Interectopic Intervals Research Articles

Ectopic cycle length estimation from the quantified distribution patterns of ventricular bigeminy and trigeminy.

BackgroundEctopic cycle length (ECL) and the distribution patterns of ventricular bigeminy and trigeminy, expressed as their postextrasystolic intervals (PEIs) and interectopic intervals (IEIs), have been poorly pursued.ObjectiveBased on modulation theory, we hypothesized that the PEIs of bigeminy and trigeminy determine their IEIs and ECL.MethodsAmbulatory electrocardiograms of 1290 patients with ventricular premature complexes (≥3000/day) were studied. To quantify their distribution pattern on the PEI vs IEI curve (PIC), we introduced the following 2 ratios: PEI of trigeminy to PEI of bigeminy ratio (T/B-PEI) and IEI of trigeminy to IEI of bigeminy ratio (T/B-IEI). Distribution patterns were divided into 3 types by T/B-PEI: standard type (<0.90), intermediate type (between 0.90 and 1.20), and reverse type (>1.20). ECL was defined as the average of the bigeminy and trigeminy intervals in the standard type, and bigeminy intervals in the other 2 types.ResultsT/B-IEI disclosed significant linear relationship with T/B-PEI (P < .0001). ECLs were longest in the standard type (1905 ± 347 ms; n = 426), followed by the intermediate type (1520 ± 239 ms; n = 607) and reverse type (1317 ± 227 ms; n = 227) (P < .0001). Trigeminy PEI/ECL in the standard type (0.450 ± 0.074) was significantly shorter than that of the other 2 types (P < .0001).ConclusionWe confirmed that T/B-PEI determines T/B-IEI and ECL by discriminating the 3 distribution patterns. Among them, trigeminy PEI/ECL decided the 2 types of modulation by the first sinus QRS, starting at the early delay phase or the later acceleration phase.

Demonstration of Ventricular Parasystole on a Standard 12-Lead Electrocardiogram

During a clinical trial assessing the efficacy of ranolazine for the suppression of atrial fibrillation, a patient was encountered who, aside from paroxysmal atrial fibrillation, had premature ventricular complexes (PVC) on his electrocardiogram (ECG). A close examination of the ECG rhythm strip revealed that these PVC’s had: 1) a regular interectopic interval or multiple thereof (approximately 1720 ms), 2) fusion complexes with the underlying sinus rhythm QRS complexes, and 3) variable coupling intervals. This constellation of findings defines a parasystolic focus, making this rhythm sinus rhythm with ventricular parasystole. A dose of ranolazine 1000 mg po bid satisfactorily reduced the patient’s atrial fibrillation and also suppressed virtually all of the ventricular ectopy.

Intermittent atrioventricular block: What is the mechanism?

Discussion The rhythm strip shows sinus rhythm with right bundle branch block morphology. There are premature ventricular contractions (PVCs); the coupling intervals of the PVCs are variable, indicating the possibility of a parasystolic focus. However, the diagnosis of parasystole cannot be made with confidence without a long rhythm strip to measure the interectopic intervals. Figure 2A shows sinus rhythm at a cycle length of 1,000 ms. A PVC occurring at a coupling interval of 440 ms is not resetting the sinus node, as evident by a full compensatory pause of 2,000 seconds. Potential mechanisms are that the PVC

Mechanism of Ventricular Premature Contraction Showing Interpolated Bigeminy —Strong Modulation Hypothesis—

Recent advances in invasive electrocardiology dramatically revealed the unique nature of atrial fibrillation originating from the pulmonary veins. By the same invasive technique, the origin of ventricular premature contraction (VPC) has been clarified as being located in the pulmonary outflow tract, ventricular Purkinje fibers or coronary cusps. Despite these clarifications, the essential mechanism of VPCs still remains uncertain. In addition to automaticity, the possible contribution of reentrant pathway cannot be fully ruled out. To analyze the mechanism, we previously reported on a two dimensional color display of interectopic intervals in VPC patients. This display could estimate the fundamental mechanism of VPC for a full day and clearly differentiate parasystole from fixed coupling interval VPCs.In this review, first we briefly document the historical background. In order to explain the mechanism of the much more frequently observed fixed coupling interval VPCs, we introduced a new version of color display. Using this modified version, a unique electrocardiogram associated with heart rate doubling during interpolated VPC bigeminy was depicted. The role of interpolated VPCs applied to phase analysis was stressed. From the findings, we developed a strong modulation hypothesis.Clinical significance of interpolated VPC together with heart rate doubling and harmonic feature was illustrated. Our hypothesis can be applied not only to specific form of parasystole with various coupling intervals but also to fixed coupling interval VPCs. The modified display can roughly discriminate the relative ratio of parasystole cycle length from sinus cycle length. Furthermore, simple estimation of the intrinsic automaticity cycle length together with the heart rate dependence in individual patients was possible.

Mechanism of Ventricular Premature Contraction Showing Interpolated Bigeminy —Strong Modulation Hypothesis—

Recent advances in invasive electrocardiology dramatically revealed the unique nature of atrial fibrillation originating from the pulmonary veins. By the same invasive technique, the origin of ventricular premature contraction (VPC) has been clarified as being located in the pulmonary outflow tract, ventricular Purkinje fibers or coronary cusps. Despite these clarifications, the essential mechanism of VPCs still remains uncertain. In addition to automaticity, the possible contribution of reentrant pathway cannot be fully ruled out. To analyze the mechanism, we previously reported on a two dimensional color display of interectopic intervals in VPC patients. This display could estimate the fundamental mechanism of VPC for a full day and clearly differentiate parasystole from fixed coupling interval VPCs. In this review, first we briefly document the historical background. In order to explain the mechanism of the much more frequently observed fixed coupling interval VPCs, we introduced a new version of color display. Using this modified version, a unique electrocardiogram associated with heart rate doubling during interpolated VPC bigeminy was depicted. The role of interpolated VPCs applied to phase analysis was stressed. From the findings, we developed a strong modulation hypothesis. Clinical significance of interpolated VPC together with heart rate doubling and harmonic feature was illustrated. Our hypothesis can be applied not only to specific form of parasystole with various coupling intervals but also to fixed coupling interval VPCs. The modified display can roughly discriminate the relative ratio of parasystole cycle length from sinus cycle length. Furthermore, simple estimation of the intrinsic automaticity cycle length together with the heart rate dependence in individual patients was possible.

Variation in Parasystolic Cycle Length Observations of a Hypertensive Patient for Over Six Years

At the time of the first visit to our clinic, an electrocardiographic examination of a 73-year-old female patient revealed ventricular premature contractions (VPCs) with variable coupling intervals that were diagnosed as parasystole. Characteristically many of the parasystoles had no sinus contractions between two consecutive VPCs, which we referred to as pure parasystole. We first repeatedly examined variations in the length of the parasystolic cycles between January 6, 1997 and March 2, 2003 using electrocardiography. The time courses recorded over this period showed that the length of the parasystolic cycle did not remain constant, but varied irregularly within a relatively narrow range. We also recorded the length of the parasystolic cycles over 3 hours using Holter monitoring. The interectopic intervals plotted against mean sinus cycle length showed that the cycle length of pure parasystoles remained almost constant at about 1,300 ms over the 3 hours. We also examined the cycle length during exercise and found that it was slightly prolonged thereafter, while the sinus cycle length was clearly shortened after exercise. The average of six deep breathing tests showed that parasystolic cycle length did not significantly differ between deep inspiration and deep expiration, whereas the sinus cycle length during expiration was significantly longer than that during inspiration. These results indicate that the responses to both exercise and deep breathing obviously differed between the parasystolic and sinus cycle lengths.

Enhancing long-term ECG monitoring with graphic analysis of coupling intervals

By graphically identifying patterns of ventricular ectopic beat (VEB) interval characteristics, we sought to enhance arrhythmia analysis, especially in long-term ECG monitoring. Coupling intervals as a function of preceding sinus RR intervals (CI/RR diagrams) with the aid of coupling interval and interectopic interval histograms were analyzed in 172 patients with frequent VEBs. Four distinct types of CI/RR diagrams were observed: horizontal-elongated (25 patients), linear (4 patients), triangular (37 patients), and clusters separated by dot-sparse areas (17 patients). In 89 patients, no definite pattern was discerned. The patients with elongated diagrams were significantly younger, had fixed coupling, uniform QRS complexes, and lacked periodicities in their interectopic interval histograms. The linear pattern was detected in a small group with rate-related VEBs. In the group with a triangular pattern, 30% of the patients exhibited interactopic periodicities suggesting parasystole. The patients with dot-sparse areas in the CI/RR diagrams had more variable coupling and predominantly more multiform QRS complexes. We conclude that CI/RR diagrams in conjunction with coupling interval and interectopic interval histograms enhance arrhythmia analysis by identifying patterns, such as those consistent with either fixed coupling, rate dependence, parasystole, or multiform VEBs.

The diagnostic criteria for classic parasystole.

To establish a diagnostic criteria of parasystole with high sensitivity and high specificity. 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. 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. Three quantitative indices as necessary conditions have been used as diagnostic criteria for parasystole with high sensitivity and high specificity.

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

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 multiples 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.

Ectopic Ventricular Beats Originating in Ischemically‐Injured Left Ventricular Epicardium, 24 Hours Following Coronary Artery Occlusion in the Dog

Epicardial Ectopics. Introduction: Ventricular ectopic beats demonstrating: (1) depolarization in ischemically‐injured anterior epicardium preceding His‐Purkinje activation by more than 25 msec; (2) initial delta waves on the anterior chest leads of the surface ECG coincident with presystolic epicardial activation; and (3) a left bundle branch block morphology were observed in 46 of 256 anesthetized dogs evaluated 18–24 hours following anterior descending coronary artery occlusion. Methods and Results: In 18 experiments, endocardial and epicardial recordings, and signal‐averaged recordings from the left ventricle were used to determine the earliest activation time/site for epicardial ectopic beats. In these ventricular ectopic beats, early epicardial activation was coupled to the preceding beat by a constant, fixed coupling interval. Electrical activity during the interectopic interval was not detected with composite or multiple bipolar recordings, or with signal averaging from the heart. The mean coupling interval was prolonged by lidocaine from 385 ± 24to 409 ± 45 msec (P &lt; 0.01), and was decreased by epinephrine (364 ± 7 msec) and D‐600 (324 ± 32 msec)(P &lt; 0.05). Spontaneous ventricular beats of epicardial origin could be reversibly suppressed by epicardial lidocaine administration or permanently suppressed with intracoronary latex injection, eliminating presystolic potentials. Histologic examination of the epicardium revealed surviving tissue bands (0.5–2.0 mm) distributed throughout transmural infarcted epicardium. Conclusion: The present experiments demonstrate constant‐coupled ectopic ventricular beats of epicardial origin, 18–24 hours following myocardial infarction. The ventricular ectopic beats may result from abnormal automaticity or electrotonic excitation from an initiating beat across an unexcitable gap with slow conduction from the “site of origin’ to reactivate the left ventricle. (JCardiovasc Electrophysiol, Vol. 3, pp. 315–333, August 1992)

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.

Distribution patterns of ventricular premature complexes in long-term electrocardiographic recordings and their usefulness in disclosing modulated parasystole

Long-term electrocardiographic recordings from 25 patients with abundant ventricular premature complexes (VPCs) were screened with a computer program for sequences of interectopic intervals with the number of sinus beats consistent with manifest or concealed bigeminy/trigeminy. On average, 19.0% of VPCs in this patient series were followed by an uninterrupted sequence of ≥10 interectopic intervals with concealed bigeminy. The corresponding figure for concealed trigeminy was 2.2%, for manifest bigeminy 9.6%, and for manifest trigeminy 0.8%. The longest sequence with concealed bigeminy comprised 149 interectopic intervals. The corresponding figure for concealed trigeminy was 135 interectopic intervals. The sequences of concealed bigeminy occurred at significantly lower heart rates than those of concealed trigeminy. These findings can be explained by the entrainment phenomena described in experimental models of modulation of a ventricular parasystolic focus across a zone of impaired conduction.

Influence of sinus impulses on the parasystolic cycle length

Recently, it has been shown that in most clinical cases of parasystole, the parasystolic rhythm is not completely independent of the sinus rhythm. In this study, to disclose the mechanism of such “irregular” parasystole, parasystolic cycles with an intervening sinus QRS complex (XSX) were compared with their immediately adjacent pure parasystolic cycles without any intervening nonparasystolic QRS complexes (XX) in 10 cases of ventricular parasystole. In eight cases, the XSX interval was equal to or nearly equal to the adjacent pure XX interval; in one, the XSX interval was shorter than the XX interval; and in only one, the XSX interval was longer than the XX interval. In six cases in which the XSX interval was almost equal to the XX interval, calculated XSX intervals with a later intervening sinus QRS complex were obtained from the differences between the XSSX interval (ie, interectopic interval with two intervening sinus QRS complexes) and its adjacent XX interval. In five of the six cases, the calculated XSX interval was shorter than the XX interval. These observations suggest that in most cases of parasystole, early intervening sinus impulses do not change the parasystolic cycle, whereas late intervening sinus impulses shorten the parasystolic cycle. This suggests the presence of type I second-degree entrance block as the mechanism of “irregular” parasystole.

A Case Report about Anesthesia of the Patient with Ventricular Parasystole

Parasystole is of special interest among the disturbances of ectopic impulse formatioo. First, a parasystolic arrhythmia is of clinical importance because the ventricular origin ordinarily indicates the presence of organic heart disease. Second, parasystole, although not rare, is frequently overlooked because it is difficult to be differentiated from extrasystole. In this paper a ventricular parasystole is presented. A 48 year-old woman was seen with an irregular pulse rate not accompanying cardiac symptoms or signs. The chest radiograph failed to show cardiomegaly. E.K.G. revealed the dominant rhythm of sinus origin with intermittent ventricular parasystolic beats. The basic rhythm was sinus with a rate of 83 per minute. The coupling interval varied between 0.52 & 0.7 second. The shortest, calculated interectopic interval ranged from 45.2 to 49.7 (These numbers represent hundreds of a second). Occasional ventricular fusion beats appeared. She was uneventfully nephrectomized under general anesthesia with halothane-N2O-O₂for left renal empyema of tuberculosis. She dispensed well with any antiarrhythmic agent during admission

A rare variant of atrial parasystole in children

Atrial parasystole in children is more common than defined. It is an independent type of arrhythmia with high ectopic center activity. Diagnosis is possible only with electrocardiographic examination. For the left atrial form, the ECG of the right thoracic lead (V1) is the main element of examination. Atrial complex in V1 has a shield and sword shape (gentle ascending, terminal part of P,-high pointed). Electrocardiographic signs of atrial parasystole are temporal differences of pre-ectopic intervals, the multiplicity of inter-ectopic intervals, and the presence of confluent complexes.

Concealed Ventricular Bigeminy with Exceptions due to Time-Dependent Modulation of an Ectopic Rhythm

This presentation reflects a case of atypical concealed bigeminy, where some interectopic intervals contain even numbers of sinus beats. Exceptions to the rule of concealed bigeminy only occur during slowing of the sinus node. The pattern is explained on the basis of modulated parasystole, by drawing a phase-response curve which explains all the interectopic intervals on the basis of the modulating effect exerted by the sinus impulses upon a parasystolic focus.

“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 experessed 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.

Atrio-ventricular junctional parasystole: Modulation by sinus impulses

A rare case of atrio-ventricular (A-V) junctional parasystole with a quinquageminy and a trigeminy in the presence of a right bundle branch block (RBBB) is reported, in which the ectopic beats showed the same QRS complex as that of the conducted sinus beats. After taking a bath and after intravenous administration of 1.0 mg of atropine, viz. the maneuver to block the vagal effects, the short interectopic interval shortened from control of 2.65–2.70 sec to 2.08 sec, when the shortest interval of 0.98 sec was observed. Thus, the short interectopic intervals resulted from a 2:1 exit block. When the intrinsic ectopic cycle length was about 1.52 sec, the second of four intervening sinus beats in quinquageminy reset the parasystolic pacemaker and a 2:1 exit block ensued, which was attributed to entrance block failure due to a supernormal phase of excitability and conductivity in the His bundle.

Modulated ventricular parasystole manifesting as apparent Wenckebach exit block

Since Jalife and Moe 1 reported the experimental modulation of a parasystolic focus, it has become evident that a parasystolic rhythm may manifest with features different from those classically described. The modulated parasystolic cycle may become irregular as a result of influence exerted by the sinus beats, and the interectopic intervals may therefore not be mathematically related. 2–5 We present a case of modulated ventricular parasystole in which the typical diagnostic features of parasystole are lacking and in which the distribution of the ectopic beats suggests a Wenckebach form of ectopic-ventricular block.