Multiple Recording during Electrically Induced Atrial Fibrillation.

• The mechanisms of atrial fibrillation and flutter have been subjects of continuous controversy. Fibrillation is a more complicated arrhythmia than flutter, and many previous analyses of flutter have been extended to fibrillation. Since the similarity of the mechanisms underlying these two arrhythmias has not been demonstrated, many current theories on the mechanism of fibrillation are therefore not necessarily reliable. Another weakness in the various theories concerning the origin of fibrillation and flutter stems from the possibility that the mechanisms initiating these conditions may be different from the mechanisms maintaining them, so that initiation and maintenance should be considered separately. For instance, proponents of the multiple re-entry and multifocal theories of fibrillation have encountered considerable difficulty in attempting to explain how fibrillation or flutter can spontaneously terminate. In a previous study of ventricular fibrillation ' unmistakable differences in the firing time of adjacent cells were revealed by recording with intracellular electrodes. In spite of this, no such information was obtained with extracellular electrodes, and activity recorded extracellularly did not appear an adequate indication of intracellular events. However, because the electrical activity during the initial and recovery stages of fibrillation was relatively regular, it appeared possible to study propagation of excitation during these stages with extracellular electrodes. Consequently,