Wearable monitors were reasonably accurate at measuring heart rate during rest in normal sinus rhythm but much less accurate in atrial fibrillation or exercise.

Wearable monitors have become ubiquitous, but their accuracy at assessing heart rate has been unclear. In the current analysis, researchers compared the accuracy of six common wearable monitors during exercise testing in 61 patients with normal sinus rhythm and in 20 patients in atrial fibrillation. They measured heart rates at rest and then during a treadmill test using both the wearable monitor and an ECG monitor as the reference standard.

At rest, wearable devices showed reasonable accuracy; the mean absolute difference between ECG and wearable devices was 4.6 ± 8.4 beats per minute (bpm) in normal sinus rhythm and 7.0 ± 11.8 bpm in atrial fibrillation. At peak exercise, the difference was substantially larger: 13.8 ± 18.9 bpm in normal sinus rhythm and 28.7±23.7bpm in atrial fibrillation. The device underestimated the true heart rate in 62% of cases and overestimated it in 25%.

Comment: As we learn more about wearable devices, it is clear that they are imperfect. More studies have examined their ability to detect atrial fibrillation, which is their most important clinical use. Those analyses, similar to this one, have shown that not all devices perform well. The current study specifically focused on how well they capture maximal heart rate during exercise and found a very large variability. We must thus be cautious about the readings of these devices, particularly during exercise, and follow up with confirmatory diagnostic testing, especially for atrial fibrillation.

Mark S. Link, MD, Professor of Medicine and Director, Cardiac Electrophysiology, UT Southwestern Medical Center, Dallas, USA.

Quinn R, et al. Accuracy of wearable heart rate monitors during exercise in sinus rhythm and atrial fibrillation. J Am Coll Cardiol 2024; 83: 1177-1179.

This summary is taken from the following Journal Watch title: Cardiology.