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At least 775 records · Page 43Linked to original sources
PubMed1991

[Effect of ritmilen on myocardial refractility and cardiac impulse conduction in patients with paroxysmal tachycardia].

By choosing antiarrhythmic therapy, ritmilen, 3 mg/kg, was given to 30 patients with atrial, atrioventricular, reciprocal and ventricular tachycardias. The agent was found to have the highest effect on atrial myocardial refractoriness in patients with atrial tachycardias and on ventricular refractoriness in patients with ventricular tachycardias (longer effective and functional refractory periods). Intraventricular pathways are the major site of ritmilen's effect on anterograde conduction. Profound changes were found in patients with atrial and ventricular tachycardias. The cholinolytic action of ritmilen on the atrioventricular node was detected in 20% of the patients, whereas sinus rhythm increased in 90%, which may be attributable to asymmetric vagus innervation of sinoatrial and atrioventricular nodes.

Adult↗
PubMedDate not supplied

[Effect of adrenomimetic, adreno- and ganglionic-blocking agents during hyperbaric oxygenation].

Experiments on rats were made to study the action of hypotension and vasopressive agents. The effects obtained as a result of administering the drugs under common gas medium and hyperbaric oxygenation were compared. A considerable reduction of hypotensive action of alpha- and beta-adrenoblockers, ganglioblockers, beta-adrenomimetics and elimination of the effect of central alpha-adrenomimetics were discovered. The pressor effects of direct- and particularly of indirect-action alpha-adrenomimetics, as well as cardiotropic effects of beta-adrenoblockers were found to be potentiated. It is suggested that the action mode of oxygen is mediated via its direct- and primarily indirect-action adrenomimetic and beta-adrenoblocking effects. A classification of the periods of combined action of the drugs and hyperbaric oxygenation is suggested.

Adrenergic alpha-Antagonists↗
PubMed1983

Interactions between the autonomic nervous system and tachycardias in man.

We have endeavoured to present an integrated and dynamic overview of the interaction between the autonomic nervous system and cardiac arrhythmias. Our purpose was not to be comprehensive, detailed, or all inclusive but to present a clinically relevant summary of some of the areas where autonomic tone may be pertinent. Clearly, most arrhythmias are not the result of a primary autonomic nervous system disorder. However, subtle and overt alterations in autonomic tone, interacting with rate, pressure, cardiac volume, contractility, and the intrinsic myocardial electrophysiologic properties likely exert a critical influence on many cardiac arrhythmias. We wish to emphasize that autonomic effects may be temporarily concealed or overwhelmed during certain states or by the administration of drugs. However, the modulating role of neural tone and neurotransmitters is almost always present, contributing significantly to the outcome of therapy.

Anti-Arrhythmia Agents↗
PubMed1978

Exercise electrocardiography in the evaluation of cardiac dysrhythmias in children.

Exercise electrocardiography is a useful means to evaluate dysrhythmias in children and young adults. Exercise may suppress a dysrhythmia present at rest and thus suggest a relatively benign problem. It may provoke a latent dysrhythmia which is absent at rest but suggested by a history of exercise intolerance or palpitation with exertion. Exercise may also modify a dysrhythmia. Maximum exercise testing has been used to evaluate each of these situations in children. The results of testing will be presented. Since no dysrhythmias were provoked in 170 healthy children, we think that any dysrhythmia initiated by exercise in the young should be considered abnormal.

Adolescent↗
PubMed1973

Nervous activity of afferent cardiac sympathetic fibres with atrial and ventricular endings.

1. We recorded the electrical activity of single afferent cardiac fibres isolated from the third and fourth left thoracic sympathetic rami communicantes of anaesthetized cats. Their conduction velocities ranged from 12 to 32 m/sec.2. The endings of each fibre were localized to one cardiac chamber by mechanical probing of the opened heart performed at the end of the experiment.3. The impulse activity was spontaneous and, in fibres with atrial or ventricular endings, it was in phase with a particular atrial or ventricular event.4. This nervous activity increased during increases in pressure occurring in the chamber where the endings were located. Conversely, decreases in pressure were accompanied by decreased nervous discharge.5. In some experiments the left coronary artery was perfused at different flows and pressures. Brief decreases or increases in coronary flow and pressure decreased or increased, respectively, the discharge of fibres with atrial or ventricular endings. Fibres were excited by intracoronary injections of veratridine.6. Cessation of coronary pump flow increased the discharge of fibres with atrial or ventricular endings only when myocardial ischaemia was accompanied by signs of heart failure.7. These afferent cardiac sympathetic fibres which provide the spinal cord with continuous specific information on cardiac events are likely to contribute to the neural control of circulation.

Action Potentials↗
PubMed1977

Intraoperative identification of the conduction system in repair of endocardial cushion defect.

Electrophysiological identification intraoperatively of the His-Purkinje system eliminates the complication of complete heart block consequent upon repair of endocardial cushion defect (ECD). Ten patients, 6 with complete ECD and 4 with incomplete ECD, underwent repair of the defect. None of the patients developed heart block. Slight variations were noted in the location of the His bundle in 9 patients, and a major deviation was found in 1 patient with incomplete ECD. The data support the use of intraoperative recordings as a necessary acconpaniment to the operative repair of ECD.

Bundle of His↗
PubMed1978

Ultrastructure of capillaries in the conduction system of the heart in various mammals.

The capillaries in the atrioventricular node and atriventricular bundle of the heart (mammals) were investigated by thin sections and freeze-etch replicas. Fenestrated endothelial cells were found to occur in all mammals examined in this study. These fenestrations (500 +/- 50 A diameter) are bridged by a diaphragm and occur in relatively small sieve areas. In contrast to the AV-node and AV-bundle, the non-specialized myocardium is supplied by continuous capillaries. The presence of the fenestrated capillary in the conduction system of the heart may serve to increase both permeability and passive transport capacity.

Animals↗
PubMed1985

Systolic time intervals--a new technique in clinical pharmacology.

Systolic time intervals (STI) are unique in describing cardio-vascular function in terms of time alone. Although the STI were first adequately described over 60 years ago, it is only recently that they have been applied in a scientific way to the study of drug action in man. The STI are highly sensitive to changes in myocardial contractility, left ventricular filling pressure, peripheral resistance, heart rate, and intra-cardiac electrical conduction and electro-mechanical coupling. Early investigators tended to regard STI as a specific measure of contractility, and they also used inappropriate methods for correcting the STI for changes in heart rate. The reputation of the method was not enhanced by the fact that many studies were performed in an open fashion and without placebo control. Furthermore, the STI have never been popular with clinicians because they many sometimes be normal in spite of the presence of obvious severe heart disease. Now, however, STI are being used increasingly in clinical pharmacological studies. They can be recorded quickly, easily and painlessly with inexpensive apparatus which is readily available; they carry no risk, and multiple recordings can be made without discomfort. The lack of specificity of the STI can be mitigated by combining them with measurements of heart rate, blood pressure, the high-speed surface electrocardiogram, and cardiac output. The most promising applications of the STI in clinical pharmacology are as a screening test for cardiovascular activity of new compounds, and in the examination of dose-response relationships and agonist-antagonist interactions.

Animals↗
PubMed1987

Electrophysiological study in the dog of the risk of cardiac toxicity of bupivacaine.

The risk of toxic effects on the heart of bupivacaine following several kinds of locoregional anaesthesia has been investigated in the dog in situ heart by determining conduction time and effective refractory period in the various parts of the conduction system and the ventricular muscle, as well as the discharge rate of the sinus node. Bupivacaine, i.v. infused at 3 rates, 0.2, 0.3 and 0.4 mg X kg-1 X min-1, proved to have depressant effects on conduction, automatism and excitability. It slows down conduction in all the parts of the myocardium, considerably at high stimulation frequencies, but always much more in the His-Purkinje system and the ventricular contractile fibres than in the atrioventricular node, because it tends to block the sodium rather than the calcium or potassium channel. Its effect remain more moderate, indeed, on sinus automatism and atrial and mainly ventricular refractoriness. Its danger lies, therefore, in the inhibition of conduction, with atrioventricular or His bundle branch block, but more frequently reentrant arrhythmias, likely to result in ventricular fibrillation. However: these alterations are observed with very high plasma levels (about 4 to 9 micrograms X ml-1), much higher than usual peak concentrations following spinal anaesthesia (0.10 micrograms X ml-1) or even epidural anaesthesia or brachial plexus block (1.20 micrograms X ml-1); reversal of these alterations occurs rapidly (reduction by 50% within 30 min for instance), when they have not led to ventricular fibrillation or they have not been associated with circulatory collapse.

Action Potentials↗