Atrioventricular Reentrant Tachycardia (AVRT)

What you should know about this common form of SVT

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People who experience sudden episodes of tachycardia (rapid heart rates), often have one of the many varieties of supraventricular tachycardia (SVT). The term “SVT” encompasses a large number of cardiac arrhythmias that typically start and stop quite suddenly, that are almost always non-life-threatening, but that can be significantly disruptive to your life.

Atrioventricular reentrant tachycardia (AVRT) is the second most common type of SVT, accounting for about 30% of all SVTs.

What Is AVRT?

AVRT is a reentrant tachycardia. As is the case with all reentrant SVTs, people with AVRT are born with an abnormal electrical connection in the heart. In AVRT, the extra connection, which is often called an accessory pathway, joins one of the atria (the upper chambers of the heart) with one of the ventricles (the lower chambers of the heart).

Normally, the only electrical connection between the atria and the ventricles is via the normal cardiac conducting system, which consists of the AV node and the His bundle. 

In people with AVRT, the accessory pathway provides a second electrical connection between the atria and the ventricles. This second connection provides the pathway for a reentrant tachycardia.

How Does AVRT Work?

In a person with an accessory pathway, an episode of AVRT can be triggered by either a premature atrial contraction (PAC) or a premature ventricular contraction (PVC).

The premature beat, if it occurs at just the right time, can trigger a reentrant electrical impulse that travels down the normal conducting system to the ventricles, then travels back up the accessory pathway to the atria (that is, it “reenters” the atrial), then turns around and travels back down the normal conducting system, and so on.

The result is a sudden tachycardia.

The symptoms of AVRT are typical for SVT. They most often include palpitations, lightheadedness, and/or dizziness. Episodes usually last from a few minutes to several hours.

AVRT can be stopped by a PAC, a PVC, or simply by slowing conduction through the AV node. Slowing AV node conduction takes advantage of the fact that the AV node is richly supplied by the vagus nerve. So, people with AVRT can often stop an acute episode by taking action to increase the tone of their vagus nerve. This can be accomplished, for instance, by performing the Valsalva maneuver, or by immersing your face in ice water for a few seconds. (The Valsalva maneuver is quicker, more convenient, and less unpleasant, by far.)

AVRT and WPW

In some people with AVRT, the accessory pathway is capable of conducting electrical impulses in both directions (that is, from the atrium to the ventricle, and also from the ventricle to the atrium). In other people the accessory pathway can only conduct electrical impulses in one direction or the other.

This difference turns out to be important. In most people with AVRT, the impulses can only go across the accessory pathway from the ventricle to the atrium. When the impulses are able to cross in the other direction - from the atrium to the ventricle - Wolff-Parkinson-White (WPW) syndrome is said to be present. WPW is associated with clinical problems that go beyond “just” AVRT, and often needs to be treated more aggressively.

Treating AVRT

If WPW is not present and symptoms of AVRT are rare and easily stopped (say, by performing a Valsavla maneuver), then often no treatment is necessary beyond learning what to do when an episode occurs. However, if you have WPW, frequent episodes of SVT, particularly severe symptoms during episodes, or have trouble stopping episodes when they occur, then more definitive treatment should be used.

Antiarrhythmic drug therapy is often only partially effective at preventing episodes of AVRT. However, in most people with AVRT, ablation therapy is able to get rid of the accessory pathway altogether, and completely prevent any further episodes.

Sources:

Chugh A, Morady F. Atrioventricular reentry and variants. In: Cardiac electrophysiology from cell to bedside, 5th edition, Zipes DP, Jalife J. (Eds), Saunders/Elsevier, Philadelphia 2009. p.605-614.

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