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Premature Atrial Complexes (PACs)

The Most Common Type of Cardiac Arrhythmia

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Updated May 16, 2014

Written or reviewed by a board-certified physician. See About.com's Medical Review Board.

Premature atrial complexes, or PACs, are the most common variety of heart arrhythmia. In fact, PACs are so common that most people will have them occasionally.

The normal heart rhythm is controlled by a tiny structure called the sinus node, which is located near the top of the heart's right atrium. The sinus node generates the electrical signal that initiates the heartbeat and controls the heart rate. Typically, the sinus node "discharges" these electrical impulses between 50 and 90 times per minute at rest. When a person's heart rhythm is being controlled by the sinus node in this normal fashion, doctors often call it "normal sinus rhythm."

PACs can momentarily interrupt this normal sinus rhythm by inserting an "extra" heartbeat. If you have been told you have PACs, you can rest assured that you are in the majority. It is very common to have PACs; if you recorded the heart rhythm of 100 normal people for 24 hours, more than half would have at least a few PACs.

What Causes PACs?

PACs are caused by occasional, early (or premature) electrical impulses that can arise from almost anywhere within the cardiac atria. In other words, PACs are early atrial heart beats that are not produced by the sinus node.

How Important Are PACs?

PACs generally have very little medical significance, and are viewed (appropriately) by most doctors as a variation of "normal."

In recent years, doctors have learned that PACs may be important in patients who have episodes of atrial fibrillation. In many of these patients, PACs are now thought to trigger such episodes. For this reason, many of the ablation procedures that are used to treat atrial fibrillation are aimed at eliminating these PACs.

However, it remains true that in the vast majority of people who have them, PACs have no medical significance and pose no known risk.

Symptoms Of PACs

Fortunately (considering that they are so common), in most cases PACs do not cause any symptoms at all.

However, some people will experience palpitations with PACs, in which case they usually describe a "skipping" sensation, or an unusually strong heart beat. Experiencing palpitations is much more likely after ingesting alcohol, tobacco, caffeine, or medications containing stimulants, all of which are known to increase the frequency of PACs, and to make them more noticeable.

Treating PACs

Unless a person's PACs are thought to be triggering episodes of atrial fibrillation, it is almost never "necessary" to treat them.

However, occasionally a person will experience intolerable palpitations from their PACs, and treatment will become desirable. The best way to treat PACs is to avoid the substances (alcohol, caffeine, tobacco, etc.) that can make them more frequent, or make the palpitations stronger.

Rarely, the PACs are so disruptive to a person's life that it may be worth trying to suppress them with antiarrhythmic drugs. However, this is a decision that should not be taken lightly, since these drugs are often not completely effective, and often carry the risk of significant toxicity.

Ablating the areas of the atria that are producing PACs is now feasible, but this form of treatment is invasive and carries the risk of serious complications. Ablating PACs is virtually always reserved for those patients in whom the PACs are triggering more serious arrhythmias, such as atrial fibrillation.

The bottom line is that PACs are very common, and are almost always completely benign -- so unless there is a very good reason to do otherwise, by far the wisest treatment is to leave them alone.

So if you have PACs that are producing palpitations, you will want to have a long talk with your doctor before you agree to any treatment more aggressive than lifestyle changes.

Sources:

Sobotka PA, Mayer JH, Bauernfeind RA, et al. Arrhythmias documented by 24-hour continuous ambulatory electrocardiographic monitoring in young women without apparent heart disease. Am Heart J 1981; 101:753.

Fleg JL, Kennedy HL. Cardiac arrhythmias in a healthy elderly population: detection by 24-hour ambulatory electrocardiography. Chest 1982; 81:302.

Haïssaguerre M, Jaïs P, Shah DC, et al. Spontaneous initiation of atrial fibrillation by ectopic beats originating in the pulmonary veins. N Engl J Med 1998; 339:659.

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