Page 142 - YORAM RUDY BOOK FINAL

P. 142
similar to those of the earlier study 286 . There were no indications of scar substrate, prolonged

repolarization or steep repolarization gradients. ARIs were longer in female compare to male sub-
jects (261 vs. 229 ms, respectively). Peak strain was reached at about 430 ms after QRS onset. An
animation of electromechanical sequence is provided in Movie 3 (https://youtu.be/OOE9ti-PMzw).

5.4 Atrial Fibrillation (AF) 279

The substrate for AF is dynamic, with AF itself inducing remodeling and substrate modi-
fication that promote AF (AF begets AF). 290 The remodeling process includes electrophysiologic

changes at the ion channel and cellular scales, resulting in AP shortening, a modification that
promotes reentry. 291 Structural remodeling, in particular interstitial fibrosis, can lead to break-up
and fragmentation of wave fronts and to the formation of conduction block. Abnormal calcium
cycling in remodeled atrial cells can result in focal ectopic activity in AF. 291 As remodeling

progresses, these processes interact to form a complex substrate that can support a complex
activation pattern in AF.

An ECGI study in diverse population of 26 AF patients 279 (including paroxysmal, persistent,

and long-standing persistent AF) demonstrated variable activation patterns. The most common
epicardial pattern during AF consisted of multiple wavelets together with activity from focal sites
near the pulmonary veins. As a general principle, complexity of the activation pattern (defined in
terms of number of wavelets and focal sites) increased with AF duration (implying more

progressed remodeling). Examples of this principle are provided in Figures 5.7 and 5.8.

Figure 5.7 shows epicardial activation pattern of paroxysmal nonsustained AF in a young
patient with a structurally normal heart. AF was induced during an electrophysiology (EP)

study. The activation pattern is relatively simple. It is a single rotor, with a broad wave front that
involves both atria and rotates in the counter-clockwise direction. In comparison, the pattern
of long-standing persistent AF (Figure 5.8) is of much greater complexity. There are multiple
wavelets, characterized by high degree of wave front curvature and wave breaks. Focal sites are

present near pulmonary veins. Figure 5.9 shows the spectrum of complexity of AF. There are
statistical differences in the number of wavelets and focal sources when paroxysmal, persistent,
and long-standing persistent AF are compared. The observation that paroxysmal AF has less
complex wavelets and fewer focal mechanisms helps to explain the greater success of catheter

ablation in treating paroxysmal AF. Movie 4 (https://youtu.be/bgaf8-0dCBk) and Movie 5 (https://
youtu.be/Zv8onx5q0Ek) show animated activation for paroxysmal AF emanating from pulmonary
veins. Movie 6 (https://youtu.be/YECbK_1yOjw) shows the complex, multiple wavelets pattern in
long-standing persistent AF.