Atrioventricular Nodal Reentry Tachycardia (AVNRT)
Atrioventricular nodal reentrant tachycardia (AVNRT) is an arrhythmia that occurs because an extra pathway lies in or near the AV node, which causes the impulses to move in a circle and reenter areas it already passed through. At Boston Medical Center, our electrophysiologists diagnose and treat a wide variety of heart arrhythmias (problems with the heart's rate or rhythm), including AVNRT. We combine our skill, experience, and state-of-the-art technology to provide you with the best care in the New England region.
The heartbeat is regulated by an intricate electrical system that keeps it beating between 60 and 100 times per minute. Each heartbeat begins with an electrical signal in the atria (the upper chambers in the heart), which causes them to contract, or squeeze. The signals travel downward toward the ventricles, pausing for a fraction of a second in the AV node, so the ventricles can fill with blood. The signals then travel to the ventricles, which contract.
AVNRT is caused by an abnormal or extra electrical pathway in the heart. Normally, a single electrical pathway allows impulses to travel from the upper to the lower heart chambers. An extra electrical pathway allows those impulses to travel backward at the same time, starting another heartbeat. During an episode of AVNRT, the electrical impulses continuously go around the two pathways. This is known as "reentry." During AVNRT, your heart rate can increase to between 150 to 250 beats per minute.
AVNRT is classified as a paroxysmal supraventricular tachycardia (PSVT) and is the most common of these arrhythmias. Paroxysmal means that the arrhythmia begins and ends suddenly, although episodes can last from seconds to minutes to days. Supraventricular means that the arrhythmia occurs above the ventricles. "Tachy" means fast and "cardia" means heart. AVNRT is the most common PSVT and is most often not dangerous. However, if you have coronary artery disease (narrowing of the arteries that supply blood to the heart), AVNRT can cause angina (chest pain) or a heart attack.
What are the symptoms of AVNRT? AVNRT may not always cause symptoms. When symptoms do occur, they can include:
- Palpitations (awareness of your heartbeat)
- Neck and chest discomfort
- Shortness of breath
What causes AVNRT?
AVNRT is most often caused by the presence of extra pathways in the AV node, although the cause of this is unknown. Women are more likely to develop the condition than men. The extra pathway is present since birth, but most often causes an arrhythmia after the heart has reached its full size when the patient is in their 20s or 30s.
To help diagnose AVNRT, Boston Medical Center's electrophysiologists use one or more of the following tests:
- Electrocardiogram. An electrocardiogram tracks and graphs heart rhythm using electrical signals from your heart.
- Holter monitor. Because arrhythmias can happen unpredictably, doctors have developed mobile (called ambulatory) ECGs to record the heart's rhythms away from the office or lab. A Holter monitor is such a device. It monitors your heart rhythm and records it to a cassette tape.
- Event recorder. Another form of ambulatory ECG, an event recorder, is activated during episodes of fibrillation and records the heart rhythm at that time.
How is AVNRT treated?
Treatment of AVNRT will depend on your symptoms, how often you experience the arrhythmia, and whether or not you have another problem that is causing your arrhythmia.
Maneuvers. Episodes of AVNRT often can be stopped by one of several maneuvers that stimulate the vagus nerve and thus decrease the heart rate. These maneuvers are usually conducted or supervised by your doctor, but if you experience AVNRT frequently, your doctor may teach you these maneuvers. They include straining as if having a difficult bowel movement, rubbing the neck just below the angle of the jaw (which stimulates a sensitive area on the carotid artery called the carotid sinus), and plunging the face into a bowl of ice-cold water. These maneuvers are most effective when they are used shortly after the arrhythmia starts.
Anti-arrhythmic therapy. This class of prescription medications works to suppress the underlying cause of an arrhythmia. Common antiarrhythmic medications include:
- Beta-blockers. Beta-blockers block receptor cells that respond to epinephrine, a molecule produced by the adrenal gland that stimulates the heartbeat. They slow and regulate the heart rate, reduce the force of heart contractions, and also lower blood pressure and relieve chest pain.
- Calcium channel blockers. Calcium channel blockers prevent calcium from entering the cells that transmit electrical signals. They can be effective in preventing AVNRT episodes.
Radiofrequency catheter ablation. Radiofrequency catheter ablation is the destruction of heart tissue using radiofrequency energy. During ablation, a catheter (a thin, flexible tube) with an electrode tip is positioned on the area of heart tissue that is involved in the arrhythmia. The catheter delivers a burst of energy to destroy tissue that is interfering with the normal transmission of impulses through the heart's electrical system. This same day procedure is over 99% successful in curing AVRNT.
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