Electrocardiogram PL Method. (A) Electrocardiogram in orthogonal ECG leads V1 and aVF (lead I is also used). QRS subtracted ECG leads emphasize atrial activation. (B) Electrocardiogram spatial loop displayed from mutiple loops over AF cycles (right panel). Phase angles θ are calculated between times t, t + 1 for all time points t. (C) Timeseries of phase angle θ, showing periodicity that is highlighted in spectral plot. Electrocardiogram PL index is calculated from the area of the harmonics.