Reentrant Tachycardias

What is a reentrant arrhythmia?

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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.

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).

A few seconds later a new electrical impulse is generated by the sinus node, and the whole sequence repeats.

However, if a potential electrical 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 heart beats 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 is present.)

Types of Reentrant Tachycardia

There are two broad categories of reentrant tachycardias - supraventricular tachycardia (SVT); and ventricular tachycardia (VT) and ventricular fibrillation (VF).

Reentrant Supraventricular Tachycardias

The abnormal electrical connections which 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:

  • Atrial flutter, which is a special type of atrial reentrant tachycardia in which the reentrant circuit is especially large.
  • Atrial fibrillation is generally regarded as a special type of reentrant atrial tachycardia in which multiple reentrant circuits can develop.

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 - CAD - 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.

Sources:

Antzelevich C. Basic mechanisms of reentrant arrhythmias. Current Opinion in Cardiology 2001, 16:1–7

Link MS. Clinical practice. Evaluation and initial treatment of supraventricular tachycardia. N Engl J Med 2012; 367:1438.

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