An ultrasound-based imaging method for visualizing patterns of action potential propagation in the heart

An understanding of the patterns and characteristics of action potential propagation in the heart is crucial for the development of advanced methods for treating dangerous and lethal cardiac rhythm disorders. Unfortunately, visualization of these action potentials with existing methods, especially deep with the walls of the heart, has been problematic. We have been developing a new method whereby these patterns can be seen. The method calculates the locations of action potentials from the deformations they produce, as recorded in ultrasound images. An important step in developing an appropriate algorithm is to determine whether there exists a local function of the mechanical strains that marks the locations of the action potentials, or whether a fully three-dimensional inverse calculation must be performed. To study this question, we have examined the properties of deformations produced by action potentials propagating in: a 1-D fiber, an axisymmetric shell model of the heart and a 3-D model of a cube of cardiac tissue. The models and theory combine to show that incremental strain is a good marker of the action potentials wavefronts when the system and wave are essentially one-dimensional in nature. In contrast, higher dimensional structure in either the wave or the medium in which it travels produces an incremental strain field that extends out away from the wave. We conclude that determination of action potential locations will likely require a more complex calculation when wave propagation is not fundamentally one-dimensional.