Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “CIRCUS”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 253 records · Page 14Linked to original sources
PubMed1997

A philosophical approach to conjoined twins.

There are increasing numbers of attempts to surgically separate conjoined twins. Almost every type of conjoined twins have been separated, with varying results. Surgeons must often make the decision as to the desirability and feasibility of separation. These decisions are complicated by ethical problems that involve patient privacy, the allocation of shared organs, and in some instances the necessity for one twin to die to save the other. Although life as a conjoined twin would appear to be intolerable, there are historical as well as current instances of conjoined twins who have progressed to adulthood as relatively well-adjusted individuals. Thus, in some situations, it may be better not to operate on these patients. At one time or another, when individual cases have been studied by theologians, all faiths have agreed that the sacrifice of one twin to save the other is ethical. When one twin is clearly stronger than the other and has the best chance for long-term survival, it also appears to be desirable to give that twin the shared organs that allow gastrointestinal and genitourinary function and ambulation. It is now possible to predict the pattern of shared organs in most cases based on an external examination. It is no longer necessary to subject these patients to prolonged, invasive tests, which may be dangerous and provide at best incomplete information. The surgeon should take great care to protect his patients' privacy and resist efforts by the media to create a "television circus"" over these patients.

Abnormalities, Multiple↗
PubMed1991

Electrophysiologic mechanisms of ventricular arrhythmias.

In this work the electrophysiologic mechanisms of ventricular arrhythmias have been briefly summarized. Ventricular arrhythmias can be caused either by pacemaker activity or by reentrant excitation. Enhancement of normal automaticity can generate a parasystolic rhythm in normal fibers. Abnormal automaticity may arise from fibers in which maximum diastolic potential has been reduced by a variety of interventions. Triggered activity is caused by either an early (EAD) or delayed (DAD) afterdepolarization and requires a prior normal action potential for initiation. While there is growing evidence that EAD-induced triggered activity plays a significant role in the Long QTU syndrome and Torsade de Pointes, no clinical arrhythmias has definitely been ascribed to DADs, although DADs have been recorded in man after acute digoxin intoxication. Ventricular arrhythmias can be also caused by reentrant excitation, which can be subdivided into reflection or circus movement reentry (CMR). In the reflection model impulses in both directions are transmitted over the same pathway. In the CMR three models can be differentiated: the ring model, which requires a fixed anatomical obstacle; the figure-eight model and the leading circle model, where functional rather than fixed anatomical obstacles are involved.

Action Potentials↗
PubMed1987

Mechanisms for cardiac arrhythmias.

Possible cellular electrophysiological mechanisms for arrhythmias have been investigated through studies of isolated cardiac tissues. Records through extracellular and intracellular electrodes indicate that arrhythmias may result from either focal or non-focal mechanisms. Focal mechanisms include abnormal impulse initiation (normal or abnormal automaticity), triggering from either early or delayed afterdepolarizations and reflection, whereas the non-focal mechanisms are various forms of reentry due to circus movement. It is reasonable to assume that these mechanisms also occur in vivo. Although it is safe to identify macro-re-entry as the cause of some atrial and ventricular arrhythmias, for the most part direct proof of mechanism usually is lacking for the focal arrhythmias. If 'on line' activation sequence mapping techniques can be developed to quickly and specifically locate arrhythmogenic foci in the in situ heart, it may be possible to use unipolar extracellular recording techniques to identify the exact cellular electrophysiological mechanisms operating within them.

Action Potentials↗
PubMed1987

Conduction of the impulse in the ischemic myocardium--implications for malignant ventricular arrhythmias.

Ventricular arrhythmias occurring consequent to regional disturbances of myocardial perfusion are the most frequent cause of sudden cardiac death. They are related to marked changes of impulse propagation in the ischemic region, which consist of circulating excitation with re-entry. Mapping of the impulse during ventricular tachycardias and ventricular fibrillation shows that the circus movements change their shape and localization from beat to beat. Zones of tissue which block the impulse during one beat may conduct the impulse at a fast rate during the next beat. The main cause underlying this behavior is the depression of the ischemic action potential. This depression is caused by the partial inactivation and the prolonged recovery of the rapid sodium inward current. In addition to the decrease in resting potential, other factors, such as acidosis, contribute to the inactivation of the inward currents generating the upstroke of the action potential. An increase of coupling resistance between myocardial cells and/or an increase of extracellular resistance appear to be less important for explaining conduction disturbances in acute ischemia.

Action Potentials↗
PubMedDate not supplied

The dynamics of sustained reentry in a ring model of cardiac tissue.

This paper describes the dynamics of circus movement around a fixed obstacle, using a one-dimensional continuous and uniform ring model of cardiac tissue to simulate sustained reentry. The membrane ionic current is simulated by a modified Beeler-Reuter formulation in which the kinetics of the fast sodium current were updated using more recent voltage-clamp data. Changes in the ring length are used to modify the dynamics of reentry. Reentry is stable if the ring length (X) exceeds a critical value (Xcrit) and complete block occurs if X is below a minimum (Xmin). Irregular sustained reentry is observed at intermediate ring lengths, as a narrow range of aperiodic reentry near Xcrit, and a larger range of quasi-periodic reentry at shorter ring lengths. The basic pattern of irregular reentry is an alternation between long and short cycle length, action potential duration (APD), diastolic interval (DIA), wavelength, and excitable gap. In aperiodic reentry cycle length variations are small, APD and DIA fluctuations are of medium amplitude, and conduction velocity over the whole pathway is essentially constant during successive turns. Much larger fluctuations in these various quantities occur during quasi-periodic reentry, and they increase in size as X approaches Xmin. The complexity of quasi-periodic reentry patterns is related to three factors: the slope of the APD versus DIA relation, which is greater than 1, the existence of a zone of slow conduction on the ring when the excitable gap becomes quite short, and the occurrence of triggered waves of secondary repolarization and excitability recovery. In the present model, quasi-periodic reentry with triggered secondary recovery covers most of the range of ring lengths, giving rise to sustained irregular reentry. There is very close agreement between our simulation results and experimental data obtained on rings of cardiac tissue.

Action Potentials↗
PubMed2003

[Cardiac arrhythmias during pregnancy--what to do?].

METHODS: Atrial premature beats are frequently diagnosed during pregnancy, supraventricular tachycardia (atrial tachycardia, AV nodal reentrant tachycardia, circus movement tachycardia) less frequently. For acute therapy, electrical cardioversion with 50-100 J is indicated in all unstable patients. In stable supraventricular tachycardia, initial therapy includes vagal maneuvers to terminate breakthrough tachycardias. For short-term management, when vagal maneuvers fail, intravenous adenosine is the drug of first choice and may safely terminate the arrhythmia. For long-term therapy, beta-blocking agents with beta(1) selectivity are first-line drugs; class Ic agents or the class III drug sotalol represent effective and therapeutic alternatives. Ventricular premature beats are also frequently present during pregnancy and benign in most of the unstable patients; however, malignant ventricular tachyarrhythmias (sustained ventricular tachycardia, ventricular flutter, ventricular fibrillation) are less frequently observed. Electrical cardioversion is necessary in all patients with hemodynamically unstable situation and life-threatening ventricular tachyarrhythmias; in hemodynamically stable patients, initial therapy with ajmaline, procainamide or lidocaine is indicated. If prophylactic therapy is needed, beta-blocking agents with beta(1) selectivity are regarded as drugs of first choice. If this therapy proves ineffective, class Ic agents or sotalol can be considered. In patients with syncopal ventricular tachycardia, ventricular fibrillation, ventricular flutter or aborted sudden death, an implantable cardioverter-defibrillator is indicated. In patients with symptomatic bradycardia, a pacemaker can be implanted using echocardiography at any stage of pregnancy. CONCLUSIONS: The treatment of the pregnant patient with cardiac arrhythmias requires important modifications of the standard practice of arrhythmia management. The goal of therapy is to protect the patient and fetus through delivery, after which chronic or definitive therapy can be administered.

Anti-Arrhythmia Agents↗
PubMed1999

Effects of Military Training Activities on Shrub-steppe Raptors in Southwestern Idaho, USA.

/ Between 1991 and 1994, we assessed relative abundance, nesting success, and distribution of ferruginous hawks (Buteo regalis), northern harriers (Circus cyaneus), burrowing owls (Athene cunicularia), and short-eared owls (Asio flammeus) inside and outside a military training site in the Snake River Birds of Prey National Conservation Area, southwestern Idaho. The Orchard Training Area is used primarily for armored vehicle training and artillery firing by the Idaho Army National Guard. Relative abundance of nesting pairs inside and outside the training site was not significantly different from 1991 to 1993 but was significantly higher on the training site in 1994 (P &le 0.03). Nesting success varied among years but was not significantly different inside and outside the training site (P > 0.26). In 1994, short-eared owl and burrowing owl nests were significantly closer to firing ranges used early in the spring before owls laid eggs than were random points (P < 0.001). In 1993, distances from occupied burrowing owl nests to firing ranges used early in the year were similar to those from random points to the same firing ranges (P = 0.16). Military activity contributed to some nesting failures from 1992 to 1994, but some pairs nested successfully near military activity. KEY WORDS: Distribution; Military impacts; Nesting success; Raptors; Relative abundance; Shrub-steppe

Journal Article↗
PubMed2004

Helminth fauna of Falconiform and Strigiform birds of prey in Galicia, Northwest Spain.

This is a survey of the helminth fauna of 285 individuals of 14 species of birds of prey (Falconiformes and Strigiformes) from Galicia (northwest Spain), namely Buteo buteo, Accipiter nisus, A. gentilis, Milvus migrans, M. milvus, Pernis apivorus, Circus pygargus, Falco tinnunculus, F. peregrinus, F. subbuteo, Tyto alba, Strix aluco, Asio otus and Athene noctua. A total of 15 helminth species were detected, namely 8 nematodes ( Eucoleus dispar, Capillaria tenuissima, Synhimantus laticeps, Microtetrameres sp., Physaloptera alata, Procyrnea leptoptera, Hovorkonema variegatum and Porrocaecum angusticolle), 4 cestodes ( Cladotaenia globifera, Paruterina candelabraria and Mesocestoides sp.), 2 trematodes ( Neodiplostomum attenuatum and Strigea falconis), and 1 acanthocephalan ( Centrorhynchus globocaudatus). The helminth communities observed were basically similar, although there were marked differences in species richness, which was higher in falconiforms (except for A. gentilis) than in strigiforms. More specifically, species richness was highest in B. buteo (13 species), followed by A. nisus (11 species). In the falconiforms, the helminth species present generally exhibited a clear relationship with host diet. In the strigiforms, by contrast, species richness was lower than expected given the host's diet, suggesting that a different explanation is needed.

Animals↗
PubMed2006

Density-dependent regulation of population size in colonial breeders: Allee and buffer effects in the migratory Montagu's harrier.

Expanding populations offer an opportunity to uncover the processes driving spatial variation in distribution and abundance. Individual settlement decisions will be influenced by the availability and relative quality of patches, and by how these respond to changes in conspecific density. For example, conspecific presence can alter patch suitability through reductions in resource availability or territorial exclusion, leading to buffer effect patterns of disproportionate population expansion into poorer quality areas. However, conspecific presence can also enhance patch suitability through Allee effect processes, such as transmission of information about resources or improved predator detection and deterrence. Here, we explore the factors underlying the settlement pattern of a growing population of Montagu's harriers (Circus pygargus) in Spain. The population increased exponentially between 1981 and 2001, but stabilised between 2001 and 2004. This population increase occurred alongside a remarkable spatial expansion, with novel site use occurring prior to maximum densities in occupied sites being reached. However, no temporal trends in fecundity were observed and, within sites, average fecundity did not decline with increasing density. Across the population, variance in productivity did increase with population size, suggesting a complex pattern of density-dependent costs and benefits. We suggest that both Allee and buffer effects are operating in this system, with the benefits of conspecific presence counteracting density-dependent declines in resource availability or quality.

Animal Migration↗
PubMed1983

Effect of amiodarone in paroxysmal supraventricular tachycardia with or without Wolff-Parkinson-White syndrome.

In Wolff-Parkinson-White (WPW) syndrome, the two most commonly occurring arrhythmias are circus movement tachycardia (CMT) and atrial fibrillation (AF). In 70% of patients with clinically documented CMT in whom the arrhythmia could be initiated by programmed electrical stimulation of the heart, the same CMT could still be initiated after long-term oral amiodarone administration. Spontaneous clinical recurrence of the arrhythmia was, however, observed in only 10% of patients. This finding suggests that the beneficial effect of amiodarone on CMT is primarily based on the prevention of the CMT-initiating premature beat. This may also apply to atrioventricular nodal reentrant tachycardia, in which amiodarone is also extremely effective in preventing relapses. The role of amiodarone in other forms of reentrant, or ectopic, supraventricular tachycardias is less well defined. During AF in WPW syndrome, the ventricular rate is related to the duration of the anterograde refractory period of the accessory pathway. Amiodarone prolongs this value, resulting in the reduction of ventricular rate during AF. Unfortunately, in the presence of a short anterograde refractory period of the accessory pathway, amiodarone results in only a small amount of lengthening of this value. In these patients the beneficial effect of amiodarone may primarily be related to the prevention of episodes of AF. We also found that the effect of oral amiodarone on the duration of the anterograde refractory period of the accessory pathway can (1) be abolished by sympathetic stimulation with isoproterenol and (2) be predicted from the effect of ajmaline or procainamide given intravenously. These observations clearly have practical clinical implications.

Ajmaline↗
PubMed1987

Limitations of bipolar and unipolar conditioning stimuli for inhibition in the human heart.

Noncapturing, conditioning electrical stimuli (Sc) delivered within the ventricular refractory period can prolong refractoriness and prevent later stimuli from eliciting a propagated response (inhibition). The purpose of this study was to further define the spatial effects of Sc, to determine if the effects of Sc can be enhanced by the use of unipolar as opposed to bipolar stimulation, and to evaluate the effect of Sc on the physiologic spread of excitation during atrioventricular reentry tachycardia. In 23 patients the right ventricular refractory period was determined before and after the introduction of bipolar, unipolar cathodal, and unipolar anodal noncapturing Sc with pulse widths of 2 or 9 msec and strengths of twice diastolic threshold and 10 MA. Pacing and conditioning stimuli were delivered at the same site and at sites separated by 3 mm. During ventricular pacing both bipolar and unipolar Sc prolonged the ventricular refractory period by greater than or equal to 10 msec in 22 of 23 patients when both Sc and pacing stimuli were delivered to the same site. However, when Sc was delivered 3 mm away from the pacing stimuli, the ventricular refractory period increased by greater than or equal to 10 msec in only 1 of 17 patients who received bipolar Sc and in none of 13 patients who received unipolar Sc. In seven patients bipolar conditioning stimuli were delivered as close as possible to the atrial insertion of an accessory atrioventricular connection during circus movement tachycardia with a well-localized accessory pathway. Sc did not terminate or slow tachycardia in any patient.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1987

Effects of intravenous sotalol in patients with atrioventricular accessory pathways.

Effects of intravenous injection of 0.6 mg/kg sotalol, a beta-blocking agent with additional class III properties, were studied by means of electrophysiologic techniques in 14 patients, seven with the Wolff-Parkinson-White syndrome and seven with concealed atrioventricular (AV) accessory pathways. Sotalol brought about a significant increase in the retrograde effective refractory period of the anomalous pathway, whereas changes in the antegrade effective refractory period were more variable. In five of nine patients with electrically induced reciprocating tachycardia sotalol prevented the initiation of sustained reentry. In most cases the suppression of the circus movement was the result of the development of AV nodal block. Thus our data support the use of sotalol for the treatment of tachycardias incorporating anomalous AV conduction pathways.

Adolescent↗
PubMed1988

Changes in cycle length at the onset of sustained tachycardias--importance for antitachycardiac pacing.

We analyzed changes in the spontaneous cycle length of sustained tachycardia during the first 100 beats after electrophysiologic initiation of sustained monomorphic ventricular tachycardia (VT), atrioventricular nodal tachycardia (AVNT), and circus movement tachycardia incorporating an accessory pathway (CMT). The mean cycle length of VT was 288 +/- 75 msec, for AVNT this value was 388 +/- 63 msec, and for CMT this value was 348 +/- 76 msec. After initiation, in all three types of tachycardia changes in cycle length of up to +/- 15% to 25% were observed. The changes in cycle length ranged from +12% to -18% in patients with VT, from +17% to -15% in patients with AVNT, and from +17% to -15% in patients with CMT. The mean percentage of changes during the first 100 beats of tachycardia was 7.0 +/- 4.7% (VT), 9.5 +/- 5.4% (AVNT) and 8.3 +/- 5.4% (CMT). Patients with VT and AVNT showed both a constant increase or decrease or alteration of the rate of tachycardia. In no patient with CMT was there a constant decrease in cycle length after initiation. The mean time to achieve the maximal increase or decrease in cycle length was 13 +/- 6 and 11 +/- 9 seconds in patients with VT and 16 +/- 3 and 20 +/- 7 seconds in patients with AVNT. In patients with CMT, the mean time to achieve the maximal increase (10 +/- 7 seconds) or decrease (20 +/- 9 seconds) varied markedly.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1989

Flecainide acetate in the treatment of supraventricular tachycardias: value of programmed electrical stimulation for long-term prognosis.

Twenty patients with recurrent symptomatic supraventricular tachycardia were studied to estimate the efficacy of flecainide in the long-term treatment of these arrhythmias and to evaluate the prognostic value of programmed electrophysiologic stimulation. All patients had their arrhythmia inducible at baseline evaluation. Nine patients had a Wolff-Parkinson-White (WPW) syndrome, five had a concealed bypass tract, and two had dual atrioventricular (AV) nodal pathways. In the remaining patients there was an intraatrial reentry circuit. Previous medication was no to five antiarrhythmic drugs (mean 2.4 drugs). At baseline, a circus movement tachycardia was induced in 12, AV nodal tachycardia was induced in two, atrial tachycardia was induced in three, atrial fibrillation was induced in five, and a flutter was induced in two patients. After flecainide, 2 mg/kg intravenously in 10 minutes, six patients no longer had their arrhythmia inducible. In the WPW patients, atrial fibrillation was no more inducible. In 65% of the patients there was no recurrence during a follow-up period of 11 +/- 10 months. None of the six patients who no longer had their arrhythmia inducible had a recurrence of the tachycardia over a period of up to 3 years. Seven of the other 14 patients (who still had their arrhythmia inducible) had a recurrence of the tachycardia. Positive and negative predictive values are 50% and 100%, respectively. We conclude that flecainide prevents recurrences of supraventricular tachycardias in 65% of patients with inducible supraventricular tachycardias during a mean follow-up of 11 months. Programmed electrical stimulation has a high negative predictive value in this setting. Flecainide is especially effective in preventing atrial fibrillation in patients with WPW syndrome.

Adult↗
PubMed1983

Electrophysiologic effects of lorcainide on the accessory pathway in the Wolff-Parkinson-White syndrome.

The electrophysiologic effects of lorcainide, a class I antiarrhythmic agent with local anesthetic properties, were studied in 20 patients with the Wolff-Parkinson-White syndrome. After intravenous administration of lorcainide (2 mg/kg), the sinus cycle length decreased in all patients from 705 +/- 117 to 636 +/- 94 ms (p less than 0.001). The atrioventricular conduction time lengthened from 84 +/- 22 to 94 +/- 22 ms (p less than 0.01) and the QRS duration increased from 92 +/- 19 to 120 +/- 29 ms (p less than 0.001). The effective refractory period of the atrium increased from 230 +/- 27 to 243 +/- 35 ms (p less than 0.05), whereas the ventricular refractoriness was unaffected. Retrograde conduction over the accessory pathway was blocked in 5 of 18 patients after lorcainide; in the remaining 13 patients a prolongation from 107 +/- 32 to 162 +/- 57 ms (p less than 0.001) was found. Anterograde conduction over the accessory pathway was blocked in 6 patients, and in all other patients it increased considerably. Circus movement tachycardia could be induced in 14 patients before and in 10 patients after the drug. The shortest R-R interval during tachycardia lengthened from 326 +/- 40 to 364 +/- 67 ms (p less than 0.05). The tachycardia zone was unaffected by lorcainide. In 15 patients atrial fibrillation was induced. After lorcainide anterograde conduction during atrial fibrillation was blocked (n = 5). The shortest R-R interval over the accessory pathway during induced atrial fibrillation increased from 228 +/- 35 to 304 +/- 103 ms (p less than 0.05). Intravenous administration of lorcainide produced a pronounced negative dromotropic effect on the conduction properties of the accessory pathway. Lorcainide appears to be a promising new antiarrhythmic agent in patients with the Wolff-Parkinson-White syndrome.

Adolescent↗
PubMed1984

Electrophysiologic and clinical effects of intravenous and oral encainide in accessory atrioventricular pathway.

The effect of intravenous and oral encainide was studied in 12 patients with an accessory atrioventricular pathway (AP). Eight patients had Wolff-Parkinson-White syndrome and 4 had a concealed AP. Electrophysiologic studies were performed before and after intravenous encainide, 1.0 to 1.5 mg/kg, and 4 weeks after oral encainide, 75 to 200 mg/day. Mean follow-up was 19 +/- 6 months. During sinus rhythm, intravenous and oral encainide significantly prolonged the AH and HV intervals. In patients with Wolff-Parkinson-White syndrome, after intravenous encainide, anterograde conduction over the AP was blocked in 3 patients, and the anterograde effective refractory period (ERP) of the AP was markedly increased in 3. Five of these 6 patients had a control value of the anterograde AP ERP of less than 270 ms. Anterograde AP block was maintained in 2 patients after oral encainide therapy. Retrograde AP block or marked increase of retrograde AP ERP was seen in 4 of 9 patients after intravenous encainide and in 2 of 7 after oral therapy. Encainide either prevented induction of circus movement tachycardia (intravenous, 4 of 11 patients; oral, 2 of 7 patients) or significantly prolonged tachycardia cycle length (intravenous, 7 of 11 patients; oral, 5 of 7 patients). During long-term follow-up of 9 patients, 6 patients had no recurrences of tachyarrhythmia after individual adjustment of encainide dosage. One patient had worsening of supraventricular tachycardia after intravenous encainide therapy and 4 patients complained of visual blurring; in 1 patient it was so severe that it required withdrawal of the drug.(ABSTRACT TRUNCATED AT 250 WORDS)

Administration, Oral↗
PubMed1984

Differential diagnosis of tachycardia with narrow QRS complex (shorter than 0.12 second).

One hundred eighty-seven patients with clinically documented supraventricular tachycardia with a narrow QRS complex were admitted for electrophysiologic study. The diagnoses after this study were circus movement tachycardia using an accessory pathway in 50 patients, atrioventricular nodal tachycardia in 50 patients, atrial flutter in 50 patients, atrial tachycardia in 27 patients and an incessant tachycardia retrogradely using a slowly conducting accessory pathway in 10 patients. On retrospective analysis, 5 criteria on the 12-lead electrocardiogram during tachycardia were analyzed for their value in making the diagnosis of site of origin. These criteria were P-wave location, axis of the P wave, atrial rate, alternation of the QRS complex and atrioventricular relation. Fifty-seven patients with a narrow QRS tachycardia were prospectively studied using the 5 criteria. A correct diagnosis was made in 48 of the 57 patients (84%). Thus, in most patients with a narrow QRS tachycardia, information from the 12-lead electrocardiogram is adequate for diagnosis.

Adolescent↗
PubMed1984

Differential effects of sotalol and metoprolol on induction of paroxysmal supraventricular tachycardia.

Seventeen patients with recurrent paroxysmal supraventricular tachycardia (SVT) underwent serial electrophysiologic studies to compare the effects of i.v. sotalol (1.5 mg/kg) and i.v. metoprolol (0.15 mg/kg). The plasma concentrations of sotalol (2.1 +/- 1.1 microgram/ml) and metoprolol (67 +/- 15 ng/ml) were within the therapeutic range. Before drug administration, sustained SVT could be reproducibly induced in all patients. Sotalol prevented induction of sustained SVT in 10 of 17 patients (59%) and metoprolol in 4 (28%) (p less than 0.05). In 6 of 8 patients with atrioventricular (AV) nodal reentrance, the site of action of sotalol was the anterograde or the retrograde limb, reflecting an increase in refractoriness in both pathways of the circus movement. In 4 of 9 patients with AV reentrance, the site of action of sotalol was exclusively the AV nodal pathway; conduction through the extranodal accessory tract appeared to be unchanged, but its anterograde effective refractory period was prolonged (from 285 +/- 25 to 322 +/- 28 ms, p less than 0.001; mean +/- standard deviation). In the 7 patients in whom sotalol did not prevent sustained SVT, the tachycardia cycle length increased from 347 +/- 42 to 392 +/- 45 ms (p less than 0.01). Compared with sotalol, metoprolol had qualitatively similar but quantitatively less potent effects on the AV nodal pathways; however, different from sotalol, metoprolol had no effect on extranodal accessory tracts. The study suggests that at therapeutic plasma concentrations, sotalol would be effective in preventing clinical SVT in a significant proportion of patients refractory to metoprolol; because sotalol not only has beta-blocking properties but also results in acute prolongation of the action potential duration, this combination of class II and III activity may contribute to its superior prophylactic efficacy compared with pure beta blockade.

Adult↗