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At least 433 records · Page 24Linked to original sources
PubMed1992

Strategies for mode selection in antibradyarrhythmia pacing.

A systematic technique is described for selecting an appropriate mode of antibradycardia pacing on the basis of 10 clinical criteria. A computer model of the selection process was developed with input from more than 41 implanting physicians, and implemented together with a database management system for keeping track of mode selections and identifying cases in which the modes selected by the implanters differed from those recommended by the model. The selection technique, which can be used without a computer, is presented in detail with a decision-tree representation of the model and an explanation of the rationale behind each of its 39 possible recommendations.

Algorithms↗
PubMedDate not supplied

[Role of the autonomic nervous system in early arrhythmias in acute myocardial infarct in the rabbit].

In order to evaluate the influence of the autonomic nervous system in the incidence and characteristics of the early arrhytmias that follows myocardial infarction, we have developed an experimental myocardial infarction in rabbits by acute occlusion of the left ventricular artery. The influence of adrenergic and cholinergic suppression over rhythm disorders and hemodynamics changes after experimental infarction in the rabbit was also studied. We found that after the acute experimental infarction in the rabbit heart, arose an early stage of rhythm disorders in 60% of the animals. In a group of animals that were injected with Practolol before coronary occlusion, the incidence of arrhythmias was 25% and in a group of animals with vagotomy prior to occlussion none of them developed rhythm disorders. It was concluded that the model is highly steemed for the study of early arrhytmias and that automatic nervous system has an important role in the incidence of such arrhythmias.

Acute Disease↗
PubMedDate not supplied

[The pacemaker cells of the heart: their electrical activity and the effect of autonomic neuromediators].

The review is concerned with mechanisms of rhythmogenesis in pacemaker cells of the heart and with action of autonomic transmitters on these cells. Most attention is paid to background conditions in the action of transmitters and to secondary effects of their influences: on the basis of these background conditions and secondary effects are explained some of the mechanisms of many phenomena associated with neural influences on heart rate (vagal escape, "paradoxical" positive vagal effect, phase-dependent neural influences). Two types of transmitter influences on pacemaker cells are distinguished: the controlling influences and the modulating ones. The controlling influences can serve to set up the heart rate to a strictly determined level, and with the modulating ones only the limits of possible regulation of heart rate can be approximately shifted. The controlling influences are realized through the action of acetylcholine on IAch-channel, sensitive only to that transmitter: on the other hand, the modulating influences are performed through the actions of acetylcholine and catecholamines on voltage-dependent currents determining the rhythmogenesis in pacemaker cells--ICa, IK and Ih. Biochemical mechanisms of the two kinds of influences are discussed; the modulating ones are realized through some second-messenger systems.

Animals↗
PubMed1990

Emulation of conduction system functions in the hearts of early mammalian embryos.

The conduction system functions of atrioventricular sequential contractions, atrioventricular delay, and coordination of ventricular contraction were examined in rat embryos at the earliest functional stage of cardiac development (before cardiac looping, n = 6) and shortly after looping (n = 15). Atrioventricular sequential contractions were observed in all embryos, and contractions appeared to originate in the left sinus horn. Atrioventricular delay was present in both prelooped (132 +/- 32 ms) and looped (141 +/- 15 ms) hearts. Before looping, contractions traveled from proximal ventricle to bulbus cordis, a distance of 253 +/- 27 microns, in 72 +/- 22 ms. After looping, contractions crossed an increased intraventricular distance (520 +/- 28 microns, p less than 0.005) in substantially less time (16 +/- 7 ms, p less than 0.005). Sinoatrial and atrioventricular nodal functions are emulated in both prelooped and looped hearts of early mammalian embryos, and His-Purkinje system function is emulated in looped hearts.

Animals↗