Computer simulation of cardiac propagation: effects of fiber rotation, intramural conductivity, and optical mapping

Cardiac propagation characteristics such as anisotropy ratio and conduction velocities are often determined experimentally from epicardial measurements. We hypothesize that these measurements have inaccuracies due to intramural fiber rotation and transmural electrotonic interactions. We also hypothesize that optical mapping (OM) recordings compound the error, due to contributions from deeper layers. In this study, we studied propagation in a three-dimensional computer model of a slab of tissue with varying thickness and a 120° fiber rotation. Simulation results were further processed to reconstruct OM signals. As expected, simulation results demonstrated that the direction of wave propagation on the epicardial surface is not aligned with the epicardial fiber orientation. This angle difference was most pronounced for thin tissue, and decreased with decreasing intramural conductivity and increasing tissue thickness. This difference also increased with time elapsed poststimulus, as the contribution from deeper layers increased. Observations were confirmed experimentally with OM measurements from isolated rat hearts. Simulations also predicted that OM causes an additional error in measurements due to activity in deeper layers being less aligned. Several alternative approaches for the estimation of fiber orientation and anisotropy ratio were evaluated. Those based on conduction velocity measurements yielded the most accurate estimates when applied to noise-free simulated data.