Action of Mephentermine on Arrhythmias Due to Pulsus Alternans, Rapidly Discharging Single Atrial Foci and Prolonged P-R Intervals

1957 ◽  
Vol 191 (3) ◽  
pp. 481-486 ◽  
Author(s):  
M. J. Oppenheimer ◽  
P. R. Lynch ◽  
G. Ascanio
Keyword(s):  
Sinus Rhythm ◽  
Refractory Period ◽  
Conduction Time ◽  
Digitalis Intoxication ◽  
Methyl Group ◽  
Slow Conduction ◽  
Normal Series ◽  
Pulsus Alternans ◽  
Conduction Velocities ◽  
Regular Rhythm

Slow conduction velocities play a role in pulsus alternans and digitalis intoxication and possibly in the arrhythmia due to a rapidly discharging atrial aconitine focus. In the ventricle mephentermine increases conduction velocity, shortens refractory period and A-V conduction time. The present study investigates the usefulness of mephentermine in these conditions. Pulsus alternans was reverted to a normal series of mechanical contractions by mephentermine. The same agent provided periods of regular rhythm during the presence of an atrial aconitine focus; in two cases a permanent sinus rhythm was established. The prolonged P-R interval due to intoxication with acetyl strophanthidin was restored to normal by mephentermine. The action of mephentermine is specific since compounds with addition or subtraction of one methyl group or the hydroxy-mephentermine were ineffective against a circus flutter.

Evidence for Slow Conduction Areas during Pacing in Patients with Sinus Rhythm, and their Relation to the Site of VT Origin.

1994 ◽  
Vol 35 (1) ◽  
pp. 1-13 ◽  
Author(s):  
Masaomi CHINUSHI ◽  
Yoshifusa AIZAWA ◽  
Yoriko KUSANO ◽  
Takashi WASHIZUKA ◽  
Akira SHIBATA
Keyword(s):  
Sinus Rhythm ◽  
Slow Conduction

Effects of diltiazem on atrioventricular conduction and arterial blood pressure: correlation with plasma drug concentrations

1984 ◽  
Vol 62 (12) ◽  
pp. 1479-1486 ◽  
Author(s):  
Jean-Paul Clozel ◽  
Jacques Billette ◽  
Gilles Caillé ◽  
Pierre Théroux ◽  
Richard Cartier
Keyword(s):  
Blood Pressure ◽  
Plasma Concentration ◽  
Refractory Period ◽  
Plasma Concentrations ◽  
Atrioventricular Conduction ◽  
Gas Liquid Chromatography ◽  
Conduction Time ◽  
Arterial Blood ◽  
Drug Concentrations ◽  
Atrial Conduction Time

Atrial and atrioventricular conduction variables were studied at control and at the end of each of six consecutive 45-min diltiazem administration periods in eight closed chest-anesthetized dogs. Diltiazem was given as a bolus (50 μg/kg, i.v.) followed by an infusion (0.5 μg∙kg−1∙min−1); doses were doubled in subsequent periods. The plasma concentrations, measured by gas–liquid chromatography, ranged from 8 to 1400 ng/mL and correlated strongly with the doses (r = 0.92; p < 0.01). The Wenckebach cycle length, basic conduction time, and functional refractory period of the atrioventricular (AV) node increased proportionally with plasma concentration (respective r = 0.90, 0.89, 0.80; p < 0.01). The minimum mean plasma concentrations affecting these variables significantly were 37, 83, and 175 ng/mL, respectively. Second or third degree AV blocks developed in all dogs for plasma concentrations between 379 and 1400 ng/mL. In four dogs which were given isoproterenol (0.2 μg∙kg−1∙min−1), these blocks disappeared within 1 min. Atrial conduction time and functional refractory period were slightly but significantly shortened by diltiazem with mean plasma concentrations of 175 ng/mL and over. His–Purkinje intervals were not significantly changed by diltiazem. Systolic and diastolic arterial pressures were decreased by diltiazem (r = −0.64, r = −0.79; p < 0.01) starting with a mean plasma concentration of 83 ng/mL. We conclude that AV nodal conduction variables are progressively prolonged with increasing plasma concentrations of diltiazem; plasma concentrations affecting blood pressure and AV nodal variables overlap; and the AV blocks produced by toxic concentrations of diltiazem can be corrected by isoproterenol.

scholarly journals Slowly-conducting pyramidal tract neurons in macaque and rat

2019 ◽  
Author(s):  
A Kraskov ◽  
D Soteropoulos ◽  
I Glover ◽  
RN Lemon ◽  
SN Baker
Keyword(s):  
Motor Cortex ◽  
Pyramidal Tract ◽  
Recurrent Inhibition ◽  
Anatomical Studies ◽  
Slow Conduction ◽  
Pyramidal Tract Neurons ◽  
Conduction Velocities ◽  
Myelinated Fibres ◽  
Anaesthetised Rats

SummaryAnatomical studies report a large proportion of fine myelinated fibres in the primate pyramidal tract (PT), while very few pyramidal tract neurons (PTNs) with slow conduction velocities (CV) (< ∼10 m/s) are reported electrophysiologically. This discrepancy might reflect recording bias towards fast PTNs or prevention of antidromic invasion by recurrent inhibition of slow PTNs from faster axons. We investigated these factors in recordings made with a polyprobe (32 closely-spaced contacts) from motor cortex of anaesthetised rats (n=2) and macaques (n=3), concentrating our search on PTNs with long antidromic latencies. We identified 21 rat PTNs with antidromic latencies > 2.6 ms and estimated CV 3-8 m/s, and 67 macaque PTNs (> 3.9ms, CV 6-12 m/s). Spikes of most slow PTNs were small and present on only some recording contacts, while spikes from simultaneously recorded fast-conducting PTNs were large and appeared on all contacts. Antidromic thresholds were similar for fast and slow PTNS, while spike duration was considerably longer in slow PTNs. Most slow PTNs showed no signs of failure to respond antidromically. A number of tests, including intracortical microinjection of bicuculline (GABAA antagonist), failed to provide any evidence that recurrent inhibition prevented antidromic invasion of slow PTNs. Our results suggest that recording bias is the main reason why previous studies were dominated by fast PTNs.

Physiological properties of individual cerebral axons studied in vivo for as long as one year

1985 ◽  
Vol 54 (5) ◽  
pp. 1346-1362 ◽  
Author(s):  
H. A. Swadlow
Keyword(s):  
Conduction Velocity ◽  
Cortical Neurons ◽  
Refractory Period ◽  
Antidromic Activation ◽  
Conduction Velocities ◽  
Supernormal Period ◽  
Velocity Changes ◽  
The Stability ◽  
Over Time

The long-term stability of conduction velocity and recovery processes were studied in a fast-conducting (corticotectal) and in a more slowly conducting (visual callosal) axonal system. Chronic microelectrode recording methods were used in conjunction with antidromic activation via electrical stimulation at one or more axonal site. These methods enabled 54 axons to be studied for greater than 20 days and seven of these cells to be studied for 101-448 days. The conduction velocities of corticotectal axons were characteristic of myelinated axons and were very stable over time. The conduction velocities of most callosal axons were characteristic of nonmyelinated axons, and 68% of callosal axons had conduction velocities that were stable over long periods of time. Of the remaining callosal axons, approximately one third showed an increase in conduction velocity (8-14%), whereas two thirds showed a progressive and systematic decrease in conduction velocity (6-81%). These changes in conduction velocity were distributed along the callosal axon, rather than limited to a single segment of axon. Although the refractory period of callosal and corticotectal axons showed considerable variability over time, the minimal interval between two conducted impulses was stable. The stability of this property was remarkable because the minimal interspike intervals of different axons with similar conduction velocities often differed greatly. Callosal axons show a supernormal period of increased conduction velocity following the relative refractory period and a subsequent subnormal period of decreased conduction velocity following a burst of prior impulses. In different callosal axons the magnitude of the velocity changes (percent change) differs greatly, even among axons of the same conduction velocity. For a given axon, however, these properties are very stable over time. These results on axonal properties may be useful in studies requiring the examination of extracellular responses of individual neurons over long periods of time. Antidromic latency provides a useful means of identifying a cell, particularly when conduction times are long. The stability of the minimal interspike interval and the supernormal period within individual axons make them suitable as ancillary criteria in identifying individual neurons. These three measures are independent of spike amplitude and waveform, and together they provide a "signature" by which individual cortical neurons can be identified over periods that represent a significant portion of the lifespan of adult mammals.

Rate-dependent functional properties of retrograde atrioventricular nodal conduction in experimental animals

1993 ◽  
Vol 265 (4) ◽  
pp. H1257-H1264 ◽  
Author(s):  
G. O'Hara ◽  
R. Gendreau ◽  
J. Billette ◽  
F. Amellal ◽  
M. Nayebpour ◽  
...  
Keyword(s):  
Functional Properties ◽  
Time Constant ◽  
Refractory Period ◽  
Conduction Time ◽  
Experimental Animals ◽  
Rate Dependent ◽  
Activation Rate ◽  
Anesthetized Dogs ◽  
Atrioventricular Nodal Conduction ◽  
Conduction Properties

While rate-dependent atrioventricular (AV) nodal functional properties play a major role in determining antegrade AV nodal conduction, their existence and characteristics have not been assessed during retrograde AV nodal impulse propagation. Pacing protocols were used to study selectively AV nodal recovery, facilitation, and fatigue in 6 isolated, superfused rabbit AV nodal preparations and in 11 morphine-chloralose anesthetized dogs. All three properties were identifiable during retrograde AV nodal activation in rabbits. Retrograde recovery and fatigue were clearly demonstrated in dogs, but facilitation could not be evaluated because of echo beats during retrograde premature stimulation. Functional properties were qualitatively similar during retrograde and antegrade propagation; however, important quantitative differences were noted. The time constant for recovery from activation was significantly greater in the retrograde [rabbits, 69 +/- 8 (SE) ms; dogs, 93 +/- 11 ms] compared with the antegrade direction (rabbits, 50 +/- 5 ms; dogs, 58 +/- 4 ms; P < 0.05 vs. retrograde for each species). The magnitude of fatigue resulting from sustained increases in rate was also substantially greater in the retrograde direction in both rabbits (17 +/- 2 vs. 10 +/- 1 ms antegrade, P = 0.01) and dogs (20 +/- 4 vs. 6 +/- 1 ms antegrade, P < 0.01). Conduction time and refractory period were both greater in the retrograde compared with antegrade direction, and directional differences in conduction properties were magnified as activation rate increased.(ABSTRACT TRUNCATED AT 250 WORDS)

The Effects of Ouabain on Atrioventricular Junctional Automaticity and Conductivity Studied in the Dog

1974 ◽  
Vol 52 (3) ◽  
pp. 624-631 ◽  
Author(s):  
Victor Elharrar ◽  
Réginald A. Nadeau ◽  
Fernand Roberge ◽  
Gérald A. Porlier ◽  
Claude Pelletier
Keyword(s):  
Refractory Period ◽  
Conduction Time ◽  
His Bundle

In the anesthetized dog, the effects of ouabain injected intravenously and directly into the atrioventricular (A-V) node artery were studied. Automaticity within the A-V junction was decreased after a dose of ouabain, 30 μg/kg given intravenously (i.v.), whereas automaticity of ventricular specialized fibers was increased after a dose of 40 μg/kg i.v. The decrease of automaticity within the A-V junction was accompanied by an increased duration of the functional refractory period of this structure and by a prolongation of conduction time through the A-V junction as determined from the His bundle electrogram.

Studies on hexactinellid sponges. II. Excitability, conduction and coordination of responses in rhabdocalyptus dawsoni (lambe, 1873)

1983 ◽  
Vol 301 (1107) ◽  
pp. 401-418 ◽  
Keyword(s):  
Electrical Stimulation ◽  
Refractory Period ◽  
Conduction System ◽  
Conduction Time ◽  
Pumping Power ◽  
Chemical Signalling ◽  
Conduction Pathway ◽  
Electrical Impulses ◽  
Effector Response ◽  
Hexactinellid Sponges

Rhabdocalyptus can arrest its feeding current. The response is initiated by mechanical or electrical stimulation, and is coordinated through the sponge by a conduction system, having a precise excitability threshold and conducting on an all-or-none basis. All parts are excitable and conduct. Individuals in colonial assemblages are coordinated. Spontaneous as well as evoked arrests are observed. There is evidence of scattered pacemaker sites. Conduction is diffuse and unpolarized, and occurs with a velocity of 0.26 ± 0.07 cm s -1 at 11 °C. The conduction system is probably the trabecular syncytium. Isolated dermal membrane (‘pure’ trabecular tissue, without flagella or contractile elements) conducts. Mechanical and chemical signalling mechanisms are discussed. It is concluded that they cannot account for the phenomena observed, but that conduction must involve electrical impulses. The effectors responsible for current arrests are almost certainly the flagella of the flagellated chambers. It is assumed that they stop beating on receiving an arrest signal through the conduction pathway. The waveforms of arrests recorded with a thermistor flowmeter are best interpreted in terms of sudden, all-or-none cessation of pumping, with slow, gradual recovery of full pumping power. The flagella probably beat feebly at first on becoming active again following an arrest. The effector response shows a refractory period of 30 s. Responses occur with short latency. Delays are attributable to conduction time. The system is fatigueable. Numerous parallels exist with the behaviour of the stigmatal cilia in the ascidian branchial sac, both in the characteristics of the effector response and in the mechanism of coordination.

scholarly journals A Computational Study of the Electrophysiological Substrate in Patients Suffering From Atrial Fibrillation

2021 ◽  
Vol 12 ◽  
Author(s):  
S. Pagani ◽  
L. Dede' ◽  
A. Frontera ◽  
M. Salvador ◽  
L. R. Limite ◽  
...  
Keyword(s):  
Atrial Fibrillation ◽  
Cardiac Electrophysiology ◽  
Computational Study ◽  
Pulmonary Veins ◽  
Coupled System ◽  
Density Mapping ◽  
Slow Conduction ◽  
Conduction Velocities ◽  
Ectopic Beats

In the context of cardiac electrophysiology, we propose a novel computational approach to highlight and explain the long-debated mechanisms behind atrial fibrillation (AF) and to reliably numerically predict its induction and sustainment. A key role is played, in this respect, by a new way of setting a parametrization of electrophysiological mathematical models based on conduction velocities; these latter are estimated from high-density mapping data, which provide a detailed characterization of patients' electrophysiological substrate during sinus rhythm. We integrate numerically approximated conduction velocities into a mathematical model consisting of a coupled system of partial and ordinary differential equations, formed by the monodomain equation and the Courtemanche-Ramirez-Nattel model. Our new model parametrization is then adopted to predict the formation and self-sustainment of localized reentries characterizing atrial fibrillation, by numerically simulating the onset of ectopic beats from the pulmonary veins. We investigate the paroxysmal and the persistent form of AF starting from electro-anatomical maps of two patients. The model's response to stimulation shows how substrate characteristics play a key role in inducing and sustaining these arrhythmias. Localized reentries are less frequent and less stable in case of paroxysmal AF, while they tend to anchor themselves in areas affected by severe slow conduction in case of persistent AF.

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