Just because wearable digital health devices can track biometric data and send alerts, that doesn’t mean the alerts make a difference in health outcomes. In 2015, we wrote about an Apple Watch user who contacted his cardiologist after noticing extreme heart rate variations on the watch. The physician subsequently implanted a pacemaker in an outpatient procedure. At the time we noted the continued concerns for health data accuracy and security. Jump forward to 2018 and the FDA cleared the Apple Watch used with AliveCor’s KardiaBand for detecting atrial fibrillation (AFib) to prevent strokes and other cardiac events. Also in 2018, Apple and Stanford Medicine introduced the Apple Heart Study to explore how the Apple Watch and other wearables can help users respond to irregular heart rhythm alerts.

The three current Apple Watch model — the Apple Watch Series 7, Apple Watch SE, and Apple Watch Series 3 — send high and low heart rate and Irregular heart rhythm notifications. Fitbit, Withings, Samsung, and other smart watches also have FDA clearance to identify and send alerts about potential AFib. So, we’re more protected than ever, right?

Not so much, according to a new study by the Cedars-Mount Sinai Medical Center published in the Journal of Informatics in Health and Biomedicine. The Cedars-Mount Sinai study set out to determine if Apple’s AFib alerts will actually help prevent strokes. The study analyzed data of 1,802 patients who connected their Apple Watches to their Cedars-Mount Sinai electronic health records (EHRs). The researchers’ aim was to estimate the proportion of high-risk patients who would be prescribed anticoagulation medication. People with AFib have five times the chance of having a stroke than normal and anticoagulants reduce that risk of strokes.

According to the study abstract, based on Apple Watch AFib alerts alone, only 0.25% of the patients in the study would be candidates for new anticoagulation. This miniscule result pales in comparison to 36% of the patients who would receive anticoagulation recommendations after a new AFib diagnosis. The study itself is paywalled and we did not have access to read the specific findings including demographics and other factors.

The Verge reported that study author Josh Pevnick said most of the Apple Watch users in the study were younger than the age group that is usually prescribed anticoagulants. Anticoagulants are typically prescribed for older people with AFIB, but not for younger people unless there is an additional stroke risk factor. The Verge quoted Pevnick saying, “Most of the people who are connecting their devices wouldn’t have anticoagulants recommended anyway, even if they were found to have atrial fibrillation, so it wasn’t going to change any prescribing.”

The study conclusion does suggest that clinical and demographic EHR data could help identify patients who could most benefit from wearing devices such as the Apple Watch to detect AFib. The study also self-notes its limitations including a lack of a comparison group who didn’t connect their devices to their EHRs. One take away from this study is that just because some watches can detect irregular heart rhythms, that fact alone doesn’t mean they will save lives or prevent strokes. Another view, however, is that if you are in a demographic where an AFib alert could make a difference, that it could be a good idea to wear a heart-tracking watch.