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Hayashi K, Tsurugi T, Koyama J, Okumura K, Abe H, Wilkoff BL. Successful defibrillation by modifying from fixed-tilt to tuned-duration defibrillation waveform: When less is more? HeartRhythm Case Rep 2022; 8:702-706. [PMID: 36310725 PMCID: PMC9596389 DOI: 10.1016/j.hrcr.2022.07.019] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022] Open
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A framework of current based defibrillation improves defibrillation efficacy of biphasic truncated exponential waveform in rabbits. Sci Rep 2021; 11:1586. [PMID: 33452293 PMCID: PMC7810866 DOI: 10.1038/s41598-020-80521-9] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/17/2020] [Accepted: 12/22/2020] [Indexed: 11/08/2022] Open
Abstract
Defibrillation is accomplished by the passage of sufficient current through the heart to terminate ventricular fibrillation (VF). Although current-based defibrillation has been shown to be superior to energy-based defibrillation with monophasic waveforms, defibrillators with biphasic waveforms still use energy as a therapeutic dosage. In the present study, we propose a novel framework of current-based, biphasic defibrillation grounded in transthoracic impedance (TTI) measurements: adjusting the charging voltage to deliver the desired current based on the energy setting and measured pre-shock TTI; and adjusting the pulse duration to deliver the desired energy based on the output current and intra-shock TTI. The defibrillation efficacy of current-based defibrillation was compared with that of energy-based defibrillation in a simulated high impedance rabbit model of VF. Cardiac arrest was induced by pacing the right ventricle for 60 s in 24 New Zealand rabbits (10 males). A defibrillatory shock was applied with one of the two defibrillators after 90 s of VF. The defibrillation thresholds (DFTs) at different pathway impedances were determined utilizing a 5-step up-and-down protocol. The procedure was repeated after an interval of 5 min. A total of 30 fibrillation events and defibrillation attempts were investigated for each animal. The pulse duration was significantly shorter, and the waveform tilt was much lower for the current-based defibrillator. Compared with energy-based defibrillation, the energy, peak voltage, and peak current DFT were markedly lower when the pathway impedance was > 120 Ω, but there were no differences in DFT values when the pathway impedance was between 80 and 120 Ω for current-based defibrillation. Additionally, peak voltage and the peak current DFT were significantly lower for current-based defibrillation when the pathway impedance was < 80 Ω. In sum, a framework of adjusting the charging voltage and shock duration to deliver constant energy for low impedance and constant current for high impedance via pre-shock and intra-shock impedance measurements, greatly improved the defibrillation efficacy of high impedance by lowering the energy DFT.
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OKAMURA HIDEO, DESIMONE CHRISTOPHERV, KILLU AMMARM, GILLES EMILYJ, TRI JASON, ASIRVATHAM ROSHINI, LADEWIG DEJAEJ, SUDDENDORF SCOTTH, POWERS JOANNEM, WOOD-WENTZ CHRISTINAM, GRAY PETERD, RAYMOND DOUGLASM, SAVAGE SHELLEYJ, SAVAGE WALTERT, BRUCE CHARLESJ, ASIRVATHAM SAMUELJ, FRIEDMAN PAULA. Evaluation of a Unique Defibrillation Unit with Dual-Vector Biphasic Waveform Capabilities: Towards a Miniaturized Defibrillator. PACING AND CLINICAL ELECTROPHYSIOLOGY: PACE 2017; 40:108-114. [DOI: 10.1111/pace.12979] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/16/2016] [Revised: 10/14/2016] [Accepted: 10/25/2016] [Indexed: 11/29/2022]
Affiliation(s)
- HIDEO OKAMURA
- Division of Cardiovascular Diseases; Mayo Clinic; Rochester Minnesota
| | | | - AMMAR M. KILLU
- Division of Cardiovascular Diseases; Mayo Clinic; Rochester Minnesota
| | | | - JASON TRI
- Division of Cardiovascular Diseases; Mayo Clinic; Rochester Minnesota
| | | | | | | | - JOANNE M. POWERS
- Division of Cardiovascular Surgery; Mayo Clinic; Rochester Minnesota
| | | | - PETER D. GRAY
- Employees and equity owners in CardioThrive; Walnut Creek California
| | | | - SHELLEY J. SAVAGE
- Employees and equity owners in CardioThrive; Walnut Creek California
| | - WALTER T. SAVAGE
- Employees and equity owners in CardioThrive; Walnut Creek California
| | - CHARLES J. BRUCE
- Division of Cardiovascular Diseases; Mayo Clinic; Rochester Minnesota
| | | | - PAUL A. FRIEDMAN
- Division of Cardiovascular Diseases; Mayo Clinic; Rochester Minnesota
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Wilson D, Moehlis J. Toward a More Efficient Implementation of Antifibrillation Pacing. PLoS One 2016; 11:e0158239. [PMID: 27391010 PMCID: PMC4938213 DOI: 10.1371/journal.pone.0158239] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/23/2016] [Accepted: 06/12/2016] [Indexed: 11/18/2022] Open
Abstract
We devise a methodology to determine an optimal pattern of inputs to synchronize firing patterns of cardiac cells which only requires the ability to measure action potential durations in individual cells. In numerical bidomain simulations, the resulting synchronizing inputs are shown to terminate spiral waves with a higher probability than comparable inputs that do not synchronize the cells as strongly. These results suggest that designing stimuli which promote synchronization in cardiac tissue could improve the success rate of defibrillation, and point towards novel strategies for optimizing antifibrillation pacing.
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Affiliation(s)
- Dan Wilson
- Department of Mechanical Engineering, University of California Santa Barbara, Santa Barbara, CA 93106, United States of America
- * E-mail:
| | - Jeff Moehlis
- Department of Mechanical Engineering, University of California Santa Barbara, Santa Barbara, CA 93106, United States of America
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Okamura H, Friedman PA, Inoue Y, Noda T, Aiba T, Yasuda S, Ogawa H, Kamakura S, Kusano K, Espinosa RE. Single-Coil Defibrillator Leads Yield Satisfactory Defibrillation Safety Margin in Hypertrophic Cardiomyopathy. Circ J 2016; 80:2199-203. [DOI: 10.1253/circj.cj-16-0428] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Affiliation(s)
- Hideo Okamura
- Department of Cardiovascular Medicine, National Cerebral and Cardiovascular Center
- Division of Cardiovascular Diseases, Mayo Clinic
| | | | - Yuko Inoue
- Department of Cardiovascular Medicine, National Cerebral and Cardiovascular Center
| | - Takashi Noda
- Department of Cardiovascular Medicine, National Cerebral and Cardiovascular Center
| | - Takeshi Aiba
- Department of Cardiovascular Medicine, National Cerebral and Cardiovascular Center
| | - Satoshi Yasuda
- Department of Cardiovascular Medicine, National Cerebral and Cardiovascular Center
| | - Hisao Ogawa
- Department of Cardiovascular Medicine, National Cerebral and Cardiovascular Center
| | - Shiro Kamakura
- Department of Cardiovascular Medicine, National Cerebral and Cardiovascular Center
| | - Kengo Kusano
- Department of Cardiovascular Medicine, National Cerebral and Cardiovascular Center
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Uyguanco ER, Berger A, Budzikowski AS, Gunsburg M, Kassotis J. Management of high defibrillation threshold. Expert Rev Cardiovasc Ther 2014; 6:1237-48. [DOI: 10.1586/14779072.6.9.1237] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
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Pariaut R, Saelinger C, Vila J, Deforge W, Queiroz-Williams P, Beaufrère H, Zimmerman M, Saile K, Reynolds CA. Evaluation of shock waveform configuration on the defibrillation capacity of implantable cardioverter defibrillators in dogs. J Vet Cardiol 2012; 14:389-98. [PMID: 22819488 DOI: 10.1016/j.jvc.2012.05.002] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/07/2012] [Revised: 05/16/2012] [Accepted: 05/18/2012] [Indexed: 11/25/2022]
Abstract
BACKGROUND Implantable cardioverter defibrillators (ICD) are programmed to detect ventricular arrhythmias and terminate them by delivering an electrical shock. A defibrillation threshold (DFT) at least 10 J below the maximum device output is recommended for successful therapy. Shock waveform configuration is a programmable parameter used to achieve a low DFT. It is hypothesized that a fixed-pulse configuration results in lower defibrillation energy requirements than a fixed-tilt configuration. ANIMALS 10 mongrel dogs. MATERIALS AND METHODS ICD generator and transvenous lead were surgically implanted. Defibrillation threshold was determined using a protocol guided by the upper limit of vulnerability. Fixed-pulse and fixed-tilt (50%/50%) waveform configurations were tested in a random order. Plasma cardiac troponin I (cTnI) was measured for signs of myocardial injury. RESULTS The experiment was completed in 9 dogs. Overall mean DFT value was 424 ± 88 V (9.2 ± 3.9 J). Mean differences among voltage, energy and impedance at the DFT for fixed-pulse (422 ± 97 V, 9.1 ± 4.2 J, 62.6 ± 13.8 Ω) and fixed-tilt (426 ± 83 V, 9.3 ± 3.8 J, 62.8 ± 18.5 Ω) configurations were not statistically significant (All P > 0.21). Cardiac TnI concentration changed from 0.03 ng/mL (95% CI: 0.02-0.04) at baseline to 0.11 ng/mL (95 CI: 0.08-0.16) after DFT was obtained with the first waveform configuration and 0.19 ng/mL (95% CI: 0.13-0.28) at the end of the study period. There were no significant changes in heart rate, end-tidal CO2 and blood pressure over time (all P > 0.09). CONCLUSION The tested ICD device and lead placement reliably produced acceptable DFT values, based on a 10-J safety margin below the maximum device output. A benefit of fixed-pulse configuration could not be demonstrated over the standard fixed-tilt waveform. Signs of acute myocardial damage from repeated high-voltage shocks and episodes of ventricular fibrillation seemed of limited clinical significance.
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Affiliation(s)
- Romain Pariaut
- Department of Veterinary Clinical Sciences, School of Veterinary Medicine, Louisiana State University, Baton Rouge, LA, USA.
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Neuzner J, Carlsson J. Dual- versus single-coil implantable defibrillator leads: review of the literature. Clin Res Cardiol 2012; 101:239-45. [DOI: 10.1007/s00392-011-0407-z] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/18/2011] [Accepted: 12/23/2011] [Indexed: 11/25/2022]
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Sanders WE, Malkin RA, Richey MW, Masson SC, Ransbury TJ, Urtz MW, Ideker RE. Implantable intravascular defibrillator: evaluation of defibrillation waveforms with inferior vena cava electrode system. Pacing Clin Electrophysiol 2011; 34:577-83. [PMID: 21208244 DOI: 10.1111/j.1540-8159.2010.03006.x] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
BACKGROUND A percutaneously placed, totally intravascular defibrillator has been developed that shocks via a right ventricular (RV) single-coil and titanium electrodes in the superior vena cava (SVC) and the inferior vena cava (IVC). This study evaluated the defibrillation threshold (DFT) with this electrode configuration to determine the effect of different biphasic waveform tilts and second-phase durations as well as the contribution of the IVC electrode. METHODS Eight Bluetick hounds (wt = 30-40 kg) were anesthetized and the RV coil (first-phase anode) was placed in the RV apex. The intravascular defibrillator (PICD®, Model no. IIDM-G, InnerPulse Inc., Research Triangle Park, NC, USA) was positioned such that the titanium electrodes were in the SVC and IVC . Ventricular fibrillation was electrically induced and a Bayesian up-down technique was employed to determine DFT with two configurations: RV to SVC + IVC and RV to SVC. Three waveform tilts (65%, 50%, and 42%) and two second-phase durations (equal to the first phase [balanced] and truncated at 3 ms [unbalanced]) were randomly tested. The source capacitance of the defibrillator was 120 μF for all waveforms. RESULTS DFT with the IVC electrode was significantly lower than without the IVC electrode for all waveforms tested (527 ± 9.3 V [standard error], 14.5 J vs 591 ± 7.4 V, 18.5 J, P < 0.001). Neither waveform tilt nor second-phase duration significantly changed the DFT. CONCLUSION In canines, a totally intravascular implantable defibrillator with electrodes in the RV apex, SVC, and IVC had a DFT similar to that of standard nonthoracotomy lead systems. No significant effect was noted with changes in tilt or with balanced or unbalanced waveforms.
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Kroll MW, Schwab JO. Achieving low defibrillation thresholds at implant: pharmacological influences, RV coil polarity and position, SVC coil usage and positioning, pulse width settings, and the azygous vein. Fundam Clin Pharmacol 2010; 24:561-73. [DOI: 10.1111/j.1472-8206.2010.00848.x] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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Barr RC, Nolte LW, Pollard AE. Bayesian quantitative electrophysiology and its multiple applications in bioengineering. IEEE Rev Biomed Eng 2010; 3:155-68. [PMID: 22275206 PMCID: PMC3935245 DOI: 10.1109/rbme.2010.2089375] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Bayesian interpretation of observations began in the early 1700s, and scientific electrophysiology began in the late 1700s. For two centuries these two fields developed mostly separately. In part that was because quantitative Bayesian interpretation, in principle a powerful method of relating measurements to their underlying sources, often required too many steps to be feasible with hand calculation in real applications. As computer power became widespread in the later 1900s, Bayesian models and interpretation moved rapidly but unevenly from the domain of mathematical statistics into applications. Use of Bayesian models now is growing rapidly in electrophysiology. Bayesian models are well suited to the electrophysiological environment, allowing a direct and natural way to express what is known (and unknown) and to evaluate which one of many alternatives is most likely the source of the observations, and the closely related receiver operating characteristic (ROC) curve is a powerful tool in making decisions. Yet, in general, many people would ask what such models are for, in electrophysiology, and what particular advantages such models provide. So to examine this question in particular, this review identifies a number of electrophysiological papers in bioengineering arising from questions in several organ systems to see where Bayesian electrophysiological models or ROC curves were important to the results that were achieved.
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Affiliation(s)
- Roger C. Barr
- Departments of Biomedical Engineering and Pediatrics, Duke University, Durham, NC 27708 USA
| | - Loren W. Nolte
- Department of Electrical and Computer Engineering, Pratt School of Engineering, Duke University, Durham, NC 27708 USA
| | - Andrew E. Pollard
- Departments of Biomedical Engineering and Pediatrics, Duke University, Durham, NC 27708 USA
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Irnich W. From defibrillation theory to clinical implications. PACING AND CLINICAL ELECTROPHYSIOLOGY: PACE 2009; 33:814-25. [PMID: 20025700 DOI: 10.1111/j.1540-8159.2009.02660.x] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
BACKGROUND Our defibrillation theory claims that the mean voltage threshold is a hyperbolic function of pulse duration and that voltages below rheobase should be avoided as being counterproductive. Truncation of the pulse just at rheobase level yields minimal stored energy thresholds. To verify or falsify this theory, animal experiments were carried out. MATERIAL AND METHODS In two animal experiments, 212 defibrillation thresholds in 22 swine were determined with different biphasic pulses of which 92 were optimally truncated in phase 1. Step-up test procedure was used with the first successful shock defined as "threshold." RESULTS Experimental proof is gained that truncation according to "rheobase condition" shows lowest stored energy. A ranking order of stored energy thresholds demonstrates that (1) lower output capacitances reduce needed energy, and (2) pulse durations shorter or longer than optimal increase needed energy. The voltage-pulse-content threshold is linearly correlated with pulse duration. CONCLUSIONS Truncation above or below rheobase increases the stored energy threshold. Voltage averaged during pulse duration is a hyperbolic function of pulse duration. The stored energy is reduced with decreasing output capacitance. The experimental results do not only fully verify our theory, they also suggest clinical implications: (1) the current usage of the "constant tilt concept" in implantable cardioverter defibrillator (ICD) should be abandoned in favor of "optimal truncation concept," (2) an algorithm developed for calculating optimal truncation proved to be useful so that incorporation into ICD for automatic adjustment is recommended, and (3) the output capacitance should be reduced from about 100 microF to 60 to 70 microF.
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Affiliation(s)
- Werner Irnich
- Justus-Liebig-University, Faculty of Medicine, Giessen, Germany.
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Li Y, Wang H, Cho JH, Didon JP, Bisera J, Weil MH, Tang W. Comparison of efficacy of pulsed biphasic waveform and rectilinear biphasic waveform in a short ventricular fibrillation pig model. Resuscitation 2009; 80:1047-51. [DOI: 10.1016/j.resuscitation.2009.05.013] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/10/2008] [Revised: 05/12/2009] [Accepted: 05/15/2009] [Indexed: 11/15/2022]
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Daubert JP, Sheu SS. Mystery of biphasic defibrillation waveform efficacy is it calcium? J Am Coll Cardiol 2008; 52:836-8. [PMID: 18755346 DOI: 10.1016/j.jacc.2008.05.041] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/19/2008] [Accepted: 05/20/2008] [Indexed: 11/28/2022]
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VARMA NIRAJ, EFIMOV IGOR. Right Pectoral Implantable Cardioverter Defibrillators: Role of the Proximal (SVC) Coil. PACING AND CLINICAL ELECTROPHYSIOLOGY: PACE 2008; 31:1025-35. [DOI: 10.1111/j.1540-8159.2008.01130.x] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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Dosdall DJ, Sweeney JD. Extended charge banking model of dual path shocks for implantable cardioverter defibrillators. Biomed Eng Online 2008; 7:22. [PMID: 18673561 PMCID: PMC2527568 DOI: 10.1186/1475-925x-7-22] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/15/2008] [Accepted: 08/01/2008] [Indexed: 11/15/2022] Open
Abstract
Background Single path defibrillation shock methods have been improved through the use of the Charge Banking Model of defibrillation, which predicts the response of the heart to shocks as a simple resistor-capacitor (RC) circuit. While dual path defibrillation configurations have significantly reduced defibrillation thresholds, improvements to dual path defibrillation techniques have been limited to experimental observations without a practical model to aid in improving dual path defibrillation techniques. Methods The Charge Banking Model has been extended into a new Extended Charge Banking Model of defibrillation that represents small sections of the heart as separate RC circuits, uses a weighting factor based on published defibrillation shock field gradient measures, and implements a critical mass criteria to predict the relative efficacy of single and dual path defibrillation shocks. Results The new model reproduced the results from several published experimental protocols that demonstrated the relative efficacy of dual path defibrillation shocks. The model predicts that time between phases or pulses of dual path defibrillation shock configurations should be minimized to maximize shock efficacy. Discussion Through this approach the Extended Charge Banking Model predictions may be used to improve dual path and multi-pulse defibrillation techniques, which have been shown experimentally to lower defibrillation thresholds substantially. The new model may be a useful tool to help in further improving dual path and multiple pulse defibrillation techniques by predicting optimal pulse durations and shock timing parameters.
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Affiliation(s)
- Derek J Dosdall
- Department of Biomedical Engineering at the University of Alabama at Birmingham, Birmingham, Alabama, USA.
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Wang J, Tang W, Brewer JE, Freeman G, Chang YT, Weil MH. Comparison of rectilinear biphasic waveform with biphasic truncated exponential waveform in a pediatric defibrillation model. Crit Care Med 2007; 35:1961-5. [PMID: 17581484 DOI: 10.1097/01.ccm.0000277505.00407.5d] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
OBJECTIVE To compare the rectilinear biphasic waveform with a biphasic truncated exponential waveform for pediatric defibrillation. DESIGN Prospective, randomized study. SETTING Experimental laboratory of a university-affiliated research institute. SUBJECTS Male domestic piglets (4-24 kg). INTERVENTIONS Eleven piglets (4-8 kg), which represented a patient <1 yr old, and ten piglets (16-24 kg), which represented a pediatric patient between the ages of 2 and 8 yrs, were anesthetized, intubated, and mechanically ventilated. Ventricular fibrillation was induced and maintained for 30 secs, and a predetermined shock was then delivered to defibrillate. Following defibrillation, the animal was permitted to stabilize hemodynamically for 4 mins. Fifty shocks were applied to each animal using a randomization schedule based on a predetermined permutation of 50. The 50 shocks were 25 shocks for each rectilinear biphasic and biphasic truncated exponential waveforms, comprising five shocks at five energy settings. Each group of five shocks was fixed at a predetermined energy value, depending on the body weight of the animal. Dose-response curves were constructed using logistic regression. Aortic pressure, electrocardiogram, left ventricular pressure, and left ventricular pressure value of 40 mm Hg were continually measured. MEASUREMENTS AND MAIN RESULTS Dose-response curves determined defibrillation thresholds at 50% (D50) and 90% (D90) probability of success. The rectilinear biphasic waveform defibrillated with <90% of the D50 and D90 energies required for a biphasic truncated exponential waveform. The rectilinear biphasic waveform also successfully defibrillated with significantly less energy per body weight and per heart weight compared with a biphasic truncated exponential waveform. CONCLUSIONS The rectilinear biphasic waveform has superior defibrillation performance compared with a biphasic truncated exponential waveform in a piglet defibrillation model for young children.
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Affiliation(s)
- Jinglan Wang
- Weil Institute of Critical Care Medicine, Rancho Mirage, CA, USA
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Kroll MW, Swerdlow CD. Optimizing defibrillation waveforms for ICDs. J Interv Card Electrophysiol 2007; 18:247-63. [PMID: 17541815 DOI: 10.1007/s10840-007-9095-z] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/02/2006] [Accepted: 02/25/2007] [Indexed: 11/29/2022]
Abstract
While no simple electrical descriptor provides a good measure of defibrillation efficacy, the waveform parameters that most directly influence defibrillation are voltage and duration. Voltage is a critical parameter for defibrillation because its spatial derivative defines the electrical field that interacts with the heart. Similarly, waveform duration is a critical parameter because the shock interacts with the heart for the duration of the waveform. Shock energy is the most often cited metric of shock strength and an ICD's capacity to defibrillate, but it is not a direct measure of shock effectiveness. Despite the physiological complexities of defibrillation, a simple approach in which the heart is modeled as passive resistor-capacitor (RC) network has proved useful for predicting efficient defibrillation waveforms. The model makes two assumptions: (1) The goal of both a monophasic shock and the first phase of a biphasic shock is to maximize the voltage change in the membrane at the end of the shock for a given stored energy. (2) The goal of the second phase of a biphasic shock is to discharge the membrane back to the zero potential, removing the charge deposited by the first phase. This model predicts that the optimal waveform rises in an exponential upward curve, but such an ascending waveform is difficult to generate efficiently. ICDs use electronically efficient capacitive-discharge waveforms, which require truncation for effective defibrillation. Even with optimal truncation, capacitive-discharge waveforms require more voltage and energy to achieve the same membrane voltage than do square waves and ascending waveforms. In ICDs, the value of the shock output capacitance is a key intermediary in establishing the relationship between stored energy-the key determinant of ICD size-and waveform voltage as a function of time, the key determinant of defibrillation efficacy. The RC model predicts that, for capacitive-discharge waveforms, stored energy is minimized when the ICD's system time constant taus equals the cell membrane time constant taum, where taus is the product of the output capacitance and the resistance of the defibrillation pathway. Since the goal of phase two is to reverse the membrane charging effect of phase one, there is no advantage to additional waveform phases. The voltages and capacitances used in commercial ICDs vary widely, resulting in substantial disparities in waveform parameters. The development of present biphasic waveforms in the 1990s resulted in marked improvements in defibrillation efficacy. It is unlikely that substantial improvement in defibrillation efficacy will be achieved without radical changes in waveform design.
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Affiliation(s)
- Mark W Kroll
- Department of Biomedical Engineering, University of Minnesota, Minneapolis, MN, USA.
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Boriani G, Edvardsson N, Biffi M, Silvestri P, Martignani C, Valzania C, Diemberger I, Moulder JC, Mouchawar G, Poci D, Branzi A, Kroll MW. Plateau waveform shape allows a much higher patient shock energy tolerance in AF patients. J Cardiovasc Electrophysiol 2007; 18:728-34. [PMID: 17504256 DOI: 10.1111/j.1540-8167.2007.00846.x] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
OBJECTIVES To evaluate the possible pain reduction of the plateau waveform in atrial fibrillation (AF) patients. BACKGROUND Previous studies have indicated that reduced amplitude waveforms would be less painful than a conventional (65/65% tilt) biphasic waveform. Computer modeling suggested that a moderately long (10-12 msec) plateau (flat topped) shock waveform would deliver equivalent effectiveness with the lowest possible peak amplitude. METHODS We enrolled 27 patients at two sites with persistent AF with a total of 220 shocks delivered during internal atrial cardioversion using an interleaved crossover design. Patient response was scored in three ways: (1) a verbally reported discomfort score, (2) visual analog scale (VAS), and (3) a blinded observer reporting a contraction score. RESULTS All scores were significantly reduced (P < 0.0001) by the plateau waveform with impressive statistics: Verbal discomfort (3.51 +/- 0.13 to 2.89 +/- 0.12), VAS (7.00 +/- 0.56 to 5.91 +/- 0.36), and contraction scores (1.94 +/- 0.12 to 1.62 +/- 0.12). The average pain threshold shift (TS) for the Verbal score was 2.34, while that for the VAS score was 2.30. (This means that the patient typically could tolerate 2.34 times as much energy with the plateau waveform for the same level of verbally reported discomfort.) The contraction TS was less at 1.57. Response scores were also corrected for the shock sequence number to control for the sensitization effect from multiple shocks. This increased the TS for the Verbal score to 3.58, but the shock number was not significant for the VAS. A pulmonary artery electrode return was associated with lower pain compared with a coronary sinus position. CONCLUSION A plateau shaped biphasic waveform resulted in significantly increased shock energy pain tolerances. Controlling for session sensitization, patients tolerated over three times as much energy for the same verbally reported discomfort score.
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Affiliation(s)
- Giuseppe Boriani
- Institute of Cardiology, University of Bologna, Az. Osp. S. Orsola-Malpighi, Bologna, Italy
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Keane D, Aweh N, Hynes B, Sheahan RG, Cripps T, Bashir Y, Zaidi A, Fahy G, Lowe M, Doherty P, Kroll MK. Achieving Sufficient Safety Margins with Fixed Duration Waveforms and the Use of Multiple Time Constants. PACING AND CLINICAL ELECTROPHYSIOLOGY: PACE 2007; 30:596-602. [PMID: 17461867 DOI: 10.1111/j.1540-8159.2007.00718.x] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
INTRODUCTION There are several options to achieve a sufficient safety margin in a patient with a high defibrillation threshold (DFT), with varying and typically modest success. Programming fixed (millisecond) durations of both phases of a biphasic waveform in an implantable cardioverter defibrillator (ICD) has demonstrated utility. METHODS We established an informal multisite registry of ICD implanting facilities. Each facility agreed to attempt the use of fixed duration waveforms whenever there was an inadequate safety margin with tilt-based waveforms. A 3.5-ms-based fixed duration shock was tried first. If that failed to achieve a 10-J safety margin then a 2-ms-based shock was used. We also tabulated an HEDFT (high estimate DFT) as precise DFTs were not determined. RESULTS Sixteen patients (15 M, 1 F) were entered into the registry (age 58.2 +/- 17.9 years) with ejection fractions of .30 +/-.11. Superior vena cava coils were used in 7 patients according to physician preference. The tilt-based HEDFTs were 35.4 +/- 3.2 J delivered and 35.8 +/- 3.3 J stored energy. The 3.5-ms based shocks were evaluated on 14 patients and the HEDFT fell to 23.4 +/- 6.3 J delivered (P < 0.0001) and 26.2 +/- 6.9 J stored energy (P < 0.0001). The 2-ms-based fixed duration shocks were then evaluated on 6 patients and the delivered energy HEDFT was 22.2 +/- 5.8 J (P = 0.001 vs. tilt-based shocks) while the stored energy HEDFT was 27.9 +/- 6.4 J (P = 0.01 vs. tilt-based shocks). Using the better of the two fixed duration waveforms, the mean safety margin was improved from -1.2 +/- 1.9 J to 9.5 +/- 5.9 J (P < 0.00001). Multivariate predictors of the safety margin improvement were the absence of the Superior Vena Cava (SVC) coil and absence of Ventricular fibrillation (VF) presentation. Four patients still required lead repositioning after the use of the fixed duration waveforms. No additional leads were implanted. CONCLUSION The use of a selection of directly programmed fixed duration biphasic shocks had a striking impact on the HEDFT for these difficult patients. Adequate safety margins were obtained for 12 of 16 patients with no lead manipulation or other approaches.
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Affiliation(s)
- David Keane
- Cardiac Arrhythmia Service, St. Vincent's University Hospital, Dublin, Ireland
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Sharma V, Qu F, Nikolski VP, DeGroot P, Efimov IR. Direct measurements of membrane time constant during defibrillation strength shocks. Heart Rhythm 2007; 4:478-86. [DOI: 10.1016/j.hrthm.2006.12.015] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/18/2006] [Accepted: 12/02/2006] [Indexed: 11/17/2022]
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Malkin RA, Guan D, Wikswo JP. Experimental evidence of improved transthoracic defibrillation with electroporation-enhancing pulses. IEEE Trans Biomed Eng 2006; 53:1901-10. [PMID: 17019853 DOI: 10.1109/tbme.2006.881787] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
UNLABELLED There is considerable work on defibrillation wave form optimization. This paper determines the impedance changes during defibrillation, then uses that information to derive the optimum defibrillation wave form. METHODS PART I Twelve guinea pigs and six swine were used to measure the current wave form for square voltage pulses of a strength which would defibrillate about 50% of the time. In guinea pigs, electrodes were placed thoracically, abdominally and subcutaneously using two electrode materials (zinc and steel) and two electrode pastes (Core-gel and metallic paste). RESULTS PART I The measured current wave form indicated an exponentially increasing conductance over the first 3 ms, consistent with enhanced electroporation or another mechanism of time-dependent conductance. We fit this current with a parallel conductance composed of a time-independent component (g0 = 1.22 +/- 0.28 mS) and a time-dependent component described by g delta (1-e(-t/tau)), where g delta = 0.95 +/- 0.20 mS and tau = 0.82 +/- 0.17 ms in guinea pigs using zinc and Cor-gel. Different electrode placements and materials had no significant effect on this fit. From our fit, we determined the stimulating wave form that would theoretically charge the myocardial membrane to a given threshold using the least energy from the defibrillator. The solution was a very short, high voltage pulse followed immediately by a truncated ascending exponential tail. METHODS PART II The optimized wave forms and similar nonoptimized wave forms were tested for efficacy in 25 additional guinea pigs and six additional swine using methods similar to Part I. RESULTS PART II Optimized wave forms were significantly more efficacious than similar nonoptimized wave forms. In swine, a wave form with the short pulse was 41% effective while the same wave form without the short pulse was 8.3% effective (p < 0.03) despite there being only a small difference in energy (111 J versus 116 CONCLUSIONS: We conclude that a short pulse preceding a defibrillation pulse significantly improves efficacy, perhaps by enhancing electroporation.
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Affiliation(s)
- Robert A Malkin
- Department of Biomedical Engineering, Hudson 136, P.O. Box 90281, Durham, NC 27708, USA.
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Krasteva VT, Kerkhof PLM. On the optimal defibrillation waveform--how to reconcile theory and experiment? IEEE Trans Biomed Eng 2006; 53:1725-6; author reply 1726-7. [PMID: 16916112 DOI: 10.1109/tbme.2006.878551] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
Medical intervention by electrical current as applied to humans or animals may have tremendous therapeutic impact if delivered while being carefully controlled. Otherwise, the situation can be harmful in terms of injury or even become lethal. These consequences demand close inspection of all relevant biological and technical factors. Regarding methods to counter fibrillation of the heart substantial progress has been made, but defining a gold standard for the waveshape and energy delivery remains a serious challenge. The anticipated answer is not simply a range somewhere between a maximum and a minimum, but most likely an "intelligently" selected case-specific optimum, delicately positioned between effective and unsafe. Combining insight from theory with pertinent experimental findings may offer a clearer view on an unresolved issue that often points to a cross-road of life and death.
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Malkin RA, Jackson SR, Nguyen J, Yang Z, Guan D. Experimental verification of theoretical predictions concerning the optimum defibrillation waveform. IEEE Trans Biomed Eng 2006; 53:1492-8. [PMID: 16916083 DOI: 10.1109/tbme.2006.876643] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
The efficacy of electrical therapy at terminating ventricular fibrillation is highly dependent on the waveform used. We present experimental results which test one theory for defibrillation waveform dependence. Forty-four defibrillation waveforms (22 monophasic, 22 biphasic) were designed according to the theoretical construct of Fishier (2000). The waveforms were then tested on 67 male guinea pigs (46 for monophasic, 21 for biphasic waveforms) using a custom designed defibrillator and 12-mm subcutaneous disc electrodes. There was considerable agreement between the theoretical and experimental results. For example, as predicted, the ascending exponential waveform of 1 ms proved to be the most effective (86.4%) monophasic waveform, where efficacy is the number of successful shocks divided by the total number delivered. In addition, the efficacy decrease with duration increase was accurately predicted by the model for monophasic waveforms. For biphasic waveforms, as predicted by the model, when the first phase was optimized, an increase in second phase duration caused an increase in defibrillation efficacy (10 of 11 tested duration pairs). We conclude that the theoretical framework adequately explains the mechanism by which the defibrillation waveform affects efficacy for monophasic waveforms and, in at least one aspect, biphasic waveforms.
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Affiliation(s)
- Robert A Malkin
- Biomedical Engineering, Duke University, Durham, NC 27708, USA.
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Kroll MW, Efimov IR, Tchou PJ. Present Understanding of Shock Polarity for Internal Defibrillation: The Obvious and Non-Obvious Clinical Implications. PACING AND CLINICAL ELECTROPHYSIOLOGY: PACE 2006; 29:885-91. [PMID: 16923006 DOI: 10.1111/j.1540-8159.2006.00456.x] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/23/2023]
Abstract
BACKGROUND Uncertainty about the best electrode configuration has combined with the programming flexibility in modern implantable cardioverter-defibrillators (ICDs) to result in routine polarity reversal during an implant to deal with a high defibrillation threshold (DFT). We feel that this practice is not always supported by the clinical data and the present scientific understanding of defibrillation. METHOD A meta-analysis of the clinical studies on ICD shock polarity was performed. Subgroup analyses were also performed to test the impact of high DFTs, various tilts, and the use of the hot can electrode. A review of the basic research surrounding the effects of polarity in defibrillation is also presented. RESULTS A total of 224 patients were studied. The use of an anodal right ventricular (RV) coil lowers the mean DFT by 14.8% (P = 0.00001). It provides thresholds equal to or lower than cathodal defibrillation in 83% of patients. The fraction of patients with lower anodal DFTs was 94/224 versus 38/224 for cathodal polarity. This phenomenon may be explained by virtual electrode effects. In particular, anodal electrodes tend to produce collapsing wavefronts while cathodal electrodes tend to produce expanding proarrhythmic wavefronts. CONCLUSION In an ICD implant, the RV coil should be the anode. Furthermore, DFT testing beginning with cathodal defibrillation is most likely unnecessary and needlessly extends the procedure's duration and increases the risks for the patient.
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Affiliation(s)
- Mark W Kroll
- California Polytechnic University, St. Louis, Missouri 55323, USA.
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Denman RA, Umesan C, Martin PT, Forbes RN, Kroll MW, Anskey EJ, Burnett HE. Benefit of millisecond waveform durations for patients with high defibrillation thresholds. Heart Rhythm 2006; 3:536-41. [PMID: 16648057 DOI: 10.1016/j.hrthm.2006.01.027] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/17/2005] [Accepted: 01/24/2006] [Indexed: 11/19/2022]
Abstract
BACKGROUND Patients with a high defibrillation threshold (DFT) present an atypical but vexing problem with regard to implantable cardioverter-defibrillator (ICD) therapy. Their implant procedures are lengthy and involve more risk of complications. These patients often sustain a reduced safety margin that may compromise their survival. OBJECTIVES The purpose of this study was to evaluate the use of fixed millisecond duration model-optimized biphasic waveforms compared with conventional tilt-based waveforms in patients having a high DFT. METHODS We compared a 65%/65% tilt biphasic waveform to a millisecond duration biphasic waveform based on the biphasic burping theory using a 90-microF shock capacitor. RESULTS Fifty-four patients were evaluated. Mean DFT with tilt was reduced from 11.0 +/- 5.5 J to 8.8 +/- 4.1 J, for a mean reduction of 20% (P < .0001). For the 13 patients with tilt-based DFTs > or = 15 J, DFT was reduced from 18.7 +/- 4.1 J to 13.4 +/- 3.5 J, for a mean DFT reduction of 28% (P = .009). The population peak DFT was reduced from 29.0 J to 17.5 J, for a 41% reduction (P = .03). CONCLUSION Use of simple millisecond biphasic waveforms instead of conventional tilt-based waveforms can lead to substantial reductions in DFT, especially in patients with high DFT.
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Affiliation(s)
- Russell A Denman
- Department of Cardiology, The Prince Charles Hospital, Brisbane, Australia
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Pak HN, Liu YB, Hayashi H, Okuyama Y, Chen PS, Lin SF. Synchronization of ventricular fibrillation with real-time feedback pacing: implication to low-energy defibrillation. Am J Physiol Heart Circ Physiol 2003; 285:H2704-11. [PMID: 12893637 DOI: 10.1152/ajpheart.00366.2003] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Wavefront synchronization is an important aspect preceding the termination of ventricular fibrillation (VF). We evaluated the defibrillation efficacy of a novel multisite pacing algorithm using optical recording-guided synchronized pacing (SyncP) in the excitable gaps. We compared the effects of SyncP with traditional overdrive pacing (ODP) at 90% of the VF cycle length (VFCL) and high-frequency pacing (HFP; 43-215 Hz) on spontaneous VF termination in isolated rabbit hearts. For SyncP, the pacing current was triggered by the activation of a reference site and was delivered when the optical potential of the pacing site was in an excitable gap. We measured VFCL and the spatial dispersion of VFCL (SDCL) from five points (3 points in the paced area and 2 points in the nonpaced area) and the distribution of phase singularities during the prepacing, pacing, and postpacing periods. The results showed that 1) the VF termination rate of SyncP (16.0%, n = 106) was higher than that of ODP (2.1%, n = 48, P < 0.01) or HFP (1.6%, n = 129, P < 0.0001); 2) energy consumption for SyncP (7.6 +/- 9.3 mJ) was significantly lower than that of ODP (14.0 +/- 14.8 mJ, P < 0.0001); and 3) SyncP, but not ODP or HFP, decreased SDCL in the paced area during the pacing (P < 0.01) and postpacing (P < 0.05) periods compared with the prepacing period. We conclude that SyncP is effective in inducing wavefront synchronization and is more effective at facilitating spontaneous VF termination than non-SyncP.
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Affiliation(s)
- Hui-Nam Pak
- Department of Medicine, Cedars-Sinai Medical Center and David Geffen School of Medicine, University of California, Los Angeles, 90048, USA
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Schönegg M, Schöchlin J, Bolz A. Patient-dependent current dosing for semi-automatic external defibrillators (AED). BIOMED ENG-BIOMED TE 2003; 47 Suppl 1 Pt 1:302-5. [PMID: 12451846 DOI: 10.1515/bmte.2002.47.s1a.302] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
Abstract
The improvements in semiconductors and modern circuitry allow new waveforms to be created for treating life-threatening heart fibrillation. A comparison of common waveforms shows that there is no definite optimal waveform. Especially in the case of early defibrillation by novices, the question of dosage should be re-discussed. While a physician may be able to dose the intensity of the therapeutic electric shock, one can't expect that from someone having no medical training. Common AEDs have predefined energy levels, that are delivered to a patient regardless of the patient's size and weight, etc. Current-based defibrillation provides a therapy matched to patient parameters, keeping the myocard stress as low as possible so that the heart has better chances of resuming a normal rhythm.
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Affiliation(s)
- M Schönegg
- FZI Forschungszentrum Informatik Karlsruhe, Germany.
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Roberts SJ, Guan D, Malkin R. The defibrillation efficacy of high frequency alternating current sinusoidal waveforms in guinea pigs. Pacing Clin Electrophysiol 2003; 26:599-604. [PMID: 12710320 DOI: 10.1046/j.1460-9592.2003.00100.x] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
There have been few basic studies of alternating current (AC) defibrillation, despite growing interest in the ability of AC to terminate or alter ongoing fibrillation. Based on fibrillation threshold testing, it has been suggested that cardiac tissue is most sensitive to long duration, low strength AC stimulation at around 50 Hz. This has not been directly tested for defibrillation. Two subcutaneous electrodes were placed 40 mm apart on opposing aspects of the guinea pig thorax. Seven seconds were allowed to elapse between fibrillation initiation and defibrillation. The tested waveforms were at 50, 100, 200, 500, and 1000 Hz with 2, 4, 8, 16, and 32-cycles. The efficacy of every waveform was measured using a single stimulus in a large population of animals. Forty-one guinea pigs were used in the fixed energy group. Thirty-three guinea pigs were used in the fixed amplitude group with additional 1-cycle waveforms tested. The 200-Hz and the 2-cycle waveforms were significantly more efficacious than those at other frequencies (P < 0.02) and other durations (P < 0.001). The 50-Hz waveforms were the least successful. Amplitude, not duration or energy, was the determinate of efficacy for 2-cycle (the most efficacious) waveforms. Unlike low strength stimulation, defibrillation strength stimuli are most effective with high frequency (200 Hz) pulses (2 cycles).
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Affiliation(s)
- Scott J Roberts
- Department of Biomedical Engineering, University of Memphis, Memphis, Tennessee, USA
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Meunier JM, Trayanova NA, Gray RA. Entrainment by an extracellular AC stimulus in a computational model of cardiac tissue. J Cardiovasc Electrophysiol 2001; 12:1176-84. [PMID: 11699528 PMCID: PMC2837923 DOI: 10.1046/j.1540-8167.2001.01176.x] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
INTRODUCTION Cardiac tissue can be entrained when subjected to sinusoidal stimuli, often responding with action potentials sustained for the duration of the stimulus. To investigate mechanisms responsible for both entrainment and extended action potential duration, computer simulations of a two-dimensional grid of cardiac cells subjected to sinusoidal extracellular stimulation were performed. METHODS AND RESULTS The tissue is represented as a bidomain with unequal anisotropy ratios. Cardiac membrane dynamics are governed by a modified Beeler-Reuter model. The stimulus, delivered by a bipolar electrode, has a duration of 750 to 1,000 msec, an amplitude range of 800 to 3,200 microA/cm, and a frequency range of 10 to 60 Hz. The applied stimuli create virtual electrode polarization (VEP) throughout the sheet. The simulations demonstrate that periodic extracellular stimulation results in entrainment of the tissue. This phase-locking of the membrane potential to the stimulus is dependent on the location in the sheet and the magnitude of the stimulus. Near the electrodes, the oscillations are 1:1 or 1:2 phase-locked; at the middle of the sheet, the oscillations are 1:2 or 1:4 phase-locked and occur on the extended plateau of an action potential. The 1:2 behavior near the electrodes is due to periodic change in the voltage gradient between VEP of opposite polarity; at the middle of the sheet, it is due to spread of electrotonic current following the collision of a propagating wave with refractory tissue. CONCLUSION The simulations suggest that formation of VEP in cardiac tissue subjected to periodic extracellular stimulation is of paramount importance to tissue entrainment and formation of an extended oscillatory action potential plateau.
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Affiliation(s)
- J M Meunier
- Department of Biomedical Engineering Tulane University, New Orleans, Louisiana 70118-5674, USA.
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Bain AC, Swerdlow CD, Love CJ, Ellenbogen KA, Deering TF, Brewer JE, Augostini RS, Tchou PJ. Multicenter study of principles-based waveforms for external defibrillation. Ann Emerg Med 2001; 37:5-12. [PMID: 11145764 DOI: 10.1067/mem.2001.111690] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
STUDY OBJECTIVE The efficacy of a shock waveform for external defibrillation depends on the waveform characteristics. Recently, design principles based on cardiac electrophysiology have been developed to determine optimal waveform characteristics. The objective of this clinical trial was to evaluate the efficacy of principles-based monophasic and biphasic waveforms for external defibrillation. METHODS A prospective, randomized, blinded, multicenter study of 118 patients undergoing electrophysiologic testing or receiving an implantable defibrillator was conducted. Ventricular fibrillation was induced, and defibrillation was attempted in each patient with a biphasic and a monophasic waveform. Patients were randomly placed into 2 groups: group 1 received shocks of escalating energy, and group 2 received only high-energy shocks. RESULTS The biphasic waveform achieved a first-shock success rate of 100% in group 1 (95% confidence interval [CI] 95.1% to 100%) and group 2 (95% CI 94.6% to 100%), with average delivered energies of 201+/-17 J and 295+/-28 J, respectively. The monophasic waveform demonstrated a 96.7% (95% CI 89.1% to 100%) first-shock success rate and average delivered energy of 215+/-12 J for group 1 and a 98.2% (95% CI 91.7% to 100%) first-shock success rate and average delivered energy of 352+/-13 J for group 2. CONCLUSION Using principles of electrophysiology, it is possible to design both biphasic and monophasic waveforms for external defibrillation that achieve a high first-shock efficacy.
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Affiliation(s)
- A C Bain
- Survivalink Corporation, Minneapolis, MN, USA.
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Krasteva V, Iliev I, Cansell A, Daskalov I. Automatic adjustment of biphasic pulse duration in transthoracic defibrillation. J Med Eng Technol 2000; 24:210-4. [PMID: 11204244 DOI: 10.1080/03091900050204250] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023]
Abstract
Many studies have proven that biphasic defibrillation pulses are more efficient than the damped sinusoid monopolar waveform. Transthoracic resistance was shown to change during the two phases. On the other hand, it was proven that transthoracic resistance plays an important role in the defibrillation process, yielding the current for selected energy or voltage. Pre-shock measurement of the resistance may lead to improved selection. Stabilized current defibrillators are of low stored-to-delivered energy ratio. Therefore, automatic dynamic adjustment of some defibrillator parameters with respect to transthoracic resistance changes seems rational. An approach is known for modifying the pulse duration, in order to deliver a selected energy. A method is proposed here and an experimental defibrillator is developed for dynamic pulse duration adjustment with the purpose of obtaining a desired optimal time-course of the cardiac cell transmembrane potential.
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Affiliation(s)
- V Krasteva
- Centre of Biomedical Engineering, Bulgarian Academy of Sciences, Acad. G. Bonchev str. block 105, Bulgaria
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Yamanouchi Y, Fishler MG, Mowrey KA, Wilkoff BL, Mazgalev TN, Tchou PJ. New approach to biphasic waveforms for internal defibrillation: fully discharging capacitors. J Cardiovasc Electrophysiol 2000; 11:907-12. [PMID: 10969754 DOI: 10.1111/j.1540-8167.2000.tb00071.x] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
INTRODUCTION The use of two independent, fully discharging capacitors for each phase of a biphasic defibrillation waveform may lead to the design of a simpler, smaller, internal defibrillator. The goal of this study was to determine the optimal combination of capacitor sizes for such a waveform. METHODS AND RESULTS Eight full-discharge (95/95% tilt), biphasic waveforms produced by several combinations of phase-1 capacitors (30, 60, and 90 microF) and phase-2 capacitors (1/3, 2/3, and 1.0 times the phase-1 capacitor) were tested and compared to a single-capacitor waveform (120 microF, 65/65% tilt) in a pig ventricular fibrillation model (n = 12, 23+/-2 kg). In the full-discharge waveforms, phase-2 peak voltage was equal to phase-1 peak voltage. Shocks were delivered between a right ventricular lead and a left pectoral can electrode. E50s and V50s were determined using a ten-step Bayesian process. Full-discharge waveforms with phase-2 capacitors of < or =40 microF had the same E50 (6.7+/-1.7 J to 7.3+/-3.9 J) as the single-capacitor truncated waveform (7.3+/-3.7 J), whereas waveforms with phase-2 capacitors of > or =60 microF had an extremely high E50 (14.5+/-10.8 J or greater, P < 0.05). Moreover, of the former set of energy-efficient waveforms, those with phase-1 capacitors of > or =60 microF additionally exhibited V50s that were equivalent to the V50 of the single-capacitor waveform (344+/-65 V to 407+/-50 V vs 339+/-83 V). CONCLUSION Defibrillation efficacy can be maintained in a full-discharge, two-capacitor waveform with the proper choice of capacitors.
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Abstract
Recent investigations connected with implantable defibrillators yielded new data on heart electrophysiology, resulting in reassessment of existing and advancing of new types of electrical impulses. Different electrical equivalent circuits were proposed for modelling intracardiac and transthoracic defibrillation pulse waveforms, comprising generator, electrode interface and tissue resistances. We attempted modelling of the transmembrane voltage Vm time course, induced by different applied voltage Vs waveforms, taking into account only the shapes and the relative Vs and Vm amplitudes. The excitable cell membrane impedance Zm was modelled with higher resistance and lower capacitance, so that a shunting effect on the generator and tissue resistances was avoided. The result was a very simple equivalent circuit. We proposed criteria for efficient defibrillation pulse waveforms yielding a straightforward approach to model existing and new pulses and to assess their efficiency.
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Affiliation(s)
- V Krasteva
- Centre of Biomedical Engineering, Bulgarian Academy of Sciences, Sofia, Bulgaria
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Mittal S, Ayati S, Stein KM, Knight BP, Morady F, Schwartzman D, Cavlovich D, Platia EV, Calkins H, Tchou PJ, Miller JM, Wharton JM, Sung RJ, Slotwiner DJ, Markowitz SM, Lerman BB. Comparison of a novel rectilinear biphasic waveform with a damped sine wave monophasic waveform for transthoracic ventricular defibrillation. ZOLL Investigators. J Am Coll Cardiol 1999; 34:1595-601. [PMID: 10551711 DOI: 10.1016/s0735-1097(99)00363-0] [Citation(s) in RCA: 85] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
OBJECTIVES We compared the efficacy of a novel rectilinear biphasic waveform, consisting of a constant current first phase, with a damped sine wave monophasic waveform during transthoracic defibrillation. BACKGROUND Multiple studies have shown that for endocardial defibrillation, biphasic waveforms have a greater efficacy than monophasic waveforms. More recently, a 130-J truncated exponential biphasic waveform was shown to have equivalent efficacy to a 200-J damped sine wave monophasic waveform for transthoracic ventricular defibrillation. However, the optimal type of biphasic waveform is unknown. METHODS In this prospective, randomized, multicenter trial, 184 patients who underwent ventricular defibrillation were randomized to receive a 200-J damped sine wave monophasic or 120-J rectilinear biphasic shock. RESULTS First-shock efficacy of the biphasic waveform was significantly greater than that of the monophasic waveform (99% vs. 93%, p = 0.05) and was achieved with nearly 60% less delivered current (14 +/- 1 vs. 33 +/- 7 A, p < 0.0001). Although the efficacy of the biphasic and monophasic waveforms was comparable in patients with an impedance < 70 ohms (100% [biphasic] vs. 95% [monophasic], p = NS), the biphasic waveform was significantly more effective in patients with an impedance > or = 70 ohms (99% [biphasic] vs. 86% [monophasic], p = 0.02). CONCLUSIONS This study demonstrates a superior efficacy of rectilinear biphasic shocks as compared with monophasic shocks for transthoracic ventricular defibrillation, particularly in patients with a high transthoracic impedance. More important, biphasic shocks defibrillated with nearly 60% less current. The combination of increased efficacy and decreased current requirements suggests that biphasic shocks as compared with monophasic shocks are advantageous for transthoracic ventricular defibrillation.
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Affiliation(s)
- S Mittal
- New York Hospital-Cornell Medical Center, New York, USA
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White JB, Walcott GP, Wayland JL, Smith WM, Ideker RE. Predicting the relative efficacy of shock waveforms for transthoracic defibrillation in dogs. Ann Emerg Med 1999; 34:309-20. [PMID: 10459086 DOI: 10.1016/s0196-0644(99)70124-1] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
STUDY OBJECTIVE Previous work has shown that a passive membrane model using a parallel resistor-capacitor circuit is capable of predicting optimal waveforms for transvenous defibrillation. This study tested the ability of that model to predict optimal waveforms for transthoracic defibrillation. METHODS This study was divided into 3 parts, each of which determined transthoracic defibrillation thresholds (DFTs) in 6 dogs for several different waveform shapes and durations. For each part, strength-duration relationships were determined from both experimental and model data and then compared with test model predictions. Part 1 DFTs were determined at various durations for 3 different monophasic waveforms-the ascending ramp, descending ramp, and square waveform. Part 2 DFTs were determined for 3 biphasic waveforms. Phase 1 was a 30-ms ascending ramp, and phase 2 was an ascending ramp, a descending ramp, or a square waveform. Part 3 DFTs were determined for 3 biphasic waveforms with very short second-phase durations. Phase 1 was a 30-ms ascending ramp, and phase 2 was a descending ramp. RESULTS For part 1, the model was able to predict the relative defibrillation efficacy of the 3 monophasic waveforms ( P < .05). For parts 2 and 3, the model was able to predict the biphasic waveforms with the lowest DFTs. These predictions were based on the criterion that the model response at the end of the second phase should return to or slightly pass the model response value at the beginning of the first phase. CONCLUSION The resistor-capacitor model successfully predicted the relative defibrillation efficacy of several different waveforms delivered transthoracically.
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Affiliation(s)
- J B White
- Department of Physiology, University of Alabama at Birmingham, 35292-0019, USA
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Leonelli FM, Wang KE, King C, Brewer J, Donohoo AM, Kroll MW. Energy steering of biphasic waveforms using a transvenous three electrode system. Pacing Clin Electrophysiol 1999; 22:849-54. [PMID: 10392381 DOI: 10.1111/j.1540-8159.1999.tb06807.x] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The optimal electrode configuration for endocardial defibrillation is still a matter of debate. Current data suggests that a two pathway configuration using the right ventricle (RV) as cathode and a common anode constituted by a superior vena cava (SVC) and a pectoral can (C) is the most effective combination. This may be related to the more uniform voltage gradient created by shocks delivered using this configuration. We hypothesized that more effective waveforms could be obtained by varying the distribution of the shock current between the two pathways of a three electrode endocardial defibrillation system. In 12 pigs, we compared the characteristics and the defibrillation efficacy of six biphasic waveforms discharged using either a two (RV-->C) or a three (RV-->SVC + C) electrode combination with the following configurations: Configuration 1 (W1): the RV apical coil was used as a cathode and the subcutaneous C as anode (RV-->C). Configuration 2 (W2): The RV was used as cathode and the combination of the atriocaval coil (SVC) and the subcutaneous C as anode (RV-->SVC + C). Configuration 3 (W3): The RV-->C was used for the first 25% of f+ and RV-->SVC + C for the remainder of the discharge including f 2 Configuration 4 (W4): The RV-->C was used for the first 50% of f+ and RV-->SVC + C for the remainder of the discharge including f 2 Configuration 5 (W5): The RV-->C was used for the first 75% of f+ and RV-->SVC + C for the remainder of the discharge including f 2. Configuration 6 (W6): The RV-->C was used for f+ and RV-->SVC + C for f 2. As an increasing fraction of the waveform was discharged using the RV-->SVC + C pathways, the impedance and the pulse width decreased while the tilt, the peak, and the average current significantly increased. The waveforms delivered using the RV-->SVC + C configuration for 100% or 75% of their duration had significantly lower stored energy DFT than the other waveform. Current distribution between three endocardial electrodes can be altered during the shock and generates waveforms with different characteristics. Shocks with 75% or more of the current flowing to the RV-->SVC + C required the lowest stored energy to defibrillate. This method of energy steering could be used to optimize current delivery in a three electrodes system.
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Affiliation(s)
- F M Leonelli
- Division of Cardiovascular Medicine, University of Kentucky, Lexington, USA
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Mehdirad AA, Love CJ, Stanton MS, Strickberger SA, Duncan JL, Kroll MW. Preliminary clinical results of a biphasic waveform and an RV lead system. Pacing Clin Electrophysiol 1999; 22:594-9. [PMID: 10234712 DOI: 10.1111/j.1540-8159.1999.tb00500.x] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
Biphasic defibrillation waveforms have provided a reduction in defibrillation thresholds in transvenous ICD systems. Although a variety of biphasic waveforms have been tested, the optimal pulse durations and tilts have yet to be identified. A multicenter clinical study was conducted to evaluate the performance of a new ICD biphasic waveform and new RV active fixation steroid eluting lead system. Fifty-three patients were entered into the study. Mean age was 63 years with a mean ejection fraction of 36.8%. Primary indication for implantation was monomorphic ventricular tachycardia alone (54.7%). Forty-eight patients (90.6%) were implanted with an RV shocking lead and active can alone as the anodal contact. The ICD can was the cathode. In four cases (7.5%), an additional SVC or CS lead was used due to a high DFT with the RV lead alone. In an additional case, a chronic SVC lead was used although the RV-Can DFT was acceptable. DFT for all cases at implant was 9.8 +/- 3.7 J. Repeat testing at 3 months for a subset of patients showed a reduction in DFT (7.4 +/- 3.0 J), P value = 0.03. Sensing and pacing characteristics of the RV lead system remained excellent during the study period (acute 0.047 +/- 0.005 ms at 5.4 V and 9.9 +/- 6.2 mV R wave; chronic 0.067 +/- 0.11 ms at 5.4 V and 9.3 +/- 5.4 mV R wave). It is concluded that this lead system provides good acute and chronic sensing and pacing characteristics with good DFT values in combination with this waveform.
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Affiliation(s)
- A A Mehdirad
- Division of Cardiology, Ohio State University, Columbus, USA
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Schuder JC, McDaniel WC. Relationship between efficacy of defibrillation shocks and frequency characteristics of shock waveforms. J Cardiovasc Electrophysiol 1998; 9:1043-54. [PMID: 9817556 DOI: 10.1111/j.1540-8167.1998.tb00882.x] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
INTRODUCTION Using the Fourier transform, it is possible to replace each time domain representation of a defibrillatory shock by a unique frequency domain representation in which the shock waveform is defined in terms of a complex number function of frequency and typically described as an amplitude in amperes per hertz (or, closely related, joules per hertz) and an associated frequency-dependent phase angle. METHODS AND RESULTS The present article describes the conceptual basis of the Fourier transform, sketches a simplified mathematical framework for deriving frequency domain parameters, considers properties crucial to interpreting defibrillatory-type shocks when expressed in the frequency domain, and then presents a series of shock waveforms in the frequency domain. Although not definitive, knowledge of the energy distribution with frequency alone, usually presented in joules per hertz, is shown to yield considerable insight into the probable comparable efficacy of uniphasic/biphasic rectangular, untruncated/truncated uniphasic exponential, and various biphasic "single capacitor" waveforms. CONCLUSION In general, efficacy in achieving ventricular defibrillation is improved by parameter changes that shift a larger percentage of the delivered energy into a mid-frequency range (very roughly, 40 to 160 Hz). With further study, the frequency domain approach may prove to be a useful tool in the a priori selection of optimal defibrillatory shock waveforms.
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Affiliation(s)
- J C Schuder
- Division of General Surgery, University of Missouri, Columbia 65212, USA
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Sims JJ, Miller AW, Ujhelyi MR. Disparate effects of biphasic and monophasic shocks on postshock refractory period dispersion. THE AMERICAN JOURNAL OF PHYSIOLOGY 1998; 274:H1943-9. [PMID: 9841521 DOI: 10.1152/ajpheart.1998.274.6.h1943] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The magnitude by which a defibrillation shock extends the refractory period immediately postshock (refractory period extension, RPE) does not explain why biphasic shocks defibrillate with greater efficacy than monophasic shocks. It may be that spatial heterogeneity of RPE is a more important regulator of defibrillation efficacy. We measured RPE in 15 pentobarbital-anesthetized swine using 400-V biphasic and monophasic shocks of equal pulse duration at three discrete myocardial sites. Spatial heterogeneity of RPE was calculated as the difference between the maximum and minimum values of the three recording sites. Monophasic shocks produced greater magnitude of RPE than biphasic shocks at all sites tested (82 +/- 6 to 99 +/- 13 and 64 +/- 6 to 68 +/- 5 ms, respectively; P < 0.05). However, RPE dispersion was significantly less with biphasic shocks versus monophasic shocks (29 +/- 4 and 48 +/- 7 ms, respectively; P < 0.05). This suggests that one potential mechanism by which biphasic shocks defibrillate with greater efficacy is limiting postshock spatial heterogeneity of refractoriness. Thus these data support our hypothesis that RPE heterogeneity is a more likely predictor of defibrillation efficacy than magnitude of RPE.
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Affiliation(s)
- J J Sims
- University of Georgia College of Pharmacy, Medical College of Georgia, and Augusta Veterans Affairs Medical Center, Augusta, Georgia 30912, USA
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Swerdlow CD, Kass RM, O'Connor ME, Chen PS. Effect of shock waveform on relationship between upper limit of vulnerability and defibrillation threshold. J Cardiovasc Electrophysiol 1998; 9:339-49. [PMID: 9581950 DOI: 10.1111/j.1540-8167.1998.tb00922.x] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
INTRODUCTION The upper limit of vulnerability (ULV) correlates with the defibrillation threshold (DFT). The ULV can be 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-microF capacitor. In the 60- to 110-microF group (n = 30), DFT and ULV were compared for a clinically used 110-microF waveform and a novel 60-microF 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-microF group, the current and voltage at the ULV and DFT were higher for the 60-microF waveform (P < 0.0001), but 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 r2 = 0.75, P < 0.001; biphasic r2 = 0.82, P < 0.001) and the 60- to 110-microF group (60 microF r2 = 0.81 P < 0.001; 110 microF r2 = 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-microF versus 110-microF 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-microF vs 110-microF 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-microF 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.
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Affiliation(s)
- C D Swerdlow
- Division of Cardiology, Cedars-Sinai Medical Center, Los Angeles, California, USA.
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Yamanouchi Y, Brewer JE, Mowrey KA, Kroll MW, Donohoo AM, Wilkoff BL, Tchou PJ. Sawtooth first phase biphasic defibrillation waveform: a comparison with standard waveform in clinical devices. J Cardiovasc Electrophysiol 1997; 8:517-28. [PMID: 9160228 DOI: 10.1111/j.1540-8167.1997.tb00820.x] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
INTRODUCTION A major limitation in a conventional truncated exponential waveform is the rapid drop in current that results in short duration of high current or longer duration with a lower average current. We hypothesized that increasing the first phase average current by boosting the decaying waveform prior to phase reversal may improve defibrillation efficacy. METHODS AND RESULTS To better simulate a "rectangular" waveform during the first phase, a "sawtooth" defibrillation waveform was constructed using "parallel-series" switching of capacitances (each 30 microF) during the first phase. This permitted a boost in the voltage late in the first phase. This sawtooth biphasic waveform (sawtooth) was compared to two clinical waveforms: a 135-microF capacitance (control-1) and a 90-microF capacitance (control-2) waveform. Defibrillation threshold (DFT) parameters were evaluated in 13 anesthetized pig models using a system consisting of a transvenous right ventricular apex lead (anode) and a left pectoral "hot can" electrode (cathode) system. DFT was determined by a "down-up down-up" protocol. The stored energy for sawtooth, control-1, and control-2 was 10.5 +/- 2.8 J, 12.3 +/- 3.7 J*, and 12.2 +/- 2.8 J*, respectively (*P < or = 0.01 vs sawtooth). The average current of the first phase for sawtooth, control-1, and control-2 was 7.6 +/- 1.3 A, 4.7 +/- 0.9 A*, and 6.2 +/- 0.9 A*, respectively (*P = 0.0001 vs sawtooth). CONCLUSION A sawtooth biphasic waveform utilizing a "parallel-series" switching system of smaller capacitors can improve defibrillation efficacy. A higher average current in the first phase generated by such a waveform may contribute to more efficient defibrillation by facilitating myocyte capture.
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Affiliation(s)
- Y Yamanouchi
- Department of Cardiology, Cleveland Clinic Foundation, Ohio 44195, USA
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