Electrocardiographic Leads Which Record Potential Variations Produced by the Heart Beat at a Single Point

In a recent publication we have shown that if the assumptions upon which Einthoven's equilateral triangle is founded are valid the potential of the right arm (VR). the potential of the left arm (VL), and the potential of the left leg (VF) at any given instant in the cardiac cycle are defined by the following equations:where e1, e, e3 represent the deflections in standard leads I, II and III respectively at the chosen instant. It will be seen that at every instantLet suitable electrodes be placed upon the right arm, left arm and left leg in the same manner as in taking ordinary electrocardiograms and let these electrodes be connected, each through a resistance R, to one and the same terminal. Providing that the 3 resistances (R) are equal and sufficiently great so that this procedure does not materially alter the potential variations produced by the heart beat at the extremities, it may be shown that the potential of this central terminal will not be significantly influenced by the heart beat and may be taken as zero throughout the cardiac cycle. If an instrument which has a resistance sufficiently high so that it may be regarded as a potentiometer is connected to this terminal and to any body point, it will record the potential variations produced by the heart beat at the latter point. In this way VR, VL and VF may be directly recorded by connecting the recording instrument to the central terminal and the electrode in contact with the proper extremity, and the characteristics of the electric field set up in the body by the heart beat may be easily investigated. Lead VL, as indicated by equation (2), gives a direct measure of the index employed by Lewis, White and others for determining the grade of right or left preponderance present.