Document Detail


Timing of the upper limit of vulnerability is different for monophasic and biphasic shocks: implications for the determination of the defibrillation threshold.
MedLine Citation:
PMID:  9309741     Owner:  NLM     Status:  MEDLINE    
Abstract/OtherAbstract:
The upper limit of vulnerability (ULV) has been used in clinical studies to predict the DFT in patients with ICDs. Despite the ULV-DFT correlation, uncertainties about the optimal timing of the ULV determination remain. Previous studies using monophasic or biphasic shock waveforms reported differences in the ULV timing with respect to the electrocardiographic T wave. The purpose of this study was to directly compare the ULV timing for mono- versus biphasic T wave shocks. In ten isolated rabbit hearts, mono- and biphasic shocks were delivered randomly during the vulnerable window and at varying shock strengths to determine the ULV. The ULV timing was expressed as the coupling interval at the ULV, the myocardial repolarization state at the ULV measured by monophasic action potential recordings, and the relation between the ULV and the peak of the simultaneously recorded volume conducted T wave. The ULV for biphasic shocks occurred at longer coupling intervals than for monophasic shocks (188.0 +/- 9.5 ms vs 173.5 +/- 8.8 ms, P < 0.001). This resulted in a more repolarized myocardial state at the ULV for biphasic than for monophasic shocks (81.1% +/- 7.5% vs 66.9% +/- 9.0%, P = 0.002). The ULV for monophasic shocks occurred predominantly during the upslope of the T wave (8.0 +/- 9.7 ms before the peak of the T wave) whereas the ULV for biphasic shocks occurred at or after the peak of the T wave (5.9 +/- 9.3 ms after the peak of the T wave) (P < 0.001). Biphasic shocks delay the timing of the ULV as compared to monophasic shocks. This is important for the prediction of the DFT by ULV measurements.
Authors:
S Behrens; C Li; M R Franz
Publication Detail:
Type:  Comparative Study; Journal Article; Research Support, Non-U.S. Gov't; Research Support, U.S. Gov't, Non-P.H.S.    
Journal Detail:
Title:  Pacing and clinical electrophysiology : PACE     Volume:  20     ISSN:  0147-8389     ISO Abbreviation:  Pacing Clin Electrophysiol     Publication Date:  1997 Sep 
Date Detail:
Created Date:  1997-11-06     Completed Date:  1997-11-06     Revised Date:  2006-11-15    
Medline Journal Info:
Nlm Unique ID:  7803944     Medline TA:  Pacing Clin Electrophysiol     Country:  UNITED STATES    
Other Details:
Languages:  eng     Pagination:  2179-87     Citation Subset:  IM    
Affiliation:
Cardiology Division, Veteran Administration Medical Center, Washington, DC 20422, USA.
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MeSH Terms
Descriptor/Qualifier:
Action Potentials / physiology
Animals
Cardiac Pacing, Artificial
Electric Countershock / instrumentation,  methods*
Electrocardiography
Heart Conduction System / physiopathology
Male
Rabbits
Time Factors
Ventricular Fibrillation / etiology,  physiopathology,  therapy*

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


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