The pendulum of Fontan fenestration

In the 50 years since the introduction of the Fontan procedure for single ventricle palliation (1), the clinical indications as well as the surgical techniques have substantially evolved.

Initially the indication for Fontan completion was following the “Ten Commandments”: (I) age <4 years; (II) presence of sinus rhythm; (III) normal systemic venous return; (IV) normal right atrial volume; (V) mean pulmonary artery pressure <15 mmHg; (VI) pulmonary arteriolar resistance <4 Wood Units/m²; (VII) pulmonary/aorta ratio >0.75; (VIII) single (left) ventricle ejection fraction >0.60; (IX) competent mitral valve; (X) absence of pulmonary artery distortion (2).

The preoperative selection criteria for Fontan completion have expanded from the original “Ten Commandments” to a more liberal application, accepting higher-risk patients with “functionally” univentricular hearts (3,4); also including children with a single lung (5).

The decision-making regarding a Fontan fenestration as part of completion has shifted as well, with the pendulum swinging back and forth between infrequent utilization to near universal use over time.

Hillel Laks (6) introduced the concept of an “adjustable atrial septal defect” to temporarily reduce the excessively elevated systemic venous pressure after a Fontan procedure and reduce immediate post-operative complications. The name “fenestration”, termed by Nancy D. Bridges (7), was universally adopted to define a surgically created communication between the diverted systemic venous return and the lower pressure pulmonary atrium (Figure 1). With the goal of a shorter post-operative recovery, the use of a Fontan fenestration gained increased attention with both surgical techniques utilized for Fontan completion, lateral tunnel as well as extracardiac connection (8,9).

Figure 1 Drawing of the fenestration, constructed for the lateral tunnel (left) and for the extracardiac conduit (right). Modified from: Téllez L, Rodríguez-Santiago E, Albillos A. Fontan-associated liver disease: a review. Ann Hepatol 2018;17:192-204. SVC, superior vena cava; PA, pulmonary artery; RA, right atrium; FC, fenestrated conduit; IVC, inferior vena cava.

Immediately after its introduction, the indications for a Fontan fenestration were limited to high-risk candidates, as defined by pre-operative mean pulmonary arterial pressure ≥15 mmHg and/or presence of moderate or severe degree of systemic atrio-ventricular valve regurgitation. Fenestration reduced the systemic venous pressure, resulting in increased lymphatic drainage with an associated reduction in pleural effusions. A fenestration also provided adequate preload to the systemic single ventricle which reduced the post-operative low cardiac output state (8). The only available prospective randomized study comparing patients undergoing fenestrated versus non-fenestrated Fontan completion demonstrated a reduction in the length of stay in the intensive care unit and hospital (10).

Because of the positive outcomes, the indication for fenestration was then extended to almost all patients, regardless the level of pre-operative risk, and became commonplace for a Fontan procedure.

However, the benefits of fenestration in the early post-operative period were at the expense of late complications such as lower systemic oxygenation with prolonged cyanosis, risk of long-term systemic thromboembolism, and potential need for later intervention to close the fenestration. Fortunately, following an additional procedure and anesthetic exposure to close the fenestration, patients had improved resting and exercise oxygenation, lowered maximal heart rate during exercise, and increased exercise duration (11-13).

Despite the ability to mitigate the short-term effects, fenestration became limited, as at the beginning of its utilization, to patients with strict requirements, such as increased risks of complications in the immediate post-operative period, as reported by us (14).

Two systematic literature reviews and meta-analysis have focused upon the early outcomes of a Fontan fenestration, demonstrating a mix benefit in the immediate period, with reduced amount of chest drains and subsequent shorter stay in hospital as the only positive aspects (15,16). Our meta-analysis instead focused on late outcomes, with patients requiring either late closure or creation and/or reopening of a fenestration made at the time of Fontan completion (17). We found that, following fenestration closure, there was a significant increase in the mean arterial oxygen saturation of 7.9% [95% confidence interval (CI): 6.4–9.4%, P<0.01], at expense of a significant increase in the mean cavo-pulmonary pressure of 1.4 mmHg (95% CI: 1.0–1.8 mmHg, P<0.01) (17). The literature data for fenestration creation and/or reopening didn’t allow any meaningful conclusion (17).

In addition to clinical study, mathematical and computational fluid dynamic models have also compared flow and hemodynamics for Fontan patients with and without a fenestration (18). These studies have sought to quantify the effects of different sizes of the fenestration (19) as well as alternative designs of Fontan circulation, different from the traditional surgical options (20).

The pendulum has since swung back. There has been a steady increase in the use of Fontan fenestration based on much broader indications. Largely related to better post-operative management, the option of Fontan completion has been extended to different patient populations, including patients undergoing completion at younger age, and with complex congenital heart defects, such as hypoplastic left heart syndrome (21), heterotaxy syndrome (22), and single ventricle physiology with associated total anomalous pulmonary venous connection (23). Because of these changes in the risk stratification of the patients accepted for surgery (24), the cohort of patients presented for Fontan completion are frequently at high risk for a complicated post-operative course. With the increasing complexity of patients undergoing a Fontan, surgical centers have begun to reconsider the use of fenestration and in some centers, especially those accepting the highest risk cases, it is used nearly universally.

As illustrated by the varying pattern of fenestration use, there is a substantial lack of high-quality scientific evidence supporting any therapeutic decision (17,25). Thus, in clinical practice, the decision to perform a fenestration and its size is based on the personal and institutional experience in relationship to the morphologic and pathophysiologic characteristics of a specific patient.

Acknowledgments

Funding: None.

Footnote

Provenance and Peer Review: This article was commissioned by the editorial office, Translational Pediatrics for the column “Pediatric Heart”. The article has undergone external peer review.

Peer Review File: Available at https://tp.amegroups.com/article/view/10.21037/tp-22-562/prf

Conflicts of Interest: All authors have completed the ICMJE uniform disclosure form (available at https://tp.amegroups.com/article/view/10.21037/tp-22-562/coif). The regular column “Pediatric Heart” was commissioned by the editorial office without any funding or sponsorship. AFC serves as an unpaid Deputy Editor-in-Chief of Translational Pediatrics from July 2022 to June 2024. AFC and JDS served as the unpaid Guest Editors of the column. The authors have no other conflicts of interest to declare.

Ethical Statement: The authors are accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved.

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