Apple Watch Better At Finding Arrhythmias Than We Thought

A new analysis of data from Apple’s joint heart study with Stanford has found that the Apple Watch is capable of detecting more rhythm abnormalities than we thought it could.

The Apple Heart Study was designed to test the Apple Watch’s ability to detect abnormal heart rhythms. Participants whose Watches notified them of potential arrhythmias received an ECG patch that would monitor their heart rhythms over a longer period of time. The data showed that the Watch was pretty good at detecting certain arrhythmias, including atrial fibrillation. Case closed; marketing and legal can sleep easy. This story is not a bombshell. It’s about the value of the data that would otherwise be ignored.

What this new look at data from the Apple Heart Study revealed is that while the Watch did what it said it could, it was also capable of detecting several other important patterns in participants’ heartbeats — patterns the researchers hadn’t necessarily been looking for in the original study. Many participants had extra, out-of-rhythm atrial or ventricular contractions. “Even if you didn’t find atrial fibrillation, we were finding a lot of people who had something else that probably needed some clinical attention,” said Marco Perez, director of the Inherited Arrhythmia Clinic at Stanford University Medical Center.

According to the new study (PDF), about a third of the 400,000 participants who had initially received the abnormal-heartbeat warning eventually also presented atrial fibrillation (a-fib). Another forty percent had some other kind of rhythm abnormality detected. The report also found that almost a third of study participants who hadn’t had an a-fib detected after getting the arrhythmia warning later reported that they’d had the condition diagnosed outside the study. Once a person has had an arrhythmia detected, they’re likely to need future attention. This is what scientists mean when they say that things “fall out of the data.”

Atrial fibrillation is strongly associated with a high risk of stroke. Fibrillation can also be described as “flutter,” and during atrial fibrillation the top of the heart can kick and flutter at a rapid pace. Sometimes you can feel it, and sometimes you can’t. It causes turbulence within the atrium and can tear apart platelets, which can form a clot inside the blood vessels that becomes an embolism or stroke. The risk is low during any individual fibrillation event, but over time it adds up. I have my dad’s a-fib; I care about this.

Like the optical devices they use in a hospital to find a vein before drawing blood, the Apple Watch’s ECG relies on optics to do its work. It illuminates the skin, and then measures the minute changes in skin color as blood enters and leaves with the pulse. After that, it’s just software pattern recognition. The technology isn’t the revolution here. For a person who’s monitoring their heart health, subtle signals are often important. A false alarm is much less terrible than a no-expenses-paid stay in the ICU.

The upshot of all this is that while cardiologists aren’t certain how to respond to all these detected patterns, the ECG technology used in the Apple Watch is being thoroughly tested and has proven effective. It’s not a magic bullet, but for those looking for the feature, it can help you keep a sharper eye out for the kind of heart problem that can really wreck your day later in life.

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