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Automaticity has been described in Mahaim pathways, both spontaneously and during radiofrequency ablation. We describe an unusual case of automatic rhythm from a Mahaim pathway presenting as parasystole. The parasystolic beats were also found to initiate tachycardia, resulting in initial presentation with incessant tachycardia and tachycardia induced cardiomyopathy.

Background: The clinical relevance and prognostic implications of ventricular parasystole are unknown., Objectives: This study sought to assess the prevalence of ventricular parasystole in patients with implantable cardioverter-defibrillators (ICDs) and ventricular parasystole's association with ventricular arrhythmias and conduction system abnormalities., Methods: This study retrospectively evaluated patients who underwent ICD interrogation at a single center between June 1, 2019, and August 31, 2020, and reviewed all available ICD and electrocardiogram data. This study identified patients with ventricular parasystole and compared the prevalence of ventricular fibrillation (VF), ventricular tachycardia (VT), and new conduction system abnormalities in those with ≥5 years of intrinsic QRS-complex electrocardiograms to those without parasystole., Results: This study included 374 patients (age 57 ± 21 years, 72% male, 45% nonischemic, 32% ischemic cardiomyopathy), of which, 104 (28%) had VT only, 39 (10%) VF only, and 10 (3%) both VT/VF. Ventricular parasystole was identified in 33 patients (9%); parasystolic foci were predominantly from the His-Purkinje system. Compared with those without parasystole, patients with parasystole had a significantly higher rate of VF (36% vs 11%; P < 0.01), but not VT (42% vs 29%; P = 0.12). Patients with parasystole, compared with those without parasystole, had a higher prevalence of new conduction abnormalities, particularly progressive intraventricular conduction delay (11 of 18 [61%] vs 12 of 83 [14%]; P < 0.01) and new right bundle branch block (4 of 18 [22%] vs 1 of 83 [1%]; P < 0.01)., Conclusions: Ventricular parasystole was strongly associated with new conduction system abnormalities and VF in patients who have cardiomyopathy with ICDs, suggesting a potential link between VF and His-Purkinje damage in this patient population., Competing Interests: Funding Support and Author Disclosures Dr Bradfield and Dr Shivkumar are supported by National Institutes of Health grant OT2OD028201. Dr Do has received research funding and speaker fees from Medtronic Inc. All other authors have reported that they have no relationships relevant to the contents of this paper to disclose., (Copyright © 2023 American College of Cardiology Foundation. Published by Elsevier Inc. All rights reserved.)

The article presents a case study of an 81 year old female patient with a history of nonischemic cardiomyopathy who presented for an evaluation of repeated presyncope and fatigue. A discussion of electrocardiography which was conducted on the patient,and revealed that her QRS complexes had narrowed prematurely, is presented. Factors which could have led to the premature narrowing are discussed.

Developing better methods for risk stratification for tachyarrhythmicsudden cardiac remains a major challenge for physicians andscientists. Since the transition from sinus rhythm to ventriculartachycardia/fibrillation happens by different mechanisms in differentpeople, it is unrealistic to think that a single measure will beadequate to provide a good index for risk stratification. We describeefforts to analyze the dynamical properties of ventricular prematurecomplexes over 24 hours in an effort to understand the underlyingmechanisms of ventricular arrhythmias and to better understand thearrhythmias that occur in individual patients. Twodimensional density plots, called heartprints, correlate characteristic features of thedynamics of premature ventricular complexes and the sinus rate. Heartprints show distinctive characteristics in individual patients. Based on a better understanding of the natures of transitions fromsinus rhythm to sudden cardiac and the mechanisms of arrhythmia priorto cardiac arrest, it should be possible to develop better methods forrisk stratification.

Aims: Discrete, fragmented, local voltage potentials (LVPs) have been observed in electrograms recorded at the ablation site in patients undergoing radiofrequency ablation for arrhythmias originating in both the right and left ventricular outflow tract; however, the incidence and the significance of the LVP with respect to arrhythmogenesis is uncertain. [ABSTRACT FROM PUBLISHER]

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. [ABSTRACT FROM AUTHOR]

Spontaneously beating embryonic chick heart cell aggregates were stimulated with current pulses delivered either as periodic trains, or at a fixed delay after each action potential. Following stimulation at fixed rates faster than the intrinsic rate, there was a transients slowing of the spontaneous rhythm. This response, called overdrive suppression, can lead to a complex evolution of rhythms. During periodic stimulation there is a continuum of dropped beat patterns, and during fixed delay stimulation bursting activity appears. This study provides a conceptual basis for understanding analogous rhythms in the intact heart. [ABSTRACT FROM AUTHOR]

A 43-year-old female with a chief complaint of palpitation was subjected to clinical electrophysiological studies. Initial standard 12-lead EGG revealed that her palpitation was caused by fascicular parasystole firing at the basic cycle length of 1.25-1.40 seconds, and that both sinus and parasystolic beats were associated with left anterior fascicular block and tachycardia-dependent RBBB. His-bundle electrocardiogram suggested that the parasystolic focus was located in the proximal portion of the anterior fascicle of the left bundle branch and that the site of tachycardia-dependent conduction block was located in the main right bundle branch. These findings suggest that diffuse pathological changes in the intraventricular conducting system were responsible for both the conduction block and automatic impulse formation in the present case. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

An asymptomatic 3 1/2-year-old boy demonstrated parasystolic ventricular tachycardia with AV dissociation, early sinus capture beats, marked variability in coupling intervals between conducted and ectopic beats, fusion beats, and interectopic intervals which were multiples of the ectopic cycle length. The arrhythmia initially responded to quinidine, reappeared over an 11-month observation period, and finally was suppressed at a high quinidine dose. An invasive and noninvasive work-up failed to demonstrate organic heart disease. [ABSTRACT FROM AUTHOR]

As recently described by Moe et al., parasystolic modulation implies that the ectopic cycle length of a parasystolic focus can be increased or decreased by electrical influences transmitted across the zone of protection. A search for this phenomenon was made in nine patients with intermittent ventricular parasystole resulting from protection only during specific portions of the cycle. All nine patients had a period of relatively early protection affecting the initial 55-67% of the cycle preceding a period of resetting during which the parasystolic focus was discharged and fully recycled. In addition, two patients had a period of relatively late parasystolic protection. Pseudo-resetting (apparent resetting in the surface leads without interruption of activity within the parasystolic focus itself), seen throughout the entire period of late protection in these two patients, and during the relatively refractory period in one patient, was identified because the R waves causing apparent resetting were encompassed by parsystolic-to-parasystolic intervals equalling twice the ectopic cycle length. Our findings indicate that parasystolic modulation did not occur in the type of intermittent ventricular parasystole included in this study. That is, the parusystolic focus was either not affected (not modulated) during specific (early or late) portions of the cycle, or normally reset (discharged and fully recycled, but neither depressed, nor enhanced) in other portions of the cycle. This study does not exclude the occurrence of modulation in other types of parasystole, nor in some automatic nonparasystolic rhythms. [ABSTRACT FROM AUTHOR]

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., electrotonic) 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. [ABSTRACT FROM AUTHOR]

A mathematical model of modulated parasystole was used to study the characteristics of entrainment of a ventricular ectopic pacemaker by ventricular activations of sinus nodal origin under conditions of constant and variable heart rate. To mimic physiological fluctuations in heart rate due to sympathetic and parasympathetic influences, the sinus nodal cycle length was modulated by three sinusoidal waves of different frequencies simultaneously (0.025, 0.1, and 0.25 Hz). To simulate the electrotonic influence of ventricular activity on the cycling of the parasystolic pacemaker, the pacemaker was modulated according to biphasic phase-response relationships characterized by an early delay phase and a late acceleration phase. A wide range of intrinsic sinus nodal cycle length to ectopic pacemaker cycle length ratios was examined. Each simulation run consisted of the computation of 1,000 pacemaker firings. Entrainment (periodic firing, sometimes combined with a periodic manifest arrhythmia) was classified into four categories: simple entrainment (periodic pacemaker firing pattern accompanied by a periodic manifest arrhythmia), complex entrainment (similar, but with a periodic manifest arrhythmia covering more than one basic firing pattern), concealed entrainment (periodic firing, no periodic manifest arrhythmia), and no entrainment. The results indicate that physiologically relevant variability of heart rate can result in electrocardiographic patterns of modulated parasystole in which entrainment of the ectopic pacemaker by the sinus rhythm is not as readily apparent. With increased variability of heart rate, simple entrainment may convert into complex, complex into concealed, and concealed entrainment into patterns that show no entrainment at all. The data should aid in our understanding and ability to recognize the various electrocardiographic manifestations of modulated parasystole. [ABSTRACT FROM AUTHOR]

The coexistence of a parasystolic focus, tachycardia dependent right bundle branch aberrancy, and an AV accessory pathway is reported here. This condition was present in a 40-year-old man, which led to an incessant AV reciprocating tachycardia. Further electrophysiological study revealed that the parasystolic focus was located somewhere in the His bundle; endocardial mapping disclosed a right posterior accessory pathway. Radiofrequency current was delivered at the atrial level of the right posterolateral AV groove and successfully ablated the accessory pathway, leading to a dramatic improvement in cardiac function. In conclusion, the recognition of the electrophysiological mechanism of incessant supraventricular tachycardia was of crucial importance for the therapy decision. A definitive intervention using radiofrequency catheter ablation should be considered early and not postponed in patients with tachycardia-Induced cardiomyopathy. [ABSTRACT FROM AUTHOR]

Mechanisms of fixed coupled ventricular ectopic complexes (VECs) were studied in the monitoring ECGs of 7 patients with the aid of a special purpose computer. Over 80% of the 4500 fixed coupled VECs studied had coupling intervals restricted to a range of 120 ms. The actual coupling interval varied between subjects. No special part of diastole exhibited the property of fixation.In five patients there was evidence of parasystole despite the fixed coupling. In two of these the ectopic period was clearly different from the sinus period. In the other three a difference was evident between inter-ectopic and sinus intervals, but the ectopic period could not be determined due to absence of short inter-ectopic intervals. Absence of some intervals was due to exit block or consistent coincidence of ectopic stimuli with ventricular refractoriness. In all five patients the inter-ectopic intervals showed progressive adjustment so as to become equal to a multiple of the sinus period. The coupling interval, which indicated the preferred phase relationship of the two rhythms, was altered by small changes in the sinus period. These adjustments were greater manifestations of the synchronising effects, already described, of sinus rhythm on a ventricular parasystolic rhythm.By contrast the VECs of two other patients exhibited very different characteristics. In one, the VECs restricted to 40 ms after the T wave in early diastole were probably due to ventricular re-excitation. In the other, runs of idioventricular rhythm and VECs in late diastole were due to an escape pacemaker rhythm. [ABSTRACT FROM PUBLISHER]

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 wellknown ‘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. [ABSTRACT FROM PUBLISHER]

Ventricular parasystole was studied in three patients. Long periods of the ECG were analysed allowing features of the ectopic mechanism to be deduced. The ECGs were recorded on magnetic tape and analysed with the aid of special purpose and digital computers. Sinus rhythm was found to alter the periodicity of the ectopic rhythm and to adjust its phase relation–ship relative to sinus rhythm. These effects were more marked when the ectopic period was similar to the sinus period or its multiple. In one patient phase adjustment resulted in periods of bigeminy with fixed coupling. The adjustment of periodicity and phase probably results from subthreshold stimuli due to sinus rhythm modifying the function of spontaneous depolarization of the ectopic pacemaker. [ABSTRACT FROM PUBLISHER]

Abstract: Parasystole can be subtle, making the diagnosis difficult to recognize. [Copyright &y& Elsevier]

A 76-year-old man with a history of atrial septal defect repair underwent radiofrequency (RF) ablation of typical atrial flutter. During electrophysiological study, incessant sharp potentials were recorded, originating from the ostium of the inferior vena cava (IVC), and dissociated from atrial activity. During sinus rhythm, these potentials propagated to the atria and caused premature complexes when falling beyond the atrial refractory period. Electro-anatomical mapping revealed the presence of the earliest potential in the postero-lateral ostium of the IVC, propagating to the septal region. After RF isolation of the IVC, the patient has remained arrhythmia-free over a 5-year follow-up. (PACE 2010; e62–e64) [ABSTRACT FROM AUTHOR]

Competing Interests: Funding Support and Author Disclosures The authors have reported that they have no relationships relevant to the contents of this paper to disclose.

A patient with sick sinus syndrome following the Senning operation was also found to hove concealed atrial parasystole during intracardiac electrophysiological study. This atrial parasystolic pattern could be converted to atrial bigeminy by changing the atrial drive rate. [ABSTRACT FROM AUTHOR]

The article describes the case of 26-year-old female with a history of nonischemic dilated cardiomyopathy secondary to valvular disease from Marfan sydrome whose post-orthotopic heart transplant was complicated by hyperacute rejection. Topics discussed include the electrocardiogram reading of the patient, the possible origin of the parasystolic focus and the occurrence of atrial parasystole.