Fast optical monitoring of microscopic excitation patterns in cardiac muscle

Many vital processes depend on the generation, changes, and conduction of cellular transmembrane potentials. Optical monitoring systems are well suited to detect such cellular electrical activities in networks of excitable cells and also tissues simultaneously at multiple sites. Here, an exceptionally fast array system (16 x 16 photodiodes, up to 4,000,000 samples per second, 12-bit resolution) for imaging voltage-sensitive dye fluorescence, permitted real time measurements of excitation patterns at a microscopic size scale (256 pixels within an area of 1.8–8 mm2), in rat cardiac muscle in vitro. Results emphasize a recent hypothesis for cardiac impulse conduction, based on cardiac structural complexities, that is contradictory to all continuous cable theory models.