Introduction

Fontan fenestration stenting radiation dose optimization has become an urgent priority in congenital interventional cardiology as the population of Fontan survivors grows and their need for repeated catheter-based interventions escalates. The Fontan procedure—first described in 1971 and now performed in over 3,000 patients annually worldwide—directs systemic venous return to the pulmonary arteries without an intervening ventricle, creating a passive pulmonary circulation entirely dependent on transpulmonary pressure gradients. Over time, this physiology generates a predictable cascade of complications: rising pulmonary vascular resistance, declining cardiac output, and the development of venovenous collaterals that shunt desaturated blood back to the systemic circulation, causing progressive cyanosis and exercise intolerance.[1]

Transcatheter management of these complications—fenestration creation or stenting to decompress the Fontan circuit, fenestration closure when pulmonary vascular resistance normalizes, and embolization of venovenous collaterals to eliminate right-to-left shunting—has transformed outcomes for Fontan patients. However, these interventions are among the most fluoroscopy-intensive in pediatric and adult congenital practice. Extensive collateral coiling runs may involve 10–20 individual coil deployments, each requiring magnified fluoroscopy and confirmatory angiography. Wire traversal through the Fontan baffle, often tortuous and requiring multiple exchanges, adds further fluoroscopy time. For adolescent and adult Fontan patients, whose body habitus approaches adult dimensions, the dose penalty of prolonged exposure is substantial.[2]

For interventional cardiologists, radiographers, and cath lab administrators caring for Fontan patients, mastering dose reduction during these procedures is therefore a clinical imperative. The cumulative radiation burden from serial Fontan interventions—diagnostic catheterizations, hemodynamic assessments, fenestration manipulations, and repeated collateral embolizations—can approach deterministic skin injury thresholds across a patient's lifetime. This article presents a comprehensive, evidence-based fluoroscopy protocol for Fontan fenestration stenting radiation dose optimization, integrating projection selection, exposure parameter modulation, low-frame-rate DSA, road mapping, and scatter protection with SATPRO lead-free bismuth drapes.

Fontan physiology and intervention targets

The passive pulmonary circulation

The Fontan circulation is unique in cardiac physiology: systemic venous return flows directly to the pulmonary arteries without a pumping chamber, driven entirely by the pressure gradient between the central veins and the pulmonary venous atrium. This passive flow is exquisitely sensitive to any increase in pulmonary vascular resistance, obstruction within the Fontan pathway, or loss of cardiac output. When pulmonary vascular resistance rises—whether from chronic pulmonary microvascular disease, thrombus formation, or anatomical obstruction—Fontan pressure increases, cardiac output falls, and systemic venous congestion develops.[3]

The anatomical substrate for intervention depends on the type of Fontan connection. Atriopulmonary Fontans (the original technique, now largely abandoned) direct right atrial appendage flow to the pulmonary artery, creating a large atrial chamber prone to dilation, thrombus, and arrhythmia. Lateral tunnel Fontans use an intra-atrial baffle to direct inferior vena caval flow to the pulmonary artery, while extracardiac conduit Fontans use a prosthetic tube (typically 18–20 mm diameter) to connect the inferior vena cava directly to the pulmonary artery. Each variant presents distinct fluoroscopic challenges: atriopulmonary Fontans require extensive angiography to define atrial anatomy and baffle integrity, while extracardiac conduit Fontans demand precise visualization of the conduit-to-pulmonary artery anastomosis.[4]

Hemodynamic assessment and intervention thresholds

Diagnostic cardiac catheterization in Fontan patients is performed to assess: Fontan pathway pressure (normal <15 mmHg), pulmonary artery pressure, pulmonary vascular resistance, ventricular end-diastolic pressure, and the presence of obstructive lesions or collaterals. Intervention is indicated when Fontan pressure exceeds 15 mmHg with cardiac index below 2.5 L/min/m², when oxygen saturation falls below 85% due to significant venovenous collaterals, or when arrhythmias suggest baffle obstruction or atrial dilation.[5]

The diagnostic phase itself contributes significantly to the Fontan fenestration stenting radiation dose. Hemodynamic assessment requires multiple pull-back measurements, often with simultaneous pressure recording in the femoral vein, Fontan pathway, pulmonary artery, and ventricle. Each catheter position change requires fluoroscopic guidance, and the complete diagnostic dataset may involve 20–30 minutes of fluoroscopy before any intervention begins. Optimizing the diagnostic phase—using stored pressure tracings, minimizing unnecessary catheter exchanges, and performing selective rather than comprehensive angiography—is essential for overall dose management.

Fenestration stenting and closure indications

The fenestration as a pressure-release valve

A Fontan fenestration is a small (4–8 mm) communication between the Fontan pathway and the pulmonary venous atrium, intentionally created during the initial Fontan procedure to allow right-to-left shunting and decompression of the Fontan circuit. This "pop-off" mechanism protects cardiac output in the early post-operative period, when pulmonary vascular resistance is elevated and the Fontan circulation is not yet fully adapted. Fenestrations reduce Fontan pressure by 3–5 mmHg and improve cardiac output by 10–15%, at the cost of mild systemic desaturation (85–92% oxygen saturation).[6]

Over time, as pulmonary vascular resistance normalizes and cardiac output improves, the fenestration becomes hemodynamically unnecessary. Persistent right-to-left shunting through the fenestration causes chronic cyanosis, polycythaemia, and an increased risk of paradoxical embolism and stroke. Transcatheter fenestration closure is therefore indicated when: Fontan pressure is below 12 mmHg, cardiac index exceeds 2.5 L/min/m², oxygen saturation remains below 90% despite optimal medical management, and there is no significant pulmonary artery stenosis or ventricular dysfunction.[7]

Fenestration stenting for failing Fontan physiology

In patients with failing Fontan physiology—characterized by elevated Fontan pressure (>18 mmHg), declining cardiac output, and refractory pleural effusions or protein-losing enteropathy—fenestration stenting (rather than closure) may be indicated. This seemingly paradoxical approach creates or enlarges a fenestration in patients whose original fenestration has spontaneously closed or who never had one. The stented fenestration acts as a controlled pressure-release valve, reducing Fontan pressure and improving cardiac output at the cost of accepting mild cyanosis.[8]

Fenestration stenting is technically demanding. The operator must traverse the Fontan pathway, identify the precise location of the atrial septal defect or baffle fenestration, and deploy a stent (typically 6–10 mm diameter) that bridges the Fontan and atrial chambers without obstructing either. The procedure requires high-resolution magnified fluoroscopy, often in multiple projections, and may involve 45–60 minutes of fluoroscopy time. Without dose optimization, Fontan fenestration stenting radiation dose can exceed 1.5 Gy air kerma in adolescent patients.

Venovenous collateral embolization

Pathophysiology of venovenous collaterals

Venovenous collaterals develop in 15–30% of Fontan patients, most commonly in the 5–15 years following the initial procedure. These abnormal vascular channels connect the systemic venous circulation (superior vena cava, inferior vena cava, or azygos vein) to the pulmonary venous atrium or left atrium, bypassing the pulmonary capillary bed and causing right-to-left shunting. The mechanism is thought to be chronic venous hypertension within the Fontan pathway, which stimulates angiogenesis and the recruitment of embryonic venous channels that would normally remain closed.[9]

Collaterals may be single or multiple, small (<2 mm) or large (>8 mm), and may arise from any systemic venous tributary. The most common sites are: azygos-to-left atrial collaterals (via the azygos and hemiazygos veins), internal mammary-to-pulmonary venous collaterals, phrenic vein collaterals, and hepatic vein-to-left atrial collaterals. Each collateral adds a measurable right-to-left shunt; when the total Qp:Qs shunt fraction exceeds 1.2:1, systemic oxygen saturation typically falls below 85%, causing symptomatic cyanosis and exercise intolerance.

Embolization technique and procedural workflow

Transcatheter embolization of venovenous collaterals is the treatment of choice for symptomatic shunting. The procedure involves femoral venous access, traversal of the Fontan pathway, and selective engagement of each collateral origin. Diagnostic angiography defines collateral anatomy, flow direction, and drainage site. Embolization is typically performed with pushable or detachable coils for small collaterals (<4 mm) and vascular plugs (Amplatzer Vascular Plug II or IV) for larger vessels (>4 mm).[10]

The fluoroscopic demand of collateral embolization is substantial. Each collateral requires: (1) selective catheter engagement and diagnostic angiography in at least two projections, (2) microcatheter advancement to the collateral origin or a safe distal landing zone, (3) device deployment under magnified fluoroscopy, and (4) post-embolization angiography to confirm complete occlusion. In patients with 10–15 collaterals, the procedure may involve 8–12 cine acquisitions and 60–90 minutes of fluoroscopy time. The cumulative Fontan fenestration stenting radiation dose from extensive collateral embolization can exceed 2.0 Gy air kerma in adult Fontan patients if unoptimized protocols are used.

Projection optimization for dose reduction

Straight AP for wire traversal and device manipulation

The single most effective strategy for reducing Fontan fenestration stenting radiation dose during prolonged procedures is projection optimization. The straight anteroposterior (AP, 0°) projection provides the shortest beam path through the thorax and abdomen, minimizing tissue attenuation and scatter generation. For the majority of Fontan interventions—wire traversal through the Fontan circuit, catheter exchanges, and coil positioning during collateral embolization—AP or shallow LAO (≤15°) provides adequate visualization while reducing entrance skin dose by 25–35% compared with steep oblique views.[11]

The protocol mandates that straight AP (0°) be used as the default projection for all non-critical phases of the procedure. This includes: femoral venous access and sheath insertion, wire traversal from the inferior vena cava through the Fontan baffle or conduit, catheter exchanges, and coil delivery during collateral embolization. Steep LAO (30°–45°) should be reserved for three specific moments: (1) defining the Fontan circuit and fenestration anatomy during initial diagnostic angiography, (2) confirming stent or device position across the fenestration, and (3) post-intervention assessment to rule out device migration or residual shunt.[12]

LAO 30°–45° for Fontan circuit and fenestration visualization

The LAO 30°–45° projection is the optimal working angle for visualizing the Fontan circuit and fenestration because it opens the atrial septum and baffle geometry, separating the Fontan pathway from the pulmonary venous atrium. In this projection, the fenestration appears as a discrete circular or oval defect in the atrial septum or baffle, allowing precise measurement and device sizing. For atriopulmonary Fontans, LAO 40°/cranial 20° provides the best separation of the right atrial appendage from the pulmonary artery, profiling the anastomotic site for stenosis assessment.

However, LAO 30°–45° significantly increases beam path length through the thorax, raising both entrance skin dose and scatter generation. The protocol emphasizes that this projection should be used selectively—only for the moments when fenestration anatomy must be precisely defined. All preparatory and interventional steps should revert to AP or shallow angles immediately afterward. In adolescent and adult Fontan patients, where tissue thickness approaches adult dimensions, the dose penalty of prolonged LAO angulation is particularly severe and must be actively managed.

Steep obliques for venovenous collaterals

Venovenous collaterals often arise from unusual anatomical locations—azygos veins posterior to the heart, phrenic veins along the diaphragm, or hepatic veins within the liver—and require steep oblique or cranial/caudal angulation for full visualization. Steep RAO (60°–90°) may be necessary to profile azygos collaterals, while steep LAO (60°–90°) with caudal angulation (20°–30°) may be required for hepatic vein collaterals. These extreme angles deliver the highest dose of any projection and must be used with extreme parsimony.[13]

The protocol recommends a "collateral projection protocol": for each collateral, acquire a single diagnostic cine run in the optimal oblique angle, then store the image as a roadmap. All subsequent device manipulation—microcatheter advancement, coil delivery, and plug deployment—should be performed in AP or shallow angles using the stored roadmap for guidance. This approach can reduce steep-angle exposure time by 70–80% in multi-collateral cases.

Exposure parameters and age-specific protocols

Child exposure settings (1–10 years)

Fontan interventions in children demand pediatric-optimized exposure parameters. The protocol recommends pulsed fluoroscopy at 3.75 fps for all non-critical phases, with tube potential at 60–72 kV and tube current at 20–70 mA. These settings reflect the modest thoracic tissue thickness of school-age children (typically 12–18 cm anteroposterior diameter) while providing sufficient penetration for the Fontan pathway and pulmonary vasculature.[14]

For cine acquisition during diagnostic angiography and post-intervention assessment, 7.5 fps may be used briefly. However, the default should remain 3.75 fps, and operators should be trained to release the fluoroscopy pedal immediately when the diagnostic information is obtained. The use of last-image hold for equipment exchanges and procedural pauses eliminates unnecessary continuous fluoroscopy, reducing dose by 10–15% per procedure.

Adolescent and adult exposure settings

Adolescent and adult Fontan patients—now comprising over 40% of the Fontan population—require parameters that bridge pediatric and adult protocols. Tube potential increases to 75–90 kV with 80–250 mA, reflecting greater tissue thickness and the need for beam penetration through the adult chest. However, the pulse rate should remain at 3.75 fps for all non-critical phases, with brief activation of 7.5 fps only for stent deployment or complex coil positioning.[15]

Obese adult Fontan patients (BMI >35) present a particular challenge. The automatic exposure control (AEC) system drives kV upward to 95–120 kV and mA to 300–750 mA, significantly increasing scatter generation. For these patients, copper spectral filtration (0.6–0.9 mm Cu) is mandatory to harden the beam and reduce low-energy scatter. The detector should be positioned as close to the chest wall as possible (within 15 cm), and SATPRO bismuth scatter drapes are essential over the torso and upper abdomen.

Low-frame-rate DSA and road mapping

DSA at 1–3 fps for collateral embolization

Digital subtraction angiography (DSA) at low frame rates is transformative for reducing Fontan fenestration stenting radiation dose during collateral embolization. Conventional cine acquisition at 15 fps delivers approximately 0.3–0.5 mGy per second. DSA at 1 fps reduces this to 0.02–0.03 mGy per second—a 90% dose reduction—while still providing sufficient temporal resolution for coil and plug visualization. At 3 fps, the dose is approximately 0.06–0.09 mGy per second, a 70–80% reduction compared with cine.[16]

The protocol mandates low-frame-rate DSA at 1–3 fps for all collateral embolization procedures. At 1 fps, each frame is acquired as a discrete exposure with full image quality, and the sequence can be played back at higher speed for review. For coil deployment, 3 fps provides adequate visualization of coil frame expansion and positioning. The only exception is the final post-embolization angiographic run, where 7.5 fps may be used briefly to confirm complete occlusion and rule out distal embolization.

Road mapping for fenestration and collateral navigation

Road mapping—storing a contrast-filled mask image and overlaying it onto live fluoroscopy—is invaluable for Fontan interventions. For fenestration stenting, a roadmap from an initial angiographic run allows the operator to navigate wires and sheaths to the fenestration without repeated contrast injections. For collateral embolization, road mapping from the diagnostic run guides microcatheter advancement and device positioning, eliminating the need for repeated cine acquisitions during each coil deployment.[17]

Modern angiography systems offer motion-compensated road mapping, which adjusts for patient motion and respiratory drift. This is particularly valuable in Fontan patients, where respiratory variation can displace the Fontan baffle by 5–10 mm. Motion-compensated road mapping maintains registration accuracy during prolonged procedures, reducing the need for repeat mask acquisitions and contrast reinjection. In experienced centres, road mapping reduces total cine acquisition count by 50–60% during Fontan interventions.

Scatter mitigation with SATPRO protection

Source-based scatter attenuation in Fontan procedures

Scatter radiation poses a significant occupational hazard during Fontan interventions, particularly during prolonged collateral embolization runs. The X-ray beam interacts with the thoracic skeleton, Fontan baffle material (Dacron or PTFE), surgical clips, sternal wires, and contrast-filled cardiac chambers, generating a 360° scatter field. The operator, positioned on the patient's right side for femoral venous access, receives the highest scatter dose when the tube is in LAO projection—the most common working angle for fenestration visualization. In adult Fontan patients, where tissue thickness and beam parameters are higher, operator hand dose can approach action levels during complex cases.[18]

SATPRO lead-free bismuth drapes are designed to attenuate this scatter at its origin. For Fontan interventions, the drape should be positioned over:

• The entire chest wall from clavicles to xiphoid process, covering the Fontan circuit and collateral origins.
• The upper abdomen, where lateral scatter from the diaphragm and liver is significant during cranial angulation.
• The lower abdomen and pelvis, which are non-target zones during Fontan interventions but receive substantial scatter from the primary beam.
• The groin access site, to protect against backscatter from the femoral venous entry region.

The SATPRO lead-free scatter drape contains bismuth oxide particles suspended in a polymer matrix, providing attenuation equivalent to 0.5 mm lead without the weight or toxicity. Clinical phantom studies demonstrate that SATPRO drapes reduce operator hand dose by 55–65% during prolonged structural procedures and lower patient backscatter dose by 15–20%.[19]

Shielding configuration for specific Fontan procedures

For fenestration stenting or closure, the operator stands on the patient's right side, exposed to left-sided scatter during LAO projection. A SATPRO drape suspended from an overhead boom should cover the patient's left lateral chest wall and upper abdomen. An additional sterile drape placed over the right lower chest wall protects the assistant and anaesthesia team. For extensive collateral embolization, where projections shift repeatedly between AP, LAO, and steep obliques, a full-torso SATPRO drape combined with a ceiling-suspended lead acrylic shield positioned between the operator and the patient creates comprehensive protection.

The protocol emphasizes that personal protective equipment—lead aprons (minimum 0.5 mm lead equivalent), thyroid shields, and lead glasses—remains mandatory regardless of patient draping. SATPRO reduces the scatter load, but does not eliminate it. In high-volume centres performing more than 50 Fontan interventions annually, the combination of SATPRO draping, lead acrylic shields, and dosimetry feedback has been shown to keep operator whole-body dose below 2 mSv per year.

Dose monitoring and cumulative tracking

Real-time dose feedback

Systematic dose monitoring is essential for any programme performing Fontan interventions. Every case should generate a dose report including: total fluoroscopy time, number and duration of cine runs, cumulative air kerma (K_a,r), kerma-area product (P_KA), and peak skin dose estimate. In Fontan practice, these data take on heightened importance because patients will return for repeated procedures—diagnostic catheterizations, fenestration adjustments, and collateral embolizations—across their lifetime.[20]

Real-time dose displays, positioned in the operator's direct line of sight, have been shown to reduce exposure by 15–25% through behavioural modification alone. In Fontan cases, where procedural times are long and the temptation to acquire "just one more" cine run is strong, real-time feedback is particularly effective: operators naturally reduce fluoroscopy time and cine acquisition when they see cumulative dose approaching institutional alert levels.[21]

Cumulative dose registries for Fontan patients

Fontan patients should have a dedicated cumulative dose registry that tracks total air kerma, total PKA, and estimated peak skin dose across all catheterization episodes. Alert thresholds should be established at 50% and 75% of accepted lifetime limits, triggering mandatory review of future procedural planning. For patients who may undergo 10–15 procedures across childhood and adulthood, cumulative tracking is the only mechanism to prevent deterministic skin injury and manage stochastic risk.[22]

The following diagnostic reference levels are proposed for Fontan interventions based on current literature and institutional best practice:

Conclusion

Fontan fenestration stenting, fenestration closure, and venovenous collateral embolization represent some of the most fluoroscopy-intensive interventions in congenital and adult interventional cardiology. The unique physiology of the Fontan circulation—passive pulmonary blood flow, chronic venous hypertension, and the inevitable development of collateral pathways—creates a population of patients who require repeated catheter-based interventions across their lifetime. For these patients, cumulative radiation dose is not an abstract concern but a measurable clinical risk that demands systematic management from the first procedure through every subsequent intervention.

The protocol presented here integrates five pillars of dose reduction: projection optimization (straight AP as the default for wire traversal and device manipulation, with steep LAO reserved for fenestration visualization and steep obliques reserved for collateral definition only), exposure parameter modulation (pulsed fluoroscopy at 3.75 fps, age-appropriate kV/mA selection, and copper spectral filtration for adult patients), low-frame-rate DSA (1–3 fps for collateral embolization, reducing dose by 60–90% compared with cine), road mapping (eliminating redundant cine runs through stored reference images), and scatter mitigation (SATPRO lead-free bismuth drapes, micro-collimation to the collateral bed, and strategic shielding). Together, these measures can reduce cumulative air kerma by 50–60% compared with unoptimized workflows, without compromising procedural precision or safety.

For children, the emphasis must remain on anti-scatter grid removal (in patients under 20 kg), low frame rates, and aggressive micro-collimation as the foundational dose reduction strategies. For adolescents and adults, the principles remain identical, with increased kV and mA reflecting greater tissue thickness, and mandatory SATPRO draping for all cases. The use of documented projection angles, road mapping, and low-frame-rate DSA to eliminate redundant cine runs, combined with cumulative dose registries that track exposure across a patient's entire interventional history, ensures that radiation safety is managed as a longitudinal priority rather than a per-procedure afterthought.

Ultimately, radiation safety in Fontan interventions is not achieved by any single technique, but by the systematic application of ALARA principles at every step—from pre-procedural planning through final coil release. Institutions that adopt structured dose-monitoring, operator feedback loops, and standardized scatter-protection protocols will see the greatest reductions in long-term stochastic risk for both patients and catheterization laboratory staff. For the growing population of Fontan survivors, who have already overcome extraordinary anatomical challenges, this commitment to dose optimization is not merely best practice—it is a clinical obligation that honours their survival with the safest possible care.

Further reading

References