Apple Watch's built-in ECG could detect multiple heart arrhythmias, follow-up analysis finds

Back in 2018, after years spent striving toward a goal of having its eponymous wearable recognized as a legitimate medical device, Apple earned an FDA clearance for the electrocardiogram function embedded in the Apple Watch. The agency’s nod allowed wearers to perform on-the-spot heart rhythm analyses, then receive alerts if any irregularities were identified, potentially indicating the presence of atrial fibrillation.

The FDA’s decision was based on early findings of the Apple Heart Study, which began in 2017 and enrolled more than 400,000 participants to perform regular ECGs with the Apple Watch. The study ultimately found that of those who received irregular pulse notifications from the device, about 84% were confirmed through a follow-up clinical consultation to have been in afib at the time of the alert.

A new analysis of that study’s data, however, focused on the remaining 16% of that group, assessing whether the Apple Watch could ultimately be used to identify arrhythmias other than afib.

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Led by researchers from Apple and the Stanford University School of Medicine on behalf of their colleagues who led the original study, the analysis found that about 100 people in the study group were eventually diagnosed with a handful of other arrhythmias after receiving the irregular pulse notification, including premature atrial complexes and premature ventricular contractions, atrial tachycardia and nonsustained ventricular tachycardia.

The researchers focused on a subset of 450 study participants who received the potential afib alert from the wearable and were subsequently given ECG patches to wear for a week to track their heart rate. After that, afib was diagnosed in only about a third of the participants.

Among the 297 Apple Watch users not found to have afib, about 40% were later diagnosed with another type of arrhythmia. According to the researchers, those findings indicate that the device’s ECG capabilities could—and perhaps should—someday be expanded and refined to alert wearers to potential arrhythmias other than just afib.

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That said, the researchers noted that they weren’t yet sure how widespread the benefits would be if other arrhythmia analyses were added to the Apple Watch. For one thing, about one-third of the participants who wore the ECG patch for a week with no signs of afib were later diagnosed with the condition, upping the overall accuracy rate of the wearable’s afib alerts and overshadowing the need for other arrhythmia alerts.

Additionally, even though some of the non-afib arrhythmias detected have been linked to stroke and other serious heart conditions, the researchers wrote, “available evidence does not suggest improvement in outcomes if these rhythms are treated or therapies aimed at reducing ischemic stroke risk are initiated.”

With that in mind, they concluded that before new arrhythmia-detecting features are added to the Apple Watch, further research should be gathered on the best approaches to managing and treating non-afib arrhythmias.

“In parallel to refining approaches for early identification of AF patients who would benefit from treatment, defining optimal care for patients with detection of incidental arrhythmias other than AF is needed,” they wrote.