Document Detail

Electrophysiologic deterioration after one-minute fibrillation increases relative biphasic defibrillation efficacy.
MedLine Citation:
PMID:  10868738     Owner:  NLM     Status:  MEDLINE    
INTRODUCTION: The probability of survival decreases to 70% after 2 minutes of ventricular fibrillation. Biphasic shocks are more effective than monophasic shocks in terminating short-duration (<30 sec) ventricular fibrillation. We tested the hypotheses that developing ischemia changes the electrophysiologic characteristics of fibrillation and that the relative efficacy of biphasic shocks increases as electrophysiologic characteristics deteriorate. METHODS AND RESULTS: Monophasic (12 msec) and biphasic (6/6 msec) shocks (1 to 4 A) were tested in random order in isolated rabbit hearts after 1-minute ischemic fibrillation. Monophasic action potentials showed only a sporadic occurrence of electrical diastole after 5 seconds of fibrillation (24% of action potentials in the right ventricle and 18% in the left ventricle). After 60 seconds of fibrillation, diastole (17.83+/-1.14 msec in the right ventricle and 21.52+/-1.16 msec in the left ventricle) appeared after almost every action potential (P < 0.0001 compared with 5 sec), despite a lack of change in fibrillation cycle length and dominant frequency. Monophasic I50 was 2.89 A, and biphasic I50 was 1.4 A (77% reduction in energy). Normalized curve width decreased 28%. Retrospective analysis showed that shocks delivered early in the fibrillation action potential had a greater probability of succeeding (89%) than shocks delivered late (30%; P < 0.001). CONCLUSION: After 1-minute ischemic fibrillation, diastolic intervals occur during fibrillation. Therefore, defibrillation shocks have an approximately 29% probability of interacting with the fibrillation action potential during diastole. At this time, biphasic shocks produced a more deterministic defibrillation threshold and became even more efficacious (I50 B/M = 0.48) than at short fibrillation durations (I50 B/M = 0.7).
O H Tovar; J L Jones
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Publication Detail:
Type:  In Vitro; Journal Article; Research Support, U.S. Gov't, P.H.S.    
Journal Detail:
Title:  Journal of cardiovascular electrophysiology     Volume:  11     ISSN:  1045-3873     ISO Abbreviation:  J. Cardiovasc. Electrophysiol.     Publication Date:  2000 Jun 
Date Detail:
Created Date:  2000-10-19     Completed Date:  2000-10-19     Revised Date:  2007-11-14    
Medline Journal Info:
Nlm Unique ID:  9010756     Medline TA:  J Cardiovasc Electrophysiol     Country:  UNITED STATES    
Other Details:
Languages:  eng     Pagination:  645-51     Citation Subset:  IM    
Department of Physiology and Biophysics, Georgetown University, Washington, DC, USA.
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MeSH Terms
Electric Countershock / standards*
Myocardial Ischemia / etiology,  physiopathology
Time Factors
Ventricular Fibrillation / complications,  physiopathology*,  therapy*
Grant Support

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