Which condition is best identified by the presence of a "Himalayan P wave" on an ECG?

The presence of a "Himalayan P wave" on an ECG is most characteristic of atrial septal defect (ASD), not Ebstein's anomaly. In patients with an ASD, the right atrium becomes enlarged due to increased blood flow returning from the lungs, which leads to a distinctive appearance of the P wave on the ECG. This tall, peaked P wave is referred to as the "Himalayan P wave" because of its resemblance to the shape of the Himalayan mountains.

Ebstein's anomaly, while it can be associated with various ECG findings, specifically features such as a short PR interval and accessory conduction pathways, rather than the specific P wave morphology seen in ASD. Wolff-Parkinson-White syndrome presents with a short PR interval and a delta wave due to pre-excitation, and pulmonary hypertension alters ventricular response but does not lead to characteristic changes like the Himalayan P wave.

Understanding the specific ECG changes associated with these conditions is crucial for adequate diagnosis and subsequent management. In the case of ASD, the tall, biphasic P waves on the ECG highlight the increased right atrial pressures and the underlying shunt physiology, thus making it the best answer for identifying this specific condition.