Posture, the manifest heart vector, and the volume conductor

The effects of the left and right lateral postures on the tetrahedral and cube frontal planar vectorcardiograms were studied in 25 patients of whom 2 had total situs inversus and one an acquired dextroposition. In a second group of 11 patients the effects of the prone as well as of the lateral postures were studied, but only with respect to the tetrahedral frontal loop. The results indicated that the anatomic rotation of the heart about its various axes cannot account for most of the changes. Much can be explained by a shift of the heart as a whole toward the dependent side. This alters the characteristics of the body as a volume conductor, which may be expressed as changes of the effective axes of the leads especially the X leads. In turn, these change the manifest vector. The image point of the left arm appears to be especially sensitive to postural effects. Some of the results are as yet unexplained. The manifest vectors of extrasystoles showed a different amount of postural deviation than did that of normal beats in the same individual. This could be explained readily by the rule that the deviation of the manifest vector by deviating lead axes is greatest for those vectors oriented perpendicularly to the axes and minimal for those parallel to the axes.