Distinguishing between ‘AV node dependent’ and ‘AV node independent’ tachycardia carries significant therapeutic implications. What exactly do these important terms mean?

We need to distinguish between tachycardia (a rapid ventricular rate) and the underlying rhythm disturbance generating that tachycardia (the arrhythmia).

In an ‘AV node dependent tachycardia’, generation and maintenance of the underlying arrhythmia depends on conduction of depolarization through the AV node. In contrast, in an ‘AV node independent tachycardia’, the rapid ventricular rate (the tachycardia) may depend on conduction of depolarization through the AV node but generation and maintenance of the underlying arrhythmia does not. We illustrate this critical difference in the brief videos which follow. Before watching the videos please study the figure below.

 

Figure 1. Tissues coloured black do not conduct depolarization. The AV node transmits depolarization into the bundle of His leading to depolarization of the right and left ventricles via the right and left bundle branches (blue arrows). One thing to note, most normal individuals have one conducting tract from the atria into the AV node (black arrow). Individuals affected by the common tachyarrhythmia, AV Node Rentrant Tachycardia (AVNRT), have two. One of these tracts a) conducts and depolarizes at the normal rate while the second b) conducts depolarization slowly and repolarizes rapidly.

Video: An AV node dependent tachycardia: AV node re-entrant tachycardia (AVNRT).

 

While many of the most common types of AV node independent tachycardia require transmission of depolarization through the AV node to generate a tachycardia, generation and maintenance of the underlying arrhythmia does not depend on conduction of depolarization through the AV node. These tachycardia are said to be AV node ‘independent’.

Video: Atrial flutter: an example of an AV node independent tachycardia.

 

Giving an agent such as adenosine to a patient with an ‘AV node dependent tachycardia’ will often terminate the underlying arrhythmia and is usually an effective therapy. However, in some cases, giving such an agent to an ‘AV node independent tachycardia’ can result in cardiac arrest.