Body surface distribution of electrical potential during atrial depolarization and repolarization

Limited information is available documenting body surface isopotential distributions during atrial excitation and recovery. To expand the current data base, body surface isopotential maps from 40 normal subjects were examined. Data were acquired at a gain of 10,000 and isopotential distributions constructed at 2-msec intervals from the onset of the P wave to the onset of the QRS complex. During the initial half of the P wave, a left midprecordial maximum dominated the distribution. Negative potentials existed over the upper back. Subsequently, the maximum migrated to the left; negative potentials moved into precordial areas. Near the end of the P wave, the maximum shifted to the left back as a minimum evolved over the midprecordium. This minimum increased in intensity and remained stationary throughout the PR segment. These patterns are consistent with previously reported epicardial records from canine preparations documenting initial right and then left atrial activation, and repolarization beginning before the end of excitation and enveloping much of the posterior atrial epicardium with low-level positive potential. All distributions had but a single maximum and/or minimum, consistent with a single dipole equivalent cardiac generator.