Sinus Rhythm Vs. Premature Atrial Contraction (Multiple) on Your Watch ECG

Sinus Rhythm PAC ECG
Qaly Heart
Qaly is built by Stanford engineers and cardiologists, including Dr. Marco Perez, a Stanford Associate Professor of Medicine, Stanford Cardiac Electrophysiologist, and Co-PI of the Apple Heart Study.

Key Takeaways

Got other questions on Sinus Rhythm or PAC? See the Qaly guides on Sinus Rhythm and PAC:

Introduction

The heart is a remarkable organ that functions by responding to electrical signals, triggering contractions that pump blood throughout our bodies. Electrocardiograms (ECGs) are tools that provide visual representations of these heartbeats. The development of smartwatch technology has made it possible to observe and monitor heart rhythms, like sinus rhythm and premature atrial contractions (PACs), right on our wrists. To understand premature atrial contraction vs sinus rhythm, one must grasp the nuances of these two rhythms. Let’s dive in.

What’s Sinus Rhythm?

Sinus rhythm, or normal sinus rhythm, is considered the standard rhythm of a healthy heart. In this pattern, electrical signals originate from the sinoatrial (SA) node located in the right atrium, initiating each heartbeat and ensuring they occur at a steady, regular rate.

Sinus Rhythm read on a Samsung Watch ECG through the Qaly app.
Sinus Rhythm read on a Samsung Watch ECG through the Qaly app.

On an ECG, sinus rhythm is characterized by a distinct P wave (indicating atrial contraction) followed by the QRS complex (signifying ventricular contraction), then the T wave (representing ventricular relaxation). This cycle repeats at a rate of 60-100 times per minute in adults at rest. Here’s more on what sinus rhythm looks like on your watch ECG.

Sinus Rhythm read on a Samsung Watch ECG through the Qaly app.
Sinus Rhythm read on a Samsung Watch ECG through the Qaly app.

What’s a Premature Atrial Contraction (PAC)?

On the other hand, premature atrial contractions are early beats that originate from the atria — the upper chambers of the heart. When multiple PACs occur, they appear as irregular early beats on an ECG. While occasional PACs are usually benign, frequent PACs can sometimes indicate underlying heart disease or trigger other arrhythmias. 

PACs read on a Fitbit ECG through the Qaly app.
PACs read on a Fitbit ECG through the Qaly app.


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On an ECG, PACs are identified by an early and often different-looking P wave, followed by a QRS complex and a compensatory pause. Here’s more on what a PAC looks like on your watch ECG.

PACs read on a Samsung Watch ECG through the Qaly app.
PACs read on a Samsung Watch ECG through the Qaly app.

What’s the Difference Between Sinus Rhythm and PAC?

When comparing sinus rhythm vs PAC, or premature atrial contraction vs sinus rhythm, the significant difference is the origin of the heartbeats. While sinus rhythm originates from the sinus node and has a regular pattern, PACs are early beats that arise from the atria and can make the heart rhythm seem irregular due to the premature beats.

PACs read on a Samsung Watch ECG through the Qaly app.
PACs read on a Samsung Watch ECG through the Qaly app.

In terms of health impacts, sinus rhythm is the regular, natural rhythm of a healthy heart. In contrast, occasional PACs are typically benign and may not cause any symptoms or require treatment. However, frequent PACs or a sudden increase in PACs, especially if accompanied by symptoms such as palpitations, dizziness, or shortness of breath, should warrant medical attention.

In conclusion, using an ECG-equipped smartwatch allows you to monitor these rhythms in the comfort of your home. Understanding these rhythms aids in early detection of any irregularities, which could be a stepping stone to proactive cardiac care. It's important to remember, however, that while these devices are useful health tools, they don't replace a thorough evaluation by a healthcare professional. Stay informed, stay proactive, and stay heart healthy!

Still Not Sure if It’s Sinus Rhythm or Premature Atrial Contraction (Multiple) on Your ECG?

Differentiating between sinus rhythm vs PAC on your ECG can be tricky. If you’re still looking for help interpreting your ECG further, check out the Qaly app on App Store or Play Store. On Qaly, human experts will interpret your ECGs within minutes, day or night. Try out the Qaly app today!

Wondering if it's Sinus Rhythm or PACs? On the Qaly app, human experts will interpret your ECGs for Sinus Rhythm and PACs within minutes. Get started today.

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App Store - Download Qaly | ECG Reader
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Wondering if it's Sinus Rhythm or PACs? On the Qaly app, human experts will interpret your ECGs for Sinus Rhythm and PACs within minutes. Get started today.

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