Body surface maps of ectopic P waves originating in the left atrium in the dog.

Body surface maps of the P wave in dogs stimulated at various sites on the atria were prepared to find diagnostic signs to detect the origin of left atrial rhythm. Body surface electrograms from 87 points on the thorax and 8-12 points on the epicardial surface of both atria were simultaneously recorded. The body surface P maps disclosed characteristic findings according to whether the site of the stimulation was at the lower right atrium (RA) or the upper, middle, or lower left atrium (LA). In the LA rhythm, the maximum of the P maps moves from the left to the right chest during the later phase of atrial excitation, while it goes from the right to the left in the sinus or the RA rhythm. In the P maps of the rhythm originating in the upper LA, the minimum always stays at a position on the chest above the location of the maximum, while the negative potential areas are above the positive ones. The maps of the middle LA rhythm show that the maximum and the minimum are located horizontally to each other on the chest. The positive and negative areas cover both sides of the chest, separated by zero lines running vertically. In the low LA rhythm, the maximum is always located at a position on the chest above the minimum, and the positive areas are above the negative ones. These results indicate that mapping of the body surface P waves is a valuable method for diagnosing left atrial rhythm and for detecting the approximate location of its origin.