Heart Education

Ectopic Beats: How to Identify Them on Your Apple Watch ECG

Learn about ectopic beats like PACs and PVCs, their patterns on the Apple Watch ECG, and what they might indicate about your heart health.

Introduction

Do you remember the last time your heart was fluttering, jumping, pounding, or skipping a beat? You may have experienced a premature electrical impulse in the heart’s cycle known as an “ectopic beat,” or “premature beat.”


Why Do Ectopic Beats Occur?

Your heart is a thing of marvel — most cells in your heart are capable of beating all on their own. To keep your heart beating at a regular pace, a cluster of cells known as the sinoatrial (SA) node acts as the heart’s natural pacemaker. Sometimes, however, one of your other heart cells beats at a faster pace and causes other cells to follow the new march of its drum. This leads to a premature heartbeat, also known as an ectopic heartbeat.

When your heart experiences these premature beats, a brief pause usually follows where the SA node resets itself before the next beat. This can cause a feeling of an extra beat or a skipped beat, along with a fluttering sensation. Usually, ectopic heartbeats are asymptomatic: nearly everyone experiences a few ectopic heartbeats every day. But frequent occurrences could be linked to heart problems.

So what are the different types of ectopic beats? And how can you identify them on your smartwatch ECG? Let’s dive in.


Types of Ectopic Beats

Ectopic heartbeats fall into one of three buckets depending on the source of the electrical impulse: PACs (atrial), PVCs (ventricular) and PJCs (junctional).

Premature Atrial Contraction (PAC)

PAC beat on an Apple Watch ECG. Notice how the PAC beat occurs earlier than expected, has a normal QRS complex, and is followed by a longer pause before the next normal beat.


A premature atrial contraction (PAC) occurs when an extra heartbeat originates in the atria — or top of the heart — in a location other than the SA node.


How to Identify a PAC

The hallmark of a PAC is a premature P wave observed before the next expected normal beat. This premature P wave usually has a different shape: it can be wider, or taller, narrower or shorter, even upside-down. This really depends on where exactly in the atria the PAC is coming from. If it comes from somewhere near the SA node, it could look like a normal P wave. Additionally, a normal-looking QRS complex follows most PACs. Finally, PACs cause the natural pacemaker to "reset," which results in a longer interval before the next normal beat.


Premature Ventricular Contraction (PVC)

PVC beat on an Apple Watch ECG. Notice how the PVC has a wide QRS complex, no preceding P wave, and looks different from the normal heart beats.

A premature ventricular contraction (PVC) occurs when an extra heartbeat originates in the ventricles, or bottom of the heart.


How to Identify a PVC

You can identify a PVC by its wide and bizarre QRS complex. The QRS complex of the PVC beat is typically wider than that of a normal beat. Also, PVCs interfere with the normal sinus rhythm by coming in before the next anticipated beat. Finally, you’ll notice that there’s no P wave before the QRS complex of a PVC beat.


Unifocal vs. Multifocal PVC

Unifocal PVCs look identical in appearance, and they originate from a single ectopic site.


Unifocal PVCs. Notice how the PVCs are identical in appearance.


Multifocal PVCs, on the other hand, arise from two or more ventricular sites. They also have different QRS shapes.


Multifocal PVCs. Notice how the PVC at the top has a different shape than the two PVCs at the bottom.



Premature Junctional Contraction (PJC)

PJC beat. The PJC beat has no P wave.


A premature junctional contraction (PJC) occurs when an extra heart beat originates at the connection between the top of the heart (atrium) and the bottom (ventricle), in or near the atrioventricular (AV) node.

How to Identify a PJC

To identify a PJC, look for a premature QRS complex that shows up before the next expected normal beat. The P wave is either absent or upside down, and you’ll usually see it after the beginning of the QRS complex. Additionally, the QRS complex will look similar in shape to that of a normal beat.


Frequency of Premature Beats

Ectopic beats can either be isolated, or they can appear in groups.


Isolate: Single occurrence of an ectopic beat.

An isolated PAC.


An isolated PVC.


Couplet: Two consecutive ectopic beats.

A PAC couplet, also known as an atrial couplet. This occurs when two extra heart beats in a row originate at the top of the heart (atria).

A PVC couplet, also known as a ventricular couplet. This occurs when two extra heart beats in a row originate at the bottom of the heart (ventricles).


Run: Three or more consecutive premature beats.

A PVC run, also known as a ventricular run.


A PAC run, also known as an atrial run.


Pattern of Ectopic Beats

Ectopics can often occur in repeating patterns. Let’s look at the most common ones.

Bigeminy: An ectopic occurs after every normal beat.

PVCs in bigeminy pattern, also known as ventricular bigeminy. Notice how there’s a PVC occurring every other beat.
PACs in bigeminy pattern, also known as atrial bigeminy.


Trigeminy: An ectopic occurs after every two normal beats.

PVCs in trigeminy pattern, also known as ventricular trigeminy. Notice how for every two normal beats, there’s one PVC.


PACs in trigeminy pattern, also known as atrial trigeminy.


Are Ectopic Beats Cause for Concern?

Nearly everyone experiences a few ectopic beats every day, which is completely normal. Most people don’t feel these extra heartbeats; however, some are particularly sensitive to them, often describing the sensation as a “skipped heartbeat” or “extra heartbeat.”

If more than 1% of your heartbeats throughout a full day are ectopic, this may be a sign that there’s something going on. It’s difficult to know if you have frequent ectopics with a single, 30-second ECG strip. However, if you see more than one ectopic on the same 30-second ECG strip, this should make you wonder whether or not you may have frequent ectopics. This may be a good reason to check additional ECGs and talk to your healthcare provider, who will likely want to check your ectopic count with a continuous heart monitor.

Frequent ectopic beats can be caused by either electrical problems in the heart, or problems with the structure or heart muscle itself. Conditions such as high blood pressure, diabetes, and obesity can lead to abnormal heart muscle and, consequently, more ectopic beats than normal. Those with advanced heart conditions such as coronary disease or heart failure can also have more ectopic beats than normal. Conversely, a very high number of ectopic beats (such as over 15% PVCs) can lead to heart weakening. For these reasons, it’s always a good idea to talk to your healthcare provider if you seem to have frequent ectopics.

Marco Perez - Co-founder of ReadMyECG
ReadMyECG Team
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