Table 2.

Electrocardiogram characteristics (duration and amplitude).

Variables, Units		Lead	Standard ECG	Smartwatch ECG	Correlation Coefficient	p-Value	Bias * (95% LoA)
Duration (millisecond), mean ± SD	P Wave	I	76.79 ± 11.69	76.54 ± 11.58	0.94	0.001	0.25 (−7.44 to +7.94)
		II	77.27 ± 13.15	77.89 ± 13.15	0.94	0.001	−0.62 (−9.82 to +8.58)
		III	77.39 ± 14.66	78.64 ± 13.91	0.96	0.001	−0.01 (−7.28 to +7.26)
	PR Interval	I	172.21 ± 24.55	171.36 ± 24.69	0.98	0.001	0.85 (−8.01 to +9.71)
		II	173.73 ± 29.99	172.69 ± 29.17	0.97	0.001	1.04 (−11.55 to +13.63)
		III	172.07 ± 28.26	172.65 ± 27.62	0.96	0.001	−0.68 (−16.32 to +14.95)
	QRS Complex	I	87.44 ± 11.70	87.67 ± 11.18	0.94	0.001	−0.23 (−7.86 to +7.39)
		II	88.84 ± 10.73	89.01 ± 10.46	0.93	0.001	−0.17 (−8.18 to +7.84)
		III	87.08 ± 14.54	87.23 ± 14.00	0.95	0.001	−0.14 (−9.30 to +9.01)
	QT Interval	I	369.66 ± 44.26	369.93 ± 44.36	0.99	0.001	0.04 (−11.05 to +11.13)
		II	368.42 ± 42.19	367.44 ± 40.67	0.98	0.001	0.09 (−9.90 to +11.87)
		III	369.57 ± 42.36	369.22 ± 42.18	0.99	0.001	0.35 (−9.98 to +10.96)
	T Wave	I	132.41 ± 24.72	133.10 ± 24.81	0.97	0.001	−0.32 (−12.53 to +11.88)
		II	132.81 ± 24.43	133.13 ± 23.93	0.97	0.001	−0.32 (−12.53 to +11.88)
		III	133.76 ± 24.15	133.82 ± 23.17	0.98	0.001	−0.06 (−8.34 to +8.21)
Amplitude (millivolts), mean ± SD	P Wave	I	0.20 ± 0.06	0.22 ± 0.07	0.78	0.001	−0.01 (−0.10 to +0.07)
		II	0.23 ± 0.09	0.24 ± 0.95	0.89	0.001	−0.01 (-0.09 to +0.08)
		III	0.21 ± 0.08	0.21 ± 0.08	0.83	0.001	−0.01 (−0.09 to +0.09)
	QRS Complex	I	1.79 ± 0.68	1.84 ± 0.70	0.96	0.001	−0.04 (−0.38 to +0.28)
		II	1.97 ± 0.84	1.94 ± 0.78	0.89	0.001	0.02 (−0.73 to +0.78)
		III	1.94 ± 0.64	1.97 ± 0.65	0.90	0.001	−0.02 (−0.60 to +0.55)
	T Wave	I	0.29 ± 0.15	0.32 ± 0.15	0.89	0.001	−0.02 (−0.16 to +0.11)
		II	0.32 ± 0.17	0.32 ± 0.15	0.82	0.001	0.00 (−0.19 to +0.20)
		III	0.28 ± 0.16	0.29 ± 0.18	0.72	0.001	−0.01 (−0.27 to +0.23)

* Bias was calculated by Bland-Altman analysis; ECG: electrocardiogram; LoA: limits of agreement.