Technical characterization of the single-lead electrocardiogram signal from four different smartwatches and its clinical implications

FUNDING ACKNOWLEDGEMENTS: Type of funding sources: Public Institution(s). Main funding source(s): Department of Cardiology, University Hospital Basel, University of Basel, Switzerland Institute for Medical Engineering and Medical Informatics, School of Life Sciences, University of Applied Sciences and Arts Northwestern Switzerland, Muttenz, Switzerland BACKGROUND: Smartwatches with the capability of single-lead electrocardiograms (ECGs) acquisition have been established as valuable tool for the detection of atrial fibrillation (AF). For the currently available smartwatches, however, the technical specification of the acquired ECG signal is unclear. PURPOSE: The aim of the current study was to characterize quantitatively the raw signal of the single-lead ECG of four currently available smartwatches (Apple watch series 6, Withings ScanWatch, Samsung Galaxy Watch 4, Fitbit Charge 5) and assess their clinical applicability based on their technical features. METHOD: A bench test was performed applying a synthetic, well-characterized signal to the electrodes of the watches (Figure: (A) Apple watch series 6, (B) Withings ScanWatch, (C) Samsung Galaxy Watch 4, (D) Fitbit Charge 5). The frequency response to this input signal was acquired and Bode plots were calculated (Figure, second column: Bode diagrams show the frequency response (upper) and the phase angles (lower)). To compare the ECG characteristics of the four watches, the synthetical response to a pre-recorded surface ECG dataset was calculated based on the frequency characteristics determined above (Figure, third column: The synthetical raw signal is shown in grey, the response of the watch in blue). RESULTS: The frequency responses of all four watches shows a bandpass filter, with an additional 50/60 Hz narrow-band filter (Figure). While the recommended high-pass cut-off at 0.5 Hz was fulfilled by all devices (1), a low-pass cut-off was observed for all devices below 70Hz (instead of 150Hz) resulting in a significantly damped signal. In detail, a damping of -6dB, corresponding to a signal amplitude reduction of 50%, was observed above 70 Hz and below 0.4 Hz for all watches. A QRS complex amplitude reduction was observed for the Apple, Withings and Samsung watch. A pronounced noise filtering is visible for the Samsung and Fitbit Smartwatch. A difference for the clinically relevant characteristic fiducial points, such as the onset of the P-wave or QRS complex, cannot be observed in these examples. However, when using the tangent method to detect the end of the T-wave to calculate the QTc value, a difference between the measures can be observed for the Withings Watch. CONCLUSION: The technical characteristics in terms of filtering characteristics of the single-lead ECG from four commercially available smartwatches differ and must be taken into consideration when attempting to use smartwatches beyond the detection of AF. [Figure: see text]