Session S94.5

Use of Ultrasound Imaging to Map Propagating Action Potential Waves in the Heart

NF Otani, S Luther, R Singh*, RF Gilmour Jr

Cornell University
Ithaca, NY, USA

Patterns of reentrant action potential waves, often called spiral waves, are suspected to be responsible for both ventricular fibrillation and ventricular tachycardia in the heart. However, the three-dimensional spatial structure of these waves has never been clearly seen experimentally, and therefore theories describing the nonlinear dynamical properties of these waves have never been experimentally verified. The difficulty is that existing imaging modalities lack the necessary field of view and/or temporal or spatial resolution when applied to a non-repetitive phenomenon such as ventricular fibrillation. The objective of our study is to develop a new, ultrasound-based imaging modality that will allow visualization of these waves deep within cardiac tissue. In this paper, we describe our preliminary efforts to develop the necessary mathematical and computational tools required to convert the mechanical deformations seen in ultrasound images of the heart into the action potential induced stresses that caused them. The locations of these active stresses will then serve as markers for the locations of the action potentials. We have created two, related, fully three-dimensional finite element models for this purpose--one that calculates the tissue displacements given an active stress field, and one that calculates or estimates the active stresses given the subset of displacements we expect to see in 2-D or 3-D ultrasound images. Computations were performed in both the absence and presence of expected errors in the measurement of muscle fiber orientation (10% error in orientation angle). We find that the method can determine with 100% accuracy the cells that are and are not in regions of active stress for the 3-D, no-error case. The accuracy falls to 76% for the worst case (the case of 2-D data with fiber direction errors); however, even for this case, we find that the apparent motion of an active stress field representing plane wave action potential propagation is easily discernible when the results of the computation are viewed as a movie. We conclude that the new method shows promise when used with hypothetical 2-D or 3-D ultrasound data, and thus warrants continued computational and experimental study.

(Abstract Control Number: 227)