Sinus Nodal Reentrant Tachycardia (SNRT)

cardiac rhythm
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Sinus nodal reentrant tachycardia is a fairly rare type of supraventricular tachycardia (SVT). SVTs are rapid heart arrhythmias originating in the atria of the heart.

What Is Sinus Nodal Reentrant Tachycardia?

Sinus nodal reentrant tachycardia is a reentrant tachycardia. As is typical for reentrant tachycardia, sinus nodal reentrant tachycardia occurs because there is an extra electrical connection within the heart, which is present from birth.

In sinus nodal reentrant tachycardia, the extra connection - and indeed the entire reentrant circuit that produces the arrhythmia - is located within the tiny sinus node.

What Are the Symptoms?

The symptoms of SNRT are similar to the symptoms most often seen with any kind of SVT. The most prominent symptom is palpitations, though some people with this arrhythmia will also experience a “lightheaded” kind of dizziness.

As with most SVTs, symptoms usually begin abruptly and without any particular warning, and they disappear equally abruptly - most often lasting from a few minutes to several hours.

The sinus node is richly supplied by the vagus nerve, so patients with sinus nodal reentrant tachycardia can often stop acute episodes by taking steps to increase the tone of their vagus nerve, such as performing the Valsalva maneuver, or immersing their face in ice water for a few seconds.

Comparison To Similar Arrhythmias

Inappropriate sinus tachycardia (IST) is similar to sinus nodal reentrant tachycardia since both of these arrhythmias arise from the sinus node. However, their characteristics differ substantially.

Sinus nodal reentrant tachycardia is a reentrant tachycardia, so it starts and stops abruptly, like turning on and off a light switch.

When the patient is not having an actual episode of tachycardia, his or her heart rate and heart rhythm remain entirely normal.

In contrast, IST is an automatic tachycardia. Consequently, it does not start and stop abruptly but rather, it more gradually accelerates and gradually decelerates. Also, the heart rate in patients with IST often is never actually entirely "normal.” Instead, the heart rate almost always remains at least somewhat elevated, even when it is producing no symptoms.

Treating Sinus Nodal Reentrant Tachycardia

If episodes of tachycardia are uncommon, and especially if the episodes can be easily stopped by increasing vagal tone, patients with sinus nodal reentrant tachycardia may not require any medical therapy at all - aside from coaching on how to recognize that the arrhythmia is occurring, and how to stop it.

If more intensive treatment is required - either because of frequent episodes or difficulty in terminating episodes - drug therapy is often effective. Taking a beta blocker or a calcium channel blockers will often greatly reduce the frequency of episodes, and/or make them easier to stop.

If sinus nodal reentrant tachycardia is particularly troublesome and does not respond to less invasive therapy, ablation therapy is often effective in getting rid of the arrhythmia altogether. However, it is difficult to ablate the extra electrical pathway in the sinus node without also damaging the remainder of the sinus node. So the ablation procedure has a fairly high risk of producing significant sinus bradycardia, to the point that a permanent pacemaker may be required.

Thus, attempts to find noninvasive therapy should always be made before considering ablation therapy for sinus nodal reentrant tachycardia.

Sources:

Gomes JA, Mehta D, Langan MN. Sinus node reentrant tachycardia. Pacing Clin Electrophysiol 1995; 18:1045.

Tracy CM, Akhtar M, DiMarco JP, et al. American College of Cardiology/American Heart Association 2006 update of the clinical competence statement on invasive electrophysiology studies,catheter ablation,and cardioversion: a report of the American College of Cardiology/American Heart Association/American College of Physicians Task Force on Clinical Competence and Training developed in collaboration with the Heart Rhythm Society. J Am Coll Cardiol 2006; 48:1503.

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