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Normal Human Ventricular Activation
Noninvasive ECGI Isochrones

Measured Isochrones

Figure 5.5. Ventricular isochrones of normal activation. Top: ECGI data from three subjects.
Numbers indicate locations of early activation sites. LAD: left anterior descending coronary
artery. RVOT: right ventricular outflow tract. Adapted from Ramanathan et. al. [286] courtesy of
Proceedings of the National Academy of Sciences (PNAS). Bottom: directly recorded isochrones in
isolated undiseased human hearts. Adapted from Durrer et. al. [287] with permission from Wolters
Kluwer Health, Inc.

Normal Ventricular Repolarization

In contrast to the dynamic potential patterns during activation, epicardial potential patterns
during repolarization are relatively static (Figure 5.6A, compare the top and bottom panels).

These characteristics reflect the different underlying processes of activation and repolarization.
The activation process involves a fast changing, propagating wave front. Repolarization, on the
other hand, is of large spatial extent; it engulfs the ventricles and does not involve a dynamically
propagating wave front. Figure 5.6C shows recovery times (RT) isochrones (recovery time

contains the local activation time; it is the sum of local activation time plus the duration to
complete local repolarization). Figure 5.6D shows activation – recovery intervals (ARI), where
activation times are subtracted from the recovery times. AS such, ARI reflects the duration of
local activity and is a surrogate for local action potential duration (APD) 263, 264 . ARI reflects local

repolarization only, without the contribution of the activation sequence. Note the striking similarity
between the RT map (panel C) and the ARI map (panel D). This implies that in the normal heart
during sinus rhythm the effect of the activation sequence on repolarization is very small and
repolarization is determined mostly by local repolarization properties (local APD). This is so because

normal activation via the Purkinje system is a fast process and spatial differences in activation
times are much smaller than in repolarization times. Consequently, to a good approximation,