## **Core Concept**
The P wave in an electrocardiogram (ECG) represents atrial depolarization. The morphology of the P wave can vary depending on the lead used. In a normal ECG, the P wave is typically upright in leads I, II, and V4-V6, but its appearance can be biphasic in certain leads due to the orientation of the atrial depolarization vector.

## **Why the Correct Answer is Right**
The correct answer, , often shows a biphasic P wave in a normal ECG. This is because the P wave in lead V1 is usually biphasic, with a positive deflection (representing depolarization of the right atrium) followed by a negative deflection (representing depolarization of the left atrium). This biphasic appearance occurs due to the orientation of the atrial depolarization wavefront relative to the lead V1 electrode.

## **Why Each Wrong Option is Incorrect**
- **Option A:** Lead I typically shows an upright P wave in a normal ECG, as the depolarization wavefront moves towards the lead I electrode.
- **Option B:** Lead II usually shows an upright P wave as well, reflecting the normal depolarization sequence of the atria.
- **Option D:** Lead V6 typically shows an upright P wave, similar to leads I and II, as the depolarization wavefront moves towards this electrode.

## **Clinical Pearl / High-Yield Fact**
A key point to remember is that a biphasic P wave in lead V1 is a normal finding. However, if the P wave is deeply inverted or shows a significant change in morphology in other leads, it may indicate an abnormality such as left atrial enlargement or an ectopic atrial rhythm.

## **Correct Answer:** . V1.