**Core Concept**
Mobitz II heart block, also known as Wenckebach block, is a type of second-degree atrioventricular (AV) block characterized by progressive prolongation of the PR interval on consecutive beats, culminating in a dropped beat. This phenomenon occurs due to a block in the AV conduction system, specifically at the level of the AV node.

**Why the Correct Answer is Right**
Mobitz II heart block is typically associated with conditions that affect the AV node, such as ischemia, inflammation, or degenerative diseases. The mechanism involves a progressive delay in AV conduction, resulting from a gradual increase in the refractory period of the AV node. This can be caused by an increase in the duration of the action potential in the AV node, leading to a prolongation of the PR interval.

**Why Each Wrong Option is Incorrect**
**Option A:** Mobitz II heart block is indeed seen in conditions affecting the AV node, such as Lyme disease, which can cause AV nodal dysfunction.
**Option B:** Mobitz II heart block is also associated with inferior wall myocardial infarction, which can cause ischemia and dysfunction of the AV node.
**Option C:** Similarly, Mobitz II heart block can be seen in conditions that affect the His-Purkinje system, such as cardiac sarcoidosis.
**Option D:** However, Mobitz II heart block is not typically associated with bundle branch block, which is a condition that affects the His-Purkinje system and is characterized by a consistent pattern of QRS complex widening.

**Clinical Pearl / High-Yield Fact**
A key feature of Mobitz II heart block is the progressive prolongation of the PR interval, culminating in a dropped beat. This phenomenon is often referred to as a "dropped beat" or "non-conducted P wave".

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