Document Detail

Can shocks timed to action potentials in low-gradient regions improve both internal and out-of-hospital defibrillation?
MedLine Citation:
PMID:  9988004     Owner:  NLM     Status:  MEDLINE    
During the first minute of fibrillation, circulating wavefronts excite new fibrillation action potentials almost immediately following termination of the preceding action potential. The extension of refractoriness hypothesis states that a successful defibrillating shock must produce a uniform postshock refractoriness of a specific optimal duration throughout the ventricle, which blocks these wavefronts and terminates fibrillation. We hypothesized that, if shocks are appropriately timed early in the fibrillation action potential in low-voltage-gradient regions, postshock refractoriness will already be long and the shock need not be strong enough to further extend it. This will result in a lower defibrillation threshold (DFT). This hypothesis was tested in the isolated rabbit heart model. Shocks were synchronized to monophasic action potentials recorded from a low-intensity region. An up/down protocol was used. I50 for early shocks was 17% lower than that for late shocks (31% decrease in E50). Standard deviation of I50 was reduced from 32% for late shocks to 18% for early shocks. Therefore, shock synchronization improves both DFT and intersubject variability during early fibrillation. As fibrillation duration increases, action potential frequency decreases and periods of diastole occur. Because of these ischemic changes, it is uncertain whether shock timing can produce similar improvements in defibrillation under out-of-hospital conditions.
J Jones; W Noe; O Tovar; Y Lin; W Hsu
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Publication Detail:
Type:  Comparative Study; In Vitro; Journal Article; Research Support, U.S. Gov't, Non-P.H.S.; Research Support, U.S. Gov't, P.H.S.; Review    
Journal Detail:
Title:  Journal of electrocardiology     Volume:  31 Suppl     ISSN:  0022-0736     ISO Abbreviation:  J Electrocardiol     Publication Date:  1998  
Date Detail:
Created Date:  1999-04-13     Completed Date:  1999-04-13     Revised Date:  2009-11-11    
Medline Journal Info:
Nlm Unique ID:  0153605     Medline TA:  J Electrocardiol     Country:  UNITED STATES    
Other Details:
Languages:  eng     Pagination:  41-4     Citation Subset:  IM    
Department of Physiology and Biophysics, Georgetown University and DVAMC, Washington, DC 20422, USA.
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MeSH Terms
Action Potentials / physiology*
Ambulatory Care / methods*
Electric Countershock*
Heart Rate
Ventricular Fibrillation / physiopathology*,  therapy
Grant Support

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

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