Late last year, Apple (AAPL -0.82%) released the latest version of its cutting-edge timepiece, the Apple Watch Series 4. The device possesses a number of health-related features; an updated electrical heart-rate sensor is embedded in the back crystal, and electrodes are built into the digital crown (the small button on the side).

These advancements, in conjunction with its operating system, WatchOS 5, allows the device to monitor the wearer's heart rate; it can notify users if it detects an unusual heart rhythm, alerting them to a potentially life-threatening heart condition. In late 2017, Apple launched a study in conjunction with Stanford Medicine to test the accuracy of the Apple Watch in detecting atrial fibrillation (also known as AFib), the most common form of irregular heartbeat, which can lead to strokes, blood clots, and heart attacks. The ailment often remains undiagnosed, since many people don't experience any symptoms.

The results of the study were just released, and they're eye-opening.

An iPhone with a description of the Apple Heart Study, and an Apple Watch with a notification reading "Irregular Heart Rhythm Observed"

Image source: Apple.

Biggest. Study. Ever.

In November 2017, Apple began enrolling participants in a clinical trial in collaboration with Stanford Medicine, to test the effectiveness of the Apple Watch at detecting AFib; the response from wearers was massive. Late last year, a paper published in the American Heart Journal called it "the largest screening study of atrial fibrillation ever done," with an unprecedented 419,093 users in all 50 states opting to participate.

Researchers from Stanford and Apple released preliminary results of the study last week. The research concluded that "wearable technology can safely identify heart rate irregularities that subsequent testing confirmed to be atrial fibrillation, a leading cause of stroke and hospitalization in the United States."

Just 0.5% of all study participants received an "irregular heart rhythm" warning, helping quell concerns about the potential for too many notifications. Upon receiving an AFib alert, participants were asked to schedule a telemedicine consultation with a doctor involved in the study. Among participants who received irregular-pulse notifications and followed up by using an electrocardiography patch over the next week, 34% were found to have atrial fibrillation. This isn't surprising, since AFib is an intermittent condition that might not show up in subsequent monitoring.

Results from the Apple Watch were compared with a simultaneous electrocardiogram (ECG), showing that the device was highly effective at detecting AFib. The study reported that 84% of patients who received the irregular-pulse notification were found to be in a state of atrial fibrillation at the time of the notification.

"The performance and accuracy we observed in this study provides important information as we seek to understand the potential impact of wearable technology on the health system," said Marco Perez, M.D., associate professor of cardiovascular medicine and one of the study's principal investigators.

"The results of the Apple Heart Study highlight the potential role that innovative digital technology can play in creating more predictive and preventive healthcare," said Lloyd Minor, M.D., Dean of the Stanford School of Medicine. "Atrial fibrillation is just the beginning, as this study opens the door to further research into wearable technologies and how they might be used to prevent disease before it strikes -- a key goal of precision health."

The positive results are a huge win for Apple, helping to validate the medical applications of the company's digital technology.

Check out the latest earnings call transcript for Apple.

An Apple Watch with a "rhythm suggestive of Atrial Fibrillation" notification

Image source: Apple.

A broader move into healthcare

This is all part of a larger move by Apple into the realm of healthcare. The company recently announced a landmark deal with the U.S. Department of Veterans Affairs (VA) that makes Apple's Health Records feature available to veterans using the iPhone. This follows a move late last year to hire engineers in order to develop custom chips to process data from the Apple Watch's health, wellness, and fitness sensors.

Apple has been vocal about its ambitions in the healthcare field. This successful investigational study is an important step along that path.