Unipolar leads made by this method are prefixed by the letter V (which stands for voltage) followed by subscript numbers 1 to 6, which indicate the corresponding chest sites.
A lead taken by this method is called a unipolar lead. Actually the electrical potential of the central terminal is not truly zero because the right arm, left arm, and left leg are not equidistant from each other and from the heart, the body tissues vary in resistance and the heart and the extremities do not lie in exactly the same plane in the body.
The final six leads in the standard 12-lead ECG are designated as the precordial leads and are also unipolar leads
. These leads view the transverse plane of the body from anterior to posterior.
It is now over 100 years since the limb leads of the electrocardiogram (ECG) were introduced (1), 75 years since the unipolar chest leads were designed (2) though only 65 years since the precordial electrode positions were standardised (3) and approximately the same time since augmented unipolar leads
were introduced (4).
Approved in 2001, the Prime ECG uses 72 unipolar leads
placed in a vest-like distribution over the front, back, and sides of the patient's torso to obtain a three-dimensional view of cardiac electrical activity.
Similarity index was significantly lower in LVH patients than in normal subjects both in 62 leads (0.73 [+ or -] 0.067 vs 0.77 [+ or -] 0.044, p=0.03) and in 12 unipolar leads
(V1-V8, V3R, VR, VL, VF) extracted from the map (0.77 [+ or -] 0.075 vs 0.81 [+ or -] 0.045, p=0.03).