High-resolution high-speed synchronous epifluorescence imaging of cardiac activation

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Abstract
An optical imaging technique with high spatial and temporal resolution was developed to record fractional changes in laser-induced epifluorescence associated with the cardiac transmembrane potential during and after the application of monophasic point stimuli. The technique takes advantage of the repeatability of the recorded events, and uses a synchronized laser strobing mechanism to overcome the speed limitation inherent to slow-scan charge-coupled device cameras, and achieves an effective frame rate of 500 frames/s at a spatial resolution of 100×100 pixels in a single frame with a pixel resolution of 75 μm. The signal-to-noise ratio can be improved with boxcar averaging. Patterns of virtual cathode and anode with distinctive regions of simultaneous depolarization and hyperpolarization during stimulation are demonstrated with stimuli applied to the resting myocardium of an isolated rabbit heart. The technique described in this article provides a powerful tool for investigating repeatable dynamics in the function of electrically active tissue.