# Tetralogy of Fallot: Primary Repair and Long-Term Management

## Overview

Tetralogy of Fallot (TOF) is the most common cyanotic congenital heart defect, accounting for 3-5% of all congenital heart disease. The four classic components described by Fallot in 1888 are a large non-restrictive perimembranous/malalignment-type ventricular septal defect, an overriding aorta with rightward deviation of the aortic root over the VSD, right ventricular outflow tract obstruction (RVOTO) that ranges in severity from infundibular stenosis to pulmonary atresia, and right ventricular hypertrophy that develops secondary to RVOTO. The fundamental embryologic defect is anterior malalignment of the conal (outlet) septum. Primary complete repair in infancy is now the standard of care.

## Anatomy and Pathophysiology

### Spectrum of RVOT Obstruction

RVOT obstruction in TOF exists along a spectrum. Infundibular (subvalvar) stenosis involves muscular hypertrophy of the RVOT and has a dynamic component. Pulmonary valve stenosis features a bicuspid or dysplastic valve, and most patients have combined infundibular and valvar stenosis. Supravalvar stenosis involves main pulmonary artery or branch PA hypoplasia. At the extreme end, pulmonary atresia with VSD (TOF/PA) represents the most severe form of the disease.

### VSD Characteristics

The VSD in TOF is large, non-restrictive, and of the malalignment type. It is located beneath the overriding aorta and bordered posteroinferiorly by the conduction system (bundle of His). RV and LV pressures equalize through the defect.

### Hemodynamics

The degree of cyanosis is determined by the severity of RVOT obstruction, not by VSD size. Patients with mild RVOTO have a predominantly left-to-right shunt and appear pink ("pink Tet"), while those with severe RVOTO develop a right-to-left shunt with systemic desaturation and cyanosis. "Tet spells" (hypercyanotic episodes) result from dynamic infundibular spasm causing acute right-to-left shunting and are managed with knee-chest positioning, oxygen, morphine, IV phenylephrine, volume resuscitation, and beta-blocker therapy (esmolol).

### Associated Anomalies

A right aortic arch is present in 25% of patients. Anomalous coronary arteries occur in 3-5%, with the LAD arising from the RCA and crossing the RVOT being critical to identify before surgery. An ASD or PFO (pentalogy of Fallot) may be present. Aortopulmonary collaterals (MAPCAs) are found in TOF/PA. Approximately 15% of TOF patients carry the 22q11.2 deletion (DiGeorge syndrome).

<image>Anatomy of tetralogy of Fallot showing the four cardinal features: malalignment VSD, overriding aorta, RVOT obstruction, and RV hypertrophy</image>

## Surgical Management

### Timing of Repair

Primary complete repair in infancy is the preferred approach, typically performed at 3-6 months of age. Earlier repair (neonatal) is undertaken for severe cyanosis or duct-dependent pulmonary blood flow. A staged approach with initial palliation followed by later repair is reserved for very small or premature neonates, complex coronary anatomy crossing the RVOT, or severely hypoplastic pulmonary arteries requiring growth before repair.

### Palliative Procedures (When Staging)

The modified Blalock-Taussig-Thomas (mBTT) shunt places a Gore-Tex graft from the subclavian or innominate artery to the ipsilateral PA, providing augmented pulmonary blood flow and allowing pulmonary artery growth. Ductal stenting offers a catheter-based alternative in neonates. RVOT stenting provides catheter-based palliation to relieve infundibular obstruction.

### Primary Complete Repair: Technique

The repair is performed through a median sternotomy with CPB, moderate hypothermia, aortic cross-clamp, and cardioplegia.

#### VSD Closure

The preferred approach is through a right atriotomy using the transatrial-transpulmonary approach to avoid ventriculotomy. A Dacron or Gore-Tex patch is placed with interrupted pledgeted sutures. Sutures are placed on the RV side of the septum posteroinferiorly to avoid the bundle of His, and complete closure with no residual shunt is the goal.

#### RVOT Obstruction Relief

Infundibular resection involves removing obstructing muscle bundles through the tricuspid valve or a limited infundibulotomy. Pulmonary valvotomy or valvectomy through commissurotomy addresses the stenotic pulmonary valve. When the pulmonary annulus is severely hypoplastic (Z-score less than -2 to -3), a transannular patch (TAP) is placed, extending from the RVOT across the annulus to the main PA. This results in obligate pulmonary regurgitation, making valve annulus preservation preferable when possible for better long-term RV function. When an anomalous coronary artery crosses the RVOT, or in TOF/PA, an RV-PA conduit using a homograft or bovine jugular vein conduit (Contegra) is placed.

#### Approach Philosophy: Valve-Sparing vs. Transannular Patch

Valve-sparing repair aims to preserve the native pulmonary valve whenever possible, resulting in a lower incidence of late pulmonary regurgitation and reduced need for pulmonary valve replacement. An intraoperative RV/LV pressure ratio of less than 0.7-0.85 is considered acceptable. The transannular patch is used when valve-sparing repair results in unacceptable residual RVOTO, accepting free PR in exchange for adequate RVOT relief with the understanding that the patient will likely need PVR in adulthood.

| Feature | Valve-Sparing Repair | Transannular Patch (TAP) |
|---------|---------------------|--------------------------|
| RVOT approach | Infundibular resection +/- pulmonary valvotomy | Patch extends across annulus onto MPA |
| Pulmonary regurgitation | Minimal to mild | Free (obligate) |
| Acceptable residual RVOTO | RV/LV pressure ratio < 0.7-0.85 | Minimal residual gradient |
| Late PVR requirement | Lower | Higher (majority by adulthood) |
| Long-term RV function | Better preserved | Progressive RV dilation from chronic PR |
| Ideal candidate | Adequate annular Z-score (> -2 to -3) | Severely hypoplastic annulus (Z-score < -2 to -3) |

<image>Surgical repair of tetralogy of Fallot showing transatrial VSD patch closure, infundibular muscle resection, and comparison of valve-sparing versus transannular patch RVOT reconstruction</image>

## Postoperative Management

ICU monitoring with arterial and central venous lines is standard. RV restrictive physiology is common in the early postoperative period, manifesting as elevated CVP with preserved cardiac output and antegrade PA flow during atrial contraction on echocardiography. This is managed with preload optimization and slow ventilator weaning. Junctional ectopic tachycardia (JET) is the most common early postoperative arrhythmia and is managed with cooling, minimizing inotropes, and amiodarone. Complete heart block occurs in 1-3% of cases, and temporary pacing wires are placed at the time of surgery. Residual VSD requires reintervention if the Qp:Qs exceeds 1.5:1 with hemodynamic significance.

## Long-Term Outcomes and the Growing Population of Adults

### Survival

Thirty-year survival after TOF repair exceeds 90%, and the majority of patients with repaired TOF are now adults. However, lifelong follow-up is required because repaired TOF is not cured TOF.

### Chronic Pulmonary Regurgitation

Chronic PR is the most important long-term sequela, especially after transannular patch repair. RV volume overload leads to progressive RV dilatation and dysfunction, manifesting as exercise intolerance, arrhythmia, and heart failure. Cardiac MRI is the gold standard for assessing RV volumes and quantifying PR, using the RV end-diastolic volume index (RVEDVi) and RV end-systolic volume index (RVESVi).

### Indications for Pulmonary Valve Replacement (PVR)

PVR is indicated for symptomatic severe PR with RV dilatation. In asymptomatic patients, PVR is recommended when the RVEDVi reaches 150-160 mL/m2 or higher, when the RVESVi reaches 80-90 mL/m2 or higher, when there is progressive RV dilatation or declining RV function, sustained arrhythmia (VT or atrial arrhythmia), moderate-severe tricuspid regurgitation, or declining exercise capacity on objective testing. Timing is critical because surgery should be performed before irreversible RV dysfunction develops.

| PVR Indication | Threshold / Criterion |
|---------------|----------------------|
| Symptomatic severe PR | Any degree of RV dilation with symptoms |
| RVEDVi (asymptomatic) | >= 150-160 mL/m2 |
| RVESVi (asymptomatic) | >= 80-90 mL/m2 |
| RV function | Progressive decline on serial imaging |
| Arrhythmia | Sustained VT or new atrial arrhythmia |
| Tricuspid regurgitation | Moderate to severe |
| Exercise capacity | Objective decline on serial testing |
| QRS duration | > 180 ms (risk factor for VT/SCD) |

### Surgical PVR

A bioprosthetic valve is placed in the pulmonary position using a homograft, bioprosthetic valve, or Contegra conduit. Concomitant procedures may include tricuspid valve repair, RVOT aneurysm resection, and arrhythmia surgery. Operative mortality is low at 1-2% in experienced centers, with expected valve durability of 10-15 years (younger patients may need multiple replacements).

### Transcatheter PVR

The Melody valve (Medtronic) and SAPIEN valve (Edwards) provide catheter-based PVR options. These are best suited for patients with prior RV-PA conduits that provide a landing zone. The native RVOT after transannular patch is often too large for current transcatheter valves, though emerging self-expanding valves such as the Harmony and Alterra Adaptive Prestent are addressing this population. Advantages include avoidance of reoperative sternotomy, though limitations include infective endocarditis risk (approximately 2% per year) and limited sizing options.

### Arrhythmia and Sudden Death

Ventricular tachycardia is the most feared arrhythmia and carries a risk of sudden cardiac death (SCD). Risk factors include wide QRS duration (greater than 180 ms), severe PR, RV dysfunction, and prior palliative shunts, with an annual SCD risk of 0.1-0.2% per year. Atrial arrhythmias, especially atrial flutter (intra-atrial reentrant tachycardia), are common. Electrophysiology study and ablation are performed for documented or suspected VT, and ICD implantation is used for secondary prevention or selected primary prevention.

<image>Cardiac MRI in adult with repaired TOF showing dilated right ventricle from chronic pulmonary regurgitation, with volume measurements for PVR decision-making</image>

## Clinical Pearls

An anomalous LAD from the RCA crossing the RVOT must be identified preoperatively because it changes the entire surgical approach, requiring a conduit instead of a transannular patch. Valve-sparing repair is the goal, and accepting some residual RVOTO (RV/LV ratio less than 0.7-0.85) is preferable to obligate free pulmonary regurgitation. Every repaired TOF patient needs lifelong follow-up because the "second act" of TOF is managing chronic pulmonary regurgitation in adulthood. Cardiac MRI is the gold standard for timing PVR, and one should not wait until the RV is irreversibly dilated. A QRS duration greater than 180 ms on ECG in repaired TOF is a red flag for VT risk and warrants electrophysiologic evaluation. JET is the most common early postoperative arrhythmia after TOF repair, and early recognition with patient cooling is essential. Finally, 22q11.2 deletion screening should be performed in all TOF patients because it impacts anesthetic management (hypocalcemia, immune deficiency) and family counseling.

## References
- Baumgartner H et al. "2020 ESC Guidelines for the management of adult congenital heart disease." *Eur Heart J*. 2021.
- Stout KK et al. "2018 AHA/ACC Guideline for the Management of Adults With Congenital Heart Disease." *Circulation*. 2019.
- Geva T. "Indications for pulmonary valve replacement in repaired tetralogy of Fallot." *Circulation*. 2013.
- Therrien J et al. "Optimal timing for pulmonary valve replacement in adults after tetralogy of Fallot repair." *Am J Cardiol*. 2005.
- Gatzoulis MA et al. "Risk factors for arrhythmia and sudden cardiac death late after repair of tetralogy of Fallot." *Lancet*. 2000.