This article provides a more comprehensive discussion of the treatment strategies for tetralogy of Fallot from a professional’s perspective, which is an important reference for patients and parents. Tetralogy of Fallot is the most prevalent form of cyanotic congenital heart disease. How and when to treat tetralogy of Fallot has a lifelong impact on the well-being of many patients. The vast majority of tetralogy of Fallot require palliative or radical surgical treatment.
Tetralogy of Fallot ( TOF), also known as Tetralogy of Fallot, Tetralogy of Fallot, Tetralogy of Fallot,, Tetralogy of Fallot, Tetralogy of Fallot, Tetralogy of Fallot, and Tetralogy of Fallot, is the most common form of cyanotic congenital heart disease, accounting for approximately 12-14% of congenital heart disease, 50% to 90% of cyanotic congenital heart disease, and 0.03% to 0.06% of births. In recent years, there has been a lot of progress in the understanding and treatment of this disease, and almost all patients with TOF can be treated surgically with good results. However, there are still differences in the understanding of certain issues.
I. Right ventricular outflow tract stenosis
The right ventricular outflow tract stenosis in TOF varies, and can be located in the funnel, pulmonary valve, pulmonary annulus, pulmonary trunk, and its branches.
( I ) Funnel stenosis.
This is a characteristic feature of typical TOF, accounting for approximately 25% of cases. The hypertrophic anterior wall, septal bundle, wall bundle, and supraventricular ridge surround the stenosis, and a third ventricle is formed between this stenosis and the pulmonary valve
( B ) Pulmonary valve stenosis.
Approximately 75% of patients with TOF have varying degrees of pulmonary stenosis, with only 5% having stenosis as the main obstructive lesion alone, and the proportion of two valve malformations has been reported to vary from 25% to 70%. The leaflets of the stenotic valve, whether two- or three-valve, are generally thickened and more severe, resulting in reduced leaflet mobility and obstruction. In some cases, the valve is so poorly developed that only leaflet remnants remain in 3% to 5% of cases, called pulmonary valve agenesis. In funnel stenosis combined with pulmonary stenosis, there may be a fibrous annulus stenosis proximal to the pulmonary valve without a third ventricle. Fibrous annular stenosis may also be located in the middle of the funnel.
( C ) Pulmonary annular stenosis.
The pulmonary annulus is similar to the funnel section and is a myocardial structure when normal. The diameter of the pulmonary annulus in TOF is the opposite of normal, almost always smaller than the aortic annulus, and is thickened by fibrosis and loses its diastolic properties. The pulmonary annulus is rarely stenosed in larger third ventricles; conversely, if the third ventricle is small, the endocardial fibrous tissue at the annulus is hyperplastic, forming varying degrees of annular stenosis. In the case of tubular stenosis in the funnel, there is always severe stenosis of the annulus.
( IV ) Pulmonary artery and branch stenosis.
The pulmonary artery trunk in TOF is almost always narrower than the aorta. Diffuse right ventricular outflow tract hypoplasia is particularly notable for its stenosis, and the main pulmonary artery is mostly less than half the diameter of the aorta and is shorter than normal, shifting posteriorly to the left.
( V ) Pulmonary artery collateral circulation.
TOF is mostly associated with larger caliber and well-expanded bronchial collateral arteries. The largest collateral flow is the main-pulmonary collateral arteries ( APCAs ), which are most common in cases of pulmonary atresia and rare in cases of TOF with general pulmonary stenosis, usually 1 to 3 branches, large and scattered, originating from the mid-superior segment of the thoracic descending aorta and continuing with the interlobular or intralobular segment of the pulmonary artery.
Some large APCAs enter the hilar segment of the right or left pulmonary artery, where the hilar pulmonary artery can degenerate. Less commonly, a single large APCAs is attached to the terminal side of the hilar pulmonary artery. Rarely, a single large APCA continues with the hilar segment of the pulmonary artery (end to end), called “common arterial trunk type IV”. Therefore, large APCAs are often associated with anomalous branches and incomplete distribution of pulmonary arteries in the hilar region. They may also be associated with single or multiple, limited or segmental pulmonary artery stenosis and/or diffuse pulmonary artery hypoplasia.
II. Ventricular septal defect
In typical TOF, the ventricular defect is located under the aortic valve, adjacent to or involving the membranous septum, and when the funicular septum is absent, the ventricular defect is located not only under the aortic valve, but also under the pulmonary valve. This is the so-called sub-stem ventricular defect.
Third, aortic riding
In patients with TOF, the aortic root is rotated, enlarged, and more anteriorly displaced than normal, and its opening rides over both ventricles. Because the ascending aorta is more anteriorly displaced than normal, it often partially obscures the smaller pulmonary artery when viewed intraoperatively. The rightward shift of the aorta over the right ventricle is characteristic of TOF, and its degree varies between 30% and 90%, usually around 50%.
IV. Right ventricle
Due to right ventricular hypertrophy, the right ventricular inflow tract portion (sinus portion) has an enlarged appearance compared to a normal heart, so the septum shifts left and the left ventricle position shifts back (cis-clockwise transposition).
V. Left ventricle
The thickness of the left ventricle is generally normal in TOF. In severe TOF and severe cyanosis, the left ventricular end-diastolic volume is normal or slightly smaller. Even if the left ventricle is slightly smaller, its thickness is generally normal. True hypoplasia of the left ventricle and mitral valve is rare.
Concomitant malformations
There are many concomitant malformations in TOF, with the right aortic arch being the most common, accounting for about 25% of cases. Other common ones include atrial septal defect (9%), permanent left superior vena cava (8%), left anterior descending branch of the coronary artery originating from the right coronary artery (4%), patent ductus arteriosus (4%), multiple ventricular defects (2%), complete atrioventricular canal malformation (2.2%), and aortic closure insufficiency.