Document Detail

Characterization of refractory period extension by transcardiac shock.
MedLine Citation:
PMID:  2040057     Owner:  NLM     Status:  MEDLINE    
BACKGROUND: To better understand the refractory period extension (RPE) produced by transcardiac shocks and its possible role in defibrillation, we measured RPE under various experimental conditions. METHODS AND RESULTS: Using ventricular pacing in pentobarbital-anesthetized dogs, we characterized RPE in relation to the anatomic site of pacing, the local voltage gradient (LVG) produced by the shocks at the pacing site, and the pacing rate and pacing current used to make the measurements. We also determined if RPE persisted into the next refractory period after the shock and measured RPE at the end of 30-second episodes of acute ischemia to the pacing site, which were caused by occluding the left anterior descending artery. Each anatomic site tested showed RPE, which increased sharply with increasing LVG at lower levels but less sharply at higher LVG. The RPE versus LVG was approximated with an exponential curve that had an exponential constant of about 5-6 V/cm. At faster pacing rates, RPE occurred earlier in the refractory period but was unchanged when expressed as a percent increase of refractory period. RPE did not vary with the pacing current and was present only in the refractory period during which the shock was delivered. The RPE was not significantly altered by acute ischemia. These results show that transcardiac shocks selectively extend the refractory period of tissue proportional to the LVG and the timing of the shock in the refractory period. They are consistent with the concept that RPE prevents depolarization from tissue directly excited by a shock from propagating to tissue that was refractory to that same shock. CONCLUSIONS: The insensitivity of RPE to short ischemic episodes and the presence of RPE at increased activation rates suggest that RPE might exist under conditions of fibrillation and be a major determinant of the success or failure of defibrillation.
R J Sweeney; R M Gill; P R Reid
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Publication Detail:
Type:  Journal Article; Research Support, Non-U.S. Gov't    
Journal Detail:
Title:  Circulation     Volume:  83     ISSN:  0009-7322     ISO Abbreviation:  Circulation     Publication Date:  1991 Jun 
Date Detail:
Created Date:  1991-07-08     Completed Date:  1991-07-08     Revised Date:  2010-03-24    
Medline Journal Info:
Nlm Unique ID:  0147763     Medline TA:  Circulation     Country:  UNITED STATES    
Other Details:
Languages:  eng     Pagination:  2057-66     Citation Subset:  AIM; IM    
Department of Electrophysiology Research, Eli Lilly and Company, Indianapolis, Ind.
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MeSH Terms
Acute Disease
Cardiac Pacing, Artificial*
Coronary Disease / physiopathology
Refractory Period, Electrophysiological*
Time Factors

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

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