What is fenestration in the Fontan procedure?

What is Fenestration in the Fontan Procedure?

A Fontan fenestration is a surgically created right-to-left shunt or "pop-off" valve in the Fontan circuit that allows systemic venous blood to bypass the pulmonary circulation and enter the systemic circulation, thereby maintaining cardiac output and reducing systemic venous pressure at the expense of arterial oxygen saturation. 1

Purpose and Mechanism

The fenestration functions as a pressure relief mechanism in patients with single-ventricle physiology who have undergone Fontan palliation. 1 Specifically:

• Creates an intentional right-to-left shunt at the atrial level that allows deoxygenated blood to reach the systemic circulation 1
• Maintains cardiac output in patients with borderline Fontan physiology or anatomy, including those with diminished ventricular function, pulmonary artery distortion, or elevated pulmonary vascular resistance 1
• Reduces systemic venous hypertension by providing an escape route when Fontan pathway pressure becomes elevated 1

Clinical Benefits

The American Heart Association guidelines identify several potential advantages of fenestration creation 1:

• Improved operative survival for high-risk patients undergoing Fontan conversion
• Decreased chest tube drainage in the postoperative period (55% reduction in total drainage) 2
• Shorter hospital stays (41% reduction in hospitalization time) 2
• Improved cardiac output and lower incidence of arrhythmias in late follow-up
• Fewer additional postoperative procedures (67% reduction) 2

Trade-offs and Risks

The hemodynamic benefits come with important compromises 1:

• Systemic arterial desaturation due to mixing of deoxygenated blood with oxygenated blood
• Risk of paradoxical thromboembolism if fenestration remains patent long-term, given the obligatory atrium-level shunt in the setting of cyanosis and low-flow venous circulation 1
• Potential for increased hypoxemia that may contribute to multiorgan dysfunction 1

Evolution of Practice

Current practice has evolved significantly regarding fenestration use 3, 4:

• Selective rather than routine use: In 2002,87.5% of Fontan patients received fenestrations, compared to only 6.3% in 2008 3
• Extracardiac conduit considerations: Fenestration is not necessary in most patients when an extracardiac conduit technique is used, and should be assessed after cardiopulmonary bypass when hemodynamics can be evaluated accurately 4
• Risk stratification determines need: Patients with higher preoperative pulmonary vascular resistance, higher common atrial pressure, and other risk factors are more likely to benefit 4

Closure Strategy

The ultimate goal remains complete separation of systemic and pulmonary circulations 1. Closure is typically performed via transcatheter techniques:

• Timing: After the immediate postoperative period, once hemodynamics stabilize 1
• Testing protocol: Complete hemodynamic catheterization with temporary occlusion for 10-20 minutes to assess tolerance 1
• Acceptable hemodynamics for closure: Improved systemic oxygen saturation with only modest rise in Fontan pressure or fall in cardiac output 1
• Devices used: ASD occluders, patent foramen ovale occluders, VSD occluders, embolization coils, vascular plugs, or covered stents 1

AHA Recommendations

The American Heart Association provides a Class IIa recommendation (Level of Evidence C) that it is reasonable to consider transcatheter closure of a chronic Fontan fenestration if the patient has favorable hemodynamics and tolerates test occlusion. 1

Emergency Indications

In the immediate postoperative setting, fenestration creation or enlargement may be indicated 1:

• Class IIa recommendation: Atrial septostomy to augment cardiac output is indicated for immediate postoperative patients with nonfenestrated Fontan (or inadequate fenestration) who have low cardiac output secondary to elevated pulmonary vascular resistance unresponsive to medical therapy 1
• Chronic failure: May also be considered for patients with chronically failing Fontan physiology or protein-losing enteropathy 1

Common Pitfalls

• Leaving fenestrations patent indefinitely increases thromboembolic risk without clear long-term benefit 1
• Routine fenestration in all patients is no longer justified given excellent outcomes without fenestration in standard-risk patients 3, 4
• Inadequate hemodynamic assessment before closure can lead to Fontan failure 1