Figure 1.

Schematic presentation of the QRS vector loop and the maximum QRS vector in space. QRS_elevation (A) is the angle between the maximum QRS vector and an axis perpendicular to the horizontal plane, 0° being the vector directed downwards. QRS_azimuth (B) is the angle between the projected maximum QRS vector on the horizontal plane (XZ) and the left extremity of the X axis, 0° being the vector pointed to the left. Forward vector directions are defined as 0° to 180°, and backward vector directions as 0° to 180°, respectively.