What are the two types of second degree AV blocks?

What are the two types of second degree AV blocks?

• A. Those that occur in the atrial node
• B. Those that occur in the SA node
• C. Those that occur in the AV node and those that occur below it
• D. Those that block only ventricular conduction

Answer: (C)

Second-degree AV blocks are characterized by a specific interruption in the conduction pathways between the atria and the ventricles, and they can be classified based on their location in the conduction system. The correct classification is into two types: those that occur within the AV node and those that occur below it.

The two primary types are:

1. Mobitz Type I (Wenckebach): This often occurs at the level of the AV node, where there is a progressive elongation of the PR interval until a non-conducted beat occurs.

2. Mobitz Type II: This type usually arises below the AV node, in the His-Purkinje system. It features a consistent PR interval with sudden non-conduction of a beat without prior lengthening.

Understanding the distinction is crucial for the management and prognostication of patients with these blocks, as Mobitz Type II is generally more concerning due to its potential to progress to complete heart block. Other options do not accurately reflect the two types of second-degree AV blocks, as they either confuse the signaling pathways or focus on conduction issues that do not represent the typical classification used in clinical practice.