In which condition are all impulses blocked at the AV node, preventing transmission to the ventricles?

In which condition are all impulses blocked at the AV node, preventing transmission to the ventricles?

• A. Second-degree AV block
• B. First-degree AV block
• C. Third-degree AV block
• D. Bundle branch block

Answer: (C)

In third-degree AV block, also known as complete heart block, there is a total failure of electrical impulses from the atria to the ventricles due to a blockage at the AV node. This means that although the atria continue to contract and generate impulses independently, these signals do not reach the ventricles, leading to a dissociation between atrial and ventricular activity. As a result, the ventricles rely on an escape rhythm from a secondary pacemaker, which is typically slower than the normal sinus rhythm. This condition can lead to significant clinical implications, such as bradycardia and impaired cardiac output. In contrast, first-degree AV block involves a prolonged PR interval but does not result in the complete blockade of impulses. Second-degree AV block can be subdivided into types like Mobitz type I (Wenckebach), where some impulses are blocked but not all, and Mobitz type II, which may also allow some impulses through. Lastly, bundle branch block affects the conduction within the ventricles themselves, rather than the transmission from the atria to the ventricles, which is why it does not describe the complete block at the AV node seen in third-degree AV block.

In third-degree AV block, also known as complete heart block, there is a total failure of electrical impulses from the atria to the ventricles due to a blockage at the AV node. This means that although the atria continue to contract and generate impulses independently, these signals do not reach the ventricles, leading to a dissociation between atrial and ventricular activity. As a result, the ventricles rely on an escape rhythm from a secondary pacemaker, which is typically slower than the normal sinus rhythm. This condition can lead to significant clinical implications, such as bradycardia and impaired cardiac output.

In contrast, first-degree AV block involves a prolonged PR interval but does not result in the complete blockade of impulses. Second-degree AV block can be subdivided into types like Mobitz type I (Wenckebach), where some impulses are blocked but not all, and Mobitz type II, which may also allow some impulses through. Lastly, bundle branch block affects the conduction within the ventricles themselves, rather than the transmission from the atria to the ventricles, which is why it does not describe the complete block at the AV node seen in third-degree AV block.