Photon scattering effects in optical mapping of propagation and arrhythmogenesis in the heart

Abstract

Background: Optical mapping is a widely used experimental tool providing high-resolution recordings of cardiac electrical activity. However, the technique is limited by signal distortion due to photon scattering in the tissue. Computational models of the fluorescence recording are capable of assessing these distortion effects, providing important insight to assist experimental data interpretation.

Methods: We present results from a new panoramic optical mapping model, which is used to assess distortion in ventricular optical mapping signals during pacing and arrhythmogenesis arising from 3-dimensional photon scattering.

Results/conclusions: We demonstrate that accurate consideration of wavefront propagation within the complex ventricular structure, along with accurate representation of photon scattering in 3 dimensions, is essential to faithfully assess distortion effects arising during optical mapping. In this article, examined effects include (1) the specific morphology of the optical action potential upstroke during pacing and (2) the shift in the location of epicardial phase singularities obtained from fluorescent maps.

FIGURE 1

Wavefront propagation in the rabbit ventricular bidomain model following apical and endocardial stimulation. A Epicardial optical V_opt (left) and transmembrane V_m (center) distributions as well as an apex-base cross section depicting intramural Vm distribution (right), for apical (top, 50ms after pacing stimulus) and endocardial (bottom, 6ms after pacing stimulus) stimulation. B Highlighted regions show local wavefront propagation direction, depicted by black arrows. The optical detection site on the epicardium is shown by the solid circle, with the approximate scattering volume depicted by the dashed partial-circle. C Action potential traces for V_m and V_opt from epicardial recording sites whose locations are shown by white crosses in the left-hand images of Figure 1A. Action potential upstrokes are presented in D.

FIGURE 2

A (Left) Epicardial distribution of V_m (top) and V_opt (bottom) during an episode of arrhythmia induction with an electric shock (snap-shots at 39ms post-shock). White curved arrows indicate the direction of rotation in the figure-of-eight reentrant pattern. Solid black circles indicate the location of the epicardial phase singularity on the epicardial surface. Dashed black arrows show the relative shift in these locations between V_m and V_opt maps. (Right) Transmural apex-base (top) and anterior-posterior (bottom) cross-sections of V_m distribution depicting the location of the intramural filaments (shown in black). Highlighted in-sets show schematic diagrams of the complex orientation of the filament in the upper LV wall. B Examples of filaments with normal (top) and complex (bottom) orientations relative to the epicardial surface, and the scattering volume associated with the epicardial recording site.