**Core Concept**
The treatment of Tetralogy of Fallot (TOF) involves surgical intervention to alleviate right ventricular outflow tract obstruction and increase systemic blood flow. TOF is characterized by four classic features: ventricular septal defect, pulmonary stenosis, right ventricular hypertrophy, and an overriding aorta.

**Why the Correct Answer is Right**
The modified Blalock-Taussig (BT) shunt is a palliative surgical procedure used to increase pulmonary blood flow in patients with TOF. It involves creating a systemic-to-pulmonary artery shunt using a synthetic graft, typically between the subclavian artery and the pulmonary artery. This shunt allows oxygenated blood to bypass the obstructed pulmonary valve and enter the pulmonary circulation, thereby increasing pulmonary blood flow and reducing cyanosis. The modified BT shunt is often performed in infants and young children before definitive repair, such as the complete repair of TOF.

**Why Each Wrong Option is Incorrect**
**Option B:** The Fontan procedure is a palliative surgical procedure used to treat complex congenital heart defects with single-ventricle physiology, such as tricuspid atresia or hypoplastic left heart syndrome. It is not typically used to treat TOF.

**Option C:** The Glenn shunt, also known as the bidirectional Glenn procedure, is a palliative surgical procedure used to increase pulmonary blood flow in patients with TOF or other single-ventricle heart defects. However, it involves creating a superior vena cava-to-pulmonary artery shunt, which is different from the modified BT shunt.

**Option D:** The Rastelli operation is a surgical procedure used to treat transposition of the great arteries, not TOF. It involves creating a systemic-to-pulmonary artery shunt and an aortic-to-ventricular septal defect conduit.

**Clinical Pearl / High-Yield Fact**
In patients with TOF, the modified BT shunt is often performed before definitive repair to alleviate cyanosis and improve oxygenation. It is essential to monitor these patients closely for signs of pulmonary overcirculation, such as respiratory distress or failure.

**Correct Answer:**
✓ Correct Answer: A. Modified BT shunt