“But for the Blind Spot”: Accuracy and Diagnostic Performance of Smart Watch Cardiac Features in Pediatric Patients

Background The Apple Watch™ (AW) offers heart rate (HR) tracking by photoplethysmography (PPG) and single-lead ECG recordings. The accuracy of AW-HR and diagnostic performance of AW-ECGs among children during both sinus rhythm and arrhythmias have not been explored. Objective The primary objective was to assess accuracy of AW-HR measurements compared to gold-standard modalities in children during sinus rhythm and arrhythmias. Secondary objectives included identification of non-sinus rhythms using AW-ECGs. Methods Subjects ≤18 years wore an AW during 1) telemetry admission, 2) electrophysiology study (EPS), or 3) exercise stress test (EST). AW-HRs were compared to gold-standard modality values. Recorded AW-ECGs were reviewed by three blinded pediatric electrophysiologists. Results 80 subjects (median-age 13 years, IQR 1.0-16.0, 50% females) wore AW (telemetry [41%, n=33], EPS [34%, n=27], or EST [25%, n=20]). 1,090 AW-HR measurements were compared to time-synchronized gold-standard modality HR values. Intraclass correlation coefficient (ICC) was high 0.99 (0.98-0.99) for AW-HR during sinus rhythm, when compared to gold-standard modalities. ICC was poor comparing AW-HR to gold-standard modality HR in tachyarrhythmias (ICC 0.24-0.27) due to systematic undercounting of AW-HR values. 126 AW-ECGs were reviewed. Identification of non-sinus rhythm by AW-ECG showed a sensitivity of 89-96% and a specificity of 78-87%. Conclusions We found high levels of agreement for AW-HR values with gold-standard modalities during sinus rhythm, and poor agreement during tachyarrhythmias, likely due to hemodynamic effects of tachyarrhythmias on PPG-based measurements. AW-ECGs had good sensitivity and moderate specificity in identification of non-sinus rhythm in children.