Reentrant Path Research Articles

Type A alternating Wenckebach periodicity in the re-entrant path of ventricular extrasystoles

A patient with ventricular extrasystoles is reported in whom Type A alternating Wenckebach periodicity in the re-entrant path of the extrasystoles is suggested for the first time. Namely, it appears that 2:1 exit block occurs at a proximal level in the re-entrant path and block of the Wenckebach form occurs at a distal level in the path. The presence of three-level block in the re-entrant path is also suggested in this patient.

Detailed activation sequence in the region of electrically induced ventricular fibrillation in dogs.

We determined the details of ventricular activation sequence during the onset of ventricular fibrillation in 6 dogs. Unipolar electrograms were simultaneously recorded from 192 ventricular epicardial sites evenly spaced in a 3 by 3 cm square area surrounding 2 central sites to which stimuli for inducing fibrillation were delivered. In 5 dogs, 2 to 10 msec duration pulses with amplitudes of 150 to 220 v were used to induce fibrillation, and in 1 dog, 3 successive permature stimuli of 3 v intensity were used to induce fibrillation. In 2 dogs the pattern of activation at the onset of fibrillation was compatible with local reentrant paths near the stimulus site. Fibrillation was induced with a single high intensity pulse in both of these dogs. In the other 4 dogs, the pattern of activation at the onset of fibrillation was highly suggestive of reentrant paths distant from the stimulating electrodes. In 3 of these dogs fibrillation was induced by a single high intensity pulse and in the other it was induced by 3 repetitive stimuli. Activation patterns resembling supraventricular activation occurred prior to fibrillation in the latter animal. The data demonstrate 2 distinct modes of onset of electrically induced ventricular fibrillation. The findings support local reentry in the region of the stimulus site as the mode of onset of fibrillation in some animals and possible reentry at sites distant from the stimulus site with participation of the specialized conduction system in other animals. The differences in mode of onset of electrically induced fibrillation may be responsible for instability of fibrillation threshold measurements in some animals. In addition the role of the specialized conduction system in the onset of fibrillation may be responsible for the effects of sympathetic and vagal stimulation on fibrillation threshold.

Mechanisms of ventricular parasystole.

Eight cases of ventricular parasystole are reported. In all these cases, regardless of whether parasystole seems intermittent or "continuous," the presence of second degree entrance block of the Mobitz type I was suggested. Parasystole alternated with concealed extrasystolic bigeminy showing occasional reentrant extrasystoles. Such intermittent parasystole appears to originate in the reentrant path of extrasystoles. Reentrant extrasystolic bigeminy was seen in a comparatively rapid sinus rhythm, whereas parasystolic bigeminy was seen in a comparatively slow sinus rhythm. The difference between the interectopic intervals during parasystolic bigeminy and during (manifest or concealed) extrasystolic bigeminy was comparatively small so that occasionally the difference was not distinct; on such an occasion the case showed a seemingly "continuous" parasystole. These observations strongly suggest the possibility that most cases of parasystole, whether intermittent or "continuous," may be governed by incomplete entrance block of the second degree.

Intermittent Parasystole Originating in the Reentrant Path of Ventricular Extrasystoles

This report indicates the presence of intermittent ventricular parasystole alternating with ventricular extrasystoles caused by the reentrant mechanism, in which the parasystolic focus is located within the reentrant path. Intermittent parasystole in this case shows second-degree entrance block. When a sinus impulse falls in the absolute refractory period of the ventricular-ectopic junction, the ectopic focus is protected from it. When a sinus impulse falls in a considerably late period of the ectopic cycle, which is long after the absolute refractory period of the ventricular-ectopic junction, the parasystolic rhythm is also not disturbed by it. Although in this late period the sinus impulse enters the ventriculare-etopic junction, it interferes with the next ectopic impulse within the junction and therefore cannot reach the ectopic focus. When a sinus impulse falls before the previously mentioned period but still long after the absolute refractory period of the ventricular-ectopic junction, it reaches the ectopic focus after a comparatively short time of ventricular-ectopic conduction, which results in resetting of the parasystolic rhythm; however, when a sinus impulse falls shortly after the absolute refractory period of the ventricular-ectopic junction, it reaches the ectopic focus after a marked delay in conduction, and thereafter it occasionally becomes a reentrant extrasystole.

A possible explanation for the nuclease limit digestion pattern of chromatin.

The general pattern of DNA fragments in the limit digest of nuclease-treated chromatin could arise from a single, unique nuclease-susceptible site per nucleosome. If DNA binds to the histone core of the nucleosome along a circularly re-entrant path, the location of the DNA entrance and exit can occur at any of a number of distinct sites. This very specific type of heterogeneity together with the natural 10-fold periodicity of DNA B can account for the observed digestion pattern. Such a general picture of the nucleosome structure could also easily explain how nucleosomes might move along the DNA. This type of structure should be easy to distinguish experimentally form more conventional explanations of the origin of the limit digest pattern of chromatin.

Slug following a Closed Trail

MY attention was drawn a few days ago to a brown slug, about 2½ inches long, which had made for itself a closed iridescent track on the concrete flooring of a conservatory. I could not find at what point it had got on to the curve, which ran at one end into a damp part of the concrete, but, in four hours from the time I first saw the slug, it had made three complete circuits and two-thirds of a fourth, always keeping the whole of its body on the trail. The latter, of a uniform breadth of 3/16 inch, varied considerably in curvature, but nowhere presented any very sharp corners, and measured, roughly, forty inches round. Though the rate of progression was sufficiently slow, the slug rested on the track for seven hours, after which, thinking it dead, I touched it and found it had not quite dried up. Indeed, without elongating its body, it began to move and laboriously shifted its position by about an inch. There it remained (the time being then 10 p.m.), waiting, perhaps, for the influence of a more humid atmosphere, for morning found it moist and healthy, breakfasting more than a yard from the near and damp end of the track, which it must have reached by completing the fourth circuit, as there was no trail other than the closed one alluded to. If slugs are in the habit of following old trails, it does not appear that the present specimen had any previous experience of a re-entrant path, but that it depended solely on ocular intelligence of the path in advance.

2. Note on the Theory of the “15 Puzzle”

[After this note had been laid before the Council, the new number (vol. ii. No. 4) of the “American Journal of Mathematics” reached us. In it there are exhaustive papers by Messrs Johnston and Story on the subject of this American invention. The principles they give differ only in form of statement from those at which I had independently arrived. I have, therefore, cut down my paper to the smallest dimensions consistent with intelligibility.—P. G. T.]The essential feature of this puzzle is that the circulation of the pieces is necessarily in rectangular channels. Whether these form four-sided figures, or have any greater (even) number of sides, the number of squares in the channel itself is always even. (This is the same thing as saying that a rook's re-entrant path always contains an even number of squares. This follows immediately from the fact that a rook always passes through black and white squares alternately. The same thing is true of a bishop's re-entering path, for it is a rook's upon a new chess-board formed by the alternate diagonals of the squares on the original board.) That there may be circulation in the channel, one of its squares must be the blank one.