An Overview of Reentrant Tachycardias

Reentrant tachycardias are a family of rapid cardiac arrhythmias caused by abnormal electrical connections in the heart. These abnormal connections form potential electrical circuits, which can disrupt the normal heart rhythm.

The Normal Heart Rhythm

With the normal heart rhythm (which is called normal sinus rhythm), the heart’s electrical impulse originates in the sinus node, and spreads evenly across the heart’s atrial chambers (causing the atria to contract), and then moves on to spread evenly across the heart’s ventricular chambers (causing the ventricles to contract). The heart muscle cells then "recharge," and a little while later (typically, 60-100 times per minute), a new electrical impulse is generated by the sinus node and the whole sequence repeats.

Reentrant Heart Rhythms

Reentrant arrhythmias can occur if an abnormal electrical connection is present in the heart—that is, an electrical pathway that isn’t supposed to be there, connecting two areas that should not be connected. Abnormal electrical connections can be congenital, or they can form as a result of heart disease. If such a connection exists, it can form an electrical circuit.

When such a potential circuit is present in the heart, a reentrant arrhythmia becomes possible. A reentrant arrhythmia occurs if one of the heart’s electrical impulses—either a normal sinus node impulse or an abnormal electrical impulse generated by a premature atrial complex (PAC) or a premature ventricular complex (PVC)—enters the circuit under just the right conditions.

Such an impulse can become “captured” within the circuit, in such a way that it begins begins spinning around the circuit, over and over again. With each lap around the circuit, the impulse produces a new heart beat. This new, abnormal rhythm is called a reentrant arrhythmia because the electrical impulse “re-enters” the circuit with each lap. 

Since there is no pause between heartbeats during a reentrant arrhythmia (because the impulse spins continuously around the circuit), typically the heart rate during a reentrant arrhythmia is quite rapid. That is, tachycardia occurs. 

Types of Reentrant Tachycardia

There are two broad categories of reentrant tachycardias based on where in the heart they occur: supraventricular tachycardias (SVT); and ventricular tachycardias (VT), including ventricular fibrillation (VF). VT and VF are considered together here.

Reentrant Supraventricular Tachycardias

The abnormal electrical connections that cause SVT most often are present from birth, so these arrhythmias are usually seen in healthier, younger people. Reentrant SVT can cause significant symptoms, but is only rarely dangerous or life-threatening. The different varieties of SVT are generally named according to the nature of the reentrant circuit that produces them. The major kinds of SVT include:

• Sinus node reentrant tachycardia (SNRT), in which the reentrant circuit involves the sinus node
• AV nodal reentrant tachycardia (AVNRT), in which the reentrant circuit involves the AV node
• Atrial reentrant tachycardia, in which the reentrant circuit is contained within the atria
• Atrioventricular reentrant tachycardia (AVRT), in which the reentrant circuit contains an electrical connection (a “bypass tract”) between the atria and the ventricles—there are several varieties of bypass-tract reentrant tachycardia, but the most well known is Wolff-Parkinson-White syndrome (WPW)
• Atrial flutter, a special type of atrial reentrant tachycardia in which the reentrant circuit is especially large
• Atrial fibrillation, generally regarded as a special type of reentrant atrial tachycardia in which multiple reentrant circuits can develop within the atria

Atrial fibrillation is different from other kinds of reentrant SVT, in that it is usually not due to a congenital abnormality of the heart’s electrical system but rather is often caused by the development of underlying heart problems. Atrial fibrillation is, therefore, more often seen in older individuals than are the other kinds of SVT.

Reentrant Ventricular Tachycardias

In contrast to SVT, the extra electrical connections that produce VT or VF are usually not present from birth. Instead, these connections result from the scarring of heart muscle that occurs with some types of heart disease (especially coronary artery disease or heart failure).

This means that the people who are prone to develop VT or VF are usually older, and tend to have significant underlying heart disease. Unfortunately, the risk of having VT or VF is common in CAD and heart failure, and is the reason why so many people with these conditions experience sudden cardiac death.

Treatment

The treatment of a reentrant tachycardia depends on the specific type of arrhythmia that is present and the symptoms it is causing. If the arrhythmia occurs only very rarely, lasts only a few seconds, and causes trivial symptoms, perhaps no treatment is needed at all. Life-threatening arrhythmias require aggressive treatment. 

Treatment may include anti-arrhythmic medication, ablation therapy, or an implantable defibrillator.

A Word From Verywell

Reentry is a common mechanism of both atrial and ventricular tachycardias. Reentrant tachycardias, which can occur at any age, can vary in significance between a mild annoyance to life-threatening. Anyone with unexplained episodes of tachycardia should be evaluated by their doctor.