Anomalous pulmonary venous connection

Embryology

The embryonic rudiments of the lungs, pharynx and tracheobronchial tree originate from the initial part of the primary digestive tube. At an early stage of embryonic development, the vascular plexus of the primary digestive tube - the visceral plexus - surround the rudiments of the lungs. As lung differentiation progresses, part of the visceral plexus forms the pulmonary vascular plexus. Its direct connection with the heart is absent and the pulmonary vessels drain through the visceral plexus.

The final connection of the pulmonary vessels with the heart depends on the connection of the protrusion of the sinoatrial part of the heart (common pulmonary vein) with the pulmonary part of the visceral plexus. This protrusion forms to the left of the developing primary septum. When these formations connect, the primary communications between the pulmonary part of the visceral plexus and the cardinal and umbilical vein systems gradually decrease. 

The pulmonary venous vessels begin to drain through four separate large pulmonary veins into the common pulmonary vein, which flows into the common atrium. The common pulmonary vein is a temporary anatomical formation. In the process of differential growth, it is incorporated into the left atrium in the form of four separate pulmonary veins.

The embryological basis of most pulmonary vein anomalies is impaired development of the common pulmonary vein. If the protrusion of the sinoatrial part of the heart with the pulmonary venous plexus does not connect, the pulmonary veins are drained in a more primitive way through the systemic veins.

Classification

Main forms:

• Partial anomalous pulmonary venous connection (PAPVC);
• Total anomalous pulmonary venous connection (TAPVC);
• Congenital pulmonary stenosis.

By drainage level:

• Infracardiac type;
• Intracardiac type;
• Supracardiac type.

Partial anomalous pulmonary venous connection (PAPVC)

Anatomy

The pulmonary veins most often flow into either the right atrium or the SVC / IVC. The most common variant is PAPVC at the level of the superior vena cava and ASD of the venous sinus type. The right parts of the heart may be slightly enlarged.

Hemodynamics

Hemodynamic disorders are the same as in the presence of ASD - pulmonary blood flow is increased due to blood recirculation through the lungs. Its volume depends on the number of abnormal veins, the presence and size of ASD and the magnitude of pulmonary vascular resistance. Perceptible hemodynamic disturbances occur with an increase in pulmonary blood flow by one and a half times or more.

If one vein is drained into the right atrium or its tributaries, the volume of the left-right shunt is about 20% of the total pulmonary blood flow. This insignificant amount of hypervolemia does not manifest itself clinically.

If all the pulmonary veins, except one, are drained abnormally, the physiology and clinical manifestations correspond to TAPVR. If the veins of one lung flow abnormally, pulmonary blood flow depends on the magnitude of pulmonary vascular resistance and atrial extensibility.

Workup

• Echocardiography, CT. Visualization of the defect. 
• ECG. Often normal results. Signs of overload of the right heart, right bundle branch block can be detected.
• Chest X-ray. Changes characterize the magnitude of the excess blood flow through the right heart. Symptoms may be absent in the neonatal period (high general pulmonary resistance), and manifest as the general pulmonary resistance decreases. Specific signs that indicate an abnormal pulmonary vein connection can be detected. For example, if the pulmonary veins flow into the vena cava superior, its lower part will be dilated, which looks like an expansion of the heart’s shadow above the outline of the right atrium or double density inside the upper edge of the atrium.
• Cardiac catheterization with aortography. It is used in difficult cases for differential diagnosis. The most informative is the introduction of contrast drug into the pulmonary artery. This allows you to detail the anatomy of the path of pulmonary venous blood to the right heart.

Clinical presentation

Clinical manifestations depend on the number of pulmonary veins draining into the right heart. Abnormal connection of one pulmonary vein does not manifest itself clinically. 

Children are usually asymptomatic even with abnormal connection of half of the pulmonary veins. Objective clinical signs correspond to ASD: fixed splitting of the second heart sound.

With the progression of pulmonary hypervolemia and arterial hypertension, clinical symptoms such as poor exercise tolerance, increased fatigue, dyspnea, and repeated respiratory infections appear.

Treatment

The volume of the left-right blood shunt determines indications for surgery. It is indicated if pulmonary blood flow is 1.5 times or more higher than systemic. The optimal age for surgery is 2–5 years. The goal of surgical treatment is to redirect the blood flow to the left heart by creating intracardiac tunnels using patches.

Total anomalous pulmonary venous connection (TAPVC)

Anatomy

According to the clinical classification of Darling et al., 4 types of TAPVC are distinguished depending on the level of drainage of the pulmonary veins:

1. Supracardial - the drainage of the pulmonary veins into the superior vena cava (right or left).
2. Intracardial - drainage of the pulmonary veins directly into the right atrium or into the coronary sinus.
3. Infracardial - drainage of the pulmonary veins into the inferior vena cava or hepatic veins, portal vein, etc.
4. Mixed - a combination of the options described above. 

Hemodynamics

The presence of an atrial septal defect or an open oval window is vital for these patients. 

Arterial and venous blood enters the right atrium, then through the ASD it partially enters the left atrium, and then goes into the systemic circulation. If the communication between the right and left atrium is small, the amount of blood that is shunted into the left atrium is negligible. In addition to the low oxygenation of the systemic blood, its amount is also reduced. The size of the right heart increases. With a large defect between the atria, a sufficient amount of blood enters the systemic circulation and from here vascular resistance of both systemic and pulmonary circulation and the extensibility of the ventricles determine the distribution of blood.

TAPVC without venous obstruction

Due to the fact that vascular resistance is almost equal at birth, the distribution of blood flow between the large and small circles is approximately the same. During the first weeks of life pulmonary vessels develop, pulmonary arterial resistance decrease and the volume of mixed venous blood entering the small circle gradual increase. Pulmonary blood flow is several times higher than systemic. 

As a rule, blood in the right atrium mixes well, so blood saturation in the right ventricle, pulmonary artery, left atrium, left ventricle and aorta is equal to that in the right atrium.

TAPVC with pulmonary venous obstruction

Obstruction of the pulmonary veins increases capillary pressure, which can lead to pulmonary edema. Over time, there is a spasm of arterioles, a decrease in the permeability of the pulmonary capillaries. Over time, pulmonary hypertension develops, the pressure in the right ventricle rises. Due to an increase in pressure in the pulmonary artery system, blood oxygenation and, accordingly, saturation decreases.

Workup

• Echocardiography, CT. Visualization of the defect and localization of the abnormal drainage. Doppler echocardiography can detect the presence of pulmonary veins obstruction.
• ECG. A typical sign of this defect is a high pointed wave ‘P’ in II or in the right leads, which reflects an increased right atrium. The electrical axis of the heart is deflected to the right, signs of right ventricle hypertrophy, manifested by high voltage in the right leads and incomplete right bundle branch block.
• Chest X-ray. Signs of increased pulmonary blood flow. The right atrium and right ventricle are dilated and hypertrophied, the arc of the pulmonary artery swells. In the presence of abnormal drainage of the pulmonary veins into the vena cava superior, its dilatation is manifested by bulging of the right upper edge of the heart shadow. Typical radiological signs are usually absent in the first months of life and are often observed in older children and adults. 
• Cardiac catheterization with aortography. It is performed to clarify important details that were not clarified during the EchoCG study.

Clinical presentation

The clinical presentation depends on the pulmonary vascular resistance, the size of the communication and the functionality of the right ventricle.

TAPVC without pulmonary venous obstruction. Symptoms at birth may be absent. Over time, recurrent respiratory infections, feeding disorders, physical retardation, and symptoms of heart failure are common.

TAPVC with pulmonary venous obstruction. In the first hours of life, symptoms may be absent. Then, progressive shortness of breath, cyanosis, and symptoms of heart failure become specific.

Treatment

Surgical treatment is indicated for all children with this CHD. The aim of the treatment is to direct the pulmonary venous return to the left atrium by creating a connection between the common pulmonary vein and the left atrium, interrupting the connection of the pulmonary vein collector with systemic venous circulation and closing the ASD. 

Before surgery, all four pulmonary veins and their abnormal connection should be identified to exclude a mixed type of defect. The operation is performed under cardiopulmonary bypass. Circulatory arrest is usually necessary due to the intense blood flow from the venous collector. TAPVR with pulmonary venous obstruction is an emergency surgical situation. In the presence of a non-obstructive type of the defect, basic therapy is aimed at the treatment of heart failure, correction of metabolic disorders. Surgical treatment is performed during the first months of life. When a diagnosis of TAPVR with a small / restrictive ASD is established, the Rashkind procedure is performed to increase the volume of blood flow in the pulmonary circulation.

Congenital pulmonary stenosis

Anatomy

Pulmonary veins flow into the left atrium. One, several or all pulmonary veins can be narrowed. The obstruction is based on various mechanisms: it may be a discrete region of middle layer hypertrophy or the proliferation of the intima of the damaged pulmonary vein outside the parenchyma, at the place where it flows into the left atrium. The narrowing can be expressed to varying degrees, up to complete atresia. Intima proliferation is also found in the intrapulmonary sections of the veins in both the affected and healthy lungs. Stenosis of the pulmonary veins is usually accompanied by hypertrophy of the medial layer of arterioles.

Workup

• Echocardiography, CT. Visualization of the defect.
• ECG. Usually reflects hypertrophy of the right ventricle and expansion of the right atrium.
• Chest X-ray. The heart is slightly increased due to hypertrophy of the right ventricle, the arc of the pulmonary artery is enlarged, the pulmonary pattern is asymmetric, with increased vascularization of the intact lung segments.
• Cardiac catheterization with aortography. Pulmonary hypertension is noted. The pulmonary wedge pressure is increased on the side of the obstruction. Angiography can detect the lengthening of the passage time of a contrast drug through the affected lung. 

Clinical presentation

Constant dyspnea and frequent pneumonia inevitably precede right ventricular failure and pulmonary hemorrhage. Most patients are cyanotic.

A physical examination reveals signs of pulmonary hypertension, such as an elevated apex of the heart, and accented pulmonary component of II heart sound. Usually a short systolic murmur is heard.

Treatment

Surgical treatment of stenosis is aimed at eliminating the narrowing and creating an adequate connection of the pulmonary veins with the left atrium.