Types of Supraventricular Tachycardia (SVT)

Supraventricular tachycardia (SVT) is a category of rapid cardiac arrhythmias that originate in the heart’s atrial chambers. Supraventricular means “above the ventricles,” and tachycardia is a fast heart rate.

This article explains the symptoms, causes, and most common types of SVT.

Symptoms of SVT

There are several different kinds of SVT, but to a person who has SVT, all of them tend to feel the same. While SVT is rarely life-threatening, any type of SVT can be pretty difficult to tolerate. SVT generally produces:

• Heart palpitations (heart beats faster)
• Chest pain
• Fatigue
• Lightheadedness
• Weakness

While the symptoms with all types of SVT are similar, there are significant differences in treatment. So when a doctor is treating a person with SVT, it is crucial to figure out which kind of SVT it is.

There are two broad categories of SVTs: “reentrant” and “automatic” SVT.

Reentrant SVT

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

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

Types of Reentrant SVT

The names given to the various types of reentrant SVT can be confusing, but the key is that the terms indicate the location of the extra connection within the heart.

The most common varieties of SVT include:

• Atrioventricular nodal reentrant tachycardia (AVNRT): This is a more common type of SVT. It is characterized by a rapid, irregular heartbeat that stops and starts suddenly.
• Atrioventricular reciprocating tachycardia (AVRT): This type of SVT includes Wolff-Parkinson-White Syndrome (WPW). It tends to be more common in adolescents, though does happen in adults.
• Sinus nodal reentrant tachycardia (SNRT): This type of SVT is less common. In this type, the extra electrical connection is located in the sinus node.
• Intra atrial reentrant tachycardia (IART): This type of SVT is more common in adults with congenital heart disease than in others.
• Atrial flutter: This type is usually not life-threatening, but it can increase the risk of having a stroke. This type usually occurs in the right atrium. People at risk include those who have obesity, lung disease, sleep apnea, hyperthyroidism, and other heart conditions.

Treatment

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

Automatic Tachycardias

Unlike reentrant SVT, extra electrical connections in the heart do not cause automatic SVT. Instead, cells in the heart produce their electrical impulses, which take over.

Typically, electrical impulses produced by the “pacemaker” cells of the heart located in the sinus node control the heart rhythm. But in automatic SVT, cells in some other location within the atria (upper chamber of the heart) begin producing their own electrical impulses. These impulses are more rapid than the impulse in the sinus node, and thus they take over the heart’s rhythm and produce an automatic SVT.

Types of Automatic SVT

Automatic SVTs are much less common than reentrant SVTs. They usually occur only in people who have a significant medical illness, such as:

• Severe lung disease
• Uncontrolled hyperthyroidism
• Acute conditions severe enough to require intensive hospital care

The most common types of automatic SVT include:

• Focal atrial tachycardia (Focal AT): This type is characterized by rapid heartbeat and usually affects people with too many catecholamines, a toxic reaction to digoxin (heart medication), congenital heart disease, and cardiomyopathy (heart muscle disease).
• Sinus tachycardia: This usually occurs as a result of exercise, illness, and anxiety. When there is not an identifiable natural trigger, there may be an underlying medical condition.
• Inappropriate sinus tachycardia (IST): This irregular heart rhythm is generated in the sinus node and is not detectable on an ECG. Doctors sometimes misdiagnose this as anxiety. It may be more common in people with dysautonomia (an automatic nervous system disorder).
• Atrial fibrillation (Afib): This type of rapid heart rate can occur in people with congenital heart conditions or in people who have heart damage from high blood pressure, heart disease, or heart attack. However, it can also occur in people without heart damage. People at higher risk are those who are older, have excess weight, and are sedentary.
• Junctional tachycardia: A junctional rhythm originates from the atrioventricular node (cells near the heart’s center that coordinate the heartbeat). Junctional tachycardia is a heart rate over 100 beats per minute (BPM).

Treatment

Automatic SVTs are usually quite challenging to treat since there is no extra electrical connection to ablate. In addition, 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, the arrhythmia will have disappeared once a patient with automatic SVT has recovered enough to be discharged from the intensive care unit (ICU).

Summary

SVT is a category of rapid heart rate that originates within the heart chamber. People with SVT experience heart palpitations and sometimes fatigue, weakness, dizziness, and chest pain.

There are two broad categories of SVT. Reentrant SVT occurs when someone is born with an extra electrical connection in their heart. Automatic SVT is less common and usually occurs in people with significant medical conditions. Within these categories, there are various types of SVT.