Probing Field-Induced Tissue Polarization Using Transillumination Fluorescent Imaging

Abstract

Despite major successes of biophysical theories in predicting the effects of electrical shocks within the heart, recent optical mapping studies have revealed two major discrepancies between theory and experiment: 1), the presence of negative bulk polarization recorded during strong shocks; and 2), the unexpectedly small surface polarization under shock electrodes. There is little consensus as to whether these differences result from deficiencies of experimental techniques, artifacts of tissue damage, or deficiencies of existing theories. Here, we take advantage of recently developed near-infrared voltage-sensitive dyes and transillumination optical imaging to perform, for the first time that we know of, noninvasive probing of field effects deep inside the intact ventricular wall. This technique removes some of the limitations encountered in previous experimental studies. We explicitly demonstrate that deep inside intact myocardial tissue preparations, strong electrical shocks do produce considerable negative bulk polarization previously inferred from surface recordings. We also demonstrate that near-threshold diastolic field stimulation produces activation of deep myocardial layers 2-6 mm away from the cathodal surface, contrary to theory. Using bidomain simulations we explore factors that may improve the agreement between theory and experiment. We show that the inclusion of negative asymmetric current can qualitatively explain negative bulk polarization in a discontinuous bidomain model.

A New Optrode Design for Intramural Optical Recordings

“…This is consistent with previous optical measurements of shock-induced polarizations on the cut transmural surface in left ventricular wedge preparations [1] and measurements obtained noninvasively in isolated right ventricular preparations [10]. Such Δ V m could represent secondary sources of polarization formed by microscopic discontinuities in the tissue structure.…”

Cardiac Response to Low-Energy Field Pacing Challenges the Standard Theory of Defibrillation

“…24, 25 However, other experiments at near-threshold field strengths reported the lack of activation on the myocardial surface under the cathode, which suggested that surface polarization was indeed very small and could not be explained by existing models. 11, 26 Nevertheless, these findings failed to attract attention to this significant inconsistency. A major criticism of previous experimental reports questioning the validity of the existing models 27 was that the observations were likely experimental artifacts caused by tissue damage.…”

“…The preparations were perfused through respective coronary arteries, mounted between mesh field electrodes, and stained with the near-infrared dye DI-4-ANBDQBS (40 μM) as described previously. 11 Figure 1a shows a schematic of the experimental setup. A pulsed electric field was applied transmurally from planar mesh electrodes, sufficiently sparse for passage of both illumination light and voltage-sensitive fluorescence signals.…”

Toward microendoscopy-inspired cardiac optogeneticsin vivo: technical overview and perspective

“…Additionally, recorded signals at larger depths can become distorted, as fluorescence imaging is depth integrated for two-dimensional imaging techniques such as optical mapping, making it hard to understand the threedimensional (3-D) wave propagation in whole hearts. Larger penetration depths and improved signal qualities have been demonstrated in whole hearts 30,[32][33][34] and heart slices 27,[37][38][39][40] using near-infrared voltage-sensitive dyes; however, imaging depth still remains limited. Thus, optical recordings of important features of the conduction system, such as the PS lying close to the endocardial surface, 41 have remained unexplored in the intact heart due to the inadequacies of current imaging methods.…”

“…High-resolution CCD cameras and EMCCD cameras have been popular for use in optical mapping [5][6][7][30][31][32][33][34][37][38][39][40]127,128,144 and microendoscopy due to their high-spatiotemporal resolution. EMCCD cameras take advantage of avalanche processes to perform the on-chip electron multiplication to enhance SNRs, have higher frame rates, and improved quantum efficiency.…”