Using a smartwatch to record precordial electrocardiograms: a validation study

Background: Smartwatches which support recording of a single-lead electrocardiogram (ECG) are increasingly being used worldwide, mainly for detection of atrial fibrillation. Recordings beyond the wrist are anecdotal as their reliability remains unknown.

Aim: This clinical validation study assessed the reliability of an Apple Watch (AW) to obtain frontal and precordial leads as compared with standard 12-lead ECGs in both healthy subjects and patients with underlying heart disease.

Methods: In 100 subjects (80 with ECG anomalies), a standard 12-lead ECG was performed, followed by AW recordings of the standard Einthoven leads (leads I, II, and III) and precordial leads V1, V3, and V6. Seven parameters (P, QRS, ST and T-wave amplitudes, PR, QRS, and QT intervals) were compared through a Bland-Altman analysis including bias (mean difference), absolute offset (mean absolute difference), and 95% limits of agreement.

Results: No significant differences were observed for any parameter across any lead, except for R-wave measured across precordial leads V1, V3, and V6 where significantly greater amplitudes were measured by the AW, (0.20 mV; 0.19mV; 0.49 mV respectively; p = 9x10-7; p = 7x10-4; p = 6x10-14, respectively), indicating overestimation by the AW. There were no significant differences in absolute offset or bias for any parameters of any leads (p > 0.05).

Conclusion: ECGs recorded with the AW on the wrist but also on other positions had comparable durations and amplitudes compared to standard 12-lead ECG. The AW can be used to record frontal and precordial leads, paving the way for broader clinical applications.