Tetralogy of Fallot

Definition: TOF is the most common cyanotic congenital heart disease. It accounts for 5% to 10% of all congenital heart disease, and has an incidence of approximately 1:2000 live births. Classically described with the cardiac constellation of:

1. Ventricular septal defect (usually large)

2. Overriding aorta

3. Right ventricular outflow tract obstruction (subvalvular, valvular, supravalvular)

4. Right ventricular hypertrophy.

A wide spectrum of TOF exists, including the variants of pulmonary stenosis (TOF-PS), pulmonary atresia (TOF-PA/MAPCA) and absent pulmonary valve (TOF-APV).

Right sided arch in 25% of cases.

Physiology:

Decreased pulmonary blood flow (TET-spells) due to RVOT obstruction and increased PVR or/and congestive cardiac failure (diuretics, digoxin, nutrition).

Diagnosis:

Echo

Management of cyanotic spells:

• Oxygenation
• Volume expansion: 10 ml/kg IV colloid/crystalloid
• Sedation: IV morphine 10-50 mcg/kg; or fentanyl 1 mcg/kg
• Posture: head down position/knees-to-chest (increase VR; mild pressure over femoral arteries to increase SVR)
• Vasopressor: metaraminol 5-10 mcg/kg IV or phenylephrine 5-10 mcg/kg, then 1-5 mcg/kg/min IV/(SC)
• Esmolol 100-500 mcg/kg (titratable) +/- infusion

Preoperative preparation:

ECG, CXR, CUS, FBE, clotting, UECs, PRBC (4), FFP (2), platelets (2), cryoprecipitate (2).

Methylprednisolone 10mg/kg 12 hrs and 6 hrs pre surgery in neonates.

Surgery:

Timing: dependant on anatomical associations, degree of pulmonary stenosis and development of pulmonary arteries:

1. Complete correction at 3-6 mths

• Patch repair VSD
• Resection of infundibular muscle
• Pulmonary valvotomy +/- transannular patch.

2. Staged procedure with BTS (BT-Shunt) in severe cyanosis or hypercyanotic spells in neonatal period.

10-15% require re-operation to relieve RVOTO +/- residual VSD.

Majority require pulmonary valve replacement for incompetence in the medium-to-long term.

Postoperative management:

• Keep intubated, ventilated, sedated and paralysed for 24 hrs
• Inotropes: milrinone plus dopamine or noradrenaline
• Haemodynamics: age adjusted, in neonates: SBP >60 mmHg, MAP >40 mmHg (increasing over time), LAP 8-12 mmHg, CVP 8-12 mmHg
• Respiratory: normoxaemia, normocapnea
• Fluid restriction: 1ml/kg/hr, trophic feeds
• Haemostasis
• Keep normothermia (except in JET → cool to 35°C)

Specific problems:

• Low cardiac output state: expect 6-12 hrs post bypass, mainly diastolic dysfunction
• Arrthymias: JET; decrease inotropes, overdrive pacing, add noradrenaline, cooling, amiodarone
• Diastolic RV dysfunction: restrictive physiology, usually transient phenomena lasting 48-72 hrs. may require inotropes for improving of diastolic dysfunction
• Residual RVOTO: ECHO confirmation +/- reoperation
• Pulmonary regurgitation: as above
• Residual VSD: as above

Outcome:

Perioperative mortality: 3 – 8%

Long term survival 85 – 90%

References:

[1] Critical Heart Disease in Infants and Children; 2nd ed, Nichols et al: Tetralogy of Fallot with and without pulmonary atresia

[2] Lancet, 2009; 374: 1462-71: Apitz et al: Tetralogy of Fallot

[3] World J Surg, 34: 658-668; 2010: Starr J: Starr et al: Tetralogy of Fallot: Yesterday and Today.

[4] DVD 2004: Something the Lord made (Alan Rickman, Mos Def)

[5] Pediatr Cardiol. 2013 Mar 5. Dodgen et al: Characteristics and Hemodynamic Effects of Extubation Failure in Children Undergoing Complete Repair for Tetralogy of Fallot.

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