983515.fig.001a
(a)
983515.fig.001b
(b)
Figure 1: The first three leads of ECG devised by Einthoven constitute the Einthoven triangle [1]. Lead I is used as the reference lead and is located at 0 degrees. Positive designations increase by 30 degree increments in a clockwise direction to 180 degrees. Lead II appears at 60 degrees. Augmented limb leads (aVL, aVR, aVF) are unipolar limb leads, containing only a positive pole. aVL is designated at −30 degrees, aVF at 90 degrees, and lead aVR at −150 degrees.