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The effects of isoproterenol on induction of circus movement tachycardia were studied in 21 patients with an accessory atrioventricular pathway. Forty-six studies were performed. Thirteen patients were studied before and during administration of isoproterenol without antiarrhythmic drugs (group A). Ten patients (including 2 from group A) were studied before and during administration of isoproterenol while receiving oral treatment with amiodarone (group B). Ability to initiate circus movement tachycardia before or during administration of isoproterenol by programmed stimulation was correlated with the relation of circus movement tachycardia to exercise in these patients. (Seven patients in group A and 7 in group B had circus movement tachycardia related to exercise.) Isoproterenol significantly shortened sinus cycle length, duration of the QRS complex during sinus rhythm, anterograde effective refractory period of the accessory pathway, and circus movement tachycardia cycle length, owing to shortening of the AH interval during the arrhythmia. Isoproterenol made initiation of circus movement tachycardia possible in patients in whom the arrhythmia could not be initiated before. However, this effect did not correlate with the relation of the spontaneously occurring circus movement tachycardia to exercise. The electrophysiologic effects produced by isoproterenol did not differ between patients with and without exercise-related tachycardia. In all patients in whom circus movement tachycardia was initiated before administration of isoproterenol, the tachycardia was still inducible during administration of that drug. It is concluded that isoproterenol facilitates initiation of circus movement tachycardia in patients with an accessory pathway, mainly by facilitating anterograde conduction over the atrioventricular node.(ABSTRACT TRUNCATED AT 250 WORDS)
Circus movements, which involve the circumferential rotation of a hyaline cytoplasmic protrusion, occur in cells obtained by EDTA dissociation of gastrula-stage Xenopus laevis embryos. Only a few dissociated blastula-stage cells show circus movements, more early gastrula-stage cells show them, and nearly all late gastrula-stage cells show them. Circus movements cease in cells prior to mitosis and begin again in daughter cells after mitosis is completed. In early gastrulae, only 17% of prospective endodermal cells show circus movements while 79% of prospective mesodern, archenteric roof, and posterior neural ectoderm do so. Isolated cells as well as groups of cells in vitro are often propelled by circus movements. There is an obvious antagonism between cell contact and circus movements. The morphogenetic significance of circus movements and blebbing locomotion is discussed.
Mapping studies of atrial flutter in both the canine sterile pericarditis model and the right atrial enlargement model commonly reveal single loop reentrant circuits in the lower posterior part of the right atrium. Functional bidirectional conduction block and natural anatomical obstacles comprise the central obstacle for reentrant impulse during circus movement atrial flutter. Because the relative roles of anatomical obstacles, in combination with functional barriers, anisotropic conduction, and slow conduction can not be readily assessed with current electrophysiological techniques, an atrial activation model was developed to study the mechanisms of circus movement atrial flutter. A discrete state model consisting of 4096 logically connected cardiac elements was used to simulate atrial activation; an inexcitable region simulating the inferior vena cava (IVC) was also incorporated in the model. Atrial flutter was induced by programmed premature stimulation. Anisotropic conduction velocity properties, regional variations in slow conduction, regional refractory gradients and stimulation parameters were specified for each simulation. The reentrant circuit generally consisted of a single reentrant impulse which circulated around a continuous line of functional bidirectional conduction block joined to the IVC. Rapid pacing, 5-30 ms shorter than the spontaneous reentrant cycle length, was applied to entrain and/or terminate the rhythm. The results of this study demonstrate that patterns of initiation, entrainment, termination and reinitiation of circus movement atrial flutter mimic results from in vivo activation mapping studies. We find that sustained circus movement atrial flutter circuits depend on: 1) natural anatomical obstacles to stabilize reentrant circuits, and 2) anisotropic conduction properties to reduce the degree of functional conduction block needed to maintain circus movement. Rapid pacing of simulated circus movement atrial flutter demonstrated that the entrainment criteria can be satisfied in a two-dimensional syncytium.
Circus movements, involving circumferential rotation of a hyaline cytoplasmic blister and endoplasmic flow, occur in EDTA-dissociated gastrula stage Rana pipiens embryos. Such cell movements occur in very few cells taken from pre-gastrula stage embryos. During gastrulation, there is a progressive increase in the proportion of a population of cells that is engaged in circus movements. Circus movements do not occur in dividing cells. Individual cells in culture, as well as small clusters of cells in vitro, are jostled about in an apparently aimless fashion over short distances by circus movements, although the translocation of masses of cells over long distances is substantially greater than the translocation of isolated cells. In an early gastrula stage normal embryo, cells from around the site of blastopore invagination are most active in circus movements. Cells taken from different stages of arrested hybrid embryos show variable depression in the formation of rotating hyaline blebs. Aggregates of cells from arrested hybrid embryos are also relatively immobile in culture. The morphogenetic significance of circus movements in normal embryos and gastrula-arrest hybrid embryos is discussed.
Circus movements are a peculiar kind of cell movement, seen in many amphibian cells, that involve the formation of a hyaline protrusion from the cell surface and rotation of this blister around the circumference of the cell. Studies of cells from normal Rana pipiens embryos have shown a close correlation between circus movements in vitro and gastrulation related cell movements in vivo. Cells from two developmentally arrested hybrid embryos (R. pipiens female X R. sylvatica male and R. pipiens female X R. catesbiana male) are deficient in circus movements to an extent that corresponds to their gastrulation deficiencies. This study reports on the preparation of two new hybrids (R. pipiens female X R. temporaria male (temp) and R. pipiens female X R. clamitans male (clam)). Cells from temp embryos show some circus movements but the proportion of cells displaying such movements does not increase with increasing developmental age to the same extent as is seen in cells from normal embryos. Cells from clam embryos show very few circus movements at any developmental age. These aberrations in the onset and extent of circus movements are discussed in relation to characteristic morphogenetic events that occur in normal embryos and in these two new arrested hybrid embryos.
Living neurons are usually first identifiable in primary cultures at the time of neurite initiation, and studies of excitability have been restricted largely to the subsequent period. A morphological early marker is described that identifies neurons for whole-cell voltage-clamp recordings before neurite initiation. Video time-lapse recordings of cultured cells dissociated from neurectoderm of Xenopus neural plate stage embryos reveal cells demonstrating circus movements, in which blebs of plasma membrane propagate around the cell circumference within a period of several minutes. All neurons demonstrate circus movements before morphological differentiation; the fraction of cells exhibiting circus movements that differentiate morphologically depends on the substrate on which they are cultured. Blockade of circus activity with cytochalasin B does not prevent neuronal differentiation. Circus movements are not neurectoderm-specific because they similarly predict differentiation of myocytes developing in mesodermal cultures. Initially inexcitable, neurons develop voltage-dependent K+, Na+, and Ca2+ currents during the period of several hours in which they exhibit circus movements. The early development of depolarization-induced elevations of [Ca2+]i several hours before morphological differentiation corresponds to the previously described onset of functionally significant spontaneous elevations of [Ca2+]i in these neurons and demonstrates a role for early expression of voltage-dependent ion channels.
The value of the 12-lead electrocardiogram for distinguishing atrioventricular (AV) nodal reciprocating tachycardia from circus movement AV tachycardia utilizing a retrograde accessory pathway was studied in 100 patients with narrow QRS complex tachycardia. Intracardiac electrograms showed AV nodal reciprocating tachycardia in 40 patients and circus movement AV tachycardia in 60. The 12-lead electrocardiograms recorded during tachycardia were randomly sorted and reviewed by 4 experienced cardiac electrophysiologists who were blinded to the diagnosis associated with each tracing, the relative proportion of each arrhythmia and the hypotheses to be tested. Each reviewer was asked to indicate the location of the P wave relative to the QRS complex, electrical axis of the P wave in the frontal and horizontal planes and presence or absence of QRS alternation, and to interpret the most likely mechanism. The performance of published electrocardiographic criteria to differentiate AV nodal reciprocating tachycardia from circus movement AV tachycardia was evaluated. The overall accuracy of the reviewers' interpretations was 75%, similar to the accuracy of the predefined criteria when applied by these observers (71% correct, difference not significant). Interobserver agreement of reviewer interpretations was 76% and the intraobserver agreement was 78%. Features associated with circus movement AV tachycardia by univariable analysis were P waves after the QRS complex, faster tachycardia rates and QRS alternation. Multivariable analysis showed that only the location of the P wave relative to the QRS complex was independently associated with the mechanism of tachycardia (p = 0.002). QRS alternation was found by multivariate analysis to be associated with the rate but not the mechanism of the tachycardia.
OBJECTIVES: The objectives of this study were to determine the mechanisms responsible for the initiation and the termination of episodes of circus movements and to describe the characteristics of these circuits in rat myometrium. STUDY DESIGN: By means of simultaneous recordings from 240 sites in Wistar rats at 17, 19, or 21 days' gestation, a spatial and temporal analysis was performed on the electrical activation from the beginning until the end of 22 episodes of circus movements. RESULTS: The initiation of reentry was caused by (1) transient unexcitable areas at the beginning of the burst or (2) lines of conduction blocks. Circus movements were terminated by (1) reversal of recruitment (decruitment) at the end of the burst, (2) occurrence of lines of conduction blocks, or (3) interruption of the circuit. On average circuits rotated for 6 revolutions during 2 seconds. In most cases circuits remained stable; sometimes circuits drifted along the tissue and occasionally multiple wavelets were seen instead of a single circuit. CONCLUSIONS: Spatial nonhomogeneities in conduction caused by transient unexcitable areas play a major role in both the initiation and the termination of episodes of circus movements in the pregnant rat myo-metrium. In addition, most circuits remained in a single location, although sometimes meandering or even fibrillatory activity was seen.
BACKGROUND: We have shown that atrial flutter (AF) in dogs with sterile pericarditis is commonly due to a single-loop reentrant circuit in the lower right atrium comprised of a functional or functional/anatomic obstacle and a slow zone of conduction (SZ) between the central obstacle and the atrioventricular (AV) ring. The goals of the present study were 1) to establish that the epicardial SZ is the critical component of circus movement AF and 2) to identify the optimal site within the epicardial SZ at which interruption of circus movement can be accomplished by ablative techniques. METHODS AND RESULTS: We analyzed the atrial activation patterns during epicardial cooling of the SZ with as N2O-cooled probe in eight dogs (five with clockwise [CW] reentrant circuit, one with counterclockwise [CCW] reentrant circuit, and two with both CW and CCW reentrant circuits around the same pathway). In all eight dogs, cooling (-5 to +5 degrees C for 5-20 seconds) the narrow isthmus at the inferoposterior part of the SZ between the central obstacle and the AV ring reversibly terminated the reentrant circuit, whereas cooling outside this area failed to terminate the reentrant circuit. The circus movement was not observed to continue along alternate pathways when conduction in this critical zone was interrupted. Both CW and CCW reentrant circuits could be terminated from the same site within the SZ. Cooling resulted in slowing of conduction in the SZ (55 +/- 15 msec) in both CW and CCW reentrant circuits. Cooling-induced termination of CW reentrant circuits was characteristically associated with oscillations of conduction in the cooled zone of the last three cycles before termination and conduction block occurred within the cooled zone. The last "manifest" reentrant cycle was associated with the longest conduction delay in the cooled zone. However, this delay was not necessarily reflected in the length of the last reentrant cycle because of compensatory acceleration of conduction in the rest of the pathway. On the other hand, in CCW reentrant circuits, conduction block occurred abruptly at the distal border of the SZ and without significant oscillations of conduction. CONCLUSIONS: The present study provides convincing evidence that single-loop circus movement in this model is critically dependent on an obligatory conduction in a SZ in the inferoposterior portion of the free right atrial wall between a functional obstacle and the AV ring. Because the atrial myocardium behaves electrophysiologically as a two-dimensional surface, the results of this study may help to guide the endocardial electrode catheter ablative technique for treatment of clinical AF.
The type of equipment used to transport circus tigers, environmental factors experienced during transport, and resultant body temperatures of tigers transported were surveyed during hot and cold weather conditions with six different circus tiger acts. Dataloggers recorded interior and exterior temperatures, relative humidity, and radiant heat at 5-min intervals during each trip. Microdataloggers fed to the tigers recorded body temperature and were recovered from eight Bengal (Panthera tigris tigris), Siberian (P. t. altaica), or Bengal-Sumatran (P. t. tigris-P. t. sumatrae) cross tigers from four different circuses. Three basic types of systems were used by circus acts to transport tigers: freestanding cages mounted on wheels that were winched or pushed into a semitrailer for transport, cages built into the trailer itself, and weather-resistant units transported on flatbed railcars or flatbed truck trailers. The highest temperature encountered inside a trailer was 37.3 degrees C in hot weather conditions, but overall, temperatures were usually between 21.1-26.7 degrees C. Temperature inside the trailers did not appear to be affected by movement and did not generally exceed ambient temperatures, indicating adequate insulation and passive ventilation. During cold weather trips, the lowest temperature inside the trailers was -1.1 degrees C, occurring during an overnight stop. Interior temperatures during cold weather transport stayed 2-6 degrees C warmer than ambient temperatures. The body temperatures of the tigers were unaffected by extreme temperatures. The only changes observed in body temperature were increases of 1-2 degrees C caused by activity and excitement associated with loading in several groups of tigers, regardless of whether it was hot or cold weather. Whenever measured, carbon monoxide and ammonia were below the detectable concentrations of 10 and 1 ppm. respectively. Overall, transport did not appear to have any adverse effects on the tigers' ability to thermoregulate.
Seven (2.31%) circus workers of two circus companies visiting Amritsar were detected to be suffering from leprosy. Whether or not they acquired the disease during their stay in circus is not so important, but it is necessary to detect and treat these itinerant persons. Our experience clearly underlines the necessity for undertaking surveys of various workers living in crowded conditions (like circus), because of their occupation.
A 30 year old woman with Wolff-Parkinson-White syndrome underwent electrophysiologic study for investigation of circus movement tachycardia utilizing the accessory pathway for retrograde conduction. The accessory pathway was located on the right side. Episodes of circus movement tachycardia with left and right bundle branch block were induced. Some episodes of circus movement tachycardia with left bundle branch block terminated spontaneously. Two episodes of spontaneous termination at the level of the atrioventricular (A-V) node were preceded by prolongation of the H-V interval causing delay in atrial activation. This delayed atrial cycle was then followed paradoxically by spontaneous termination of the tachycardia in the A-V node. A similar phenomenon could be demonstrated reproducibly with single echo beats induced by coronary sinus extrastimuli. It appears that retrograde concealed penetration of the A-V node through the bundle branch system during anterograde left bundle branch block is the most likely mechanism for this phenomenon.
Infranodal conduction delay is an uncommon mechanism of initiation of circus movement tachycardia in the Wolff-Parkinson-White syndrome. A patient with a concealed left free wall atrioventricular accessory pathway who underwent electrophysiological study is presented. During atrial extrastimulus testing, a pattern of alternating bundle branch block was observed and was most marked after the administration of intravenous procainamide. Conversion from right bundle branch block to left bundle branch block was reproducibly associated with the initiation of circus movement tachycardia utilizing the normal conducting system antegradely and the accessory pathway retrogradely. Initiation of tachycardia was critically related to the increase in the HV interval associated with left bundle branch block. Of interest, conduction in the right bundle branch became progressively slower as the prematurity of the atrial extrastimulus increased, whereas conduction time through the left bundle branch remained fixed prior to block. Implications of these findings are discussed. To our knowledge, this is the first report of alternating bundle branch block during atrial extrastimulus testing as a mode of initiation of circus movement tachycardia in the Wolff-Parkinson-White syndrome.
Circus-movement tachycardia was studied using voltage-sensitive merocyanine-rhodanine dyes (dye XVII and NK2761). Excitatory waves were optically measured simultaneously from eight different regions of a ring of tissue formed from frog atrium. Application of acetylcholine in Ca2+-free solution (10(-10)-10(-9) g/ml) shortened the duration of optical action signals to cause nonuniform change in optical signal durations in about 60% of the preparations. Circus-movement tachycardia was produced by proper reduction and regional nonuniformity of optical signal durations. Under these circumstances it is easy to evoke circus-movement tachycardia by giving an extra stimulus to the site that shows a difference in optical signal durations.
The fine structure of lobopodia in dissociated embryonic cells of the freshwater fish, Oryzias latipes, was observed with the electron microscope in order to understand the mechanism of the circus movements which they display. Dense material (grandular or fibrillar) is present in the zone between the lobopodium and the endoplasm, as well as in the cortical layer around the cell circumference. The direction of lobopodial movement is related to the distribution of this dense material. The band between the lobopodium and the endoplasm is conspicuous and is connected to the cortical dense layer around the cell periphery at the advancing front of the lobopodium, while the dense material is usually almost absent beneath the cell membrane in the anterior region of the lobopodium. The band between lobopodium and endoplasm is blurred or disrupted near the hind end of the lobopodiu, where the peripheral dense layer is well developed. In situ localization of actin/heavy meromyosin complexes in the cell showed that the dense material has actin-like properties. Cytochalasin B(0-5 mug/ml) induced constriction of the neck of the bleb, shrinkage of the endoplasm, and herniation of the endoplasmic contents to the enlarged hemispherical bleb, and thus arrested the circus movement. On the basis of these results, an hypothesis concerning the mechanism of circus movement is proposed and discussed.
By means of intracardiac recordings and programmed electrical stimulation of the heart, the combination effect of verapamil and disopyramide on induction of circus movement tachycardia was studied in 8 patients with anomalous extranodal atrioventricular (A-V) pathway. In 4 of 6 patients who manifested reproducible circus movement tachycardia, verapamil, 0.2 mg/kg intravenously administered, prevented the induction of tachycardia by increasing the A-V nodal refractoriness. Disopyramide in a dose of 2 mg/kg was injected 30 minutes after the start of verapamil administration, when prolongation of the A-V nodal conduction time (A-H interval) had continued in most of the patients. Disopyramide lengthened the effective refractory period of the anomalous pathway in all patients in whom this could be determined. The A-H interval, which had been prolonged by verapamil, was shortened in 4 patients and about unchanged in the remaining 4. After addition of disopyramide, sustained tachycardia could be induced in 2 patients who had lost the ability of initiating circus movement tachycardia after verapamil administration. Thus, disopyramide, when administered together with verapamil, may block the effect of verapamil on the A-V node by its anticholinergic action. A concomitant prescription of disopyramide with verapamil in expectation of the depression of both the anomalous pathway and the A-V node may have an untoward outcome.