The study was not designed to assess the algorithm as a screening tool or to measure sensitivity, specificity, or false positive results. The algorithm was designed to minimize false positive findings,
3 and the low incidence of notifications reflects this intent. Furthermore, the algorithm was not designed to detect short episodes of atrial fibrillation, and participants with a low burden of atrial fibrillation could have been missed. The study objective was not to address the use of the Apple Watch as a population screening tool. Patients using this technology should be aware that the absence of an irregular pulse notification does not exclude possible arrhythmias. Conversely, notification based on an irregular pulse from a photoplethysmography signal should not be used for a definitive diagnosis of atrial fibrillation. Since rhythm-detection technologies are rapidly evolving, additional studies using features such as wearable ECG monitoring devices will need to be performed as the technology becomes available. Nevertheless, uncertainty remains about the benefits of diagnosing and treating asymptomatic atrial fibrillation, particularly in persons whose episodes of atrial fibrillation are of 6 hours’ duration or less.
There was no direct physical contact with participants from the time of enrollment and consent to interaction with the telemedicine provider and ECG patch monitoring. Although our siteless, pragmatic study design allowed us to enroll more than 400,000 participants in 8 months, we relied on the participants’ assessments regarding their eligibility for inclusion and regarding outcomes. Substantial loss to follow-up results in uncertain validity and generalizability inherent to this design. At enrollment, persons with previous atrial fibrillation were asked not to participate, but several participants who received notifications later reported a history of atrial fibrillation. Although we mitigated this misclassification by verifying enrollment criteria at the study visit, this kind of misclassification illustrates the challenges of relying on the participants themselves to assess enrollment eligibility and outcomes.
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