Clinical electrocardiography / by Sir Thomas Lewis.

  • Thomas Lewis
Date:
1913
Catalogue details

Licence: Public Domain Mark

Credit: Clinical electrocardiography / by Sir Thomas Lewis. Source: Wellcome Collection.

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    copper-zinc couple. But the wave of contraction passes to d and as it reaches this point it subsides at p. The distal end becomes active while the proximal end is resuming the quiescent state ; as an accompaniment of this change, d becomes relatively negative to p, and the swing of the recorder is reversed. Thus the whole electric effect consists of two deflections which are in opposite directions, a simple diphasic effect. Now if the stimulus is applied at the distal end (Fig. 9i?) the direction of contraction is reversed ; under these circumstances d first shows relative negativity and later p ; a diphasic curve is still obtained, but the directions of swing; are the reverse of those seen when the contraction travels from p to d. It will be evident that the recorded curve will also show reversed phases if, stimulation being at the proximal end, the connections to the galvanometer are reversed (Fig. 90). Thus experimental study teaches us that the shape of an electric curve is controlled by (1) the direction of the contraction wave in the muscle investigated, and this is governed by the point at which the contraction arises ; and (2) by the lie of this muscle in relation to the leading off electrodes. The full explanation of individual deflections in electrocardiograms is a difficult matter ; for the arrangement of the muscle fibres is very complicated and the contraction wave courses along them in a direction which changes from time to time and from point to point ; nevertheless, by arguing along general lines, we may formulate certain fundamental conclusions. It is known that all normal hearts yield, from a given lead, electrocardiograms which have a certain fixity of form. Although the curves taken from no two subjects are alike, yet by experience we may learn the limits of variation which are compatible with health.