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PubMed1976

Multifocal ventricular parasystolic tachycardia.

Two cases of spontaneous multifocal ventricular parasystolic rhythm are described. One case showed double and the other fivefold parasystole. All seven foci had an enhanced rate of discharge, ranging from 57 to 102/min and at least three of them showed exit block. Though beats from three foci displayed very short coupling intervals, occasionally interrupting the terminal part of the preceding T wave, in none of the cases was repetitive firing or ventricular fibrillation seen. Both patients had organic heart disease and both are still alive six months after the arrhythmia was first recorded. Problems in the diagnosis of multiple parasystole and some mechanisms which may be responsible for irregular interectopic intervals are discussed. It is concluded that multiple parasystole is probably not a very rare arrhythmia if long strips of simultaneously recorded multiple leads are available.

Cardiac Complexes, Premature↗
PubMed1989

Beyond pure parasystole: promises and problems in modeling complex arrhythmias.

The dynamics of pure parasystole, a cardiac arrhythmia in which two competing pacemakers fire independently, have recently been fully characterized. This model is now extended in an attempt to account for the more complex dynamics occurring with modulated parasystole, in which there exists nonlinear interaction between the sinus node and the ectopic ventricular focus. Theoretical analysis of modulated parasystole reveals three types of dynamics: entrainment, quasiperiodicity, and chaos. Rhythms associated with quasiperiodicity obey a set of rules derived from pure parasystole. This model is applied to the interpretation of continuous electrocardiographic data sets from three patients with complicated patterns of ventricular ectopic activity. We describe several new statistical properties of these records, related to the number of intervening sinus beats between ectopic events, that are essential in characterizing the dynamics and testing mathematical models. Detailed comparison between data and theory in these cases show substantial areas of agreement as well as potentially important discrepancies. These findings have implications for understanding the dynamics of the heartbeat in normal and pathological conditions.

Animals↗
PubMed1975

Multiform ventricular ectopic rhythm. Evidence for multiple parasystolic activity.

Six patients whose standare electrocardiograms showed multiform ventricular ectopic rhythm were studied. All patients had advanced organic heart disease and a significant intraventricular conduction defect (left bundle branch block in five and right bundle branch block plus left anterior hemiblock in one). The ventricular arrhythmia was generally resistant to antiarrhythmic therapy. Five of the six patients died after 2 to 6 months form the period of observation from terminal heart failure. None died suddenly. The ventricular arrhythmia did not seem to be directly related to mortality in any patient. Critical analysis of several long rhythm strips in each case revealed that discharge from multiple ventricular parasytolic foci shared in the multiform ventricular activity. The concurrent discharge of a minimum of three parasytolic foci and a maximum of six foci was found in the same case with a total of 24 parasystolic foci in the six patients. There was a remarkable constancy of the QRS configuration of all parasytolic foci over periods of observation of up to 16 months. However, 22 out of 24 parasystolic rhythms showed significant variation in the apparent rhythm or the administration of drugs. Fourteen parasytolic foci showed evidence of exit block, some of which were exaples of a rapid parasystole with a high degree of exit block. The study suggests that multiform ventricular ectopic rhythm may, in part, be due to the concurrent discharge of multiple parasystolic foci.

Aged↗
PubMed1986

Modulated parasystole originating in the sinoatrial node.

A computer model of "modulated sinus parasystole" was devised in which two sinus pacemakers interacted electrotonically, entraining each other's periodicity according to their beat-to-beat phasic relationships. Depending on the preestablished rules, the model gave rise to various rhythm patterns that were similar to those recorded in patients with sinoatrial arrhythmias. The validity of the model in predicting clinically observed rhythm disturbances was tested in a case of sinoatrial extrasystolic activity. The sinoatrial origin of parasystolic discharges giving rise to various patterns of group beating in this case was diagnosed according to the following electrocardiographic criteria: premature P waves having contour identical to P waves of basic beats, variable coupling intervals, and absence of compensatory pauses (i.e., returning cycles having duration similar to that of the basic P-P interval). For the analysis, it was assumed that two distinct but closely apposed sinoatrial pacemaker centers were competing for activation of the heart. The model accurately simulated the arrhythmias in the electrocardiographic trace. The best fit was found when the two pacemakers interacted on the basis of "resetting" in one direction and electronic modulation in the other. In fact, under appropriate conditions, the model matched precisely all frequency-dependent patterns of extrasystolic activity observed in the trace. We conclude that the modulated parasystole hypothesis can readily explain the mechanism of sinus extrasystolic discharges whose returning cycle equals the basic P-P interval. Moreover, the model predicts that, when the rules for mutual entrainment between "dominant" and parasystolic sinus pacemaker are appropriate, the returning cycle can be shorter than the basic cycle.

Aged↗
PubMed1979

Apparent suppression of ventricular parasystole by cardiac pacing.

Complete disappearance of ventricular parasystolic beats by cardiac pacing with the rates of near multiples of the parasystolic rate was observed in 2 patients with ventricular parasystole. This finding represents a clinical counterpart of recently demonstrated experimental and mathematical models of electrotonic modulation of the parasystolic discharge.

Adolescent↗
PubMed1975

[Left atrial parasystole].

A case of atrial parasystole is described in a 55-year-old female with multivalvular heart disease, treated with high doses of digitalis and showing first-degree av block. The left atrial origin of the parasystolic P waves was supported by their distinctive morphology, especially in lead V1, and the sequence of left and right atrial activation. Depending on the refractory state of the myocard, there was a greater shortening of the av conduction time during the parasystolic discharge than during sinus beats indicating a caudal localization of the parasystolic center.

Arrhythmias, Cardiac↗
PubMed1989

[Autoregulation of ventricular parasystole. The triphasic phase response curve].

In the previously published examples where parasystolic rhythms were modulated and entrained, the electrotonic events came from the action potentials arising from the surrounding myocardium. In the two present cases, a ventricular parasystolic focus was entrained by the electrotonic image of the action potentials resulting from its own discharges. The electronic transmission across the protection zone being delayed, the resulting ventricular action potentials were able to automodulate, and entrain, the parasystolic focus according to a triphasic phase response curve. The development of the theory of parasystolic modulation may explain certain bizarre EKG recordings.

Action Potentials↗
PubMedDate not supplied

[Suppression, capture and modulation of ventricular parasystole].

Few clinical studies have dealth with annihilation, entrainment and modulation of ventricular parasystolic rhythm. Parasystolic modulation was diagnosed in 9 nonmedicated patients because single, 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. In two 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.

Arrhythmias, Cardiac↗
PubMed1985

[Modulation and suppression of parasystolic ventricular pacemakers].

Using a three part model of canine false tendon in which an inexcitable gap intervenes between the proximal and distal region of Purkinje fibers, Jalife and Moe recently individualized a biological model of parasystole and showed how the electrotonic depolarization can modulate, entrain or annihilate pacemaker activity. We report the ECG of 9 patients with parasystole (as assessed by the direct recording of ectopic cycle length) in which the early nonparasystolic beats delayed whereas the late shortened the parasystolic cycle length. The phase response curve is specific for a given patient. In two cases a nonparasystolic impulse falling at a critical point in the ectopic cycle length was followed by the suppression of any parasystolic activity on the surface EKG. The recently described phenomenon called pace maker annihilation is thus discussed.

Electrocardiography↗
PubMed1984

[Differential diagnosis of linked parasystole and extrasystole].

The differentiation between linked parasystole and extrasystole was based on functional tests with exercise and atropin as stimuli. A total of 116 patients (71 with parasystole and 45 with extrasystole) were investigated. Two mechanisms involved in parasystole with fixed links between ectopic complexes were identified: 1) a mechanism of simple quantitative correlation between two pace-makers, 2) a mechanism of the principal pace-maker being discharged with impulses from the parasystolic one. Extrasystole is based on the trigger mechanism of relationship between ectopic excitation and the impulse from the principal pace-maker. Prolonged ECG recording established limits for the maximum interval of links between monotopic extrasystoles and the interectopic interval for paired extrasystole. Extrasystole was shown to be incapable of generating a pace of its own, i.e. a succession of three or more ectopic complexes of similar morphology.

Arrhythmias, Cardiac↗
PubMed1980

[Cordarone treatment of parasystole].

Cordarone was used in the treatment of 15 patients with various forms of parasystole. There were 9 cases with ventricular and 5 with atrial parasystole. Cordarone was prescribed according to the following schedule: 200 mg three times daily for the first 10 days and 200 mg twice daily in the next 20 days. A clear positive effect was produced in 14 patients. In 13 cases parasystoles disappeared on the first to tenth day of treatment. The number of parasystoles reduced considerably in one case. The drug had no positive effect on one patient.

Adolescent↗
PubMed1978

[Relationship between ventricular extrasystole and parasystole].

Monomorphic ventricular extrasystoles, no less than 30 within an hour, were revealed in 89 of 300 patients with chronic ischemic heart disease during continuous 24-hour ECG recording on magnetic tape. A fixed type of the linkage interval (oscillations of no more than 0.1 sec) was established in 58 (62%) and the variable tupe (oscillations of more than 0.1 sec) in 31 (38%) patients. Oscillations in the linkage interval of more than 0.1 sec gave grounds to suspect parasystole. A deeper analysis revealed parasystole in 8 cases (2.6% of the total number of patients), the remaining cases were included in the group of extrasystoles with a variable non-parasystolic type of the linkage interval. This group of extrasystoles occupies an intermediate position between para- and extrasystole. The large number of transitional forms between extra- and parasystole suggests their common origin.

Aged↗
PubMed1996

Effect of adenosine on ventricular parasystole.

The cases of two patients with ventricular parasystole revealed a new depressive effect of adenosine on ventricular parasystolic activity. To the authors' knowledge, this is the first report that clearly demonstrates the disappearance of "true" parasystole.

Adenosine↗
PubMed1996

Two cases of ventricular parasystole associated with ventricular tachycardia.

In two patients, ventricular parasystole (VP) was associated with ventricular tachycardia (VT), and in one patient, catheter ablation was successful. In patient 1, with dilated cardiomyopathy, VP led to VT, which converted to ventricular fibrillation. In patient 2, VP led to symptomatic nonsustained polymorphic VT. The origin of parasystolic focus was determined by endocardial mapping, and a radiofrequency current was delivered to patient 2. Both VP and VT disappeared immediately, and no recurrence has been observed during a follow-up of 8 months. Catheter ablation to the parasystolic focus was effective and a relationship between VP and VT was strongly suggested.

Cardiomyopathy, Dilated↗
PubMedDate not supplied

Cardiac resonant oscillations in terms of finite-dimensional group representation in atrial parasystole.

In order to understand the variation of the atrial parasystolic cycle lengths and mutual interactions of sinus node and atrial parasystolic pacemakers, a representation theory for finite groups of invertible linear transformation on a vector space is considered. A quantitative description of manifest atrial parasystolic cycles can be provided by the mapping in the group multiplication with the use of numerical factors of 2, 4 square root of 2 pi, 2/ 4 square root of 2 pi and 2 4 square root of 2 pi. These represent operators of a linear transformation in matrix multiplication of the similarity transformation representing an isomorphism.

Aged↗
PubMed1989

Electrotonic modulation of parasystole in children.

This paper presents four cases of pediatric extrasystole which did not fulfil the diagnostic criteria for parasystole. By calculating various ectopic intervals, we established the phase-response curve demonstrating that sinus electrotonic activities modulated the parasystolic focus in each case. Our results showed these cases to be modulated parasystole.

Adolescent↗
PubMed1986

Supernormal modulation of ventricular parasystole: the triphasic phase-response curve.

Modulation of ventricular parasystole by sinus beats has been shown both in vitro and in vivo to result in a classic biphasic phase-response curve. The first clinical presentation of 3 cases of supernormal modulation of ventricular parasystole resulting in a triphasic phase response curve is reported. Supernormal modulation reflects an unexpected early enhancement expedition of the ectopic ventricular impulses. An alternative explantation for the triphasic phase-response curve is the discharge and resetting of the parasystolic focus by critically timed sinus impulses.

Adult↗
PubMed1989

A computer-based model of parasystolic activity modulated by ventricular activation in the open-chest dog.

The modulated parasystole hypothesis proposed by Moe has been suggested as a common mechanism of a wide variety of arrhythmias. To represent the arrhythmic patterns defined by the model as an actual ECG trace, a "hybrid" experimental system was devised. The system consisted of the intact canine heart connected to a microcomputer that operated as the modulated parasystolic pacemaker. An intrinsic cycle length of the "ectopic" pacemaker was modulated by the phase-dependent effect of the activity of the intact heart in situ. Discharges in the "ectopic" pacemaker were transmitted to the right ventricle. The result was that the theoretically defined patterns of the ectopic activity were represented as real ECG traces. Some published examples of intermittent parasystole that had been attributed to other complex mechanisms were accurately reproduced when the estimated phase response curves were set in the "ectopic" pacemaker. A wide variety of clinical eCG tracings of ventricular arrhythmias may be reproduced by this hybrid experimental model.

Animals↗