Tetralogy of Fallot and Pulmonary Stenosis

Morphology

In 1988 Fallot published the morphological findings of the hearts in patients presenting with ‘la maladie bleue’. He identified a relatively constant set of four
features, these being of an interventricular communication, subpulmonary muscular obstruction, a biventricular connection of the aortic valve, and concentric right ventricular hypertrophy. Two key points should be borne in mind when considering the morphology of the tetralogy of Fallot, one is that although the distinctive features of the lesion are found in the great majority of cases, there are many subtle differences such that no two cases are exactly alike. Second, when tetralogy is accompanied by pulmonary atresia, it is the morphology of the pulmonary arterial supply that is the central feature.

Outlet septum. The central feature in the tetralogy of Fallot is related to the abnormal outlet septum, and the subsequent abnormal relationships it has with the ventriculoinfundibular fold and septomarginal trabeculation. Recall that any muscle bundle that separates the ventricular outflow tracts is termed the outlet septum, while any muscle bundle that separates an arterial valve from an atrioventricular valve is termed the ventriculoinfundibular fold. The septomarginal trabeculations is the extensive septal trabeculations of the right ventricle, and has anterior and posterior limbs. The two limbs of the septomarginal trabeculation typically cradle the ventricular septal defect. The septoparietal trabeculations are a series of muscle bars which extend to the parietal wall of the right ventricle. The moderator band, which is an example of a septoparietal trabeculation, arises apically from the septomarginal trabeculation and courses to the parietal wall, supporting the anterior papillary muscle of the tricuspid valve.

The outlet septum, which in the normal heart is a small and relatively insignificant structure, is hypertrophied and located in the right ventricle in hearts with the tetralogy of Fallot. It is buried between the anterior and posterior limbs of the septomarginal trabeculation, and has both a parietal and septal extension. The septal extension is deviated anteriorly and cephalad to join the septomarginal trabeculation, thus narrowing the subpulmonary infundibulum. The parietal extension courses upwards and over the tricuspid valve to join the ventriculoinfundibular fold.

Interventricular communication. When viewed from the right ventricle, the typical ventricular septal defect is a malalignment, juxta-aortic defect that is cradled by the anterior and posterior limbs of the septomarginal trabeculation. The top of the defect is made of the aortic valve annulus and the ventriculoinfundibular fold. The bottom of the defect is the crest of the ventricular septum, reinforced on the right-ventricular side by the limbs of the septomarginal trabeculation. Three types of defects are commonly recognized, the area of greatest variability being in the posterior and inferior aspect of the defect, the area of greatest concern with respect to the conduction tissue:

• In about 80% of cases, there is fibrous continuation between the tricuspid, mitral and aortic valves. In such cases, the penetrating bundle courses through the area of fibrous continuity.
• In about 20% of cases, there is muscular continuation between the posterior limb of the septomarginal trabeculation and the ventriculoinfundibular fold. In such cases, there is a complete muscular rim around the defect, and the bundle of His is deeply embedded within muscle and crosses the ventricular septum some distance from the postero-inferior edge of the defect. It is thus safe to close this type of defect by placing sutures through the muscular rim, as long as they do not penetrate deeply into the left-ventricular side of the defect.
• A third type of rare defect exists in association with tetralogy. This is a doubly-committed, subarterial defect that is due to hypoplasia of the outlet septum. In such cases, the aortic and pulmonary valves are separated by a thin band of fibrous tissue, and in about half of such cases, the pulmonary valve annulus is severely hypoplastic or nearly atretic.

Additional ventricular septal defects occur in approximately 3% of cases. These are typically either muscular defects or associated with a common atrioventricular valve.

Subpulmonary muscular obstruction. The subpulmonary stenosis in the tetralogy of Fallot is due principally to the antero-cephalad deviation of the outlet septum. The antero-cephalad deviation accounts for the posterior and majority of the subpulmonary stenosis, while the anterior component of the stenosis is usually formed from hypertrophied septoparietal trabeculations. Additional hypertrophy of the apical trabeculations may produce more proximal stenosis and give the arrangement often referred to as double-chamber right ventricle.

Biventricular connection of the aortic valve. The degree of aortic override can vary in different examples of tetralogy. There can be almost exclusive connection to the right ventricle to almost exclusive connection to the left ventricle. Measurements demonstrate that there is true dextrorotation of the aorta in tetralogy, and in extreme cases, the morphology becomes analogous to that of double outlet right ventricle.

Concentric right ventricular hypertrophy. Concentric right ventricular hypertrophy is secondary to right ventricular outflow tract obstruction. In neonates with symptomatic tetralogy, the degree of right ventricular hypertrophy is markedly reduced, forming a basis on which to correct this lesion prior to the onset of right ventricular hypertrophy.

Associated lesions

Pulmonary valvar & arterial abnormalities. Although the subpulmonary infundibulum is the narrowest part of the pulmonary outflow tract in most cases of tetralogy of Fallot with pulmonary stenosis, other lesions of the outflow tract and pulmonary arteries are also frequent. Pulmonary valvar stenosis is a common accompaniment, due either to unicommissural domed stenosis, a bileaflet valve, or a trileaflet valve with commissural fusion or rudimentary, thickened leaflets. Pulmonary atresia may also occur with tetralogy, and in the setting of an absent arterial duct, may be associated with nonconfluent branch pulmonary arteries and aorto-pulmonary collaterals. If the arterial duct is patent in utero, confluent pulmonary arteries without significant aorto-pulmonary collaterals is the rule. Finally, there be complete absence of the pulmonary valve leaflets, resulting in pulmonary insufficiency in utero and marked dilatation of the pulmonary trunk. Tetralogy with pulmonary atresia and tetralogy with absent pulmonary valve leaflets are considered further below. Anomalous origin of a branch pulmonary artery is not an infrequent finding in tetralogy. An anomalous left pulmonary artery typically arises from the arterial duct, while the rare anomalous right pulmonary artery may arise directly from the aorta. Many combinations of anomalously arising branch pulmonary arteries are also possible.

Other lesions. Many other lesions may accompany tetralogy. Among the most common are a right aortic arch, patent foramen ovale, an atrial septal defect, a second ventricular septal defect, a common atrioventricular valve, and anomalous origin of the anterior descending coronary artery from the right coronary artery.

Preoperative Diagnosis

The central clinical feature of TOF is cyanosis, which is mostly continuous but can be intermittent, and the infant may develop hypoxic spells. During a hypoxic crisis, the typical short, harsh systolic ejection murmur along the left sternal border may be absent. The chest radiograph shows a normal-size heart with a prominent right ventricular contour, an absent or deficient pulmonary artery segment, and an upwardly displaced apex (coeur en sabot). Peripheral pulmonary markings are usually diminished. Frequently, the aortic arch is on the right side (25%). The electrocardiogram is nonspecific, although a persistent upright T-wave in the right precordial leads indicates right ventricular hypertrophy. With recent advances in echocardiography, particularly with the addition of color Doppler techniques, the echocardiographic diagnosis makes an appropriate operative strategy possible in the majority of patients in tetralogy of Fallot with pulmonary stenosis. Echocardiography has proved remarkably accurate in demonstrating additional ventricular septal defects, defining the origin and the course of the proximal right and left coronary arteries, evaluating atrioventricular valve anatomy and function, and also outlining the anatomy of the central pulmonary artery, including the origin of the left pulmonary artery. Only if the echocardiographic findings are not clear about any of these issues are cardiac catheterization and cineangiography undertaken. However, if the infant has a history of one or more previous palliative operations, and if there is concern about iatrogenic pulmonary artery distortion, the presence of aorto-pulmonary collaterals, or pulmonary vascular obstructive disease, cardiac catheterization is still indicated.

Indications for operation

Nearly 70% of patients with tetralogy of Fallot and pulmonary stenosis require an operation during the first year of life because of hypoxic spells or persistent hypoxemia (resting arterial oxygen saturation less than 70%). Approximately 30% of neonates with tetralogy of Fallot and pulmonary stenosis die within the first year of life if untreated. In the past, palliative aorto-pulmonary shunt operations were favored because of high mortality and morbidity from primary repair in the very young. As a result of the development of hypothermic circulatory arrest or low-flow hypothermic cardiopulmonary bypass, improved anesthetic management of neonates and infants, and advances in postoperative care, mortality and morbidity after early one-stage repair of tetralogy of Fallot has decreased dramatically, and such repair is currently favored in many centers. This approach avoids the additional risk of two operations and eliminates early and late complications of shunt operations such as a non-functioning shunt, partial or complete occlusion of a pulmonary artery, or development of pulmonary vascular obstructive disease.

There is increasing evidence that early repair of congenital heart anomalies minimizes secondary damage to vital organs, particularly of the heart itself, the lungs, and the brain. In tetralogy of Fallot with pulmonary stenosis, it is hoped that by eliminating or reducing right ventricular outflow tract obstruction early in life, the stimulus for pathologic right ventricular hypertrophy will be eliminated, thus preserving ventricular systolic and diastolic function and also electrical stability of the myocardium. In addition, by eliminating cyanosis as early as possible, the adverse effects of cyanosis on the central nervous system may also be reduced. Observations in the past that neonatal hearts have less ability to adapt to sudden increases in stroke volume or that neonates are more susceptible to the damaging effects of cardiopulmonary bypass are true; nevertheless, they remain within the range of biologic tolerance, as evidenced by the excellent results obtained with neonatal arterial switch operations for anatomic repair of transposition of the great arteries. It is likely that, excluding patients who have tetralogy of Fallot with pulmonary atresia or other significant associated anomalies (such as the absent pulmonary valve syndrome), results of early repair of tetralogy of Fallot in neonates will soon parallel those obtained in infants beyond the first month of life.

It is important to emphasize once more that tetralogy of Fallot with pulmonary stenosis is different from tetralogy of Fallot with pulmonary atresia and pulmonary circulation dependent on aorto-pulmonary collaterals It must also be understood that very young patients with tetralogy of Fallot with pulmonary stenosis are still at a greater risk of dying within the first year of life than are older patients; the risk is significantly greater for those who have severe cyanosis or cyanotic spells. The current slightly increased mortality after repair in the first few months of life is still significantly less than the mortality associated with the natural history of this disease in this age group. Therefore, primary repair at the time of presentation is indicated in such patients. Aside from extracardiac causes (e.g., intracerebral bleeding, generalized sepsis, or acute necrotizing enterocolitis), the only contraindication to primary repair in the very young is anomalous origin of the anterior descending coronary artery from the right coronary artery. In this case, a systemic-to-pulmonary shunt (preferably a modified Blalock-Taussig shunt) is recommended, followed later by interposition of a conduit.

Surgical management

Historical note. Surgical treatment of TOF was initiated by Blalock and Taussig in 1945 with the establishment of the subclavian artery-to-pulmonary artery anastomosis. Klinner et al. in 1962, were the first to interpose a prosthetic conduit between the subclavian artery and the pulmonary artery, a technique that was further refined by de Leval and colleagues. Laks and Castaneda added an occasionally helpful modification of the Blalock-Taussig shunt, using the subclavian artery ipsilateral to the aortic arch. In 1946, Potts et al. introduced the descending aorta-to-left pulmonary artery anastomosis, in 1955 Davidson reported the first central aorto-pulmonary shunt by direct suture, and in 1962 Waterston performed the ascending aorta-to-right pulmonary artery anastomosis, an important alternative to the Blalock-Taussig and Potts operations. In 1948, both Sellors’s and Brock expanded the scope of palliative operations by adding closed pulmonary valvotomy and infundibulectomy.

In an imaginative and daring effort, on April 31, 1954, Lillehei and collaborators, using controlled cross circulation in a 10-month-old boy, carried out the first intracardiac repair of tetralogy of Fallot; this included closure of the ventricular septal defect and relief of the right ventricular outflow tract obstruction under direct vision. In Lillehei’s original cross-circulation series of 11 tetralogy of Fallot repairs, six patients were less than 2 years old. In fact, remarkably, the first, and youngest, patient (10 months old at the time of operation) is well and working as a physician. The first successful repair of tetralogy of Fallot using a heart-lung machine was accomplished by Kirklin and associates in 1955. Lillehei recognized the need for enlarging the right ventricular infundibulum with a patch and extended the patch across a stenotic pulmonary valve annulus as early as 1956. The use of a nonvalved prosthetic conduit from the right ventricle to the pulmonary artery for the treatment of tetralogy of Fallot with pulmonary atresia was first reported by Klinner. Ross and Somerville first reported the interposition of a valved aortic homograft for repair of tetralogy of Fallot with pulmonary atresia in 1966. However, after the initial success with tetralogy of Fallot repair in infancy, subsequent attempts at early repair carried a high mortality rate, and the two-stage repair became universally favored. In 1969, Barratt-Boyes and Neutze successfully reinitiated primary repair of symptomatic infants with tetralogy of Fallot with pulmonary stenosis.

In addition to the important contributions by surgeons in the use of nonvalved and valved conduits for repair of tetralogy of Fallot with pulmonary atresia, and the innovative techniques of percutaneous balloon dilatation and occlusion of collateral arteries developed by interventional cardiologists, much is owed to Edwards and McGoon, Thiene et al., Haworth and Macartney, and Rabinovitch et al. They significantly advanced our knowledge of the anatomy and histology of aorto-pulmonary collaterals, their intraparenchymal connections with pulmonary artery branches, and the effect of pulmonary blood flow on the pulmonary parenchyma.

Reoperation for tetralogy of Fallot

Reoperation after initial repair of tetralogy of Fallot ranges from 2-10%[380], becoming distinctly uncommon after the first 5 postoperative years. Reoperation is performed most commonly to close a residual ventricular septal defect or to relieve residual right ventricular outflow tract obstruction. Other indications include repair or replacement of an incompetent tricuspid valve, repair of an right ventricular outflow tract aneurysm, to close a residual atrial septal defect, to repair a residual surgical shunt, to enlarge a stenotic branch pulmonary artery, or to relieve residual pulmonary valve insufficiency. A complete investigation including echocardiography and cardiac cineangiography is particularly important to diagnosis all residual defects prior to repair.

The operative mortality for all reoperations ranges between 10 - 20%. A significant residual ventricular septal defect is considered present if the Qp:Qs is 1.5 or greater, or in symptomatic patients with a lower Qp:Qs. A residual ventricular septal defect should be considered in any patient with early postoperative pulmonary dysfunction, failure to thrive, or CHF, or in patients with dyspnea or exercise intolerance late after repair. Residual right ventricular outflow tract obstruction may be at the infundibulum, pulmonary valve and/or annulus or the main branch pulmonary artery. It may be the sole residual defect after primary repair or, more often, may be associated with other defects. A peak systolic gradient of > 50 mg Hg is considered significant and is generally an indication for reoperation, particularly in the symptomatic patient.