A recent case report in the Annals of Emergency Medicine described how the FitBit Charge HR, a wrist-mounted activity tracker, was “interrogated” to help manage a patient with new onset atrial fibrillation after a seizure.

Rudner et al presented the case of a patient who presented to an emergency department after a seizure and was found to be in atrial fibrillation (AF). After his post-ictal state resolved, he was unable to recall any changes in symptoms indicating the onset of the heart arrhythmia (he had no prior history of atrial fibrillation) as he was asymptomatic. However, the patient happened to be wearing a FitBit Charge HR, synced with his smart phone. This was interrogated, and noted a sudden increase in the Fitbit heart rate at the time of the seizure. With this data helping provide a timeframe for event onset, electrocardioversion was performed, sinus rhythm restored, and the patient was discharged from the emergency department.

We have covered mobile activity trackers several times in the past, primarily their use to encourage more active lifestyles through step-counting (pedometer) features. These devices, utilizing accelerometer technology to determine movement, offer great potential in healthcare, particularly for weight loss and exercise promotion.

However, the actual clinical significance of physiologic data like the Fitbit heart rate from these devices remains unclear, as Fitbit, Mi Band, and other popular mobile trackers are not considered approved medical devices. As stated in the Annals of Emergency Medicine article, “use of their information to make medical decisions is at the clinician’s own discretion.” In this case, defining the duration of AF is critical. After about 48 hours, the chances of a clot having formed in the left atrium (that could fly off to the brain after a cardioversion) become significant. Here, clinicians used the jump in heart rate to define the time of onset and, since it was recent, they felt comfortable proceeding with cardioversion.

There are also limitations with the Fitbit heart rate worth considering here though. For example, the patient was asymptomatic from his AF while in the emergency department. While the heart rate did jump at the time of his seizure, it’s also plausible that he had been in AF prior to the seizure and it was just a rapid ventricular response that was triggered by the seizure. Assessment of factors like beat-to-beat variability can be helpful in figuring that out, as some apps are trying to do, but it’s not clear whether the Fitbit Charge HR would be accurate enough to do that.

Of note, the Fitbit heart rate didn’t go over 150, despite paramedics noting a pulse of 190, consistent with previous reports of decreased accuracy as heart rates increase. The authors suggest several clinical scenarios in which activity tracker data may be helpful, such as syncope, dizziness, and even cardiac arrest.

It’s likely we will continue to see such reports of consumer-grade activity tracking devices helping aid in both diagnostic and therapeutic clinical roles as these devices mature and increase in popularity. And with companies from Google to Fitbit aiming to eventually make these devices “medical grade,” these reports could be foreshadowing what may in the future be standard practice.