Fenestrated Fontan #2: Surgical Procedure

1. Operative Objective and Physiologic Rationale

The extracardiac Fontan completes total cavopulmonary connection by directing inferior vena caval blood through a prosthetic conduit to the pulmonary arteries. Because no subpulmonary ventricle drives blood across the pulmonary vascular bed, pulmonary blood flow depends on the pressure gradient between the systemic veins and the pulmonary venous atrium. Even modest elevations in pulmonary vascular resistance, ventricular filling pressure, or intrathoracic pressure can therefore raise systemic venous pressure and reduce ventricular preload.

A Fontan fenestration is a deliberately created communication between the extracardiac conduit and the atrium. It functions as a controlled right-to-left shunt. When Fontan pathway pressure exceeds atrial pressure, a portion of systemic venous blood bypasses the pulmonary circulation and enters the systemic ventricle. This reduces systemic venous pressure and preserves ventricular preload and cardiac output, but necessarily lowers systemic arterial oxygen saturation.

The early clinical value of this pressure-relief mechanism was demonstrated in a prospective randomized study in which fenestration reduced total chest tube drainage by 55%, hospital stay by 41%, and additional postoperative procedures by 67% [1]. Subsequent evidence reviews have generally supported an early postoperative benefit, particularly through fewer pleural effusions, shorter hospitalization, and reduced early Fontan failure, while emphasizing that routine fenestration has not consistently improved long-term outcomes [2].

The operative goal is therefore not merely to create a hole. The surgeon must construct a predictable communication that provides sufficient decompression without producing excessive cyanosis, while preserving an unobstructed Fontan pathway.

2. Completion of the Extracardiac Fontan Pathway

2.1 Conduit-to-Pulmonary Artery Anastomosis

The superior end of the extracardiac conduit is anastomosed to the inferior aspect of the central pulmonary artery confluence. The opening should be sufficiently broad to distribute flow toward both lungs without anastomotic narrowing, conduit angulation, or preferential streaming.

The central and branch pulmonary arteries must be inspected before completing the anastomosis. Residual narrowing related to previous pulmonary artery reconstruction, distortion adjacent to the bidirectional Glenn anastomosis, or asymmetric branch pulmonary artery development should be addressed with patch augmentation when necessary. Pulmonary artery geometry is not a secondary consideration: the minimum pulmonary artery cross-sectional area strongly influences total cavopulmonary connection energy loss and resting cardiac output [3].

The conduit should follow a smooth course without rotation, redundancy, or tension. Its final position must be assessed with the heart filled because an apparently satisfactory conduit may become compressed between the atrium, ventricle, diaphragm, pericardium, or sternum after separation from cardiopulmonary bypass.

2.2 Separation of the Atrium From the Inferior Vena Caval Cuff

The right atrium is divided from the inferior vena caval cuff. The atrial side is closed securely, while an adequate cuff of native tissue is retained for the inferior conduit anastomosis. The closure must be hemostatic and should not narrow the inferior vena cava or distort the adjacent atrial wall intended for fenestration.

The inferior vena caval opening should remain wide and circular. Excessive tissue incorporation or uneven suture tension may purse-string the cuff and create a fixed obstruction immediately proximal to the conduit. Such narrowing increases hepatic and systemic venous pressure and cannot be compensated for by the fenestration.

2.3 Conduit-to-Inferior Vena Caval Anastomosis

The inferior end of the extracardiac conduit is anastomosed to the inferior vena caval cuff. The suture line should create a smooth transition without step-off, torsion, or narrowing. Conduit length must be sufficient to avoid tension but not excessive enough to permit kinking.

The conduit should be oriented so that one surface lies directly adjacent to a suitable portion of the atrial wall. This relationship is important for constructing a short, straight fenestration without an intervening tunnel. Before proceeding, the entire Fontan pathway should be assessed as one continuous structure: inferior vena cava, proximal conduit anastomosis, conduit body, pulmonary artery anastomosis, central pulmonary arteries, and both branch pulmonary arteries.

3. Selection of the Fenestration Site

The fenestration is created between the extracardiac conduit and the adjacent atrium. The ideal site has the following characteristics:

• Direct conduit-to-atrial apposition
• Minimal distance between the two lumens
• Sufficient exposure for side-clamping and suturing
• Freedom from tension after cardiac filling
• No anticipated compression by surrounding structures
• Adequate separation from fragile tissue or another atrial suture line

The fenestration should not form a long or angulated channel because resistance depends not only on the nominal diameter but also on channel length, geometry, and pressure gradient. The surgeon must anticipate the final three-dimensional relationship after the heart is filled and the lungs are ventilated.

A side-to-side configuration appears favorable for sustained patency. In a multicenter cohort using initial fenestration diameters of 2.7–5.0 mm, side-to-side anastomosis was independently associated with patency at 1 year, whereas the initial diameter was not significantly associated with patency [4]. These findings suggest that anastomotic geometry and tissue configuration may be at least as important as the measured opening size.

4. Creation of the Conduit Opening

The atrium is controlled with a side-biting clamp. Partial-occlusion clamps are applied to the extracardiac conduit to control blood flow while preserving its overall geometry. The clamps should provide adequate exposure without crushing the expanded polytetrafluoroethylene material or narrowing the entire Fontan pathway.

A 2.7-mm circular opening is punched in the conduit. The opening is then calibrated with an approximately 3-mm Hegar dilator. Calibration confirms that the prosthetic edge is unobstructed and that the effective diameter is not smaller than intended.

A circular punch produces a more reproducible opening than an irregular incision. The opening should be inspected for incomplete tissue removal, residual strands, or deformation caused by the clamps. Excessive manipulation of the conduit should be avoided because folding or inward inversion of the prosthetic wall can reduce the functional lumen.

The 2.7-mm punch and approximately 3-mm calibration represent a specific operative strategy rather than a universally established optimal size. Published surgical series have used a wide range of fenestration diameters, configurations, and calibration methods. The nominal diameter alone does not fully describe the effective shunt because flow is also determined by the conduit-to-atrial pressure gradient, anastomotic length, suture-related narrowing, and subsequent tissue remodeling.

5. Conduit-to-Atrial Anastomosis

A corresponding opening is created in the side-clamped atrial wall, and the conduit opening is anastomosed directly to the atrium. The anastomosis should be short, circumferential, hemostatic, and free of tension.

Fine, evenly spaced sutures help preserve a circular lumen. Deep bites may reduce the effective diameter, whereas widely spaced or shallow bites may result in bleeding. Excessive atrial tissue should not be incorporated into the opening because a redundant tissue edge can function as a flap and intermittently obstruct flow. Similarly, the conduit wall should not fold inward during knot tying.

Before clamp release, the communication and atrium must be meticulously de-aired. The atrial side communicates with the systemic circulation, and retained air may enter the systemic ventricle and arterial tree. The clamps should be released gradually while the surgeon observes the anastomosis for bleeding, distortion, or collapse.

6. Fenestration Size as a Hemodynamic Compromise

Increasing fenestration size generally reduces resistance to right-to-left flow. This may lower Fontan pressure and increase ventricular preload and cardiac output, but the accompanying increase in deoxygenated shunt flow reduces arterial oxygen saturation.

A computational model demonstrated that, in selected high-risk Fontan conditions, a range of fenestration sizes may reduce systemic venous pressure while maintaining relatively constant systemic oxygen availability. The increased cardiac output may partially compensate for the reduction in arterial oxygen content [5]. However, these findings are model-based and do not define a universally applicable clinical diameter.

A small retrospective study of 20 patients with 4–8-mm fenestrations demonstrated the same physiologic trade-off clinically. Larger fenestrations correlated with shorter pleural drainage duration and hospital stay but with a smaller perioperative improvement in oxygen saturation [6]. Fenestration diameter was not associated with the overall incidence of complications. Because this study was small, single-center, and included relatively late Fontan completion, its findings should not be interpreted as evidence that 4–8-mm fenestrations are appropriate for all patients.

The available evidence therefore supports individualized sizing rather than a single optimal diameter. Relevant variables include body size, pulmonary artery pressure, pulmonary vascular resistance, ventricular end-diastolic pressure, atrioventricular valve competence, ventricular function, anticipated pleural effusion risk, and acceptable postoperative oxygen saturation.

7. Separation From Cardiopulmonary Bypass

7.1 Establish Adequate Preload

The Fontan circulation is highly preload dependent. During separation from cardiopulmonary bypass, sufficient intravascular volume is required to establish passive pulmonary blood flow and ventricular filling. Underfilling may produce low cardiac output despite technically satisfactory anatomy.

Excessive volume loading should also be avoided. It may elevate systemic venous pressure, increase tissue edema, and worsen pleural drainage. Volume administration should be guided by Fontan pressure, atrial pressure, systemic arterial pressure, ventricular filling, systemic perfusion, and echocardiographic findings.

7.2 Minimize Pulmonary Vascular Resistance

Because there is no subpulmonary pump, small increases in pulmonary vascular resistance can substantially impair Fontan flow. Ventilation and anesthetic management should avoid:

• Hypoxemia
• Hypercarbia
• Acidosis
• Hypothermia
• Atelectasis
• Excessive positive end-expiratory pressure
• Excessive mean airway pressure
• Pulmonary overdistension

Lung recruitment must be balanced against the adverse effect of elevated intrathoracic pressure on systemic venous return. Selective pulmonary vasodilator therapy may be used when pulmonary vascular resistance remains elevated.

7.3 Preserve Ventricular and Valvar Function

The systemic ventricle must accept the available preload at a low filling pressure. Ventricular dysfunction, significant atrioventricular valve regurgitation, or elevated ventricular end-diastolic pressure reduces the effective pressure gradient across the pulmonary circulation.

Sinus rhythm and atrioventricular synchrony are particularly important. Junctional rhythm or loss of atrial contribution may increase atrial pressure and decrease cardiac output. Vasoactive therapy should be individualized to preserve ventricular performance, systemic vascular resistance, coronary perfusion, and end-organ blood flow.

8. Confirmation of Fenestration Patency

Fenestration function should be assessed immediately after separation from cardiopulmonary bypass using integrated physiologic and imaging data.

A patent fenestration commonly produces a decrease in systemic oxygen saturation because systemic venous blood enters the atrium. This expected desaturation supports the presence of right-to-left flow. However, the magnitude of desaturation depends on fenestration size, Fontan-to-atrial pressure gradient, pulmonary blood flow, pulmonary venous oxygenation, and cardiac output.

Echocardiography should confirm flow from the conduit into the atrium. Color Doppler evaluates direction and patency, while spectral Doppler can characterize the velocity pattern. The examination should also assess:

• Both conduit anastomoses
• Inferior vena caval drainage
• Central and branch pulmonary arteries
• Ventricular systolic and diastolic function
• Atrioventricular valve regurgitation
• Pulmonary venous return
• Residual intracardiac or extracardiac shunts

Absent visible flow does not always indicate technical occlusion. Flow may be intermittent or minimal when Fontan and atrial pressures are similar. Conversely, severe desaturation may reflect excessive fenestration flow, high pulmonary vascular resistance, pulmonary artery obstruction, elevated atrial pressure, or pulmonary venous desaturation.

9. Technical Failure Modes

Restricted fenestration flow may result from an undersized opening, suture-related narrowing, conduit-wall inversion, atrial tissue prolapse, an elongated channel, external compression, thrombus, or unfavorable conduit-to-atrial alignment. When high Fontan pressure or low cardiac output persists, the communication should be inspected rather than assuming that the problem is exclusively pulmonary vascular.

Excessive shunting requires assessment of the entire Fontan circulation. Reducing the opening without correcting pulmonary artery obstruction, high pulmonary vascular resistance, ventricular dysfunction, or elevated filling pressure may eliminate an essential pressure-relief pathway.

Large fenestrations can produce clinically significant cyanosis and exercise intolerance. Limited experience in three patients demonstrated that transcatheter placement of an atrial flow regulator with a predetermined orifice could reduce an excessively large fenestration while maintaining decompressive patency [9]. This approach illustrates the importance of preserving some shunt flow when complete closure would cause unacceptable venous hypertension.

10. Long-Term Implications

Fenestration patency frequently changes over time. In a multicenter cross-sectional study performed a median of approximately 8 years after Fontan completion, only 19% of surgically created fenestrations remained open. Among confirmed closures, 59% had been closed by catheter intervention, 1% surgically, and 40% had apparently closed spontaneously [7]. Persistent patency was associated with lower resting oxygen saturation and greater medication use but not with significant differences in exercise performance, ventricular function, growth, stroke, thrombosis, or functional health status.

A national registry study of 1,233 patients found no difference in survival or freedom from Fontan failure between fenestrated and nonfenestrated extracardiac Fontan groups after propensity matching. Fenestration was associated with reduced early pleural drainage but lower late oxygen saturation, without a demonstrated long-term survival benefit [8].

More recent multicenter data suggest that persistent patency may have different implications in selected patients. At 1 year, patients with a patent fenestration had a higher systemic ventricular end-diastolic pressure than those with spontaneous closure, but protein-losing enteropathy occurred less frequently during follow-up [4]. Because the number of events was small and treatment was not randomized, this association should be interpreted cautiously. Persistent patency may be beneficial in some high-risk circulations, but it may also identify patients who physiologically cannot tolerate closure.

The fenestration should therefore be regarded as a dynamic component of Fontan management. Continued patency, spontaneous closure, transcatheter closure, or reduction should be determined by systemic venous pressure, cardiac output, ventricular filling pressure, oxygen saturation, exercise tolerance, lymphatic complications, and overall Fontan performance.

11. Operative Principles

• Construct an unobstructed extracardiac Fontan pathway before creating the fenestration.
• Correct central or branch pulmonary artery narrowing when necessary.
• Preserve a wide inferior vena caval cuff and avoid conduit torsion or compression.
• Select a short, direct conduit-to-atrial site suitable for side-to-side anastomosis.
• Create a controlled 2.7-mm conduit opening and confirm patency with an approximately 3-mm Hegar dilator.
• Avoid atrial tissue prolapse, conduit inversion, and suture-related narrowing.
• De-air the atrial communication meticulously.
• Wean from cardiopulmonary bypass with adequate preload and low pulmonary vascular resistance.
• Confirm patency using oxygen saturation trends, echocardiography, and pressure measurements.
• Interpret fenestration function within the entire Fontan circulation rather than considering it a substitute for correction of anatomic obstruction or unfavorable ventricular physiology.

References

[1] Lemler MS, Scott WA, Leonard SR, Stromberg D, Ramaciotti C. Fenestration improves clinical outcome of the Fontan procedure: a prospective, randomized study. Circulation. 2002;105(2):207-212.

[2] Toncu A, Rădulescu CR, Dorobanţu D, Stoica Ș. Does routine fenestration improve early and late postoperative outcomes in patients undergoing Fontan palliation? Interact Cardiovasc Thorac Surg. 2020;30(5):773-779.

[3] Dasi LP, KrishnankuttyRema R, Kitajima HD, Pekkan K, Sundareswaran KS, Fogel M, Sharma S, Whitehead K, Kanter KR, Yoganathan AP. Fontan hemodynamics: importance of pulmonary artery diameter. J Thorac Cardiovasc Surg. 2009;137(3):560-564.

[4] Horie S, Shikata F, Oka N, Okamura T, Kondo R, Kaneko M, Takei T, Matsunaga Y, Matsui K, Hataoka T, Konaka H, Ono M, Miyaji K. Impact of fenestration patency on long-term Fontan outcomes. Eur J Cardiothorac Surg. 2026;68(2):ezag047.

[5] Ahmad Z, Jin LH, Penny DJ, Rusin CG, Peskin CS, Puelz C. Optimal fenestration of the Fontan circulation. Front Physiol. 2022;13:867995.

[6] Van LTK, Vi HN, Bang HT. Association between fenestration size and early postoperative outcomes following Fontan surgery: a five-year single-center experience in Vietnam. Heart Surg Forum. 2026;29(2):50681.

[7] Atz AM, Travison TG, McCrindle BW, Mahony L, Quartermain MD, Williams RV, Breitbart RE, Lu M, Radojewski E, Margossian R, Covitz W, Gersony WM. Late status of Fontan patients with persistent surgical fenestration. J Am Coll Cardiol. 2011;57(24):2437-2443.

[8] Ko H, Song J, Chi SA, Lee SY, Kim SJ, Lee CH, Park CS, Choi ES, An HS, Kang IS, Yoon JK, Baek JS, Lee JY, Lee J, Huh J, Ahn KJ, Jung SY, Cha SG, Kim YH, Lee YS. The long-term effects of the fenestration in patients with extracardiac Fontan circulation: a multicenter Korean cohort study based on the national Fontan registry. Front Cardiovasc Med. 2024;11:1341882.

[9] Sonawane BS, Sivakumar K. Transcatheter reduction in size of large undesirable fenestrations following extracardiac conduit Fontan surgery with off-label use of Occlutech atrial flow regulator. Ann Pediatr Cardiol. 2020;13(3):260-263.