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Figure 3.25. Effect of curvature on propagation. Experiments in a perfused rabbit ventricular
epicardial layer. Left: point stimulation produces a convex excitation front. Right: line stimula-
tion produces an almost flat front. Numbers show activation times (msec); isochrones are 3 msec
apart. Average longitudinal velocity of curved wave is 13% slower than that of flat wave. From Knis-
ley and Hill [241]. © 1995 IEEE. Reprinted, with permission, from S. B. Knisley and B. C. Hill, “Effects
of bipolar point and line stimulation in anisotropic rabbit epicardium: assessment of the critical
radius of curvature for longitudinal block,” in IEEE Transactions on Biomedical Engineering, vol.
42, no. 10, pp. 957-966, Oct. 1995, doi: 10.1109/10.464369.

It should be noted that the theoretical principles above are based on observations in ho-

mogeneous and uniform tissue. In the heart, heterogeneities of membrane properties and tissue
structure affect spiral wave characteristics. In particular, spatial gradients of membrane excitabili-
ty or repolarization can cause the spiral wave to drift, while structural Inhomogeneities can cause
anchoring of the spiral wave, rendering it stationary.