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Random nature of fibrillation leads to the probabilistic nature of defibrillation
Journal of Electrocardiology Vol. 32 Supplement 1999
R a n d o m N a t u r e of F i b r i l l a t i o n L e a d s t o t h e P r o b a b i l i s t i c N a t u r e of D e f i b r i l l a t i o n
P a t r i c k D. W o l f , P h D , a n d R a j e s h P e n d e k a n t i ,
The mechanism of the probabilistic nature of defibrillation is not understood. We hypothesize that it is the r a n d o m nature of the wavefronts interacting with the shock field that causes this characteristic. We studied eight dogs with epicardial mapping to determine if the preshock state of the m y o c a r d i u m could predict the o u t c o m e of the shock. A right ventricle-superior vena cava (RV/SVC) electrode configuration was used to deliver biphasic defibrillation shocks. An initial V50 was d e t e r m i n e d using a 3 turning point protocol and followed by 21 + 7 shocks using an u p - d o w n protocol. Activation wavefronts were recorded from 524 electrodes applied to the ventricles in an elastic sock with 4 m m interelectrode spacing. The signals from the tip of the RV catheter and from the defibrillation electrodes were also recorded. The electrogram on each electrode immediately before the shock was characterized as either on the upstroke or the downstroke. This characterization by slope was used to indicate either activation (downstroke) or recovery (upstroke). Each electrogram was characterized for each shock and the
PhD*
probabilities of success, P(s), given a downstroke (P(s[d)) and given an upstroke (P(s[u)), were calculated. If the o u t c o m e of the shock was i n d e p e n d e n t of the state of the epicardial tissue t h e n P(s[u) would equal P(sld ). The average defibrillation voltage was 550 + 170 V. The P(s) for all shocks was 49% + 6%, the average P(slu ) and P(sld ) for all electrodes was 48 +_ 4 and 52 + 8, respectively (P = NS). P(s[u) and P(sld ) for the catheter leads were not significantly different. W h e n each electrode was considered individually, 2 electrode locations had P(slu ) > P(sld) and 34 electrodes had P(sld ) > P(slu ). In this later group, 32 electrodes covered a 5 cm 2 area of the LV free wall. These electrodes had an average P(s[d) of 70 + 6% (P < .05 compared to all other electrodes). This area of the left ventricle (LV) has been s h o w n to be the low gradient region for the RV/SVC configuration. W h e n the activations in this area were combined such that the shock occurred w h e n the electrograms on two electrodes 1 cm apart (16 pairs) were both in their downstroke, the P(sld ) increased to 75% _+ 6% (P < .05 compared to one electrode). The wavefronts occurring in this region at the time of the shock had a significant predictive value for the o u t c o m e of the shock. This finding d e m o n strates that the state of the m y o c a r d i u m in a small region of the LV determines, at least in part, the o u t c o m e of the shock. This result has implications for the t h e o r y of defibrillation and suggests possible device e n h a n c e m e n t s .
From the Center for Emerging Cardiovascular Technologies, Duke University, Durham, North Carolina, and *St. Jude Medical Sunnyvale, California. Reprint requests: Patrick D. Wolf, PhD, Department of Biomedical Engineering, Duke University, Box 90281, Durham, NC 27708. Copyright © 1999 by Churchill Livingstone ® 0022-0736/99/320S-0019510.00/0
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R a n d o m N a t u r e of F i b r i l l a t i o n L e a d s t o t h e P r o b a b i l i s t i c N a t u r e of D e f i b r i l l a t i o n
P a t r i c k D. W o l f , P h D , a n d R a j e s h P e n d e k a n t i ,
The mechanism of the probabilistic nature of defibrillation is not understood. We hypothesize that it is the r a n d o m nature of the wavefronts interacting with the shock field that causes this characteristic. We studied eight dogs with epicardial mapping to determine if the preshock state of the m y o c a r d i u m could predict the o u t c o m e of the shock. A right ventricle-superior vena cava (RV/SVC) electrode configuration was used to deliver biphasic defibrillation shocks. An initial V50 was d e t e r m i n e d using a 3 turning point protocol and followed by 21 + 7 shocks using an u p - d o w n protocol. Activation wavefronts were recorded from 524 electrodes applied to the ventricles in an elastic sock with 4 m m interelectrode spacing. The signals from the tip of the RV catheter and from the defibrillation electrodes were also recorded. The electrogram on each electrode immediately before the shock was characterized as either on the upstroke or the downstroke. This characterization by slope was used to indicate either activation (downstroke) or recovery (upstroke). Each electrogram was characterized for each shock and the
PhD*
probabilities of success, P(s), given a downstroke (P(s[d)) and given an upstroke (P(s[u)), were calculated. If the o u t c o m e of the shock was i n d e p e n d e n t of the state of the epicardial tissue t h e n P(s[u) would equal P(sld ). The average defibrillation voltage was 550 + 170 V. The P(s) for all shocks was 49% + 6%, the average P(slu ) and P(sld ) for all electrodes was 48 +_ 4 and 52 + 8, respectively (P = NS). P(s[u) and P(sld ) for the catheter leads were not significantly different. W h e n each electrode was considered individually, 2 electrode locations had P(slu ) > P(sld) and 34 electrodes had P(sld ) > P(slu ). In this later group, 32 electrodes covered a 5 cm 2 area of the LV free wall. These electrodes had an average P(s[d) of 70 + 6% (P < .05 compared to all other electrodes). This area of the left ventricle (LV) has been s h o w n to be the low gradient region for the RV/SVC configuration. W h e n the activations in this area were combined such that the shock occurred w h e n the electrograms on two electrodes 1 cm apart (16 pairs) were both in their downstroke, the P(sld ) increased to 75% _+ 6% (P < .05 compared to one electrode). The wavefronts occurring in this region at the time of the shock had a significant predictive value for the o u t c o m e of the shock. This finding d e m o n strates that the state of the m y o c a r d i u m in a small region of the LV determines, at least in part, the o u t c o m e of the shock. This result has implications for the t h e o r y of defibrillation and suggests possible device e n h a n c e m e n t s .
From the Center for Emerging Cardiovascular Technologies, Duke University, Durham, North Carolina, and *St. Jude Medical Sunnyvale, California. Reprint requests: Patrick D. Wolf, PhD, Department of Biomedical Engineering, Duke University, Box 90281, Durham, NC 27708. Copyright © 1999 by Churchill Livingstone ® 0022-0736/99/320S-0019510.00/0
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