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Iijima K, Zhang H, Strachan MT, Huang J, Walcott GP, Rogers JM. Right ventricular insertion promotes reinitiation of ventricular fibrillation in defibrillation failure. Heart Rhythm 2021; 18:995-1003. [PMID: 33508518 PMCID: PMC8169561 DOI: 10.1016/j.hrthm.2021.01.022] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/30/2020] [Revised: 01/04/2021] [Accepted: 01/18/2021] [Indexed: 11/15/2022]
Abstract
BACKGROUND Shocks near defibrillation threshold (nDFT) strength commonly extinguish all ventricular fibrillation (VF) wavefronts, but a train of rapid, well-organized postshock activations (PAs) typically appears before sinus rhythm ensues. If one of the PA waves undergoes partial propagation block (wavebreak), reentry may be induced, causing VF to reinitiate and the shock to fail. OBJECTIVE The purpose of this study was to determine whether wavebreak leading to VF reinititation following nDFT shocks occurs preferentially at the right ventricular insertion (RVI), which previous studies have identified as a key site for wavebreak. METHODS We used panoramic optical mapping to image the ventricular epicardium of 6 isolated swine hearts during nDFT defibrillation episodes. After each experiment, the hearts were fixed and their geometry scanned with magnetic resonance imaging (MRI). The MRI and mapping datasets were spatially coregistered. For failed shocks, we identified the site of the first wavebreak of a PA wave during VF reinitiation. RESULTS We recorded 59 nDFT failures. In 31 of these, the first wavebreak event occurred within 1 cm of the RVI centerline, most commonly on the anterior side of the right ventricular insertion (aRVI) (23/31). The aRVI region occupies 16.8% ± 2.5% of the epicardial surface and would be expected to account for only 10 wavebreaks if they were uniformly distributed. By χ2 analysis, aRVI wavebreaks were significantly overrepresented. CONCLUSION The anterior RVI is a key site in promoting nDFT failure. Targeting this site to prevent wavebreak could convert defibrillation failure to success and improve defibrillation efficacy.
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Affiliation(s)
- Kenichi Iijima
- Department of Biomedical Engineering, University of Alabama at Birmingham, Birmingham, Alabama
| | - Hanyu Zhang
- Department of Biomedical Engineering, University of Alabama at Birmingham, Birmingham, Alabama
| | - Matthew T Strachan
- Department of Biomedical Engineering, University of Alabama at Birmingham, Birmingham, Alabama
| | - Jian Huang
- Department of Medicine, University of Alabama at Birmingham, Birmingham, Alabama
| | - Gregory P Walcott
- Department of Medicine, University of Alabama at Birmingham, Birmingham, Alabama
| | - Jack M Rogers
- Department of Biomedical Engineering, University of Alabama at Birmingham, Birmingham, Alabama.
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Xing C, Jin Q, Zhang N, Liu S, Lin C, Wu Q, Luo Q, Liu A, Wu L. Effect of flunarizine on defibrillation outcomes and early refibrillation in a canine model of prolonged ventricular fibrillation. Exp Physiol 2019; 104:1630-1637. [PMID: 31465138 PMCID: PMC6899960 DOI: 10.1113/ep087068] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/25/2018] [Accepted: 08/23/2019] [Indexed: 11/20/2022]
Abstract
New Findings What is the central question of this study? Can successful electrical shock in combination with a delayed after‐depolarization (DAD) blocker suppress early refibrillation episodes following long duration ventricular fibrillation (LDVF)? What is the main finding and its importance? Flunarizine significantly reduced the activation of LDVF and early ventricular fibrillation (VF) recurrence following LDVF, suggesting that DADs potentially contribute to refibrillation in prolonged VF. Thus, DAD inhibition can be used as an adjunctive therapy for electrical defibrillation to treat prolonged VF and suppress refibrillation following LDVF.
Abstract This study attempts to detect changes in the defibrillation threshold (DFT) at different stages of ventricular fibrillation (VF) (short duration VF, SDVF; long duration VF, LDVF) and during early refibrillation following successful defibrillation of LDVF by giving flunarizine, a blocker of delayed after‐depolarizations (DADs). Twelve beagles were divided into two groups (the control group, n = 6; and the flunarizine group, n = 6). Two 64‐electrode basket catheters were deployed into the left and the right ventricles for global endocardium mapping. The DFTs of SDVF and LDVF were determined at 20 s and 7 min, respectively, after VF induction in each group. Any refibrillation episodes were recorded within 15 min after the first successful defibrillation of LDVF. In the flunarizine group, the SDVF‐DFT values before and after the drug were not significantly different. The 7 min LDVF‐DFTs were markedly reduced by 26% (P < 0.05, the control group) and 38% (P < 0.01, the flunarizine group) compared to the 20 s SDVF‐DFTs within each group. The difference between SDVF‐DFT and LDVF‐DFT after flunarizine was larger than that in the control group (213 ± 65 vs. 120 ± 84 V, P < 0.05). The number of refibrillation episodes per animal (1.3 ± 1.0) following successful defibrillation of LDVF after flunarizine was 48% of that in controls (2.7 ± 2.0, P < 0.05). The effect of flunarizine on SDVF‐DFT and LDVF‐DFT indicates that the role of DADs in the defibrillation mechanism may differ as VF continues. Flunarizine significantly reduced early VF recurrence following LDVF, suggesting that DADs potentially contribute to refibrillation in a canine model of prolonged VF.
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Affiliation(s)
- Chaofan Xing
- Department of Cardiology, Shanghai Rui Jin Hospital, Shanghai Jiao Tong University School of Medicine, Shanghai, China
| | - Qi Jin
- Department of Cardiology, Shanghai Rui Jin Hospital, Shanghai Jiao Tong University School of Medicine, Shanghai, China
| | - Ning Zhang
- Department of Cardiology, Shanghai Rui Jin Hospital, Shanghai Jiao Tong University School of Medicine, Shanghai, China
| | - Shaohua Liu
- Department of Cardiology, Shanghai Rui Jin Hospital, Shanghai Jiao Tong University School of Medicine, Shanghai, China
| | - Changjian Lin
- Department of Cardiology, Shanghai Rui Jin Hospital, Shanghai Jiao Tong University School of Medicine, Shanghai, China
| | - Qiong Wu
- Department of Cardiology, Shanghai Rui Jin Hospital, Shanghai Jiao Tong University School of Medicine, Shanghai, China
| | - Qingzhi Luo
- Department of Cardiology, Shanghai Rui Jin Hospital, Shanghai Jiao Tong University School of Medicine, Shanghai, China
| | - Ao Liu
- Department of Cardiology, Shanghai Rui Jin Hospital, Shanghai Jiao Tong University School of Medicine, Shanghai, China
| | - Liqun Wu
- Department of Cardiology, Shanghai Rui Jin Hospital, Shanghai Jiao Tong University School of Medicine, Shanghai, China
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Li L, Zheng X, Dosdall DJ, Huang J, Pogwizd SM, Ideker RE. Long-duration ventricular fibrillation exhibits 2 distinct organized states. Circ Arrhythm Electrophysiol 2013; 6:1192-9. [PMID: 24243784 DOI: 10.1161/circep.113.000459] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
BACKGROUND Previous studies showed that endocardial activation during long-duration ventricular fibrillation (VF) exhibits organized activity. We identified and quantified the different types of organized activity. METHODS AND RESULTS Two 64-electrode basket catheters were inserted, respectively, into the left ventricle and right ventricle of dogs to record endocardial activation from the endocardium during 7 minutes of VF (controls, n=6). The study was repeated with the K(ATP) channel opener pinacidil (n=6) and the calcium channel blocker flunarizine (n=6). After 2 minutes of VF without drugs, 2 highly organized left ventricular endocardial activation patterns were observed: (1) ventricular electric synchrony pattern, in which endocardial activation arose focally and either had a propagation sequence similar to sinus rhythm or arose near papillary muscles, and (2) stable pattern, in which activation was regular and repeatable, sometimes forming a stable re-entrant circuit around the left ventricular apex. Between 3 and 7 minutes of VF, the percent of time ventricular electric synchrony was present was control=25%, flunarizine=24% (P=0.44), and pinacidil=0.1% (P<0.001) and the percent of time stable pattern was present was control=71%, flunarizine=48% (P<0.001), and pinacidil=56% (P<0.001). The remainder of the time, nonstable re-entrant activation with little repeatability was present. CONCLUSIONS After 3 minutes, VF exhibits 2 highly organized endocardial activation patterns 96% of the time, one potentially arising focally in the Purkinje system that was prevented with a K(ATP) channel opener but not a calcium channel blocker and the other potentially arising from a stable re-entrant circuit near the apical left ventricular endocardium.
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Affiliation(s)
- Li Li
- Departments of Medicine, Biomedical Engineering, and Physiology, University of Alabama at Birmingham; and Department of Internal Medicine, CARMA Center, University of Utah, Salt Lake City
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Jin Q, Zhang N, Zhou J, Lin CJ, Pang Y, Gu G, Shen WF, Wu LQ. The effect of pinacidil on postshock activation and ventricular defibrillation threshold in canine hearts. Acta Pharmacol Sin 2012; 33:1488-94. [PMID: 23064720 DOI: 10.1038/aps.2012.96] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022] Open
Abstract
AIM To determine the postshock activation patterns with both successful and failed shocks in a canine model of ventricular fibrillation, and whether piniacidil, an early after-depolarization (EAD) inhibitor, altered the defibrillation threshold (DFT) and postshock activation patterns. METHODS In 6 beagles, a basket catheter with 64 unipolar electrodes was placed in the LV for global endocardial mapping, a monophasic action potential catheter was inserted into the LV apex, and a catheter with the negative electrode in the right ventricle and the positive electrode in the superior vena cava was inserted for defibrillation. The DFT, 90% action potential duration (APD(90)) and activation recovery interval (ARI) were evaluated before and after pinacidil administration (loading dosage 0.5 mg/kg and maintenance dosage 0.5 mg·kg(-1)·h(-1), iv). Electrical heterogeneities were defined with the dispersion of ARI. After successful and failed shocks with near-DFT strength, the earliest postshock activation patterns (focal or nonfocal endocardial activation), interval and location were detected. RESULTS Pinacidil significantly decreased APD(90) (from 178±16 ms to 168±18 ms) and ARI from (152±10 ms to 143±10 ms) at pacing cycle length of 300 ms. The drug significantly increased VF activation rate (from 10.0±1.9 Hz to 10.8±2.0 Hz). The drug did not affect the dispersion of ARI, neither it changed DFT (baseline: 480±110 V; pinacidil: 425±55 V, P>0.05). The earliest postshock activation arose locally on the LV apical endocardium before and after the drug treatment. Pinacidil significantly prolonged the postshock cycle length of cycles 2 to 5 for the successful episodes but not for the failed episodes. CONCLUSION Pinacidil increases the postshock cycle length suggesting that EAD may play a role in postshock activation, while it fails to alter DFT suggesting that EAD produced by shock does not determine a defibrillation success or failure.
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Defibrillation threshold varies during different stages of ventricular fibrillation in canine hearts. Heart Lung Circ 2012; 22:133-40. [PMID: 23021977 DOI: 10.1016/j.hlc.2012.08.059] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/18/2012] [Revised: 08/09/2012] [Accepted: 08/29/2012] [Indexed: 11/23/2022]
Abstract
BACKGROUND Recent studies have shown that short duration ventricular fibrillation (SDVF) and long duration ventricular fibrillation (LDVF) are maintained by different mechanisms. The objective of this study is to evaluate how the defibrillation threshold (DFT) varies over the duration of fibrillation since the mechanism of VF maintenance changes as VF progresses. METHODS Twelve canines were randomly divided into two groups (Group A and B, n=6 each). DFTs were measured three times in each group: SDVF (20s), LDVF (3min in Group A and 7min in Group B) and the first episode of refibrillation after successful defibrillation for LDVF. Two 64-electrode baskets used to globally map the endocardium were deployed into the left ventricle and right ventricle, respectively. RESULTS LDVF-DFT in Group A was significantly higher than that of Group B (628±98V vs 313±81V, P<0.001). In Group B, the DFT of refibrillation was significantly increased compared with the LDVF-DFT (570±199V vs 313±81V, P=0.035) but did not differ from the DFT of refibrillation in Group A (570±199V vs 638±116V, P=0.39). Highly synchronised activation patterns on the left ventricular endocardium were observed between 3 and 7min of LDVF in Group B but not within 3min-LDVF in Group A or during refibrillation in each group. CONCLUSIONS DFT varied during different stages of VF. The highly synchronised activation patterns exhibiting after 3min VF might contribute to the decreased LDVF-DFT.
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Farid TA, Nair K, Massé S, Azam MA, Maguy A, Lai PFH, Umapathy K, Dorian P, Chauhan V, Varró A, Al-Hesayen A, Waxman M, Nattel S, Nanthakumar K. Role of KATP channels in the maintenance of ventricular fibrillation in cardiomyopathic human hearts. Circ Res 2011; 109:1309-18. [PMID: 21980123 DOI: 10.1161/circresaha.110.232918] [Citation(s) in RCA: 42] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
RATIONALE Ventricular fibrillation (VF) leads to global ischemia. The modulation of ischemia-dependent pathways may alter the electrophysiological evolution of VF. OBJECTIVE We addressed the hypotheses that there is regional disease-related expression of K(ATP) channels in human cardiomyopathic hearts and that K(ATP) channel blockade promotes spontaneous VF termination by attenuating spatiotemporal dispersion of refractoriness. METHODS AND RESULTS In a human Langendorff model, electric mapping of 6 control and 9 treatment (10 μmol/L glibenclamide) isolated cardiomyopathic hearts was performed. Spontaneous defibrillation was studied and mean VF cycle length was compared regionally at VF onset and after 180 seconds between control and treatment groups. K(ATP) subunit gene expression was compared between LV endocardium versus epicardium in myopathic hearts. Spontaneous VF termination occurred in 1 of 6 control hearts and 7 of 8 glibenclamide-treated hearts (P=0.026). After 180 seconds of ischemia, a transmural dispersion in VF cycle length was observed between epicardium and endocardium (P=0.001), which was attenuated by glibenclamide. There was greater gene expression of all K(ATP) subunit on the endocardium compared with the epicardium (P<0.02). In an ischemic rat heart model, transmural dispersion of refractoriness (ΔERP(Transmural)=ERP(Epicardium)-ERP(Endocardium)) was verified with pacing protocols. ΔERP(Transmural) in control was 5 ± 2 ms and increased to 36 ± 5 ms with ischemia. This effect was greatly attenuated by glibenclamide (ΔERP(Transmural) for glibenclamide+ischemia=4.9 ± 4 ms, P=0.019 versus control ischemia). CONCLUSIONS K(ATP) channel subunit gene expression is heterogeneously altered in the cardiomyopathic human heart. Blockade of K(ATP) channels promotes spontaneous defibrillation in cardiomyopathic human hearts by attenuating the ischemia-dependent spatiotemporal heterogeneity of refractoriness during early VF.
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Abstract
Electrical shock has been the one effective treatment for ventricular fibrillation for several decades. With the advancement of electrical and optical mapping techniques, histology, and computer modeling, the mechanisms responsible for defibrillation are now coming to light. In this review, we discuss recent work that demonstrates the various mechanisms responsible for defibrillation. On the cellular level, membrane depolarization and electroporation affect defibrillation outcome. Cell bundles and collagenous septae are secondary sources and cause virtual electrodes at sites far from shocking electrodes. On the whole-heart level, shock field gradient and critical points determine whether a shock is successful or whether reentry causes initiation and continuation of fibrillation.
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Affiliation(s)
- Derek J Dosdall
- Departments of Medicine, University of Alabama at Birmingham, Birmingham, Alabama 35294, USA.
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Purkinje activation precedes myocardial activation following defibrillation after long-duration ventricular fibrillation. Heart Rhythm 2009; 7:405-12. [PMID: 20061187 DOI: 10.1016/j.hrthm.2009.11.025] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/08/2009] [Accepted: 11/25/2009] [Indexed: 11/20/2022]
Abstract
BACKGROUND While reentry within the ventricular myocardium (VM) is responsible for the maintenance of short-duration ventricular fibrillation (SDVF; VF duration <1 minute), Purkinje fibers (PFs) are important in the maintenance of long-duration ventricular fibrillation (LDVF; VF duration >1 minute). OBJECTIVE The purpose of this study was to test the hypothesis that the mechanisms of defibrillation may also be different for SDVF and LDVF. METHODS A multielectrode basket catheter was deployed in the left ventricle of eight beagles. External defibrillation shocks were delivered with a ramp-up protocol after SDVF (20 seconds) and LDVF (150 seconds). Earliest VM and PF activations were identified after the highest energy shock that failed to terminate VF and the successful shock. RESULTS Defibrillation was successful after 36 +/- 12 and 181 +/- 14 seconds for SDVF and LDVF, respectively. The time after shock delivery until earliest activation was detected for failed shocks and was significantly longer after LDVF (138.7 +/- 24.1 ms) than after SDVF (75.6 +/- 8.7 ms). Earliest postshock activation after SDVF typically initiated in the VM (14 of 16 episodes), while it always initiated in the PF (16 of 16 episodes) after LDVF. Sites of earliest activity during sinus rhythm correlated with sites of earliest postshock activation for PF-led cycles but not for VM-led cycles. CONCLUSION Earliest recorded postshock activation is in the Purkinje system after LDVF but not after SDVF. This difference raises the possibility that the optimal defibrillation strategy is different for SDVF and LDVF.
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Sims J, Knisley S. Epicardial Conductors Can Lower the Defibrillation Threshold in Rabbit Hearts. IEEE Trans Biomed Eng 2009; 56:1196-9. [DOI: 10.1109/tbme.2008.2005067] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
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Vitebskiy SA, Khrestian CM, Waldo AL. Termination of a tachyarrhythmia by flunarizine is not a specific marker for a triggered mechanism. Heart Rhythm 2007; 4:1544-52. [PMID: 17974494 DOI: 10.1016/j.hrthm.2007.08.018] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/04/2007] [Accepted: 08/15/2007] [Indexed: 10/22/2022]
Abstract
BACKGROUND Prior studies have indicated that tachyarrhythmia termination by flunarizine demonstrates a triggered mechanism. This concept was not confirmed in atrial tachyarrhythmias. OBJECTIVE The purpose of this study was to test the hypothesis that flunarizine will not terminate reentrant atrial flutter (AFL). METHODS We administered flunarizine (2 mg/kg intravenously over 2 minutes) in 11 episodes of reproducibly inducible, sustained AFL in eight canines with sterile pericarditis. If flunarizine terminated AFL, we studied AFL reinducibility. We also studied pacing thresholds, refractoriness, and intra-atrial conduction time during closed-chest studies and pacing at selected cycle lengths (CLs) from selected sites before and after flunarizine administration. Atrial mapping (510 electrodes) assessed the epicardial activation sequence during AFL and its termination in six episodes. Four AFL episodes were studied in the closed-chest state. RESULTS Flunarizine increased AFL CL in all episodes (mean 21 ms; range 7-49 ms), which is explained by slowing conduction in the AFL reentrant circuit, principally in the area of slow conduction. AFL was terminated in 10/11 episodes after drug initiation (mean 3.7 minutes; range 0.5-6.5 minutes) by block in the area of slow conduction. AFL was then not immediately reinducible until >20 minutes after drug administration. Flunarizine had no meaningful effect on atrial pacing thresholds for capture or refractoriness and only affected conduction time in the area of slow conduction in the reentrant circuit. CONCLUSIONS Flunarizine (1) causes progressive slowing and block in the area of slow conduction of the AFL reentrant circuit in the canine sterile pericarditis model and (2) is effective in terminating reentrant AFL and so is not a specific marker for a triggered mechanism.
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Affiliation(s)
- Sergey A Vitebskiy
- Case Western Reserve University, University Hospitals Case Medical Center, Cleveland, Ohio 44106, USA
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Abstract
I am deeply grateful and honored to receive the 2006 Distinguished Scientist Award from the Heart Rhythm Society. Many outstanding individuals have received this award since it was established in 1982, and it is humbling to realize that my small feet are walking in the footsteps of these giants. I would be remiss if I did not thank the numerous colleagues, fellows, and students who performed most of the work leading to the papers of which I am a coauthor.
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Affiliation(s)
- Raymond E Ideker
- Division of Cardiovascular Disease, Department of Medicine, University of Alabama, Birmingham, Alabama 35294-0019, USA.
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Seidl K, Denman RA, Moulder JC, Mouchawar G, Stoeppler C, Becker T, Weise U, Anskey EJ, Burnett HE, Kroll MW. Stepped defibrillation waveform is substantially more efficient than the 50/50% tilt biphasic. Heart Rhythm 2006; 3:1406-11. [PMID: 17161781 DOI: 10.1016/j.hrthm.2006.08.017] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/08/2006] [Accepted: 08/08/2006] [Indexed: 11/25/2022]
Abstract
BACKGROUND Even with biphasic waveforms, patients with high defibrillation thresholds (DFTs) still are seen; thus, improved defibrillation waveforms may be of clinical utility. The stepped waveform has three parts: the first portion is positive with two capacitors in parallel, the second is positive with the capacitors in series, and the last portion is negative, also with the capacitors in series. OBJECTIVES The purpose of this study was to assess the clinical utility of improved defibrillation waveforms. METHODS We measured the delivered energy DFT in 20 patients in a dual-site study using the stepped waveform and a 50/50% tilt biphasic truncated exponential as the control. All shocks were delivered using an arbitrary waveform defibrillator, which was programmed to mimic two 220-microF capacitors (110 microF in series and 440 microF in parallel). RESULTS The peak voltage at DFT was reduced in 19 of the 20 patients. The median peak voltage was reduced by 32.0%, from 472 V to 321 V (P <.001). The median energy DFT was reduced by 33%, from 11.7 J to 7.8 J (P = .008). The mean voltage and energy were reduced by 25.3% and 20.2%, respectively. On average, the stepped waveform was able to defibrillate as well as the 50/50% tilt biphasic, with 33% more energy. The benefit was more pronounced in patients with either a lower ejection fraction or a superior vena cava coil. The benefit of the stepped waveform had an inverse quadratic correlation with the resistance (r(2) = 0.47), suggesting that the capacitance values chosen for the stepped waveform were close to optimal for a 35-Omega resistance. CONCLUSION The stepped waveform reduced the DFT compared to the 50/50% tilt waveform in this preliminary study.
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Karagueuzian HS. On Early Afterdepolarization, Triggered Activity, and Defibrillation Shock Failure. J Cardiovasc Electrophysiol 2006; 17:456; author reply 456-7. [PMID: 16643376 DOI: 10.1111/j.1540-8167.2006.444_1.x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
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Zheng X, Walcott GP, Smith WM, Ideker RE. Reply to the Editor:. J Cardiovasc Electrophysiol 2006. [DOI: 10.1111/j.1540-8167.2006.444_2.x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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Bourn DW, Gray RA, Trayanova NA. Characterization of the relationship between preshock state and virtual electrode polarization-induced propagated graded responses resulting in arrhythmia induction. Heart Rhythm 2006; 3:583-95. [PMID: 16648066 DOI: 10.1016/j.hrthm.2006.01.024] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/25/2005] [Accepted: 01/22/2006] [Indexed: 11/21/2022]
Abstract
BACKGROUND Studies have demonstrated that failed defibrillation shocks often are followed by an electrically quiescent period (isoelectric window); however, the underlying mechanisms remain incompletely understood. We recently suggested a new mechanism termed "virtual electrode polarization-induced propagated graded responses" (VEPiPGRs) that might play a role in the origin of the global postshock activation following the isoelectric window. OBJECTIVES The purpose of this study to elucidate the circumstances under which VEPiPGR activations originate for shocks given to paced right ventricular preparations. Specifically, we examined the dependence of VEPiPGRs on coupling interval (CI) and shock polarity and whether VEPiPGRs emerge preferentially on the epicardium or the endocardium. METHODS Simultaneous endocardial and epicardial activity in isolated right ventricular preparations (n = 4) was imaged optically following shocks of strength +/-5A. All VEPiPGRs were analyzed, and the time T from shock end to activation onset was recorded (isoelectric window is the smallest T among activations that propagated globally). RESULTS VEPiPGR activations occurred for CIs in the range from 80 to 150 ms. Average duration of T was 64.5 +/- 18.15 ms, with T decreasing as CI increased (Tmax = 82 ms, Tmin = 46 ms, linear-fit slope = -0.675). The average earliest CI at which cathodal (+5A) shocks resulted in VEPiPGRs was 87 ms compared with 116 ms for anodal (-5A) shocks. All VEPiPGR activations emerged first on the epicardium in a focal pattern, and all induced ventricular fibrillation. CONCLUSION The global activation that terminates the isoelectric window could result from VEPiPGRs that find an exit pathway. VEPiPGRs originate at the sites of maximum action potential abbreviation by the shock, always on the epicardium for the preparation used here.
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Affiliation(s)
- David W Bourn
- Department of Biomedical Engineering, Tulane University, New Orleans, Louisiana 70118, USA
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