Left-sided Superior Vena Cava

The left-sided superior vena cava (LSVC), also known as persistent left superior vena cava (PLSVC), represents a common anomaly of the systemic venous system. While typically considered a normal variant when isolated and draining into the coronary sinus, its presence, especially in combination with other cardiac defects or abnormal drainage, carries significant clinical implications.

1. Definition and Prevalence: 

A persistent LSVC is the most common systemic venous anomaly. It is observed in approximately 0.3% of the general population when coexisting with a normal right superior vena cava (RSVC). Its incidence is higher in children with congenital heart defects, occurring in 3% to 5% of these patients.

2. Embryological Basis 

The persistent LSVC results from the failure of regression of the left anterior cardinal and left common cardinal veins during embryonic development. The levoatrial cardinal vein also represents an embryologic connection.

3. Anatomy and Drainage Patterns 

The drainage site of a persistent LSVC is crucial for determining its clinical significance:

• Drainage to the Right Atrium (RA) via the Coronary Sinus:

  • In the vast majority of cases (92%), the persistent LSVC drains into the right atrium through an intact coronary sinus. This is generally considered a normal anatomical variant and is typically devoid of clinical symptoms or hemodynamic consequences because all systemic venous return ultimately reaches the right atrium.

  • The LSVC in this configuration usually courses anteriorly to the left pulmonary artery and aortic arch, passing between the left atrial appendage and left pulmonary veins before entering the coronary sinus within the left atrioventricular groove.

  • A dilated coronary sinus is a characteristic echocardiographic finding that often indicates the presence of a persistent LSVC.

  • A connecting vein between bilateral superior venae cavae (LSVC and RSVC) is present in about 60% of cases. The size of this connecting vein is inversely proportional to the size of the persistent LSVC.

  • In rare instances, the RSVC may be absent, leading to the LSVC becoming the sole channel for superior caval drainage. These patients may have a higher incidence of atrial arrhythmias.

• Drainage Directly into the Left Atrium (LA):

  • In approximately 8% of cases, the persistent LSVC drains directly into the left atrium.

  • This drainage pattern usually results from the absence or unroofing of the coronary sinus.

  • When the LSVC drains directly into the LA, it can cause systemic arterial desaturation (cyanosis), as unoxygenated systemic venous blood bypasses the pulmonary circulation and enters the systemic arterial circuit.

  • If there is no connecting vein between bilateral SVCs and no interatrial communication, patients present with decreased oxygen saturation early in infancy.

  • If a connecting vein exists with a small or absent interatrial communication, the LSVC can decompress blood from the LA into the right SVC and RA, which are lower-pressure chambers. This phenomenon is characterized by retrograde (cephalad) flow along the left SVC. This flow pattern constitutes a left-to-right shunt, similar to an atrial septal defect or partial anomalous pulmonary venous return, and can lead to right ventricular volume overload.

• Other Drainage Patterns:

  • Rarely, a persistent LSVC may drain via a left pulmonary vein, representing a partially persistent left SVC.

  • In cases of right isomerism, a LSVC can exceptionally connect directly to the roof of a common atrium, with an associated absence of the coronary sinus.

4. Associated Conditions 

Persistent LSVC is frequently found alongside other congenital heart defects and extracardiac anomalies:

• It is seen in 20% of patients with Tetralogy of Fallot.

• It is more common in patients with tricuspid atresia than in normal hearts.

• In hypoplastic left heart syndrome (HLHS), a persistent LSVC is present in about 5% of cases.

• It can be associated with common atrioventricular canal defects.

• Complex cardiac defects such as cor biloculare (one atrium and one ventricle), conotruncal abnormalities, and asplenia syndrome are commonly associated when the LSVC drains directly to the LA.

• Atrial septal defects (single atrium, secundum ASD, primum ASD) are also frequently co-occurring anomalies.

• Patients with a single LSVC (especially in the absence of a RSVC) may have a significantly higher incidence of atrial arrhythmias compared to those with bilateral SVCs.

• When a persistent LSVC is found in combination with other cardiac defects, there is a high incidence of extracardiac anomalies.

• When a LSVC is seen in fetal life, coarctation must be ruled out. 

5. Clinical Significance and Pathophysiology

• Isolated LSVC to Coronary Sinus/RA: As noted, this variant generally has no clinical consequences and individuals are asymptomatic.

• LSVC to Left Atrium: This connection leads to the shunting of deoxygenated systemic venous blood into the left side of the heart, resulting in cyanosis. Even as an isolated lesion, it poses a risk for paradoxical embolus, cerebrovascular accident, and intracranial abscess.

• Surgical Planning: Identifying a persistent LSVC is crucial before cardiac surgery, as it can impact the cannulation approach during the initiation of cardiopulmonary bypass. In procedures like the bidirectional Glenn, if bilateral SVCs lack a connecting vein, bilateral cavopulmonary anastomoses may be required. Failure to recognize the LSVC can lead to a persistent right-to-left shunt and continued desaturation post-surgery (deoxygenated blood entering the systemic atrium who is supposed to receive the oxygenated pulmonary venous blood).

• Obstruction: Occasionally, the LSVC may course behind the left pulmonary artery, passing between it and the left bronchus. This anatomical arrangement, sometimes referred to as the "anatomic vise," can lead to obstruction of the LSVC, affecting venous return.

• Management: If a well-developed connecting vein is present, surgical ligation of the LSVC may be performed. For LSVC draining directly into the LA, surgical repair is often indicated, which might involve ligation of the LSVC or its reimplantation into the RA or pulmonary artery. Creating an intra-atrial baffle to redirect flow is also a preferred surgical approach. Ligation of a LSVC when there is coronary sinus ostium atresia or stenosis may lead to severe myocardial complications.

6. Echocardiographic and Imaging Features 

Echocardiography is the primary modality for diagnosing persistent LSVC:

• Dilated Coronary Sinus: The most common echocardiographic clue is the presence of a dilated coronary sinus. This can be visualized on parasternal long-axis or apical four-chamber views. It is the most frequent cause of coronary sinus dilation.

• Direct Visualization: A LSVC can be directly visualized using suprasternal notch cross-sectional echocardiography, where it appears as a vascular structure on the left side of the transverse aorta. A short-axis view at the base of the heart may also reveal it alongside the transverse aorta.

• "Three-Vessel View": In the "three-vessel view" (which typically shows the main pulmonary artery, aorta, and superior vena cava), a persistent LSVC can be identified as a "fourth vessel" located to the left of the pulmonary artery.

• High Left Parasagittal View: A high left parasagittal view provides good delineation of the LSVC and its continuity with the coronary sinus.

• Suprasternal Short-Axis View: This view can display both the LSVC and RSVC, and their relationship to the ascending aorta. If present, a connecting vein can often be visualized in this view.

• Color Doppler Flow Mapping:

  • Color mapping sweeps in a subcostal short-axis (sagittal) view can demonstrate supero-inferior flow from both SVCs into the heart.

  • Doppler interrogation helps confirm the low-velocity venous flow pattern characteristic of the LSVC, aiding in differentiation from other nearby vascular structures like a branch pulmonary artery or the left atrial appendage.

  • If the LSVC drains directly to the LA, antegrade flow (towards the LA) will be observed along its course. Conversely, if a connecting vein is present and blood is decompressing from the LA, retrograde (cephalad) flow may be seen in the LSVC.

• Contrast Echocardiography: Injecting agitated saline into a left arm vein will cause the appearance of contrast in the dilated coronary sinus before it reaches the right atrium (if draining to the CS). If the LSVC drains directly to the LA, contrast will appear in the LA first.

• Prenatal Diagnosis: In fetal life, persistent LSVC is often suspected when a dilated coronary sinus is observed in four-chamber and long-axis views of the left ventricle. The LSVC itself can be identified in cross-section as an additional vessel left of the pulmonary artery in the prenatal three-vessel view.

7. Management Considerations 

While an isolated LSVC draining to the coronary sinus requires no specific management, its identification is crucial for surgical planning, particularly in complex congenital heart disease cases. Surgical intervention may be necessary if the LSVC causes significant shunting to the left atrium leading to cyanosis or right ventricular volume overload, or if it is obstructed.

References:

• Moore KL, Persaud TVN, Torchia MG. The developing human-clinically oriented embryology. 10th ed. Philadelphia, PA: W.B. Saunders; 2016

• Allen HD, Driscoll DJ, Shaddy RE, Feltes TF. Moss & Adams’ heart disease in infants, children, and adolescents: including the fetus and young adult. Philadelphia, PA: Lippincott Williams and Wilkins; 2011.

• Rudolph AM. Congenital diseases of the heart: clinical-physiological considerations. 3rd ed. Philadelphia, PA: Wiley-Blackwell; 2009.

• Lintermans J. 2D echocardiography in infants and children. Boston, MA: Kluwer Academic Publishers.

• Lopez L, Colan SD, Frommelt PS, et al. Recommendations for quantification methods during the performance of a pediatric echocardiogram: a report from the Pediatric Measurements Writing Group of the American Society of Echocardiography Pediatric and Congenital Heart Disease Council. J Am Soc Echocardiogr. 2010;23:465–95.

• Butera G, Chessa M, Eicken A, Thomson J. Cardiac Catheterization for Congenital Heart Disease: From Fetal Life to Adulthood. Milan, Italy: Springer-Verlag Italia; 2015.

• Bergersen L, Foerster S, Marshall AC, Meadows J, editors. Congenital Heart Disease, The Catheterization Manual. New York, NY: Springer Science+Business Media; 2009.

• Grattan M. Atrioventricular Septal Defect. In: Dipchand AI, et al., editors. Manual of Cardiac Care in Children. Cham, Switzerland: Springer Nature Switzerland AG; 2024.

• Goldstein BH, Petit CJ, Qureshi AM, et al. Comparison of management strategies for neonates with symptomatic tetralogy of fallot. J Am Coll Cardiol. 2021;77(8):1093–106.

Echocardiography Example

Short axis views. We can appreciate the branch pulmonary arteries. We can also visualize the pulmonary veins draining into the left atrium. The Right sided SVC is also seen near the aorta in colour (red flash). We can appreciate the "3-vessels" view: R-SVC, Aorta, PA. R-SVC is smaller than aorta, who is smaller than MPA. 

4 chamber view looking at the right atrium and the dilated coronary sinus. 

Subcostal views outliing the left-sided SVC entering via the coronary sinus. 

Suprasternal view outlines the 2 SVC.

Aortic Arch View to rule out coarctation, which can be associated with a L-SVC