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PubMed2001

His-bundle parasystole masquerading as exercise-induced 2:1 atrioventricular block.

We describe a case of symptomatic pseudo-AV block due to His-bundle parasystole masquerading as exercise-induced 2:1 AV block. Electrophysiologic study revealed the presence of His-bundle parasystole, and the fluctuation of parasystolic cycle length could be explained by the concept of modulated parasystole. Modulated parasystole is a possible explanation for maintenance of stable 2:1 AV conduction at an atrial rate of specific range during exercise.

Aged↗
PubMed1999

The diagnostic criteria for classic parasystole.

OBJECTIVE: To establish a diagnostic criteria of parasystole with high sensitivity and high specificity. METHODS: After excluded from nonparasystole and each variant parasystoles, based on the electrocardiographic data obtained from 61 patients with classic parasystole, we selected the quantitative indices which could reflect the features of ectopic focus with complete entrance block as the diagnostic criteria for parasystole. RESULTS: The common features of the electrocardiograms of this group were: 1) Take the earliest recorded eight interectopic intervals in which at least four intervals containing sinus beats or other beats having activated to the area within the ectopic focus. When in case of deficiency, it will fill up a vacancy in order. The ratios of the shortest coupling interval to the shortest ectopic cycle length (ECL) were all less than 80%; 2) The coefficients of variation of the eight ECLs were all less than 6%; 3) The maximal differences of coupling intervals were all equal to or more than 0.11 second. CONCLUSION: Three quantitative indices as necessary conditions have been used as diagnostic criteria for parasystole with high sensitivity and high specificity.

Electrocardiography↗
PubMed2004

Extrapotentials and allorhythmias as an expression of experimental parasystole.

UNLABELLED: The aim of the study was to investigate the dynamics of experimental parasystole taking into consideration the peculiarities of recurrent arrhythmias recorded in clinical settings. MATERIAL AND METHODS: The experiments were conducted on isolated right atria of seven chinchilla rabbits. Parasystolic arrhythmias using periodical one-site electrostimulation were provoked in one atrium, where the sinus node was not affected, and in two atria with the spontaneous low value activity of pacemakers. The parasystolic arrhythmias by the dual-site periodical pacing were provoked in four atria, in which the spontaneous activity had disappeared, while the membrane potential of cardiomyocytes remained at the level of 70 to 80 mV. RESULTS: The parasystolic arrhythmias of the shape of single extrapotentials were obtained in atria when the periods of excitation impulses were within the limits of 0.9-1.2 s, and the differences between these periods being relatively small (0.04-0.2 s). The increase of these differences resulted the various allorhythmias. In cases of single extrapotentials, the recurrence periods of arrhythmias reached 5.6-29 s; while in cases of allorhythmias they shortened to 2.4-4.8 s. CONCLUSION: The parasystoles in isolated atria of rabbits can be induced by two competitive excitation sources. They may manifest themselves through single extrapotentials or allorhythmias, whose form depends on the duration of the periods of excitation impulses, the difference between these durations, as well as on effective refractory periods of atrial cardiomyocytes. The determination and evaluation of the recurrence period of these arrhythmias can serve in any given clinical situation as a supplementary criterion.

Action Potentials↗
PubMedDate not supplied

Parasystolic property of the ectopic focus.

Among 4476 ECGs recorded from May 1972 to April 1973, 206 ECGs showed various arrhythmias. All ECGs showing any kind of arrhythmia were recorded for 2 to 4 minutes in order to obtain more than 3 premature beats in one tracing. Of 141 ECGs with premature beats from 126 cases, more than 2 interectopic parasystolic intervals could be measured in 122 cases (96.8% of those with premature beats and 2.7% of all the patients examined). More than 3 coupling intervals could be measured in 117 patients with premature beats. In only 13 of these 117 cases (11.1%), the coupling interval varied less than 0.04 second and less than 0.02 second in 2 cases (1.7%). 1) The parasystolic cycle length ranged between less than 0.20 and more than 2.51 seconds with 82.8% of them being in a range between 0.21 and 1.00 second. 2) The fluctuation rate of the parasystolic cycle length ranged between less than 1.0 and more than 15.1. It was between less than 1.0 and 5.0 in 56,6%, between 5.1 and 10.0 in 30.0% and between 10.1 and more than 15.1 in 13.1%. 3) Fusion beats were observed in 44 of 122 cases in which the interectopic parasystolic cycle length could be determined (36.1%). Of these 44 fusions 14 were found in atrial, 14 in A-V junctional and 16 in ventricular parasystole. 4) Theories of re-entry and ectopic enhancement were discussed.

Adult↗
PubMed1984

Annihilation, entrainment and modulation of ventricular parasystolic rhythms.

Annihilation and one-to-one entrainment of modulated parasystolic rhythms in humans has not been previously discussed. In 9 nonmedicated patients, it was possible to measure the intrinsic, parasystolic ectopic cycle length given by the intervals between 2 consecutive parasystolic beats without any interposed nonparasystolic beat. The corresponding values varied between 960 and 2,350 ms (corresponding to rates between 62 and 26 beats/min). In addition, modulation could be determined, because nonparasystolic beats falling during the initial 59% of the cycle prolonged the parasystolic cycle length (by 12 to 37.5%), whereas those that fell later in the cycle shortened it (by 9 to 25%). Plotting this prolongation or shortening as a function of the temporal position of the nonparasystolic beats in the cycle yielded biphasic response curves, of which 7 were symmetric and 2 asymmetric. In 2 patients, episodes of concealed one-to-one entrainment were initiated by late nonparasystolic (sinus) beats and, later on, terminated by early ventricular extrasystoles. In 2 other patients (and in 2 separate occasions) nonparasystolic beats, falling in part of the cycle located in between those of maximal delay and acceleration, produced pacemaker annihilation (cessation of automatic activity for the remaining monitoring time). Parasystolic annihilation and concealed entrainment may be one of the causes that can explain the large, spontaneous, day-to-day variability in the incidence of ectopic ventricular beats reported in Holter recordings. Nevertheless, future prospective studies performing interventions that can change the sinus and ectopic rates are required to corroborate our finding.

Arrhythmias, Cardiac↗
PubMed1979

Coupling interval, exit block, and periodicity of ventricular parasystolic rhythm.

The electrocardiograms in this study of parasystolic rhythm were tape recorded and then analysed with a special purpose hybrid computer. The rate of appearance of specific inter-ectopic intervals was shown to change significantly with small changes in either the sinus or parasystolic pacemaker period. Natural changes in the period of the ectopic pacemakers were observed over several hours. Changes amounting to 14% within 10 min and 18% overall were observed in one patient, and a gradual lengthening of 10% over 3 h in another. A previously undescribed form of exit block has been discovered in one patient where the block remained active for a given time only after propagation from the parasystolic focus. Different interectopic intervals were shown to contribute to specific and restricted coupling interval locations in diastole. Hence this form of exit block, by preventing some inter-ectopic intervals from propagating, limited the locations in diastole in which parasystolic ectopic complexes could appear. In this case later diastolic complexes were inhibited and hence fusion complexes were completely absent. Parasystolic rhythm, with and without the exit block described, was simulated successfully by a digital computer. The simulations aided our understanding of the clinical data.

Aged↗
PubMed1986

Ventricular parasystole: a chronobiologic study.

Previous works have reported circadian rhythms for several cardiovascular parameters. A chronobiologic rhythm is characterized by: mesor (a rhythm-determined average), amplitude (half difference between the highest and lowest values), and acrophase (timing of high point in degrees and/or in hours) along with 95% confidence limits. We performed 24-hour ECG Holter monitoring in seven patients (mean age, 50.6 years) with ventricular parasystole (VP) in order to determine whether the chronotropic activity of parasystolic foci has a circadian rhythm similar to that of the sinus node. For each Holter recording parasystolic rates (PRs) and heart rates (HRs) were calculated every hour. Furthermore, a mean hourly PR and a mean hourly HR were calculated from the hourly PRs and HRs of the patients. The statistic chronobiologic analysis was done by single and mean cosinor methods. Correlation between mean hourly PR and HR was evaluated by Pearson's 'r' coefficient. A statistically significant rhythm (P less than 0.05) was found for the single and mean rhythms both of HR and PR. In our patients, HR had acrophase at 1.27 P.M., mesor at 73.28 beats/min, and amplitude at 9.53 beats/min, whereas PR had acrophase at 1.42 P.M., mesor at 38.31 beats/min, and amplitude at 3.64 beats/min. Chronobiological data and the high direct correlation between mean hourly HRs and mean hourly PRs (r = 0.96, P less than 0.001) indicate a similar circadian variability of the chronotropic activity of sinus nodes and parasystolic foci. Although several hypotheses can be made, responsiveness of parasystolic foci to circadian variations of the autonomic nervous system tone (sympathetic and/or vagal) and/or circulating substances (particularly catecholamines) seems the more probable one for explaining our findings.

Adolescent↗
PubMed1982

Modulation of parasystolic activity by nonparasystolic beats.

We studied 12 patients with ventricular parasystole in whom pacemaker activity could be modulated by nonparasystolic beats (NPBs). In six patients (group 1) in whom the intrinsic parasystolic cycle length (XX interval) was obtained without interposed NPBs, we found that NPBs falling during the first half of the cycle prolonged the XRX interval (containing one NPB) and that NPBs falling during the second half of the cycle abbreviated the XRX interval; both effects were maximal when NPBs fell close to the middle of the cycle and were separated by a reversal point. However, because of mutual interference between parasystolic beats and NPBs, only 13.2-43.4% of the parasystolic cycle could be effectively scanned. We also found that the XRX and RX intervals were linearly related. This relationship served to establish that in six patients in whom the XX interval was not obtained (group 2), modulation showed a similar behavior, although neither the reversal point nor the sense of the modulation could be determined. In this report, we suggest diagnostic criteria of parasystolic modulation.

Arrhythmias, Cardiac↗
PubMed1983

Parasystole, reentry, and tachycardia: a canine preparation of cardiac arrhythmias occurring across inexcitable segments of tissue.

A protected ectopic focus created in tissue excised from one heart was allowed to interact with the activity of the intact heart of another animal. The protected focus consisted of a Purkinje fiber in which a narrow central zone was rendered inexcitable. The model permitted us to study parasystole, modulated parasystole, reentry, and tachycardia in the same preparation. At moderate levels of electrotonic influence across the region of block, frequency scans revealed wide zones of pacemaker entrainment. The incidence and pattern of premature ventricular contractions generated were always a sensitive function of heart rate. Parasystolic patterns could be converted to apparent reentrant patterns by simple alteration of the atrial driving rate or the level of block. Suppression of pacemaker automaticity converted a modulated parasystole model to one of pure reentry. Reciprocation of the impulse across the inexcitable tissue segment generated a ventricular tachycardia that could be initiated and terminated by a single properly timed event. Our observations suggest that ectopic activity that behaves like parasystole and activity characteristic of what is commonly diagnosed as reentry, including tachycardia and idioventricular rhythms, may be a manifestation of a common mechanism whose arrhythmic expression differs as a continuous function of heart rate, level of block, or level of automaticity.

Animals↗
PubMed1999

Modelling a parasystolic rhythm in a heart-transplant patient.

A parasystole from a heart-transplant patient is analysed using a beat-to-beat RR interval time series obtained from an electrocardiogram (ECG). The dysrhythmia, resulting from the co-existence of two pacemakers, the sinus node and an ectopic focus, presents distinctive regular patterns, with transitions from one pattern to another occurring abruptly. It is shown that the parasystolic rhythm can be simulated by a model involving two oscillators firing at fixed rates, under the restriction that neither is allowed to fire during the other's refractory period. It is found that the structure of the generated RR time series is essentially determined by the ratio of the periods of the two oscillators. In the case of a heart-transplant patient with a small heart-rate variability as a result of heart denervation, the model predicts the RR intervals with an error of less than 6% for an 80-beat sequence. From a physiological point of view, the results imply that the interaction between the two pacemakers in the heart is fairly weak, and hence the parasystole observed in the heart-transplant patient can be modelled as pure parasystole.

Adult↗
PubMedDate not supplied

Atrial parasystole.

A case of the relatively rare atrial parasystole is reported, and this interesting cardiac arrhythmia is reviewed. Atypical deviations from classical parasystole are reviewed, and modern concepts of parasystole as they differ from traditional, classical parasystole are addressed.

Diagnosis, Differential↗
PubMed1979

Coexistence of ventricular parasystole and ventricular couplets: mechanism and clinical significance.

In 78 consecutive patients with uniform ventricular ectopic complexes and without heart disease, ventricular couplets were present significantly more often when the coupling interval of ventricular ectopic complexes was variable than when it was fixed (P less than 0.04). In 69 consecutive patients with couplets, the prevalence of a variable coupling interval was significantly greater than that of (55 versus 14 cases; P less than 0.001). Among 55 patients with a variable coupling interval, ventricular parasystole was probable in 38 and possible in 17 patients. These results suggest that the association between ventricular couplets and parasystole is not coincidental. Of several possible mechanisms responsible for this association reentry within the parasystolic focus or its vicinity is the most probable. This may explain the observation that the couplets are seldom followed by consecutive ventricular ectopic complexes or ventricular tachycardia. If this hypothesis is correct, the clinical significance of ventricular couplets in the presence of ventricular parasystole may be similar to that of single reentrant ventricular ectopic complexes.

Electrocardiography↗
PubMed1989

Modulated parasystole as a mechanism of ventricular ectopic activity leading to ventricular fibrillation.

The electrocardiograms of 2 patients with frequent premature ventricular complexes characterized by variable coupling intervals and fusions with sinus activations were analyzed according to the modulated parasystole and reflection hypotheses of Moe et al. In addition, the ectopic activity was associated with couplets, tachycardia and ventricular fibrillation. Departures from the "classic" criteria of parasystole could not be explained satisfactorily if a completely protected (insulated) pacemaker was assumed. In each instance a triphasic response curve could be constructed, suggesting that modulated parasystole was the mechanism common to both patients. Couplets and runs of ventricular tachycardia were ascribed to single and repetitive reflection, respectively, in the presence of supernormal excitability of the ectopic pacemaker, the ventricle or both. In these patients, fibrillation probably resulted from spatial nonuniformity of the ventricular response to the reflected event during a phase of vulnerability. This study suggests that modulated parasystole in the presence of supernormal excitability may lead to very severe arrhythmias and trigger ventricular fibrillation. In the clinical setting, such patients may be misdiagnosed because of atypical features.

Adult↗
PubMed1990

Intermittent ventricular parasystolic bigeminy accompanied by reentrant ventricular extrasystoles.

An extremely rare case of intermittent ventricular parasystolic bigeminy is presented, in which coexisting reentrant ventricular extrasystoles of sinus origin, showing mainly trigeminy, and those of ventricular parasystolic origin, showing a close coupling to the ventricular parasystolic beat, are demonstrated. Such a unique case has never been reported. Timely parasystolic exit block occurring just prior to the anterograde ventricular activation of the sinus impulse was considered to be of critical importance in developing the reentrant extrasystolic trigeminy.

Aged↗
PubMed1976

Coexisting ventricular and blocked atrial parasystole.

A rare instance showing non-conducted atrial parasystole coexisting with ventricular parasystole is presented and a related subject is briefly discussed. The importance of recognizing parasystole is again emphasized because the ordinary extrasystoles, particularly ventricular in origin, are frequently digitalis-induced, while parasystole, which superficially resembles the ordinary extrasystoles, does not seem to be related to digitalis.

Cardiac Complexes, Premature↗
PubMed1988

Modulation of atrioventricular junctional parasystole during atrial pacing.

In this report we describe a case of a 68-year-old man with atrioventricular junctional parasystole in whom atrial pacing caused marked changes in the arrhythmic pattern. During atrial pacing at a cycle length of 960 ms, the duration of the ectopic cycle length was influenced by the interval between the parasystolic and nonparasystolic beat. A shorter interval from nonparasystolic to ectopic beat prolonged the ectopic cycle length and a longer one shortened it. Pacing at a cycle length of 900 ms completely suppressed the parasystole. Both of these changes are most likely due to modulation and entrainment of the parasystolic rhythm. During spontaneous variation of the sinus cycle length over 24 hours of ambulatory ECG recording, modulation could not be confirmed; however, there was parallel variation of the ectopic and sinus cycle lengths which suggests that both pacemakers were under the influence of the autonomic nervous system.

Aged↗
PubMed1988

Ventricular tachycardia with alternating cycle lengths: self-entrainment of parasystolic rhythm?

A patient had ventricular tachycardia with cycle lengths consistently varying between 400 and 490 ms. Arrhythmias with a similar electrocardiographic pattern had been thought to result from the regular activity of an automatic pacemaker with either 3:2 exit block of the Wenckebach type or alternation in exit conduction times. However, the findings in our patient could also be explained by postulating the existence of modulated ventricular parasystole having 3:2 exit block or with alternating (short-long) exit conduction times. In either case, the action potentials elicited by the parasystole must have reached (with variable delays) the ventricular tissue beyond the zone of protection to produce electrotonic depolarizations which, in turn, were reflected back to the ectopic focus itself. This resulted in runs of 2:3 or 2:2 "self-entrainment" of the parasystolic pacemaker. Similar phenomena have been produced in biologic and mathematical models of modulated parasystole.

Action Potentials↗
PubMed1970

Atrial parasystole.

Two cases of atrial parasystole showing the various manifestations of the arrhythmia are presented. Analysis of the underlying mechanisms shows that atrial parasystolic bigeminy with ;reversed' coupling is a form of escape-capture begeminy, sinus escapes being followed by an ectopic capture of the atria. Reasons are given for the rarity of atrial fusion beats. The similarities and differences between atrial and ventricular parasystole are explored. It is suggested that an atrial parasystolic pacemaker may lie within a major atrial preferential conducting pathway, and may consist of a congenitally ectopic fragment of sinus nodal tissue. The clinical significance of the arrhythmia is discussed; the associated diseases apparently represent a cross-section of medical ward experience.

Aged↗