During a pediatric cardiology rotation, you review the autopsy findings of a 2-month-old infant who died from severe cyanosis and pulmonary hypoplasia. The pathologist identifies complete mixing of systemic and pulmonary venous blood at the atrial level. Which is the most common type of total anomalous pulmonary venous return (TAPVR) in this case?

## Most Common Type of Total Anomalous Pulmonary Venous Return **Key Point:** Supracardiac (SVC) type TAPVR is the most common variant, accounting for 45–50% of all TAPVR cases. ### Classification of TAPVR by Drainage Site | Type | Frequency | Drainage Site | Associated Finding | CXR Sign | | --- | --- | --- | --- | --- | | **Supracardiac (SVC)** | 45–50% | Right SVC or left brachiocephalic vein | Partial anomalous PVR common | Snowman/figure-of-8 | | **Cardiac (CS)** | 25–30% | Coronary sinus | Associated with heterotaxy | Straight left heart border | | **Infracardiac (IVC)** | 20–25% | Descending aorta or portal vein | Pulmonary hypoplasia, pulmonary stenosis | Increased vascularity | | **Mixed** | 5–10% | Multiple sites | Rare | Variable | ### Pathophysiology of Supracardiac TAPVR ```mermaid flowchart TD A[All pulmonary veins drain to SVC/brachiocephalic vein]:::outcome A --> B[Complete mixing of oxygenated and deoxygenated blood at RA]:::outcome B --> C[Obligatory ASD/PFO for survival]:::action C --> D[Right-to-left shunt across ASD]:::outcome D --> E[Systemic desaturation and cyanosis]:::urgent F[Increased pulmonary blood flow] --> G[Pulmonary edema and heart failure]:::urgent B --> F ``` ### Clinical Features of Supracardiac TAPVR **High-Yield:** Supracardiac TAPVR typically presents: - Later in infancy (weeks to months) compared to infracardiac type - With mild to moderate cyanosis (SaO₂ 75–85%) - Signs of congestive heart failure (pulmonary edema, hepatomegaly) - "Snowman" or "figure-of-8" sign on CXR (pathognomonic) ### Diagnostic Features **Clinical Pearl:** The snowman sign is created by the vertical vein (left brachiocephalic vein) and dilated SVC forming the upper part of the figure-8, with the heart forming the lower loop. This is highly specific for supracardiac TAPVR. **Mnemonic: SCIFI = Supracardiac = Commonest, Figures-of-8, Infants (later presentation)** ### Management - **Acute:** PGE1 to maintain ductus arteriosus patency; balloon atrial septostomy (Rashkind procedure) to improve mixing - **Definitive:** Surgical anastomosis of common pulmonary vein to left atrium (typically within first weeks of life) ### Why Supracardiac is Most Common **Key Point:** Embryologically, supracardiac TAPVR results from failure of the common pulmonary vein to develop and connect to the left atrium, with the pulmonary veins draining into the sinus venosus system — a relatively common embryological error.