bubble_chart Overview

Tetralogy of Fallot (TOF) is the most common cyanotic congenital heart disease in children, comprising four malformations: pulmonary stenosis, ventricular septal defect, overriding aorta, and right ventricular hypertrophy. Pulmonary stenosis reduces pulmonary blood flow and increases right ventricular pressure, causing part or most of the systemic venous blood to flow into the left ventricle and the overriding aorta through the ventricular septal defect. This results in a right-to-left shunt, leading to decreased arterial oxygen saturation. The severity of clinical manifestations correlates with the degree of pulmonary stenosis—the more severe the stenosis, the greater the right-to-left shunt.

bubble_chart Auxiliary Examination

1. X-ray examination: Typically, the heart appears boot-shaped with a rounded and upturned apex and a concave waist. The heart usually shows no significant enlargement or only mild to grade II enlargement, predominantly in the right ventricle, while the right atrium may also exhibit grade I enlargement. The left atrium and left ventricle remain normal. Accompanying features may include a right-sided aortic arch causing widening of the upper mediastinal shadow, reduced hilar shadows, fine pulmonary vascular markings, and a reticular shadow indicative of collateral circulation.
2. Electrocardiogram: Right axis deviation and right ventricular hypertrophy are observed, particularly in older children. Lead II may show tall and peaked P waves, and some cases may present with incomplete right bundle branch block.
3. Echocardiography: The long-axis view of the left ventricle reveals a widened aorta, with the anterior wall and ventricular septum showing an interrupted echo and overriding the ventricular septum. The right ventricular anterior wall and ventricular septum are thickened, and the right ventricular outflow tract is narrowed. The short-axis view of the aorta demonstrates narrowing of the right ventricular outflow tract and the condition of the pulmonary valve. Pulsed Doppler can detect the turbulent flow spectrum of systolic stenosis in the right ventricular outflow tract, while color Doppler reveals an abnormal blood flow shunt from the right ventricle into the aorta during systole.
4. Cardiac catheterization and angiography: Right heart catheterization shows increased right ventricular systolic pressure, equal to that of the left ventricle and aorta. Due to severe pulmonary stenosis, catheter advancement into the pulmonary artery may be obstructed and pose risks, so it is generally avoided. Selective right ventricular angiography remains a reliable method for diagnosis and differential diagnosis, allowing anatomical assessment of the type and extent of pulmonary stenosis and the ventricular septal defect, which aids surgical planning. Typical findings include simultaneous opacification of the aorta and pulmonary artery after right ventricular contrast injection. The lateral view shows the aorta overriding the ventricular septum with a generally normal relationship to the pulmonary artery. Stenosis of the infundibulum may be observed, as well as stenosis of the pulmonary valve, annulus, or main pulmonary artery. A third ventricle may also be visible.

bubble_chart Diagnosis

1. Symptoms: Typical tetralogy cyanosis usually appears between six months to one year after birth, gradually worsening with growth and development, intensifying after activity or crying, accompanied by dyspnea and a characteristic posture—squatting. Exercise tolerance is poor, and hypoxic episodes are common, particularly noticeable in infants aged 1–2 years, manifesting as severe dyspnea, dysphoria, aggravated cyanosis, weak crying, loss of consciousness, and spasms. These episodes may last from a few minutes to several hours before spontaneous recovery, though they can occasionally be fatal. The episodes are often associated with muscular rigidity and spasms in the infundibular region of the right ventricle. Triggers may include waking, crying, defecation, or feeding. There is varying degrees of growth and developmental impairment. Heart failure or arrhythmias are generally rare.
2. Signs: Delayed growth and development, nutritional status below that of peers, often accompanied by clubbing of fingers and toes. The apical impulse is not prominent. A grade 3–4 ejection systolic murmur can be heard at the left sternal border in the second or third to fourth intercostal spaces and at the apex, possibly accompanied by a thrill. The loudness of the murmur is inversely proportional to the degree of infundibular stenosis; in severe cases, the murmur may be faint or even inaudible. The pulmonary second sound is single and accentuated.

bubble_chart Treatment Measures

Medical Treatment

1. Monitor the degree of hypoxia, limit physical activity, and avoid hypoxic episodes.
2. Ensure adequate daily fluid intake, especially during summer or episodes of diarrhea, to prevent dehydration and avoid excessive blood viscosity leading to thrombosis.
3. Iron-deficiency anemia is a trigger for hypoxic episodes; it must be corrected with iron supplements or, in severe cases, small blood transfusions.
4. In case of a hypoxic episode, place the child in a knee-chest position with legs flexed. If necessary, administer subcutaneous morphine at 0.2 mg/kg to relieve symptoms immediately. Prolonged hypoxia may cause metabolic acidosis, which should be corrected with sodium bicarbonate. Oral propranolol at 1 mg/kg daily for weeks or months can help prevent episodes. Oxygen inhalation during an episode is generally ineffective.

Surgical Treatment

Currently, the mortality rate for definitive surgery is around 3%, with satisfactory outcomes. Therefore, every case should aim for a one-time corrective procedure. The optimal age for surgery is 2–5 years. Surgery should be performed earlier under the following conditions:

1. Recurrent severe hypoxic episodes with poor response to treatment;
2. Progressive worsening of cyanosis and severe polycythemia, with hemoglobin exceeding 200 g/L or hematocrit >65%.

Over 90% of survivors after corrective surgery show good long-term outcomes, with disappearance of cyanosis, improved physical activity, and near-normal life. Poor prognosis is associated with unsatisfactory relief of right ventricular outflow tract obstruction or residual shunts. Patients with postoperative #-degree atrioventricular block require permanent pacemaker implantation. However, due to continuous surgical advancements, such complications are now rare.