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Apple’s ECG innovation is more and less than it appears

One of the biggest surprises during Apple’s September event was that the Watch Series 4 will have the ability to take an ECG. An electrocardiogram (also abbreviated as EKG) measures the electrical activity of the heart and can provide early warning of serious problems. Users around the world immediately tweeted examples of how their own or relatives’ heart conditions were either picked up by an ECG or could have been avoided if they’d had quicker access to one. The feature will detect atrial fibrillation, a fast and irregular heartbeat that’s often symptomless.

ECG for Apple Watch users isn’t entirely new. AliveCor’s $99 Kardia Mobile band incorporates two electrodes on which the user places their finger to take an ECG, viewed in an app. Approved by the FDA a year ago, it’s what doctors call a ‘one–lead’ ECG. The Watch Series 4’s sensor works on a similar principle, using one electrode on the back of the Watch, in contact with the skin, and another in the crown which the user simply touches to complete the circuit.

Compared to the 12–lead ECGs used by medics, one–lead systems are less accurate. A 2015 study published in the Journal of Electrocardiology found portable devices agreed with hospital monitors less than half the time. Neither the Watch’s FDA approval as a medical device, nor its on– stage endorsement by the American Heart Association, imply it will work better than other available one–lead ECGs, and it’s not recommended for patients under 22 or those with some existing conditions. The FDA says it’s ‘not intended to provide a diagnosis’.

Since millions of people have atrial fibrillation, large numbers of Apple Watch users could end up being referred for checks, with only a minority requiring treatment. But it undoubtedly has the potential to save lives — quite an ambition for a watch. The feature will be activated later in the year, and has yet to be approved outside the US.