Tag Archives: PACs

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,


AliveCor (Kardia) Has A Premature Beat Problem: How PVCs and PACs Confuse The Mobile ECG Device

The skeptical cardiologist has many patients who are successfully using their AliveCor/Kardia devices to monitor for episodes of atrial fibrillation (afib).

However, a significant number of patients who have had atrial fibrillation also have premature beats. Sometimes patients feel these premature beats as a skipping or irregularity of the heart beat. Such palpitations  can mimic the feeling patients get when they go into atrial fibrillation.

The ideal personal ECG monitor, therefore,  would be able to reliably differentiate afib from premature beats for such patients.

Premature Beats: PVCs and PACs

I’ve discussed premature ventricular contractions (PVCs) here and here.  Premature beats can also originate from the upper chambers of the heart or atria.

Such  premature atrial contractions (PACs) have generally been considered benign in the past but a recent study showed that frequent (>30 s per hour) PACs  or runs of >20 PACs in a row were associated with a doubling of stroke risk.

For patients who experience either PVCs or  PACs the AliveCor device is frequently inaccurate.

PACs Misdiagnosed As Atrial Fibrillation

Here is a panel of recordings made by a patient of mine who has had documented episodes of atrial flutter in the past and who monitors his heart rhythm with Alivecor regularly:

Of the ten recordings , four were identified as “possible atrial fibrillation.”

Unfortunately only one of the four “possible atrial fibrillation” recordings has any atrial fibrillation: this one has 7 beats of afib initially then changes to normal sinus rhythm (NSR).

The other 3 recordings identified by AliveCor as afib are actually normal sinus rhythm with premature beats.

The first 3 beats are NSR. Fourth beat is a premature beat

In addition, frequently for this patient AliveCor yields an “Unclassified” reading for NSR with PACs as in this ECG:

PVCs Misread As Atrial Fibrillation

I wrote about the first patient I identified in my office who had frequent PVCs which were misdiagnosed by AliveCor as afib here.

Since then, I’ve come across a handful of similar misdiagnoses.

One of my patients began experiences period palpitations 5 years after an ablation for atrial fibrillation. He obtained an AliveCor device to rec  ord his rhythm during episodes.

For this patient,, the AliveCor frequently diagnoses “possible atrial fibrillation” but  all of his episodes turn out not to be afib. In some cases he is having isolated PVCs:

The first 3 beats in the lower strip are NSR. The fourth beat (purpose circle) is a PVC. AliveCor interpreted this as afib

At other times he has periods of atrial bigeminy  which are also called afib by AliveCor. In this tracing he has atrial bigeminy and a PVC.



PVCs Read As Normal

Premature beats sometimes are interpreted by AliveCor as normal. A reader sent me a series of  recordings he had made when feeling his typical palpitations. all of which were called normal. Indeed, all of them but one showed NSR. However on the one below the cause of his palpitations can be seen: PVCs.

The NSR beats (blue arrows) followed at times by PVCs (red arrows))

I obtained the “Normal”  tracing below from a patient in my office with a biventricular pacemaker and frequent PVCs who had no symptoms.

Paced beats (blue arrows) PVCs (red arrows)

PVCs Read As Unclassified 

A woman who had undergone an ablation procedure to eliminate her very frequent PVCS began utilizing AliveCor to try to determine if she was having recurrent symptomatic PVCs. She became quite frustrated because AliveCor kept reading her heart rate at 42 BPM and giving her an unclassified reading.

AliveCor is always going to call rhythms (other than afib) unclassified when it counts a  heart rate less than 50 BPM or greater than 100 BPM.

In this patient’s case, every other beat was a PVC (red circles). Her PVCs are sufficiently early and with low voltage so the AliveCor algorithm cannot differentiate them from T Waves and only counts the normal sinus beats toward heart rate.

Accurate AliveCor Readings

I should point out that many of my patients get a very reliable assessment from their devices. These tracings from a woman with paroxysmal atrial fibrillation  are typical: all the Normal readings are truly normal and all the atrial fibrillation readings are truly atrial fibrillation with heart rates  above 100.

AliveCor’s Official Position on Premature Beats

The AliveCor manual states

The Normal Detector in the AliveECG app notifies you when a recording is “normal”.  This means that the heart rate is between 50 and 100 beats per minute, there are no or very few abnormal beats, and the shape, timing and duration of each beat is considered normal.

What qualifies as “very few” abnormal beats is not clear. The manual goes on to state that the AliveCor normal detector has been designed to be conservative with what it detects as normal.

What is clear is that premature beats  significantly confuse the AliveCor algorithm. Both PVCs and PACs can create a false positive diagnosis of atrial fibrillation when it is not present.

Consequently, if you have afib and premature beats you cannot be entirely confident that a reading of afib is truly afib. Strongly consider having the tracing reviewed by a cardiologist before concluding that you had afib.

On the other hand if you are experiencing palpitations and make a recording with Alivecor that comes back as normal do not assume that your heart rhythm was totally normal. While highly unlikely to be afib, your palpitations could still be due to PACs or PVCs.

If a patient of mine has an abnormal or questionable AliveCor recording it is currently a very simple process for me to review the recording online  through my AliveCor doctor dashboard. The recordings can also be emailed to me.

Coralively Yours,