Construction and interpretation of body surface maps

Abstract

A SINGLE SURFACE MAP of the cardiac electrophysiologic activity portrays the variation in space of the potentials generated by the heart, for a single instant in time. Often a sequence of such maps is used to show the variation in the spatial distribution of potentials for a sequence of time instants throughout one or more cardiac cycles. Surface maps are most commonly used to portray the spatial variation over the body surface of humans or animals; however, in recent years surface maps showing the electrical activity over the epicardium or other cardiac structures also have come into frequent use. The merits of examining the variation of cardiac potentials in space were recognized by the first cardiac electrocardiographers. For example, Waller’ in 1888 published a diagram showing the potential distribution he expected on the body surface. Short histories of electrocardiographic thoracic mapping have been presented by Lepeschkin’ and Taccardi3 The beginning of more modern measurement of surface maps often is associated with the work of Nahum, Mauro, and co-workers4 in about 1952. The principal advantage of examining potential variation in space, rather than in time, is that the relationship between the spatially distributed electrical sources within the heart and the potential distributions produced on the epicardial or body surfaces for any instant in time can be considered independently of the relationship that exists at any other instant of time. The analogous relation with respect to time does not hold, i.e., it is not the case that an individual electrocardiogram describing voltage versus time is produced by the variation in time of the electrical sources in the heart at a single spatial location. The fact that the spatially distributed sources within the heart produce the corresponding surface maps instant by instant is the basis for the interpretation of surface maps. In particular, there is a more or less direct relationship between the spatial distribution of the cardiac sources and the observed spatial distributions of potentials on the epicardial or body surfaces. This relationship exists to a degree that is often intuitively obvious, and certainly to a degree that can be exploited by mathematical calculations.