An unusual case of auricular parasystole showing “exit” block

Katz, Louis N.; Eschelbacher, J.L.; Strauss, Sidney

doi:10.1016/s0002-8703(37)90281-3

Cited by 16 publications

(1 citation statement)

References 6 publications

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“…Thus in figures 1 to 5, the cycles, both those actually measured and those calculated, do not vary by more than 0.05 second, which is within the limits of errors of measurement. If criteria used for the differential diagnosis of paroxysmal tachycardias35 were applied, much greater variations could be allowed in the case of a ventricular focus, but this would render the diagnosis of parasystole very difficult.3 As a matter of fact, parasystole has been recognized in the face of an apparent irregularity of its pacemaker by assuming either a temporary "break through" of the impulses of the extraneous dominant pacemaker past the barrier of protection of the ectopic focus (intermittent parasystole) 2, 14, 21, 23, 46 or a temporary release of an "exit block"9 15,16,30 which had kept many of its impulses confined exclusively to the immediate region of the parasystolic pacemaker. Furthermore, variations in the manifest cycle of the parasystolic beats can be expected with varying degrees of delayed con-duction of impulses from the ectopic center to the surrounding myocardium such as occurs in second degree A-V block.4 ' 7, 12, 14, 15, 29 This latter factor will become manifest in the form of varying A-V conduction times, when the parasystolic focus is located in the A-V node, as in figure 4.…”

Section: The Regularity Of the Parasystolic Pacemakermentioning

confidence: 99%

Parasystole

Pick¹

1953

Circulation

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Five instances of parasystolic rhythm are presented in which detailed analysis revealed some particular physiologic aspect pertinent to the understanding of this type of disturbance of rhythm. In four cases the ectopic parasystolic focus was localized in the ventricles and in one in or near to the A-V junction; in two of the former instances the site of the ectopic focus appeared to be the interventricular septum. The mechanism of protection of the parasystolic center, while not identical in every case, might be effected by an area of true block, as exemplified by one instance. Parasystole offers the rare opportunity to determine the refractory phase of the A-V junction or of the ventricular myocardium in the human heart. Occasionally parasystolic rhythm may appear in association with other types of manifest multiple cardiac pacemakers and produce very complex arrhythmias, which can be resolved by application of known physiologic principles.N ORMALLY, rhythmic contraction of the entire heart is initiated and maintained by a single pacemaker, the sinus node. It dominates all other potential pacemakers by virtue of its relatively faster rate of cyclic discharge. Simultaneous activity of two cardiac pacemakers occurs in A-V dissociation; here, each pair of chambers, the auricles and ventricles, is governed entirely, or for the most part, by its own pacemaker. Rarely, two rhythmic and completely independent pacemakers operating at different rates can be seen to be in competition for the activation of the ventricles or of the auricles. Such a condition is termed parasystole. 243 maker to impulses of the dominant rhythm has been accepted as a fact although its explanation remains controversial.The present report deals with some observations bearing on the mechanism of parasystole. Five electrocardiograms which satisfy criteria postulated3" 33 for the diagnosis of parasystolic rhythm were analyzed. The methods used for analysis and the conclusions which were derived are described in the legends of figures 1 to 5 and this approach can he followed by studying the corresponding diagrams. Each case illustrates a particular physiologic aspect of parasystolic rhythm.Thus, figure 1 presents an example of ventricular parasystole in its "purest" form with its implications concerning the operation of the refractory period and of interference. In figures 2 and 3 the site of a ventricular parasystolic focus appears to be revealed by a consideration of the contour of ectopic and dominant beats; moreover, figure 3 seems to provide some clue as to the mechanism of "protection" of such a parasystolic ectopic focus. In figure 4, a parasystolic focus in, or close to, the A-V node appears to be shielded from other impulses passing the A-V junction in both directions. Factors responsible for the apparent irregularities of the manifestation of this parasystolic pacemaker are revealed by detailed analysis, and the duration of the refractory phase of A-V junctional tissues can be estimated closely.

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Section: The Regularity Of the Parasystolic Pacemakermentioning

confidence: 99%