What are the EKG characteristics of a third-degree AV block?

The EKG characteristics of a third-degree AV block, also known as complete heart block, primarily feature regular P-P intervals and A-V rhythms with inconsistent QRS complexes. In this condition, the atria and ventricles beat independently of each other, which leads to a disassociation between the P waves (representing atrial depolarization) and the QRS complexes (representing ventricular depolarization).

This is indicative of the fact that the electrical signals originating from the atria are not being conducted to the ventricles effectively. While the atria may continue to contract at a normal rate (indicated by regular P-P intervals), the QRS complexes may appear irregular as they are produced by a separate ventricular pacing mechanism or may occasionally not occur at all, leading to an inconsistency in their appearance.

This phenomenon distinguishes third-degree AV block from other arrhythmias where there might be a more coordinated relationship between the atrial and ventricular depolarization.