Junctional tachycardia: the heart in the fast lane 

The heart is a muscle that works tirelessly to pump blood throughout our entire body. It consists of four chambers – two atria and two ventricles – and is controlled by a complex electrical system. Like a conductor leading an orchestra, this system sends electrical signals that trigger the rhythmic contraction of the atria and ventricles. These electrical signals originate in the atria and travel to the ventricles through an electrical conduction system called an atrioventricular (AV) node located at the junction between the atria and the ventricles. The atria also fill the ventricles, which then pump blood to all the organs. In healthy people, this rhythm is regular, with a resting heart rate typically ranging from 60 to 100 beats per minute.

A heart rhythm disorder or cardiac arrhythmia is when the heart does not beat at a normal and/or regular rate.

Arrhythmia or junctional tachycardia refers to heart rhythm disorders that originate in the junction between the atria and ventricles.

There are several forms of junctional arrhythmia, but this type of arrhythmia generally occurs when an extra conduction fiber forms between the atria and ventricles, in addition to the normal conduction pathways. 

This small fiber can be located in various areas:

• near the AV node (this fiber is called a “slow pathway”) 
• or elsewhere (called an “accessory pathway”). 

The arrhythmia results from an electrical circuit traveling through the AV node in one direction, while the additional fiber (slow or accessory pathway) travels in the other.

In certain specific forms of accessory pathways, there may be a low (but not zero) risk of ventricular arrhythmia that can lead to sudden cardiac death. In such cases, ablation is required to permanently treat the issue.

Symptoms

In almost all cases, a junctional tachycardia episode is symptomatic and characterized by very strong palpitations. The tachycardia is regular, with a heart rate often ranging between 180 and 240 beats per minute. These episodes often last from a few minutes to several hours. They can stop spontaneously or after performing vagal maneuvers (e.g. breathing techniques). In some cases, it may be necessary to inject medication intravenously to stop the episodes.

Diagnosis

An electrocardiogram (ECG or EKG) can be used to diagnose junctional tachycardia during an episode by providing an electrical recording of the patient’s heart rhythm.

Certain forms of accessory pathways can also be visible on the ECG even in the absence of an episode. This condition is called ventricular pre-excitation. This type of accessory pathway may be present on an ECG without causing the symptoms of junctional arrhythmia. However, these are the forms that can lead to a risk of sudden cardiac death.

There are now several methods for performing an ECG: 

• A standard ECG can be performed during an appointment with your primary care physician, cardiologist or in the emergency room.
• A Holter ECG : this is a device that continuously records the heart’s rhythm over a 24 to 72-hour period.
• Smart devices:
  • Most smart watches and some smartphones (using the camera flash on your finger) can detect an irregular and rapid heart rhythm suggestive of atrial fibrillation, but they do not provide an ECG trace that can confirm the diagnosis with certainty. They then advise the user to schedule an appointment with a physician.
  • Some smart watches and other “AliveCor” devices allow you to directly record an ECG trace which you can then share with your physician. 

The diagnosis is sometimes complicated by short-duration episodes that do not always allow sufficient time to perform an ECG. This issue can now be resolved with smart devices that patients can keep with them.

Treatment

The presence of an accessory pathway, even in the absence of junctional arrhythmia symptoms, always warrants an ablation procedure to treat this additional fiber due to the associated risk of sudden cardiac death.

In all other situations, junctional arrhythmias do not cause serious complications aside from symptoms that can sometimes be quite severe and significantly affect the patient’s quality of life. The treatment therefore depends on the frequency and intensity of the episodes patients experience. 

In the case of disabling symptoms, it is possible to:

• treat the episodes with long-term antiarrhythmic medication;
• perform an ablation procedure by inserting catheters into the heart to permanently destroy the extra fiber causing the arrhythmias.

Reviewed and approved by Romain Tixier, MD, Cardiologist at Bordeaux University Hospital (CHU)