Apple Heart Study Evaluates Smartphone App to Detect Atrial Fibrillation


March 16, 2019—The American College of Cardiology (ACC) announced that preliminary data from the Apple Heart study were presented by Mintu Turakhia, MD, at the ACC's 68th Annual Scientific Session, being held March 16–18 in New Orleans, Louisiana.

The Apple Heart study was designed to evaluate how well the Apple Watch (Apple Inc.) can identify and prompt subsequent clinical evaluation for atrial fibrillation (AF). The preliminary data showed that the Apple Watch was able to detect AF in a small group of patients who had been alerted by an app as having an irregular heartbeat.

Investigators from Stanford University School of Medicine in Stanford, California, are conducting the study. Dr. Turakhia, the study's Coprincipal Investigator, is associate professor of cardiovascular medicine at Stanford. Apple Inc. funded the study.

The study specifically evaluated a mobile app that uses the watch’s existing light sensor technology (photoplethysmography) to intermittently measure blood flow activity and detect subtle changes that might indicate an irregular contraction or heartbeat. The Apple Watch generates a tachogram. If an irregular tachogram is seen, then more frequent tachogram collection occurs. The tachograms are analyzed by an algorithm to determine if an irregular rhythm may be present and, if so, a notification is sent to the watch. “The app continuously gathers data in the background without the wearer of the device doing anything, so it’s very opportunistic in this way,” stated Dr. Turakhia in the ACC announcement

According to ACC, the main study goals were to determine:

  • The proportion of participants with an irregular pulse watch notification who have AF on a subsequent electrocardiography (ECG) patch worn at home
  • How well the algorithm on the watch matched the ECG findings
  • The percentage of patients who received a notification who went on to seek medical help through the app

Of the 419,297 people who self-enrolled in this prospective study between November 2017 and July 2018, approximately 2,100 (0.5%) received an irregular pulse notification, which was triggered if the sensor detected five out of six repeat tachograms of an irregular pulse within a 48-hour period.

Participants who received a notification were also prompted to contact the study doctor through the app. Based on a video consultation on their device, it was decided whether the person should wear an ECG patch, sent by mail, to measure the heart’s activity and potentially identify AF. Participants wore the patch for up to 7 days and then sent it back to determine whether AF was evident.

In total, 658 participants were sent a patch and 450 were returned and included in the analyses. One-third (34%) of the participants who had received an irregular pulse notification on their watch and wore the ECG patch over a week later were then found to have AF based on the ECG reading. Investigators said this finding is not entirely unexpected.

When comparing pulse detections on the watch with simultaneous ECG patch recordings among 450 participants who wore both at the same time, investigators found that the positive predictive value for the tachogram was 71%, and the positive predictive value for the notification was 84%.

Of the participants who received an irregular pulse notification via the app to confer with a study doctor to determine next steps, approximately 50% initiated contact with the study doctor, but the investigators noted that the others may have sought care elsewhere. In subsequent surveys, 57% of people who got an alert said they sought medical attention outside of the study regardless of whether they had been seen virtually by a study doctor.

Participants were required to have an Apple Watch (series 1, 2 or 3) and a compatible iPhone (iPhone 5S or later), be age ≥ 22 years, and be a United States resident. The newer Apple Watches that feature a built-in ECG app were not part of this study. Participants downloaded the application to their device and were subsequently given information about the study, questions to help verify their eligibility and prompts to provide signed consent. The study excluded those who said they were taking an anticoagulant for any reason or had current or previous AF. Surveys were used to collect information about patient-reported outcomes.

Notification rates in people younger than 40 years of age were very low (0.16%) and were more frequent in those older than 65 years (approximately 3%).

Dr. Turakhia noted that the overall study population represented a cross section of cardiovascular risk: 5% had diabetes, 21% had high blood pressure; 1% had a previous stroke, and 38% were obese based on body mass index. Approximately one-third of people who received a notification had a CHADS-VASc score ≥ 2.

In the ACC announcement, Dr. Turakhia commented, “[Overall], this study improves our understanding of how this wearable technology and app works in the real-world setting and how well the technology can detect long periods of AF. Notifications of heart rhythm irregularities were low, an important finding given concerns about over notification, and we were able to see what happened downstream after participants received a notification.”

He stated further, “AF 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% of people who were still having [signs of] AF on the ambulatory ECG, that doesn’t mean that 66% didn’t have AF. It just means that AF may not have been there at the time. These parameters help us understand how we, as clinicians, should think about these notifications. This is encouraging because it tracks with our understanding of AF as being more common as you get older.”

As outlined in the ACC press release, study limitations included: reliance on self-reported data from participants; enrollment did not reach the target of 500,000 participants; investigators hoped 75,000 participants would be 65 years or older.

However, the investigators believe this virtual study creates the groundwork for future studies that look to leverage wearable technologies to support heart health outside of the clinic. A next step is to study how this technology can be used in complement with other technologies such as real-time ECG and other validated tools to manage heart rhythm problems. “It really represents 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.” stated Dr. Turakhia.


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