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PubMed1991

Lack of prognostic value of syncope in patients with Wolff-Parkinson-White syndrome.

Syncope in patients with Wolff-Parkinson-White syndrome may be considered a premonitory event heralding the future development of sudden death. Therefore, the clinical and electrophysiologic data of 101 patients with Wolff-Parkinson-White syndrome referred for invasive evaluation of known arrhythmias were reviewed to assess the incidence and clinical relevance of syncope. Thirty-six patients reported the occurrence of one or more syncopal episodes (group 1) and 65 patients had no syncope (group 2). These two groups did not differ significantly with regard to age, gender, incidence and characteristics of arrhythmia, clinical history, frequency of arrhythmic events and presence of associated cardiac disease. There were 10 patients in group 1 and 12 in group 2 who had ventricular fibrillation. There were no statistical differences between the two groups with respect to the effective refractory period of the right atrium, atrioventricular node, accessory pathway and right ventricle. Furthermore, no differences between the two groups were noted with respect to cycle length of circus movement tachycardia, mean heart rate during atrial fibrillation, and minimum RR interval during atrial fibrillation. In addition, the accessory pathway location was not significantly different between group 1 and group 2. The occurrence of syncope could not be predicted from any electrophysiologic finding and this symptom had a low sensitivity and specificity for recognition of dangerous rapid heart rates. Furthermore, the prognostic value of syncope was less accurate and predictive than the shortest RR interval during atrial fibrillation and the anterograde effective refractory period of the accessory pathway for aborted sudden death occurrence.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1991

Onset of induced atrial flutter in the canine pericarditis model.

To test the hypothesis that induced atrial flutter evolves from a transitional rhythm, the onset of 99 episodes of induced atrial flutter (mean cycle length 135 +/- 18 ms) lasting greater than 5 min in 40 dogs with sterile pericarditis was first characterized. In 85 (86%) of the 99 episodes, atrial flutter was preceded by a brief period (mean 1.4 +/- 0.9 s, range 0.4 to 42) of atrial fibrillation. Then, in 11 open chest studies, atrial electrograms were recorded simultaneously from 95 pairs of right atrial electrodes during the onset of 18 episodes of induced atrial flutter (mean cycle length 136 +/- 16 ms). Atrial flutter was induced by a train of eight paced atrial beats, followed by one or two premature atrial beats (7 episodes) or rapid atrial pacing (11 episodes). A short period of atrial fibrillation (mean cycle length 110 +/- 7 ms) induced by atrial pacing activated the right atrium through wave fronts, which produced a localized area of slow conduction. Then unidirectional conduction block of the wave front occurred for one beat in all or a portion of the area of slow conduction. This permitted the unblocked wave front to turn around an area of functional block and return through the area of slow conduction that had developed the unidirectional conduction block, thereby initiating the reentrant circuit. The location of the unidirectional block relative to the direction of the circulating wave fronts determined whether the circus movement was clockwise or counterclockwise. The area of slow conduction and unidirectional conduction block occurred where the wave front crossed perpendicular to the orientation of the atrial muscle fibers, suggesting a role for anisotropic conduction. These areas included the high right atrial portion of the sulcus terminalis (10 episodes), the low right atrial portion of the sulcus terminalis (4 episodes) and the pectinate muscle region (4 episodes). It is concluded that the development of a localized area of slow conduction in the right atrium followed by unidirectional conduction block in this area produced during a short period of atrial fibrillation or rapid atrial pacing is necessary for atrial flutter to occur in this model.

Animals↗
PubMed1986

Linking phenomenon during atrial stimulation with accessory pathways.

Linking is an electrophysiologic phenomenon in which each successive impulse entering a macroreentry circuit propagates preferentially along 1 limb because of the functional impedance to conduction in the contralateral limb produced by the previous impulse. Electrophysiologic studies were performed in 12 patients with a bidirectionally conducting accessory pathway. Linking was analyzed while 1:1 atrioventricular conduction took place through the normal pathway. When atrial pacing (at the same cycle length) could be initiated during sinus rhythm in patients with rapidly conducting accessory pathways, linking was dynamically maintained by repetitive local refractoriness (interference). When it could be initiated during the usual type of orthodromic circus movement tachycardia, linking was sustained by actual impulse collision, the underlying mechanism having also been called entrainment. When it could be initiated during sinus rhythm in a patient with a slowly conducting accessory pathway, linking was maintained by impulse collision, but the underlying mechanism could not be called entrainment because stimulation had not been started during tachycardia. This study showed that 2 terms--linking and entrainment--may be applied to the same mechanism and, conversely, that the same name could not be used in reference to the same mechanism when pacing was initiated under different circumstances. However, using the proposed conceptual formulation for linking, it is apparent that seemingly diverse mechanisms associated with macroreentry circuits involving accessory pathways are, in fact, variations on a common electrophysiologic theme.

Adolescent↗
PubMed1998

Mechanisms of atrial fibrillation and action of drugs used in its management.

Drugs remain the mainstay of treatment of patients with atrial fibrillation (AF). An understanding of the mechanisms of AF and of atrioventricular (AV) conduction provides a basis for the understanding of the mechanisms of antiarrhythmic drug action. Although ectopic activity from a focus may initiate AF, re-entry is the usual mechanism of maintenance. In its classical form, reentry takes the form of circus movements around fixed anatomic structures. However, leading circle and anisotropic variants of reentry may arise as a result of functional variations of refractoriness or anistropic conduction. Electrical remodeling during AF favors its persistence. Reentry may be prevented by prolongation of the refractory period. Class III antiarrhythmic drugs prolong refractoriness by blockade of outward potassium currents. Class I drugs prolong refractoriness by delaying the recovery of of the sodium current. Many class I drugs also have potassium channel-blocking action. In AF the rate of conduction of rapid impulses to the ventricle is controlled by conduction over the AV node. Blockade of the L-type calcium channels, activation of the muscarinic and adenosine A1 receptors, or beta-adrenergic blockade will slow conduction over the AV node. The adverse cardiovascular effects of drugs used to treat AF can be predicted on the basis of their mechanisms of action. The current focus of drug development is on specific potassium channel blockers.

Animals↗
PubMed1995

Aborted sudden death in the Wolff-Parkinson-White syndrome.

In a population of 690 patients with Wolff-Parkinson-White (WPW) syndrome referred to our hospital from January 1979 to February 1995, 15 patients (2.2%) had an aborted sudden death out of the hospital. This retrospective study examines their clinical and electrophysiologic characteristics. Gender, accessory pathway localization, and presence of multiple accessory pathways were compared between patients with and without spontaneous ventricular fibrillation (VF). Whereas gender and the presence of multiple accessory pathways did not significantly differ between both groups, septally located pathways occurred significantly more often in the VF group. In patients with aborted sudden death, spontaneous VF was found significantly more often in men (13 of 15). VF was the first manifestation of the WPW syndrome in 8 patients. The remaining 7 patients had documented episodes of atrial fibrillation, circus movement tachycardia, or both (n = 2). Ten of the 15 patients were exercising or under emotional stress at the time of aborted sudden death. Only 1 patient had 2 accessory pathways. The location of the accessory pathway was septal (midseptal or posteroseptal) in 11 patients, left lateral in 4, and right lateral in 1).

Adolescent↗
PubMed1976

The effects of vision on the general locomotor behaviour of the goldfish, Carassius auratus.

Comparison of the locomotor behaviour of normal, unilaterally and bilaterally blinded goldfish (Carassius auratus) demonstrated the roles of perspective vision (depth perception), which requires binocular vision, and of vision provided by only one eye, in the control of locomotion. Because normal and bilaterally blinded fish exhibited similar size and direction of angles of turn, a similar number of consecutive turns in the same direction and the same turning frequency, normal, binocular vision plays no role in the control of turning behaviour. Unilaterally blinded fish exhibited a strong bias in turning behaviour which resulted in their displaying circus movements toward the blinded side, a direction opposite to that reported by others for both invertebrates and vertebrates with unilateral sensory elimination. The mean step length was significantly increased by both uni-and bilateral blinding, and its temporal relationship with turning frequency and distance swum was also changed. Perspective vision (binocular) therefore controls these parameters. The significantly lower velocity of bilaterally blinded fish and the similarity between the other two test groups, indicated that sight by one eye only was sufficient to mediate velocity control.

Animals↗
PubMed1998

Polymorphic ventricular tachycardias induced by D-sotalol and phenylephrine in canine preparations of atrioventricular block: initiation in the conduction system followed by spatially unstable re-entry.

OBJECTIVE: Polymorphic ventricular tachycardias (PVT) occur spontaneously in canine hearts under the combination of D-sotalol (S), bradycardia and phenylephrine (PE). We investigated the hypotheses that: (1) the activation patterns of the initial PVT beats would be consistent with an origin in the ventricular conduction system; and (2) the inhomogeneous prolongation of repolarisation intervals can provide refractory barriers for re-entrant activity. METHODS: Unipolar electrograms were recorded from 127 epicardial (EPI) sites with a sock electrode array as well as from intramural and endocardial sites during PVTs. Electrograms were analysed to generate isochronal maps and measure the spatial distribution of activation-recovery intervals (ARI). RESULTS: Under S (9.9-14.5 mg.l-1), spontaneously terminating PVTs (cycle length of 270 +/- 43 ms, n = 45) (mean +/- s.d.) occurred when a PE bolus (10-50 micrograms.kg-1) was injected. The first beat of the PVTs occurred with a coupling interval of several hundred ms to the preceding idioventricular beat (IDV) without any bridging activity and its earliest EPI breakthrough occurred in areas overlying the terminations of the right or left bundle branch. ARI values measured in IDV (295 +/- 47 ms) were significantly prolonged prior to PVT (462 +/- 92 ms). Prolongation was greater in apical than in basal epicardial areas, and at endocardial than epicardial sites (to > 500 ms). Maximum delays > 200 ms developed in the regions of marked ARI prolongation and, in later beats, circus movement re-entry occurred around refractory barriers, shifting between various regions of the ventricles. CONCLUSION: Thus, PVTs occurring spontaneously under conditions of delayed repolarisation originate from shifting sites in the ventricular conduction system and re-entrant activity shifting between various regions of the ventricle may occur in later beats of the more sustained arrhythmias.

Adrenergic alpha-Agonists↗
PubMed1994

Complex dynamic order in ventricular fibrillation.

Self-sustained circus movement of excitation has long been discussed as the underlying mechanism of ventricular fibrillation. This concept now appears to have found general acceptance. Mapping studies are very expensive and do not permit observations to be isolated from varying external influences. The authors have therefore used a simple cellular automation for studying the basic principles of excitation spreading during ventricular fibrillation under various conditions. Highly ordered spiral waves, described in other computer models, previously interpreted as fibrillation were encountered. Comparisons of pseudo-electrocardiograms created by the cellular automaton with original electrocardiographic recordings showed similarity in the time series and in fast Fouriér transformation. Modulation of refractory times often led to the termination of model fibrillation. Clinical evidence suggests that maintenance of the 1/f (RR-variability) variations produced by the autonomic nervous system exerts a protective effect on the evolution of ventricular fibrillation.

Computer Simulation↗
PubMed1992

Intercellular conduction velocity variability as the basis for re-entrant arrhythmias in the ischemic myocardium.

Re-entrant arrhythmias are the major cause of death from cardiovascular disease. A number of models or mechanisms have been proposed to explain the generation of re-entrant arrhythmias in the ischemic or damaged heart. However, none of these models can qualitatively predict the formation of re-entry movements with no modifications of the basic electrophysiologic characteristics of the myocardium. In this presentation we evaluate the concept that the generation of re-entrant arrhythmias is due to increased variance in the conduction characteristics of the cardiac tissue, rather than to modification of these properties. Using a model of a homogeneous two-dimensional matrix of excitable conducting cells, we derived the relationship between the relative standard deviation (RSD) and the probability of occurrence of a local ordered dispersion of velocities shown to have the potential to result in circular propagation. This probability was found to be insignificant when the RSD was lower than 10%, but increased dramatically for RSDs greater than 10%. On the basis of experimental RSD, the calculated probability for circus movement formation is one in 10,000 normal heart beats and one in two ischemic heart beats. The model provides new insight into the mechanism of re-entrant arrhythmias as well as new tools for diagnosis.

Arrhythmias, Cardiac↗
PubMed2000

Paired-associate learning and memory interference in schizophrenia.

Patients with frontal lobe damage have been shown to exhibit disproportionate impairments of second list learning as a result of interference effects. Based upon the assumption that schizophrenia is associated with frontal dysfunction, we attempted to explore how various manipulations of paired-associate learning tasks would interfere with schizophrenic patients' memory performance. Patients with schizophrenia were administered four tests of paired-associate learning, in which cue and response words were manipulated to increase interference across two study lists. In two tests of paired-associate learning (AB-AC test), cue words used in one list were repeated in a second list but were associated with different response words (e.g. lion-hunter, lion-circus). One version of this test employed moderately related word pairs and the other version employed unrelated word pairs. In the other two tests (AB-ABr test), all words used in one list were repeated in a second list but were rearranged to form new pairs. Again, one version of this test used moderately related word pairs and the other version used unrelated word pairs. We hypothesized that patients with schizophrenia would exhibit disproportionate impairment of second-list learning as a result of interference effects and that they would do especially poorly in the AB-ABr task, where the word pairs were unrelated. However, these predictions were not supported. Furthermore, it was difficult to tease apart a specific problem in list discrimination from the generally poor memory of the schizophrenic patients. We suggest that the susceptibility to these interference effects in patients with schizophrenia is not a specific problem in cognition, but rather one that is confounded by general memory problems.

Adolescent↗
PubMed2000

Child characteristics which impact accuracy of recall and suggestibility in preschoolers: is age the best predictor?

OBJECTIVE: The purpose of the present study was to determine whether individual difference factors of metamemory, intelligence, and temperament can improve the ability to predict accuracy of recall and suggestibility in preschoolers. METHOD: Fifty-six children ranging in age from 43 months to 83 months (M = 61, SD = 9) were recruited from 13 child care centers in a rural southeastern town. Children participated in a "Circus Day" event conducted by two female undergraduate psychology students dressed as clowns. Approximately 10 days (M = 10; SD = 2) after the event, children were interviewed regarding their experiences. RESULTS AND CONCLUSIONS: Bivariate correlations and multiple regression analyses were performed in order to determine which factors were related and unique contributors to accuracy of recall and suggestibility. Of principal importance is the finding that child characteristics such as metamemory ability, intellectual functioning, and temperament may indeed be helpful in determining a child's capacity to accurately recall information in an interview, although for the most part age is the best predictor. Findings also underscore the importance of considering a child's SES and race when planning and conducting interviews with young children. Possible explanations for these findings as well as implications for future research and clinical application are discussed.

Child↗
PubMed1997

Radiofrequency ablation of tachyarrhythmias in patients with Ebstein's anomaly.

We performed radiofrequency catheter ablation in five patients associated with Ebstein's anomaly to cure their refractory tachyarrhythmias. The presenting arrhythmias were four cases of orthodromic circus movement tachycardia using accessory pathways as a requisite limb, including one case of a Mahaim fiber and one of atrial flutter of common variety. All accessory pathways, including the Mahaim fiber, were ablated by RF energy delivered through the catheter placed at the AV annulus rather than the displaced anatomical AV groove. Interestingly, the antegrade or retrograde conduction interval over these accessory pathways was relatively longer than that of usual accessory pathways, and the accessory pathway potential was fractionated in some cases. The location of the atrioventricular node was displaced from the usual position to the postero-inferior area of Koch's triangle in one case. The configuration of the flutter wave was larger than usual in height as well as in width. All tachyarrhythmias were cured by RF catheter ablation. In the case of RF catheter ablation for patients with Ebstein's anomaly, close attention is indispensable in order to accomplish it safely and successfully, because of the anatomical and functional differences peculiar to Ebstein's anomaly.

Cardiac Catheterization↗
PubMed2001

A variant of the endotheliotropic herpesvirus in Asian elephants (Elephas maximus) in European zoos.

Newly discovered, lethal elephant endotheliotropic herpesviruses (EEHV) have been identified in both Asian (Elephas maximus) and African (Loxodonta africana) elephants. Carried by otherwise healthy African elephants they can be fatal mainly for young Asian elephants. Since zoos often harbour both elephant species, we conducted a survey on the presence of EEHV in Asian elephants from 12 European zoos, 3 circuses and 1 Israeli zoo. Here, we demonstrate that all EEHV that have affected Asian elephants so far belong to the EEHV1 group. We also describe the detection and the partial sequencing of an endotheliotropic herpesvirus variant (named EEHV1b) in Asian elephants, being either an EEHV endogenous to Asian elephants or indicating different sources (African elephants) of infection.

2-Aminopurine↗
PubMed1991

Atrial fibrillation in patients with an accessory pathway: importance of the conduction properties of the accessory pathway.

To investigate how the electrophysiologic properties of the accessory pathway affect the occurrence of atrial fibrillation in the Wolff-Parkinson-White syndrome, programmed stimulation data of 57 patients with overt pre-excitation and 33 patients with a concealed accessory pathway with documented circus movement tachycardia were reviewed. Atrial fibrillation had occurred spontaneously in 31 (54%) of the 57 patients with the Wolff-Parkinson-White syndrome and in 1 (3%) of the 33 with a concealed accessory pathway (p less than 0.001). Sustained atrial fibrillation was induced in 23 of 31 patients with the Wolff-Parkinson-White syndrome and spontaneous atrial fibrillation (Group A), in 7 of 26 patients with the Wolff-Parkinson-White syndrome without spontaneous atrial fibrillation (Group B) and in 5 of 33 patients with a concealed accessory pathway (Group C). The anterograde effective refractory period of the accessory pathway was shorter in Group A than in Group B (252 versus 297 ms, p less than 0.001). There were no differences among groups in PA interval, right to left atrium conduction time, cycle length of tachycardia and atrial and retrograde accessory pathway effective refractory period. Atrial fibrillation is more frequent in patients with the Wolff-Parkinson-White syndrome than in those with a concealed accessory pathway. Patients with overt pre-excitation and atrial fibrillation have a shorter anterograde accessory pathway refractory period. It seems therefore that the anterograde rather than the retrograde conduction properties of the accessory pathway are the critical determinants of atrial fibrillation in the Wolff-Parkinson-White syndrome.

Adult↗
PubMed1983

Endocardial mapping by simultaneous recording of endocardial electrograms during cardiac surgery for ventricular aneurysm.

A technique was developed for the simultaneous recording of 30 endocardial electrograms during cardiac surgery in patients undergoing aneurysmectomy or endocardial resection, or both, for medically intractable ventricular tachycardia. An inflatable balloon covered with 30 terminals at distances of 1.5 to 2 cm was used to record from the entire endocardial surface; a smaller silicone rubber sheet with 30 terminals at distances of 0.7 cm was used to obtain a better spatial resolution. The multielectrodes were inserted into the left ventricular cavity by way of an incision in the aneurysm. A transportable minicomputer was used for the acquisition and analysis of the signals. After initiation of ventricular tachycardia by programmed stimulation, signals of a 1.5 second period were stored and analyzed. The earliest activated terminal could be determined within 2 to 5 minutes. The technique was applied in 32 patients and proved especially useful in those patients in whom sustained tachycardia could not be evoked and in whom conventional mapping with a roving electrode would have been impossible or very time consuming. In all patients, the isochronic maps showed that the ectopic impulses originated from a rather localized area and no evidence was found for large endocardial circus movements, thereby excluding these as a mechanism underlying the tachycardia. Isochronic maps, depicting activation sequences during consecutive ectopic beats with the same QRS morphologic features, showed the same site of origin in all but six patients.(ABSTRACT TRUNCATED AT 250 WORDS)

Cardiac Catheterization↗
PubMed1984

Reentrant ventricular arrhythmias in the late myocardial infarction period. II. Burst pacing versus multiple premature stimulation in the induction of reentry.

Isochronal maps of ventricular activation were analyzed in dogs 1 to 5 days after infarction utilizing a 64 channel multiplexer. Only dogs in which circus movement reentry could not be induced by a single premature stimulus were analyzed. Reentrant rhythms could be successfully induced equally by multiple (double or triple) premature stimuli and by burst pacing. Successive premature stimuli as well as successive beats during burst pacing resulted in progressively longer arcs of functional conduction block or slower circulating wave fronts, or both, that succeeded in reexciting myocardial zones on the proximal side of the arc of block to initiate reentry. However, for manifest reentry to be induced by burst pacing, the paced run had to be terminated after the beat that resulted in a critical degree of conduction delay. Otherwise, reentrant activation could be confined (concealed) by the subsequent paced wave front, which could also arrive earlier to the reentrant circuit zone of slow conduction resulting in block and interruption of reentry. Termination of a paced run after this beat would not result in reentry. If the paced run was extended past this beat, a new sequence of ventricular activation patterns characterized by progressively longer arcs of block or slower conduction, or both, developed again. The number of beats in a paced run that could initiate reentry varied with the cycle length of pacing, as well as in different experiments, and was difficult to standardize. It is therefore concluded that random burst pacing as a technique for induction of reentrant rhythms should probably be abandoned in favor of multiple premature stimulation.

Animals↗
PubMed2004

The ghost of Saddam and UN sanctions.

Events in the past 10-15 years have meant that Iraq's once highly sophisticated health-care system has fallen to rack and ruin. To fight the very low morale, Iraqi people are making use of many approaches, some of which are unconventional, such as circus entertainment to raise spirits in paediatric wards. This Reportage looks at the events that have lead to the current health-care crisis in Iraq through the eyes of those living and working there. It is based on interviews done by Jo Wilding, an independent humanitarian activist and writer working on various grassroots rehabilitation and solidarity projects in Iraq, in Al Mansour teaching hospital, Shahid Adnan hospital, the centre for Nuclear Medicine, and the Ministry of Health in Baghdad.

Health Services Accessibility↗