RBBB with left Axis Detion Is characteristic of
**Core Concept**
Right Bundle Branch Block (RBBB) with left axis deviation is a specific electrocardiographic (ECG) pattern that indicates a type of conduction abnormality in the heart. It is characterized by a prolonged QRS duration in the right precordial leads (V1-V2) and left axis deviation, suggesting a disruption in the normal conduction pathway of the heart.
**Why the Correct Answer is Right**
The combination of RBBB with left axis deviation is typically associated with a condition known as LBBB (Left Bundle Branch Block) mimicking RBBB, or a condition where the left bundle branch is affected, but not the right. This is due to the fact that the left bundle branch is usually activated before the right bundle branch, and when the left bundle branch is affected, it can result in a pattern that resembles RBBB with left axis deviation. The underlying mechanism involves delayed activation of the left ventricle, leading to a prolonged QRS duration and left axis deviation.
**Why Each Wrong Option is Incorrect**
* **Option A:** This is incorrect because RBBB typically shows right axis deviation, not left axis deviation.
* **Option B:** This is incorrect because conditions that affect the right bundle branch, such as RBBB, typically do not show left axis deviation.
* **Option D:** This is incorrect because conditions that affect the left bundle branch, such as LBBB, typically show left axis deviation, but the right bundle branch is not affected.
**Clinical Pearl / High-Yield Fact**
It's essential to remember that RBBB with left axis deviation is not a typical ECG pattern and requires careful interpretation to determine the underlying cause.
**Correct Answer: C. LBBB mimicking RBBB**