- Your ECG's QRS Interval shows how long it takes for your heart's electrical signal to spread through your heart's lower chambers, or ventricles, during your heartbeat.
- A wide QRS Interval is 120 milliseconds or longer, which can be a sign of abnormalities in your heart's bundle branches, scarring in your heart's ventricles, or Wolff-Parkinson-White Syndrome.
- A narrow QRS Interval is 80 milliseconds or shorter, and is typically considered normal.
Got other questions on your PQRST Intervals? See the complete set of Qaly guides on PQRST Intervals:
- What P Waves Look Like on Your ECG
- PR Interval on Your ECG - Short, Normal, and Prolonged
- QTc Interval on Your ECG - Short, Normal, and Prolonged
- What PR, QRS, and QTc Intervals Mean on Your ECG
- How to Read an ECG: Stanford Cardiologist Explains
- The Ultimate Cardiologist's Guide to the Smartwatch ECG
Hello, heart hero. In your quest to identify that irregular heart rhythm you just felt, you may have come across the term QRS Interval. With your trusty watch ECG now in hand, you may be wondering, "What does QRS Interval mean on my watch ECG?" Or you might be thinking, "Is a narrow or wide QRS Interval dangerous?" In this guide, we'll help answer these questions. Let's dive in.
What's an Electrocardiogram?
Before diving into QRS Intervals, it's important to understand exactly what an electrocardiogram, or ECG is. (If you're confident in your understanding of an ECG and how it relates to QRS Intervals, though, skip on ahead to the next section for some visual examples of QRS Intervals).
To start, remember how your heart beats? It produces an electrical signal, which squeezes and unsqueezes your heart, which in turn pumps your blood to your lungs for oxygen and then out to the rest of your body.
As that electrical signal flows through your heart, the ECG on your watch shows it to you in the form of PQRST waves. Every time your heart completes one heartbeat, it completes one full cycle of that electrical signal flowing through your heart. And as that electrical signal flows through your heart, it produces different waves on your ECG that capture the squeezing and relaxing of your heart with each heartbeat, which are represented on your ECG as a PQRST wave.
So What's a QRS Interval?
After the P Wave comes the QRS Complex. You'll recognize this one, since it's usually the tall spike in your ECG. When your heart's electrical signal moves down into your heart's lower chambers, or ventricles, it first moves through specialized wires in your heart called right and left bundle branches (also known as your His-Purkinjee system). These wires help spread your heart's electrical signal as evenly as possible. Your QRS Complex captures your electrical signal spreading down into and through your ventricles, and the beginning of the final squeeze that pushes the blood in your heart back out into the rest of your body.
Your QRS Interval starts at the beginning of your QRS Complex, and ends at the end of your QRS Complex. It measures how long it takes for your heart's electrical signal to spread through your heart's lower chambers, or ventricles. Sometimes, you QRS may not look as tall and spiky as it does in the picture below. Here's what low voltage QRS looks like on a watch ECG and KardiaMobile EKG.
What's the Normal Range for a QRS Interval?
Your QRS Interval is considered normal from 80 milliseconds to 120 milliseconds. A normal QRS indicates that your heart's ventricles are activating within the expected timeframe.
What's a Wide QRS Interval?
Your QRS Interval is considered wide at 120 milliseconds or higher. A wide QRS can be a sign of an underlying heart abnormality.
Is a Wide QRS Interval Dangerous?
Your QRS Interval widens when your heart's electrical signal takes longer than normal to spread through your ventricles. You'll often see this when abnormalities in your heart affect one of those specialized electrical fibers we discussed, called your right and left bundle branches. You may see this in the case of Sinus Rhythm with wide QRS. Scarring in your heart's ventricles, can also cause your heart's electrical signal to spread more slowly through your ventricles, which would lead to a wider QRS Interval. You'll also see a wide QRS Complex in Wolff-Parkinson-White (WPW) Syndrome. Here's what a WPW ECG looks like. As always, if you're showing signs of a wide QRS Interval, consult your healthcare provider as soon as possible to rule out any underlying heart conditions.
What's a Narrow QRS Interval?
Your QRS Interval is considered narrow at 80 milliseconds or lower. A narrow QRS usually means your heart's electrical signal is moving quickly and correctly through its main pathways. If your QRS is less than 0.10 seconds, it's considered "narrow." This can be seen in normal heart rhythms or in fast rhythms that start from the upper part of your heart. A narrow QRS can often look like a tall spike on your ECG.
Is a Narrow QRS Interval Dangerous?
Your QRS Interval narrows when the time it takes for your heart's lower chambers, or ventricles to squeeze becomes shorter. This can happen due to various reasons, including a higher heart rate, changes in how your heart's electrical signal moves through your ventricles, certain medications, and in cases where a bundle branch block (either right or left) is present and then resolves back to normal. It's important to note that unlike wide QRS, a narrow QRS Interval is generally considered normal; however, as always, if you're showing signs of a narrow QRS Interval, consult your healthcare provider to rule out any underlying heart conditions.
Well, that just about wraps up our guide on what QRS Intervals look like on your watch ECG. We hope this could be of some help to you.
If you still need help measuring your ECGs' QRS Intervals, don't worry, we understand how scary and confusing it can be to experience irregular heartbeats. That's why we created the Qaly app for you and for the hundreds of millions of people around the world who live with heart palpitations and abnormal heart rhythms. On the Qaly app, human experts will measure your ECGs' QRS Intervals within minutes for clarity and peace of mind.
To get started with the Qaly app for free, grab the Qaly app from the App Store or Play Store today. If you have any more questions, or if you need our help in any other way, don't hesitate to reach out to us at email@example.com.
As always from the team at Qaly, stay heart healthy ❤️