Optical Imaging of the Heart

Abstract

Abstract-Optical techniques have revolutionized the investigation of cardiac cellular physiology and advanced our understanding of basic mechanisms of electrical activity, calcium homeostasis, and metabolism. Although optical methods are widely accepted and have been at the forefront of scientific discoveries, they have been primarily applied at cellular and subcellular levels and considerably less to whole heart organ physiology. Numerous technical difficulties had to be overcome to dynamically map physiological processes in intact hearts by optical methods. Problems of contraction artifacts, cellular heterogeneities, spatial and temporal resolution, limitations of surface images, depth-offield, and need for large fields of view (ranging from 2ϫ2 mm 2 to 3ϫ3 cm 2 ) have all led to the development of new devices and optical probes to monitor physiological parameters in intact hearts. This review aims to provide a critical overview of current approaches, their contributions to the field of cardiac electrophysiology, and future directions of various optical imaging modalities as applied to cardiac physiology at organ and tissue levels. Key Words: optical mapping Ⅲ fluorescent probes Ⅲ electrophysiology Ⅲ arrhythmia Ⅲ defibrillation M ammalian physiology has an ingrained hierarchy with molecular and cellular physiology at its base, followed by the interactions of large populations of cells and organ systems, and finally the integration of multiple organ functions of an entire animal. For the past 4 decades, cardiovascular physiology has been dominated by a "reductionist" approach, focusing on cellular mechanisms. Major strides have been accomplished in our understanding of cellular mechanisms, including metabolism, intracellular signaling, trafficking, ion channel structure, function, and expression. With a greater understanding of cellular mechanisms came the growing realization that organs such as the heart are composed of several types of interacting cells with significant and important heterogeneities of properties, cell-to-cell coupling, and function within each group. Thus, an understanding of molecular and cellular mechanisms must still be integrated to explain the more complex organ system while taking into account spatial and temporal heterogeneities of cell functions throughout the organ.Unfortunately, experimental methodologies available for studies at the organ level are not as abundant as at the cellular scale. Nonoptical imaging modalities, including positron emission tomography, magnetic resonance, and ultrasound imaging have only started to bridge molecular and organ physiology using novel contrast agents. 1 On the other hand, optical modes of imaging, in combination with parametersensitive probes have already demonstrated their ability to overcome the problem of spatiotemporal resolution in two dimensions for a wide range of applications from single molecular events to in vivo whole animal physiology.Fluorescence has been used to measure a wide range of physiological parameters in cells and tissues...

NADH Fluorescence Imaging of Isolated Biventricular Working Rabbit Hearts

“…It is especially useful in studies of cardiac arrhythmias, particularly those that use fluorescence imaging of transmembrane potential 20 . An advantage is that the entire epicardium of the isolated heart can be observed 21,22 .…”

Cell cultures as models of cardiac mechanoelectric feedback

“…Readouts of cellular calcium can also be obtained by optical mapping (Fast, 2005). Excellent reviews of optical mapping approaches on cardiac tissue have been published for intact tissue (Efimov et al, 2004) and cultured cell monolayers (Entcheva and Bien, 2006). Compared with microelectrode array measurements of cardiac electrical activity, optical mapping not only provides higher spatial resolution without recording artifacts which can arise from electrical stimulators, but can readily be integrated into a test system where different mechanical perturbations are applied to the cardiac tissue.…”

Reconstruction and Quantification of Diffusion Tensor Imaging-Derived Cardiac Fibre and Sheet Structure in Ventricular Regions used in Studies of Excitation Propagation

“…The fibre and sheet architecture throughout the ventricles could itself be a substrate for arrhythmias, including ventricular tachycardia and fibrillation, and sudden cardiac death, as has been suggested in both experimental [18,48,58,60] and theoretical [9,14,22] studies. Ventricular wedge preparations are widely used in the optical imaging of excitation during arrhythmias [21], but in order to correctly interpret the results from such wedge experiments, detailed descriptions of cardiac ventricular geometry and architecture will be required, along with an understanding of how this cardiac structure influences the propagation of excitation. Furthermore, fibre orientation can change during certain pathological conditions such as hypertrophy [25] and ischaemic heart disease [47,65], and so a complete understanding of such pathologies will require information about how cardiac geometry and architecture changes with disease.…”