How do the hemifontan and bidirectional Glenn procedures differ in technique, indications, and outcomes for a child with single‑ventricle physiology?

Hemifontan vs. Bidirectional Glenn: Technical and Clinical Differences

Both the hemifontan and bidirectional Glenn procedures achieve the same physiological goal—connecting the superior vena cava to the pulmonary arteries for stage 2 single-ventricle palliation—but differ fundamentally in their surgical technique and implications for subsequent Fontan completion. 1, 2

Surgical Technique

Bidirectional Glenn (BDG)

• Involves an end-to-side anastomosis of the divided superior vena cava to the undivided right pulmonary artery, creating direct connection where SVC blood flows to both lungs simultaneously 2
• The SVC is transected and its cardiac end is oversewn or ligated 2
• The pulmonary artery remains intact and undivided, allowing bilateral pulmonary perfusion 2
• This is a definitive connection that does not require modification at Fontan completion 1

Hemifontan

• Creates an atriopulmonary anastomosis between the dome of the right atrium and the underside of the right pulmonary artery while maintaining SVC continuity 3
• The SVC remains connected to the atrium but is baffled internally to direct flow toward the pulmonary arteries 3
• Requires patch augmentation to create the connection between atrial tissue and pulmonary artery 3
• At Fontan completion, this patch must be taken down and the connection revised, adding technical complexity to the third stage 3

Key Technical Distinctions

The critical difference is that the bidirectional Glenn creates a permanent SVC-to-PA connection that remains unchanged at Fontan, while the hemifontan requires surgical revision during Fontan completion. 2, 3

• In BDG, the SVC is completely disconnected from the heart and directly anastomosed to the PA 2
• In hemifontan, the SVC maintains anatomic continuity with the atrium through an internal baffle system 3
• The hemifontan technique theoretically preserves more atrial tissue and may facilitate easier Fontan completion in some anatomic scenarios 3

Physiological Outcomes

Both procedures provide identical hemodynamic results during the stage 2 period, with approximately 50% 20-year survival and superior outcomes compared to systemic-to-pulmonary shunts 2

• Both direct SVC blood to bilateral pulmonary arteries, preventing pulmonary arteriovenous malformations that occur with classic Glenn (which only perfuses the right lung) 2, 4
• Both eliminate volume loading on the single ventricle compared to BT shunts 2
• Both require identical pre-operative assessment including cardiac catheterization to evaluate pulmonary artery anatomy and eliminate collateral vessels 2

Clinical Considerations for Procedure Selection

The choice between hemifontan and bidirectional Glenn is primarily surgeon preference and institutional practice, as no high-quality comparative data demonstrates superiority of either technique 1, 2

• Centers performing hemifontan cite theoretical advantages in preserving atrial tissue for future Fontan 3
• Centers performing BDG emphasize the simplicity of avoiding revision at Fontan completion 2
• Both procedures are typically performed at 4-6 months of age as stage 2 palliation 1, 2

Common Pitfalls to Avoid

• Inadequate pre-operative assessment of pulmonary artery anatomy can compromise outcomes with either technique, requiring comprehensive evaluation of PA size, stenoses, and distortion 1, 2
• Failure to identify and address systemic-to-pulmonary collaterals before surgery reduces effectiveness of the cavopulmonary connection 1, 2
• Venovenous collaterals developing post-procedure that drain to the pulmonary venous atrium require transcatheter embolization to prevent cyanosis 1
• Collaterals draining below the diaphragm should be embolized before Glenn but can be left until Fontan completion if the patient is asymptomatic 1

Progression to Fontan

Both procedures serve as intermediate steps toward Fontan completion, which has approximately 90% 10-year survival in optimal candidates 2

• Fontan completion involves connecting the IVC to the pulmonary arteries, completing total cavopulmonary connection 1, 2
• The hemifontan requires takedown of the atriopulmonary patch during Fontan, while BDG anatomy remains unchanged 3
• Pre-Fontan evaluation must confirm mean PA pressure <15 mmHg, preserved ventricular function, and adequate PA size regardless of prior stage 2 technique 1, 2