A Comparative Analysis of Signal Quality and Morphological Fidelity in ECG Smartwatches

This study provides a direct objective comparison of the ECG signal quality and morphological features preservation of four leading commercial smartwatches: the Apple Watch Series 9, Samsung Galaxy Watch 6, Fitbit Sense 2, and Withings ScanWatch, using a controlled dataset. The Philips TC30 is used as the reference standard. ECG signal quality is assessed through Signal-to-Noise Ratio (SNR), Standard Deviation of Baseline Wander and Power Spectral Density (PSD), while the preservation of the morphological features is assessed through comparing the performance differences of our J-point and ST deviation automatic detection algorithms when run on each watch’s recordings separately. J-point detection is assessed by comparing each device’s performance against the reference device, while ST deviation is assessed using simulator defined ground truth values. The Apple Watch and Withings ScanWatch had the best SNR, while the Samsung Galaxy Watch had much lower values. The Withings ScanWatch had the most stable baseline, while the Fitbit Sense 2 had the most variable baseline. All devices showed a consistent negative bias in J-point detection, which suggests that internal signal processing tends to smooth out small changes in waveforms. For ST-segment classification, the Apple Watch achieved the most balanced performance across sensitivity and specificity. These results give researchers and clinicians data-driven advice on how to choose the best device for their specific needs.