What does a third degree AV block cause?

What does a third degree AV block cause?

• A. Incomplete block of atrial stimuli transmission
• B. Completely blocks the conduction of atrial stimuli to the ventricles
• C. Enhances conduction from atria to ventricles
• D. Only affects the ventricular pacing

Answer: (B)

A third degree AV block, also known as complete heart block, occurs when there is a total failure of electrical conduction from the atria to the ventricles. This means that the atrial impulses are completely blocked from reaching the ventricles, resulting in dissociation between the two. The atria may still contract and send signals, but these signals do not propagate to the ventricles. Therefore, while atrial activity continues, the ventricles rely on an alternative pacemaker, usually found within the ventricles themselves, to maintain a heartbeat.

This condition can lead to significant bradycardia (slow heart rate) because the ventricles may take longer to fire on their own and can lead to further complications if not addressed, such as syncope or heart failure. Understanding the mechanism of a third degree AV block is crucial for recognizing its impact on cardiac function and the need for potential interventions, such as pacemaker implantation.