Optical study on the generation of experimental arrhythmias with re-entry of the excitatory waves

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Multiple-site optical recordings of transmembrane voltage activity, using a voltage-sensitive dye and a multi-element photodiode array, were employed to monitor the tachycardia-like excitation in the rat atrium. Atrial preparations dissected from adult rat hearts were stained with a merocyanine-rhodanine dye (NK2761), and the action potentials were recorded simultaneously from many sites. We used a bathing medium containing 2,3-butanedione monoxime (20 mM) to reduce the contraction-related light scattering. The tachycardia-like excitation with a cycle length of about 250 - 450 ms was evoked either by a train of electrical stimuli (5-20 Hz/ 1-2 sec) or regular stimuli of 0.5-1 Hz applied with bipolar electrodes. The events lasted for various time periods (10 sec - over 10 min) and often terminated spontaneously. The spread of excitation was assessed optically, and we mapped the conduction patterns of the excitatory waves. These maps indicate that the excitatory waves often propagated in a quasi-circular pathway which often surrounded the ostium of the superior vena cava. However, several other patterns, such as "blocked areas" without anatomical obstacle, ectopic foci of pacemaking activity and more complex patterns with multiple wavefront, were also observed.