What ECG feature is observed in left atrial enlargement?

In the context of left atrial enlargement, the presence of a wide M-shaped P wave in lead II is a significant characteristic. This is due to the anatomical and electrical changes that occur in the heart when the left atrium becomes enlarged. As the left atrium enlarges, it takes longer for the electrical impulse to traverse the dilated atrial tissue, which alters the morphology of the P wave.

The M-shaped appearance, with two distinct peaks, indicates that there is a delay in the depolarization of the left atrium, which is reflective of its enlargement. This unique pattern can be observed on the ECG and is critical for identifying left atrial enlargement, making it a key feature for clinicians interpreting ECGs.

In contrast, options related to peaked P waves, flat T waves, or shortened PR intervals are not characteristic of left atrial enlargement and do not indicate this condition specifically. Thus, the M-shaped P wave serves as an important diagnostic indicator in the context of left atrial enlargement.