What is a primary characteristic of 3rd Degree AV Block?

A primary characteristic of 3rd Degree AV Block is the complete dissociation between atrial and ventricular activity. In this type of block, the electrical signals originating in the atria do not reach the ventricles due to a complete interruption in communication between the atrioventricular node and the ventricles. This leads to the atria contracting independently from the ventricles, resulting in a situation where the heartbeats of the two chambers do not coordinate.

The atrial rate and the ventricular rate can each be determined separately. Typically, the atrial rate is faster than the ventricular rate, resulting in this dissociation. This can create distinct rhythms for the atria and ventricles, leading to potential clinical symptoms such as bradycardia and may require medical intervention.

In contrast, a consistent PR interval, a high heart rate, or regular R-R intervals would suggest different types of conduction disturbances or heart rhythms and do not apply to 3rd Degree AV Block as the key feature is that there is no synchronized relationship between the atrial and ventricular activities.