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,



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

  1. I just received a 24 hour Holter test report with twenty-seven percent (27%) PACs, more than 25,000 in 24 hours, which my PCP believes is of np cencern becasue I haven’t had any symptoms he’s seen. From my readings this frequency is so far above the definitions “high frequency” used to suggest an increased risk of future AF as to make it a virtual certainty. I’ve also seen a correlation with other symptoms like peripheral numbness and lab reports of above normal range K levels.

    Is my concern justified enough to see a cardiologiost?

    • See a cardiologist – many articles on this site and others about consequences of high PAC burden.

  2. Thanks for all the clear resources on this site! I (38, F, no prior issues) started noticing significant palpitations about three months ago. I got a 48-hour Holter and the initial interpretation suggested SVT. However, my cardiologist disagreed, determining that the report showed PACs instead. (This does fit better with how I experience the palpitations—as thudding and skipping, not as racing.) I am on 12.5mg/day of metropolol, and this has lessened but not eliminated palpitations that I notice. (I am curious whether the actual burden has changed…) My resting pulse is usually in the 50s, but this causes no noticeable problems such as dizziness or fatigue.
    My cardiologist said that she considered my TTE normal and no cause for concern, though it did indicate hypertrophied papillary muscles. (All other measurements were normal.) This, of course, got me reading about HCM, though I learned, and my cardiologist confirmed, that hypertrophied papillary muscles in themselves are not diagnostic of HCM.
    I suspect that anxiety and poor sleep increase my palpitations, but there’s a vicious cycle where the palpitations give me anxiety and make me afraid to sleep, and so on. I enjoy doing not-too-intense running (usually 15 to 30 minutes daily), and I seem to tolerate exertion just fine—I have never experienced pain, distress, unusual shortness of breath, or the like. But reading about HCM, and occasionally feeling the PACs and twinges, makes me fearful of doing this exercise.
    Lately, I have been feeling a slight tightness, or perhaps coldness, around my chest, though I know this is most likely from anxiety, straining muscles when doing planks, or any of a number of other causes. But it’s really affecting my ability to go about my day-to-day activities and think about, well, anything else.
    Should I advocate for getting a stress echocardiogram and/or another Holter report and avoid exercise in the meantime? How concerned should I be, now or in the future, about the hypertrophied papillary muscles? Finally, I’ll add that my potassium came in at 3.9 and I am interested in trying to raise this since I hear that it helps reduce palpitations for many people—I eat a large baked potato most days, but that might not move the needle enough.

    • AC,
      An isolated reading of “hypertrophied papillary muscles” on an echocardiogram is strange. If your cardiologist is expert at echo and considers it normal I would trust her judgement and try to banish thoughts of HCM from your mind.
      Your chest tightness may well be musckuloskeletal but if you have concerns then doing a stress echo seems reasonable.
      See my article on treatment of PVCs, I deal with potassium in detail.
      Dr. P

  3. I underwent an atrial fib ablation last April, stayed on Metoprolol and Sotalol until January this year. EP took me off Sotalol, within a day I was experiencing irregular heart beats and confirmed PACs. I took Magnesium Citrate since I was also experiencing some constipation, within 90 minutes my heart rate/rhythm returned to NSR. I posed the question to the EP AP, who told me that magnesium may have a positive effect on heart rhythm. In fact no one checked my magnesium levels for four months leading up to my ablation. Since then I’ve read many NIH/PubMed articles detailing how important adequate magnesium levels are to heart rhythm/rate. After that I researched as best I could the types and efficacy of Magnesium-Taurate, Magnesium-Malate, Magnesium-L-Threonate, etc., and have been taking these supplements which have kept my irregular rhythms at bay. Considering we eat low carbohydrate diet (in fact keto, my wife goes to a keto neurologist), and i have a R.O. water filter that not only filters heavy metals and toxins but also filters out the beneficial elements like magnesium, and without significant organically grown produce like root vegetables and combined with the knowledge that ~60% or more of the bodies magnesium stores are in bone tissue, ~40% stored in intra-cellular, and less that 1% is floating around in blood it seems any blood magnesium tests are marginally representative at best for any given persons optimal magnesium level, note I didn’t say RDA range or sufficient range since my body may simply need more than yours. Last thought for those that read these comments, corporate grown farm produce are lacking in the natural nutrients eat organic produce if you can afford it, and you will still likely need supplements, but get labs if you can. My labs were within the normal range just after the ablation, and since taking supplements I have yet to get labs, but they’re ordered so likely tomorrow.

    • Don,
      Thanks for these observations on your case and the benefit of magnesium.
      Are you taking Mg Taurate, Malate, and L-threonate?
      Dr P

      • Hi Dr. Pearson,

        Yes, I’ve been taking Magnesium Taurate, Magnesium-L-Threonate, and Magnesium Malate. I had labs drawn last week. My Magnesium level came back in range, maybe in the upper third of the range. So far so good, with no identified arrythmias. The Magnesium Taurate is targeted for cardiac health, but I figured the others would not hurt me.

  4. Something worth noting that I have not read about anywhere is exercise. I am a 61 year old male who had a PFO closure in Feb of 2019. The procedure was done to rid myself of the blood thinner I was taking. It was believed that to PFO caused my stroke back in 2014. Two months after closing the PFO I developed afib identified by wearing a halter. Afib was a common occurrence after this procedure but it was expected to subside in the near future. I continued to feel arrhythmias in and suspected that the afib would never go away. Further tests indicated that it was not afib but that i was having PAC’s. At the time I was experiencing between 20,000 and 25,000 per day. I was a terrible experience and I found it very depressing. The cardiologist told me they were benign and that they we nothing to worry about. He suggested beta blockers to slow my heart making them less noticeable but my heart can currently beat as low as 50 bpm. In August of this year I decided I decided I would try an exercise routine significantly more stimulating that the one I had at that time. After exercising daily for 30 minutes at a time accelerating my heartrate to above 140 bpm for at least 20 minutes of the routine my PAC’s stopped. Three months later continuing my exercise I have not had a single PAC. Small price to pay for the way I am now feeling. I never thought I would feel this good again. Exercise is less expensive that drugs with no adverse side effects. Sounds like a prescription for life. For the record I was always in fair physical shape. 5’10 ant 180 pounds.

    • Joe,
      Thanks for sharing this interesting case history. That is fantastic that your PACs went away after beginning your more intense cardio exercise routine. Now, in addition to all the other benefits of exercise we can add PAC relief.
      I’m preparing a post on PFO closure. One of the post-procedure issues I worry about is atrial fibrillation as was apparently seen in your case. Without knowing more details about your stroke in 2014 I can’t say whether I would have recommended PFO closure for you in 2019. What was the blood thinner you wished to rid yourself of and are you rid of it or just on another one?
      Dr P

  5. Hello Dr. A. What a wonderful find this site is. The first step is reassurance when it comes to PVC’s and APC’s, your blogs just reminded me of that. I had holter monitoring three times over the last 15 years. Most recently 4 years ago. It was only on the third try did my dr. (this time a cardiologist) explain to me that I had very rare ectopic activity. 37 total events, no runs, no bi’s or tri’s. However, I know that they are increasing but my PCP (this year) after ordering an echo, ecg and stress test that were all normal didn’t recommend another holter. My question is are there any reliable 24 hour monitors that are good for consumer use that would reliably screen for ectopics? thank you so much!

    • Charles,
      thank you.
      There are consumer devices which continuously record your rhythm but none that I know of that give you an accurate summary of the presence and quantity of ectopics.
      Dr P

  6. One comment of note: the Kardia device, while better at identifying PAC’s (it calls the supraventicular ectopy), it still occassionally will misdiagnose a bout of PAC’s as AFIB. I have had a couple of 30 second strips with 6-7 PAC’s that I sent to my cardiologist – he identified them as sinus rhythm with PAC’s not AFIB. SO it is much less frequent than before, but not perfect is sorting out what is PAC’s and what is AFIB

  7. Hi Dr. P., thanks for the interesting article. Have you any thoughts on the relationship between blood pressure and episodes of increased PAC frequency? My own observations of a single case are that systolic BP consistently drops by 20mmHg along with a corresponding feeling of malaise during such episodes (>5 PACs/minute at rest). BP immediately returns to normal afterwards and I’m wondering if your experience backs this up.

    • I haven’t seen significant drops in BP with PACs.
      If a catecholamine surge was creating PACs I would expect, the oppose, in fact with the BP rising.

  8. I peeked at the source article about the aviators and found this: “From 1575 consecutive cardiac catheterizations reviewed, 303 aviators met the above inclusion criteria”. Apparently the “normal” aviators had all had cardiac caths, and only a small proportion of those met all the inclusion criteria. Strong set-up for a selection bias, and very different from a random sample of normal aviators. I feel this may be somewhat misleading to the average reader of your blog.

  9. Hello, I am 41 and 2 months ago out of the blue I started getting symptomatic PACs (sensations in my throat and and chest). ECG showed normal sinus rhythm. 48-hr Holter monitor results: No significant arrhythmias seen. Predominant rhythm: NSR with occasional PACs (1.3% burden) and average HR 65 bpm.

    1. You mentioned frequent PACs are considered > 1.0% of total heartbeats. My results showed 1.3% burden but it was labeled as ‘occasional’. Does the classification change the approach for treatment and further diagnostics?
    2. What type of test would be done to see whether one has a diseased atrium?

  10. Hi, I was just curious. I have a lot of chest and arm pains. The cardiologist put a monitor on me for a day, but it was one of my “better” days when the chest issues and (sometimes) feels like the heart is thumping harder than normal—so I didn’t think they would find anything. Nurse said they found like 120 PACs had it on for 24 hours. Don’t see doctor till next week. Is that a low number for PACs in a day?

  11. Are excessive PAC’s more worrisome than PVC’s? All the literature I can find says that PAC’s are a greater risk for developing AF.

    I am currently having 10-15 PAC’s a minute with normal sinus rhythm and are waiting for the results of a 14 day ZIO XT patch monitor…

    • Alan, I have the similar situation and am in day 10 of my 14 day ZIO XT patch. In my situation, the PAC come in episodes, several days with none then they’ll occur for a full day (incl overnight) then back to normal sinus rythm. What was your outcome?

  12. Can you explain why you wonder first if >100 beats in a day could be a possible indicator that PAC could predict adverse outcomes, and then later state that “Frequent PACs (more than 1% of total heart beats) are a marker of increased risk of atrial fibrillation, stroke, and death.”

    That’s a big difference in range between them. Wouldn’t 1% of total beats in 24 hours for say an 80 bpm heart rate be over 1,000 beats in a day? I’ve seen both of these figures mentioned in other articles and am confused by the discrepancy. Thanks so much for any clarification.

  13. Hello, I came across this post after doing tons of research over the years. I’m a 25 year old male and developed PACs on exercise about 3 to 4 years ago. Every time my heart reaches around 160bpm, I start getting PACs relatively frequently. This also just happens when I get rushes of adrenaline, or sometimes even when standing up too quickly.

    My cardiologist explained they were PACs, but didn’t provide much information. She said I was fine, but noted I had “mild” mitral valve prolapse.

    Do you have any additional info on PACs during exertion? I would really appreciate any info you have. I have been searching for years.

    Thank you

    • Little is known on this topic. The one published study I found ( found frequent APCs with treadmill exercise to be an independent risk factor for the development of afib. The study is a weak observational study. We know that frequent PACs at rest are associated with more afib and this study doesn’t have info on the resting frequency of PACs.

  14. I have those “skipped” beats and doctor says they are premature atrial contractions. I can hear each heartbeat due to my tinnitus and now i am having the PAC’s every 3 or 5 or 10 beats. Should i see a cardiologist instead of my internal med doc?

    • That is a good question. In general, I would say if a patient feels like their problem might be better addressed by a specialist, especially if symptoms are poorly controlled, it is appropriate to ask if a specialist consultation is warranted.

  15. 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.


  16. 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?

    • 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

      • 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.

        • 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

  17. 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?

  18. 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?

    • 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.

      • 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.

        • Curious if in the past year you have gained any fresh insights about your frequent PACs. I started having them out of the blue this May –at first about 13,000/day and now that has increased to 20,000+. In addition, for the first time ever I suddenly have high blood pressure (150/100)–this didn’t start until November. So for the first 6 months of the very frequent PACs my blood pressure was fine–totally normal as it always has been. But as the PACs got worse, suddenly a spike in bp. Very concerning. Have seen different EPs and they all basically pat me on the head and tell me my heart is healthy and strong and that PACs are totally benign and not life threatening. Of course, I am now on meds, which have normalized the bp and dropped the PACs down to about 8,000/day. Just wondered if you have learned anything that might shed light on the condition. Thanks!

  19. 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!

    • 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.


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