Types of Supraventricular Tachycardia (SVT)

Supraventricular tachycardia (SVT) is a category of rapid cardiac arrhythmias that originate in the atrial chambers of the heart. (“Supraventricular” simply means “above the ventricles.”)

Medical monitor screen
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There are several different kinds of SVT, but to a person who has SVT, all of them tend to feel about the same. They generally produce palpitations, and often lightheadedness, and while they are almost never life-threatening, any type of SVT can be quite difficult to tolerate.

While the symptoms with all types of SVT are similar, when it comes to treatment there are important differences. So when a doctor is treating a person with SVT, it is important to figure out which kind of SVT it is. The SVTs are split into two broad categories: "reentrant" and "automatic" SVT.

Reentrant SVT

Most people who have SVT have been born with an extra electrical connection in their hearts. These extra connections form a potential electrical circuit.

Under certain conditions, the heart’s electrical impulse can become “entrapped” within this circuit, spinning around and around it continuously. With each lap, a new heartbeat is generated, producing tachycardia. The kind of tachycardia produced by these extra connections is called reentrant tachycardia.

Most Common Types of Reentrant SVTs

The names given to the various types of reentrant SVT can be confusing, but the key is that the names indicate where the extra connection is located within the heart. The most common varieties of SVT are listed here. Click on the link to read about the specific characteristics of each type:

While the treatment options for all these types of reentrant SVT include both ablation procedures and medications, the "best" treatment depends to a large extent on the specific type.

Automatic Tachycardias

One type of SVT is not caused by extra electrical connections in the heart. This type of SVT is called “automatic SVT.”

Normally, the heart rhythm is controlled by electrical impulses produced by the "pacemaker" cells of the heart, located in the sinus node.

But in automatic SVT, cells in some other location within the atria begin producing their own electrical impulses, more rapidly than the sinus node does, thus taking over the rhythm of the heart and producing an automatic SVT.

Automatic SVTs are much less common than reentrant SVTs. They usually occur only in people who have a significant medical illness, especially severe lung disease, uncontrolled hyperthyroidism, or many acute illnesses severe enough to require intensive hospital care.

Automatic SVTs are usually quite difficult to treat directly, since there is no extra electrical connection that can be ablated, and since antiarrhythmic drugs often do not work very well in suppressing these arrhythmias. So the real treatment of automatic SVT is an indirect form of therapy, namely, treating the underlying medical illness. Almost invariably, once a patient with automatic SVT has recovered enough to be discharged from the intensive care unit, the arrhythmia will have disappeared.

One special variety of automatic SVT is not due to an acute illness and tends to be chronic and difficult to manage. This is inappropriate sinus tachycardia (IST), which merits a discussion of its own.

Note: While atrial fibrillation is technically a form of SVT, it is considered to be in a category of its own.

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