A physician wishes to obtain two simultaneous ECG in frontal

A physician wishes to obtain two simultaneous ECG in frontal plane from leads that have lead vector at right angles. The signals will be used to generate a VCG. Describe how you would go about obtaining these two signals and suggest a test to determine whether the leads are truly orthogonal.

Solution

Consider there are three planes where the ECG signals are projected.Say X,Y,Z.When the X,Y and X,Z planes are analyzed simultaneously, the mean QRS vector (and the other vectors) projects perpendicularly from the transition “plane” rather than the transition “line” of the single plane system. In other words, when the frontal plane and the horizontal plane are isolated and individually analyzed, the mean QRS transition appears as a line across the diameter of the circle. In actuality, this “line” is actually a “plane” when both systems (frontal and horizontal) are analyzed simultaneously and the mean vectors (QRS, T and P) project perpendicularly from this plane into both systems.The axis of the ECG is the major direction of the overall electrical activity of the heart. It can be normal, leftward (left axis deviation or LAD), rightward (right axis deviation or RAD), or indeterminate (northwest axis). The QRS axis is the most important to determine, however the P wave or T wave axis can also be measured.To determine the QRS axis, the limb leads need to be examined (not the precordial leads).