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PubMed1996

Reverse effects of exercise on the sinus and parasystolic cycle lengths.

Ventricular arrhythmias are the primary concern in the exercise laboratory. It has recently been suggested that in not a few cases, ventricular premature complexes are governed by modulated parasystole and not by ordinary extrasystolic rhythm. In many cases, however, it is difficult to differentiate between parasystole and ordinary extrasystoles. Few reports are available on the effect of exercise in cases of "true" parasystole. This study investigated the effect of exercise on the parasystolic cycle length 11 cases of true ventricular parasystole, in which one or more "pure" parasystolic cycles containing no intervening nonectopic QRS complexes were found. In all cases, in contrast to an acceleration of the sinus rate, a definite decrease in the parasystolic rate was found. In no case did complete suppression occur. These findings suggest that the effects of exercise on ordinary ventricular extrasystolic rhythm and on ventricular parasystole may be considerably different from each other.

Adult↗
PubMed1986

Rate-dependent patterns of modulated ventricular parasystole.

The effects of ventricular pacing on the arrangement of ventricular parasystolic beats were studied in 14 patients. By analyzing the effects of various pacing rates and modalities, it was found that both rate and pattern of manifest parasystolic beats were intimately related to the rate and coupling interval of the paced rhythm. Our findings indicate that fixed coupling of ectopic beats is not incompatible with parasystole; modulated parasystole may manifest as fixed rate classic parasystole; a parasystolic pacemaker can be entrained by a wide range of driving rates both above and below the intrinsic rate of the parasystole; and with different driving rates, these rate-dependent patterns can be observed in the same patient. Our observations suggest that spontaneous or drug-induced changes in the heart rate can lead to major alterations in the frequency and patterns of ventricular parasystole.

Electrocardiography↗
PubMed1992

Failure of parasystolic impulses to appear on schedule. Exit block due to concealed conduction of sinus impulses.

A 45-year-old patient free of any heart disease was admitted to the hospital with an electrocardiographic pattern of ventricular parasystole. The parasystolic rhythm was relatively fast, such that several consecutive ectopic complexes manifested. A later tracing reflected only isolated parasystolic complexes with long and fixed coupling intervals. The interectopic intervals, however, were once more in multiple of the parasystolic cycle as directly measured during the phases of undisturbed parasystolic rhythm. In the latter tracing, several scheduled parasystolic impulses did not yield a response, despite calculation suggesting that these impulses occurred outside the refractory period. In other words, an exit block was present. Analysis of the tracing suggests that the exit block was caused by concealed penetration of the sinus impulses into the ectopic-ventricular junction. That is, any sinus impulse penetrates into the junction and renders it refractory, in such a way that only parasystolic impulses that are relatively late within the sinus cycle may be conducted to the surrounding myocardium and result in a parasystolic complex.

Cardiac Complexes, Premature↗
PubMed1978

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.

Adult↗
PubMed1984

Second degree entrance block with supernormal conduction in intermittent ventricular parasystole.

A patient with intermittent ventricular parasystole is reported in whom the presence of second degree entrance block with supernormal conduction was suggested for the first time. In this patient, ventricular extrasystoles with variable coupling frequently occurred. The QRS configuration of the extrasystoles was different from that of the parasystolic beats. When extrasystoles did not occur, the parasystolic beat was never seen because the conducted sinus impulse always reset the parasystolic rhythm. When an extrasystole occurred 0.52 sec or more after the preceding sinus beat, this extrasystolic impulse also reset the parasystolic rhythm. On the other hand, when an extrasystole occurred between 0.47 and 0.51 sec after the sinus beat, the parasystolic focus was protected from this extrasystolic impulse. When, however, an extrasystole occurred in a short terminal portion of the T wave of the preceding sinus beat, this extrasystolic impulse reset the parasystolic rhythm again, suggesting entrance block failure during the supernormal phase.

Arrhythmias, Cardiac↗
PubMed1987

Unusual electrocardiographic patterns of modulated parasystole.

Modulation of a parasystolic rhythm implies that the latter is affected by nonparasystolic beats in predictable ways. When modulation occurs the diagnosis of ventricular parasystole cannot be made by applying the well-known 'classical' criteria. This report deals with clinical tracings from three cases having modulated parasystole with unusual characteristics. Case 1 showed a 24-hour diurnal variability of parasystolic modulation characterized by its occurrence during only part of the period of sleep (from 1 to 5 am). In case 2, modulated ventricular parasystole produced episodes of intermittent ventricular bigeminy with fixed coupling resembling those attributed to a reentry mechanism. The proper diagnosis was made when the sinus cycle length changed abruptly. Finally, in case 3, the idionodal rhythm from a patient with complete AV block was shown to be not only parasystolic, but also modulated. In addition, the idionodal rhythm was entrained (captured) in a concealed fashion by paced beats so that the post-pacing events did not conform with those occurring during overdrive pacing of parasystolic nonmodulated, or nonparasystolic, idionodal rhythms. These findings constitute the clinical counterpart of experimental studies performed with microelectrode techniques.

Adult↗
PubMed1992

Differentiation between parasystole and reentry in concealed bigeminy.

There are two different theories to explain the mechanism of concealed bigeminy: one is '2:1 concealed reentry'; the other is 'irregular parasystole.' Two exemplary cases of the even-number variant of concealed bigeminy are presented. In case 1, the mechanism can be explained by an irregular parasystole due to a modulated parasystole; however, findings during temporary sinus arrest caused by vagal stimulation indicate that this case is not governed by a parasystole, but by a 2:1 concealed reentry. In case 2, the mechanism can be explained by a 2:1 concealed reentry without parasystole; however, findings during temporary sinus arrest indicate that this case is governed by an irregular parasystole due to a type-I second-degree entrance block. Thus, in cases of concealed bigeminy without pure ectopic cycles, it does not seem easy to explain the mechanism of concealed bigeminy on the theory of a modulated parasystole.

Adult↗
PubMed1978

Double irregular ventricular parasystole: rate-dependent entrance block and "supernormal" exit conduction.

An analysis of electrocardiograms from a patient with spontaneous double irregular ventricular parasystole is presented. Irregularity in one of the two parasystoles was produced by intermittence based on rate-dependent (phase 3) entrance block, and in the other parasystole it was attributed to "supernormal" exist conduction. Critical analysis of electrocardiograms revealed that first degree block, rate-dependent block, and "supernormal" conduction in the exit pathway may account for the alterations in the arrangement and manifestation of the parasystolic beats. An electrocardiographic approach to these properties of the parasystolic structure and demonstration of double ventricular parasystole with irregularity in both parasystoles has not previously been found in the literature.

Arrhythmias, Cardiac↗
PubMedDate not supplied

Double atrial parasystole showing intermittent trigeminy.

Atrial parasystole arising from two different ectopic atrial foci, namely, double atrial parasystole, showed intermittent trigeminy due to 3:1 exit block, in which both the ectopic atrial rates were around the sinus rate. Atrial trigeminy showing positive P waves in leads II and III continued, then intermittent atrial parasystole with negative P waves in leads II and III took over. The double atrial parasystole was considered to be interspersed with reentrant atrial beats. Other possible mechanisms to cause a disruptive influence on the trigeminy of the atrial parasystole with positive P waves in leads II and III are: (a) concealed intraatrial reentry with resetting by the sinus impulse; and (b) delayed capture by the impulse of the third preceding sinus beat, and the subsequent 3:1 exit block. On the other hand, the atrial parasystole with negative P waves in leads II and III tended to show long interectopic intervals, in which some of the parasystolic beats exhibited a coupling to the third preceding sinus beat. This suggested prompt resetting by the sinus impulse and the ensuing 3:1 exit block.

Aged↗
PubMed1985

[Mechanisms of the occurrence of parasystole and extrasystole].

Mechanisms involved in the development of parasystole and extrasystole are substantiated on the basis of vast clinical material (261 patients with parasystole and 45 with extrasystole). The use of functional tests employing exercise and atropine contributed to both the correct diagnosis of parasystole and extrasystole and a logical explanation of the mechanisms governing their development. Prolonged ECG recording identified, for the first time ever, the limits of the maximum admissible coupling interval for normotopic extrasystole, as the preliminary diagnosis of the nature of the arrhythmia was only made after the said tests. Parasystole was shown to be rooted in a pathologic automatism, and extrasystole, in the summation of extrasystolic focus potentials and the principal pacemaker potential during movement as well as the principal pacemaker impulse along the route of the minor circular wave on Purkinje' level. The localization of ectopic foci in parasystole and extrasystole confirms the hypothesis of the mechanisms involved in these arrhythmias. A parallel study of parasystole and extrasystole defined parasystole as active heterotopia, and extrasystole, as passive heterotopia incapable of generating a rhythm.

Arrhythmias, Cardiac↗
PubMed2002

[Parasystole].

Parasystole is usually an extrasystolic rhythm which can occur at every level, but particularly in the ventricle. It is admitted that the parasystolic focus is protected from the environing myocardium by an entry block but can manifest itself. Actually, a pure unidirectional block does not exist and the environing myocardium affects the parasystolic rhythm by an electrotonic current which modulates the output. A non-parasystolic complex which occurs prematurely in the parasystolic cycle delays it. Conversely it accelerates the cycle when it occurs late. By this fact, a parasystole pacing is possible and can lead to a fixed coupling. This arrhythmia is frequently unknown and can be experimentally, reproduced by a sucrose gap preparation.

Animals↗
PubMed1977

Intermittent parasystole with concealed extrasystolic bigeminy during myocardial infarction.

A 72-year-old man demonstrated persistent intermittent ventricular parasystole for 6 days during an acute inferior wall myocardial infarction. Entrance block failure occurred at a critical interval of 1.24 sec. after parasystolic beats with resetting of the parasystolic cycle length. The first ectopic beat in each parasystolic series showed coupling to its second preceding conducted beat, and successive cycle lengths in each series usually showed gradual shortening. Concealed extrasystolic bigeminy was also demonstrated between parasystolic series with the number of intervening conducted beats conforming to the formula 2n + 2. After interpolated parasystolic beats, this formula became 2n + 3.

Aged↗
PubMed1976

Mechanism of escape, extrasystolic, and parasystolic arrhythmias. Study on an electrical analogue.

A simple analogue of the heart consisting of a system of neon relaxation oscillators is presented. The analogue may display rhythm patterns similar to sinus rhythm, escape rhythm, isorrhythmic dissociation with synchronization, atrial extrasystoles, ventricular extrasystoles, and parasystole. The strict rules followed by these arrhythmias, as well as the deviations from the rules commonly followed by the equivalent heart arrhythmias, may be easily reproduced on the analogue. Such features are the Treppe phenomenon and captured beats in escape rhythm, fixed coupling intervals in extrasystoles, partial or complete atrioventricular block in very premature atrial extrasystoles, prolongation of the period following an atrial extrasystole, interpolated premature beats, complete compensatory pause and the rule of bigeminy in ventricular extrasystoles, slight instability of the parasystolic period, multiple length parasystolic periods slightly different from the exact multiples of the parasystolic idioperiod, preference of the parasystoles for certain phase in the sinus cycle, synchronization at a phase difference and fluctuation repeatedly and without interruption from a parasystolic to an extrasystolic rhythm and synchronization in escape rhythm with isorrhythmic dissociation. The mechanisms involved in these phenomena are discussed in detail. The striking similarity between the properties of the cardiac pacemakers and those of the relaxation oscillators on the one hand and betwen the rhythm patterns of the heart and those of the analogue on the other may permit the hypothesis that the mechanisms operating in the analogue may be used in analyzing and understanding heart arrhythmias.

Arrhythmias, Cardiac↗
PubMed1976

Parasystole and its variants.

Various mechanisms that cause deviations from the classical manifestations of a parasystolic rhythm are reviewed and illustrated by selected clinical electrocardiograms. They consist of: (1) Transient or continued fixed coupling of the ectopic beats, due to (a) synchronization of basic and parasystolic rhythms; (b) reversed coupling of the basic to the ectopic rhythm (unidirectional protection); (c) the operation of supernormal phase of excitability; and (d) intermittent parasystole, due to gap in the protection of the parasystolic center. (2) Irregularities in response to a regular parasystolic discharge may be caused by a second degree exit block, usually of Mobitz type II, rarely of type I. An electrophysiologic basis for the emergence and maintenance of parasystolic rhythms appears to be abnormal states of spontaneous diastolic (phase 4) depolarization in otherwise latent subsidiary cardiac pacemakers.

Arrhythmia, Sinus↗
PubMed1984

[Modulated parasystole. An arrhythmia waiting for diagnostic criteria. Deductive analysis of a case].

We report a case of ventricular parasystole in which the long interectopic intervals are always less than a multiple of the short interectopic intervals. Assuming a regular ectopic discharge, the above said phenomenon could theoretically be due to relative prolongation of the short interectopic intervals caused by delayed ectopic-ventricular conduction of the second consecutive conducted impulse (a Wenckebach-like phenomenon). Nevertheless, this hypothesis may be ruled out in this case by the analysis of a long tracing. The unusual relationship between the interectopic intervals may be explained assuming the modulation of the parasystolic activity by sinus beats. Experimental work has shown that despite the protection (or entrance) block, the sinus or dominant rhythm may affect the automaticity of a parasystolic focus by means of electrotonic influence. It has been pointed out that sinus impulses falling in the first part of the ectopic cycle delay the next ectopic discharge, while relatively late sinus beats (falling in the last 30-40% of the ectopic cycle) are able to anticipate the delivery of the parasystolic impulse. The phenomenon of modulation is marked by a characteristic biphasic phase-response curve. In the reported case a phase-response curve has been obtained, which explains the parasystolic cycle variations according to the phase of the cycle in which the sinus beats fall. The obtained curve is quite similar to those observed experimentally, therefore the diagnosis of modulated parasystole appears to be very likely.(ABSTRACT TRUNCATED AT 250 WORDS)

Arrhythmias, Cardiac↗
PubMed1977

Parasystole associated with fixed coupling ventricular ectopic activity.

In 5 patients ventricular parasystole and fixed coupling ectopic beats were recorded. In two cases ventricular parasystole and bigeminism acted intermittently. In one case the spontaneous transition from ventricular parasystole into parasystolic tachycardia with "reverse coupling" and finally to ventricular bigeminy could be illustrated. In all these cases ventricular parasystole and fixed coupling extrasystolic activity seems to be a close related mechanism. In other two cases there was a mathematical relationship between the sinus and parasystolic discharge rate which explained the periodic fixed coupling of ectopic beats. In one of these cases His bundle electrography was helpful in documenting the ventricular origin of ectopic beats.

Adolescent↗
PubMed1997

Intermittent parasystole with exit block.

A 53-year-old patient had a complex ventricular arrhythmia, which most likely was an intermittent pure (nonmodulated) parasystole, due to protection limited to the first part of the cycle coexisting with exit block. However, other interpretations of the observations were possible. Foremost among these was modulated parasystole with partial protection or with an attenuated or nondetectable early delaying phase, with exit block. Interestingly, the parasystole appeared to have fulfilled the dynamic rules regarding the number of sinus beats interposed between manifest parasystolic beats, as has been reported for pure or weakly modulated parasystole. This case corroborates unusual manifestations of an arrhythmia, which because of its newly found complexities and various possible interpretations seems to be discussed with decreasing frequency in most textbooks on general cardiology.

Electrocardiography↗
PubMed1999

Intermittent sinus bigeminy as an expression of sinus parasystole: a case report.

A case of sinus parasystole is reported. The diagnosis of sinus parasystole is relatively difficult because there is no difference between the basic sinus P wave and the parasystolic wave. Sinus parasystole is diagnosed according to the following electrocardiographic criteria: (1) premature P waves having contour identical to P waves of basic beats; (2) intervals between premature P waves mathematically related. In the case reported, the coupling intervals during long phases of intermittent sinus bigeminy were nearly fixed, because there was little variability in the returning cycles, making the diagnosis of sinus parasystole difficult.

Aged↗