The Electrical Axis of the Heart

Now, take the sum of all of the millions of vectors found in the ventricles of the heart. We’ll wait a few minutes while you add them up. That final vector, after all of the addition, subtraction, and direction changes, is known as the electrical axis of the ventricle (Figure 4-4). In the same way, each wave and segment has its own respective vector. There is a P-wave vector, a T-wave vector, an ST-segment vector, and a QRS vector. The ECG is a measurement of these vectors as they pass under an electrode. That’s it! It is an electronic representation of the electrical movement of the main vectors passing under an electrode, or a lead. In the next pages, we will discuss only the QRS vector.

An illustration shows that after the addition of all ventricular vectors in the heart, the resulting vector is the electrical axis pointing downward and to the left.

Figure 4-4 Sum of all ventricular vectors = electrical axis.

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