Apple Heart Study Identifies AFib in Small Group of Apple Watch Wearers

Offering a glimpse at how wearable technology may help flag potential health problems, the Apple Watch was able to detect atrial fibrillation (AFib) in a small group of people who had received an alert of an irregular heartbeat, said researchers presenting results from the Apple Heart Study at ACC.19 in New Orleans.

The Apple Watch and corresponding Heart Study app uses photoplethysmography to intermittently measure blood flow activity and detect subtle changes that might indicate an irregular heartbeat. A tachogram is then created and is analyzed by an algorithm. The aim of the study, presented by Mintu Turakhia, MD, MS, was to identify patients with an irregular pulse watch notification who have AFib on a subsequent electrocardiogram (ECG) patch. 

A total of 419,297 people self-enrolled in the study. Participants could not have AFib or be taking anticoagulants and were required to have an Apple Watch and compatible iPhone. They were given information about the study when they downloaded the Heart Study app. Detection of five of six repeat tachograms of an irregular pulse within a 48-hour period triggered a notification to be sent via the app. Participants receiving a notification were prompted to contact the study doctor through the app for a video consultation to determine if the participant should wear an ECG patch. The patch was worn for up to seven days.

The primary endpoints were AFib >30 seconds on ECG patch and simultaneous AFib on ECG patch and tachogram.

A pulse notification was received by 2,161 participants (0.52 percent). Notification rates were most frequent in participants over age 65 (slightly >3.0 percent) and lowest among those under 40 (0.16 percent). Patches were sent to 658 participants and 450 were returned and included in the analysis. AFib was identified in 34 percent of those who received a notification and wore the ECG patch.

"AFib can come and go, particularly early on in the course of the disease. It's not surprising for it to go undetected in subsequent ECG patch monitoring. So while only 34 percent of people who were still having AFib on the ambulatory ECG, that doesn't mean that 66 percent didn't have AFib. It just means that AFib may not have been there at the time," Turakhia said. "These parameters help us understand how we, as clinicians, should think about these notifications."

The positive predictive value (PPV) for the tachogram was 71 percent and the PPV for notification was 84 percent. About half of participants receiving an irregular pulse notification contacted a study doctor. Subsequent surveys showed that 57 percent of participants who received an alert sought medical care outside of the study regardless of whether they had been seen virtually by a study doctor. "This is encouraging because it tracks with our understanding of AFib as being more common as you get older," Turakhia said, adding that the overall study population represented a striking cross section of cardiovascular risk.

The study had several limitations, including reliance on self-reported data from participants and the potential for a high number of false positive heart rhythms that could then lead to further unnecessary tests and undue anxiety for patients.  Additionally, the target enrollment of 500,000 participants, with 75,000 aged 65 or older, was not reached. Editor-in-Chief Kim A. Eagle, MD, MACC, also noted that while the watch and corresponding app "offers promise," its accuracy is still far short of more traditional and currently used monitoring techniques. "This is just a glimpse of the future, but we have a ways to go," he said.

Turakhia said the trial does represent "a paradigm shift" for how clinical studies can be conducted. "We don't have to bring people into a brick and mortar clinic and give the study intervention," he said.

Keywords: ACC19, ACC Scientific Session Newspaper, Atrial Fibrillation, Arrhythmias, Cardiac, Sports

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