What is the management and treatment of Tetralogy of Fallot, a cyanotic congenital heart disease?

Tetralogy of Fallot: Cyanotic Congenital Heart Disease

Definition and Anatomy

Tetralogy of Fallot is a cyanotic congenital heart defect characterized by four anatomical components: subpulmonary infundibular stenosis, a ventricular septal defect (VSD), an overriding aorta (less than 50% override), and right ventricular hypertrophy. 1

The anatomical features include:

• Large subaortic VSD that is typically single and in the subaortic position 1
• Pulmonary valve stenosis with a small, stenotic valve in most cases 1
• Pulmonary artery abnormalities including hypoplasia of the pulmonary trunk or branch pulmonary arteries, with stenosis at any level being common 1
• Right aortic arch present in approximately 25% of cases 1
• Coronary artery anomalies most commonly involving the left anterior descending coronary artery 1
• Associated defects including secundum ASD, atrioventricular septal defect (especially with Down syndrome), and occasionally absent pulmonary artery (most often left-sided) 1

Surgical Management Strategy

Complete surgical repair should be performed in the first year of life, typically before 6 months of age, with current mortality rates below 2%. 2, 3

Primary Complete Repair (Preferred Approach)

• Performed as the primary procedure in most patients after 6 months of age who are asymptomatic and weigh more than 4 kg 3
• Consists of VSD closure and relief of right ventricular outflow tract (RVOT) obstruction 1
• Relief of RVOT obstruction may include simple resection of infundibular stenosis, but if the pulmonary annulus is hypoplastic, transannular patch placement or pulmonary valve replacement may be required 1
• Coronary anatomy must be defined preoperatively to avoid interruption of an anomalous anterior descending coronary artery crossing the RVOT 1

Staged Approach (Palliative Shunt First)

Modified Blalock-Taussig shunt followed by complete repair at 6-12 months is indicated for:

• Symptomatic patients (hypercyanotic spells, ductal-dependent pulmonary circulation) weighing less than 4 kg 3
• Asymptomatic patients weighing less than 4 kg with threatened pulmonary artery isolation 3

Long-Term Outcomes and Surveillance

Long-term survival after tetralogy repair is excellent, with 35-year survival approximately 85% and 30-year survival ranging from 68.5% to 90.5%. 1, 4

Mandatory Annual Follow-Up

All patients with repaired tetralogy of Fallot require annual surveillance including: 1

• History and physical examination
• ECG assessment
• Assessment of RV function by echocardiography
• Periodic exercise testing to objectively assess functional capacity and detect exertional arrhythmias 1

Common Residual Lesions Requiring Monitoring

Pulmonary regurgitation is the most common long-term problem, leading to progressive RV dilation and dysfunction 5, 4

Residual RVOT obstruction with RV systolic pressure >50 mmHg or RV/LV pressure ratio >0.7 requires intervention 1, 5

Arrhythmias including ventricular tachycardia, atrial flutter, and atrial fibrillation are significant concerns, with sudden death incidence estimated at 2.5% per decade 1

Indications for Reintervention

Class I Indications (Must Intervene)

Pulmonary valve replacement is indicated for: 1

• Severe pulmonary regurgitation with symptoms or decreased exercise tolerance

Class IIa Indications (Should Intervene)

Pulmonary valve replacement is reasonable for severe pulmonary regurgitation with any of the following: 1

• Moderate to severe RV dysfunction
• Moderate to severe RV enlargement
• Development of symptomatic or sustained atrial and/or ventricular arrhythmias
• Moderate to severe tricuspid regurgitation

Surgery is reasonable for residual RVOT obstruction with: 1

• Peak instantaneous echocardiography gradient >50 mm Hg
• RV/LV pressure ratio >0.7
• Progressive and/or severe RV dilatation with dysfunction
• Residual VSD with left-to-right shunt >1.5:1
• Severe aortic regurgitation with symptoms or more than mild LV dysfunction
• Combination of multiple residual lesions leading to RV enlargement or reduced RV function

Arrhythmia Management

Risk Stratification

QRS duration ≥180 ms on ECG is a critical risk factor for sustained ventricular tachycardia and sudden cardiac death. 1, 5

Symptomatic Arrhythmias

Worrisome symptoms (palpitations, dizziness, syncope) mandate prompt evaluation including: 1

• Hemodynamic catheterization
• Electrophysiology study
• Echocardiography to identify repairable hemodynamic lesions

Documented sustained ventricular tachycardia or cardiac arrest requires implantable cardioverter defibrillator (ICD) placement. 1

Electrophysiology Study Indications

In adults with repaired tetralogy of Fallot with high-risk characteristics and frequent ventricular arrhythmias, electrophysiology study is useful to evaluate risk of sustained VT/VF. 1

ICD implantation is reasonable for inducible VT/VF or spontaneous sustained VT if meaningful survival >1 year is expected. 1

Catheter Ablation

For recurrent sustained monomorphic VT or recurrent ICD shocks, catheter ablation can be effective. 1

Special Populations

Pregnancy Considerations

Pregnancy is contraindicated in unrepaired tetralogy of Fallot. 1

After repair, pregnancy prognosis is good provided: 1

• No important hemodynamic residua exist
• Functional capacity is good
• RV function is no more than mildly depressed
• Sinus rhythm is maintained

Comprehensive cardiovascular evaluation is mandatory before each pregnancy. 1

Genetic Counseling

Screening for 22q11.2 microdeletion should be performed before pregnancy in patients with conotruncal abnormalities. 1

Without 22q11.2 deletion, offspring have approximately 4-6% risk of congenital heart disease; fetal echocardiography should be offered in the second trimester. 1

With 22q11.2 deletion, there is 80% lifetime prevalence of hypocalcemia due to parathyroid hypoplasia, requiring ongoing monitoring. 1, 6

Critical Perioperative Considerations

For non-cardiac surgery in repaired tetralogy patients: 5

• Maintain RV function by optimizing preload, reducing afterload, and supporting contractility
• Minimize increases in pulmonary vascular resistance by avoiding hypoxia, hypercarbia, acidosis, hypothermia, and excessive positive pressure ventilation
• Prevent tachycardia to preserve diastolic filling time and coronary perfusion
• Maintain systemic vascular resistance to prevent right-to-left shunting if residual ASD/VSD present
• Have defibrillator immediately available with antiarrhythmic medications prepared

Common Pitfalls to Avoid

Cardiomegaly on chest x-ray mandates search for residual hemodynamic lesion, most commonly pulmonary regurgitation. 1

Development of any arrhythmia (atrial or ventricular) requires investigation for underlying hemodynamic abnormality. 1

Hypoxemia postoperatively necessitates search for patent foramen ovale or ASD with right-to-left shunt. 1

RV enlargement, dysfunction, or significant tricuspid regurgitation indicates need to evaluate for residual pulmonary regurgitation. 1

Underestimating RV dysfunction in asymptomatic patients can lead to decompensation under anesthesia. 5

QRS duration >180 ms significantly increases arrhythmia risk and mandates enhanced monitoring. 5