Defibrillators can cause blood clots to be released if they caused the irregular heart rate, but can stop clots from forming by producing a normal rhythm.
Doctors noticed the patient, who had a history of seizures, was wearing a Fitbit that tracked his pulse rate and recorded it through a smartphone application. So they used the wearable to determine that irregular heart beat coincided with a grand mal seizure that had been witnessed three hours earlier.
That information allowed the doctors to administer a shock to the man's heart without the risk of releasing a clot that could have killed him.
"To our knowledge, this is the first report to use the information in an activity tracker-smartphone system to assist in specific medical decision making," the doctors said in a research paper published in the Annals of Emergency Medicine.
The story, first reported by medGadget.com, is an example of how the increased use of health-tracking devices "has the potential to provide clinicians with objective clinical information before the actual patient encounter.
"Not all activity trackers measure pulse rates, but this is the function of most value to medical providers," the research paper said.
The FitBit Charge HR, worn by the patient at the time of his seizure, determines pulse rate through a pulsed light-emitting diode and a light-sensing photodiode to measure light reflected from blood in capillaries. That data allows the Fitbit to detect alterations in capillary blood volume, and a computer algorithm then filters out noise and calculates an accurate pulse rate.
According to the researchers, any number of symptoms resolve themselves before a patient gets to a doctor or ER: Syncope, palpitations, dizziness, and even chest pain are all frequently self-limited complaints, leaving healthcare professionals with limited information on which to base a diagnosis.
"In many instances, knowledge of the patient's pulse rate at the event could help in establishing a firmer diagnosis," the research paper said. "These devices could also be used to establish the time when detection of pulse activity was lost, which might help to identify patients for whom resuscitative efforts might be futile."