Tetralogy of fallot is characterized by following except

**Core Concept**
Tetralogy of Fallot (TOF) is a congenital heart defect characterized by a combination of four key anomalies: ventricular septal defect (VSD), pulmonary stenosis, right ventricular hypertrophy, and an overriding aorta. This complex defect disrupts normal blood flow and oxygenation.

**Why the Correct Answer is Right**
The four components of TOF are a result of abnormal development of the embryonic heart. The VSD allows blood to flow between the left and right ventricles, while the pulmonary stenosis obstructs blood flow from the right ventricle to the lungs. The right ventricular hypertrophy is a compensatory response to the increased resistance in the pulmonary artery. The overriding aorta is a result of the malalignment of the aorta and pulmonary artery during embryogenesis.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect as TOF does not typically present with a secundum atrial septal defect (ASD). The VSD in TOF is usually a perimembranous defect.
* **Option B:** This option is incorrect as TOF is characterized by pulmonary stenosis, not pulmonary atresia. While both conditions involve obstruction of blood flow to the lungs, the degree of obstruction is different.
* **Option C:** This option is incorrect as TOF is not characterized by an absent pulmonary valve. The pulmonary valve is typically present, but the pulmonary artery is narrowed or obstructed.

**Clinical Pearl / High-Yield Fact**
TOF is one of the most common cyanotic congenital heart defects, and its diagnosis is often suspected based on clinical presentation and confirmed by echocardiography.

**Correct Answer:** D.