A Fitbit Charge HR activity tracker might have just saved a 42-year-old man's life, leading doctors to electrically-shock his heart based on Fitbit data.

The man ended up in the emergency room after having a seizure, and doctors noticed that he had atrial fibrillation, meaning that his heartbeat was fast and irregular. Fitbit data helped doctors determine whether or not it was caused by the seizure, so they'd know if an electrical cardioversion would be suitable.

The patient had the seizure 20 minutes before getting to the E.R., but doctors were initially unsure if his atrial fibrillation was chronic or triggered by the seizure. This difference is crucial, because there's the risk of a stroke.

If the condition was chronic, the electrical cardioversion could trigger a stroke. If, on the other hand, it was not chronic and instead caused by the seizure, not performing that electrical cardioversion to address the arrhythmia could also trigger a stroke.

Luckily, the man's Fitbit tracker helped solve this puzzle and led doctors to perform the cardioversion, shocking the man's heart back to normal.

"During the patient's examination, it was noted that he was wearing a wrist activity tracker (Fitbit Charge HR, Fitbit, San Francisco, Calif.), which was synchronized with an application on the patient's smartphone, recording his pulse rate as part of a fitness program," the medical staff explain in a report.

Doctors accessed the app on the patient's smartphone and noticed that the baseline rate doubled around the time of the seizure.

Simply put, the man's Fitbit proved that it was the seizure that caused the atrial fibrillation, which, in turn, gave doctors the green light to perform the cardioversion.

A cardioversion uses electricity to shock a patient's heart rate back to normal, in such cases.

This marks the first time ever that a fitness tracker served such an important role in a person's diagnostic and treatment. So far, trackers such as Fitbit and others did hold great promise in helping medical staff, but doctors mainly use them to encourage or monitor the patient's activity.

For the 42-year-old man, however, the Fitbit Charge HR assisted doctors in making a special and crucial medical decision, likely saving his life in the process.