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At least 19 recordsLinked to original sources
PubMed1982

Electronic pacemaker models of parasystole. With special reference to artificial intermittent parasystole with phase 3 and phase 4 protection and to parasystolic modulation.

This study deals with a method of analysis of artificial pacemaker function which can be used to understand the electrocardiographic manifestations of some spontaneous rhythms. The modes of operation of 11 normally-functioning QRS-inhibited (VVI) pacemakers resembled those of spontaneous automatic nonprotected (nonparasystolic) rhythms. The function of 11 continuous asynchronous (fixed rate or VOO) pacemakers was similar to that of continuous-parasystolic rhythms. In 12 patients with malfunctioning QRS-inhibited (VVI) pacemakers, an abnormally-prolonged pacemaker refractory period was equivalent to intermittent parasystole with phase 3 protection; and non-sensing during the terminal portions of the cycle was the iatrogenic counterpart of intermittent parasystole with phase 4 protection. Premature beats occurring within the periods of phase 3 and phase 4 protection were "encompassed" by ectopic intervals equalling the ectopic cycle length, or twice the ectopic cycle length. Therefore, they were manifested differently from the "decelerating" and "accelerating" phases of modulation since premature beats occurring during the letter phases may be encompassed by ectopic intervals which are longer and shorter, respectively, than the ectopic cycle length. Because in previous reports the search for these phenomena was based on premises established "a priori," future studies should be designed to analyze tracings of "group beating" where no previous conclusions have been reached.

Arrhythmias, Cardiac↗
PubMed1988

"Irregular" ventricular parasystole: the influence of sinus rhythm on a parasystolic focus.

Fifteen cases of ventricular parasystole were analyzed to determine whether the interectopic intervals were regular, as expressed by long intervals being exact multiples of the short ones, or not. The regularity of the interectopic intervals was assessed by means of the variation index: the ratio of the maximal difference between various measurements of the parasystolic cycle length and the mean parasystolic cycle length. Three out of 15 cases had a variation index less than 5, and were classified as "regular parasystole." Twelve cases were associated with a variation index greater than 7.5, and were classified as "irregular parasystole." The cases of irregular parasystole were then analyzed to determine whether the variability of the interectopic intervals was casual or dependent on action of the sinus beats. A parasystolic resetting by critically timed sinus impulses (a form of intermittent parasystole) was evident in three cases. The irregularity in the remaining nine cases was due to modulation (viz., due to electrotonic influence exerted by the sinus beats on the parasystolic focus). In every case of modulated parasystole a phase-response curve was constructed, which enabled an analysis of all the interectopic intervals on the basis of a time-dependent effect exerted by the sinus impulses on an otherwise rhythmic parasystolic focus.

Adolescent↗
PubMed1976

[A case reported of double parasystole-combined atrial and ventricular parasystole- (author's transl)].

Parasystole is an arrhythmia resulting from simultaneous activity of two independent impulse-forming foci, one of which is protected by the other. Ventricular parasystole which arises from an ectopic focus situated in ventricule is relatively common. On the contrary, supraventricular parasystole which is centered in the atria or atrioventricular junction, is extremely rare. Kaufmann and Rothberger studied first parasystole as an entity, and they reported the first case of atrial parasystole. However, the first correctly mentioned example of atrial parasystole was described by Jervell. In the previous paper, we described one observation on atrial parasystole and discussed on its consisting-mechanism. The occurrence of ventricular parasystole is not a rarity, since it has been estimated to be present once in every 1,200 electrocardiograms taken in a general hospital. In contrast, well-documented cases of atrial parasystole are exceedingly rare, and since the first case of it was reported by Kaufmann and Rothberger, only 25 cases have hitherto been reported. In the present paper is described and discussed a case of the extremely rare combination of atrial and ventricular parasystole with exit block and fusion phenomenon...

Arrhythmias, Cardiac↗
PubMed1997

Effect of standing on ventricular parasystole: shortening of the parasystolic cycle length.

OBJECTIVE: To investigate the effect of standing on the parasystolic cycle length in cases of "true" ventricular parasystole. METHODS: Parasystolic cycle length and sinus cycle length were measured during lying and standing in eight men with true ventricular parasystole. These cycle lengths were also measured after exercise in the lying position. RESULTS: In all cases, parasystolic cycle length and sinus cycle length both shortened on standing, by a mean of 6.4% and 17.8%, respectively, compared to lying. In all cases, the rate of shortening of the parasystolic cycle length was less than that of the sinus cycle length. Parasystolic cycle length was prolonged after exercise, in contrast to a shortening of the sinus cycle length. CONCLUSIONS: Influences on the parasystolic cycle length are not always in the same direction as on the sinus cycle length. This suggests that the effect of autonomic changes on parasystolic rhythm is not always parallel to that on sinus rhythm.

Adolescent↗
PubMed1990

Protection of the ventricular parasystolic focus due to interference of sinus and parasystolic impulses in the ventricular-ectopic junction.

A 50-year-old man with intermittent ventricular parasystolic bigeminy is reported in whom the parasystolic focus was protected from late intervening sinus impulses. This is the first report to suggest the presence of protection due to interference in parasystolic bigeminy. The findings in this case suggest that when a sinus impulse falls in a late period of the parasystolic cycle, it travells so slowly along the ventricular-ectopic junction that it is unable to reach the parasystolic focus before the spontaneous occurrence of the next parasystolic impulse; as a result, the sinus impulse interferes with the next parasystolic impulse in the ventricular-ectopic junction. Thus it is suggested that the parasystolic focus is protected from the sinus impulse because of the interference and not because of an entrance block. This reinforces the concept of a second-degree entrance block as a mechanism of parasystole.

Arrhythmias, Cardiac↗
PubMed1976

Double ventricular parasystole. Supernormal phase of conduction as a mechanism of intermittent parasystole. Report of a case.

A rare case of spontaneous double ventricular parasystole was studied in depth, together with a critical review of similar cases in the literature. The discussion was focused on 1) the variation of the shortest interectopic interval (SIEI), 2) entrance block and its failure, 3) supernormality as a mechanism of intermittence, and 4) effects of lidocaine and atropine on such an arrhythmia. In double ventricular parasystole a greater than usual variation in the SIEI tended to occur in one of the two parasystolic groups. If, however, such variations were too great in the face of otherwise parasystolic rhythm, presence of intermittence was confirmed. A temporary loss of the entrance block was deemed primarily responsible for the intermittency. That is to say, invasion, discharge, and resetting of one parasystolic focus by another parasystolic impulse during the supernormal phase of the ventricle was considered the cause of an intermittence. In a strict sense, this is the first report in the literature in which the supernormality was clearly indicated as one mechanism of intermittent ventricular parasystole. The advantage of the concept of double ventricular parasystole as compared to single parasystole in defining such a mechanism is stressed.

Arrhythmias, Cardiac↗
PubMed1994

Differentiation between parasystole and extrasystoles. Influence of vagal stimulation on parasystolic impulse formation.

Recently, it has been shown that when a sinus impulse falls late in the parasystolic cycle, it usually hastens the next ectopic discharge. Thus, in many cases, the classic criteria for the diagnosis of parasystole (ie, varying coupling intervals and constant shortest interectopic intervals) cannot be used. To differentiate between parasystole and extrasystoles in such cases, the influence of vagal stimulation on parasystolic impulse formation was investigated in seven cases of "true" parasystole in which one or more "pure" ectopic cycles without any intervening nonectopic QRS complexes were found spontaneously. In all cases pure ectopic cycles were found during sinus arrest caused by vagal stimulation; namely, none of the cases showed extreme prolongation of the parasystolic cycle. These results strongly suggest that instead of the classic criteria, vagal stimulation causing temporary sinus arrest is the optimal method for differentiation between parasystole and extrasystoles in cases without spontaneous pure ectopic cycles.

Adult↗
PubMed1992

Atrial parasystole and tachycardia. Modulation and automodulation of a parasystolic focus.

This report deals with a patient reflecting atrial parasystole and episodes of atrial tachycardia. The P' waves during tachycardia were identical to the parasystolic P' waves. Atrial parasystole was at times regular, as revealed by a precise mathematical relationship between the interectopic intervals, and on other occasions irregular. Irregularity was due to modulation, namely electrotonic influence exerted by the sinus impulses upon the parasystolic focus. Atrial tachycardia occurred only during the periods when atrial parasystole was modulated. Atrial tachycardia has been interpreted as due to automodulation, a situation where the propagated parasystolic impulse exerts an electrotonic influence on the ectopic focus itself, leading to a marked unexpected acceleration of the ensuing parasystolic discharge.

Aged↗
PubMed1996

Irregular sinus parasystole due to intermittency and modulation of parasystolic activity.

A case of intermittent sinus parasystole in which the parasystolic focus is protected from the dominant sinus rhythm only during the second half of its intrinsic cycle is reported. In addition, a modulating (i.e., electronic) effect is often clearly exerted from the dominant rhythm upon the focus during the protected period. Coexistence of both modulation and intermittency in sinus parasystole, as well as a modulating effect limited to the second part of the parasystolic cycle, have not been previously reported.

Arrhythmia, Sinus↗
PubMed1984

[Ventricular extrasystole of re-entry originating in the myocardium surrounding a parasystolic focus: a mechanism responsible for the irregularity of the interectopic intervals during parasystole].

We have observed a case of ventricular parasystole in which the ectopic beats occurred often in couplets. The analysis of the interectopic intervals suggests that the first beat of the couplet is parasystolic in origin, whereas the second one is due to a re-entry which takes place in the myocardium surrounding the parasystolic focus. Moreover, our observations lead us to speculate that an occasional supraventricular beat could cause an exit block of the parasystolic focus through a concealed re-entry.

Aged↗
PubMed1987

Ventricular parasystole and ventricular couplets: a re-entry within the parasystolic focus?

We report a 62-year-old man with a persistent ventricular rhythm originating in a parasystolic focus associated with frequent ventricular couplets with fixed coupling. Both intravenous (IV) procainamide (1 g) and propafenone (70 mg IV) promptly suppressed only the second component of ventricular couplets, suggesting that re-entry rather than enhanced automaticity was the mechanism of ventricular couplets. On the contrary, the nonresponse of ventricular rhythm and ventricular couplets to verapamil (10 mg IV) suggested that triggered activity should not play a role in the genesis of this ventricular rhythm. The mechanisms of the ventricular couplets (rapidly discharging parasystolic focus vs. re-entry) are discussed.

Arrhythmias, Cardiac↗
PubMed1989

Modulated parasystole complicating permanent ventricular pacing: the different influence of spontaneous and paced impulses upon the parasystolic rhythm.

A case of modulated ventricular parasystole observed in a patient with a VVIM pacemaker is reported. Analysis reveals that the electronic influence (modulation) effected upon the parasystolic focus by the sinus impulses is different from that exerted by the paced impulses. Furthermore, fusion beats reflect an intermediate modulating effect according to the prevalence of the sinus or the paced wavefront.

Aged↗