Four orthogonal systems of vectorcardiography that are considered to be more accurate than th(-tetrahedron and cube systems were compared. In a large majority of subjects the records made with each of the 4 systems were similar. However, in 5 of 60 subjects in whom the Z lead was studied, dissimilarities were found that were considered to be significant. The possible reasons for these dissimilarities are discussed. Comparative normalization data for the systems were obtained in the living human subject, based upon comparison of wave forms.RECENTLY 4 systems of vectorcardiography based on well-established principles of potential theory have been devised by Schmitt and Simonson,1 Frank,2 McFee and Johnston,3 and Helm.4 They each attempt to provide a more orthogonal reference frame than the cube and the tetrahedron systems. It is the purpose of this paper to report the results of a comparative study in the living human subject of these 4 systems. The study was undertaken for 2 reasons, to determine how interchangeable the results of the different systems were and to provide comparative normalization data for each system in the living subject. If the systems yielded similar results, the study would serve as a consistency cheek on the validity of the separate methods of analysis and synthesis. METHODThe 3 leads of each orthogonal reference frame were compared individually. They were paired with a common lead to produce a loop rather than being recorded as scalar leads. The latter method requires high-speed, dual-channel recording with a common lead for phase relations, and analysis of such records was found to be less obvious and informative.All studies were performed with the subject recumbent. Loops were observed directly on an oscilloscope and photographed with a Polaroid Land Z Lead. Since the anteroposterior or Z lead has been the most variable component in existing systems of vectorcardiography, the major portion of this study was devoted to it. The Z lead of each system was paired consecutively with a common X lead (Schmitt system), and the gain of the Z channel controlled so that the peak-to-peak excursion was the same for all loops. The gain was then recorded for normalization information. The Z leads of the Frank and the Schmitt SVEC III systems were employed as described by these authors in their original communications.1' 2 The sponge electrode of Helm4 and the multiple bank of electrodes of McFee and Johnston3 are described as follows.The sponge electrode consisted of a thin plastic sponge moistened with a saturated solution of sodium chloride. Two sizes of sponge were used on the anterior chest wall to record the Z lead. A large sponge 10 inches square was positioned to cover the area from the first to the seventh interspace and from approximately the right midelavicular line to a line between the V4 and V5 positions. A smaller sponge with dimensions of 8Y2 inches from right to left and 612 inches from top to bottom was placed on the precordium, extending from the level of the second to the sixth rib a...

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We study the dynamics of secondary infections on networks, in which only the individuals currently carrying a certain primary infection are susceptible to the secondary infection. In the limit of large sparse networks, the model is mapped to a branching process spreading in a random time-sensitive environment, determined by the dynamics of the underlying primary infection. When both epidemics follow the Susceptible-Infective-Recovered model, we show that in order to survive, it is necessary for the secondary infection to evolve on a timescale that is closely matched to that of the primary infection on which it depends.

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