By Richard N. Fogoros, MD 

 Medically reviewed by Yasmine S. Ali, MD, MSCI

Supraventricular tachycardia (SVT) is a family of cardiac arrhythmias that cause an inappropriately rapid heart rate. SVTs originate in the atria, the upper chambers of the heart.

Paroxysmal atrial tachycardia (PAT) is an older name for SVT that you still may hear on occasion. An estimated two to three out of every 1,000 people have SVT, with 62% of cases occurring in women.1

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SVT Symptoms

SVT commonly produces palpitations—a feeling of having extra heartbeats or a racing heart.1

During an episode of SVT, the heart rate is at least 100 beats per minute but is usually closer to 150 beats per minute. In some people, the heart rate can become substantially faster than that—in some cases, over 200 beats per minute.2

In addition, a person can experience:

  • Lightheadedness

  • Dizziness

  • Fainting

  • Weakness

  • Fatigue

  • Dyspnea (shortness of breath)

Typically, SVT and any associated symptoms a person may have occur in discrete episodes. These episodes often begin suddenly and stop suddenly. They can last anywhere from a few seconds to several hours.

The episodic nature of SVT can be misleading, and some people—women in particular—may be misdiagnosed as having anxiety or panic attacks at first, especially because their physical examination may not reveal any abnormalities.1

SVT may slightly impact your day or, if it occurs often enough, it can become very disruptive to your life. Fortunately, SVT is only rarely life-threatening.1

Causes

SVT occurs due to a problem with the electrical connections in the heart. Usually, the electricity of the heart flows along a set pathway in a specific order.

Sometimes, the heart may form an extra connection that can suddenly disrupt the normal electrical patterns within the heart, temporarily establish new electrical patterns, and produce the arrhythmia.2

To rule out other types of tachycardia or an underlying heart disease, your healthcare provider will ask you about any possible factors that may be triggering symptoms.

For example, certain types of SVT can be triggered by stress, caffeine, strenuous exercise, or lack of sleep.1 It's also possible that SVT may have no known trigger at all.

Certain medical problems can cause or worsen a rapid heart rate, like anemia or hyperthyroidism.3 The SVT caused by such medical disorders is usually different from the more typical SVT, in that it tends to be more persistent.

Adequate treatment usually requires aggressively treating the underlying medical problem.

Arrhythmias are common both in people who have heart disease and people who have a structurally normal heart. According to Braunwald's Heart Disease, arrhythmias can be harmless. But they can also be a sign of a life-threatening, underlying condition.4

Types

There are three types of tachycardia that fall within the umbrella of SVT:1

  • Atrioventricular nodal re-entrant tachycardia (AVNRT): Women are twice as likely as men to have AVNRTs, as the arrhythmia is tied to a sex hormone imbalance that is common during the luteal phase of the menstrual cycle.

  • Atrioventricular reciprocating tachycardia (AVRT): Two-thirds of children with SVT have AVRT—the predominant pediatric arrhythmia. This type of SVT is slightly more common in males.5

  • Atrial tachycardia (AT): Chronic ATs are most prevalent in adults who have congenital heart disease. No sex is more likely to have ATs than the other.6

In children and adults, the symptoms of all three SVTs are the same. Infants with SVT may breathe faster than normal, or seem extra fussy or sleepy.6

While the range of therapeutic options is also the same, the "optimal" therapy can vary, depending on the type.

Treatment

Many people who have only very occasional and time-limited episodes of SVT opt for no specific treatment at all; they simply deal with their episodes as they occur.

Others may utilize a variety of treatments to deal with acute episodes and prevent others from occurring.

Acute Episodes

Acute episodes of SVT almost always stop spontaneously.

However, many people have learned to slow or stop their episodes through a technique called the Valsalva maneuver. By stimulating the vagus nerve, this simple, non-invasive technique safely triggers the brain to relax the flow of electricity to the heart.7

A less pleasant method of doing this is to initiate the diving reflex by immersing your face in ice water for a few seconds.

In some people, a single dose of an antiarrhythmic drug taken at the onset of SVT can help terminate the episode more quickly.

If your SVT does not stop within 15 to 30 minutes, or if your symptoms are severe, you should go to the emergency room. A healthcare provider can almost always stop an SVT episode within seconds by giving an intravenous dose of adenosine or Calan (verapamil).8

Preventive Therapies

You may also want to consider continuous therapy aimed at preventing recurrent SVT.

Most SVTs are caused by extra electrical pathways. Usually, those extra pathways can be eliminated with a procedure known as ablation.

During ablation, the extra pathways are accurately localized with electrical mapping and then treated by destroying the abnormal tissue. This can cure a large majority of SVT cases once and for all.9

Antiarrhythmic drugs can also be used in an attempt to prevent SVT. But these drugs are often only partially effective, and many of them have the potential to cause significant adverse effects.

With this in mind, and because SVT is a benign arrhythmia that may occur only infrequently, most healthcare providers are reluctant to prescribe continuous antiarrhythmic drug therapy.