Right axis deviation is seen in all except –a) VSDb) Tricuspid atresiac) Pulmonary atresiad) ASD

**Core Concept**
Right axis deviation (RAD) refers to an abnormal orientation of the electrical axis of the heart, where the mean electrical axis is between +90° and +180°. This deviation is often seen in conditions that affect the right ventricle or the conduction system of the heart.

**Why the Correct Answer is Right**
The correct answer is **Tricuspid atresia**. In tricuspid atresia, the tricuspid valve is absent or abnormally developed, leading to a significant reduction in the flow of blood from the right atrium to the right ventricle. As a result, the right ventricle is underdeveloped, and the electrical axis of the heart is shifted to the left, typically resulting in left axis deviation (LAD) rather than RAD. This is because the underdeveloped right ventricle has a more negative QRS complex, which is a characteristic of LAD.

**Why Each Wrong Option is Incorrect**
**Option A:** VSD (Ventricular Septal Defect) can lead to RAD due to increased volume load on the right ventricle, causing it to hypertrophy and shift the electrical axis to the right.
**Option C:** Pulmonary atresia can also cause RAD due to increased pressure and volume load on the right ventricle, leading to hypertrophy and a shift in the electrical axis.
**Option D:** ASD (Atrial Septal Defect) typically causes RAD due to increased flow of blood from the left atrium to the right atrium, resulting in increased volume load on the right ventricle and a shift in the electrical axis to the right.

**Clinical Pearl / High-Yield Fact**
It's essential to note that the presence of RAD can be a critical clue in diagnosing congenital heart diseases, particularly those affecting the right ventricle. A thorough understanding of the underlying anatomy and physiology is crucial in interpreting ECG findings in patients with suspected congenital heart disease.

**Correct Answer: D. ASD**