Electrical Potential Distribution Surrounding the Atria during Depolarization and Repolarization in the Dog

The potential distribution at the atrial surface during depolarization and repolarization was studied in intact dogs. A preparation was developed by implanting 30 to 40 miniature electrodes permanently on each atrium to record unipolar electrograms in the intact animal. Heart block was created to dissociate atrial and ventricular activity. The electrograms were recorded on magnetic tape and atrial isopotential heart maps produced with the use of a digital computer. The changing potential distribution during excitation indicated the early presence of multiple wave fronts which were related primarily to the crista terminalis, Bachmann's bundle, and a special bundle to the base of the right appendage. The interatrial septum provided a conducting bridge which had an important influence of global atrial excitation, depending on the site of impulse formation. Colliding excitation wave fronts were quite prominent. During terminal atrial excitation, repolarization maxima were present simultaneously with depolarization maxima. Repolarization was characterized by a changing potential distribution which followed the same general pattern as excitation spread; and, furthermore, the earliest areas of excitation were associated with a repolarization maximum and terminal areas of excitation were associated with repolarization minima.