Atrioventricular Nodal Reentrant Tachycardia (AVNRT)
Atrioventricular Nodal Reentrant Tachycardia (AVNRT) causes fast beating of the heart, or arrhythmia. It occurs because of one or more extra electrical pathways near the Atrioventricular or AV node allows an electrical impulse to loop back on itself or short circuit. The AV node is a conduit that allows electrical impulses to travel from the atria or upper chambers of the heart to the ventricles, or lower chambers of the heart. Typically, the AV node allows for the smooth transmission of electrical impulses from the upper to the lower chambers. When an extra connection exists within the AV node, usually called a slow pathway, a heart may go into this abnormal rhythm. Some people have this extra connection, or slow pathway, but never have an abnormal rhythm.
AVNRT is considered a paroxysmal supraventricular tachycardia (SVT) which means that it is not persistent, involves the upper chambers of the heart and causes an abnormally fast heartbeat. It is also the most common of the SVTs, with the exception of atrial fibrillation. Its effects can vary between patients and it may last anywhere from a few seconds to days at a time.
Causes of AVNRT
AVNRT most often occurs in otherwise normal hearts. The propensity to have AVNRT is likely present from birth or an early age. Thus, AVNRT may occur early on, not until late in life, or possibly despite the propensity in may never happen at all. It is not clear why some people with the propensity for AVNRT have frequent episodes that wax and wane in frequency and duration over time whereas others have rare episodes and still others never even have an single episode. Interestingly, twice as many women have AVNRT than men. Most often the first episode occurs in the teens, but occasionally age related changes result in a first episode late in life. Usually if episodes began at a very young age it is a different type of tachycardia.
When the predisposing electrical connections around the AV node exist they cause electrical impulses to loop back to the upper chambers rather than continue only down to the ventricles. Each time the impulse completes the loop it triggers an additional heartbeat and patients may have heart rates of up to 250 beats per minute.
Symptoms of AVNRT
Because of the variations in episode duration as well as the pulse rate, symptoms will vary widely between individuals. Some patients may not notice any symptoms at all, while others will find them debilitating. The most common symptoms include:
- A sensation of a fast-beating heart (palpitations)
- Fainting or lightheadedness
- Chest pain
- Trouble catching breath
- Fatigue or weakness
- Confusion (especially in the elderly)
Diagnosis of AVNRT
Because of the sporadic nature of the condition, it can be hard to diagnose AVNRT at an office consultation. The most definitive way to diagnose the condition is a 12 lead ECG while the patient is in the abnormal rhythm, such as during an ER visit. Should the fast heart rate from AVNRT not be present during the ECG recording, such as may occur during an initial cardiology or electrophysiology office consultation, it would not be possible to diagnose AVNRT at that time. Patients may be sent home with an event monitor for longer-term collection of data with the “hope” of catching one of the sporadic episodes during the monitoring period. While ambulatory monitors offer somewhat less detail versus the ECG, they may provide data that could not otherwise be obtained. A catheter based test of the electrical system, known as an electrophysiology study, may also lead to a definitive diagnosis.
Treatment for AVNRT
AVNRT is not considered, in and of itself, a dangerous condition. However, in conjunction with certain other heart conditions, it can lead to more severe consequences and even a heart attack (sometimes called demand ischemia). Being distracted the symptoms by AVNRT or passing out from them could lead to dire consequences. For this reason, any irregular heartbeat should be evaluated by a qualified clinician.
For those that experience infrequent episodes and for whom anepisode is not debilitating, there is the option to proceed only with watchful waiting. Patients must understand that this carries some risk and must be on the lookout for worsening of symptoms or condition.
The ultimate course of treatment largely depends on patient preference, co-occurring conditions and weighing the risks associated with the various options. While medication and various exercises or maneuvers are available for a patient to try, they represent only a potential improvement in symptoms and do not address the underlying issue. Further, antiarrhythmic medications can have significant side-effects that interfere with the patient’s normal daily function. An effective, long-term solution for AVNRT is a diagnostic electrophysiology (EP) study and subsequent catheter ablation.
As with most SVTs, there are several potential treatment options, each with their own benefits and drawbacks.