TOTAL ANOMALOUS PULMONARY VENOUS RETURN (TAPVR)

Total anomalous pulmonary venous return (TAPVR) is a rare congenital heart disease, accounting for 1-2% of all congenital heart defects. In this condition, the pulmonary veins do not connect directly to the left atrium but instead drain into the systemic venous system. This anomaly prevents the direct return of oxygenated blood to the left heart and the systemic circulation, leading to hypoxemia and neonatal cyanosis.

Under normal conditions, the four pulmonary veins convey oxygenated blood to the left atrium, allowing its distribution in the systemic circulation. In TAPVR, the pulmonary veins follow abnormal pathways that lead to mixing of arterial and venous blood, altering the hemodynamic balance.

• Supracardiac: The pulmonary veins drain into a supradiaphragmatic vein, such as the innominate vein, and then into the superior vena cava. This is the most common variant and is less frequently associated with significant drainage obstruction.
• Cardiac: The pulmonary veins drain directly into the right atrium or through the coronary sinus, usually resulting in less severe pulmonary hypertension compared to other variants.
• Infracardiac: The pulmonary veins drain below the diaphragm, usually into the portal vein, hepatic veins, or inferior vena cava. This form is often characterized by severe drainage obstruction, leading to severe pulmonary hypertension.
• Mixed: The pulmonary veins drain into multiple anomalous sites, combining features of the previous variants.

The critical element of TAPVR is the absence of a direct connection between the pulmonary veins and the left atrium, leading to the complete anomalous pulmonary venous return into the systemic circulation. The oxygenated blood from the lungs does not directly reach the systemic circulation but instead enters the right heart, mixing with deoxygenated venous blood.
This phenomenon necessitates the presence of a atrial septal defect (ASD), such as a patent foramen ovale or a large atrial septal defect, which allows a partial passage of oxygenated blood from the right atrium to the left atrium. This condition generates a right-to-left shunt, causing hypoxemia and cyanosis.
In cases where the anomalous drainage is obstructed, the pulmonary venous flow encounters increased resistance, causing pulmonary congestion and severe neonatal pulmonary hypertension. This results in rapid clinical deterioration with severe respiratory distress and hypoxia that is refractory to oxygen therapy. Conversely, if the drainage is not obstructed, the condition may present with milder symptoms, gradually manifesting as progressive heart failure.

Clinical Manifestations

In cases where the pulmonary venous drainage is obstructed, pulmonary venous flow encounters significant resistance, leading to pulmonary congestion and severe neonatal pulmonary hypertension. The neonate presents with severe central cyanosis at birth, poorly responsive to oxygen therapy, associated with severe respiratory distress, tachypnea, and intercostal retractions. Persistent pulmonary hypertension leads to reduced pulmonary compliance with neonatal pulmonary edema, while right heart failure manifests with hepatomegaly and signs of cardiogenic shock in severe cases. When the drainage is not obstructed, symptoms may be milder and insidious. The neonate may exhibit cyanosis of variable severity, often not evident in the first hours of life, followed by feeding difficulties and poor growth in the first months. Progression may lead to congestive heart failure, with hepatomegaly and signs of right heart overload.

Diagnosis

Transthoracic echocardiography with Doppler is the first-line diagnostic method, capable of identifying the anomalous connection of the pulmonary veins, the dilation of the right heart chambers, and the presence of a right-to-left shunt through the atrial septal defect. If echocardiography does not provide a clear picture, cardiac magnetic resonance imaging (MRI) or CT angiography can be used for better visualization of the anomalous pulmonary venous pathways. In complex clinical cases, cardiac catheterization may be necessary to assess pulmonary pressures and shunt magnitude.

Treatment

The only definitive treatment for TAPVR is early surgical correction, which consists of creating a direct connection between the pulmonary veins and the left atrium, eliminating the anomalous drainage. The procedure also includes closing the atrial septal defect to prevent residual right-to-left shunting. In cases of significant venous return obstruction, surgery must be performed urgently, often within the first hours or days of life, to prevent the progression of pulmonary hypertension and hemodynamic deterioration.
In non-obstructed cases, surgical treatment can be planned within the first weeks of life to avoid progressive deterioration of cardiac and pulmonary function.

Prognosis and Follow-up

Surgical mortality in specialized centers is below 5%, but the success of the procedure depends on early diagnosis and appropriate preoperative management. In patients operated on promptly, long-term survival is excellent, with normal growth and development. However, regular follow-up is crucial to monitor the potential development of pulmonary venous return stenosis, a complication that can arise postoperatively.
In conclusion, TAPVR is a critical congenital heart disease requiring early diagnosis and prompt surgical intervention. Surgery is highly effective, but long-term monitoring is essential to ensure optimal outcomes and prevent late complications.

References
1. Agostino D. A., Palatta S., Toscano A., Palamides S., Thomasset R., Minervini B., Vitale S., Di Paolo A. *Ritorno venoso anomalo polmonare totale sopradiaframmatico: l’importanza della valutazione clinica.* Area Pediatrica, 2019; 20(2): 79-81.
2. Ruscazio M., Bassareo P. P., Martis S., Marras A. R., Meloni L. *Il ritorno venoso polmonare anomalo parziale: diagnosi precoce e complicanze postchirurgiche per una patologia rara e di difficile individuazione.* Giornale Italiano di Cardiologia, 2008; 9(7): 513-517.
3. Cincotta A., Gemma P., Arpaia F., Vitale R., Colombo E., Vanzulli A. *Ritorno venoso polmonare anomalo parziale sinistro associato ad ostruzione secondaria della vena anonima.* La Radiologia Medica, 2019; 124(6): 606-610.
4. Karamlou T., Gurofsky R. C., Al S. R., Coles J. G., Williams W. G., Caldarone C. A., Van Arsdell G. S. *Factors influencing early and late outcomes following repair of total anomalous pulmonary venous connection: An analysis of 377 patients.* European Journal of Cardio-Thoracic Surgery, 2007; 31(1): 99-106.
5. Seale A. N., Carvalho J. S., Gardiner H. M., Prasad S. K., Robertson N. J., Uemura H., McCarthy K. P., Ho S. Y. *Total anomalous pulmonary venous connection: Impact of prenatal diagnosis.* Ultrasound in Obstetrics & Gynecology, 2009; 33(1): 43-49.
6. Corno A. F., Botta U., Hurni M., Payot M., Sekarski N., Tozzi P., von Segesser L. K. *Outcome after surgical correction of total anomalous pulmonary venous connection.* The Journal of Thoracic and Cardiovascular Surgery, 2007; 133(3): 665-673.