When I first started testing out the new EKG feature on the Apple Watch Series 4 — availale Thursday via the free Watch OS 5.1.2 software upgrade — the last thing I expected was to find something abnormal with my heart rhythm. But that’s exactly what happened when I was cross-referencing the Watch’s readings with medical-grade EKG equipment at the doctor’s office.
“We see on your Apple Watch the same early heartbeat that we see on the EKG,” said Dr. Gregory Marcus, professor of medicine and a cardiac electrophysiologist at UCSF Medical Center as I sat on the hospital bed with cables attached to my body and an Apple Watch Series 4 on my wrist.
The results from the Apple Watch EKG showed the same irregular beat as the doctor’s EKG.
“These early beats are very common … but they can lead to problems in the long term. So we should talk a little bit more about that,” he added.
Heart-rate tracking has always been a big part of the Apple Watch and fitness trackers in general. But until now, it’s mainly been used for activity tracking and calorie counting.
With the update to Watch OS 5.1.2, heart rate will play a more important role on the Apple Watch as we get access to the two new FDA-cleared features that Apple announced at its September keynote. There’s an abnormal heart rhythm alert for all Apple Watches, except for the first-generation model, and an electrocardiogram (EKG or ECG) exclusive to the Series 4. Both of which could help warn of potentially life threatening heart conditions.
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Video: We tested the Apple Watch EKG against a hospital EKG
Measuring heart rate
Heart-rate tracking isn’t new to wearables. Smartwatches and fitness trackers have for years used LEDs and optical sensors on the back to measure the changes in blood flow under the surface of the skin, aka your pulse. When the heart beats, more blood gets pumped into the blood vessels absorbing more light. Between beats when there’s less blood, more light gets reflected back into the receivers of the watch.
Setup the Irregular heart rate notification from the Health app on the Apple Watch Series 1 and beyond.
In 2017, the Apple Watch became proactive about how it used heart rate information by adding the high heart rate notifications to the watch, which let users know when their heart spiked above a certain level and later added the low heart rate notifications. These notifications had already been helping users detect serious conditions.
But the heart rate only measures beats per minute, or the frequency of the heart beat over time and not the patterns between each beat known as heart rhythm.
“You can have a regular rhythm that is very fast or too slow … And similarly, one can have an irregular rhythm that is of a normal rate, that is too fast or too slow,” said Dr. Marcus.
With the new Irregular rhythm notification, the Apple Watch uses the optical sensor to measure heart rhythm and alert users when it detects an irregular pattern that may be atrial fibrillation (AFib), a type of arrhythmia that can increase your risk of stroke and other serious heart complications. This feature will only work for adults over the age of 22 and won’t help if you’ve already been diagnosed with AFib.
EKG on the Apple Watch
To make a definitive diagnosis, a doctor needs more information than what the pulse can provide.
“Sometimes those beats are so early that the heart hasn’t had adequate time to fill, even though electrically there may be an early beat that’s happening,” said Dr. Marcus. “We would want to have an electrical confirmation of a diagnosis of atrial fibrillation before we decide on acting on that and not base it in general, on the pulse recording alone,” he added.
That’s where the EKG comes in. An EKG uses electrodes to measure the electrical activity that results from each expansion and contraction of the heart. A hospital-grade EKG generally consists of 10 electrodes placed on different..