Which one of the following is the most common cause of cyanotic heart disease –
**Core Concept**
Tetralogy of Fallot (TOF) is a congenital heart defect characterized by four classic components: ventricular septal defect, pulmonary stenosis, right ventricular hypertrophy, and an overriding aorta. It is a cyanotic congenital heart disease, resulting in reduced oxygenation of blood.
**Why the Correct Answer is Right**
Tetralogy of Fallot is the most common cyanotic congenital heart disease due to the presence of a large ventricular septal defect (VSD) and pulmonary stenosis (PS), leading to a significant right-to-left shunt. This results in deoxygenated blood bypassing the lungs and entering the systemic circulation directly. The overriding aorta further contributes to the mixing of oxygenated and deoxygenated blood.
**Why Each Wrong Option is Incorrect**
* **Option A:** Transposition of the great arteries (TGA) is another cyanotic congenital heart disease, but it is less common than TOF. In TGA, the aorta arises from the right ventricle, and the pulmonary artery arises from the left ventricle.
* **Option B:** Tricuspid atresia is a rare cyanotic congenital heart disease characterized by the absence or abnormality of the tricuspid valve, leading to right-sided hypoplasia.
* **Option C:** Ebstein's anomaly is a congenital heart defect characterized by an abnormal tricuspid valve and right ventricular hypoplasia. While it can cause cyanosis, it is less common than TOF.
**Clinical Pearl / High-Yield Fact**
Tetralogy of Fallot can present with a "tet" sign on chest X-ray, which refers to the "boot-shaped" heart due to the right ventricular hypertrophy.
**Correct Answer:** C. Tetralogy of Fallot