What will a posterior hemiblock look like on an EKG?

What will a posterior hemiblock look like on an EKG?

• A. Normal QRS with a Q wave in lead II
• B. Normal or slightly wide QRS complexes with a deep S wave in lead I
• C. Widened QRS complexes with ST segment elevation
• D. Normal QRS with inverted T waves in lead III

Answer: (B)

A posterior hemiblock, which is a type of intraventricular conduction delay affecting the left bundle branch system, typically manifests on an EKG as a wider than normal QRS complex combined with specific deflections in various leads. The correct answer indicates a normal or slightly wide QRS complex along with a deep S wave in lead I.

In posterior hemiblock, the left posterior fascicle is affected, leading to a delayed conduction that can create distinct changes in the EKG tracing. Specifically, a deep S wave in lead I suggests that the electrical impulse is not traveling efficiently through the left posterior fascicle, meaning that the left ventricle is not depolarizing in the typical manner. The normal or slightly wide QRS reflects that the overall conduction system is still functioning, albeit with some delay, resulting in a relatively normal appearance of QRS complexes rather than significant widening associated with other conditions such as a complete block.

This characteristic pattern helps in distinguishing posterior hemiblock from other conduction abnormalities, reinforcing its unique presentation on the EKG.