What Are the Different Types of Fontan Procedures, and What Are Their Associated Issues?

Different surgical techniques have been used over time to restore a series circulation in patients with single ventricle physiology (Figure 69.1). Initially, atriopulmonary Fontan repairs were most common in which the right atrium would be anastomosed to the pulmonary artery. The rationale for this procedure was that the right atrium would become “ventricularized” and serve as a subpulmonic pumping chamber. With time, it became evident that such remodeling did not occur, and that complications such as atrial arrhythmias and thrombus formation were prevalent.

Figure 69.1 Illustration of intra-atrial Fontan (right) and lateral tunnel Fontan (left). SVC and IVC, superior and inferior vena cava, respectively. Illustration by Adam C. Adler, MD.

To minimize the risk of atrial dilation, de Leval et al. introduced the total cavopulmonary anastomosis. Initially conceived as the intracardiac lateral tunnel, this repair brings the superior vena cava to the pulmonary artery, and baffles the inferior vena cava blood to the inferior aspect of the pulmonary artery using an intraatrial conduit. While a small amount of native atrium is retained in this repair to provide growth potential, the risk of atrial arrhythmia and thrombosis is theoretically minimized.

The most recent modification to the Fontan repair has been the introduction of the extracardiac conduit. Here, an interposition graft is placed outside of the heart connecting the transected inferior vena cava and the underside of the pulmonary artery. The impetus for this repair was to avoid pulmonary or systemic venous obstruction in patients with small atria or anomalous venous return. Due to its ease of placement, it has become widely adopted as the technique for Fontan completion. Drawbacks to the extracardiac conduit include a lack of growth potential and a theoretic risk of thrombosis due to the prosthetic graft. Outcomes between the lateral tunnel and extracardiac Fontan have essentially been equivalent.

What Is the Time Frame for Fontan Completion Surgery?

The usual time frame for Fontan completion is between the ages of two to five years. As the patient grows, the percentage of blood return from the lower extremities increases. The blood returning to the lungs from the upper extremities and head becomes a smaller percentage of total venous return and the patient becomes progressively more cyanotic. The ideal age for Fontan completion varies, but attempts to balance the years the patient is cyanotic and the need for revisions, as these conduits do not grow with the patient.

What Is the Purpose of Fenestrating a Fontan, and What Implications Does This Have on Saturation?

A fenestration is a hole created at the time of the Fontan completion between the conduit and the pulmonary venous atrium. This can be accomplished with both the lateral tunnel and extracardiac Fontan. The goal of the fenestration is to maintain cardiac output at the expense of a decrease in saturation in those patients who may be at risk of having significantly elevated Fontan (pulmonary arterial) pressures. This may be the case in patients with elevated pulmonary vascular resistance, ventricular dysfunction, or atrioventricular valve regurgitation.

Because filling of the systemic ventricle is dependent on passive blood flow through the pulmonary vasculature, any factor that adds resistance to this pathway can lead to a decrease in cardiac output and further elevations in both the Fontan and central venous pressures. The fenestration in this setting can be thought of as a “pop-off” valve in situations where these pressures increase. During a period of increased peak inspiration pressure, blood can return to the ventricle through the fenestration which serves as a right-to-left reversible shunt.

Saturations should be in the high 80s to low 90s in patients with fenestrations, with some variability due to the extent of right-to-left shunting across the fenestration.

What Are Other Unique Causes of Desaturation in a Fontan?

Beyond a fenestration, resting saturations <90% may indicate intrapulmonary arteriovenous shunting or the development of systemic venous-to-pulmonary venous collaterals. Both act as extracardiac right-to-left shunts.

Is There Such a Thing as a “Good” Fontan?

The ideal Fontan circulation would have normal sinus rhythm, low atrial pressures, and a low transpulmonary gradient (the difference between the pulmonary arterial pressure and the pulmonary wedge or left atrial pressure).

Implicit in this setting would be preserved systolic and diastolic ventricular function, and no residual inflow or outflow obstructions. Examples of such obstructions to flow include:

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  pulmonary arterial or pulmonary venous stenosis

  
  
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  elevations in pulmonary vascular resistance

  
  
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  atrioventricular valve regurgitation or stenosis

  
  
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  systolic or diastolic ventricular dysfunction

  
  
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  ventricular outflow tract obstruction

  
  
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  aortic insufficiency or stenosis

  
  
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  recurrent coarctation of the aorta

While Fontan circulation provides a means of palliation for patients with single ventricle physiology, significant long-term sequelae remain. Over time, lack of a pumping mechanism providing active preload to the lungs leads to progressive issues. Each time the pulmonary or intrathoracic pressure is elevated (i.e., under stress, exercise, or Valsalva), stress in the form of elevated pressure is placed on the venous circulation. The physiologic consequence of the Fontan is cavopulmonary hypertension with a relative decrease in ventricular preload, stroke volume, and cardiac output. In addition, patients with single morphologic right ventricles develop complications related to a right ventricle ejecting against high pressures.