Fig. 2.

Photographs show how to position the Apple Watch for obtaining precordial electrocardiograms. The precordial leads are recorded as CR₁ through CR₆, corresponding, respectively, to the locations of V₁ (4th intercostal space right parasternal), V₂ (4th intercostal space left parasternal), V₃ (between V₂ and V₄), V₄ (5th intercostal space midclavicular line), V₅ (5th intercostal space anterior axillary line), and V₆ (5th intercostal space midaxillary line).

From Spaccarotella CAM, Polimeni A, Migliarino S, Principe E, Curcio A, Mongiardo A, et al. Multichannel electrocardiograms obtained by a smartwatch for the diagnosis of ST-segment changes. JAMA Cardiol 2020;5(10):1176-80.²¹ Used under the terms of the Creative Commons CC-BY license.