Which description best matches a typical right bundle branch block on ECG?

• A. Wide QRS with rsR' pattern in V1 and broad S waves in I and V6
• B. Wide QRS with an rs pattern in V1
• C. Narrow QRS with deep S in V1
• D. Wide QRS with rsR' pattern in V1 and broad S waves in I and V6

Answer: (D)

Recognizing the classic ECG features of a right bundle branch block. When the right bundle is blocked, the right ventricle activates later than the left, so the overall depolarization takes longer and the QRS becomes wide (>120 ms). In the V1 lead you typically see an rsR' morphology, meaning a small initial R wave followed by a taller second R'—an M-shaped pattern reflecting late right ventricular activation. In the lateral leads (I and V6), the delayed right ventricular activation produces broadened, terminal S waves. So the description that fits best is a wide QRS with an rsR' pattern in V1 and broad S waves in I and V6. The other options don’t capture both the rsR' in V1 and the broad S waves in the lateral leads, or they describe patterns (like a narrow QRS) not consistent with RBBB, or omit the key R' feature.