Mechanisms for stroke and afib related to atrial cardiomyopathy

Premature Atrial Contractions: Are They Benign Or Malignant?

In the last few weeks the skeptical cardiologist has had a run on patients with premature atrial contractions (PACs).

I’ve discussed in detail premature ventricular contractions (PVCs) here and here. They are the most common cause of an individual feeling that their heart is skipping a beat or fluttering briefly, something we term palpitations.

Premature beats, which can be either PVCS or PACs, in addition to causing palpitations, are the most common cause of an irregular pulse detected by a blood pressure device or a health care worker,

What Causes Premature Atrial Contractions?


Like PVCs, PACs occur when electrically active tissue in the heart decides to fire off (or depolarize) before it has received the signal from the normal pacemaker of the heart, the sinus node. In the case of PACs, the rogue tissue is in one of the atria, the upper chambers of the heart.

In the ECG recording below, the PAC (labeled APC) occurs earlier than expected (prematurely). The normal (sinus) beats occur at regular intervals and are all preceded by p waves of normal configuration which are the normal electrical signature of atrial contraction. The larger spike that follows the p wave (the QRS complex) represents ventricular depolarization and is unchanged from the normal sinus beats because activation of the ventricle is normal with PACs.

These early beats, in and of themselves, are felt to be benign.

Premature Atrial Contractions Are Very Common


They are extremely common when we monitor ECG rhythm for an extended period, even in young, totally normal individuals. More common, in fact, than PVCs.

For example, in a select group of male aviators

Rare, occasional, frequent and very frequent isolated atrial ectopy occurred in 72.9%, 2.6%, 2.3% and 0.3%, respectively. The same categories of isolated ventricular ectopy occurred in 40.9%, 7.9%, 3.3% and 0.0%.

Frequency of isolated ectopy was classified as a percentage of the total beats on the Holter monitor: rare (< or =0.1%), occasional (>0.1 to 1.0%), frequent (>1.0 to 10%) and very frequent (>10%).

Thus, the majority of the time we will see some PACs in normal subjects who we monitor for 24 hours by ECG.

It was also common to see two PACs in a row (an atrial couplet or pair). Atrial couplets occurred in 14.5% of these aviators.

The highlighted box from the 3 lead Holter monitor recording below shows an atrial couplet.

atrial tach holter
The QRS complex of the premature atrial complex (PAC) is usually preceded by a visible P wave that has a slightly different shape or different PR interval from the P wave seen with sinus beats. The PR interval of the PAC may be either longer or shorter than the PR interval of the normal beats. In some cases the P wave may be subtly hidden in the T wave of the preceding beat.

When 3 or more  premature atrial beats occur in a row, we start calling this nonsustained supraventricular tachycardia.

Nonsustained supraventricular and ventricular tachycardia (duration 3 to 10 beats) occurred in 4.3% (13/303) and 0.7% (2/303), respectively of those normal male aviators.

PACs Are More Common As We Age


One study found that in normal individuals over age 50 years , 99% had at least 1 PAC during 24 -hour Holter monitoring. The PAC prevalence strongly increased with age from about one per hour in those aged 50 to 55 years to 2.6 per hour among those aged ≥70 years.

Another study analyzed 24 hour holter recordings at 5 year intervals and found the frequency of PACs (and PVCs) increased significantly in all age groups over that time span.

Screen Shot 2019-11-10 at 6.35.20 AM

APCs And Atrial Fibrillation


Not uncommonly, when a patient has PACs, especially if they are frequent, computer ECG interpretations mistakenly diagnose atrial fibrillation. This happens regularly even with a full, medical-grade 12-lead ECG. Fortunately, such ECGS are still over-read by cardiologists who usually make the correct diagnosis.

The computerized algorithms that single lead mobile ECG devices like Apple Watch 4 and AliveCor’s Kardia similarly are frequently confused by premature beats, especially APCs. I wrote about this in detail in my post on PVCS and PACs here.

Sometimes the devices will diagnose “possible atrial fibrillation” in a patient with frequent PACs in sinus rhythm and sometimes “unclassified.”

In addition, patients with very frequent APCs show a higher tendency to develop atrial fibrillation and a higher risk of cardiovascular complications.

The Various Names Of The Extra Beats


Whereas a consensus has been achieved (for the most part) on the term for early beats from the ventricles (premature ventricular contractions or PVCs ) the term for PACS varies from one cardiologist to another and one paper to another.

If I enter in

“atrial premature”

into my EMR problem list search, multiple naming options appear (all with the same ICD code of I49.1)

In addition, you  may also encounter the terms atrial ectopy, premature atrial beats or various combinations of “supraventricular” with either contraction, beats or ectopy.

The two most popular acronyms are APCs or PACs and I am guilty of using these interchangeably and seemingly randomly.

Premature Atrial Contractions: Markers For Atrial Cardiomyopathy?


Through most of my cardiology life I had considered PACs to be totally benign. And certainly, in and of themselves they cause no problems other than occasional palpitations. However, studies in the last decade have shown consistent associations between frequent PACs and stroke, death and atrial fibrillation.

Some researchers have suggested the concept of “atrial cardiomyopathy” to explain this association. A diseased atrium could be the reason for PACs and atrial fibrillation as well as stroke and death as opposed to atrial fibrillation being the primary cause of increased cardiovascular events.

Clearly, PACS, stroke and CV disease share common risk factors such as age and obstructive sleep apnea making cause and effect difficult to sort out. Could PACs and atrial fibrillation represent different phenotypes of atrial cardiomyopathy?

These data on frequent PACs raise a whole host of questions which remain unanswered.

Is there a frequency of PACS ( say >100 per 24 hours) which is useful in predicting adverse outcomes?

Are there clinically measurable predictors of which  patients with frequent PACs are most likely to have to poor outcomes?

Does treatment of PACs (say with anticoagulation therapy or suppression) in the absence reduce risk of CV events?

The Bottom Line On PACs


  1. Premature atrial contractions are very common in normal individuals and increase with aging.
  2. They can cause palpitations and an irregular pulse but are benign in and of themselves.
  3.  Frequent PACs (more than 1% of total heart beats) are a marker of increased risk of atrial fibrillation, stroke, and death.
  4. The concept of a diseased atrium (atrial cardiomyopathy)  causing both atrial dysrhythmias and raising the risk of stroke and death helps to explain these associations.
  5. More research is needed to answer the important clinical questions related to the independent significance of frequent PACs and what treatments might be warranted.

Semipalpitatingly Yours,


13 thoughts on “Premature Atrial Contractions: Are They Benign Or Malignant?”

  1. Thank you so much Anthony!
    Always timely! I’ve had a few of these lately, apparently related to some of the things I eat (…soja sauce with sushi: SO MUCH salt! and other unidentified stuff…), and I was somewhat freaked out.
    I am not a student of cardiology (my Harrison’s textbook dates back to 1976…), but a patient of cardiology, just in need of reassurance.
    Again: thank you so mcuh for this blog.
    Merry Chrsitmas and a Rich New Year to you and your family!

    1. Thank you Dr A – your advice confirms my concerns, and that the blithe reassurance from experts that no action was needed for PVCs and PACs was misplaced. In my situation it seems food is an issue.

      Chemicals in food can contribute to a wide variety of symptoms.

      Some foods have long been recognised as triggers for migraine, so a similar connection with cardiac neural connections and activity seems plausible.

      It is possible that the very high levels of amines in food could contribute to cardiac symptoms after a tasty or spicy meal. This does seem to be likely in my own situation, and I have started a low amine diet. Early days but seemingly an improvement.

      The Mediterranean Diet is very high in amines.

      Please see this link for more.

      Alcohol has long been recognised as a trigger for AF, so prudently I am now a total abstainer, festive season gatherings excepted.

      Would be interesting to hear from others as to the effects certain foods and alcohol has on them.

  2. My 48 hour Holter of a month ago yielded 10,414 atrial ectopic beats. Symptomatic; quite disconcerting.
    If you were to go about treating a situation like this medically, what anti-arrhythmics would you start trying?
    Everybody responds differently, right?

    1. Do you have obstructive sleep apnea?
      That was my problem, and my atrial flutter and occasional bouts of PVCs practically disappeared with treatment of that condition.
      Good luck! And happy Holidays.

      1. Thanks. Nope. All other risk factors: nope. It’s just me??
        I did have my fourth ablation for atrial arrhythmia just in September. Not a full success. I’m hoping to avoid further “intrusions” with medication.

  3. Is there any medication to decrease PACs or PVCs?
    My cardiologist prescribed metoprolol and while it has reduced my resting heart rate and maybe relaxed me, when I objectively measured it using a Holter Monitor there was no change in frequency of the PVCs.
    However for some unknown reason my EF went down on my echo so the cardiologist is monitoring for PVC induced cardiomyopathy?

  4. Just catching up on blog again, great post. Quick question, had a 48 hr holter 2 yrs ago due to palps. Report sited 631 PACs with avg HR of 67 min HR 41 and max 134, no PVCs. Referring to your summary regarding the 1% rule frequency I tried to find total counted beats during recording and could not find it. So I utilized the average HR of 67 and proceeded to calculate total number of beats for 48 hrs and then divided. Would that be a efficacious way of determining frequency and is it typical for holter reports not to document total beats during recording?

    1. Christian,
      The full Holter monitor is typicaly 40 pages long and has a ridiculous amount of data in it which includes total number of beats.
      Your method would be accurate for total beats.
      However, the content (and accuracy) of the physician generated report from a Holter varies wildly and typically does not include total beats.
      If there are a high number of PAC or PVCs i report out the absolute number and the percent.
      You might ask the entity that did the holter if you could get a PDF of the full recording. Then you will likely be driven mad by all the data

      1. Thanks Dr. P, does the holter raw data highlight problematic wave issues or do you have to go through the recording and find them? If it does highlight the problems, does it specify what they are or does the cardiologist have to interpret? I figured it was probably automated but I always wondered.

        1. The Holter systems have sophisticated algorithms which highlight abnormalities. Techs review these for accuracy and create a summary which includes rhythm strips.
          Docs review the summaries and create a report

  5. I just suddenly began having tons of palpitations one month ago–out of the blue. Holter showed PACs 13.2% of the time, couplets 4.5% and 62 runs of PATS during the 24 hours. All heart testing was negative-zero heart issues. Breathing is shallow and I get exerted immediately…can barely climb one flight of stairs. I am 63 and super fit and healthy. WHAT GIVES??

    The EP put my on beta blocker and flecanide, which has softened the arrhythmias, but they are still going on all day long and my lungs do not seem right.


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