Tetralogy of Fallot is a common form of cyanotic congenital heart disease, accounting for about 10% of congenital heart disease. It is the first among cyanotic congenital heart diseases, accounting for more than 50%. Its pathological features include right ventricular outflow tract stenosis, ventricular septal defect, aortic riding, and right ventricular hypertrophy. The severity of the disease depends on the thickness of the developing pulmonary artery; the size of the left ventricle; the age and the number of collateral vessels of the body pulmonary artery. Common problems related to the surgical treatment of tetralogy of Fallot are described as follows.
I. Timing of surgery
In recent years, due to the improvement of surgical techniques, the progress of anesthesia and extracorporeal circulation, as well as the improvement of postoperative monitoring level. This has made cardiac surgery under extracorporeal circulation safer. Therefore, the age of children who undergo tetralogy of Fallot is gradually becoming younger. However, the risk of orthopedic surgery in children under 6 months of age is still high.
Therefore, I recommend that children over 6 months of age who have good pulmonary artery development can undergo corrective surgery in hospitals with good technology and equipment. If the pulmonary artery is poorly developed and has recurrent hypoxic episodes, a body-pulmonary artery bypass should be performed first, followed by corrective surgery later. In the case of children over 2 years of age with a weight of 15 kg or more, it is recommended to perform the surgery in children with average equipment and not very experienced in performing tetralogy of Fallot. There is a clear difference in the risk of surgery between the two.
Second, the surgical approach to the problem
If the pulmonary artery development index (Nakata index) ≥ 150mm2/m2; left ventricular volume index (LVEDVI) ≥ 30ml/m2 can be done for tetralogy of Fallot correction. Those who obviously do not meet the above two indexes should not do corrective surgery to avoid the occurrence of low cardiac output syndrome after surgery. Those whose conditions do not meet to do corrective surgery can do body-pulmonary artery bypass. The purpose is to increase the pulmonary artery blood supply, which can improve the hypoxic condition and avoid hypoxic attacks on the one hand; on the other hand, it can promote pulmonary artery development. How long after the body-pulmonary artery bypass to do the corrective surgery depends on the development of the pulmonary artery and the development of the left ventricle.
Generally, corrective surgery is performed within 3 months to 1 year. The authors advocate a straight right axillary incision through the fourth intercostal opening to partially dissect the pericardium and perform an artificial vessel bridge between the ascending aorta and the right pulmonary artery. The diameter of the artificial vessel is 4 mm for those under 1 year old, 5 mm for those between 1 and 5 years old, and 6 mm for those over 5 years old.
Another method is to properly unblock the right ventricular outflow tract under extracorporeal circulation without repairing the ventricular septal defect. If the body pulmonary artery shunt has not yet achieved the purpose of the artificial vessel occlusion at this time can do another shunt.
Third, the problem of surgical methods of tetralogy of Fallot correction
First of all, we should pay high attention to do this operation under the premise of good technical skill and equipment to ensure safety. Extracorporeal circulation must be operated with advanced artificial membrane lung, blood filter and experienced perfusion surgeon. Cardiac arrest fluid should contain oxygenated blood. The evacuation of the right ventricular outflow tract should be tailored to the individual to ensure unobstructed flow and to protect right ventricular function. The criteria for unblocking the right ventricular outflow tract are described in detail on page 38 of the book “Cardiac Surgical Monitoring” published by the People’s Army Medical Publishing House.
The degree of widening of the right ventricular outflow tract is performed according to the above criteria, and if necessary, the pulmonary artery is cut straight to the left pulmonary hilar. In infants and children, widening is usually performed with an autologous pericardial slice. If the widening is greater, a flap pocket needs to be sewn in advance at the corresponding patch. This is important to ensure postoperative cardiac function. Bovine pericardial slices are also used as patches. In cases of pulmonary atresia or narrow pulmonary valve annulus, a bovine jugular vein with a valve is used as a patch for the right ventricular outflow tract with better results. Intraoperative care should be taken that the prosthetic valve corresponds to the patient’s leaflet.
In the case of stenosis at the right pulmonary artery opening, a separate widening patch is required. The sutures of the widened right ventricular outflow tract should be even and wrinkle-free, and the sutures should be appropriately stretched to avoid postoperative bleeding. The muscles near the ventricular septal defect should not be removed when the right ventricular outflow tract is unblocked, so as to avoid difficult suturing when repairing the ventricular septal defect. The right posterior inferior border of the ventricular defect can be interrupted with mattress sutures, and the remainder of the defect can be closed continuously with a double layer of slip sutures. It must be ensured that there is no residual shunt, otherwise the surgical result or even death will be seriously affected. The size of the patch should be consistent with the size of the ventricular septal defect; too large will have folds and too small will affect the left ventricular outflow tract.
IV. Prevention and treatment of low cardiac output syndrome after tetralogy of Fallot correction
In addition to cardiac ultrasound, X-ray chest film and ECG examination before surgery, CTA examination with multi-row CT should be emphasized. Make an accurate diagnosis. The incidence of postoperative low cardiac output is not high with appropriate surgical indications coupled with skilled surgical techniques. Once postoperative low blood pressure, small pulse pressure difference, low urine, high central temperature, cool end extremities, and ineffective diuretics are present, low cardiac output syndrome can be diagnosed. In addition to expanding blood volume with colloid, increasing the amount of vasoactive drugs, correcting acidosis, diuresis and treatment with adrenal corticosteroids, peritoneal dialysis should be applied as early as possible.
The earlier it is applied, the better its effect. Mild hypovolemia can often be corrected after close observation and careful treatment. Severe hypovolemia requires immediate cardiac ultrasound to identify the cause. If the heart is reversible, it is recommended to treat it with ECMO as soon as possible.
V. Ventilator treatment problems
For mild tetralogy of Fallot with good pulmonary artery development, no heavy cyanosis, no large body pulmonary artery collateral circulation, and satisfactory correction of deformity during surgery, postoperative circulatory stability with ventilator-assisted breathing can be removed within 1 day. For those with severe cyanosis before surgery, infants and children, and those weighing <10kg, the application of ventilator time should be extended to 3--5 days after surgery. This is because tetralogy of Fallot has a great impact on the patient.
The original intra-pulmonary artery pressure is very low, and after surgery the intra-pulmonary artery pressure is significantly higher than before surgery, and the lung tissue has to have an adaptation process to this. The lung tissue will have a process of congestion, edema and exudation, the length of which depends on the severity of the disease. Such patients should be treated patiently with ventilators until lung function returns to normal. If the lung function has not yet recovered, the patient will be removed from the ventilator treatment, and the patient will need to be intubated for the second time; in severe cases, it will lead to death.
Sixth, the problem of body-lung collateral circulation
It is not enough to use cardiac ultrasound alone to diagnose body-pulmonary collateral circulation before surgery. It is necessary to use CTA with multi-row CT to determine the thickness and number of collateral vessels. Thinner collateral vessels have little fractional flow, and intraoperative deep hypothermia and low flow methods are used, which do not interfere with the procedure. In some cases, the fractional flow is small even if the beginning of the collateral vessels is thick and the end is very thin.
For the collateral vessels with large fractional flow, it is best to do the surgery in the hybridization operating room, after the interventional blocking of the collateral vessels for surgical correction. It is also possible to block the collateral vessels in the catheterization room and then go into the operating room as soon as possible, because some important collateral vessels will decrease in oxygen saturation after blocking.
VII. Postoperative follow-up problems
Patients with tetralogy of Fallot correction, unlike patients with ventricular septal defects, require regular follow-up. Although the majority of patients can work and live normally, there are still a few patients with right heart insufficiency, pulmonary artery restenosis, ventricular septal residual shunt, pulmonary valve closure insufficiency, and endocarditis. It is important to identify the problems and solve them in time. Re-surgical treatment if necessary.