Evaluation of a Consumer Wearable Smartwatch for Cardiac Interval Measurement in Healthy Adults: Cross-Sectional Method Comparison Study.

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 and corrected 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) with those measured using a research-grade 3-lead electrocardiogram (ECG; Biopac) and a clinically approved single-lead patch (Cardea SOLO). METHODS: This was a cross-sectional study of 28 healthy adults aged 21 to 65 years, with a mean age of 39.4 (SD 13.0) years. Participants underwent 4 concurrent ECG measurements per device: twice seated at rest, once supine, and once after exercise. All RR and QT intervals were manually measured using standardized caliper software (EP calipers) by trained reviewers, and QTc was calculated using the Bazett formula. Agreement was assessed via repeated-measures correlation (rrm) and linear mixed-effects models (LMMs) for repeated-measures Bland-Altman analysis. RESULTS: Strong agreement was observed for RR intervals when comparing the Withings ScanWatch with both the Biopac (rrm=0.84; P<.001) and the SOLO (rrm=0.80; P<.001). Agreement was weaker for QT intervals (rrm=0.37; P=.001 compared to Biopac and rrm=0.37; P=.001 compared to SOLO) and QTc intervals (rrm=0.27; P=.01 compared to Biopac and rrm=0.27; P=.03 compared to SOLO). Bland-Altman LMM analysis demonstrated that the Withings ScanWatch systematically underestimated QT intervals, with a mean error (ME) of -42.9 (SD 30.1) milliseconds versus Biopac and -15.8 (SD 20.6) milliseconds versus SOLO. Similarly, QTc intervals were underestimated, with an ME of -51.4 (SD 32.3) milliseconds versus Biopac and -18.8 (SD 21.5) milliseconds versus SOLO. CONCLUSIONS: While the Withings ScanWatch showed strong agreement for RR interval measurement, its variability and systematic underestimation in QT and QTc measurements limited 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.