Case May 2025 - Supradiaphragmatic TAPVR

Case Prepared by Dr Gabriel Altit

Summary: This case presents a newborn with supracardiac-type TAPVR and reverse differential saturation, secondary to preferential streaming of superior vena cava (SVC) flow towars the right ventricle. In this anatomical variant, pulmonary venous return is collected into a confluence (collector) that drains via a vertical vein into the innominate vein. The resulting SVC flow—now enriched with oxygenated pulmonary venous blood—streams preferentially toward the tricuspid valve and the right ventricle, effectively increasing its oxygen content. The ductus arteriosus exhibits bidirectional flow, contributing to the phenomenon of reverse differential saturation by delivering relatively more oxygenated blood to the descending aorta (post-ductal). To help visualize this physiology, I have included schematics using a color-coded approach: Shades of blue to represent deoxygenated blood; Purple for mixed blood; Progressively deeper reds to illustrate increasing oxygen saturation. The case is accompanied by a detailed echocardiographic review, with annotated clips and explanatory legends. We also take this opportunity to review the differential diagnosis of reverse differential saturation (or reversed differential cyanosis). Three additional schematics are included to illustrate other possible etiologies: d-Transposition of the Great Arteries (d-TGA) with coarctation of the aorta; d-TGA with interrupted aortic arch; d-TGA with PPHN, where pulmonary vascular resistance exceeds systemic vascular resistance. All three conditions favor a right-to-left shunt across the PDA, delivering oxygenated pulmonary arterial blood into the descending post-ductal aorta—thus mimicking the saturation profile seen in this TAPVR case.

Upon arrival of the transport team, the infant was hemodynamically stable on CPAP 7 with FiO₂ 50%, and oxygen saturation ranged between 65–85%. A reverse differential saturation was observed, with a 10% difference between pre- and post-ductal oxygen saturations. Prostaglandin E1 (PGE1) infusion was initiated at 0.01 mcg/kg/min due to clinical suspicion of a ductal-dependent congenital heart lesion. On admission to our unit, the baby’s vital signs included HR 155 bpm, BP 59/25 mmHg (MAP 39), temperature 36.8°C, and oxygen saturations of 70% pre-ductal and 85% post-ductal. Physical exam showed a well-appearing term infant with a normal anterior fontanelle, no dysmorphic features, and intact palate. Echocardiography was performed urgently to delineate the underlying cardiac anatomy and guide further management.

Final diagnosis: Supracardiac type of Total Anomalous Pulmonary Venous Connection (TAPVC), non-obstructed. All four pulmonary veins drain into a confluence posterior to the left atrium. The confluence connects via an unobstructed left vertical vein into the innominate vein. There is the presence of a small secundum Atrial Septal Defect (ASD), measuring 0.55 x 0.58 cm. There is right-to-left shunting at the atrial level. There is a PDA present, with bidirectional flow. Mild pulmonary artery and right ventricular dilation likely secondary to increased pulmonary blood flow. 

Echocardiography pearl: Right to Left Inter-Atrial Shunt. 

When observing an inter-atrial shunt that is fully right to left, one must rule out these conditions:

1. Total anomalous pulmonary venous return/connection. All the pulmonary blood flow drains to the right atrium, as well as the systemic venous return.

2. Pulmonary Atresia with Intact Ventricular Septum (PA-IVS)

3. Tricuspid atresia

4. Severe Ebstein's Anomaly with significant tricuspid insufficiency

5. RV failure with high end-diastolic RV pressure: 

   1. Pulmonary hypertension

   2. Severe RV hypertrophy (Noonan, pre-natal ductal closure, hypertrophic cardiomyopathy). In situation where there is RV hypertrophy secondary to RVOT obstruction, the patient may still have RV hypertrophy after opening of the outflow tract (i.e.: balloon valvuloplasty dilatation of critical pulmonary stenosis). In these cases, the baby may still be with lower systemic saturation due to persistent right to left inter-atrial shunt after the procedure. As the RV remodels, the RV-end diatolic pressure drops. Reminder here that the atriums will equalize pressure with their corresponding ventricle during diastole, when the atrioventricular valves are open.  

6. Torrential flow coming back to the RA, increasing RA pressure: hepatic arterio-venous malformation, VOGM, other intra-cranial AV malformation. 

7. RV hypoplasia: morphological small RV, tuberous sclerosis with rhabdomyoma obliterating the RV cavity. 

8. RVOT obstruction: pulmonary valvular stenosis, TOF with RVOT obstruction, pulmonary valvular atresia (however, the VSD may be able to decompress the RV and the right atrial pressure may not necessarily rise). 

Reverse differential saturations - the differential diagnosis

d-TGA with PPHN, coarctation or interrupted aorta

In d-transposition of great arteries, there are 3 scenarios during which there can be reversed differential saturations. 

1. Scenario 1 - d-TGA with Coarctation of the Aorta or Scenario 2 - d-TGA with Interrupted Aortic Arch: 

   1. Deoxygenated blood enters the Right Atrium, the Right Ventricle, and reaches the ascending aorta.

   2. Oxygenated blood enters the Left Atrium, the Left Ventricle, the Pulmonary Artery. Because the duct is patent and there is a coarctation or interrupted aortic arch with underfilling / empty descending post-ductal aorta, this promotes PA to Aorta shunting. Hence, more oxygenated blood (relative to the ascending aorta) enters the descending aorta. 

2. Scenario 3 - TGA with Suprasystemic Pulmonary Vascular Resistance: 

   1. Deoxygenated blood enters the Right Atrium, the Right Ventricle, and reaches the ascending aorta.

   2. Oxygenated blood enters the Left Atrium, the Left Ventricle, the Pulmonary Artery. Because the duct is patent and the PVR >> SVR, this favours PA to Aorta shunting. Hence, more oxygenated blood (relative to the ascending aorta) enters the descending aorta. 

Echocardiography of a supracardiac TAPVR

In these subcostal short axis views, we can appreciate again the significant SVC flow coming back to the right atrium. We can also observe the pulmonary venous confluence that drains the pulmonary veins behind the left atrium. 

Colour mode delineates the 4 pulmonary veins.

Views outlining the pulmonary venous drainage to the collector that brings the pulmonary venous flow to the left-sided vertical vein (red).

Another case report example outlining the same physiological concepts:

Yap SH, Anania N, Alboliras ET, Lilien LD. Reversed differential cyanosis in the newborn: a clinical finding in the supracardiac total anomalous pulmonary venous connection. Pediatr Cardiol. 2009 Apr;30(3):359-62. doi: 10.1007/s00246-008-9314-0. Epub 2008 Oct 16. PMID: 18923862. PDF available here.