Isopotential body surface mapping in subjects of all ages: emphasis on low-level potentials with analysis of the method.
Authors: M S Spach, R C Barr, R B Warren, D W Benson, A Walston, S B Edwards
Journal: Circulation (1979)

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 con- struction 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 sur- face 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 tim- ing 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.IN THIS PAPER we consider the mapping of body surface potential distributions that primarily contain potentials under 250 ,uV, particularly those that occur during the U wave, the PR segment, and the ST seg- ment.Implicit in the mapping of low-level potential distributions during these intervals is the assumption that the methods used are precise enough to ensure that accurate patterns are depicted in the maps.Our idea was that knowledge of the locations and shapes of the U waves and the PR segments over the entire torso in normal subjects would enhance the reliability of the spatial interpretation of these deflections which, with the ST segment, are particularly sensitive to error and are most difficult to depict accurately in the form of potential distributions.Our interest in low-level potentials was stimulated by the results of experiments with simultaneously measured epicardial and body surface potential dis- tributions in intact chimpanzees" 2 and dogs.3 4These experiments showed that many of the important elec- trical events in the heart were reflected on the body surface in the low-level patterns rather than in the maxima and minima, the two features that have thus far received major emphasis in characterizing surface