Atrioventricular Nodal Reentry Tachycardia (AVNRT)

Overview

Atrioventricular nodal reentrant tachycardia (AVNRT) is a rapid heartbeat condition that develops when electrical signals form a loop in the AV node region of the heart. It is one of the most common regular rapid heart rhythm disorders and is usually more frequent in young women.

The AV node is an important structure that conducts electrical signals between the upper chambers of the heart (atria) and the lower chambers (ventricles). Normally, a single electrical pathway passes through this node. In some people, however, there are two separate electrical pathways in the AV node region: one conducts rapidly, the other slowly. When an electrical signal forms a loop between these two pathways, the heart suddenly begins to beat very rapidly.

AVNRT episodes usually begin suddenly and stop suddenly. The heart rate can rise to 150-250 beats per minute. Episodes can last anywhere from a few seconds to several hours. In some people it occurs a few times in life, while in others it recurs frequently.

AVNRT is usually not dangerous and does not lead to permanent heart damage. The symptoms can be bothersome, however, and can reduce quality of life. With modern treatment methods, episodes can be completely prevented.

Symptoms

The symptoms of AVNRT vary depending on how high the heart rate rises, how long the episode lasts, and the person's general health.

The most common symptoms are:

• Suddenly starting heart palpitations. This is the most noticeable symptom. The heart suddenly begins to beat very rapidly and regularly. The person clearly feels their heart racing in the chest. The palpitations start suddenly, as if a button has been pressed.
• Pulse sensation or fluttering in the neck. A strong pulse or pounding sensation may be felt in the neck vessels. This is a finding quite specific to AVNRT and results from the atria and ventricles contracting at the same time.
• Dizziness and lightheadedness. When the heart beats very fast, the brain may not receive enough blood. This creates dizziness.
• Shortness of breath. Breathing can become difficult during a rapid heartbeat.
• Chest discomfort or pressure. A feeling of tightness, pressure, or discomfort in the chest may be felt.
• Fatigue. When the heart beats rapidly, the body becomes tired and a sense of weakness is felt.
• Feeling of anxiety. Suddenly starting palpitations can create worry and panic.
• Frequent need to urinate. The need to urinate may increase during or immediately after an episode. This results from a hormone secreted by the heart.
• Fainting. Rarely seen but fainting can occur if the heart rate is very high or blood pressure is very low.

Symptoms usually last anywhere from a few minutes to a few hours. The episode may stop on its own or may need to be terminated with certain maneuvers or medications.

When to See a Doctor

See a doctor in the following situations:

• If you regularly experience episodes of heart palpitations that start and stop suddenly, see a cardiologist.
• If chest pain, severe shortness of breath, or fainting develops during a palpitation episode, call emergency services immediately.
• If you have experienced such an episode for the first time, evaluation is important.
• If episodes are becoming more frequent or lasting longer, see a doctor.

Causes

The underlying cause of AVNRT is the presence of two separate electrical pathways in the AV node region. This structural difference has been present since birth, but symptoms usually begin during adolescence or young adulthood.

Why these two pathways exist in some people is not fully understood. In most cases there is no hereditary condition. Rarely, however, familial inheritance can be seen.

Factors that can trigger AVNRT episodes include physical activity, emotional stress, caffeine, alcohol, inadequate sleep, dehydration, and certain medications. Often, however, episodes can begin without any obvious trigger.

AVNRT is twice as common in women as in men. Why this is the case is not clearly known, but hormonal factors are thought to play a role.

Complications

AVNRT does not lead to serious complications in most people. In some cases, however, problems can develop.

AVNRT risks may include:

• Heart failure. Long-lasting and frequently recurring rapid heartbeat can rarely weaken the heart muscle. This can occur particularly if episodes last for hours and recur over years.
• Fainting and injury. There is a risk of fainting during an episode. Head trauma or other injuries from falling can occur during fainting.
• Decline in quality of life. Frequent episodes can negatively affect daily life, work performance, social activities, and psychological state. Some people live with fear of when episodes will occur.
• Problems during pregnancy. AVNRT can cause more frequent episodes during pregnancy. It is usually not dangerous for mother or baby, however. Because medication options are limited during pregnancy, vagal maneuvers are kept in the forefront.

Diagnosis

AVNRT is diagnosed with an electrocardiogram (ECG) and sometimes advanced tests.

The diagnostic process typically includes:

• Electrocardiogram (ECG). An ECG taken during an episode confirms the diagnosis. The ECG shows narrow QRS complexes with a rapid regular rhythm. P waves are usually hidden within the QRS complexes or appear immediately after them. This finding is quite specific to AVNRT.
• Holter monitor. This is a portable ECG device worn for twenty-four hours or longer. It is used to capture episodes during daily life when episodes are infrequent.
• Event recorder. This is a small device worn for weeks or months. When you feel palpitations, you activate the device and the heart rhythm at that moment is recorded.
• Electrophysiology study. This is an advanced test performed via cardiac catheterization. Electrodes are placed inside the heart to map the electrical pathways in the AV node. AVNRT is deliberately triggered for evaluation. This test is used for both diagnostic and treatment purposes.
• Echocardiography. This images the structure and function of the heart. It is performed to investigate whether there is any underlying structural heart disease.

Treatment

The aim of AVNRT treatment is to stop episodes, prevent future episodes, and improve quality of life.

Treatment approaches include:

• Vagal maneuvers. These are the first and most important interventions that can be applied during an episode. These methods stimulate the vagus nerve to slow the AV node and break the loop. The Valsalva maneuver (bearing down while holding a deep breath) is the most effective method. Immersing the face in ice-cold water is also very effective. Carotid sinus massage (gentle massage in the neck area) can be applied under a doctor's supervision. These methods can stop most AVNRT episodes.
• Emergency medication. If vagal maneuvers do not work, medication is given intravenously. Adenosine is the first choice and can stop the episode within seconds. If adenosine does not work, calcium channel blockers such as verapamil or diltiazem are used. Beta blockers can also be effective.
• Preventive medication. In people who experience frequent episodes, medication can be used regularly to prevent episodes. Beta blockers or calcium channel blockers are used for this purpose. In some cases antiarrhythmic medications may be needed. Medication does not permanently solve the condition, however, and may require lifelong use.
• Catheter ablation. This is the most effective method for permanently treating AVNRT. A thin catheter is advanced to the heart through a vessel in the groin. Radiofrequency energy at the tip of the catheter selectively destroys the slow pathway in the AV node. The fast pathway is preserved and the heart continues normal electrical conduction. The procedure takes one to two hours and has a success rate of 95-98 percent. The risk of recurrence is below 5 percent. Most people recover completely after the procedure and no longer need medication. An overnight stay in the hospital may be required or discharge can happen the same day. A very low risk of the procedure is creating AV block, in which case a permanent pacemaker may be needed. This risk is below 1 percent, however.

What to Do in an Emergency

During an AVNRT episode you can try the following:

• Perform the Valsalva maneuver. Take a deep breath and bear down while holding your breath. Straining as if you need to use the toilet is the most effective method. Continue this maneuver for 10-15 seconds and then release. Repeat several times if necessary.
• Immerse your face in cold water. Prepare a basin of ice-cold water and immerse your face for 10-15 seconds. This method is especially effective in young people.
• Sit or lie down. Remaining standing increases the risk of fainting. Sit or lie down immediately.
• Try to stay calm. Panic can increase the heart rate even further. Try to breathe slowly and deeply.
• Ask for help. If the episode lasts longer than 15-20 minutes, if there is chest pain, or if you are fainting, call emergency services.

Living with AVNRT

After catheter ablation, most people recover completely and continue their lives without restrictions. If ablation has not been performed or if medication is being taken, certain points should be kept in mind.

If you have AVNRT, pay attention to the following:

• Learn vagal maneuvers well. Your doctor or nurse can show you the most effective vagal maneuvers. Learning these techniques allows you to intervene yourself during an episode. Many AVNRT patients can stop episodes themselves with vagal maneuvers.
• Identify triggers. Learn which factors trigger episodes. Caffeine, alcohol, inadequate sleep, dehydration, and stress are common triggers. Avoid them if possible.
• Have regular follow-up. Do not miss your cardiology appointments. The frequency of episodes and response to treatment should be monitored.
• Use your medications regularly. If you are taking medication, use it regularly as your doctor recommends. Stopping medication can increase the frequency of episodes.
• You can exercise. AVNRT does not require exercise restrictions in most people. If episodes are triggered by exercise, however, consult your cardiologist.
• Inform if you are planning pregnancy. AVNRT can cause more frequent episodes during pregnancy. The medications you are using should be reviewed. Vagal maneuvers are recommended as the first option during pregnancy.
• Inform those close to you. Tell the people around you that you have AVNRT and what they should do during an episode. They can especially help you with vagal maneuvers.

Preparing for Your Appointment

What you can do:

• Note when palpitation episodes started and how often they occur.
• How long did episodes last? Did they resolve on their own or did you go to the emergency room?
• Did you notice any triggering factors?
• Did you try vagal maneuvers? Did they work?
• List all medications and supplements you are taking.
• Mention if there is a family history of heart rhythm disorders.
• Write your questions down in advance.

Questions you can ask your doctor:

• Is the diagnosis of AVNRT certain?
• What is the most appropriate treatment for me?
• How successful and risky is catheter ablation?
• What is my risk of needing a pacemaker?
• Will I need to use medication for life?
• Can I exercise?
• I am planning pregnancy — what should I do?
• What should I do during an episode?

Your doctor may ask you:

• When did palpitation episodes begin?
• How long did episodes last?
• How did episodes end?
• Do you feel a pulse or fluttering in your neck?
• Did you notice any triggering factors?
• Did you faint during an episode?
• Is there a family history of heart rhythm disorders?
• What medications are you taking?