Optical mapping of the spread of excitation in the isolated rat atrium during tachycardia-like excitation.

Multiple-site optical recording of membrane potential activity, using the voltage-sensitive merocyanine-rhodanine dye NK2761 and a multiple-element photodiode array, was employed to monitor action potentials in an isolated rat atrial preparation. The events of tachycardia-like excitation (TE) were evoked by electrical stimulation. The conduction pattern of excitation was assessed optically by timing the feet of optical action potentials, then maps of excitation spread patterns were made. The excitatory waves often rotated around the blocked area including the ostium of the superior vena cava. Other patterns, such as reentry without anatomical obstacles, ectopic pacemaker and more complex patterns, were sometimes observed. Optical mapping during the initiation phase of TE indicated that the decrease of the conduction velocity and the appearance of blocked areas contributed the establishment of TE. On the basis of the characteristics of TE, it is suggested that TE is a metastable state of atrial rhythm. TE appears to be analogous to atrial flutter.