For a left bundle branch block, which leads display the R, R' pattern?

For a left bundle branch block, which leads display the R, R' pattern?

• A. Leads V1 and V2
• B. Leads I and II
• C. Leads V5 and V6
• D. Leads III and aVF

Answer: (C)

In a left bundle branch block (LBBB), the conduction through the left bundle branch is interrupted, causing a characteristic change in the EKG waveform. This disruption results in a specific pattern in the chest leads.

The R, R' pattern, often referred to as a "broad, notched" "M" shaped QRS complex, is typically observed in leads that are oriented toward the left ventricle. In this case, leads V5 and V6 are positioned over the left side of the heart. When LBBB occurs, it becomes challenging for the left ventricle to depolarize in a synchronized manner, leading to a delayed and split QRS complex pattern like the R, R' seen in these leads.

In contrast, leads V1 and V2 are more likely to exhibit a pattern reflecting the right-sided heart activity. While leads I and II and III and aVF may show some changes, they do not typically present the classic R, R' pattern associated with left bundle branch block as strongly as V5 and V6 do. Therefore, leads V5 and V6 are the correct leads to observe the R, R' pattern indicative of LBBB.