSD is closed with a prosthetic patch which may be anchored either with interrupted horizontal mattress sutures buttressed with small Teflon pledgets or with a continuous suture. In the posteroinferior margin of the defect the stitches are placed to the right and below its edge to minimize the possibility of injury to the conduction system. The remainder of the ventricular septum is inspected for additional defects and, if any are found, they are closed with prosthetic patches to minimize the possibility of dehiscence. The atrial septum is inspected routinely through the tricuspid valve, and small defects are closed easily through this approach. Larger defects require closure through a separate right atriotomy. The pulmonary valve is exposed through the right ventriculotomy
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and, if stenotic, a commissurotomy is performed from below or through a separate incision in the pulmonary artery. The pulmonary valve annulus is sized with Hegar dilators; when it is small, the ventriculotomy is extended across the valve ring into the pulmonary artery and trans annular patch, and either pericardium or Dacron is inserted. It is likely that the type of patch used is less important in the prevention of aneurysm formation than avoidance of residual outflow tract obstruction or intracardiac shunt. The need for transannular patching is based on a comparison of the patient's annular size with sizes listed in tables prepared by Pacifico et a1. 38 It is directed at avoiding significant residual obstruction with a postrepair right ventricular to left ventricular pressure ratio greater than 0.65. A high ratio increases the probability of low cardiac output and early postoperative death. When the right ventricular outflow tract cannot be relieved adequately by resection and valvulotomy, or if an anomalous left anterior descending coronary artery is present, it is necessary to insert a right ventricular-pulmonary artery conduit. If the distal pulmonary arteries are of adequate size the conduit may be valveless. If they are not of optimal caliber, then a valved pulmonary artery homograft is used. When a transannular patch is used, no effort is routinely made to restore pulmonary vascular competence. However, insertion of a valved homograft is recommended in patients with moderate hypoplasia of the pulmonary arteries, in congenital absence of the left pulmonary artery, and sometimes in congenital absence of the pulmonary valve since preservation of pulmonary valve function in these patients may result in improved early postoperative survival and better late hemodynamic performance. In the presence of stenosis of the origin of the left pulmonary artery, the transannular patch is extended well beyond the narrowed area. Stenosis of the right pulmonary artery, whether congenital or shunt related, requires a separate patch. This can be either pericardial or prosthetic and can be inserted without transection of the ascending aorta. On discontinuation of cardiopulmonary bypass and after hemodynamic stabilization has been achieved, the intracardiac pressures are measured. When indicated, bypass is resumed to relieve any remaining significant obstruction. Measurement of systemic, right atrial, and pulmonary artery oxygen saturation also may be performed to detect the presence of any residual left to right shunt. A small plastic catheter is left in the right and left atria for pressure monitoring, and a thermister probe is placed in the pulmonary artery through the right ventricular infundibulum for postoperative determination of cardiac output. Myocardial pacing wires are inserted prophylactically in all patients.
POSTOPERATIVE RESULTS Currently, the overall 30-day "hospital mortality" after complete repair of tetralogy of Fallot is approximately 3 to 5 per cent. There were 16 early postoperative deaths among 467 patients (3.4 per cent) who
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have undergone intracardiac repair since 1971 at Children's Hospital of Michigan. Similar results have been reported by other groups.27, 39, 40 Although the adverse influence of young age on early postoperative survival currently appears to be a decreasing risk factor,26,28 a somewhat higher postoperative death rate may be anticipated in patients below 6 months, especially among those under the age of 3 months. 27 Surgically induced complete heart block now occurs in less than 1 per cent of patients of all ages because of increased awareness of the location of the conduction system. Similarly, the incidence of residual or recurrent VSD is currently less than 4 per cent. lO
LATE POSTOPERATIVE RESULTS The majority of patients (87 per cent) surviving total correction of tetralogy of Fallot have an excellent late clinical and hemodynamic result without functional disability, need for cardiac medication, or significant residual intracardiac defects. Fair and poor results (5 and 7 per cent, respectively) are related to the presence of residual right ventricular outflow tract obstruction, VSD, ventricular arrhythmias, and late development of conduction disturbances. 39, 40 Residual right ventricular outflow tract obstruction is most commonly due to inadequately relieved stenosis at the origin of one or both main pulmonary artery branches. This obstruction tends to be progressive, is associated with significant persistent cardiomegaly, and is probably (as is significant residual VSD) an important etiologic factor in the development of outflow tract patch aneurysms. Late residual stenosis at the pulmonary valve annulus is rare and tends to decrease with time in patients who are managed by trans annular patching. This is in contrast to the tendency for significant residual stenosis to worsen in patients treated by infundibulectomy and valvulotomy alone. 39 Pulmonary valvular insufficiency generally is well tolerated in the absence of distal pulmonary artery obstruction or pulmonary vascular obstructive disease. Although it may be associated with a somewhat higher incidence of persistent cardiomegaly, it causes cardiac disability in less than 1 per cent of patients. 39, 40 Consequently, routine insertion of a homograft valve, bioprosthesis, or a monocusp at the initial operation in patients receiving a transannular patch probably is not justified. Exercise-induced ventricular ectopy, which has been demonstrated in approximately 25 per cent of postoperative patients, and late complete heart block, which develops in approximately 1 per cent of patients, probably account for the majority of the sudden unexplained deaths (3 per cent) occurring during the late postoperative period.4l Complete right bundle branch block is present postoperatively in the majority of patients and is associated with left anterior hemiblock in 3 to 7 per cent of cases. 40, 41 This type of bifascicular block has been considered by some 42 to result in late complete heart block and sudden
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death. However, it seems that the combination of right bundle branch block and left anterior hemiblock may carry an unfavorable prognosis only in patients with temporary intraoperative complete heart block, in whom the latter indicates more extensive and important surgical injury to the conduction system. 43 Postoperative cardiomegaly (cardiothoracic ratio;::: 0.55) is present in approximately 25 per cent of patients and is more common in those who are symptomatic or have a poor result. 41 The mean cardiothoracic ratio tends to be somewhat higher in patients who received a transannular patch than in those treated by infundibulectomyalone. In patients with a residual defect44 ,45 and in those operated on after early childhood,46 late hemodynamic evaluation has demonstrated abnormalities of right ventricular volume and function as well as reduced cardiac performance during exercise. Cardiac catheterization studies also have documented the frequent occurrence of residual abnormalities in clinically asymptomatic patients. 47
BE-OPERATIONS Re-operation is required during the late postoperative period for residual intracardiac abnormalities in 4 per cent of patients and usually can be performed with a surgical risk no greater than that from the original operation. 48,49 Residual or recurrent VSD with a pulmonarysystemic flow ratio greater than 1.5 generally is tolerated poorly, is associated with congestive heart failure, and requires surgical closure. Residual right ventricular outflow tract obstruction with a systolic pressure above 60 mm Hg should be surgically corrected by transannular patching when located at the infundibulum or at the annulus, or by extensive angioplasty when located at the origin of the main pulmonary artery branches. Isolated pulmonary valvular insufficiency requires insertion of a pulmonary valve when associated with persistent cardiomegaly, poor ventricular function, exercise intolerance, or persistent right-sided heart failure. True aneurysm of the outflow patch occurs in less than 3 per cent of patients. 34 , 40 It develops only when unreinforced pericardium is used and when the patch is large. It should be resected to prevent rupture and to prevent recurrent pulmonary embolization from the frequently associated mural thrombus. False aneurysms are rare and occur mainly after the use of prosthetic outflow patches. False aneurysms constitute a more serious problem when they occur at the ventricular suture lines. They are secondary to residual obstruction and excessive surgical thinning of the infundibular myocardium or infection. Re-operation also is needed occasionally to repair or replace an incompetent tricuspid valve, to insert a permanent pacemaker in a patient with late development of complete heart block, or to obliterate an incompletely closed systemic-pulmonary artery shunt.
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