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In order to obtain a meaningful ECG, a few things must be taken into account when applying the electrodes. For better conductivity they are often moistened with water or disinfectant. As a rule, the electrodes are first applied to both forearms and both ankles; then the six chest wall electrodes are positioned.

Nowadays, adhesive electrodes are commonly used. In older hospitals or doctors’ practices, so-called suction electrodes are still used, which automatically suck on the patient’s skin. For standardization, each of the six chest wall electrodes has a designation:

V1: to the right of the sternum into the 4th intercostal space
V2: to the left of the sternum into the 4th intercostal space
V3: between V2 and V4
V4: left to the intersection of the 5th intercostal space and the mid-sclavian line
V5: front axis line same height as V4
V6: middle axis line, same height as V4

Physiological background

Our heartbeat, but also every other muscle movement, is based on the targeted displacement of charged particles (ions). They flow between the inside and outside of the cell and thus create electrical potentials. In the end, every pumping action of the heart is preceded by such an electrical excitation.

But how can the electrocardiogram be explained?Starting from the pacemaker center of the heart, the sinus node, the excitation formation (depolarization) runs at a speed of about 1m/s in the direction of the heart muscle cells. Now, in simplified terms, one must imagine that when a heart muscle cell is excited, positively charged particles (cations) flow from the cell surface into the interior of the cell. In comparison to the still unexcited neighboring cell, the excited cell is now negatively charged on its surface.

This charge difference results in a so-called electric dipole. A dipole is understood to be two opposite poles of the same charge (e.g. +1 and -1), from which an electric field emanates. The excitation and thus also the electric field propagates in an ordered wave through the different structures of the heart.

Finally, the excitations of the individual heart muscle cells add up so that they can be detected by the sensitive electrodes on the body surface. The specific temporal sequence of the excitation (first the atria, then the ventricles, etc.) produces the typical wave and jagged pattern of an electrocardiogram.