**Core Concept**
Pulmonary hypertension is characterized by elevated pulmonary artery pressure, which can lead to right ventricular hypertrophy and strain. This condition can manifest on the electrocardiogram (ECG) due to the altered electrical activity associated with right ventricular enlargement and hypertrophy.

**Why the Correct Answer is Right**
The ECG feature of pulmonary hypertension is typically a right axis deviation (RAD), which is a result of the right ventricle's altered electrical activity. This deviation is often seen in the presence of right ventricular hypertrophy, a common consequence of pulmonary hypertension. The right axis deviation is caused by the increased electrical activity in the direction of the right ventricle, which is due to the hypertrophy and enlargement of the right ventricle.

**Why Each Wrong Option is Incorrect**
**Option A:** Prolonged QT interval is not a specific feature of pulmonary hypertension. It can be seen in various cardiac conditions, including electrolyte imbalances and myocardial ischemia.
**Option B:** Left axis deviation is typically seen in conditions affecting the left ventricle, such as left ventricular hypertrophy or myocardial infarction.
**Option C:** Right bundle branch block (RBBB) is a specific ECG pattern characterized by a slurred upstroke (QRS complex) in the right precordial leads, which is not a direct consequence of pulmonary hypertension.

**Clinical Pearl / High-Yield Fact**
Remember that right axis deviation can be a subtle finding on the ECG, and it is essential to carefully evaluate the entire ECG tracing, including the limb leads and precordial leads, to confirm the diagnosis.

**Correct Answer: A. Right axis deviation.