How can an incomplete right bundle branch block (IRBBB) be identified on an EKG?

An incomplete right bundle branch block (IRBBB) can be identified on an EKG by observing a widened QRS complex with an 'rSR' pattern in Lead V1. This characteristic appearance is indicative of the incomplete block, reflecting that the right bundle branch is conducting impulses but not fully. In this scenario, the initial R wave is followed by a small downward deflection (the S wave), and then another upward deflection, creating the 'rSR' pattern. This pattern occurs because the right ventricle depolarizes slightly later than the left due to the conduction delay in the right bundle branch.

The presence of a widened QRS complex indicates that the depolarization of the ventricles is taking longer than normal, which is consistent with the characteristics of IRBBB. In contrast, a completely normal QRS complex would not exhibit these features, and the identifiable patterns in Lead V1 are specifically used to make the diagnosis of IRBBB.