**Core Concept**
Right Bundle Branch Block (RBBB) is a type of conduction abnormality in the heart, characterized by delayed electrical conduction through the right bundle branch. This results in a widened QRS complex on the electrocardiogram (ECG) with a specific pattern of electrical activation.

**Why the Correct Answer is Right**
The correct answer is a cause of RBBB because it leads to the delay of electrical conduction through the right bundle branch. This can be due to various factors such as:
* **Option D:** **Bundle branch fibrosis** or scarring, which can occur due to ischemia or other cardiac conditions. This scarring disrupts the normal electrical pathway, causing a delay in conduction.
* The affected bundle branch can also be **hypertrophied**, leading to increased resistance to electrical conduction.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because it is a cause of Left Bundle Branch Block (LBBB), not RBBB.
* **Option B:** This option is incorrect because it is a cause of Wolff-Parkinson-White (WPW) syndrome, which is a different type of conduction abnormality characterized by a pre-excitation pathway.

**Clinical Pearl / High-Yield Fact**
A key feature of RBBB is the presence of an **rsR' pattern** in lead V1, which is a critical clue for diagnosing this condition on the ECG.

**Correct Answer:** D. Bundle branch fibrosis.