Sinus Nodal Reentrant Tachycardia (SNRT) Symptoms and Treatment

Sinus nodal reentrant tachycardia (also called SNRT or SANRT) is one of the arrhythmias categorized as supraventricular tachycardia (SVT), which are rapid heart arrhythmias originating in the atria of the heart. Sinus nodal reentrant tachycardia is an uncommon form of SVT.

Overview

Sinus nodal reentrant tachycardia is a reentrant tachycardia. It occurs because there is an extra electrical connection within the heart, which may be 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.

Symptoms

The symptoms of SNRT are similar to the symptoms most often seen with any kind of SVT. Symptoms may include palpitations, lightheadedness, or dizziness.

As with most SVTs, symptoms usually begin abruptly and without any particular warning. They also disappear equally abruptly—most often after a few minutes to several hours.

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

Differences From Inappropriate Sinus Tachycardia

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.

Sinus nodal reentrant tachycardia is a reentrant tachycardia, so it starts and stops abruptly, like turning on and off a light switch; and when the patient is not having an active episode of tachycardia, their 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 most people 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.

Treatment

If episodes of tachycardia are uncommon, and especially if the episodes can be easily stopped by increasing vagal tone, people with sinus nodal reentrant tachycardia may not require any medical therapy at all aside from learning 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 terminating episodes—drug therapy can be effective. Medicines like beta-blockers or calcium channel blockers may reduce the frequency of episodes and/or make them easier to stop. However, the European Society of Cardiology does note that no scientific studies have been conducted on drug therapy for SANRT.

If sinus nodal reentrant tachycardia is particularly troublesome or does not respond to less invasive therapy, ablation therapy is often effective in getting rid of the arrhythmia altogether and safely.

However, it may be technically difficult to ablate the extra electrical pathway in the sinus node without also damaging the healthy tissue. There is a risk of damage to the nearby phrenic nerve, as well as a risk of significant sinus bradycardia if the SA node is damaged (in which case a permanent pacemaker may be required).

Thus, attempts to find noninvasive therapy are reasonable to consider before undergoing ablation therapy for sinus nodal reentrant tachycardia.