Document Detail


Characteristics and mechanisms of the effects of heart rate history on transient AV nodal responses.
MedLine Citation:
PMID:  8764258     Owner:  NLM     Status:  MEDLINE    
Abstract/OtherAbstract:
The characteristics and functional origin of the changes in transient atrioventricular (AV) nodal responses with heart rate history were studied in isolated rabbit heart preparations. For this purpose, ramp stimulation sequences were applied to the atrium from different initial conditions. A ramp decrease and increase in the His-stimulus interval and a reverse sequence consisting of a ramp increase and decrease were performed starting from a control basic cycle length, after 5 min of fast rate, or with 5 min of fast rate inserted between the two ramps. The nodal conduction times (NCT) obtained during the ramp stimulations formed hysteresis loops, the direction, shape, and magnitude of which varied markedly with the nodal history. That is, the nodal response to a given ramp took a variety of forms, depending on the initial condition. The effects of the initial condition also depended on ramp direction and sequence. A paradoxical NCT-recovery relationship (decrease in NCT with shortening His-atrial interval) was consistently observed at the onset of any ramp decrease performed after 5 min of fast rate. These effects also varied with the rate used to change the nodal history. The insertion of a control cycle at every 20th beat during repeated ramp protocols allowed the determination of the contribution of the nodal property of fatigue to these effects. Fatigue was found to account for all observed hysteresis patterns. In conclusion, heart rate history can, by modulating beat-to-beat changes in fatigue, transform transient nodal responses and hysteresis observed during stimulation ramps. Interpretation of transient nodal responses thus requires exact knowledge of previous nodal history.
Authors:
J Zhao; J Billette
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Publication Detail:
Type:  In Vitro; Journal Article; Research Support, Non-U.S. Gov't    
Journal Detail:
Title:  The American journal of physiology     Volume:  270     ISSN:  0002-9513     ISO Abbreviation:  Am. J. Physiol.     Publication Date:  1996 Jun 
Date Detail:
Created Date:  1996-09-19     Completed Date:  1996-09-19     Revised Date:  2006-11-15    
Medline Journal Info:
Nlm Unique ID:  0370511     Medline TA:  Am J Physiol     Country:  UNITED STATES    
Other Details:
Languages:  eng     Pagination:  H2070-80     Citation Subset:  IM    
Affiliation:
Department of Physiology, Faculty of Medicine, University of Montreal, Quebec, Canada.
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MeSH Terms
Descriptor/Qualifier:
Animals
Atrioventricular Node / physiology*
Biomechanics
Electrophysiology
Heart Rate / physiology*
Rabbits
Time Factors

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine


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