VSD Imaging - arrhythmia

arrhythmia

Figure 1. Clockwise rotating spiral wave in canine epicardial muscle. White regions are maximally depolarized, black regions at resting potential. The spiral-shaped region of excitation rotates in time.

We work to find mechanistic explanations for the genesis and maintenance of cardiac arrhythmias. Cardiac arrhythmias are a major cause of death, particularly self-sustained arrhythmias like fibrillation. The excitation patterns underlying self-sustained arrhythmias are spiral waves (see Fig. 1) and their three-dimensional counterparts, scroll waves.

The dynamics of spiral waves and their interactions are complex. Typically, spiral waves only interact if their tips are close together, and they are then called multiarmed spirals. There are, however, also bound states with a large distance between the tips, as shown in Fig. 2. In this example, one spiral is rotating almost unaffected by the other while the other rotates around the first over time; we call such pairs of spirals master-slave pairs.

Even a single scroll wave is a complex object in itself. Fig. 3 shows a scroll wave and its organizing center, the filament, for a medium with twisted anisotropy. As a result of the anisotropy, the filament assumes a very particular shape that can be characterized as a geodesic in the metric defined by the fiber directions in the volume.

Figure 2. Simulated scroll wave in cardiac tissue. Yellow volume represents excited tissue; resting tissue is transparent. The green line marks the center of rotation, or filament, of the scroll wave. The dynamics of the scroll wave are significantly influenced by the fiber orientation of the tissue; the small figure in the lower left corner illustrates how the fibers are oriented in x-direction on the top surface closer to the y-direction at the bottom surface (in between the surfaces, the fiber rotation is linear).

Figure 3. Interaction of two spiral waves in a simulation. Thick white lines show the excitation waves, thin white lines show the tip trajectories. Arrows indicate the direction of interaction-induced drift.

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