Probing Field-Induced Tissue Polarization Using Transillumination Fluorescent Imaging

Department of Pharmacology, State University of New York Upstate Medical University, Syracuse, New York, NY, USA.
Biophysical Journal (Impact Factor: 3.97). 10/2010; 99(7):2058-66. DOI: 10.1016/j.bpj.2010.07.057
Source: PubMed


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.

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Available from: Christian W Zemlin,
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    • "(b) Corresponding activation map obtained directly from the raw optical signals over one activation cycle (courtesy of R. Dubois) (Plank et al. 2008). Another paradoxical observation was the anomalously low surface polarization, and the absence of cathodal activation during near-threshold field stimuli (Zemlin et al. 2006; Caldwell et al. 2010). These findings also challenge the conventional bidomain model and await a mechanistic explanation. "
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