Optical Mapping Of Cardiac Arrhythmias

The concept of mapping rhythmic activation of the heart dates back to the beginning of last century, with initial descriptions of reentry in turtle hearts1, to the first systematic mapping of sinus rhythm and then atrial flutter by Lewis et al2. Barker et al3 were the first to map the human heart. Initial mapping was primarily performed using single probes to record activation in different regions of the heart. The 1960’s and 70’s saw the development of computerized mapping of the human heart, e.g. in the cure of Wolf-Parkinson-White syndrome as well as in the study of Langendorff preparations4. In fact, most of the recent advances in cardiac mapping have focused on improvements in multisite recordings within the heart, with the ability to simultaneous record electrical activation from several hundreds of sites having contributed significantly to our understanding of atrial and ventricular arrhythmias. Despite these recent advances, multisite contact mapping suffers from several limitations, including the technical problems associated with amplification, gains, sampling rates, signal-to-noise ratio, and the inability to see signals during high-voltage shocks. In addition, an intrinsic limitation of current mapping techniques is their inability to provide information about repolarization characteristics of electrically active cells, thereby limiting our ability to study entire action potentials. In fact, intracellular microelectrode recordings are still considered the gold standard for the study of action potential characteristics in whole tissue. Microelectrode techniques are limited however, by an inability to record action potentials from several sites simultaneously, thereby precluding their use in high-density activation mapping. In part due to the above-mentioned limitations, the last few years have seen the development and use of voltage-sensitive dyes as a means to map not only activation, but repolarization as well. Voltage-sensitive dyes, when excited, provide an optical signal that mimics an action potential and thus allows the visualization of both activation and recovery processes in any region under view. This allows one to precisely evaluate the propagation of a wave of excitation and to measure its wavelength visually. Optical mapping techniques use imaging devices such as a photodiode array or a charge-coupled device video camera with the heart being illuminated and either continuously or spatially scanned. The basis for these techniques is the use of voltage-sensitive dyes that bind to or interact with cell membranes