Which type of block may progress to 3rd degree AV block if heart rate is slow?

• A. 1st degree AV block
• B. Mobitz type 1 block
• C. Mobitz type 2 block
• D. Complete heart block

Answer: (C)

Mobitz type 2 block is a form of second-degree AV block characterized by a consistent pattern of dropped beats without progressive prolongation of the PR interval. This type of block is particularly concerning because it often indicates that there is a significant level of conduction impairment at the AV node.

In the context of a slow heart rate, the risk of progressing to complete heart block, or third-degree AV block, increases. This is because the decreased conduction capacity can lead to more frequent and unpredictable interruptions in the electrical signals being transmitted from the atria to the ventricles. If the conduction fails entirely, it can result in a complete disconnection between atrial and ventricular activity, culminating in third-degree AV block.

Other types of blocks mentioned, like first-degree AV block and Mobitz type 1 block, generally do not carry the same risk of progressing to third-degree block, especially under normal or slow heart rates. First-degree AV block typically involves a delay in conduction that does not lead to missed beats, and Mobitz type 1 (Wenckebach) involves progressive lengthening of the PR interval before a beat is dropped, characteristic of a more predictable and benign condition. Complete heart block represents a failure of conduction altogether, rather than a progression