An Approximate Derivation for Stereoscopic Vectorcardiograins with the Equilateral Tetrahedron

I N THE study of spatial vectorcardiography in this laboratory it has been the practice to construct wire models of the spatial vectorcardiogram from its frontal and sagittal projections which are presented on two cathode-ray tubes.'' 2 These three-dimensional models seemed necessary to facilitate visualization of the spatial characteristics of the vectorcardiogram, but their construction entailed considerable time and care. To avoid the necessity of constructing such models, we have recently developed a simple electrode arrangement which permits satisfactory stereoscopic views of the spatial vectorcardiogram to be photographed directly from two cathode-ray tubes. One plane is rotated by approximately three degrees with respect to the frontal plane by displacement of its right apex backward. The other plane is rotated through an equal angle by displacement of its left apex backward. In the arrangement devised each cathoderay tube presents the projection of the vectorcardiogram onto a plane displaced slightly from the frontal plane. Since the electrical derivation of these planes involves the application of only four electrodes, right arm (RA), left arm (LA), left leg (F), and back (B), which form the apices of the equilateral tetrahedron, this