Wearable tech: Detecting arrhythmia, falls with the Apple Watch

An Apple Watch update can detect abnormal heart rhythms and even call 911 for the user; learn how it works


Recently, Apple created quite a stir in the tech world by releasing an update for the Series 4 Apple Watch which incorporates a couple of intriguing new features: arrhythmia detection and fall detection.

Now, wearable tech that can detect heart rate or count how many flights of stairs you’ve climbed is not new. Both the Apple Watch and the Fitbit have incorporated heart rate monitors and an integrated barometric pressure sensor to measure how high you’ve climbed and how hard you’ve worked for a number of years now. But Apple’s new ability to detect ECG rhythms (although still somewhat limited) and falls poses some interesting possibilities for EMS.

How does the Apple Watch detect arrhythmia?

The Series 4 Apple Watch offers the possibility of fall detection and alerting 911 anywhere where you can get cellular reception. (Photo/Flickr)
The Series 4 Apple Watch offers the possibility of fall detection and alerting 911 anywhere where you can get cellular reception. (Photo/Flickr)

Traditionally, we’ve captured ECG rhythms by using a bipolar limb lead in an electrocardiogram machine. Our commonly-used Lead II uses the electrode on the right shoulder as the negative lead, and the electrode on the left leg as the positive lead to sense electrical conduction along the normal axis of electrical conduction from the right atria down to the left ventricle. Throw in a ground electrode on the left shoulder, and you’ve got the corners of Einthoven’s Triangle, a configuration we’ve been using ever since Willem Einthoven in 1901 used a string galvanometer on subjects with their feet immersed in brine solution to capture the first ECG.

That first electrocardiogram weighed nearly 600 pounds and took five people to operate. Now, it weighs ounces and you can wear it on your wrist. There are already aftermarket wearable tech apps that use the Apple Watch in this fashion. The AliveCor KardiaBand, for example, is capable of not only detecting abnormal heart rhythms, but also has FDA approval as a medical monitoring device. Presumably, it captures an ECG by replicating the bipolar limb lead configuration; one sensor is on the inner surface of the band in contact with your wrist, and the other works by pressing your opposite thumb to an external sensor on the band.

However, Apple isn’t using a bipolar limb lead to capture abnormal heart rhythms. It uses green LED lights and corresponding photo sensors on four distinct points on the wrist to measure blood flow in the wrist. In this sense, it’s more akin to a photo plethysmograph – the technology our pulse oximeters use – than a traditional ECG, and we’ve already shown you how to use that photo plethysmograph in your clinical care.

Apple then uses a sophisticated interpretation algorithm to separate the actual heartbeat from background artifact. So, it captures abnormal rhythms, but technically isn’t an ECG. To display a graphic readout of rhythm to wearers – and presumably, allow them to make health decisions based upon it – requires FDA approval as a medical monitoring device.

The new Series 4 Apple Watch, however, does incorporate an ECG-based arrhythmia detecting feature similar to that of the aftermarket AliveCor KardiBand. The Series 4 Apple Watch incorporates the other sensor into the crown of the watch, replicating a Lead I configuration.

Apple is currently engaged in a heart study with Stanford Medicine to use its watch as an early warning system for atrial fibrillation, but Apple is careful to say at this point that its watch “detects abnormal heart rhythms,” not specifically atrial fibrillation.

Now, atrial fibrillation is one of the more common arrhythmias, but there are plenty of others. Apple’s interpretation algorithm is going to have to prove itself sophisticated enough to discern atrial fib from, say, sinus tachycardia with frequent PACs, to convince skeptical clinicians that it won’t result in an unacceptably high number of false positives. The tech is still new, but shows great promise.

Fall detection in wearable technology

Another intriguing feature of the new Apple Watch is its fall detection feature. Apple uses the accelerometer and gyroscope already integrated into the Apple Watch to detect falls now. Using data gathered from monitoring 2,500 people wearing Apple Watches in various settings, including a movement disorder clinic – over 250,000 days worth of data in all – Apple was able to isolate patterns of movement in actual falls.

The accelerometer in the Series 4 Apple Watch is capable of sampling eight times more frequently than the Series 3, and record force up to 32 G’s. This advance in recording capability, coupled with the gyroscope and an interpretation algorithm, allows the new Apple Watch to reliably detect falls. It will even call 911 for you if you don’t respond – provided you have the cellular version of the Apple Watch or are also carrying your iPhone.

This feature can really prove useful to EMS providers. How often do we run those “I’ve fallen, and I can’t get up!” calls? How often do we find the victim down for hours or even days, because they were unable to summon help? Even those with medical alarm pendants are usually tethered to their homes, unable to travel beyond the radio range of the device.

The Series 4 Apple Watch offers the possibility of fall detection and alerting 911 anywhere where you can get cellular reception. Who knows, maybe in the near future, you can also program your Apple Watch to unlock the front door for EMS responders when you fall. The technology already exists in our smart phones and smart homes, it just takes a little additional programming to enable yet another feature.

Hey, Apple? You need to get right on that. Unlock that front door as soon as you call 911 when Granny falls. While you’re at it, brew some coffee for the nice paramedics.

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