Automatic Tachycardias

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intensive care. Martin Barraud/Getty Images

Automatic tachycardias are a type of rapid cardiac arrhythmias that occur when abnormal electrical impulses are generated from somewhere within the heart.

Causes of Tachycardias

The word tachycardia simply means a rapid heartbeat, specifically, a heart rate of greater than 100 beats per minute. There are three general causes of tachycardia:

  • Normal tachycardia (or sinus tachycardia) is a normal phenomenon most of us experience each day. It occurs because the sinus node speeds up the rate at which it generates electrical impulses in response to exertion or stress. (There is one type of abnormal sinus tachycardia called inappropriate sinus tachycardia, or IST. You can read about IST here.)
  • Reentrant tachycardia is a cardiac arrhythmia caused by an abnormal electrical connection somewhere in the heart that creates a potential circuit. Reentrant tachycardias start and stop suddenly and for no apparent reason, and most often occur in people who are otherwise completely healthy.
  • Automatic tachycardias do not involve an abnormal electrical circuit but instead, are caused by the spontaneous generation of electrical impulses from somewhere other than the sinus node. These arrhythmias are often seen in people who are medically unstable.

Characteristics Of Automatic Tachycardia

In automatic tachycardias, cells in some location within the heart begin producing their own electrical impulses faster than the sinus node does, thus taking over the rhythm of the heart and producing tachycardia.

As with reentrant tachycardias, automatic tachycardias can be either supraventricular (so-called automatic atrial tachycardia, which means that the cells that are "automatically" firing are be located within the atria), or ventricular (automatic ventricular tachycardia, in which the abnormal electrical impulses are coming from the ventricles).

In addition, automatic junctional tachycardia can occur when the abnormal impulses arise near the AV node, which is near the "junction" of the atria and the ventricles).

In stark contrast to the reentrant tachycardias, automatic tachycardias are most commonly seen in people who are acutely ill.

In particular, automatic arrhythmias tend to occur in people who have acute lung disease (such as pulmonary embolus or pneumonia), acute myocardial infarction (heart attacks), or in people who have various severe abnormalities in their metabolic condition - such as low blood oxygen levels, low potassium or magnesium blood levels, or very high levels of adrenalin.

This means that automatic tachycardias are most commonly seen in particularly unstable patients in the hospital setting, such as patients in intensive care units.

There are exceptions, however. A rare condition called automatic atrial tachycardia (also called ectopic atrial tachycardia) can occur young, otherwise healthy people. Unlike reentrant atrial tachycardia, this condition tends to be persistent instead of intermittent, and can lead to tachycardia-induced heart failure. Automatic atrial tachycardia is usually treated with ablation therapy.

Treatment of Automatic Arrhythmias

In general, the most effective treatment for automatic tachycardia is to identify and reverse the underlying medical problem.

Once the patient’s lung condition, cardiac condition, or metabolic abnormalities are stabilized the arrhythmia goes away. So in almost all cases, the treatment for automatic tachycardias is to rapidly stabilize the underlying medical conditions.

Usually, when a patient who has had automatic tachycardia is healthy enough to leave the hospital, the arrhythmia has already resolved. There is no reason to consider using chronic antiarrhythmic drugs. Preventing further arrhythmias is a matter of taking whatever steps are possible to prevent a recurrence of the medical problem that caused the arrhythmia.

Sources:

Astridge PS, Kaye GC, Perrins EJ. Current approaches and future developments in automatic tachycardia detection and diagnosis. Br Heart J' 1993;70:106-1 10.

Poutiainen AM, Koistinen MJ, Airaksinen KE, et al. Prevalence and natural course of ectopic atrial tachycardia. Eur Heart J 1999; 20:694.

Moore JP, Patel PA, Shannon KM, et al. Predictors of myocardial recovery in pediatric tachycardia-induced cardiomyopathy. Heart Rhythm 2014; 11:1163.

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