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Figure 1 Representative recordings of the P-SAECG obtained from a normal volunteer. In the time domain analysis (panel A), the filtered P wave duration was defined as the point at which the voltage of the atrial signal exceeded 1 µV in the filtered P wave and returned to the 1 µV level, respectively. In the frequency domain analysis (panel B), S and E indicates the beginning and the end of P wave, respectively. The dark area indicates power spectrum area of 0–20 Hz zone and the shaded area indicates power spectrum area of 20–100 Hz zone. AR20 was the power spectrum area in the 0–20 Hz zone divided by that in the 20–100 Hz zone.