Partial and Total Anomalous Pulmonary Venous Connection

Etiology

Understanding the normal fetal heart and vasculature development is imperative to appreciate the diverse array of anatomic variations and abnormalities.

At the early stages of embryogenesis, the primordial lung buds are surrounded by the splanchnic plexus, which is the vascular plexus of the foregut. The common pulmonary vein, which forms as an evagination from the heart establishes a connection between the pulmonary plexus and the heart. Subsequently, the connections between the pulmonary venous plexus and the splanchnic plexus involute. The common pulmonary vein gets incorporated into the left atrium (LA), and four pulmonary veins individually connect directly to the left atrium. Failure of the common pulmonary vein or atresia early in its development, while the persistent of the connections between systemic and pulmonary vasculature, leads to the development of TAPVC. If only a portion of the common pulmonary vein, either right or left, becomes atretic, persisting pulmonary-systemic venous connections form PAPVC.

Anatomic Variations

Normal Variants

Normally there are two left and two right pulmonary veins that drain into the posterior wall of the heart.[2] However, the normal anatomical variants may include the confluence of two pulmonary veins draining through a single orifice or multiple branches of the veins, each draining a smaller portion of the lung but all connecting to the left atrium.

Anomalous Connections and Drainage

In anomalous venous connections, pulmonary veins connect abnormally to the systemic venous system. In anomalous venous drainage, the veins connect to the anatomically correct location, but due to an intracardiac defect, there is a mixing of the oxygenated, and the deoxygenated blood and pulmonary veins drain into the right atrium instead of the left atrium.

PAPVC

The most common form of PAPVC is where the left upper pulmonary vein drains into the left innominate vein to ultimately drain into the right atrium. Other forms of PAPVC include pulmonary veins draining into the SVC, coronary sinus, IVC, or azygos veins.

Scimitar Syndrome  

This variant of PAPVC comprises a part of or the entire or part of the right lung being drained by right pulmonary veins that connect to the IVC. The affected lung segments are often hypoplastic or have bronchial anomalies.[3] This syndrome can be associated with other cardiac anomalies such as atrial septal defects and aortopulmonary collaterals.[4] Affected infants have a poorer clinical course as compared to affected adults and children. Most infants may have pulmonary hypertension. In chest radiographs, the anomalous draining vein can be seen parallel to the right heart border, giving the appearance of a Turkish sword ("scimitar").

Sinus venosus atrial septal defects 

They occur due to the absence of the wall separating the right-sided pulmonary vein from the superior vena cava leading to the mixing of oxygenated blood from the pulmonary vein into the systemic venous system. The right side pulmonary veins are connected normally to the left atrium. 

Malposition of the septum primum

Leftward malposition of the septum primum, left to the orifices of right pulmonary veins, leads to their drainage into the right atrium, thereby leading to the anomalous pulmonary venous drainage. This is commonly associated with visceral heterotaxy.[5]

TAPVC

TAPVC implies that all the pulmonary veins connect to the systemic veins or right atrium, either by a common vertical vein or individually. Anatomically TAPVC can be divided into four subtypes based on the level of the anomalous connection as supracardiac, cardiac, infracardiac, and mixed.[6] 

• Supracardiac: Pulmonary veins anomalously connect, most commonly to the left innominate vein. Other locations for connections include SVC and azygos vein.
• Cardiac: Pulmonary veins drain into the coronary sinus or right atrium directly.
• Infracardiac: Pulmonary veins form a vertical vein and drain into the portal vein, hepatic vein, or IVC below the diaphragm 
• Mixed: In mixed-type, there is a combination of connections at different levels.

The supracardiac variety is the most common of the TAPVC.[7]

Epidemiology

TAPVC and PAPVC are uncommon congenital anomalies accounting for <1% of all congenital heart diseases.[8]

Pathophysiology

PAPVC

The main physiologic manifestation of PAPVC is similar to atrial septal defect (ASD), which is left to right shunt at the atrial level leading to recirculation of oxygenated blood through the pulmonary vasculature. The increased blood to the left side leads to dilatation of the right atrium and ventricle and increased pulmonary blood flow. The factors that determine the magnitude of left to right shunting include the number and size of the anomalous veins, the site of origin of the anomalous veins, and the size of ASD and the pulmonary vascular resistance.

TAPVC

In TAPVC, the entire oxygenated blood from the lungs returns to the right atrium. Therefore, communication between the left and right atrium is crucial for survival in TAPVC. Mixing of the oxygenated and deoxygenated blood occurs in the right atrium, which is then shunted right to the left at the level of atria. Therefore, the left atrium and aorta get mixed blood, which leads to cyanosis in patients with TAPVC.

TAPVC Without Obstruction

Supracardiac and cardiac type TAPVC are usually non obstructed. At birth, the pulmonary and systemic vascular resistances are similar. However, in the early weeks of life, there is a significant drop in pulmonary vascular resistance, leading to increased recirculation of flow in the lungs causing pulmonary over circulation. Progressive right atrial and ventricular dilation ensue. Pulmonary vascular changes over time can lead to pulmonary hypertension and right heart failure.

TAPVC With Obstruction

Infracardiac type is the most common cause of obstructive TAPVC. Pulmonary venous obstruction can occur at the level of the diaphragm, vein entering the IVC, or in the hepatic sinusoids.  Elevated pressures in the pulmonary venous system are transmitted to the lung bed leading to pulmonary edema. This, in turn, can lead to pulmonary vascular resistance, pulmonary hypertension, right ventricular hypertrophy, and right-sided heart failure. The obstructive TAPVC is usually present in the neonatal period as severe respiratory distress.[9]

History and Physical

PAPVC

Clinical presentation, similar to ASD, widely varies based on the degree of left to right shunt and associated cardiac defects.

PAPVC is also commonly associated with other cardiac anomalies, often ASD. The incidence of PAPVC is higher in patients with Turner’s syndrome.[10]

PAPVC Associated with an Atrial Septal Defect

Patients with a small degree of the shunt are usually asymptomatic, and a murmur can incidentally be found on physical exam. Moderate to large shunt leads to symptoms during childhood, but commonly these patients present with dyspnea, exertion, and other symptoms of heart failure by third to fourth decade. In late adulthood, if left untreated, a minority of patients may develop significant pulmonary hypertension leading to a reversal of shunting and development of cyanosis.

On physical exam, the findings are similar to atrial septal defects like a wide split fixed S2 and an ejection systolic murmur best heard at the left sternal border with radiation to both upper lungs. This is due to the increased flow across the pulmonary valve. There is an absence of a pulmonary systolic ejection click, unlike pathological pulmonary valve defect.  

Isolated PAPVC

One anomalous pulmonary vein usually is not clinically significant. In patients with multiple anomalous veins, clinical presentation depends upon the degree of left to right shunt and is similar to the presentation of ASD, and PAPVC with ASD.

TAPVC

TAPVC Without Pulmonary Venous Obstruction

Patients can be asymptomatic at birth. Symptoms due to pulmonary over circulation usually begin in the first few days of life. Infants can have dyspnea, feeding difficulties, and failure to thrive. The degree of cyanosis is variable, and some patients may have mild, clinically inapparent cyanosis. 

Later on, patients develop right ventricular hypertrophy and features of right ventricular failure.

Physical exam findings include fixed split S2, systolic ejection murmur, and cyanosis. Features of right ventricular hypertrophy and/or failure like right ventricular heave, loud P2, hepatomegaly, and third heart sound may be present.

TAPVC with Pulmonary Venous Obstruction

Patients with obstructed TAPVC usually present with severe respiratory distress and cyanosis in the newborn period.

Physical exam findings can include hypoxia, hypotension, and tachypnea. This is one of the common differentials for persistent pulmonary hypertension of newborns. These neonates are usually sick and require urgent surgeries.

TAPVC usually occurs as an isolated cardiac lesion, but it can also be associated with other congenital heart defects. The incidence of TAPVC is higher in patients who have heterotaxy with polysplenia or asplenia.[11]

Evaluation

Diagnostic interventions are as follows:

PAPVC[12]

Electrocardiography

ECG is oftentimes normal. It may show peaked P waves representing right atrial enlargement or rR’ pattern and the rSR’ pattern.

Chest Radiography

Chest radiograms may show cardiomegaly or increased pulmonary vascular markings. Based on the site of anomalous connections there could be the prominence of IVC or SVC shadows. In Scimitar syndrome, the course and coalescence of the scimitar veins are seen as a shadow (scimitar appearance of the chest radiograph). 

Echocardiography

Detailed imaging of all the cardiovascular structures including pulmonary veins using 2D and doppler flow is the key to diagnosis.

Other imaging modalities including Computed Tomography and Magnetic Resonance Imaging may be required to diagnose the course of the individual pulmonary veins. 

Cardiac Catheterization

Cardiac catheterization can provide a definitive diagnosis but is usually not necessary with the advent of the newer non-invasive imaging modalities.

TAPVC 

Electrocardiography

Right axis deviation and right ventricular hypertrophy are often present. In TAPVC without obstruction tall peaked P waves in lead II, suggestive of right atrial enlargement may also be seen.

Chest Radiography

In patients with TAPVC without obstruction, cardiomegaly may be seen. A characteristic figure of 8 or snowman appearance of the heart can be seen in supracardiac TAPVC. In patients with obstructed TAPVC signs of pulmonary venous congestion and edema including prominent pulmonary vascular markings, reticular opacities, and Kerley B lines can be seen.

Echocardiography

A thorough 2D and doppler interrogation are important for the diagnosis of TAPVC. It is important to image all the pulmonary veins and their course, determine if there is any obstruction to the pulmonary venous drainage and evaluate for interatrial communication or a persistent ductus arteriosus.

All patients with TAPVC have features of right ventricular overload. The right atrium and the right ventricle are enlarged. The most important finding is the inability to demonstrate the drainage of pulmonary veins into the LA. The LA can be small. In supracardiac lesions, the SVC or innominate vein may be dilated. When the pulmonary veins drain into the coronary sinus(CS), the CS can get dilated. In the infracardiac variant, TAPVC connections between pulmonary veins and the hepatic vein or portal vein can be demonstrated. The IVC can get dilated as well. One of the most important echo findings is the entire right to left shunting at the atrial septal level. 

Other imaging modalities including CT and MR imaging can also be used for diagnosis, but are usually reserved for patients when Echocardiography is inconclusive or in patients with mixed type of TAPVC when individual veins are hard to see with an echocardiogram. 

Cardiac Catheterization

Non-invasive techniques such as echocardiography, CT, and MR angiograms have largely replaced cardiac catheterization. However, in cases where additional hemodynamic information is be needed, cardiac catheterization can be considered. It can also be performed in individuals who need palliative interventional procedures (e.g. atrial septostomy) or stenting of the obstructive pulmonary vein.

Treatment / Management

PAPVC

Surgical treatment is indicated with the development of symptoms, significant left to right shunt, or evidence of right ventricular dysfunction. Otherwise, patients can be managed conservatively with close follow-up.[13] Most of the patients with sinus venosus type PAPVC need surgical correction by 2-4 years of age. However, if there is only one vein draining abnormally, then they may not need any intervention for their entire life. (B2)

Depending on the anatomy and associated heart defects, the surgical techniques can vary.

TAPVC[14]

Corrective surgery is indicated in all patients with TAPVC as soon as possible, once the clinical condition is stabilized.

Initial medical management with supportive measures can include supplemental oxygen, inotropic support, and mechanical ventilation. Balloon atrial septostomy may be needed rarely in case of restricted patent foramen ovale. In patients with obstructive TAPVC, sometimes stents are placed in the cardiac catheterization laboratory for stabilizing the neonate. This is not a ductal dependent cyanotic lesion, and there is no indication for starting prostaglandins. 

Surgery

TAPVC to coronary sinus: The common wall between the coronary sinus and left atrium is excised, which allows the drainage of blood from pulmonary veins to the LA. The orifice of the coronary sinus is then closed. ASD, if present, is also closed.

In Infracardiac and supracardiac TAPVC, an anastomosis between the left atrium and the pulmonary venous confluence is created. The vertical vein is ligated mostly in the same surgical setting unless there is significant pulmonary hypertension. Various other techniques, including intra-atrial rerouting, have also been used in complex and mixed type TAPVC.[15]

Differential Diagnosis

PAPVC

The clinical distinction between ASD and PAPVC can be difficult. Most children are asymptomatic. Imaging techniques are helpful for an accurate diagnosis. A single atrium can also present similar to PAPVC. 

TAPVC

The differential diagnoses for TAPVC includes the following:

1. Obstructed TAPVC

• Respiratory Distress Syndrome: Signs typically begin after birth, unlike TAPVC, where the presentation is slightly delayed (typically occurring after 12 hours of life).
• Persistent pulmonary hypertension of the newborn

     2. Unobstructed TAPVC:

• Large ASD, VSD
• Truncus arteriosus
• AV canal defects 
• Single ventricle lesions

Prognosis

PAPVC

Patients with a single anomalous vein and an intact atrial septum usually remain asymptomatic. The presence of untreated larger left to right shunts can lead to pulmonary vascular remodeling and subsequent development of pulmonary hypertension. Surgical corrections of PAPVC have good outcomes with a low complication rate and typically lead to an immediate resolution of symptoms. Infants with Scimitar syndrome have a poorer outcome due to complex anatomy and the presence of other co-existing cardiac anomalies.

TAPVC

In untreated patients, TAPVC is almost always fatal within the first few weeks of life. The long term survival in patients has increased with the improvement in medical management and surgical techniques.

Postoperative Course

The risk factors for increased mortality include younger age at surgery, associated cardiac lesions, hypoplastic pulmonary veins, postoperative pulmonary hypertension, and postoperative pulmonary venous obstruction (PVO).[7]

Complications

PAPVC

Untreated PAPVC, in the long term, can lead to pulmonary hypertension and right ventricular failure.

TAPVC

Postoperative complications can include pulmonary hypertension, cardiac arrhythmias, PVO, and failure to wean from the bypass.

Postoperative PVO

• Pulmonary venous obstruction is an important cause of late mortality in patients with TAPVC and is the most common reason for reoperation. PVO after repair remains difficult to treat with mortality of around 40% by three years. Preoperative risk factors include hypoplastic pulmonary veins and mixed connection. It is, therefore, important to serially monitor these patients.[7]