Complete Pulmonary Venous Anomaly in Children

　　1. Etiology

　　In the early stage of embryonic development, the pulmonary vascular bed is connected to the common cardinal vein and umbilical yolk sac venous system. Later, the right common cardinal vein differentiates into the right superior vena cava and azygos vein, and the left common cardinal vein differentiates into the left superior vena cava and coronary sinus. The umbilical yolk sac venous system differentiates into the inferior vena cava, venous duct, portal vein, etc. At 25-27 days of pregnancy, there is no direct connection with the primitive heart. In the subsequent development process, the pulmonary veins, in addition to maintaining connections with the bronchial veins, lose connections with the main veins and the yolk sac venous system, and finally merge into the primitive atrium. The presence of the connection channel between the pulmonary vein bed and the common cardinal vein and umbilical yolk sac venous system can lead to abnormal fusion of the pulmonary total vein into the right atrium or developmental disorders of the pulmonary total vein, not fused with the primitive atrium, both of which can lead to pulmonary venous connection anomalies. The blood of the pulmonary veins merges into the left common cardinal vein, leading to connections between the pulmonary veins and the left superior vena cava and coronary sinus. The blood of the pulmonary veins merges into the right common cardinal vein, then connects with the superior vena cava on the right side and the azygos vein. If the blood of the pulmonary veins merges into the umbilical yolk sac venous system, then the pulmonary veins connect with the portal vein, venous duct, or inferior vena cava. The degree of atresia of the pulmonary total vein or the degree of fusion with the primitive left atrium and the timing of occurrence form different types of pulmonary venous connection anomalies.

　　2. Pathogenesis

　　1. Pathological anatomy

　　There are many classification methods for complete pulmonary venous connection anomalies, including classification by the length of the abnormal channel (Burrough and Edwards), and by embryonic and anatomical classification (Neill), that is, connected to the left common cardinal vein, right common cardinal vein, and yolk sac vein. Generally, it is commonly classified according to the anatomical location of the abnormal connection (Darling et al).

　　(1) Type on the heart: This type is the most common, accounting for 1/2 of complete pulmonary venous connection anomalies. The left and right pulmonary veins first merge behind the left atrium to form the pulmonary vein trunk, which passes through an abnormal vertical vein in front of the left pulmonary artery and left upper bronchus and connects to the left innominate vein, merging into the superior vena cava on the right side and the right atrium. About 44% connect to the left innominate vein, and direct connections between the vertical vein and the superior vena cava on the right side are less common (11% to 15%), often combined with other cardiac anomalies.

　　(2) Cardiac type: accounting for about 30%, the pulmonary veins connect to the right atrium through a short tube or 3 to 4 holes, or the pulmonary venous confluence connects with the coronary sinus, the coronary sinus is dilated but the position is normal.

　　(3) Infracardiac type: accounting for about 13% to 24% of complete pulmonary venous connection anomaly. The left and right pulmonary veins connect to the descending vertical veins separately. Crossing the esophageal hiatus in front of the esophagus, it runs parallel to the inferior vena cava and abdominal aorta between them and downward. The most common (70% to 80%) is the connection with the portal venous system, and the connection with the venous duct, hepatic vein, or inferior vena cava is rare.

　　(4) Mixed type: rare, accounting for about 5% to 10%. The abnormal connection site of pulmonary veins has two or more. The more common ones are the connection between the left pulmonary vein and the left innominate vein, and the connection between the right pulmonary vein and the right atrium or coronary sinus. Most of them are associated with other cardiac malformations. Pulmonary venous obstruction can occur in various types of complete pulmonary venous connection anomaly. Commonly, the pulmonary venous confluence itself is narrow, and obstruction caused by external compression can also be seen in supracardiac and infracardiac cases. For example, in the infracardiac type, the venous return channel through the esophageal hiatus can be compressed externally, and the descending vertical vein connecting with the portal vein and the narrow venous duct can obstruct the return of pulmonary veins, making infracardiac type venous return obstruction more common. In the supracardiac type of complete pulmonary venous connection anomaly, the vertical vein ascends between the left pulmonary artery and left bronchus, or the vertical vein that drains into the superior vena cava on the right side ascends between the right pulmonary artery and bronchus, both of which can be compressed and narrowed. There may also be stenosis at the starting part of the vertical vein or at the connection with the left innominate vein. The obstruction in intracardiac patients is the least common.

　　2. Pathophysiology

　　Complete pulmonary venous connection anomaly, in addition to pulmonary venous abnormalities, also includes right-to-left shunts at the atrial level, such as patent foramen ovale and atrial septal defect. In complete pulmonary venous connection anomaly, deoxygenated blood from the systemic venous circulation and oxygen-rich blood from the pulmonary veins mix in the right atrium. If the atrial communication is restrictive, blood flow into the left atrium is restricted, leading to insufficient systemic perfusion volume, while the pressure in the right atrium increases, and the return of systemic and pulmonary veins is obstructed; if the atrial septal defect is large, the right-to-left shunt is smooth, and the blood flow from the right atrium to the right ventricle and left atrium depends on the compliance of the atria and ventricles and the resistance of the systemic and pulmonary circulations. The right atrium, right ventricle, and pulmonary artery expand due to increased blood flow, while the left atrium and left ventricle decrease in volume due to reduced filling. The hemodynamic changes in complete pulmonary venous connection anomaly are closely related to the presence of pulmonary venous obstruction. In the non-obstructive type, as the pulmonary vascular resistance gradually decreases after birth, the blood flow from the systemic and pulmonary veins entering the pulmonary circulation increases accordingly, and its hemodynamic changes are similar to those of large atrial septal defects. The right ventricle is overloaded with volume, causing right ventricular dilation, myocardial hypertrophy, and a significant increase in pulmonary artery pressure. In the obstructive type of complete pulmonary venous connection anomaly, the total pulmonary vein obstruction site and the middle layer hypertrophy and intimal hyperplasia of the pulmonary small arteries, the increase in pulmonary lymph fluid, and the expansion of lymphatic vessels lead to pulmonary edema, and secondary pulmonary hypertension may also occur, increasing the pressure in the right ventricle, eventually leading to right heart failure.

　　Nutritional disorders, delayed growth and development, recurrent pulmonary infections, which can lead to heart failure, pulmonary edema, and so on. During the interstitial phase of pulmonary edema, patients often have cough, chest tightness, mild shallow and rapid breathing. Physical examination may reveal wheezing in both lungs, and signs of heart源性 pulmonary edema may be found. PaO2 and PaCO2 are slightly reduced. After the fluid of pulmonary edema渗入alveoli, patients may present with pale complexion, cyanosis, severe difficulty breathing, coughing up a large amount of white or bloody frothy sputum, and wet rales in both lungs.

　　The symptoms of the patient depend on whether there is an obstruction of the pulmonary veins, the size of the atrial communication, and the presence of other congenital heart defects. In patients with small atrial communications, pulmonary hypertension and right heart failure appear early after birth, with rapid symptom development and severe condition. In patients without pulmonary vein obstruction, pulmonary hypertension appears later, but cyanosis is prominent, with a slower progression of the disease, slow growth of the infant, rapid breathing, accelerated heartbeat, and mild cyanosis, which may be misdiagnosed as pneumonia and respiratory distress syndrome. Physical examination may not reveal specific murmurs, and sometimes a systolic ejection murmur can be heard at the left sternal border at the second rib space. A diastolic rumbling murmur may be heard at the lower left sternal border. The heart dullness border may be enlarged, and an elevating pulse may be felt in the anterior chest area. Clubbing (of fingers or toes) is usually mild.

　　1. Abandon bad habits, including those of the pregnant woman herself and her spouse, such as smoking and excessive drinking.

　　2. Treat diseases that affect fetal development before pregnancy, such as diabetes, lupus erythematosus, anemia, and so on.

　　3. Actively carry out prenatal examinations, prevent colds, and try to avoid using drugs confirmed to have teratogenic effects on the fetus, as well as avoiding contact with toxic and harmful substances.

　　4. High-risk pregnant women, those with a family history of congenital heart disease, or couples with serious diseases or defects should be monitored closely.

　　1. Chest X-ray

　　1. Non-obstructive type

　　The right atrium, right ventricle, and pulmonary blood volume increase. If connected to the left innominate vein, the dilated vertical vein and left innominate vein can be seen at the left upper heart contour, and the superior vena cava can be seen on the right side, making the heart shadow typical '8' or snowman shape. This kind of performance often appears in older children, and the image is not obvious in children born a few months ago.

　　2. Obstructive type

　　The chest X-ray features are diffuse punctate reticular shadows in the pulmonary interstitium, radiating from the hilum to the periphery. When the pulmonary interstitium and alveolar edema are severe, a milky glass-like change may occur, the heart contour is unclear, but the heart is usually not enlarged. X-ray has diagnostic significance only in neonates with heart failure but a small heart shadow.

　　2. Electrocardiogram

　　Electrocardiogram right axis deviation, right ventricular hypertrophy, without pulmonary vein obstruction in children, can be accompanied by right atrial enlargement, manifested as a high and pointed P wave in lead II and right chest lead.

　　3. Echocardiography

　　When examining, if the right atrial volume load is too heavy, there is a right-to-left shunt at the foramen ovale or atrial defect, and normal pulmonary veins are not seen in the left atrium. The left atrium and left ventricle are small, and when the interatrial septum bulges to the left, one should highly suspect complete pulmonary vein atresia. The purpose of cardiac ultrasound examination is to clarify the number of ectopic pulmonary veins, the obstruction site, and the pulmonary artery pressure. When the pulmonary artery flow velocity is high, the pulmonary artery trunk can be seen to dilate.

　　1. Supracardiac type

　　The subxiphoid coronary section can see the convergence cavity of the left and right pulmonary veins separated from the left atrium, the ascending vertical vein is most easily seen in the area above the sternum, and the pulse Doppler can detect the positive blood flow spectrum in the vertical vein and the negative blood flow in the superior vena cava. If the vertical vein runs between the left pulmonary artery and the left bronchus, it can be observed through the subxiphoid sagittal section.

　　2. Intracardiac type

　　The subxiphoid coronary section can see the pulmonary veins entering the right atrium individually or after aggregation, and if the pulmonary veins are ectopically drained into the coronary sinus, the section can also show the enlargement of the coronary sinus, which needs to be differentiated from large atrial septal defects (primary atrial septal defects are located in a more anterior section).

　　3. Subcardiac type

　　The convergence cavity of the left and right pulmonary veins is also visible through the subxiphoid coronary section, followed by the downward passage of a vein through the diaphragm seen through the subxiphoid sagittal section. Color Doppler imaging shows that the main trunk of the vein is narrowed at the place of passing through the esophageal hiatus, and the blood flow is traced to the portal vein or hepatic vein, where the portal vein is often dilated.

　　4. Mixed type

　　It requires comprehensive evaluation from multiple planes. The most common mixed-type complete pulmonary vein connection is the direct entry of the right pulmonary vein into the right atrium, with the left pulmonary vein connecting to the left innominate vein through the vertical vein.

　　The situation of pulmonary vein obstruction can be estimated through continuous Doppler and color Doppler imaging. The turbulent blood flow at the narrow part is displayed as a colorful blood flow signal, with an increase in blood flow velocity at the obstruction site and a non-phase blood flow map. However, if there is a right ventricular outflow tract obstruction, insufficient pulmonary venous blood flow may obscure the above phenomenon, which is common in complex cyanotic heart disease. Prostaglandin E can be used for differentiation, and the tricuspid regurgitation detector can measure the pressure gradient between the left and right sides of the tricuspid valve, thereby clarifying the pulmonary artery pressure.

　　Four, Heart Catheter

　　For most patients, two-dimensional echocardiography and Doppler technology can understand the pulmonary venous anatomy and the details of the obstruction site, etc. Usually, there is no need for further heart catheterization, and heart catheterization is only used for complex cases and precise positioning of stenotic vessels.

　　1, Blood oxygen saturation

　　The blood oxygen saturation at the ectopic entrance of the pulmonary veins is significantly increased.

　　2, Pressure

　　When the atrial communication is very small, the pressure in the right atrium is often higher than that in the left atrium. However, if there is no difference in pressure, the existence of restrictive intracardiac communication cannot be excluded either, and the pressure in the right ventricle and pulmonary artery is slightly higher than that of the systemic circulation.

　　3, Angiography

　　Selective pulmonary venography is diagnostic for determining the location of abnormal pulmonary venous ostia. In children with obstructive type, vascular stenosis can be displayed, and the contrast agent emptying time is prolonged. However, due to the placement of a heart catheter in the pulmonary venous return channel, it can further increase the degree of obstruction, and this examination is more dangerous in infants with pulmonary vein obstruction and pulmonary hypertension.

　　Five, Magnetic Resonance Imaging

　　The abnormal connection of pulmonary veins and the narrowed parts of the venous return can also be displayed by magnetic resonance imaging, but placing the affected infant in a magnetic resonance instrument has certain risks, and there is currently no research showing that magnetic resonance imaging is superior to the above diagnostic methods.

　　Six, CT and MRI

　　CT and MRI can well display and diagnose pulmonary vein anomalies. The contrast-enhanced magnetic resonance angiography sequence is the best for diagnosing pulmonary vein anomalies. The maximum intensity projection reconstruction from multiple angles, such as sagittal, coronal, and transverse, can directly display the signs of pulmonary vein anomalies, which is very helpful in determining the type of pulmonary vein anomalies and whether there is obstruction. Complete pulmonary vein anomalies with obstruction have a significant impact on the choice of imaging diagnostic methods. Although cardiovascular angiography is the gold standard for diagnosis, it is an invasive examination. Injecting contrast agent into the pulmonary artery can still induce or worsen pulmonary edema, even with non-ionic contrast agents, posing certain risks. After pulmonary angiography, a decrease in arterial oxygen saturation may occur, and the contrast agent in the pulmonary capillary network may empty slowly. Among non-invasive examination methods, spiral CT and multi-slice spiral CT can well display and diagnose pulmonary vein anomalies, but CT also requires the use of iodinated contrast agents. Complete pulmonary vein anomalies with obstruction have certain risks even with CT examination. In addition, if the diagnosis of inferior-type complete pulmonary vein anomalies is not indicated before CT examination, the CT examination usually will not scan the abdomen, which may lead to missed diagnosis. Compared with this, CE-MRA diagnosis of pulmonary vein anomalies shows clear pulmonary veins and systemic veins without the use of iodinated contrast agents, without the risk of inducing or aggravating pulmonary edema, and is more accurate and safer for diagnosing pulmonary vein anomalies.

　　CT and MRI scans can also clearly show indirect signs that are helpful for the diagnosis of pulmonary vein anomalies, such as the enlargement of the right atrium, the enlargement of the right ventricle, the dilatation of the pulmonary artery, and the relatively smaller left ventricle. In addition, for the associated atrial septal defect, dilatation of the coronary sinus, left vertical vein, left innominate vein, and dilatation of the superior vena cava on the right, these can also be well displayed. The relationship between the transverse vein and the left atrium can also be displayed, and the multi-slice spiral CT can best show whether the coronary sinus is dilated.

　　Cardiovascular angiography

　　Pulmonary vein anomaly cardiovascular angiography can be used for selective pulmonary artery angiography or selective pulmonary vein angiography, both methods can achieve good diagnostic effects. Generally, selective pulmonary artery angiography is more commonly used for complete pulmonary vein anomalies, while selective pulmonary vein angiography is more commonly used for partial pulmonary vein anomalies. Whether pulmonary artery angiography or pulmonary vein angiography, the anteroposterior projection is mainly used, and the NIH catheter is selected. After the catheter probe enters the abnormal path, once the tip of the catheter is sufficiently free, contrast medium is injected at a speed of 5-8ml per second, with a dose of 0.5-1.0ml/kg. For selective pulmonary artery angiography, the catheter tip is located at the pulmonary trunk, left pulmonary artery, or right pulmonary artery, and contrast medium is injected at a speed of 15ml per second, with a dose of 1.5ml/kg. However, for obstructive pulmonary vein anomalies, the amount of contrast medium should be reduced appropriately. Digital subtraction angiography (DSA) can greatly help improve the diagnostic effect of selective pulmonary artery angiography. DSA subtracts the image before injecting contrast medium from the image after injecting contrast medium, leaving the image only representing the contrast medium in the heart and blood vessels, eliminating the original overlapping shadows such as bones and soft tissues, making the image clearer and better showing the ectopic pulmonary veins. Taking more images without contrast medium and carefully selecting images with the same respiratory phase for subtraction can help improve the image quality.

　　1. Children with complete pulmonary vein atresia should eat

　　Eat light, low in oil, sugar, salt, and non-spicy food, which is relatively light in taste. From a nutritional perspective, light food can best reflect the true taste of food and preserve the nutritional components of food to the greatest extent. Nutritious, pay attention to dietary balance.

　　2. Children with complete pulmonary vein atresia should avoid eating

　　Avoid spicy and刺激性 food, such as chili and other spicy seasonings.

　　1. Treatment

　　Once the condition of infants and young children is stable, radical surgery should be performed. For infants with severe pulmonary edema, hypoxemia, and low cardiac output, early treatment should include positive pressure ventilation intubation, cardiotonic drugs, diuretics, and correction of metabolic acidosis to stabilize the condition and wait for the opportunity for surgery. If possible, it is best to avoid cardiac catheterization to prevent delays in surgery time and the occurrence of other complications. It is no longer considered necessary to perform balloon atrial septostomy as a palliative procedure. If the ectopic pulmonary veins directly enter the right atrium, the right atrium can be opened, the interatrial septum can be incised, and patches can be used to isolate all left and right pulmonary veins into the left atrium; if the ectopic opening is in the coronary sinus, the interatrial septum between the left atrium and the coronary sinus can be incised, and the opening of the coronary sinus and the atrial septal defect can be sutured immediately, allowing the coronary sinus to drain directly into the left atrium; for patients with superior or inferior type pulmonary vein anomalies, a large side-to-side anastomosis should be made between the pulmonary vein trunk and the left atrium, and the atrial septal defect should be closed, while whether to ligate the pulmonary vein回流 channel remains controversial. Some advocates of open return veins believe that opening the vertical vein can prevent early postoperative left heart hypoplasia and pulmonary vein return obstruction. There have been reports that ligation of the descending venous channel can cause acute liver cell necrosis, so some surgeons suggest not suturing the vein.

　　2. Prognosis

　　If surgical treatment is not performed, the prognosis of the disease is poor. Studies have shown that 80% of patients with this type of disease die within one year of birth. Patients with pulmonary venous obstruction or those with restrictive atrial level communication may even die within a few weeks after birth. The effectiveness of surgical treatment has significantly improved, with the mortality rate of children dropping from 30% in the late 1970s to less than 10% in the late 1980s and early 1990s. The mortality rate after surgery is closely related to the preoperative condition of the child. Children with infradiaphragmatic type, those who require ventilators before surgery, and those with metabolic acidosis have a higher postoperative mortality rate. Early postoperative pulmonary hypertension can occur in children with pulmonary venous obstruction, so inhalation of NO can help dilate the pulmonary arteries and reduce mortality. The efficacy of late-stage treatment is generally good. Occasionally, late-stage pulmonary venous obstruction can also occur, which may be related to postoperative tissue reaction or anastomotic stenosis, but reoperation, balloon dilatation, or using stcnt patches can easily cause blood reflux at this location. A few children may develop arrhythmias later, including sinus bradycardia, atrial flutter, and supraventricular tachycardia, with atrial arrhythmias being the most common.