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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