It is a rapid cardiac arrhythmia that starts suddenly and without warning and stops just as abruptly. It most commonly affects younger adults. Once it first happens, it may become a recurrent problem.
AVNRT is the most common type of supraventricular tachycardia (SVT)in adults.
AVNRT is one of the reentrant tachycardias (tachycardia simply refers to a rapid heart rate). With every reentrant tachycardia, there is an abnormal electrical connection somewhere in the heart that forms a potential electrical circuit.
When one of the heart’s electrical impulses enters this circuit under just the right circumstances, it can become “captured” within the circuit. When this happens, it starts spinning around and around the circuit. Every time it does, the electrical impulse produces a new heartbeat, resulting in tachycardia.
In AVNRT, the extra connection and the entire reentrant circuit that produces the arrhythmia is located within or very close to the tiny atrioventricular node -hence the name AV nodal reentrant tachycardia.
AVNRT Symptoms
The symptoms of AVNRT are typical for SVT. They generally include one or more of the following:
Sudden onset of palpitations
Lightheadedness
Dizziness
Shortness of breath
One symptom that is often seen in AVNRT, but that occurs less frequently with other kinds of SVT, is a sensation of pounding in the neck.
During episodes of AVNRT, the atria and the ventricles are beating at the same time. Because the atria cannot eject blood into the ventricles, it is pushed upward into the neck vein—resulting in a pounding sensation.
Starting and Stopping AVNRT
The AV node is very sensitive to changes in the autonomic nervous system, the part of the nervous system that controls blood vessels and internal organs. Hence, changes in either sympathetic nervous tone (a stress response) or in the tone of the vagus nerve (parasympathetic tone, or a relaxation response) can have a major effect on the AV node.
Because much of the reentrant circuit in AVNRT is contained within the AV node, changes in the autonomic tone can have a profound effect on the arrhythmia.
While AVNRT most commonly begins without any apparent triggers, in some people it can start with exercise, periods of emotional stress, or other situations that increase sympathetic tone. In others, it can start after ingesting alcohol, tea, or coffee.
Patients with AVNRT can often stop their episodes of tachycardia by doing things to suddenly increase the tone of the vagus nerve. Performing the Valsalva maneuver often works, though more drastic steps (such as immersing their face in ice water for a few seconds) may sometimes be necessary.
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