JMIR Publications

ABSTRACT

Background:

Commercially available wearable devices, capable of measuring cardiac rhythm, are gaining popularity for convenient heart health monitoring. Accurate measurement of key intervals, specifically RR intervals for rhythm and QT/QTc intervals for arrhythmia risk, is crucial for assessing potential cardiac morbidity.

Objective:

This study aimed to evaluate the agreement of RR, QT, and QTc intervals measured by a consumer wearable device (Withings ScanWatch Series 1) against a research-grade 3-lead ECG (Biopac) and a clinically approved single-lead patch (Cardea SOLO).

Methods:

This was a cross-sectional study of 28 healthy adults age 21–65 years old, with a mean age of 39.4 (13.0). Participants underwent four concurrent ECG measurements per device: twice seated at rest, once supine, and once post-exercise. All RR and QT intervals were manually measured using standardized caliper software (EP Calipers) by trained reviewers, and QTc was calculated using Bazzett’s formula. Agreement was assessed via Pearson’s correlation coefficients (r), paired t-tests, and Bland-Altman analysis.

Results:

Strong agreement was observed for RR intervals when comparing the Withings to both the Biopac (r=.93, P<.001) and the SOLO (r=.92, P<.001). Agreement was weaker for QT intervals (r=.70 and r=.78, respectively) and QTc intervals (r=.37 and r=.56, respectively; P<.001 for all). Bland-Altman analysis indicated a systematic underestimation of QT (Mean error (ME) for Biopac: -37.8 ms (SD 29.8); vs. SOLO: -16.4 ms (SD 20.4)) and QTc (ME for Biopac: -42.3 ms (SD 32.2); vs. SOLO: -20.8 ms (SD 21.2)) by the Withings device.

Conclusions:

While the Withings ScanWatch shows strong agreement for RR interval measurement, its variability and systematic underestimation in QT and QTc measurements limit its clinical applicability for accurate assessment of arrhythmia risk. The device may serve as a valuable tool for tracking trends over time, but it is currently unreliable for precise interval screening.