Study shows Garmin PPG sensor can be used for passive Afib detection

A new study has shown the photoplethysmography (PPG) sensor on Garmin watches can be used for identifying the most prevalent heart arrhythmia – atrial fibrillation (Afib). The condition effects about 8 million people in the US and more than 30 million people across the globe. 

Fitbit is ahead of the curve when it comes to this sort of thing. It recently made available its Afib detection feature in Europe having secured the necessary regulatory approval. Passive Afib monitoring on its devices has been available since early this Spring in the US as the company had secured FDA approval earlier. Fitbit conducted a massive study with 450,000 individuals in 2021 to confirm the efficacy of its sensor and algorithm for detecting signs of Afib.

This is many times more useful than the functionality that can be found on the Apple Watch. This device can also detect Afib, but only by using an ECG sensor. Which means the measurements are on-demand rather than continuous.

Don’t be surprised if the Garmin on your wrist is soon able to detect Afib, passively in the background. A new study using the Forerunner 945 watch shows the company’s heart rate sensor can be used for this sort of thing.

PPG sensor and Afib – the study

Published in the American Heart Journal recently, the study goes under a catchy title: “Atrial fibrillation detection using ambulatory smartwatch photoplethysmography and validation with simultaneous holter recording.”

A total of 201 participants who participated in the research between March 2019 and Dec 2019 were fitted with a Garmin Forerunner 945 watch for a 24 hour period. To remind, this device has version 3.0 of the company’s ELEVATE heart rate sensor. Newer watches have the more accurate version 4.0. Study participants underwent simultaneous Holter ECG monitoring which is considered to be the Gold standard for detecting heart abnormalities.

The heart rate sensor data from the watch was run through an algorithm that excludes PPG traces of poor quality and distinguishes premature beats from sinus beats for each 5-minute segment. PPG signals that were obtained with significant wrist motion were excluded. This data was then compared to the Holter ECG as the Afib diagnostic standard.

What do the results show?

It is worth noting that the study participants were individuals who had Afib or were suspected of having the condition based on previous medical examinations. Their mean age was 66.1. A total of 56% of them were identified by the Holder as having Afib during the 24 hour observation period. Most participants in this group (a total of 96.4%) had a pre-Holter diagnosis of the condition.

When this data was compared against the Garmin, the results were impressive. It turns out of the 112 participants who had Afib, 109 participants had detectable Afib episodes in the PPG records of the Forerunner 945.

The sensitivity, specificity, and positive predicted value of Afib detection in participants was pretty high – 97.3%, 88.6%, and 91.6%. That’s right up there with the Fitbit study results. The 5-minute-segment analyses also exhibited good correlation, with a sensitivity of 97.1%, and a specificity of 86.8%.

The most frequent cause of false negatives was Afib with rapid ventricular rate. For false positives it was premature beats.

The implications

This is not the first study that demonstrates the feasibility of using the PPG sensor that can commonly be found in fitness trackers and smartwatches for detecting Afib. But to our knowledge, it is the first such research that utilised a Garmin-made watch.

The company’s devices take measurements multiple times per second, around the clock. Their sampling frequency is higher as compared to most other brands. So it is logical that they can be used to detect the condition.

The implications of using the PPG sensor are multiple. The technology:

• allows for continuous Afib monitoring by tracking the blood flow in a user’s wrist – prolonged monitoring using a Holter monitor is not practical
• is available to all – at a low cost
• is many times more convenient that going to a hospital setting to take measurements
• can be used in combination with an ECG sensor. So a user can be notified to check with the single-lead ECG if the PPG sensor suspects Afib.

This was an independent third-party study that was funded by Garmin. Which makes it clear the company has ambitions in this area. The study used an older Garmin watch so it is quite possible all of the company’s devices with ELEVATE heart rate sensors 3.0 (and above) might acquire the feature. Pretty soon the Garmin on your wrist might be able to look out for Afib as you go about your day.

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