**Core Concept**
Primary pulmonary hypertension is a progressive disease characterized by high blood pressure in the pulmonary arteries, leading to right ventricular failure. The ECG changes in primary pulmonary hypertension are primarily due to right ventricular hypertrophy and strain.

**Why the Correct Answer is Right**
The ECG features of primary pulmonary hypertension include P pulmonale (elevated P wave in leads II, III, and aVF), right axis deviation, and right ventricular hypertrophy, which can manifest as a strain pattern or a new left bundle branch block. These changes are due to the increased workload on the right ventricle. **Option C** is a classic feature of primary pulmonary hypertension, representing the right ventricular strain pattern.

**Why Each Wrong Option is Incorrect**
**Option A:** Not a typical feature of primary pulmonary hypertension. Atrial enlargement or left ventricular hypertrophy is not a direct consequence of primary pulmonary hypertension.
**Option B:** This is a feature, not an exception. Right axis deviation is commonly seen in primary pulmonary hypertension due to right ventricular hypertrophy.
**Option D:** While a new LBBB can be seen in primary pulmonary hypertension, it is not the most characteristic ECG feature, and the question asks for the exception.

**Clinical Pearl / High-Yield Fact**
Primary pulmonary hypertension is characterized by a high mortality rate, and early diagnosis is crucial for management and prognosis. The ECG is a useful tool in diagnosing and monitoring the progression of the disease.

**Correct Answer:** B.