In ventricular fibrillation, the muscle cells of the heart’s two large, lower chambers (the ventricles) lose their synchronization; instead of coordinated pumping action, the cells twitch chaotically. Without immediate medical attention, the condition leads to sudden death. Fibrillation has been connected to the formation of vortex-like spiral waves of electrical activity (see the Quick Study by Andrea Welsh, Edwin Greco, and Flavio Fenton, Physics Today, February 2017, page 78, and the articles by Leon Glass, Physics Today, August 1996, page 40, and by Alain Karma and Robert Gilmour, March 2007, page 51). Within the heart muscle, spiral waves extend into a three-dimensional analogue called scroll waves and rotate around a filament-like core. But the filaments need not be straight: They can bend, twist, and tangle. Until now, however, the filaments could not be visualized, only simulated. Using high-speed, 4D ultrasound, Jan Christoph of the Max Planck Institute for Dynamics and Self-Organization and colleagues have now observed the dynamics of mechanical filaments’ 3D structures inside an in vitro animal heart experiencing cardiac arrhythmias. The figure shows an example of the phase of two counterrotating mechanical waves recorded in the left ventricular wall, viewed from the side (main view) and top (inset). The waves encircle a U-shaped filament that extends from the surface (red points) into the heart and back. Such mechanical filaments align closely with the electrical vortex cores seen with fluorescence imaging. Moreover, the mechanical filaments could be tracked as they drifted, twisted, and interacted; they functioned as fingerprints of electrical activity, revealing the topological organization of the fibrillation in the heart wall and offering insights into the mutual coupling between mechanical and electrical waves during cardiac arrhythmias. (J. Christoph et al., Nature 555, 667, 2018.)
