**6.3 Tetralogy of Fallot (ToF)**

ToF is the most common cyanotic CHD, accounting for 10% of all CHD. It comprises of four anatomical defects: (i) VSD (ii) RVOT obstruction (iii) RV hypertrophy (iv) Over riding of aorta.

VSD is usually large, non restrictive which led to equalization of RV and LV pressures and shunting through VSD depends primarily on systemic and pulmonary vascular resistance. RVOT obstruction is dynamic due to hypertrophied infundibulum but fixed obstruction can also occur due to v pulmonary valve stenosis.

Due to reduce pulmonary flow, main and branched pulmonary arteries hypoplasia may also be seen. Right ventricular hypertrophy is more marked when VSD is restrictive. ToF may also be associated with certain defects like anomalous origin of LAD crossing the RVOT, pulmonary atresia, absent pulmonary valve and complete AV canal defect.

#### **Palliative surgery**

The classic Blalock Taussig shunt was performed in 1944 to relieve the ToF related cyanosis where end to side anastomosis of subclavian artery to pulmonary artery was performed. Today modified BT shunt is the most commonly performed palliative procedure in CHD patients where a synthetic graft is interpositioned between subclavian artery and ipsilateral pulmonary artery.

#### **Complete surgical repair**

First total correction was performed by Lillehei in 1954. Surgical correction involves infundibular muscle resection through right ventriculotomy or transpulmonarry approach. Pulmonary valve is removed or dilated accordingly and a transannular patch is placed. VSD is also closed at the same setting. Main Pulmonary artery and its branches are also inspected for narrowing. Some centres creates small ASD to counteract high right sided pressures. There is trend towards early total correction rather than palliative surgery which is followed by total correction.

#### **Anaesthetic management**

Goal of anaesthetic management is to avoid low SVR and ionotropes before bypass. If patient is on prostaglandin E1 then it should be continued in pre bypass period. Avoid catecholamine release in preoperative phase and at the time of induction by providing good premedication and adequate analgesia and anaesthesia.

Induction can be done with ketamine and fentanyl if intravenous line is in place. Inhalation induction can also be performed while maintaining SVR. Remember infundibular stenosis increased by increasing contractility and heart rate, so minimize noxious stimulus avoid catecholamine release. This is achieved by high dose fentanyl at the maintenance phase. Arterial line and central line should be placed after induction and intubation.

Acute desaturation at any time should be considered as tet spell and treated by analgesics and volume. Phenylephrine should also be available to treat low systemic vascular resistance and hypotension. Steroids given at the time of induction can help in reducing release of inflammatory markers during cardio pulmonary bypass.

TEE is helpful in assessing residual VSD and infundibular stenosis and degree of pulmonary regurgitation. In case of tet spell, give 100% O2, Phenyl ephrine, volume, increase depth of anaesthesia, hyperventilate and give bicarbonate. In addition esmolol or proponol can be tried to reduce infundibular spasm.

During postbypass period be ready for arrhythmias and heart block, RV dysfunction and coagulopathy. Ionotrpic support is mandatory in postbypass period along with high filling pressure particularly if right ventriculotomy was performed. Blood products should be available and antifibrinolytics should be started for coagulopathy.
