Exceptional types of slow heart action / by Thomas Lewis.

  • Thomas Lewis
Date:
[1913]
Catalogue details

Licence: Public Domain Mark

Credit: Exceptional types of slow heart action / by Thomas Lewis. Source: Wellcome Collection.

    6/22 page 224
    mechanism was seen to alter abruptly, and large venous waves, evidently the result of simultaneous contraction of auricle and ventricle, appeared. These might be isolated (as in Fig. 2) or in short groups (as in Figs. 3 and 4), As a general rule they occurred after relatively long pauses. Thus the longest pause in Fig. 2 is the only pause which is followed by a venous wave of this kind. In Fig. 4 the large venous waves start after the longest pause. In Figs. 3 and 4 the usual sequence follows the shortest pause. The reason for the changes will be obvious. There are two active centres of impulse-formation ; one lies in the sino-auricular region and produces the sequential beats, the other lies away from it and is ectopic ; the latter produces a slower rhythm than the former. For instance, in Fig. 2 the ectopic centre produces but a single effective impulse, and it gives rise to a response only after a rest of unusual length. The first ectopic beat of Fig. 4 may be explained in the same and customary manner. As a general rule, the ectopic rhythm, once developed, increased in rate. This is clear in Figs. 3 and 4. The new centre obeys the customary law in producing its ‘ rhythm of development’; its activity, once awakened, is enhanced. Thus it happens that the pauses between certain of the ectopic beats may be eventually shorter than the pauses between the sinus beats (as in Fig. 3). Although the examples given illustrate these relations between impulse-formation in the two centres, yet in a few curves exceptions could be found, and these exceptions probably resulted from an irregularity in the rates at which impulses were built up at the two points. The explanation which alone seems adequate to explain these successive simultaneous contractions is that they have been let loose from a common centre ; in short, that we have to deal with transient nodal rhythm. For the auricular and ventricular contractions in any cycle have precisely the same time relations to each other, although the individual cycles have varying lengths. Coincidence of auricular and ventricular contractions, the former originating in the old pace- maker, the latter in the ventricular pacemaker (idio-ventricular beats), is hardly to be thought of in the presence of this irregularity. The electro-cardiograms, corresponding to these polygraphic curves, are illustrated by Figs. 12, 14,15,and 16. The ventricular complexes of Fig. 15 are alone found; the closest comparison between these ventricular complexes and those of the normal periods fails to reveal the slightest trace of auricular repre- sentatives buried in the former. The comparison may be made most satisfactorily in the first two cycles of Fig. 14,in which the last nodal beat of a series is shown. Yet we know from the polygraphic curves that auricular and ventricular beats started simultaneously. The conclusion seems justified that the auricular representative is of abnormal form and that it is concealed by R. A comparison of these electro-cardiograms and experimental ones confirms these explanations.? Auricular representatives may be present, but may be so concealed that the electro-cardiograms require a very close comparison with simultaneous myocardiograms before these representatives are revealed. ? Unpublished observations.
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