Which of the following would be an indication of a left bundle branch block on an EKG?

A left bundle branch block (LBBB) is characterized primarily by a wide QRS complex that typically exhibits a specific pattern on the electrocardiogram (EKG). This pattern arises due to the delayed depolarization of the left ventricle as a result of the block in the left bundle branch.

In LBBB, the QRS duration is usually greater than 120 milliseconds, which results from sluggish conduction through the left bundle branch. Additionally, the characteristic features of the wide QRS complex include a notched R wave (often referred to as "M" shaped) in leads I, aVL, V5, and V6, and a deep S wave in leads V1 and V2. These features help differentiate it from other conduction abnormalities and provide a clear indication of LBBB.

Understanding this characteristic pattern is essential for accurately diagnosing LBBB on an EKG. Hence, identifying a wide QRS complex with these features would indicate the presence of a left bundle branch block.