What signifies a 3rd degree AV block?

A third-degree AV block, also known as complete heart block, is characterized by a complete dissociation between the atrial and ventricular activities. This is best indicated by the presence of P waves that are independent of QRS complexes. In this condition, the electrical signals from the atria do not reach the ventricles due to a failure of the atrioventricular node to conduct impulses, leading to a situation where the atria and ventricles beat independently of one another.

In this scenario, you will observe P waves occurring at regular intervals while the QRS complexes occur at a different rate, demonstrating that they are not correlated. Because the electrical signals are not communicating properly, the atrial rate may be much different from the ventricular rate, further confirming the diagnosis of a third-degree AV block. This independent activity is the hallmark feature that distinguishes third-degree AV block from other types of blocks or conduction disorders that may have some degree of coordination between atria and ventricles.