Isopotential Body Surface Mapping in Subjects of All Ages: Emphasis on Low-Level Potentials with Analysis of the Method

In this report we consider the body surface distribution of low-level potentials, particularly those of the U wave, the PR segment, and the ST segment in normal subjects. The long-term objective of this report is to study low-level body surface potentials, but adequate methods are required for that. Therefore, the primary emphasis in this report is artifacts that may occur in these potential distributions. Although receiving a secondary emphasis, the findings show that accurate low-level potential distributions can be recorded and they have interesting and distinctive features. The results present two features that are important in the construction of isopotential maps: 1) The normal distribution of the surface potentials characteristic of these signals, especially the U wave and the PR segment, and 2) the influence of subtracting or not subtracting these patterns in the process of constructing body surface maps for the entire cardiac cycle. An isopotential map method is described for identifying U waves. A reciprocal relationship was found between the normal body surface patterns of the U wave and the PR segment. If the period of the U wave was unfortunately chosen as the time for zero potential reference for all electrodes, the maps subsequently made for QRS and the ST segment were distorted on the anterior chest by an element of potential representing currents of terminal ventricular repolarization during overlapping T and U waves. The implication of these results is significant in that the timing of the reference baseline is critical in determining the pattern of the depicted map. These considerations are especially important in the interpretation of precordial and body surface maps recorded during exercise. The false patterns found can be quite misleading, since the baseline artifacts produce regional changes that may simulate patterns of abnormalities