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)
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)
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.
Multifocal PVCs, on the other hand, arise from two or more ventricular sites. They also have different QRS shapes.
Premature Junctional Contraction (PJC)
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.
Couplet: Two consecutive ectopic beats.
Run: Three or more consecutive premature beats.
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.
Trigeminy: An ectopic occurs after every two normal beats.
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.