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HONG KONG, CHINA. PACs, also known as atrial extra systoles or atrial premature beats, are extremely common and can be found on 24-hour Holter monitoring in over
60% of normal adults. They are usually entirely benign and do not require treatment unless they are very frequent or result in uncomfortable palpitations.
PACs originate from foci of �rogue� heart cells that decide to take on a beat of their own. Depending on when the PAC �fires�, it may not be transmitted
to the ventricles at all but, in some cases, it may cause a pause in the normal heart beat rhythm, which may or may not be followed by a more forceful ventricular contraction.
PACs can be precipitated by stress, fatigue, fever, thyrotoxicosis, tobacco, caffeine, and certain other stimulants and drugs including cold medications and
weight-loss preparations. PACs may also be a sign of underlying heart disease such as heart failure or myopericarditis. PACs can initiate atrial fibrillation
(AF), atrial flutter or supraventricular tachycardia. Research has shown that these arrhythmias originate from the same focal points that generate PACs.
PACs can be distinguished fairly easily on an electrocardiogram; they are characterized by a smaller and earlier than expected P wave. The P wave originates
in the sino-atrial node and is the electrical impulse that initiates the heart beat.
The obvious way to avoid PACs is to avoid the triggers. In more severe cases minor tranquillizers or beta-blockers may prove helpful. There is also substantial
evidence that a magnesium deficiency can increase both PACs and PVCs (premature ventricular complexes), and that magnesium supplementation can reduce them very significantly.
A group of researchers from the University of Hong Kong now reports that frequent PACs may predict the occurrence of new onset AF and may be associated with an
increased incidence of stroke, heart failure, and cardiac-related death. Their study involved 428 patients without AF and structural heart disease who underwent
24-hour monitoring for palpitations, dizziness or syncope (temporary loss of consciousness). The average age of the patients was 66 years and 44% were male.
The study participants were not entirely healthy with 45% having hypertension, 17% having diabetes, and 17% having coronary artery disease. About 45% were on
calcium channel blockers and 44% were on beta-blockers.
More than 100 PACs a day was considered to be frequent and 107 of the 428 patients (25%) fell into this category. Patients with frequent PACs were likely to
be older (71 years vs. 65 years) and were more likely to be smokers (36% vs. 25%). After a mean follow-up of 6 years, 29% of the patients in the frequent
PACs group had developed AF as compared to 9% in the non-frequent PACs group. This corresponds to an incidence of 4.83%/year in the frequent PACs group as
compared to 1.43%/year in the non-frequent group.
Cox regression analysis revealed that frequent PACs (HR: 3.22), age over 75 years (HR: 2.3), and coronary artery disease at baseline were independent predictors
of new onset AF. Cox regression analysis also showed that age over 75 years (HR: 2.2), coronary artery disease (HR: 2.2), and frequent PACs (HR: 1.6)
were independent predictors of ischemic stroke, congestive heart failure, and death.
The researchers point out that another study, which involved 687 apparently healthy individuals using 720 or more PACs a day (30 per hour) as the definition
of frequent PACs, reported an incidence of new onset AF of 1.28%/year in the frequent PACs group as compared to 0.43% in the non-frequent group.
Editor�s comment: Although current afibbers clearly do not need to worry about developing AF, it is of interest to note that frequent PACs may be associated
with an increased risk of adverse cardiovascular events. Fortunately, PACs and PVCs can pretty well be eliminated by ensuring adequate magnesium and potassium status.
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