Apple Watch Series 4 ECG Feature Rolls Out Today With watchOS 5.1.2

But perhaps the most important feature announced with the Apple Watch Series 4 was its built-in electrocardiogram (ECG) for monitoring your heart rhythms and atrial fibrillation. Apple hyped this inclusion, saying that its latest Apple Watch is the first consumer device to feature such a heart (health) conscious features. The only problem is that the ECG function and accompanying app was not enabled at launch, and is still missing in action. Apple now says that watchOS 5.1.2 will land later today and along with it will come the availability of the ECG app.

The Apple Watch Series 4 coupled with the ECG app can generate a result "similar to a single-lead electrocardiogram”. With the information gathered from the app, you can share any heart rhythm irregularities with your doctor as a precautionary measure.

Apple describes the ECG, writing:

Electrodes built into the Digital Crown and the back crystal work together with the ECG app to read your heart’s electrical signals. The ECG app can indicate whether your heart rhythm shows signs of atrial fibrillation — a serious form of irregular heart rhythm — or sinus rhythm, which means your heart is beating in a normal pattern.

Each beat of the heart sends out an electrical impulse. With the ECG app, Apple Watch Series 4 can read and record these impulses by connecting the circuit between your heart and both arms. The resulting ECG waveform, its classification, and any notes you’ve entered on related symptoms are automatically stored in the Health app on your iPhone.

A reading is taken by simply playing a finger on the digital crown (and holding it there) for 30 seconds. While it's not expected that the Apple Watch Series 4's ECG will be as accurate as medical-grade equipment that you'd find in a doctor's office or hospital, Apple along with the Food and Drug Administration were confident enough in the results that it received FDA clearance as an over-the-counter ECG tool. Apple writes:

The ECG app’s ability to accurately classify an ECG recording into AFib and sinus rhythm was validated in a clinical trial of around 600 participants. Rhythm classification from a gold standard 12-lead ECG by a cardiologist was compared to the rhythm classification of a simultaneously collected ECG from the ECG app. The study found the ECG app on Apple Watch demonstrated 98.3 percent sensitivity in classifying AFib and 99.6 percent specificity in classifying sinus rhythm in classifiable recordings. In the study, 87.8 percent of recordings could be classified by the ECG app.

Apple's watchOS 5.1.2 will be available to download for all Apple Watch users later today (likely around 1:00pm EST). Irregular heartbeat rhythm notifications will be available to Apple Watch Series 1 and later devices, while the ECG feature is only available for the Apple Watch Series 4.