The Failing Fontan or Adult Congenital Heart Disease in ICU: Unique Physiology and Resuscitation Pitfalls

Dr Neeraj Manikath , claude.ai

Abstract

Background: Adult congenital heart disease (ACHD) represents a growing population in critical care settings, with Fontan physiology presenting unique challenges that differ fundamentally from acquired heart disease. The failing Fontan circulation requires specialized understanding of single-ventricle physiology and modified resuscitation approaches.

Objective: To provide critical care physicians with evidence-based strategies for managing ACHD patients, particularly those with Fontan physiology, emphasizing the unique pathophysiology and potential resuscitation pitfalls.

Methods: Comprehensive review of current literature, guidelines, and expert consensus statements on ACHD management in critical care settings.

Results: Fontan physiology relies on passive venous return without a subpulmonary ventricle, making traditional cardiac life support algorithms potentially harmful. Key management principles include maintaining low pulmonary vascular resistance, optimizing preload, and avoiding interventions that compromise venous return.

Conclusions: ACHD patients require specialized critical care approaches. Early involvement of ACHD specialists and understanding of unique physiologic principles are essential for optimal outcomes.

Keywords: Fontan circulation, adult congenital heart disease, critical care, single ventricle, pulmonary vascular resistance

Introduction

The landscape of congenital heart disease has dramatically evolved over the past five decades. Advances in pediatric cardiac surgery have transformed previously fatal conditions into chronic diseases, creating a growing population of adults with congenital heart disease (ACHD). Currently, there are over 1.4 million adults with congenital heart disease in the United States alone, with this population growing by approximately 5% annually.¹

The Fontan circulation, first described by Fontan and Baudet in 1971, represents one of the most complex physiologic arrangements encountered in critical care.² This palliative procedure creates a single-ventricle physiology where systemic venous return bypasses the right ventricle and flows passively to the pulmonary arteries. Understanding the unique hemodynamics of Fontan physiology is crucial for intensivists, as traditional approaches to cardiac resuscitation may be ineffective or even harmful in this population.

Learning Objectives

After reviewing this article, readers should be able to:

Understand the fundamental physiology of Fontan circulation and its implications for critical care
Recognize common presentations of failing Fontan physiology
Apply modified resuscitation strategies appropriate for single-ventricle physiology
Identify key monitoring parameters and therapeutic targets
Understand when to involve ACHD specialists and cardiac surgery teams

Fontan Physiology: The Foundation of Understanding

Normal Fontan Circulation

The Fontan circulation represents a surgically created pathway where systemic venous blood flows directly to the pulmonary arteries without passing through a subpulmonary ventricle. The single functioning ventricle receives oxygenated blood from the pulmonary veins and pumps it to the systemic circulation.

🔑 Clinical Pearl: The Fontan circulation is a "preload-dependent, afterload-sensitive" system where cardiac output is primarily determined by venous return rather than ventricular contractility.

Types of Fontan Operations

Classic Fontan (1971-1980s): Direct connection of right atrium to pulmonary artery
Lateral Tunnel (1980s-1990s): Intra-atrial baffle directing venous flow
Extracardiac Conduit (1990s-present): External conduit from inferior vena cava to pulmonary artery

Modern Fontan operations typically include a fenestration—a small hole allowing right-to-left shunting that serves as a "pop-off" valve during periods of elevated pulmonary vascular resistance.³

Hemodynamic Principles

The Fontan circulation operates under unique hemodynamic principles:

Elevated Central Venous Pressure (CVP): Normal CVP in Fontan patients ranges from 12-18 mmHg, significantly higher than normal biventricular circulation
Low Cardiac Output: Typical cardiac index ranges from 2.0-2.5 L/min/m², lower than normal but sufficient for many patients
Chronically Low Oxygen Saturation: Baseline oxygen saturation typically ranges from 90-95% due to mixing and potential fenestration flow

⚠️ Pitfall Alert: Normal hemodynamic parameters in biventricular circulation may indicate crisis in Fontan physiology. A CVP of 8 mmHg might represent profound shock in a Fontan patient.

Pathophysiology of Failing Fontan

Mechanisms of Failure

Fontan failure can occur through multiple mechanisms:

1. Increased Pulmonary Vascular Resistance (PVR)

Acute: pneumonia, pulmonary embolism, hypoxia, acidosis
Chronic: pulmonary vascular disease, stenosis

2. Decreased Preload

Volume depletion, bleeding, third-spacing
Positive pressure ventilation effects
Medications reducing venous return

3. Increased Afterload

Systemic hypertension
Aortic stenosis or regurgitation
Systemic vasoconstriction

4. Arrhythmias

Atrial arrhythmias (very common due to atrial scarring and dilatation)
Ventricular arrhythmias
Bradycardia

Fontan-Associated Complications

Long-term Fontan survivors develop characteristic complications:

Protein-Losing Enteropathy (PLE): Occurs in 5-15% of Fontan patients, characterized by enteric protein loss leading to hypoproteinemia, edema, and immune dysfunction.⁴

Plastic Bronchitis: Rare but serious complication involving bronchial cast formation, potentially causing airway obstruction.

Thromboembolic Disease: Increased risk due to sluggish flow in the Fontan circuit and frequent arrhythmias.

Hepatic Fibrosis: Universal finding in long-term Fontan survivors due to chronic venous congestion.

Clinical Presentation and Assessment

Recognizing the Failing Fontan

Clinical signs of Fontan failure may be subtle and differ from typical heart failure presentations:

Early Signs:

Decreased exercise tolerance
Fatigue disproportionate to apparent clinical status
Subtle changes in baseline oxygen saturation
New or worsening arrhythmias

Advanced Signs:

Peripheral edema and ascites
Pleural effusions
Protein-losing enteropathy
Cyanosis (if fenestration present)

🔑 Clinical Pearl: The absence of typical "heart failure" signs doesn't exclude significant hemodynamic compromise in Fontan patients. Maintain high suspicion based on subtle clinical changes.

Diagnostic Evaluation

Laboratory Studies

Complete Blood Count: Assess for anemia, thrombocytopenia
Comprehensive Metabolic Panel: Evaluate renal function, acid-base status
Liver Function Tests: Often abnormal due to chronic congestion
Coagulation Studies: May be abnormal due to hepatic dysfunction
B-type Natriuretic Peptide: Less reliable than in biventricular heart failure
Arterial Blood Gas: Assess oxygenation and acid-base balance

Imaging Studies

Echocardiography: Assess ventricular function, valve function, and estimate pressures
Chest X-ray: Evaluate pulmonary edema, pleural effusions
CT or MRI: May be needed to assess Fontan pathway anatomy

🔑 Clinical Pearl: In Fontan patients, pulmonary edema is uncommon due to low pulmonary venous pressure. Look for systemic congestion instead.

Critical Care Management Strategies

Hemodynamic Management

The fundamental principle of Fontan management is optimizing the pressure gradient from systemic veins to pulmonary veins while minimizing energy losses.

Preload Optimization

Target CVP: 15-20 mmHg (higher than normal)
Fluid Management: Careful balance to avoid under- or over-resuscitation
Monitoring: Consider pulmonary artery catheter for complex cases

💎 Oyster: While high CVP seems counterintuitive, adequate preload is essential for pulmonary blood flow in Fontan physiology. Don't chase "normal" numbers.

Afterload Reduction

First-line agents: ACE inhibitors or ARBs
Avoid: Excessive vasodilation that compromises venous return
Target: Systemic vascular resistance 15-20 Wood units·m²

Reducing Pulmonary Vascular Resistance

Optimize oxygenation: Target SpO2 >95%
Avoid acidosis: Maintain pH >7.35
Consider: Inhaled nitric oxide for acute PVR elevation
Pulmonary vasodilators: Sildenafil, bosentan in select cases

Mechanical Ventilation Considerations

Positive pressure ventilation significantly impacts Fontan physiology by:

Reducing venous return
Increasing pulmonary vascular resistance
Decreasing cardiac output

Ventilatory Strategies:

Minimize PEEP: Use lowest level necessary for adequate oxygenation
Avoid high peak pressures: Limit plateau pressure <25 cmH2O
Consider: Spontaneous breathing modes when possible
Early extubation: Aggressive weaning protocols

⚠️ Pitfall Alert: High PEEP levels that are well-tolerated in normal hearts can cause cardiovascular collapse in Fontan patients.

Pharmacologic Support

Inotropic Support

First choice: Milrinone (inotrope + vasodilator + lusitrope)
Avoid: Pure vasoconstrictors (phenylephrine, vasopressin)
Consider: Low-dose epinephrine or dobutamine if needed

Antiarrhythmic Therapy

Atrial arrhythmias: Very common; consider prophylactic antiarrhythmic therapy
Rate control: Beta-blockers, calcium channel blockers
Rhythm control: Amiodarone often first choice

🔑 Clinical Pearl: Arrhythmias are poorly tolerated in Fontan physiology. Aggressive rhythm management is often necessary.

Resuscitation Pitfalls and Modified ACLS

Traditional ACLS Modifications

Standard advanced cardiac life support algorithms require significant modification for Fontan patients:

Cardiac Arrest Management

CPR considerations:
- Standard chest compressions may be less effective
- Consider higher compression rates (120/min)
- Ensure adequate venous return
Medication modifications:
- Epinephrine: Use standard doses but expect different response
- Vasopressin: Generally avoid due to pulmonary vasoconstriction
- Atropine: May be less effective due to chronotropic incompetence
Defibrillation:
- Standard protocols apply
- Consider underlying electrolyte abnormalities

Shock Management

Traditional shock classification doesn't apply well to Fontan physiology:

Modified Approach:

Focus on optimizing Fontan circuit flow
Avoid excessive fluid resuscitation
Consider fenestration closure if hypoxemia is limiting

⚠️ Pitfall Alert: Aggressive fluid resuscitation can worsen outcomes by increasing PVR and reducing cardiac output. Start with smaller boluses (5-10 mL/kg) and reassess frequently.

Procedural Considerations

Central Venous Access

Preferred sites: Avoid femoral access if possible (may compromise Fontan circuit)
Ultrasound guidance: Essential due to abnormal anatomy
Anticoagulation: Consider heparin prophylaxis

Cardioversion/Defibrillation

Lower thresholds: Earlier intervention for arrhythmias
Anticoagulation: Essential before elective cardioversion

Specific Clinical Scenarios

Scenario 1: Post-operative Fontan Patient

A 25-year-old patient presents 48 hours after Fontan revision with:

CVP: 8 mmHg (down from baseline 16 mmHg)
SpO2: 85% (down from baseline 94%)
Urine output: 0.3 mL/kg/hr

Management Approach:

Immediate assessment: Rule out bleeding, circuit obstruction
Volume resuscitation: Cautious fluid boluses with frequent reassessment
Reduce PVR: Optimize ventilation, consider inhaled NO
Imaging: Urgent echocardiogram, consider CT angiogram
Surgical consultation: Early involvement of cardiac surgery

Scenario 2: Medical Fontan with Pneumonia

A 30-year-old Fontan patient presents with pneumonia and:

Increased work of breathing
SpO2: 88% on room air
Bilateral infiltrates on chest X-ray

Management Approach:

Minimize PVR increase: Aggressive pulmonary toilet, early antibiotics
Ventilation strategy: Non-invasive ventilation if possible
If intubated: Low PEEP, pressure-limited ventilation
Hemodynamic support: Milrinone for increased PVR
Monitor for: Rapid decompensation due to PVR elevation

Scenario 3: Atrial Arrhythmia in Fontan

A 35-year-old presents with new-onset atrial fibrillation:

Heart rate: 150 bpm
Blood pressure: 85/60 mmHg
Clinical deterioration over 6 hours

Management Approach:

Immediate: Consider electrical cardioversion if unstable
Rate control: Beta-blockers or calcium channel blockers
Anticoagulation: Urgent heparinization
Rhythm control: Amiodarone loading
Long-term: Anticoagulation strategy, rhythm vs. rate control

Monitoring and Targets

Hemodynamic Targets for Fontan Patients

Parameter	Normal Biventricular	Fontan Target	Comments
CVP	2-8 mmHg	15-20 mmHg	Higher pressures needed
Mean BP	>65 mmHg	>60 mmHg	Lower targets acceptable
SpO2	>95%	90-95%	Baseline lower due to mixing
Cardiac Index	>2.5 L/min/m²	>2.0 L/min/m²	Lower baseline acceptable
SVR	15-20 Wood units	15-20 Wood units	Avoid excessive reduction

Advanced Monitoring Considerations

Pulmonary Artery Catheter

Indications:

Complex hemodynamic assessment
Guide therapy in unstable patients
Perioperative monitoring

Special considerations:

May be technically challenging due to abnormal anatomy
Wedge pressure may not reflect left heart filling
Thermodilution cardiac output may be inaccurate

Continuous Cardiac Output Monitoring

Pulse contour analysis: May be less accurate
Esophageal Doppler: Consider for perioperative monitoring
Echocardiography: Serial assessments often most valuable

When to Involve Specialists

ACHD Cardiology Consultation

Urgent consultation (within hours):

Any signs of hemodynamic instability
New arrhythmias
Suspected thromboembolism
Protein-losing enteropathy

Routine consultation (within 24 hours):

All ACHD patients admitted to ICU
Medication adjustments needed
Discharge planning

Cardiac Surgery Consultation

Emergent:

Suspected circuit obstruction
Massive bleeding
Refractory shock

Urgent:

Progressive heart failure
Recurrent arrhythmias
Consideration for transplant evaluation

🔑 Clinical Pearl: Don't hesitate to involve specialists early. ACHD patients require multidisciplinary care, and early consultation often prevents complications.

Long-term Management and Prognosis

Survival Outcomes

Long-term survival for Fontan patients has improved significantly:

10-year survival: 85-90%
20-year survival: 70-80%
30-year survival: 60-70%⁵

Factors Affecting Long-term Outcomes

Favorable factors:

Left ventricular morphology
Good ventricular function
Absence of AV valve regurgitation
Sinus rhythm maintenance

Unfavorable factors:

Right ventricular morphology
Significant AV valve regurgitation
Chronic arrhythmias
Elevated pulmonary vascular resistance

Transition to Advanced Therapies

Heart Transplantation

Consider when medical management fails
Unique challenges due to previous surgery
5-year survival post-transplant: 65-70%

Mechanical Circulatory Support

Limited experience in Fontan patients
Ventricular assist devices technically challenging
Consider as bridge to transplant

Evidence-Based Recommendations

Class I Recommendations (Strong Evidence)

Anticoagulation: All Fontan patients should receive anticoagulation unless contraindicated (Class I, Level B)⁶
Arrhythmia monitoring: Regular surveillance for arrhythmias with prompt treatment (Class I, Level B)
Specialist care: All ACHD patients should have regular follow-up with ACHD specialists (Class I, Level C)

Class IIa Recommendations (Moderate Evidence)

Pulmonary vasodilators: Consider for patients with elevated PVR (Class IIa, Level B)
Fenestration closure: May be considered in selected patients with good hemodynamics (Class IIa, Level B)
Exercise restriction: Moderate exercise restriction for most Fontan patients (Class IIa, Level C)

Future Directions and Research

Emerging Therapies

Lymphatic interventions: Targeting lymphatic abnormalities in failing Fontan
Pharmacologic support: Novel agents targeting Fontan-specific pathophysiology
Mechanical support: Development of Fontan-specific assist devices
Regenerative medicine: Tissue engineering approaches for single ventricle

Research Priorities

Long-term outcomes and quality of life studies
Optimal timing for transition to advanced therapies
Pregnancy management in Fontan patients
Exercise physiology and rehabilitation programs

Key Clinical Pearls and Oysters

🔑 Clinical Pearls

The Fontan circulation is preload-dependent and afterload-sensitive
"Normal" hemodynamic parameters may indicate crisis in Fontan patients
Arrhythmias are poorly tolerated and require aggressive management
Positive pressure ventilation significantly impacts Fontan hemodynamics
Early specialist involvement is crucial for optimal outcomes

💎 Oysters (Common Misconceptions)

"High CVP always means volume overload" - False in Fontan physiology where high CVP is necessary
"Pulmonary edema indicates left heart failure" - Rare in Fontan due to low pulmonary venous pressure
"Standard shock protocols apply" - Fontan patients require modified resuscitation strategies
"All heart failure medications work the same" - Some may be harmful in Fontan physiology

🔧 Clinical Hacks

The "Fontan Formula": CVP - PAWP = PVR × CO (useful for hemodynamic assessment)
"PEEP test": Temporary PEEP reduction often improves hemodynamics in Fontan patients
"Rhythm is king": Maintaining sinus rhythm is more important than rate control in most cases
"Less is more": Conservative fluid management often yields better outcomes

Summary and Conclusions

The failing Fontan represents one of the most challenging scenarios in critical care medicine. Success requires understanding of unique single-ventricle physiology, recognition that traditional cardiac life support approaches may be ineffective or harmful, and early involvement of specialized teams.

Key management principles include optimizing preload while minimizing pulmonary vascular resistance, aggressive arrhythmia management, and careful attention to mechanical ventilation strategies. The absence of typical heart failure signs should not provide false reassurance, as Fontan patients may decompensate rapidly with subtle clinical changes.

As the ACHD population continues to grow, intensivists must become familiar with these unique physiologic principles. Early recognition, appropriate management, and timely specialist consultation are essential for optimizing outcomes in this complex patient population.

The future holds promise for improved therapies specifically targeting Fontan physiology, but current management relies on fundamental understanding of single-ventricle hemodynamics and modified critical care approaches. Continued research and education in this field will be essential as we care for increasing numbers of ACHD survivors in our critical care units.

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Conflicts of Interest: None Funding: None

Tuesday, September 16, 2025