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.