ATTENTION is being increasingly focused IA, on the electrical events of atrial depolarization in diagnostic and experimental cardiology. Abildskovl2 has emphasized the need for further study of atrial forces in the electrocardiogram, and reports have appeared of the use of spatial vectorcardiograms for this purpose.Studies by Jouve and associates,3 and Duchosal and Sulzer4 in 1949 were the initial detailed descriptions of atrial forces in vectorcardiograms. Sano and associates,5 utilizing the method of electrical dissection described by Briller and co-workers6 reported studies of normal and abnormal patients; other authors have studied small groups of patients.7 " Scheuer and co-workers'2 recently utilized the cube system of electrode placement in the study of 128 patients, 35 of whom were normal adults and children. Mean Calibrated stationary vector loops as well as timed tracings were recorded from the oscilloscopic screen with a camera, utilizing a moving 70-mm photographic paper strip, in the frontal, horizontal, and sagittal planes (fig 2). The cube system of electrode placement was used, and tracings were taken at normal gain, two times normal gain, and four times normal gain. In addition, the orthogonal leads making up the vectorcardiogram in these planes were recorded at the same gains. Twelve or thirteen-lead electrocardiograms were made on the same day. With the timed vectorcardiographic technique, P, QRS, and T loops are separated like the components of the electrocardiogram are, and may be analyzed independently for magnitude and direction (fig 2).One hundred persons between the ages of 3 and 62 years were studied. Findings in chest x-rays, electrocardiograms, and physical examinations were within normal limits for all, and there was no overt evidence of heart disease. Thirty-one subjects were between the ages of 3 and 15 years; 69 were between 16 and 66 years.The P vectors of the electrocardiograms and vectorcardiograms were analyzed for magnitude and direction in the following manner. The P intervals on the timed vectorcardiographic records (VCG) were divided into two divisions; the first half was taken to represent mainly right atrial depolarization and the second half of the 577 by guest on May 11, 2018 http://circ.ahajournals.org/ Downloaded from