Tetralogy of Fallot is the most common complex cyanotic congenital cardiovascular malformation, which includes ventricular septal defect, pulmonary artery stenosis, right aortic position (riding on the defective ventricular septum) and right ventricular hypertrophy, of which the first two malformations are the basic lesions.
In most cases, cyanosis appears several months after birth, and in severe cases, cyanosis appears immediately after birth, shortness of breath after activity, children often feel weak, poor activity endurance, and may have hypoxic attacks during strenuous activity, crying or early morning when they first wake up: children have sudden respiratory distress, increased cyanosis, and in severe cases, convulsions and fainting may result. A few cases may have epistaxis, hemoptysis, embolism or brain abscess.
2, physical signs can be seen poorly developed, the anterior part of the chest may be bulging, with cyanosis and pestle-like fingers (toes). There is a systolic blowing jet murmur between the second and third ribs at the left edge of the sternum, which may be accompanied by tremor.
According to the medical history, the child has cyanosis, shortness of breath after activity, dyspnea, increased cyanosis, preference for squatting, stunted growth, pestle-like fingers, grade II-III systolic jet murmur between the second and third ribs at the left edge of the sternum, right ventricular hypertrophy, aortic widening, boot-shaped heart on electrocardiogram and X-ray, echocardiography, cardiac catheterization, and cardiovascular angiography can be diagnosed.
Auxiliary examinations
1, X-ray examination of the lung field is abnormally clear, the arc of the common pulmonary artery trunk is not obvious or concave, the right ventricle is enlarged, the tip of the heart is upward, and the heart shadow is in the shape of a wooden shoe (with a transverse rectangle) on the posterior anterior film. The right aortic arch is visible in nearly 1/4 of patients.
The electrocardiogram showed right ventricular hypertrophy and strain, with significantly increased R waves and inverted T waves in all leads of the right precordial region. In some patients, the P waves in the standard leads and the right precordial leads are high and sharp, indicating right atrial hypertrophy. The electrocardiographic axis is right-sided.
3. Echocardiography shows enlargement of the aortic root, which moves forward and rides over the ventricular septum. The continuity between the anterior wall of the aorta and the ventricular septum is interrupted, and the septal echogenicity is lost there, while the posterior wall of the aorta and the mitral valve remain continuous. The right ventricle is hypertrophied, and its outflow tract, pulmonary valve or pulmonary artery inner diameter is narrowed. Echocardiography can also show a right-to-left shunt from the right ventricle to the aorta.
4. Routine blood tests have a significantly higher red blood cell count, hemoglobin content and red blood cell pressure volume.
Types of surgical treatment
Bypass surgery
Bypass surgery creates a shunt between the body circulation and the pulmonary circulation to increase blood flow to the pulmonary circulation, allowing for an increase in oxygenated blood. There are methods such as anastomosis of the subclavian artery to the pulmonary artery, anastomosis of the aorta to the pulmonary artery, and anastomosis of the vena cava to the right pulmonary artery. This procedure does not change the deformity of the heart itself and is a palliative procedure, but it can create conditions for future corrective surgery.
Direct vision surgery
Direct vision surgery is performed under extracorporeal circulation to repair the ventricular septal defect, open the stenotic pulmonary valve or pulmonary artery, and remove the stenosis of the right ventricular funnel, which is a method to completely correct the malformation.
Radical surgery for tetralogy of Fallot
Indications and contraindications for surgery
1. Surgery is considered when the disease is diagnosed. Radical surgery can be postponed until 3-12 months of age in children who are asymptomatic within 3 months of birth. Patients with severe symptoms can undergo palliative surgery first and then radical surgery. Most of the patients can be cured.
2. Contraindications to surgery
(1) Peripheral pulmonary artery development and small left ventricular development are relative contraindications to surgery, and palliative surgery is feasible.
(2) Severe pulmonary hypertension after body-pulmonary artery bypass surgery is a contraindication to surgery.
Surgical methods and precautions
1. The purpose of palliative surgery is to increase pulmonary blood flow to improve the patient’s symptoms. Due to the development of cardiac surgery, the majority of patients with tetralogy of Fallot can be treated with radical surgery, while palliative surgery is decreasing year by year. The main palliative procedures are.
(1) Subclavian artery pulmonary artery anastomosis (Blalock-Taussing procedure).
(2) Descending aorta-pulmonary artery anastomosis (Potts procedure).
(3) Ascending aorta-right pulmonary artery anastomosis (Waterton procedure).
(4) Superior vena cava-right pulmonary artery anastomosis (Glenn procedure). The direct introduction of superior vena cava flow into the right pulmonary circulation causes great difficulty in intracardiac orthopedics, although some patients have good results.
(5) Closed funnel section and pulmonary valve dissection (Brock procedure) This procedure is difficult to master and is rarely used clinically.
(6) Ascending aorta and pulmonary artery anastomosis is suitable for infants under 3 months of age.
2.Radical surgery should be performed under moderate hypothermic extracorporeal circulation in children and adults; in infants and children (under 7KG), it should be performed under deep hypothermic stopping circulation and with limited extracorporeal circulation.
3.Intraoperative precautions
(1) The cooling and temperature change during extracorporeal circulation should be slow and uniform, and the difference between nasal and anal temperatures should not exceed 10 degrees, which is conducive to the protection of the lungs.
(2) When the anterior descending branch starts from the right coronary artery and crosses over the right ventricular outflow tract, be careful not to accidentally injure it. For those whose annulus does not need to be enlarged, a transverse incision can be made below the anterior descending branch for surgery. If the annulus needs to be enlarged and the anterior descending branch has a clear shape without many small branches that can be easily dissected out and pulled up with a silk wire, a longitudinal incision is feasible. However, if the anterior descending branch is difficult to distinguish the border, in order to preserve the coronary artery, only the right ventricular “external pulmonary artery canal should be made. When the incision accidentally injures the anterior descending branch, coronary artery bypass grafting should be performed.
(3) The right ventricular outflow tract incision should not be to the right, otherwise it is easy to damage the aortic valve.
(4) The right ventricular outflow tract should be unblocked satisfactorily, and the abnormal hypertrophic muscle bundle should be excised moderately, so as not to destroy the physical structure of myocardial contraction. Do not excessively resect or cut off the septal bundle, so as not to damage the right ventricular wall of the coronary artery branches produce ventricular wall necrosis and damage the septum and perforation. The wall bundle should not be excised too deeply to avoid cutting through and damaging the aortic sinus semilunar valve.
(5) Transannular patches should be performed to avoid pulmonary regurgitation to the maximum extent possible. In infants and children, the potential stenosis at the beginning of the left pulmonary artery should be fully estimated and resolved in a single operation.
(6) In adults with tetralogy of Fallot, because of heavy myocardial fibrosis and easy edema, the right ventricular incision and ventricular defect edge suture must be strong and reliable, otherwise it is easy to cause postoperative bleeding and residual shunt.
Postoperative complications
The most common complications are cerebral thrombosis (due to increased red blood cells, increased blood viscosity, and sluggish blood flow), cerebral abscess (bacterial thrombosis), and subacute bacterial endocarditis. In contrast, some postoperative complications can occur in children who are actively treated surgically.
Pulmonary complications
The main factor affecting the outcome of F4 is the developmental status of the pulmonary arteries, especially in those with small left and right pulmonary branches or even distal branches, the outcome is poor. Preoperative anemia, severe dysplasia of the pulmonary vessels and lungs, thick blood and little pulmonary blood can lead to alveolar degeneration and pulmonary capillary microthrombosis. Intraoperatively, the pulmonary vasculature is overfilled due to excessive side branches and poor pulmonary venous return, resulting in the formation of a perfused lung.
After the right ventricular outflow tract is unblocked, pulmonary blood is increased in a large amount, and the postoperative pulmonary blood perfusion is significantly higher. Combined with the brittle lungs and bronchi in infants and children, the narrow lumen and secretions, the lumen is easily obstructed, and postoperative pulmonary complications often occur, and it becomes one of the main causes of early death after F4 surgery.
Complete atrioventricular block
Complete AV block can be caused by direct intraoperative trauma, pulling or improperly positioned sutures and intraoperative hypothermia, hypoxia and ischemia, but it is mostly transient, and sinus rhythm can be restored by rewarming and removal of vena cava drainage tube, and when it is ineffective, isoproterenol (5μg/ml) 5-10μg intravenously can be used, and temporary temporary cardiac pacing and hormonal therapy.
Low cardiac output syndrome
It is mostly caused by overly complex malformation, unsatisfactory correction of surgical malformation, residual leakage of ventricular septal defect or inadequate release of outflow tract and pulmonary artery stenosis, excessive ventricular incision that impairs right ventricular function, prolonged aortic block, poor intraoperative myocardial protection, hypoplastic left heart, hypotension at room temperature, and other factors. The prevention method is to avoid the occurrence of the above-mentioned causes, to observe closely after surgery, to handle early, and to apply vasodilators such as sodium nitroprusside, supplemented with dobutamine and isoproterenol, to reduce the anterior and posterior cardiac loads, to enhance myocardial contractility, and to control hypovolemia, if insufficient blood volume or pericardial tamponade is excluded.
Hemorrhagic bleeding
F4 patients are rich in collateral circulation, coagulation mechanism disorders and long extracorporeal circulation time, which increase the chance of postoperative bleeding, and can cause pericardial tamponade, affecting cardiac function and even endangering life. The prevention and treatment methods are to shorten the time of extracorporeal circulation as much as possible, to closely monitor ACT, to carefully stop bleeding before the end of surgery, to keep the drainage tube open after surgery, to closely observe the amount of drainage fluid, and to open the chest to stop bleeding as early as possible if necessary.
Systemic capillary leakage syndrome
Leakage often occurs in neonates and small infants after extracorporeal circulation, which may be related to the release of inflammatory mediators, resulting in capillary endothelial damage, with clinical manifestations of severe systemic edema and massive exudation from the thoracic and abdominal cavities, often requiring larger doses of catecholamines and the input of large amounts of colloid fluid to maintain blood pressure, for which there is no effective prevention method, and the application of hormones may increase capillary stability.