Heart Education
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What a Premature Atrial Contraction (PAC) Looks Like on Your Watch ECG

ReadMyECG Team
Premature Atrial Contractions (PACs) - Causes, Definition, Symptoms, Treatment

Key Takeaways

Abnormal heart rhythms are a common occurrence. In a study published in the National Library of Medicine, 99% of participants over 50 had at least one event of a premature atrial contraction (PAC) in a 24-hour monitoring period. PACs are just one of the common arrhythmias or abnormal heart rhythms. Most PACs are benign.

However, some people are more likely to develop cardiac issues with frequent PACs. The good news is that your smartwatch can help you spot them, and early detection can help you make the best decision for your heart’s health.

What's a Premature Atrial Contraction (PAC)?

The heart has a specialized structure called the sinoatrial (SA) node. The SA node is responsible for conducting electrical impulses that cause the heart to contract and pump blood. A normal heartbeat for a healthy adult is 60 to 100 beats per minute. The SA node regulates this regular, steady rhythm.

On some occasions, there are electrical impulses fired by other heart chambers. A PAC occurs when the electrical impulse starts from the heart’s upper chambers, the atrium. This impulse fires prematurely, disrupting the normal heart rhythm. Most people who experience PACs report the feeling of their heart “skipping a beat.” PACs are more common as we age. However, there are other predisposing conditions:

  • Pregnancy
  • Preexisting heart problems
  • Caffeine or alcohol intake
  • High HDL cholesterol
  • Dehydration
  • Electrolyte imbalance
  • Stress and anxiety
  • Lack of sleep
  • Medications, e.g., asthma medications

How To Spot PACs on Your Watch ECG

Understanding Premature Atrial Contractions (PACs)

PACs are usually identified during a routine electrocardiogram or ECG test. Other tests that can rule out PACs are the Holter monitoring and stress tests. All of these tests will have to be done at a healthcare facility. If you are using a smartwatch with an ECG monitoring feature, you can use your smartwatch’s ECG monitoring capability to identify PACs at home.

To identify a PAC, look for the following characteristics in your ECG:

  • A premature P wave, usually with a different shape compared to the other P waves in the tracing. It can be wider, or taller, narrower or shorter, even upside-down, depending on where in the atria the PAC is coming from.
  • A narrow/normal QRS complex, identical to the other normal beats.
  • PAC is followed by a long pause as the heart works to restore its normal rhythm.
ECG - PAC beat
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.

PACs also interfere with the normal rhythm by coming in early before the next anticipated beat. If you're monitoring your ECG on your smartwatch, a professional can help point out these abnormalities.

What Patterns Do They Occur In?

Since PACs are very common, there are times that there will only be one episode of PAC in 24 hours. In cases where a PAC is recurrent, they can be identified and categorized according to their presenting pattern.

  • Bigeminy – a PAC on every second beat
  • Trigeminy – a PAC on every third beat
  • Quadrigeminy – a PAC on every fourth beat
  • Couplet – two consecutive PACs
  • Run – three or more consecutive PACs, also known as an atrial run

ECG - PACs in trigeminy pattern
PACs in trigeminy pattern, also known as atrial trigeminy. Notice how for every two normal beats, there’s one PAC.

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

Any Cause for Concern?

Occasional PACs are generally not a cause of concern for healthy individuals and should go away without any treatment. However, recent studies suggest that frequent PACs may increase a person’s chances of an ischemic stroke. A PAC is deemed frequent if there are more than 100 episodes of PACs in 24 hours.

Frequent PACs can also predispose a person to cardiac problems such as atrial fibrillation and cardiac flutter. These are conditions wherein the heart chambers no longer beat in synchronization. With the help of a professional, your smartwatch can be a helpful tool in identifying irregular heart rhythms and help you look out for your heart’s health before it’s too late.

What Are Common Symptoms and Treatment Options?

Most PAC findings are incidental because most people don’t exhibit any symptoms. However, you may need to schedule a visit to your healthcare provider if you show any of the following symptoms indicative of PACs:

  • A flutter in your chest
  • Heart pounding
  • Chest pain
  • Shortness of breath
  • Dizziness

Your healthcare provider will manage your PACs depending on the underlying cause. Some of the most common treatments for PACs are the following:

  • Regular exercise
  • Restricting alcohol and caffeine intake
  • Discontinuing tobacco use
  • Correcting electrolyte levels
  • Avoiding stress
  • Medications (beta-blockers and anti-arrhythmic drugs)
  • Surgical procedures such as cardiac ablation

Still Not Sure How to Spot PACs on Your Watch ECG?

Although heart arrhythmias such as PACs are common, you still need to be vigilant in looking out for your heart’s health. A professional can interpret your smartwatch’s ECG readings so you can have peace of mind knowing that your heart is as healthy as it can be. Don’t miss a beat with an expert ECG reading and get your smartwatch ECGs reviewed by experts for PACs within minutes on ReadMyECG (iOS or Android).

Not Sure If It's a PAC? Get Your ECG Analyzed by Experts on the ReadMyECG App.

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