What is the management approach for patients with single ventricle physiology?

Management of Single Ventricle Physiology

The management of single ventricle physiology requires staged surgical palliation culminating in the Fontan procedure, with specific perioperative strategies tailored to each stage, lifelong surveillance for complications including arrhythmias and ventricular dysfunction, and early consideration for cardiac transplantation when signs of Fontan failure emerge. 1

Anatomic Considerations

Single ventricle physiology encompasses multiple cardiac malformations where only one functional ventricle exists, including:

• Hypoplasia of the left or right ventricle 1
• Atresia of one atrioventricular valve 1
• Double-inlet ventricles 1
• Undifferentiated single ventricles 1

Although these defects represent only 1.5% of congenital heart disease cases, they account for a disproportionate share of morbidity and mortality 1, 2.

Staged Surgical Approach

Stage I: Norwood Procedure (Neonatal Period)

The initial palliation establishes four critical objectives 1, 3:

• Unobstructed systemic outflow tract through anastomosis of the main pulmonary artery to the hypoplastic aorta 3
• Unrestrictive inter-atrial communication via atrial septectomy 1, 3
• Controlled pulmonary blood flow using either modified Blalock-Taussig shunt or Sano modification (right ventricle-to-pulmonary artery conduit) 3
• Reliable coronary blood flow 1, 3

Perioperative Management for Stage I:

For neonates in prearrest state with elevated pulmonary-to-systemic flow ratio, target PaCO2 of 50-60 mm Hg by reducing minute ventilation, increasing inspired CO2, or administering opioids with or without paralysis 1.

For low cardiac output state post-Stage I, use systemic vasodilators 1:

• α-adrenergic antagonists (phenoxybenzamine) to reduce systemic vascular resistance and improve oxygen delivery (Class IIa) 1
• Milrinone or nitroprusside for patients with excessive Qp:Qs (Class IIa) 1

During cardiopulmonary arrest post-Stage I, consider ECMO early (Class IIa) 1.

Stage II: Bidirectional Glenn/Hemi-Fontan (3-6 Months)

This stage directs superior vena cava blood directly to pulmonary arteries, providing stable pulmonary blood flow without volume loading the single ventricle 1, 3.

Perioperative Management for Stage II:

For patients in prearrest state with Glenn or hemi-Fontan physiology 1:

• Hypoventilation may improve oxygen delivery (Class IIa) 1
• Negative-pressure ventilation may improve cardiac output (Class IIa) 1

Stage III: Fontan Completion (2-5 Years)

The final stage directs inferior vena cava blood to pulmonary circulation, completing separation of systemic and pulmonary circulations 1, 2, 3.

Modern Fontan modifications include 1:

• Extracardiac conduit from inferior vena cava to pulmonary artery 1
• Intra-atrial conduit (preferred when ventricular mass would lie on extracardiac conduit) 1
• Intracardiac lateral tunnel 1

During cardiopulmonary arrest in Fontan patients, consider ECMO (Class IIa) 1.

Long-Term Surveillance and Management

Routine Follow-Up Schedule

For Physiological Stage A (stable, no symptoms) 1:

• ACHD cardiologist every 12 months 1
• ECG every 12 months 1
• Echocardiography every 12 months 1
• CMR/CCT every 24-36 months 1
• Exercise testing every 24-36 months 1
• Holter monitor every 12 months 1

For Physiological Stage C-D (symptomatic or declining function) 1:

• ACHD cardiologist every 3-6 months 1
• Echocardiography or CMR annually (Class I) 1
• Pulse oximetry each visit 1
• Annual biochemical and hematological testing for liver and renal function (Class IIa) 1

Major Complications Requiring Intervention

Arrhythmias:

New-onset atrial tachyarrhythmia requires prompt management with thromboembolic prevention and electrophysiology consultation (Class I) 1. New or worsening arrhythmias should trigger search for hemodynamic abnormalities via imaging and/or catheterization (Class I) 1.

Catheter ablation is useful for intra-atrial reentrant tachycardia or focal atrial tachycardia (Class IIa) 1.

Fontan revision surgery with arrhythmia surgery is reasonable for atriopulmonary connections with recurrent arrhythmias refractory to medications and ablation, when ventricular function is preserved (Class IIa) 1.

Anticoagulation:

Vitamin K antagonist is recommended (Class I) for 1:

• Known or suspected thrombus 1
• Thromboembolic events 1
• Prior atrial arrhythmia 1

Antiplatelet therapy or anticoagulation may be considered for patients without these risk factors (Class IIb) 1.

Hepatic Complications:

Imaging (ultrasonography, CMR, CT) and laboratory evaluation for fibrosis, cirrhosis, and hepatocellular carcinoma are reasonable (Class IIa) 1.

Protein-Losing Enteropathy:

Evaluation for cardiac transplantation is reasonable when protein-losing enteropathy develops (Class IIa) 1.

Medical Therapy for Failing Fontan:

Pulmonary vasoactive medications can improve exercise capacity (Class IIa) 1:

• Bosentan demonstrated improved exercise capacity in randomized trial 1
• Other endothelin antagonists and phosphodiesterase-5 inhibitors may be considered 1

Cardiac Catheterization Indications

Catheterization is indicated (Class I) before initial Fontan surgery or revision to assess hemodynamic suitability 1.

Catheterization can be useful (Class IIa) to evaluate symptomatic patients when noninvasive testing is insufficient 1.

Catheterization may be reasonable (Class IIb) in asymptomatic patients to guide optimal therapy 1.

Exercise and Quality of Life

Regular exercise programs appropriate to patient abilities are reasonable (Class IIa) 1. However, cardiorespiratory responses remain subnormal with lower VO2max, cardiac output, and heart rate responses 1, 2. Pre-adolescents undergoing volume-unloading surgery at earlier age have better aerobic capacity 1, 2.

Common Pitfalls

The systemic circulation is often supported by a morphologic right ventricle, which is ill-designed for this purpose and prone to late failure 1. Diastolic filling abnormalities are common regardless of ventricular morphology 1, 2. Even long-term survivors often have reduced systolic function despite normal ventricular mass, likely due to absence of normal interventricular septal interaction 1.

Surgical Expertise Requirement

Surgeons with training and expertise in congenital heart disease must perform operations for single ventricle anatomy (Class I) 1.