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Figure 12-1

Mean vector through the partially depolarized ventricles.

Figure 12-1

Mean vector through the partially depolarized ventricles.

Figure 12-3
Figure 12-2

Vectors drawn to represent potentials for several different hearts, and the "axis" of the potential (expressed in degrees) for each heart.

12-2. From this zero reference point, the scale of vectors rotates clockwise: when the vector extends from above and straight downward, it has a direction of +90 degrees; when it extends from the person's left to right, it has a direction of +180 degrees; and when it extends straight upward, it has a direction of -90 (or +270) degrees.

In a normal heart, the average direction of the vector during spread of the depolarization wave through the ventricles, called the mean QRS vector, is about +59 degrees, which is shown by vector A drawn

Axes of the three bipolar and three unipolar leads.

through the center of Figure 12-2 in the +59-degree direction. This means that during most of the depolarization wave, the apex of the heart remains positive with respect to the base of the heart, as discussed later in the chapter.

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Essentials of Human Physiology

Essentials of Human Physiology

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