Supraventricular Tachycardia (SVT)

Supraventricular tachycardia, or 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). An older name for SVT, which you still may occasionally hear, is paroxysmal atrial tachycardia (PAT).

Typically, SVT occurs in discrete episodes, which most often begins very suddenly and stop equally suddenly. So the symptoms of SVT tend to appear out of nowhere and to disappear just as quickly. The duration of these episodes can be from a few seconds to several hours.

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. SVT commonly produces palpitations — a feeling of having extra heartbeats, or a racing heart — which can be quite scary. In addition, a person can experience lightheadedness and dizziness, weakness, fatigue or dyspnea (shortness of breath). This means that SVT can be pretty annoying, and if it occurs often enough, SVT can even become very disruptive to your life. Fortunately, SVT is only rarely life-threatening.

In the majority of cases, SVT occurs in people who are born with an extra abnormal electrical connection in the heart.

Under certain circumstances, these extra connections can suddenly disrupt the normal electrical patterns within the heart and temporarily establish new electrical patterns that produce the arrhythmia.

In some people, episodes of SVT can be triggered by exercise, stress, gastrointestinal symptoms (such as nausea, vomiting or constipation) or medications.

But in most people, SVT appears to occur for no particular reason at all.

Certain medical problems also seem to cause SVT, especially lung disease and hyperthyroidism. 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.

SVT is actually a family of related arrhythmias, and within this family, there are many types. The symptoms of all these types of SVT are the same. While the range of therapeutic options is also the same, the "optimal" therapy can vary, depending on the type.

So if you have SVT, you may want to ask your doctor about the specific type you have, so you can learn more about it.

Acute episodes of SVT almost always stop spontaneously after a few minutes or a few hours. However, many people have learned to stop their episodes by doing something to increase the tone of the vagus nerve. The easiest way to increase your vagal tone is to perform a Valsalva maneuver. A less pleasant method is to initiate the diving reflex by immersing your face in ice water for a few seconds.

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

You may also want to consider more chronic therapy aimed at preventing recurrent SVT. It is important to keep in mind that SVT is only rarely dangerous (but "merely" symptom-producing). This means there are many options for chronic therapy.

For instance, 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.

In the large majority of cases, SVT can be cured once and for all by an ablation procedure. Most SVTs are caused by extra electrical pathways, and usually, those extra pathways can be accurately localized by electrical mapping during an electrophysiology study and then ablated. Once the extra pathway is gone, the SVT should never come back.

Antiarrhythmic drugs can also be used to attempt to prevent SVT, but since these drugs are often only partially effective, and many of them have the potential to cause significant adverse effects, most doctors are reluctant to prescribe chronic antiarrhythmic drug therapy to treat SVT, which again is a benign arrhythmia that may occur only infrequently. In some people, however, a single dose of an antiarrhythmic drug, taken at the onset of SVT, can help terminate the episode more quickly.

SVT, while rarely life-threatening, can cause significant symptoms and can become quite disruptive to a normal life. Fortunately, almost all varieties of SVT can be successfully treated and prevented.

If you have SVT, your best bet is to talk to a cardiac electrophysiologist (a cardiologist who specializes in heart rhythm problems), who can review with you the pros and cons of all the treatment options available for your specific type of SVT.