Page 108 - YORAM RUDY BOOK FINAL

P. 108

Figure 3.24. Temporal oscillations in APD (A), diastolic interval (DI) (B), and CL (C) from a single
site in a 154-cell reentry pathway. Qusi-periodic temporal behavior is observed. Maximum degree
of CL oscillations (indicated by arrow in C) occurs where oscillations in APD and DI are at a
minimum (arrows, A and B, respectively). From Hund et. al. [239] coutesy of the American
Physiological Society. Experimental data from Frame and Simson [236] with permission from
Wolters Kluwers Health, Inc.

As stated above, the velocity of a rotating wave depends on its (convex) curvature. Because
the curvature increases from the periphery to the center of a rotating wave, the corresponding
velocity decreases and a spiral shape is formed. In the core of the rotating wave, the tip of the
spiral moves along a trajectory which depends on the excitability (degree of refractoriness) of the
surrounding tissue. For a very short excitation wavelength λ relative to the length of the tip

trajectory, head-tail interaction is minimal and the tip rotates around a stable circular core of
nonexcited (but intrinsically excitable) tissue. For a rotor trajectory similar in length to λ, an
unstable meandering trajectory is formed. For a long λ, the movement is along a stable

“Z-shaped” line. 243 This third condition holds in cardiac tissue at a normal state of excitability.
Indeed, Z-shaped lines of block were mapped in many experimental studies.