**Core Concept**
The 'Himalayan P waves' in ECG refer to a specific pattern observed in patients with high-altitude exposure, particularly in the Himalayan region. This phenomenon is attributed to the body's adaptation to the lower oxygen levels at high altitudes.

**Why the Correct Answer is Right**
At high altitudes, the body undergoes various physiological changes to compensate for the reduced oxygen levels. The 'Himalayan P waves' are a result of these adaptations, specifically the increased parasympathetic tone and the release of erythropoietin, which stimulates the production of red blood cells. This leads to an increase in the size and amplitude of the P waves in the ECG, giving them a characteristic 'Himalayan' appearance.

**Why Each Wrong Option is Incorrect**
* **Option A:** is incorrect because it does not relate to the specific physiological changes observed at high altitudes.
* **Option B:** is incorrect because it is more commonly associated with cardiac conditions such as atrial fibrillation or flutter, which does not directly relate to the 'Himalayan P waves' phenomenon.
* **Option C:** is incorrect because it is more commonly associated with electrolyte imbalances or cardiac conditions such as hyperkalemia, which does not directly relate to the 'Himalayan P waves' phenomenon.

**Clinical Pearl / High-Yield Fact**
The 'Himalayan P waves' phenomenon is a classic example of the body's adaptability to environmental changes, and it highlights the importance of considering the patient's exposure to high altitudes when interpreting ECGs.

**Correct Answer: C. High-altitude exposure.**