On the ECG of a patient with complete right bundle branch block (RBBB), which of the following findings is characteristically seen in lead V1?
- A RSR' pattern (rabbit ears) with R' > R, representing late slow right ventricular activation producing a second positive deflection ✓
- B Wide S wave representing delayed right-to-left septal activation
- C Delta wave with short PR interval representing right ventricular pre-excitation
- D Broad QRS with QS morphology representing right bundle block
Correct answer: A. RSR' pattern (rabbit ears) with R' > R, representing late slow right ventricular activation producing a second positive deflection
Explanation
In RBBB (QRS ≥120 ms), the sequence is: normal septal and LV activation first (producing the initial r wave in V1), then delayed right ventricular activation through slow myocardial conduction (not via Purkinje) produces a broad R' wave in V1. This creates the classic RSR' ('M pattern' or 'rabbit ears') in V1/V2. Lead V5/V6 shows a broad slurred S wave (delayed RV activation heading leftward is seen as a late negative deflection). The delta wave with short PR is seen in WPW (pre-excitation), not RBBB.
Reference: Guyton & Hall, Textbook of Medical Physiology, 14th ed.
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