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Normal Human Ventricular Activation

Figure 5.3. The intramural ventricular
activation sequence (isochrones) in an
isolated undiseased human heart. The
isochrones are parallel to the blood
cavities and propagation of the broad
wave front is from endocardium to
epicardium. The arrow points to the RV
breakthrough. From Durrer et. al. [287]
with permission from Wolters Kluwers
Health, Inc.

Epicardial Potentials during Normal Ventricular Activation

The activation front can be represented electrically as a layer of dipoles pointing in the
direction of propagation. Prior to epicardial breakthrough, the wave front approaches the

epicardium (cartoon in Figure 5.4A, right panel), generating a positive potential region (red + sign
in the cartoon). Upon epicardial breakthrough, the dipoles diverge, generating negative potential
at the breakthrough site (cartoon in Figure 5.4B, right panel; blue – sign). The earliest epicardial

breakthrough occurs in the RV anterior – paraseptal region and is termed RV breakthrough.
Figures 5.4A and 5.4B, left panels, show ECGI potential maps of the RV breakthrough sequence
in one subject. At 13 ms after QRS onset (Figure 5.4A) the RV epicardium is covered with positive
potentials (red + sign). Upon breakthrough at 18 ms (Figure 5.4B) the positive region is invaded by
a local negative potential minimum (blue – sign) at the breakthrough site. This RV breakthrough

sequence was mapped by ECGI in all normal hearts (seven in an earlier study 286 and additional
twenty in a later study 289 ). In the earlier study, the earliest RV breakthrough occurred at 18 ms and
latest at 24 ms; the average RV breakthrough time was 20.7 ms from QRS onset.

After the RV breakthrough, additional breakthrough minima appear on the RV and LV
epicardium (Figure 5.4C, left). Breakthroughs occur in the left anterior paraseptal region (site 2),