How accurate is Fitbit’s Passive Heart Rhythm monitor?

In a piece of recent news, the Food and Drug Administration (FDA) has given Fitbit the green light to monitor users’ passive heart rhythms in the background.

Monitoring Passive Heart Rhythm

A new photoplethysmography (PPG) algorithm can passively check a user’s heart rhythm while they’re still or asleep. If the tech detects signs of atrial fibrillation, it will immediately alert the users. Atrial Fibrillation or AFib is a type of irregular heart rhythm. According to various sources, the Fitbit parent Google submitted the algorithm to the FDA for review last month. According to Google’s blog post, the passive heart rhythm monitoring feature works as follows:

“When your heart beats, tiny blood vessels throughout your body expand and contract based on changes in blood volume. Fitbit’s PPG optical heart-rate sensor can detect these volume changes right from your wrist. These measurements determine your heart rhythm, which the detection algorithm then analyzes for irregularities and potential signs of atrial fibrillation.”

Fitbit previously received FDA clearance to use electrocardiogram (ECG) tech in 2020’s Sense Smartwatch. However, that method requires users to run ECG tests manually. Google notes that AFib can be difficult to detect as episodes can be sporadic and pass without any symptoms. Monitoring heart rhythms in the background could improve detection. AFib affects more than 33.5 million people, and those with the condition have a higher risk of stroke.

Conducting Study of PPG Algorithm

In May 2020, Fitbit conducted a study of the PPG algorithm which lasted over five months and had more than 450,000 participants. It found that the algorithm correctly identified AFib episodes 98 percent of the time. Google used ECG patch monitors for confirmation.

Fitbit will soon roll out the background heart rate monitoring and Irregular Heart Rhythm Notifications features in the US. They will be available on “a range of heart-rate enabled devices.” Apple Watch 4 and later can also passively monitor heart rhythms for signs of AFib. While neither company’s devices can make a formal diagnosis, they could prompt wearers to consult a doctor for advice should they detect possible AFib.