What is AFib? Google-owned Fitbit gets FDA approval for passive heart rate monitoring

Fitbit's atrial fibrillation (AFib) detection photoplethysmography (PPG) algorithm received approval from the U.S. FDA on Monday. The Google-owned company filed for FDA approval two weeks ago.

Fitbit's new technology mirrors that of Apple Watch's passive heart rate monitoring system, which allows wearers to check for potential signs of AFib. This is a significant level-up from its previous manual electrocardiogram (ECG) tool, which could be life-saving, but only if enough manual tests are run.

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How does this new Fitbit technology detect AFib?

In a statement, Google defined AFib as "a form of irregular heart rhythm" that has inflicted upwards of 33.5 million people globally.

The condition is significantly difficult to detect since it often presents without any symptoms and in irregular episodes. Google reported that patients with atrial fibrillation are at five times higher risk of stroke.

Fitbit's PPG algorithm seeks to detect AFib through the following methodology:

"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."

In 2020, a landmark Fitbit Heart Study enrolling 455,699 participants over five months was conducted to clinically validate the PPG algorithm.

According to data presented at the American Heart Association Scientific Sessions in 2021, Fitbit's PPG algorithm had a 98% accuracy in identifying AFib episodes. This data was corroborated by ECG patch monitors, which are designed specifically for these purposes.

Fitbit had already taken a step toward irregular heart rhythm detection in 2020 with its FDA-cleared ECG app, Fitbit Sense. However, the app only allowed spot checks where users had to take their heart rate and rhythm readings manually.

The new technology will constantly run in the background, allowing any health-focused wearable device to passively assess one's heart rhythm even while they're asleep.

Given the condition's sporadic nature, this overnight monitoring and detection system is the most optimal way to detect it.

If the technology discovers something suggestive of atrial fibrillation, the user will receive a notification through the Irregular Heart Rhythm Notifications feature.

In this case, users are highly recommended to consult their "healthcare provider or seek further assessment to help prevent a significant medical event, such as stroke."

With the PPG algorithm being approved, Fitbit now offers two methods of detecting atrial fibrillation. The existing ECG app takes a spot-check approach, relying on proactive screening by recording ECG traces that can be reviewed with healthcare providers.

Meanwhile, the newer PPG-based algorithm allows for long-term heart rhythm assessment, aiming to identify asymptomatic atrial fibrillation that could otherwise go undetected.

Google's statement reads:

"We want to make AFib detection as accessible as possible to help reduce the risk of potentially life-threatening events — like stroke — and ultimately improve overall heart health for everyone."

The company hasn't explicitly confirmed how the new technology will be available for use. However, it has promised that the PPG-based algorithm and Irregular Heart Rhythm Notifications feature will "soon" be available to U.S. consumers across a range of heart rate-enabled devices.