Measurement of the QT interval using the Apple Watch

Figure 1. Method used to collect lead I, lead II, and the V2 lead with the smartwatch. Lead I was recorded with the smartwatch on the left wrist and the right index finger on the crown (A). Lead II was obtained with the smartwatch on the left lower abdomen and the right index finger on the crown (B). Chest lead V2 was recorded with smartwatch in the fourth intercostal space left parasternal with the right index finger on the crown (C).

Figure 2. Regression analysis: correlation of mean QT-a (ms) and mean QT-e (ms). Scatterplot and fitted line showing the linear association between the QT mean interval (measured as an average of lead I, lead II, the V2 lead) performed using a smartwatch (QT-a) and standard (QT-e) ECG.

Figure 3. Comparison of QT measured with the standard ECG and the smartwatch ECG. Bland–Altman plot indicating the level of agreement between the smartwatch ECG and the standard 12-lead ECG measurement of the QT (ms) interval in lead I (A), lead II (B), and the V2 lead (C). The solid red line represents the bias and dashed red lines the upper and lower limit of agreement (LOA).

Figure 4. Comparison of QTc mean using Bazett’s, Friedericia’s, and Framingham’s formulas between standard and smartwatch ECG. Bland–Altman plot indicating the level of agreement between the smartwatch ECG and standard 12-lead ECG measurement of QTc (ms) using Bazett’s formula (three panels on the left: (A–C)); Friedericia’s formula (three panels in the center: (D–F)); and Framingham’s formula (three panels on the right: (G–I)), respectively, from the top to the bottom: lead I, lead II, and the V2 lead. The solid red line represents the bias and dashed red lines the upper and lower LOA.