The role of photon scattering in optical signal distortion during arrhythmia and defibrillation

Optical mapping of arrhythmias and defibrillation provides important insights; however, a limitation of the technique is signal distortion due to photon scattering. The goal of this experimental/simulation study is to investigate the role of threedimensional photon scattering in optical signal distortion during ventricular tachycardia (VT) and defibrillation. A three-dimensional realistic bidomain rabbit ventricular model was combined with a model of photon transport. Shocks were applied via external electrodes to induce sustained VT, and transmembrane potentials (V_m) were compared with synthesized optical signals (V_opt). Fluorescent recordings were conducted in isolated rabbit hearts to validate simulation results. Results demonstrate that shockinduced membrane polarization magnitude is smaller in V_opt and in experimental signals as compared to V_m. This is due to transduction of potentials from weakly polarized midmyocardium to the epicardium. During shock-induced reentry and in sustained VT, photon scattering, combined with complex wavefront dynamics, results in optical action potentials near a filament exhibiting i), elevated resting potential, ii), reduced amplitude relative to pacing, and iii), dual-humped morphologies. A shift of up to 4 mm in the phase singularity location was observed in V_opt maps when compared to V_m. This combined experimental/simulation study provides an interpretation of optical recordings during VT and defibrillation.