Paroxysmal supraventricular tachycardia (PSVT) is a type of abnormal heart rhythm, or arrhythmia. It occurs when a short circuit rhythm develops in the upper chamber of the heart. This results in a regular but rapid heartbeat that starts and stops abruptly.

What happens during PSVT?

A normal heartbeat begins with an electrical impulse from the sinus node, a small area in the heart's right atrium (upper chamber). PSVT occurs because of a short circuit — an abnormal electrical pathway made of heart cells — that allows electricity to speed around in a circle and repeat the signal over and over. As a result, the chambers contract rapidly, which may impair heart function and cause symptoms such as lightheadedness or shortness of breath.

What causes PSVT?

The short circuit is caused by one of three conditions and will have a different location and behavior depending on the cause.

Atrioventricular Nodal Re-entrant Tachycardia (AVNRT)

Atrioventricular nodal re-entrant tachycardia (AVNRT) is the most common cause of PSVT. It occurs when a small extra pathway exists in or near the AV node — the "gate" that sends electricity from the upper chambers (atria) to the lower chambers (ventricles). An electrical impulse that enters this pathway will circle rapidly, causing a sudden (paroxysmal), fast heartbeat in both the atria and the ventricles. AVNRT is not a life-threatening arrhythmia, but it can cause symptoms such as lightheadedness or syncope (fainting).

Wolff-Parkinson-White Syndrome (WPW)

Wolff-Parkinson-White syndrome occurs when an extra muscle fiber connects the upper and lower chambers of the heart. In normal hearts, the only connection between the upper and lower chambers is the AV node — the electrical signal passes from the atria, through the AV node, and ends in the ventricles. The presence of this extra path can encourage a "short circuit" arrhythmia known as an atrioventricular reciprocating tachycardia (AVRT). The symptoms of AVRT vary widely from mild heart racing to syncope. Due to an increased risk of sudden cardiac death, people with Wolfe-Parkinson White syndrome are advised to have curative catheter ablation.

Wolff-Parkinson-White syndrome is congenital, developing in utero. Although present from birth, the tachycardias (rapid heartbeats) that result from the abnormal electrical connection often take years or decades before they become a problem.

Atrial Tachycardia

Atrial tachycardia is responsible for about 5 percent of PSVTs. It occurs when an electrical impulse fires rapidly from a site outside the sinus node and circles the atria, often due to a short circuit.

What are the symptoms of PSVT?

PSVT is often misdiagnosed as a panic attack. Symptoms include:

• A regular but racing heartbeat of 120 to 230 beats per minute that starts and stops abruptly

• Palpitations (a feeling of fluttering in the chest)

• Weakness or fatigue

• Dizziness or lightheadedness

• Fainting (syncope)

• Chest pain

How is PSVT diagnosed?

Doctors often suspect PSVT after a careful medical history and review of a 12-lead electrocardiogram (ECG or EKG). But because PSVT is paroxysmal (occasional and sudden), an office ECG may look normal. To "catch" an episode, your doctor may give you an ECG monitor to wear at home that will record your heart rhythm over time. These include:

• Holter monitor: a portable ECG you wear continuously for one to seven days to record your heart rhythms over time

• Event monitor: a portable ECG you wear for one or two months, which records only when triggered by an abnormal heart rhythm or when you manually activate it

• Implantable monitor: a tiny event monitor inserted under your skin, worn for several years to record events that only seldom take place

However, the ultimate test of PSVT is an electrophysiological (EP) study. This test not only diagnoses the condition but also identifies the precise cause. A diagnostic EP study is always done before catheter ablation, usually as part of the same procedure. With the patient under light sedation, several narrow, flexible wires are threaded through a vein to your heart. Fine wires inside the catheter can help pinpoint any areas outside the sinus node that produce electrical signals, then remove them using catheter ablation.

How is PSVT treated?

• Valsalva maneuver: In many patients, the tachycardia episode can be stopped by bearing down or rubbing the carotid artery.

• Medications: Different types of medications are available, which vary in frequency, side effects, risks and efficacy. Because PSVT does not resolve on its own, medications would be taken for a lifetime.

• Catheter ablation: This outpatient procedure is used to treat or cure many types of heart arrhythmia, including PSVT. Catheter ablation is a mature technique known to be safe and effective. Therefore, it is considered a first-line therapy for PSVT. It is often reasonable to go straight to catheter ablation rather than trying a medication first.

Learn more about arrhythmias or visit the Johns Hopkins Electrophysiology and Arrhythmia Service.