Featured Heart health

Smartwatches as heart monitors: yay or nay?

Written by Katherine Nazimek

Smartwatches can’t take the place of your doctor, but that doesn’t mean they can’t tell you useful information about your health. These handy (and addictive) tools are well known to support healthy lifestyle behaviours – monitoring your activity levels and even your heart rate.

More recently, smartwatches have added capabilities that can flag potentially dangerous, fast or irregular heartbeats, known as atrial fibrillation (a type of arrhythmia). But should we trust these devices to tell us such important details about our hearts? Dr. Christopher Cheung, a cardiac electrophysiologist (cardiologist specializing in heart rhythm) in the Schulich Heart Program at Sunnybrook, shares his expert advice.

What is atrial fibrillation and why does it matter?

Dr. Cheung: Atrial fibrillation is the most common abnormal heart rhythm, affecting approximately 200,000 Canadians. If treated, most people with atrial fibrillation lead active, normal lives; but left untreated, it can lead to stroke and heart failure, not to mention interfere with your daily quality of life. According to the Heart and Stroke Foundation, one quarter of all strokes after age 40 are caused by atrial fibrillation. So, if we can detect atrial fibrillation early, we can prevent stroke and other life-threatening circumstances.

How do smartwatches capture your heart rhythm vs. traditional tests?

Dr. Cheung: Smartwatches use a technology called photoplethysmography. Light from the device flashes against your skin to detect blood flow and measures your heart rate using elaborate algorithms. The technology is used in other medical devices such as oxygen monitors (oximeters) and is generally accurate when you have a regular pulse.

Some smartwatches have an added feature of recording an electrocardiogram (ECG), which is the electrical signal of the heartbeat. This provides much more information, including not only heart rate but also heart rhythm. Unlike traditional cardiac tests, however, the ECG feature in a smartwatch is not always active: the user must manually record an ECG. When diagnosing an arrhythmia, we use longer-term ECG monitors, like Holter monitors, that record your ECG signals continuously for 24-48 hours. It gives us an accurate recording of your heart rate and heart rhythm during a longer period so we can assess any irregularities.

How accurate is the information from my smartwatch?

Dr. Cheung: For most healthy users, studies have shown that the heart rate measured on your smartwatch matches well with the heart rate measured with our cardiac tests – usually within five beats per minute. When it comes to irregular heart rate monitoring for atrial fibrillation, the accuracy is lower.

There have been a few large studies using the Apple Watch, FitBit, and Huawei watches to evaluate their ability to detect arrhythmia and the results have been promising, but these studies are done with mostly healthy individuals.

The challenge is that the algorithms are not perfect, so there is a risk that the watch may alarm you with an incorrect result (called a “false-positive”). Until we know more, pay attention to the information, but don’t rely on it to diagnose you.

What should I do if my smartwatch flags an irregular heartbeat?

Dr. Cheung: You don’t need to run to your doctor the second a notification of an irregular heartbeat pops up on your smartwatch but take into consideration your heart health, such as any pre-diagnosed atrial fibrillation and any symptoms you may be feeling. If you are noticing episodes of heart racing that come unexpectedly while you are at rest, a sensation of an irregular heart rate or fluttering in your chest, or even the sense of a panic attack, these can sometimes be signs of a heart arrhythmia. Take note and speak to your doctor. They may choose to order a medical-grade heart monitor to document one of these episodes and determine whether you really are having an arrhythmia.

About the author

Katherine Nazimek

Katherine Nazimek is a Communications Advisor at Sunnybrook.

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