Great case report to read if not for the ingenious use of historical heart rate data.
http://www.annemergmed.com/article/S0196-0644(16)00143-8/fulltext
As in the case report described here, the identification that the patient’s atrial fibrillation was present for only a few hours permitted him to undergo cardioversion as opposed to simply receive rate control and then an anticoagulant. Information from the activity tracker could also be used to determine the frequency of tachycardic events in a patient with intermittent atrial fibrillation and aid in determining whether long-term anticoagulation or ablative therapy were required.