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Effect of Shock Waveform on Relationship Between Upper Limit of Vulnerability and Defibrillation Threshold
Author(s) -
SWERDLOW CHARLES D.,
KASS ROBERT M.,
O'CONNOR MARK E.,
CHEN PEKGSHENG
Publication year - 1998
Publication title -
journal of cardiovascular electrophysiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.193
H-Index - 138
eISSN - 1540-8167
pISSN - 1045-3873
DOI - 10.1111/j.1540-8167.1998.tb00922.x
Subject(s) - medicine , defibrillation threshold , limit (mathematics) , shock (circulatory) , defibrillation , waveform , cardiology , electric shock , vulnerability (computing) , computer security , electrical engineering , mathematical analysis , voltage , mathematics , computer science , engineering
ULV‐DFT Waveform. Introduction : The upper limit of vulnerability (ULV) correlates with the defibrillation threshold (DFT). The ULV can he determined with a single episode of ventricular fibrillation and is more reproducible than the single‐point DFT. The critical‐point hypothesis of defibrillation predicts that the relation between the ULV and the DFT is independent of shock waveform. The principal goal of this study was to test this prediction. Methods and Results: We studied 45 patients at implants of pectoral cardioverter defibrillators. In the monophasic‐biphasic group (n = 15), DFT and ULV were determined for monophasic and biphasic pulses from a 120‐μF capacitor. In the 60‐ to 110‐μF group (n = 30), DFT and ULV were compared for a clinically used 110‐μF waveform and a novel 60‐μF waveform with 70% phase 1 tilt and 7‐msec phase 2 duration. In the monophasic‐biphasic group, all measures of ULV and DFT were greater for monophasic than biphasic waveforms (P < 0.0001). In the 60‐ to 110‐/tF group, the current and voltage at the ULV and DFT were higher for the 60‐μF waveform (P < 0.0001), hut stored energy was lower (ULV 17%, P < 0.0001; DFT 19%, P = 0.03). There was a close correlation between ULV and DFT for both the monophasic‐biphasic group (monophasic r 2 = 0.75, P < 0.001; hiphasic r 2 = 0.82, P < 0.001) and the 60‐ to 110‐μF group (60 μF r 2 = 0.81 P < 0.001; 110 μF r 2 = 0.75, P < 0.001). The ratio of ULV to DFT was not significantly different for monophasic versus biphasic pulses (1.17 ± 0.12 vs 1.14 ± 0.19, P = 0.19) or 60‐μF versus 110‐μF pulses (1.15 ± 0.16 vs 1.11 ± 0.14, P = 0.82). The slopes of the ULV versus DFT regression lines also were not significantly different (monophasic vs biphasic pulses, P = 0.46; 60‐μF vs UO‐μF pulses, P = 0.99). The sample sizes required to detect the observed differences between experimental conditions (P < 0.05) were 4 for ULV versus 6 for DFT in the monophasic‐biphasic group (95% power) and 11 for ULV versus 31 for DFT in the 60‐ to 110‐μF group (75% power). Conclusion: The relation between ULV and DFT is independent of shock waveform. Fewer patients are required to detect a moderate difference in efficacy of defibrillation waveforms by ULV than by DFT. A small‐capacitor biphasic waveform with a long second phase defibrillates with lower stored energy than a clinically used waveform.