What is the medical management of Tetralogy of Fallot (TOF)?

Medical Management of Tetralogy of Fallot

Definitive Treatment: Surgical Repair

Complete surgical repair in infancy (ideally 3-6 months of age) is the definitive treatment, addressing VSD closure, RVOT obstruction relief, pulmonary valve management, and conduit placement when necessary, achieving survival rates exceeding 98%. 1, 2

• Modern surgical repair consists of VSD closure and relief of right ventricular outflow tract obstruction through infundibular muscle resection, pulmonary valvotomy, and transannular patch placement when the pulmonary annulus is inadequate 1
• Contemporary outcomes demonstrate hospital mortality of 0-2.1% with 30-year survival exceeding 90% 1, 2, 3
• The occasional "pink tetralogy" patient with mild pulmonary obstruction and minimal cyanosis may present undiagnosed in adulthood and requires formal evaluation at an ACHD center for suitability for repair 4

Mandatory Lifelong Surveillance Protocol

All repaired TOF patients require annual follow-up with an adult congenital heart disease (ACHD) specialist for life, as pulmonary regurgitation, RV dysfunction, and arrhythmias determine long-term morbidity and mortality. 4, 1

Annual Assessment Components:

• Clinical history focusing on exercise tolerance, palpitations, dizziness, or syncope 1
• 12-lead ECG to monitor QRS duration—QRS ≥180 ms identifies high risk for sustained ventricular tachycardia and sudden cardiac death 1
• Comprehensive transthoracic echocardiography at an ACHD center assessing RV size/function, pulmonary regurgitation severity, residual RVOT obstruction, tricuspid regurgitation, and aortic root dilation 4, 1
• Cardiac MRI (the reference standard) for precise RV volume quantification and pulmonary regurgitation assessment, as echocardiography underestimates RV dysfunction 4, 1
• Periodic Holter monitoring with frequency individualized based on hemodynamics and clinical suspicion to detect ventricular arrhythmias 1
• Exercise testing to objectively assess functional capacity and detect exertional arrhythmias 1

Arrhythmia Management and Sudden Death Prevention

The incidence of sudden death in adult TOF patients is approximately 2.5% per decade, with ventricular tachycardia as the primary mechanism. 1

Risk Stratification and Intervention:

• Documented sustained ventricular tachycardia or cardiac arrest mandates immediate ICD placement 1, 2
• Worrisome symptoms (palpitations, dizziness, syncope) require immediate evaluation with hemodynamic catheterization and electrophysiology study 1
• Asymptomatic patients with nonsustained VT on surveillance monitoring should undergo electrophysiology study to refine arrhythmia risk, with consideration for surgery if significant pulmonary regurgitation exists 1
• Inducible VT/VF or spontaneous sustained VT warrants ICD implantation if meaningful survival >1 year is expected 1
• Beta blockers should be used in patients with frequent or complex ventricular arrhythmias to reduce sudden cardiac arrest risk 1
• Recurrent sustained monomorphic VT or recurrent ICD shocks can be effectively treated with catheter ablation, though ICD remains necessary due to uncertain recurrence risk after ablation 1

Reintervention Criteria

Pulmonary valve replacement (PVR) is the most common reintervention, required in 40-85% of patients 5-10 years after initial repair due to chronic pulmonary regurgitation causing progressive RV dilation and dysfunction. 1, 2

Indications for Intervention:

• Symptomatic patients with severe pulmonary regurgitation require intervention 1, 2
• Asymptomatic patients with severe pulmonary stenosis or pulmonary regurgitation PLUS progressive or severe RV enlargement or dysfunction require intervention 1, 2
• Residual RVOT obstruction with RV/LV pressure ratio >0.7 or RV systolic pressure >50 mmHg requires intervention 4, 1
• Residual shunts (ASD or VSD) with left-to-right shunt greater than 1.5:1 in appropriate anatomic location warrant interventional catheterization 4

Catheter-Based Interventions:

• Balloon angioplasty or stent implantation for branch pulmonary artery stenosis when RV pressure exceeds 50% of systemic level 4
• Elimination of residual shunts or aortopulmonary collateral vessels 4
• Dilation (with or without stent) of RVOT obstruction 4
• Percutaneous pulmonary valve implantation (emerging technique with promising results) 4

Management of Hypercyanotic Spells (Unoperated Patients)

For infants with unoperated TOF presenting with hypercyanotic spells, immediate sedation is critical to terminate the spell. 5

• Intranasal midazolam offers an effective alternative when IV access is difficult, terminating hyperpnea within 3 minutes and increasing oxygen saturation 5
• Sedation calms the child, reduces oxygen consumption, and facilitates IV placement for further management 5

Pregnancy Considerations

Pregnancy is contraindicated in patients with unrepaired TOF. 1

• After repair, pregnancy is usually well tolerated if no important hemodynamic residua exist, functional capacity is good, and RV function is no more than mildly depressed with maintained sinus rhythm 1
• Fetal risk: 4-6% risk of congenital heart disease in offspring; screening for 22q11.2 microdeletion should be performed before pregnancy for appropriate genetic counseling 4, 1
• Fetal echocardiography should be offered in the second trimester 1
• Uncorrected TOF with pregnancy carries extremely high maternal mortality risk, particularly in the first several days after delivery 4

Genetic Screening

Screening for heritable causes (e.g., 22q11 deletion) should be offered to all patients with tetralogy of Fallot. 4

• Before pregnancy or if a genetic syndrome is identified, consultation with a geneticist should be arranged 4

Critical Pitfalls to Avoid

• Underestimating RV dysfunction even in asymptomatic patients can lead to decompensation under anesthesia 1
• Delaying PVR until irreversible RV remodeling occurs worsens outcomes—intervention should occur before this threshold 1
• Ignoring QRS duration >180 ms substantially increases arrhythmia risk and should prompt enhanced monitoring 1
• The severity of pulmonary regurgitation is often underestimated by auscultation compared to Doppler echocardiography; absence of an audible diastolic murmur does not exclude significant pulmonary regurgitation 6
• Inadequate preoperative assessment without recent echocardiography and knowledge of residual lesions significantly increases risk 1