The second vector: the ventricular (interventricular) septum Note that the first vector in Figure 7 is not discussed here as it belongs to atrial activity. Inspired by MacFarlane et al (Springer, Comprehensive Electrocardiology, 2010). V1 and V5 are exploring electrodes and the reference is composed of the average of the electrodes placed on the limbs (this reference is called Wilson’s central terminal). The heart’s main electrical vectors seen from the horizontal plane. Study Figure 7 carefully, as it illustrates how the P-wave and QRS complex are generated by the electrical vectors. Figure 7 illustrates the vectors in the horizontal plane. It is fundamental to understand the genesis of these waves and although it has been discussed previously a brief rehearsal is warranted. Electrical vectors that engender the QRS complexĭepolarization of the ventricles generate three large vectors, which explains why the QRS complex is composed of three waves. The positive areas are yellow and the negative areas are green. Approximations of the net direction of the QRS-complex. Panel B in Figure 6 shows a net negative QRS complex, because the negative areas are greater than the positive area. These calculations are approximated simply by eyeballing. The QRS complex is net positive if the sum of the positive areas (above baseline) exceeds that of the negative areas (below baseline). The QRS complex can be classified as net positive or net negative, referring to its net direction.
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