Validating QT-Interval Measurement Using the Apple Watch ECG to Enable Remote Monitoring During the COVID-19 Pandemic
Authors: Marc Strik, Théo Caillol, F. Daniel Ramirez, Saer Abu-Alrub, Hugo Marchand, Nicolas Welte, Philippe Ritter, Michel Haïssaguerre, Sylvain Ploux, Pierre Bordachar
Journal: Circulation (2020)

◼ electrocardiography ◼ long QT syndrome ◼ remote consultation ◼ telemedicine S creening and monitoring for QT prolongation when certain medications are initiated are routinely performed to avoid arrhythmic complications.However, the novel coronavirus disease 2019 (COVID-19) pandemic and its proposed treatments-including hydroxychloroquine and azithromycin, which are known to prolong the QT interval 1 -raise logistical and safety concerns with established QT monitoring strategies.Recently, the American College of Cardiology made recommendations for QT monitoring in outpatients with COVID-19 on hydroxychloroquine/azithromycin, suggesting that the use of direct-to-consumer mobile devices such as the Apple Watch 1-lead ECG could be considered in cases of resource constraints or quarantines. 2The Apple Watch ECG is cleared by the US Food and Drug Administration for detecting atrial fibrillation but has not been studied for QT monitoring.Lead I (the lead recorded by the Apple Watch) may be suboptimal for measuring this interval; however, other leads can be reproduced by placing the smartwatch on the left ankle or chest. 3We therefore sought to validate the use of the Apple Watch for QT measurement, including using nonstandard smartwatch positions, in an unselected outpatient population.Between December 2019 and January 2020, 100 consecutive patients in sinus rhythm were enrolled from outpatient or emergency departments.The study was approved by our institutional review committee, and the subjects gave informed consent.Standard 12-lead ECGs were performed, followed by smartwatch electrocardiographic recordings using the Apple Watch Series 4 (Apple Inc, Cupertino, CA).After a brief demonstration, patients recorded 30-second Apple Watch electrocardiographic equivalents of lead I (AW-I; watch on left wrist), lead II (AW-II; watch on left ankle), and a simulated lead V 6 (AW-LAT; watch on left lateral chest; Figure [A]).Using commercially available software (EP Calipers, EP studios Inc, Louisville, KY), a cardiologist measured 3 RR and QT intervals to calculate the corrected QT interval (QTc) using the Bazett formula (Figure [B]).A QTc >480 milliseconds was considered high risk.Agreement between the 12-lead and Apple Watch QTc measurements was calculated with the use of the median absolute error and Bland-Altman analyses.To measure interobserver variability, all AW-I QTc measurements were repeated by a second blinded cardiologist, and the intraclass correlation coefficient was calculated on the basis of a 2-way random absolute agreement model with single measurements.Agreement on whether a tracing was interpretable was assessed with the Cohen κ statistic.T-wave amplitude was measured to evaluate its association with QTc measurement accuracy.The mean age was 67±7 years; 59% were male; and 35% had diagnosed cardiac disease.Heart rates were similar on 12-lead and Apple Watch recordings (69±11 bpm versus 70±13 bpm, respectively; P=0.2, paired Student t test).QTc intervals ranged from 336 to 530 milliseconds on 12-lead ECGs.Eight patients were identified as high risk, all of whom were similarly identified by the smartwatch.