Maps of optical action potentials and NADH fluorescence in intact working hearts

Voltage-sensitive dyes were used to stain intact perfused hearts and to simultaneously measure optical action potentials (APs) from 124 sites on the epicardium. Patterns of electrical depolarization (activation) and repolarization (recovery) along the surface of the heart were determined from the upstrokes and repolarization phases of optical APs. Standard surface extracellular techniques can detect electrical activation but not the recovery or the duration of APs. The optical recordings were previously shown to be equivalent to intracellular electrode measurements (Salama and Morad, Science Wash. DC 191: 485-487, 1976) and now reveal that AP durations are heterogeneous throughout the epicardium, with durations increasing from the base to the apex of the ventricles. In hearts beating under normal sinus rhythm, the direction and conduction velocity of the activation waves could be altered by electrical stimulation. The normal heterogeneities in AP durations became more pronounced in the presence of the Ca2+-entry blocker, verapamil. The local metabolic state of the tissue was also monitored optically through its intrinsic NADH fluorescence measured from 124 separate regions on the heart. The time course and extent of metabolic injury caused by general anoxia or by a local ischemia induced by a coronary ligation was monitored through maps of NADH fluorescence. The present technique makes it possible to correlate changes in the metabolic state of the muscle with detailed changes in patterns of electrical activity and thus provides a powerful new tool to study fundamental aspects of normal and abnormal cardiac rhythm.