The role of photon scattering in voltage-calcium fluorescent recordings of ventricular fibrillation
Bishop MJ., Rowley A., Rodriguez B., Plank G., Gavaghan DJ., Bub G.
Recent optical mapping studies of cardiac tissue suggest that membrane voltage (V m) and intracellular calcium concentrations (Ca) become dissociated during ventricular fibrillation (VF), generating a proarrhythmic substrate. However, experimental methods used in these studies may accentuate measured dissociation due to differences in fluorescent emission wavelengths of optical voltage/calcium (V opt/Ca opt) signals. Here, we simulate dual voltage-calcium optical mapping experiments using a monodomain-Luo-Rudy ventricular-tissue model coupled to a photon-diffusion model. Dissociation of both electrical, V m/Ca, and optical, V opt/Ca opt, signals is quantified by calculating mutual information (MI) for VF and rapid pacing protocols. We find that photon scattering decreases MI of V opt/Ca opt signals by 23% compared to unscattered V m/Ca signals during VF. Scattering effects are amplified by increasing wavelength separation between fluorescent voltage/calcium signals and respective measurement-location misalignment. In contrast, photon scattering does not affect MI during rapid pacing, but high calcium dye affinity can decrease MI by attenuating alternans in Ca opt but not in V opt. We conclude that some dissociation exists between voltage and calcium at the cellular level during VF, but MI differences are amplified by current optical mapping methods. © 2011 Biophysical Society.