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At least 451 records · Page 25Linked to original sources
PubMed1993

A stochastic network model of the interaction between cardiac rhythm and artificial pacemaker.

The electrical interaction between the heart and an artificial pacemaker is often complex. Because of the sophistication and diversity of dual-chamber device algorithms, even experienced cardiologists can have difficulty interpreting paced electrocardiograms (ECG's). In order to study heart-pacemaker interaction (HPI), a computer model of the cardiac conduction system has been developed which includes the effects of artificial pacemaker function and failure. The stochastic network model of cardiac conduction consists of five vertices, each representing a functional electrophysiologic element. Electrophysiologic multidimensional conditional probability functions determine the depolarization status of each vertex. The atrioventricular (AV) node is emulated using a mathematical model which includes the influence of past cycle lengths on AV nodal conduction time. Twenty-three classes of arrhythmias may be simulated and, for pacing simulation, one of 12 antibradycardia pacing modes may be chosen. Random effects of pacemaker malfunction including oversensing, undersensing, or failure-to-capture may be simulated through the use of probability distribution functions. This model should prove useful in the development of pacemaker algorithms, determining patient-specific pacemaker therapy, and predicting causes for apparent pacemaker malfunction. The model has been used in the development of an expert system to analyze paced ECG's for pacemaker function and malfunction.

Algorithms↗
PubMed1992

[Discovery of the electrical activity and conduction system of the heart].

Since our student days we have been accustomed to enumerating the individual elements of the heart's rhythmic centre and conduction system in accordance with the order of their functions, from cranial to caudal. We begin, therefore, with the sino-atrial node in the right atrium, after which comes the atrioventricular node, the bundle of His and, finally, Purkinje's fibres. The respective discoveries were made in precisely the opposite order, however. Purkinje's fibres were discovered in 1839, the bundle of His in 1893, the atrioventricular node was discovered by Aschoff and Tawara in 1905-1906 and the sinus node by Keith and Flack in 1906. The biographies of the respective discoverers and the circumstances surrounding their discoveries are dealt with briefly.

Animals↗
PubMed1990

[Morphologic characteristics of the conduction system in ischemic heart disease].

An autopsy study is presented of 32 cases (age: 45-80 years) with special examination of conduction system of the heart by morphological methods. The patients died of acute and repeat myocardial infarction, ischemic heart disease. The changes were manifested in association of disordered circulatory, destructive and compensatory-adaptative processes that are the background of conduction and rhythm disorders and depending on the degree of circulatory and metabolic disturbances in the contractile myocardium.

Aged↗
PubMed1996

A quantitative assessment of innervation in the conduction system of the calf heart.

BACKGROUND: The aim of the present investigation was to determine the relative distribution of autonomic and sensory nerves in the cardiac conduction tissues of calves. METHODS: A quantitative immunohistochemical and histochemical technique was adopted. RESULTS: Immunoreactivity to the general neuronal marker protein gene product 9.5 (PGP 9.5) demonstrated that all regions of the conduction system possessed a higher relative density of total nerves when compared with the surrounding myocardial tissues. Unlike myocardial innervation, the conduction system did not display an atrial-to-ventricular gradient in nerve density. PGP 9.5-immunoreactive nerve trunks and varicose nerve fibres were more numerous in the transitional atrioventricular node and the penetrating atrioventricular bundle than in either the sinus node, compact atrioventricular node, or bundle branches. The Purkinje network of the ventricular conduction tissues possessed a rich supply of PGP 9.5-immunoreactive nerve trunks and varicose nerve fibres. Acetylcholinesterase (AChE)-positive nerves were the main subtype identified in the sinus and atrioventricular nodes and in the ventricular conduction tissues, representing 50-80% of the area occupied by PGP 9.5-immunoreactive nerves. The compact atrioventricular node possessed AChE-positive and tyrosine hydroxylase (TH)-immunoreactive nerves in similar proportions (45%), although, in general, TH-immunoreactive nerves had a lower relative nerve density than AChE-positive nerves. Neuropeptide Y (NPY)-immunoreactive nerves represented the main peptide-containing subpopulation and occurred throughout the conduction system, displaying a similar pattern of distribution and relative density to those demonstrating TH immunoreactivity. Nerve fibres immunoreactive for somatostatin, vasoactive intestinal polypeptide, substance P, and calcitonin gene-related peptide formed relatively minor subpopulations. CONCLUSIONS: The general innervation of the bovine conduction tissues exhibits significant regional variation. Throughout all regions of the conduction system, AChE-positive nerve represented the dominant subtype when compared with TH- and NPY-immunoreactive nerves. The distribution and relative density of nerve subtypes in the tissues of the bovine conduction system are similar to those observed in man, whereas differences were observed in other regions, such as the atrioventricular bundle and bundle branches. This finding must be considered by those making interspecies comparisons.

Acetylcholinesterase↗