ECG: the first step

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"cardiac vector"

Let's assume there is a "cardiac vector". The cardiac vector is directed to the area with increased electrical activity of the heart, namely the area the heart muscle is relatively thick.

As will be discussed further later, within one cardiac cycle, the "cardiac vector" appears and disappears 3 times, namely during atrial depolarization, during ventricular depolarization, and during ventricular repolarization. Each time the direction, size and duration differs. For now, let's concentrate on the cardiac vector during ventricular depolarization. The cardiac vector is basically directed to the area the heart muscle is relatively thick. Since the area the ventricle is relatively thick in a normal subject is located left-inferior posteriorly, the "cardiac vector during ventricular depolarization" is basically directed left-inferior posteriorly.

• Naturally, the "cardiac vector during ventricular depolarization" has three direction components (superior/inferior, left/right, anterior/posterior). Namely it is spacially three-dimensional.
• The meaning of "during ventricular depolarization": In the ventricle (and atriium as well), depolarization does not take place instantly, but rather it occures over a period. The approximately 0.1 second-long period, in which the ventricular cells depolarize in succession and cells in the plateau spread, will be described as the period "during ventricular depolarization" in this material.

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