Auriculo-ventricular heart-block as a result of asphyxia / by Thomas Lewis and G.C. Mathison.

  • Thomas Lewis
Date:
[1910?]
Catalogue details

Licence: Public Domain Mark

Credit: Auriculo-ventricular heart-block as a result of asphyxia / by Thomas Lewis and G.C. Mathison. Source: Wellcome Collection.

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    a From left to right it indicates the duration of asphyxia, the rate of the auricle per minute, the P-R intervals in seconds, and the ventricular rate. The second table is similarly arranged ; the time relationships are more typical. It shows an exceptional occurrence, the break back of complete to 2: 1 heart-block.* Within two or three minutes of the onset of asphyxia the rate of the auricles and consequently that of the ventricles increases. At 14 to 4} minutes (usually early) a prolongation of the P-R interval occurs, and this is the first evidence of the subsequent fully developed heart-block. It is either accompanied or directly preceded by a retardation of the auricular rate, and the decrease may be considerable. Following upon this stage is a further and steady decrease of auricular rate, and it is associated with the appearance of other grades of heart-block, of which examples are published (Fig. 1). The prolongation of the P-R interval becomes exaggerated, and it may lengthen to double or treble the original measurement (the longest interval recorded has been 0-3 sec.). (The normal interval for cats is about 0-08 to 0-1 sec.). Within two minutes (usually less) of this evidence of diminished conductivity of impulse transmission from auricle to ventricle, auri- cular impulses fail to reach the ventricle. At first there may be an occasional dropped beat (Figs. 2 and 3), there may be dropped alternate beats (2 : 1 heart- block, Fig. 1 III). Where single beats are dropped a condition comparable to that which is found in clinical cases has been met with. The already lengthened P-R interval rapidly increases still further up to the point where the dropped beat is seen. This preliminary lengthening of the P-R interval is clearly shown in Figs. 2 and 3 and the intervals increase to such an extent that the auricular systoles (P) fall back upon the preceding ventricular systoles (R and T), so that the contraction is partially synchronous in the two chambers. The first P-R interval succeeding the failure of a ven- tricular response is invariably relatively short, a shortening which has been frequently pointed out in clinical cases and which is attributable to the long rest which precedes it. Following upon the stage of prolonged P-R interval or upon a poriag of dropped beats, 2: 1 heart-block manifests itself (Fig. 1 III). The auricular rate during this period is always markedly retarded (despite the section of the vagl, or the administration of atropine), and the P-R intervals retain their increased length. They may be shorter, or of the same length or even slightly longer than the longest P-R intervals of the preceding phase. They are usually long as in Fig. 1. The duration of the 2: 1 block is variable, but generally continues for a minute or two. It is succeeded by a period of complete heart-block, in which the auricular rate is approximately twice that of the ventricle, but in which there is no simple arithmetical ratio between the rhythms of the two chambers. There is complete dissociation, and the auricular variations (P) fall at varying times in relationship to the ventricular * This reappearance of 2: 1 heart-block does not necessarily indicate a decrease of Impairment of conductivity. It may be explained as a result of the slowing of an ideoventricular rhythm.
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