New Strategies for Studying Passive and Active Properties of Cardiac Tissue Open Access
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Cardiac muscle works as a syncytium where both electrical and mechanical elements come into play to orchestrate its highly synchronized function. Electrical properties of cardiac tissue can be classified as passive or active. These properties determine the propagation sequence and speed of electrical activation. My research has focused on developing new engineering tools to advance the study of these properties on the level of cells and that of the whole heart. To study the passive properties of the heart, impedance measurements were conducted in cell monolayers. Changes in impedance magnitudes due to perturbation of the extracellular space and cell-to-cell coupling were studied using commercially available microelectrode arrays. The results suggest that this method is useful in determining how current is redistributed between the intra- and extracellular domains.Although studies of the electrophysiology of arrhythmias over the last decade have provided a great amount of details about the cellular mechanisms, the link between changes in metabolism and arrhythmias remains poorly understood. Previous studies to understand this link on the level of the whole heart used non-beating Langendorff perfused hearts. A limitation of this model is that the heart is not contracting within the context of physiologic preload and afterload. To overcome this limitation, a biventricular working heart perfusion system was developed for dual imaging studies. This system mimics more closely in-vivo scenarios. The system was used for simultaneous imaging of NADH fluorescence and optical transmembrane potentials. One major limitation of this mode of imaging in beating hearts is the effect of motion on fluorescence signals, also called the motion artifact. To overcome this limitation, software tools were developed to reduce motion artifact in NADH imaging by triggering the cameras for acquisition only during the diastolic phase. In addition, we have developed a post acquisition processing approach of fluoresced action potentials based on wavelet multiresolution analysis. The approach streamlines the processing steps. We show how fluoresced action potentials can be decomposed and reconstructed to denoise the signals, reduce motion artifact and remove any baseline drift.