1
|
Pandit SV, Lampe JW, Silver AE. Recurrence of ventricular fibrillation in out-of-hospital cardiac arrest: Clinical evidence and underlying ionic mechanisms. J Physiol 2024; 602:4649-4667. [PMID: 38661672 DOI: 10.1113/jp284621] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/21/2023] [Accepted: 03/08/2024] [Indexed: 04/26/2024] Open
Abstract
Defibrillation remains the optimal therapy for terminating ventricular fibrillation (VF) in out-of-hospital cardiac arrest (OHCA) patients, with reported shock success rates of ∼90%. A key persistent challenge, however, is the high rate of VF recurrence (∼50-80%) seen during post-shock cardiopulmonary resuscitation (CPR). Studies have shown that the incidence and time spent in recurrent VF are negatively associated with neurologically-intact survival. Recurrent VF also results in the administration of extra shocks at escalating energy levels, which can cause cardiac dysfunction. Unfortunately, the mechanisms underlying recurrent VF remain poorly understood. In particular, the role of chest-compressions (CC) administered during CPR in mediating recurrent VF remains controversial. In this review, we first summarize the available clinical evidence for refibrillation occurring during CPR in OHCA patients, including the postulated contribution of CC and non-CC related pathways. Next, we examine experimental studies highlighting how CC can re-induce VF via direct mechano-electric feedback. We postulate the ionic mechanisms involved by comparison with similar phenomena seen in commotio cordis. Subsequently, the hypothesized contribution of partial cardiac reperfusion (either as a result of CC or CC independent organized rhythm) in re-initiating VF in a globally ischaemic heart is examined. An overview of the proposed ionic mechanisms contributing to VF recurrence in OHCA during CPR from a cellular level to the whole heart is outlined. Possible therapeutic implications of the proposed mechanistic theories for VF recurrence in OHCA are briefly discussed.
Collapse
|
2
|
Penttinen K, Prajapati C, Shah D, Rajan DK, Cherian RM, Swan H, Aalto-Setälä K. HiPSC-derived cardiomyocyte to model Brugada syndrome: both asymptomatic and symptomatic mutation carriers reveal increased arrhythmogenicity. BMC Cardiovasc Disord 2023; 23:208. [PMID: 37098502 PMCID: PMC10131315 DOI: 10.1186/s12872-023-03234-7] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/14/2022] [Accepted: 04/11/2023] [Indexed: 04/27/2023] Open
Abstract
Brugada syndrome is an inherited cardiac arrhythmia disorder that is mainly associated with mutations of the cardiac voltage-gated sodium channel alpha subunit 5 (SCN5A) gene. The clinical symptoms include ventricular fibrillation and an increased risk of sudden cardiac death. Human-induced pluripotent stem cell (hiPSC) lines were derived from symptomatic and asymptomatic individuals carrying the R1913C mutation in the SCN5A gene. The present work aimed to observe the phenotype-specific differences in hiPSC-derived cardiomyocytes (CMs) obtained from symptomatic and asymptomatic mutation carriers. In this study, CM electrophysiological properties, beating abilities and calcium parameters were measured. Mutant CMs exhibited higher average sodium current densities than healthy CMs, but the differences were not statistically significant. Action potential durations were significantly shorter in CMs from the symptomatic individual, and a spike-and-dome morphology of action potential was exclusively observed in CMs from the symptomatic individual. More arrhythmias occurred in mutant CMs at single cell and cell aggregate levels compared with those observed in wild-type CMs. Moreover, there were no major differences in ionic currents or intracellular calcium dynamics between the CMs of asymptomatic and symptomatic individuals after the administration of adrenaline and flecainide.In conclusion, mutant CMs were more prone to arrhythmia than healthy CMs but did not explain why only one of the mutation carriers was symptomatic.
Collapse
Affiliation(s)
- Kirsi Penttinen
- Faculty of Medicine and Health Technology and BioMediTech Institute, Tampere University, Tampere, 33520, Finland
| | - Chandra Prajapati
- Faculty of Medicine and Health Technology and BioMediTech Institute, Tampere University, Tampere, 33520, Finland.
| | - Disheet Shah
- Faculty of Medicine and Health Technology and BioMediTech Institute, Tampere University, Tampere, 33520, Finland
| | - Dhanesh Kattipparambil Rajan
- Faculty of Medicine and Health Technology and BioMediTech Institute, Tampere University, Tampere, 33520, Finland
| | - Reeja Maria Cherian
- Faculty of Medicine and Health Technology and BioMediTech Institute, Tampere University, Tampere, 33520, Finland
| | - Heikki Swan
- Helsinki University Hospital, Helsinki, 00290, Finland
| | - Katriina Aalto-Setälä
- Faculty of Medicine and Health Technology and BioMediTech Institute, Tampere University, Tampere, 33520, Finland
- Heart Hospital, Tampere University Hospital, Tampere, 33520, Finland
| |
Collapse
|
3
|
Single cardiomyocytes from papillary muscles show lower preload-dependent activation of force compared to cardiomyocytes from the left ventricular free wall. J Mol Cell Cardiol 2022; 166:127-136. [DOI: 10.1016/j.yjmcc.2022.02.008] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/23/2021] [Revised: 02/05/2022] [Accepted: 02/22/2022] [Indexed: 01/21/2023]
|
4
|
Kani K, Fujiu K. Electrical Storm. Int Heart J 2021; 62:1195-1198. [PMID: 34853216 DOI: 10.1536/ihj.21-662] [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: 11/18/2022]
Affiliation(s)
- Kunihiro Kani
- Department of Cardiovascular Medicine, Graduate School of Medicine, The University of Tokyo
| | - Katsuhito Fujiu
- Department of Cardiovascular Medicine, Graduate School of Medicine, The University of Tokyo
| |
Collapse
|
5
|
DiFazio MR, Thomason JD, Carpenter JW. ECG of the Month. J Am Vet Med Assoc 2021; 258:1189-1192. [PMID: 33978443 DOI: 10.2460/javma.258.11.1189] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
|
6
|
Takahashi M, Yokoshiki H, Mitsuyama H, Watanabe M, Temma T, Kamada R, Hagiwara H, Takahashi Y, Anzai T. SK channel blockade prevents hypoxia-induced ventricular arrhythmias through inhibition of Ca 2+/voltage uncoupling in hypertrophied hearts. Am J Physiol Heart Circ Physiol 2021; 320:H1456-H1469. [PMID: 33635168 DOI: 10.1152/ajpheart.00777.2020] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/21/2020] [Accepted: 02/17/2021] [Indexed: 11/22/2022]
Abstract
Ventricular arrhythmia (VA) is the major cause of death in patients with left ventricular (LV) hypertrophy and/or acute ischemia. We hypothesized that apamin, a blocker of small-conductance Ca2+-activated K+ (SK) channels, alters Ca2+ handling and exhibits anti-arrhythmic effects in ventricular myocardium. Spontaneous hypertensive rats were used as a model of LV hypertrophy. A dual optical mapping of membrane potential (Vm) and intracellular calcium (Cai) was performed during global hypoxia (GH) on the Langendorff perfusion system. The majority of pacing-induced VAs during GH were initiated by triggered activities. Pretreatment of apamin (100 nmol/L) significantly inhibited the VA inducibility. Compared with SK channel blockers (apamin and NS8593), non-SK channel blockers (glibenclamide and 4-AP) did not exhibit anti-arrhythmic effects. Apamin prevented not only action potential duration (APD80) shortening (-18.7 [95% confidence interval, -35.2 to -6.05] ms vs. -2.75 [95% CI, -10.45 to 12.65] ms, P = 0.04) but also calcium transient duration (CaTD80) prolongation (14.52 [95% CI, 8.8-20.35] ms vs. 3.85 [95% CI, -3.3 to 12.1] ms, P < 0.01), thereby reducing CaTD80 - APD80, which denotes "Cai/Vm uncoupling" (33.22 [95% CI, 22-48.4] ms vs. 6.6 [95% CI, 0-14.85] ms, P < 0.01). The reduction of Cai/Vm uncoupling was attributable to less prolonged Ca2+ decay constant and suppression of diastolic Cai increase by apamin. The inhibition of VA inducibility and changes in APs/CaTs parameters caused by apamin was negated by the addition of ouabain, an inhibitor of Na+/K+ pump. Apamin attenuates APD shortening, Ca2+ handling abnormalities, and Cai/Vm uncoupling, leading to inhibition of VA occurrence in hypoxic hypertrophied hearts.NEW & NOTEWORTHY We demonstrated that hypoxia-induced ventricular arrhythmias were mainly initiated by Ca2+-loaded triggered activities in hypertrophied hearts. The blockades of small-conductance Ca2+-activated K+ channels, especially "apamin," showed anti-arrhythmic effects by alleviation of not only action potential duration shortening but also Ca2+ handling abnormalities, most notably the "Ca2+/voltage uncoupling."
Collapse
Affiliation(s)
- Masayuki Takahashi
- Department of Cardiovascular Medicine, Hokkaido University Graduate School of Medicine, Sapporo, Japan
- Department of Cardiovascular Medicine, National Hospital Organization Hokkaido Medical Center, Sapporo, Japan
| | - Hisashi Yokoshiki
- Department of Cardiovascular Medicine, Sapporo City General Hospital, Sapporo, Japan
| | - Hirofumi Mitsuyama
- Department of Cardiovascular Medicine, Hokkaido Ohno Memorial Hospital, Sapporo, Japan
| | - Masaya Watanabe
- Department of Cardiovascular Medicine, Hokkaido University Graduate School of Medicine, Sapporo, Japan
| | - Taro Temma
- Department of Cardiovascular Medicine, Hokkaido University Graduate School of Medicine, Sapporo, Japan
| | - Rui Kamada
- Department of Cardiovascular Medicine, Hokkaido University Graduate School of Medicine, Sapporo, Japan
| | - Hikaru Hagiwara
- Department of Cardiovascular Medicine, Hokkaido University Graduate School of Medicine, Sapporo, Japan
| | - Yumi Takahashi
- Department of Cardiovascular Medicine, Hokkaido University Graduate School of Medicine, Sapporo, Japan
| | - Toshihisa Anzai
- Department of Cardiovascular Medicine, Hokkaido University Graduate School of Medicine, Sapporo, Japan
| |
Collapse
|
7
|
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.
Collapse
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
| |
Collapse
|
8
|
Yin D, Yang N, Tian Z, Wu AZ, Xu D, Chen M, Kamp NJ, Wang Z, Shen C, Chen Z, Lin SF, Rubart-von der Lohe M, Chen PS, Everett TH. Effects of ondansetron on apamin-sensitive small conductance calcium-activated potassium currents in pacing-induced failing rabbit hearts. Heart Rhythm 2019; 17:332-340. [PMID: 31513946 DOI: 10.1016/j.hrthm.2019.09.008] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/27/2018] [Indexed: 12/16/2022]
Abstract
BACKGROUND Ondansetron, a widely prescribed antiemetic, has been implicated in drug-induced long QT syndrome. Recent patch clamp experiments have shown that ondansetron inhibits the apamin-sensitive small conductance calcium-activated potassium current (IKAS). OBJECTIVE The purpose of this study was to determine whether ondansetron causes action potential duration (APD) prolongation by IKAS inhibition. METHODS Optical mapping was performed in rabbit hearts with pacing-induced heart failure (HF) and in normal hearts before and after ondansetron (100 nM) infusion. APD at 80% repolarization (APD80) and arrhythmia inducibility were determined. Additional studies with ondansetron were performed in normal hearts perfused with hypokalemic Tyrode's (2.4 mM) solution before or after apamin administration. RESULTS The corrected QT interval in HF was 326 ms (95% confidence interval [CI] 306-347 ms) at baseline and 364 ms (95% CI 351-378 ms) after ondansetron infusion (P < .001). Ondansetron significantly prolonged APD80 in the HF group and promoted early afterdepolarizations, steepened the APD restitution curve, and increased ventricular vulnerability. Ventricular fibrillation was not inducible in HF ventricles at baseline, but after ondansetron infusion, ventricular fibrillation was induced in 5 of the 7 ventricles (P = .021). In hypokalemia, apamin prolonged APD80 from 163 ms (95% CI 146-180 ms) to 180 ms (95% CI 156-204 ms) (P = .018). Subsequent administration of ondansetron failed to further prolong APD80 (180 ms [95% CI 156-204 ms] vs 179 ms [95% CI 165-194 ms]; P = .789). The results were similar when ondansetron was administered first, followed by apamin. CONCLUSION Ondansetron is a specific IKAS blocker at therapeutic concentrations. Ondansetron may prolong the QT interval in HF by inhibiting small conductance calcium-activated potassium channels, which increases the vulnerability to ventricular arrhythmias.
Collapse
Affiliation(s)
- Dechun Yin
- Krannert Institute of Cardiology and Division of Cardiology, Department of Medicine, Indiana University School of Medicine, Indianapolis, Indiana; Department of Cardiology, the First Affiliated Hospital of Harbin Medical University, Harbin, China
| | - Na Yang
- Krannert Institute of Cardiology and Division of Cardiology, Department of Medicine, Indiana University School of Medicine, Indianapolis, Indiana; Department of Gynecological and Obstetric Ultrasound, the First Affiliated Hospital of Harbin Medical University, Harbin, China
| | - Zhipeng Tian
- Krannert Institute of Cardiology and Division of Cardiology, Department of Medicine, Indiana University School of Medicine, Indianapolis, Indiana; Department of Cardiology, Central Hospital Affiliated to Shenyang Medical College, Shenyang, China
| | - Adonis Z Wu
- Krannert Institute of Cardiology and Division of Cardiology, Department of Medicine, Indiana University School of Medicine, Indianapolis, Indiana; Institute of Biomedical Engineering, National Chiao Tung University, Hsin-Chu, Taiwan
| | - Dongzhu Xu
- Krannert Institute of Cardiology and Division of Cardiology, Department of Medicine, Indiana University School of Medicine, Indianapolis, Indiana; Department of Cardiology, Faculty of Medicine, University of Tsukuba, Tsukuba, Japan
| | - Mu Chen
- Krannert Institute of Cardiology and Division of Cardiology, Department of Medicine, Indiana University School of Medicine, Indianapolis, Indiana; Department of Cardiology, Xinhua Hospital, Shanghai Jiaotong University School of Medicine, Shanghai, China
| | - Nicholas J Kamp
- Krannert Institute of Cardiology and Division of Cardiology, Department of Medicine, Indiana University School of Medicine, Indianapolis, Indiana
| | - Zhuo Wang
- Krannert Institute of Cardiology and Division of Cardiology, Department of Medicine, Indiana University School of Medicine, Indianapolis, Indiana; Department of Cardiology, Renmin Hospital of Wuhan University, Wuhan, China
| | - Changyu Shen
- Richard and Susan Smith Center for Outcomes Research in Cardiology, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, Massachusetts
| | - Zhenhui Chen
- Krannert Institute of Cardiology and Division of Cardiology, Department of Medicine, Indiana University School of Medicine, Indianapolis, Indiana
| | - Shien-Fong Lin
- Krannert Institute of Cardiology and Division of Cardiology, Department of Medicine, Indiana University School of Medicine, Indianapolis, Indiana; Institute of Biomedical Engineering, National Chiao Tung University, Hsin-Chu, Taiwan
| | | | - Peng-Sheng Chen
- Krannert Institute of Cardiology and Division of Cardiology, Department of Medicine, Indiana University School of Medicine, Indianapolis, Indiana
| | - Thomas H Everett
- Krannert Institute of Cardiology and Division of Cardiology, Department of Medicine, Indiana University School of Medicine, Indianapolis, Indiana.
| |
Collapse
|
9
|
Sendra-Ferrer M, Gonzalez MD. Ibutilide for the control of refractory ventricular tachycardia and ventricular fibrillation in patients with myocardial ischemia and hemodynamic instability. J Cardiovasc Electrophysiol 2018; 30:503-510. [PMID: 30580467 DOI: 10.1111/jce.13835] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/07/2018] [Revised: 12/11/2018] [Accepted: 12/19/2018] [Indexed: 11/30/2022]
Abstract
INTRODUCTION Recurrent ventricular tachycardia (VT) and ventricular fibrillation (VF) in patients with myocardial ischemia requiring hemodynamic support can be refractory to available antiarrhythmic agents and even to cardioversion and defibrillation. The purpose of this study was to report the effect of intravenous ibutilide in patients with a VT and/or VF storm in the presence of incomplete revascularization requiring hemodynamic support. METHODS AND RESULTS Standard continuous telemetry and frequent 12-lead electrocardiograms were obtained to determine the effect of intravenous Ibutilide in these patients. We studied six consecutive patients (age 60 ± 12 years; five males) with incomplete revascularization and mechanical support (extracorporeal membrane of oxygenation = 2; left ventricular assist device = 4) with VT/VF refractory to lidocaine and amiodarone. Intravenous ibutilide was given as a last resort for management of their ventricular arrhythmias. Intravenous ibutilide (1-2 mg) allowed restoration of sinus rhythm in three patients with persistent VF that were refractory to multiple defibrillation shocks. When the 24-hour period before and after ibutilide administration was compared, this drug markedly reduced the number of required cardioversions/defibrillations in all patients from 20 ± 9 to 0.7 ± 0.8 shocks ( P = 0.036). CONCLUSIONS In patients with myocardial ischemia requiring hemodynamic support, intravenous Ibutilide demonstrates a potent antiarrhythmic effect and can facilitate defibrillation in patients with refractory VF.
Collapse
Affiliation(s)
- Mauricio Sendra-Ferrer
- Penn State University Heart and Vascular Institute, Penn State University College of Medicine, The Milton S. Hershey Medical Center, Hershey, Pennsylvania
| | - Mario D Gonzalez
- Penn State University Heart and Vascular Institute, Penn State University College of Medicine, The Milton S. Hershey Medical Center, Hershey, Pennsylvania
| |
Collapse
|
10
|
Chen PS, Doytchinova A. Why Is Propranolol Better Than Metoprolol in Acute Treatment of Electrical Storm? J Am Coll Cardiol 2018; 71:1907-1909. [DOI: 10.1016/j.jacc.2018.02.058] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/09/2018] [Revised: 02/12/2018] [Accepted: 02/15/2018] [Indexed: 10/17/2022]
|
11
|
Jiménez MAV, Nascimento JHM, Monnerat G, Maciel L, Paiva CN, Pedrosa RC, Campos de Carvalho AC, Medei E. Autoantibodies with beta-adrenergic activity from chronic chagasic patients induce cardiac arrhythmias and early afterdepolarization in a drug-induced LQT2 rabbit hearts. Int J Cardiol 2017; 240:354-359. [PMID: 28320606 DOI: 10.1016/j.ijcard.2017.02.066] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/04/2016] [Revised: 02/07/2017] [Accepted: 02/13/2017] [Indexed: 02/08/2023]
Abstract
BACKGROUND Cardiac arrhythmias are one of the main causes of death in ChCP and other dilated cardiomyopathies. Previous studies demonstrated that ventricular arrhythmias are associated with the presence of autoantibodies with beta-adrenergic activity, Ab-β. OBJECTIVES The aim of this study was to investigate whether Ab-β, present in chronic chagasic patients (ChCP), induce cardiac arrhythmias in the pharmacological type-2 long QT syndrome model (LQTS-2). METHODS/RESULTS The LQTS2 was established by perfusion of Tyrode saline solution with a potassium channel blocker E-4031 (5μM) in isolated rabbit hearts or in rabbit cardiac strips, in order to record ECG or action potential, respectively. Autoantibodies from ChCP activating (Ab-β) or not (Ab-NR) cardiac beta 1-adrenergic receptors were used. Ab-β, but not Ab-NR, were able to significantly shorten QT, QTc and increase Tpeak-Tend interval in the LQTS-2. A positive correlation between higher QTc and Tpeak-Tend was found after Ab-β perfusion in the same model. In addition, in the LQTS-2 model, in almost 75% (11/15) of the hearts perfused with Ab-β, ventricular and atrio-ventricular electrical disturbances were observed. Atenolol abolished all Ab-β-induced arrhythmias. Ab-β, when perfused in a cellular LQTS-2, drastically reduced the action potential duration and evoked early afterdepolarization (EAD's), while Ab-NR did not modulate the AP properties in the LQTS-2. CONCLUSION The results indicate that Ab-β were able to induce cardiac arrhythmias and EAD's. This phenomenon can explain, at least in part, the cellular mechanism of Ab-β-induced arrhythmias. Furthermore, atenolol is effective for the treatment of Ab-β-induced arrhythmias.
Collapse
Affiliation(s)
| | - José H M Nascimento
- Instituto de Biofísica Carlos Chagas Filho, Universidade Federal do Rio de Janeiro, Rio de Janeiro, Brazil
| | - Gustavo Monnerat
- Instituto de Biofísica Carlos Chagas Filho, Universidade Federal do Rio de Janeiro, Rio de Janeiro, Brazil
| | - Leonardo Maciel
- Instituto de Biofísica Carlos Chagas Filho, Universidade Federal do Rio de Janeiro, Rio de Janeiro, Brazil
| | - Claudia N Paiva
- Instituto de Biofísica Carlos Chagas Filho, Universidade Federal do Rio de Janeiro, Rio de Janeiro, Brazil
| | - Roberto Coury Pedrosa
- Instituto de Biofísica Carlos Chagas Filho, Universidade Federal do Rio de Janeiro, Rio de Janeiro, Brazil
| | | | - Emiliano Medei
- Instituto de Biofísica Carlos Chagas Filho, Universidade Federal do Rio de Janeiro, Rio de Janeiro, Brazil.
| |
Collapse
|
12
|
Azam MA, Zamiri N, Massé S, Kusha M, Lai PFH, Nair GK, Tan NS, Labos C, Nanthakumar K. Effects of Late Sodium Current Blockade on Ventricular Refibrillation in a Rabbit Model. Circ Arrhythm Electrophysiol 2017; 10:CIRCEP.116.004331. [PMID: 28314848 DOI: 10.1161/circep.116.004331] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/16/2016] [Accepted: 01/19/2017] [Indexed: 12/19/2022]
Abstract
BACKGROUND After defibrillation of initial ventricular fibrillation (VF), it is crucial to prevent refibrillation to ensure successful resuscitation outcomes. Inability of the late Na+ current to inactivate leads to intracellular Ca2+ dysregulation and arrhythmias. Our aim was to determine the effects of ranolazine and GS-967, inhibitors of the late Na+ current, on ventricular refibrillation. METHODS AND RESULTS Long-duration VF was induced electrically in Langendorff-perfused rabbit hearts (n=22) and terminated with a defibrillator after 6 minutes. Fibrillating hearts were randomized into 3 groups: treatment with ranolazine, GS-967, or nontreated controls. In the treated groups, hearts were perfused with ranolazine or GS-967 at 2 minutes of VF. In control experiments, perfusion solution was supplemented with isotonic saline in lieu of a drug. Inducibility of refibrillation was assessed after initial long-duration VF by attempting to reinduce VF. Sustained refibrillation was successful in fewer ranolazine-treated (29.17%; P=0.005) or GS-967-treated (45.83%, P=0.035) hearts compared with that in nontreated control hearts (84.85%). In GS-967-treated hearts, significantly more spontaneous termination of initial long-duration VF was observed (66.67%; P=0.01). Ca2+ transient duration was reduced in ranolazine-treated hearts compared with that in controls (P=0.05) and also Ca2+ alternans (P=0.03). CONCLUSIONS Late Na+ current inhibition during long-duration VF reduces the susceptibility to subsequent refibrillation, partially by mitigating dysregulation of intracellular Ca2+. These results suggest the potential therapeutic use of ranolazine and GS-967 and call for further testing in cardiac arrest models.
Collapse
Affiliation(s)
- Mohammed Ali Azam
- From the Hull Family Cardiac Fibrillation Management Laboratory, Toronto General Hospital, University Health Network, Ontario, Canada (M.A.A., N.Z., S.M., M.K., P.F.H.L., G.K.N., N.S.T., K.N.); and Institute for Clinical Evaluative Sciences, Toronto, Ontario, Canada (C.L.)
| | - Nima Zamiri
- From the Hull Family Cardiac Fibrillation Management Laboratory, Toronto General Hospital, University Health Network, Ontario, Canada (M.A.A., N.Z., S.M., M.K., P.F.H.L., G.K.N., N.S.T., K.N.); and Institute for Clinical Evaluative Sciences, Toronto, Ontario, Canada (C.L.)
| | - Stéphane Massé
- From the Hull Family Cardiac Fibrillation Management Laboratory, Toronto General Hospital, University Health Network, Ontario, Canada (M.A.A., N.Z., S.M., M.K., P.F.H.L., G.K.N., N.S.T., K.N.); and Institute for Clinical Evaluative Sciences, Toronto, Ontario, Canada (C.L.)
| | - Marjan Kusha
- From the Hull Family Cardiac Fibrillation Management Laboratory, Toronto General Hospital, University Health Network, Ontario, Canada (M.A.A., N.Z., S.M., M.K., P.F.H.L., G.K.N., N.S.T., K.N.); and Institute for Clinical Evaluative Sciences, Toronto, Ontario, Canada (C.L.)
| | - Patrick F H Lai
- From the Hull Family Cardiac Fibrillation Management Laboratory, Toronto General Hospital, University Health Network, Ontario, Canada (M.A.A., N.Z., S.M., M.K., P.F.H.L., G.K.N., N.S.T., K.N.); and Institute for Clinical Evaluative Sciences, Toronto, Ontario, Canada (C.L.)
| | - Govind K Nair
- From the Hull Family Cardiac Fibrillation Management Laboratory, Toronto General Hospital, University Health Network, Ontario, Canada (M.A.A., N.Z., S.M., M.K., P.F.H.L., G.K.N., N.S.T., K.N.); and Institute for Clinical Evaluative Sciences, Toronto, Ontario, Canada (C.L.)
| | - Nigel S Tan
- From the Hull Family Cardiac Fibrillation Management Laboratory, Toronto General Hospital, University Health Network, Ontario, Canada (M.A.A., N.Z., S.M., M.K., P.F.H.L., G.K.N., N.S.T., K.N.); and Institute for Clinical Evaluative Sciences, Toronto, Ontario, Canada (C.L.)
| | - Christopher Labos
- From the Hull Family Cardiac Fibrillation Management Laboratory, Toronto General Hospital, University Health Network, Ontario, Canada (M.A.A., N.Z., S.M., M.K., P.F.H.L., G.K.N., N.S.T., K.N.); and Institute for Clinical Evaluative Sciences, Toronto, Ontario, Canada (C.L.)
| | - Kumaraswamy Nanthakumar
- From the Hull Family Cardiac Fibrillation Management Laboratory, Toronto General Hospital, University Health Network, Ontario, Canada (M.A.A., N.Z., S.M., M.K., P.F.H.L., G.K.N., N.S.T., K.N.); and Institute for Clinical Evaluative Sciences, Toronto, Ontario, Canada (C.L.).
| |
Collapse
|
13
|
Reher TA, Wang Z, Hsueh CH, Chang PC, Pan Z, Kumar M, Patel J, Tan J, Shen C, Chen Z, Fishbein MC, Rubart M, Boyden P, Chen PS. Small-Conductance Calcium-Activated Potassium Current in Normal Rabbit Cardiac Purkinje Cells. J Am Heart Assoc 2017; 6:JAHA.117.005471. [PMID: 28550095 PMCID: PMC5669169 DOI: 10.1161/jaha.117.005471] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
Abstract
Background Purkinje cells (PCs) are important in cardiac arrhythmogenesis. Whether small‐conductance calcium‐activated potassium (SK) channels are present in PCs remains unclear. We tested the hypotheses that subtype 2 SK (SK2) channel proteins and apamin‐sensitive SK currents are abundantly present in PCs. Methods and Results We studied 25 normal rabbit ventricles, including 13 patch‐clamp studies, 4 for Western blotting, and 8 for immunohistochemical staining. Transmembrane action potentials were recorded in current‐clamp mode using the perforated‐patch technique. For PCs, the apamin (100 nmol/L) significantly prolonged action potential duration measured to 80% repolarization by an average of 10.4 ms (95% CI, 0.11–20.72) (n=9, P=0.047). Voltage‐clamp study showed that apamin‐sensitive SK current density was significantly larger in PCs compared with ventricular myocytes at potentials ≥0 mV. Western blotting of SK2 expression showed that the SK2 protein expression in the midmyocardium was 58% (P=0.028) and the epicardium was 50% (P=0.018) of that in the pseudotendons. Immunostaining of SK2 protein showed that PCs stained stronger than ventricular myocytes. Confocal microscope study showed SK2 protein was distributed to the periphery of the PCs. Conclusions SK2 proteins are more abundantly present in the PCs than in the ventricular myocytes of normal rabbit ventricles. Apamin‐sensitive SK current is important in ventricular repolarization of normal PCs.
Collapse
Affiliation(s)
- Thomas A Reher
- The Krannert Institute of Cardiology and Division of Cardiology, Department of Medicine, Indianapolis, IN
| | - Zhuo Wang
- The Krannert Institute of Cardiology and Division of Cardiology, Department of Medicine, Indianapolis, IN.,Department of Cardiology, Renmin Hospital of Wuhan University, Wuhan, China
| | - Chia-Hsiang Hsueh
- The Krannert Institute of Cardiology and Division of Cardiology, Department of Medicine, Indianapolis, IN
| | - Po-Cheng Chang
- The Krannert Institute of Cardiology and Division of Cardiology, Department of Medicine, Indianapolis, IN
| | - Zhenwei Pan
- The Krannert Institute of Cardiology and Division of Cardiology, Department of Medicine, Indianapolis, IN
| | - Mohineesh Kumar
- The Krannert Institute of Cardiology and Division of Cardiology, Department of Medicine, Indianapolis, IN
| | - Jheel Patel
- The Krannert Institute of Cardiology and Division of Cardiology, Department of Medicine, Indianapolis, IN
| | - Jian Tan
- The Krannert Institute of Cardiology and Division of Cardiology, Department of Medicine, Indianapolis, IN
| | - Changyu Shen
- Smith Center for Outcomes Research in Cardiology, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, MA
| | - Zhenhui Chen
- The Krannert Institute of Cardiology and Division of Cardiology, Department of Medicine, Indianapolis, IN
| | - Michael C Fishbein
- Department of Pathology and Laboratory Medicine, UCLA Medical Center, Los Angeles, CA
| | - Michael Rubart
- Department of Pediatrics, Indiana University School of Medicine, Indianapolis, IN
| | - Penelope Boyden
- Department of Pharmacology, Columbia University, New York, NY
| | - Peng-Sheng Chen
- The Krannert Institute of Cardiology and Division of Cardiology, Department of Medicine, Indianapolis, IN
| |
Collapse
|
14
|
Lu HR, Gallacher DJ, Yan GX. Assessment of drug-induced proarrhythmia: The importance of study design in the rabbit left ventricular wedge model. J Pharmacol Toxicol Methods 2016; 81:151-60. [PMID: 27374776 DOI: 10.1016/j.vascn.2016.06.006] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/27/2016] [Revised: 06/22/2016] [Accepted: 06/26/2016] [Indexed: 01/09/2023]
Abstract
In the present study, we investigated an impact of the stimulation rate on the detection of the proarrhythmic potential of 10 reference compounds with effects on different cardiac ion channels in the isolated arterially-perfused rabbit left ventricular wedge preparation. The compounds were tested in the wedge model using two distinct protocols; including baseline stimulation at 1-Hz followed by a brief period at 0.5-Hz, either without an additional brief period of 2-Hz stimulation (i.e. Protocol 1) or with 2-Hz stimulation (i.e. Protocol 2). As expected, QT-prolonging drugs (ibutilide and quinidine) prolonged the QT interval, similarly increased the Torsades de Pointes (TdP) score, and elicited early afterdepolarizations (EADs) in both protocols. HMR1556 and JNJ-303 (IKs blockers) also prolonged the QT interval up to 1μM similarly in both protocols. Nifedipine (Ca(2+) antagonist) shortened the QT interval, and reduced force of contraction similarly in both protocols. However, Na(+) channel blockers (Ia, Ib, Ic) widened the QRS duration more in Protocol 2 than in Protocol 1. Furthermore, it was only possible to detect non-TdP-like ventricular tachycardia/fibrillation (VT/VF) induced by Na(+) blockers and by QT-shortening drugs (levcromakalim and mallotoxin) using the 2-Hz stimulation (Protocol 2). Our data suggest that the inclusion of a brief period of fast stimulation at 2Hz is critical for detecting drug-induced slowing of conduction (QRS widening), QT shortening and associated (non-TdP-like) VT/VF, which are distinct from the QT prolongation/TdP proarrhythmia in isolated, arterially-perfused rabbit left ventricular wedges.
Collapse
Affiliation(s)
- Hua Rong Lu
- Global Safety Pharmacology, Discovery Sciences, Janssen Research & Development, Janssen Pharmaceutica NV, Belgium.
| | - David J Gallacher
- Global Safety Pharmacology, Discovery Sciences, Janssen Research & Development, Janssen Pharmaceutica NV, Belgium
| | - Gan-Xin Yan
- Lankenau Institute for Medical Research, Wynnewood, PA, USA
| |
Collapse
|
15
|
Electro-mechanical dysfunction in long QT syndrome: Role for arrhythmogenic risk prediction and modulation by sex and sex hormones. PROGRESS IN BIOPHYSICS AND MOLECULAR BIOLOGY 2015; 120:255-69. [PMID: 26718598 DOI: 10.1016/j.pbiomolbio.2015.12.010] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Subscribe] [Scholar Register] [Received: 08/31/2015] [Revised: 11/26/2015] [Accepted: 12/15/2015] [Indexed: 12/24/2022]
Abstract
Long QT syndrome (LQTS) is a congenital arrhythmogenic channelopathy characterized by impaired cardiac repolarization. Increasing evidence supports the notion that LQTS is not purely an "electrical" disease but rather an "electro-mechanical" disease with regionally heterogeneously impaired electrical and mechanical cardiac function. In the first part, this article reviews current knowledge on electro-mechanical (dys)function in LQTS, clinical consequences of the observed electro-mechanical dysfunction, and potential underlying mechanisms. Since several novel imaging techniques - Strain Echocardiography (SE) and Magnetic Resonance Tissue Phase Mapping (TPM) - are applied in clinical and experimental settings to assess the (regional) mechanical function, advantages of these non-invasive techniques and their feasibility in the clinical routine are particularly highlighted. The second part provides novel insights into sex differences and sex hormone effects on electro-mechanical cardiac function in a transgenic LQT2 rabbit model. Here we demonstrate that female LQT2 rabbits exhibit a prolonged time to diastolic peak - as marker for contraction duration and early relaxation - compared to males. Chronic estradiol-treatment enhances these differences in time to diastolic peak even more and additionally increases the risk for ventricular arrhythmia. Importantly, time to diastolic peak is particularly prolonged in rabbits exhibiting ventricular arrhythmia - regardless of hormone treatment - contrasting with a lack of differences in QT duration between symptomatic and asymptomatic LQT2 rabbits. This indicates the potential added value of the assessment of mechanical dysfunction in future risk stratification of LQTS patients.
Collapse
|
16
|
Morotti S, McCulloch AD, Bers DM, Edwards AG, Grandi E. Atrial-selective targeting of arrhythmogenic phase-3 early afterdepolarizations in human myocytes. J Mol Cell Cardiol 2015; 96:63-71. [PMID: 26241847 DOI: 10.1016/j.yjmcc.2015.07.030] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/28/2015] [Revised: 07/16/2015] [Accepted: 07/30/2015] [Indexed: 12/19/2022]
Abstract
BACKGROUND We have previously shown that non-equilibrium Na(+) current (INa) reactivation drives isoproterenol-induced phase-3 early afterdepolarizations (EADs) in mouse ventricular myocytes. In these cells, EAD initiation occurs secondary to potentiated sarcoplasmic reticulum Ca(2+) release and enhanced Na(+)/Ca(2+) exchange (NCX). This can be abolished by tetrodotoxin-blockade of INa, but not ranolazine, which selectively inhibits ventricular late INa. AIM Since repolarization of human atrial myocytes is similar to mouse ventricular myocytes in that it is relatively rapid and potently modulated by Ca(2+), we investigated whether similar mechanisms can evoke EADs in human atrium. Indeed, phase-3 EADs have been shown to re-initiate atrial fibrillation (AF) during autonomic stimulation, which is a well-recognized initiator of AF. METHODS We integrated a Markov model of INa gating in our human atrial myocyte model. To simulate experimental results, we rapidly paced this cell model at 10Hz in the presence of 0.1μM acetylcholine and 1μM isoproterenol, and assessed EAD occurrence upon return to sinus rhythm (1Hz). RESULTS Cellular Ca(2+) loading during fast pacing results in a transient period of hypercontractility after return to sinus rhythm. Here, fast repolarization and enhanced NCX facilitate INa reactivation via the canonical gating mode (i.e., not late INa burst mode), which drives EAD initiation. Simulating ranolazine administration reduces atrial peak INa and leads to faster repolarization, during which INa fails to reactivate and EADs are prevented. CONCLUSIONS Non-equilibrium INa reactivation can critically contribute to arrhythmias, specifically in human atrial myocytes. Ranolazine might be beneficial in this context by blocking peak (not late) atrial INa.
Collapse
Affiliation(s)
- Stefano Morotti
- Department of Pharmacology, University of California Davis, Davis, CA, USA
| | - Andrew D McCulloch
- Department of Bioengineering, University of California San Diego, La Jolla, CA, USA
| | - Donald M Bers
- Department of Pharmacology, University of California Davis, Davis, CA, USA
| | - Andrew G Edwards
- Institute for Experimental Medicine, Oslo University Hospital Ullevål, Oslo, Norway; Simula Research Laboratory, Lysaker, Norway
| | - Eleonora Grandi
- Department of Pharmacology, University of California Davis, Davis, CA, USA.
| |
Collapse
|
17
|
SK channels and ventricular arrhythmias in heart failure. Trends Cardiovasc Med 2015; 25:508-14. [PMID: 25743622 DOI: 10.1016/j.tcm.2015.01.010] [Citation(s) in RCA: 40] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/01/2014] [Revised: 01/19/2015] [Accepted: 01/20/2015] [Indexed: 12/18/2022]
Abstract
Small-conductance Ca(2+)-activated K(+) (SK) currents are important in the repolarization of normal atrial (but not ventricular) cardiomyocytes. However, recent studies showed that the SK currents are upregulated in failing ventricular cardiomyocytes, along with increased SK channel protein expression and enhanced sensitivity to intracellular Ca(2+). The SK channel activation may be either anti-arrhythmic or pro-arrhythmic, depending on the underlying clinical situations. While the SK channel is a new target of anti-arrhythmic therapy, drug safety is still one of the major concerns.
Collapse
|
18
|
Morita N, Mandel WJ, Kobayashi Y, Karagueuzian HS. Cardiac fibrosis as a determinant of ventricular tachyarrhythmias. J Arrhythm 2014; 30:389-394. [PMID: 25642299 DOI: 10.1016/j.joa.2013.12.008] [Citation(s) in RCA: 64] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023] Open
Abstract
Animal and emerging clinical studies have demonstrated that increased ventricular fibrosis in a setting of reduced repolarization reserve promotes early afterdepolarizations (EADs) and triggered activity that can initiate ventricular tachycardia and ventricular fibrillation (VT/VF). Increased ventricular fibrosis plays a key facilitatory role in allowing oxidative and metabolic stress-induced EADs to manifest as triggered activity causing VT/VF. The lack of such an arrhythmogenic effect by the same stressors in normal non-fibrotic hearts highlights the importance of fibrosis in the initiation of VT/VF. These findings suggest that antifibrotic therapy combined with therapy designed to increase ventricular repolarization reserve may act synergistically to reduce the risk of sudden cardiac death.
Collapse
Affiliation(s)
- Norishige Morita
- Division of Cardiology, Department of Medicine, Tokai University Hachioji Hospital, Tokyo, Japan
| | - William J Mandel
- Translational Arrhythmia Research Section, Division of Cardiology, Department of Medicine, David Geffen School of Medicine at UCLA, Los Angeles, California
| | - Yoshinori Kobayashi
- Division of Cardiology, Department of Medicine, Tokai University Hachioji Hospital, Tokyo, Japan
| | - Hrayr S Karagueuzian
- Division of Cardiology, Department of Medicine, Tokai University Hachioji Hospital, Tokyo, Japan
| |
Collapse
|
19
|
Apamin-sensitive potassium current and the Mechanisms of ventricular arrhythmia: Perspectives in heart failure treatment. J Arrhythm 2014. [DOI: 10.1016/j.joa.2014.04.007] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022] Open
|
20
|
|
21
|
Wang L, Myles RC, De Jesus NM, Ohlendorf AKP, Bers DM, Ripplinger CM. Optical mapping of sarcoplasmic reticulum Ca2+ in the intact heart: ryanodine receptor refractoriness during alternans and fibrillation. Circ Res 2014; 114:1410-21. [PMID: 24568740 DOI: 10.1161/circresaha.114.302505] [Citation(s) in RCA: 104] [Impact Index Per Article: 10.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
RATIONALE Sarcoplasmic reticulum (SR) Ca(2+) cycling is key to normal excitation-contraction coupling but may also contribute to pathological cardiac alternans and arrhythmia. OBJECTIVE To measure intra-SR free [Ca(2+)] ([Ca(2+)]SR) changes in intact hearts during alternans and ventricular fibrillation (VF). METHODS AND RESULTS Simultaneous optical mapping of Vm (with RH237) and [Ca(2+)]SR (with Fluo-5N AM) was performed in Langendorff-perfused rabbit hearts. Alternans and VF were induced by rapid pacing. SR Ca(2+) and action potential duration (APD) alternans occurred in-phase, but SR Ca(2+) alternans emerged first as cycle length was progressively reduced (217±10 versus 190±13 ms; P<0.05). Ryanodine receptor (RyR) refractoriness played a key role in the onset of SR Ca(2+) alternans, with SR Ca(2+) release alternans routinely occurring without changes in diastolic [Ca(2+)]SR. Sensitizing RyR with caffeine (200 μmol/L) significantly reduced the pacing threshold for both SR Ca(2+) and APD alternans (188±15 and 173±12 ms; P<0.05 versus baseline). Caffeine also reduced the magnitude of spatially discordant SR Ca(2+) alternans, but not APD alternans, the pacing threshold for discordance, or threshold for VF. During VF, [Ca(2+)]SR was high, but RyR remained nearly continuously refractory, resulting in minimal SR Ca(2+) release throughout VF. CONCLUSIONS In intact hearts, RyR refractoriness initiates SR Ca(2+) release alternans that can be amplified by diastolic [Ca(2+)]SR alternans and lead to APD alternans. Sensitizing RyR suppresses spatially concordant but not discordant SR Ca(2+) and APD alternans. Despite increased [Ca(2+)]SR during VF, SR Ca(2+) release was nearly continuously refractory. This novel method provides insight into SR Ca(2+) handling during cardiac alternans and arrhythmia.
Collapse
Affiliation(s)
- Lianguo Wang
- From the Department of Pharmacology, School of Medicine, University of California, Davis (L.W., N.M.D.J., A.K.P.O., D.M.B., C.M.R.); and Institute of Cardiovascular and Medical Sciences, University of Glasgow, Glasgow, United Kingdom (R.C.M.)
| | | | | | | | | | | |
Collapse
|
22
|
Hypokalemia promotes late phase 3 early afterdepolarization and recurrent ventricular fibrillation during isoproterenol infusion in Langendorff perfused rabbit ventricles. Heart Rhythm 2013; 11:697-706. [PMID: 24378768 DOI: 10.1016/j.hrthm.2013.12.032] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/22/2013] [Indexed: 11/20/2022]
Abstract
BACKGROUND Hypokalemia and sympathetic activation are commonly associated with electrical storm (ES) in normal and diseased hearts. The mechanisms remain unclear. OBJECTIVE The purpose of this study was to test the hypothesis that late phase 3 early afterdepolarization (EAD) induced by IKATP activation underlies the mechanisms of ES during isoproterenol infusion and hypokalemia. METHODS Intracellular calcium (Cai) and membrane voltage were optically mapped in 32 Langendorff-perfused normal rabbit hearts. RESULTS Repeated episodes of electrically induced ventricular fibrillation (VF) at baseline did not result in spontaneous VF (SVF). During isoproterenol infusion, SVF occurred in 1 of 15 hearts (7%) studied in normal extracellular potassium ([K(+)]o, 4.5 mmol/L), 3 of 8 hearts (38%) in 2.0 mmol/L [K(+)]o, 9 of 10 hearts (90%) in 1.5 mmol/L [K(+)]o, and 7 of 7 hearts (100%) in 1.0 mmol/L [K(+)]o (P <.001). Optical mapping showed that isoproterenol and hypokalemia enhanced Cai transient duration (CaiTD) and heterogeneously shortened action potential duration (APD) after defibrillation, leading to late phase 3 EAD and SVF. IKATP blocker (glibenclamide, 5 μmol/L) reversed the post-defibrillation APD shortening and suppressed recurrent SVF in all hearts studied despite no evidence of ischemia. Nifedipine reliably prevented recurrent VF when given before, but not after, the development of VF. IKr blocker (E-4031) and small-conductance calcium-activated potassium channel blocker (apamin) failed to prevent recurrent SVF. CONCLUSION Beta-adrenergic stimulation and concomitant hypokalemia could cause nonischemic activation of IKATP, heterogeneous APD shortening, and prolongation of CaiTD to provoke late phase 3 EAD, triggered activity, and recurrent SVF. IKATP inhibition may be useful in managing ES during resistant hypokalemia.
Collapse
|
23
|
CHOU CHUNGCHUAN, WEN MINGSHIEN, LEE HUILING, CHANG POCHENG, WO HUNGTA, YEH SANJOU, WU DELON. Dantrolene Suppresses Ventricular Ectopy and Arrhythmogenicity with Acute Myocardial Infarction in a Langendorff-Perfused Pacing-Induced Heart Failure Rabbit Model. J Cardiovasc Electrophysiol 2013; 25:431-439. [DOI: 10.1111/jce.12320] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/29/2013] [Revised: 10/09/2013] [Accepted: 10/23/2013] [Indexed: 11/28/2022]
Affiliation(s)
- CHUNG-CHUAN CHOU
- Division of Cardiology; Department of Internal Medicine; Chang Gung Memorial Hospital; Linko Taipei Taiwan
- Chang Gung University College of Medicine; Taoyuan Taiwan
| | - MING-SHIEN WEN
- Division of Cardiology; Department of Internal Medicine; Chang Gung Memorial Hospital; Linko Taipei Taiwan
- Chang Gung University College of Medicine; Taoyuan Taiwan
| | - HUI-LING LEE
- Department of Anesthesia; Chang Gung Memorial Hospital; Taipei Taiwan
| | - PO-CHENG CHANG
- Division of Cardiology; Department of Internal Medicine; Chang Gung Memorial Hospital; Linko Taipei Taiwan
| | - HUNG-TA WO
- Division of Cardiology; Department of Internal Medicine; Chang Gung Memorial Hospital; Linko Taipei Taiwan
| | - SAN-JOU YEH
- Division of Cardiology; Department of Internal Medicine; Chang Gung Memorial Hospital; Linko Taipei Taiwan
- Chang Gung University College of Medicine; Taoyuan Taiwan
| | - DELON WU
- Division of Cardiology; Department of Internal Medicine; Chang Gung Memorial Hospital; Linko Taipei Taiwan
| |
Collapse
|
24
|
Karagueuzian HS. Letter to the editor: “The role of short QT interval and elevated LV end-diastolic pressure in the genesis of ventricular tachycardia and fibrillation”. Am J Physiol Heart Circ Physiol 2013; 305:H1405. [DOI: 10.1152/ajpheart.00581.2013] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
|
25
|
Chang PC, Hsieh YC, Hsueh CH, Weiss JN, Lin SF, Chen PS. Apamin induces early afterdepolarizations and torsades de pointes ventricular arrhythmia from failing rabbit ventricles exhibiting secondary rises in intracellular calcium. Heart Rhythm 2013; 10:1516-24. [PMID: 23835258 PMCID: PMC3832504 DOI: 10.1016/j.hrthm.2013.07.003] [Citation(s) in RCA: 61] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/20/2013] [Indexed: 11/15/2022]
Abstract
BACKGROUND A secondary rise of intracellular Ca(2+) (Cai) and an upregulation of apamin-sensitive K(+) current (I(KAS)) are characteristic findings of failing ventricular myocytes. We hypothesize that apamin, a specific I(KAS) blocker, may induce torsades de pointes (TdP) ventricular arrhythmia from failing ventricles exhibiting secondary rises of Cai. OBJECTIVE To test the hypothesis that small conductance Ca(2+) activated IKAS maintains repolarization reserve and prevents ventricular arrhythmia in a rabbit model of heart failure (HF). METHODS We performed Langendorff perfusion and optical mapping studies in 7 hearts with pacing-induced HF and in 5 normal control rabbit hearts. Atrioventricular block was created by cryoablation to allow pacing at slow rates. RESULTS The left ventricular ejection fraction reduced from 69.1% [95% confidence interval 62.3%-76.0%] before pacing to 30.4% [26.8%-34.0%] (N = 7; P < .001) after pacing. The corrected QT interval in failing ventricles was 337 [313-360] ms at baseline and 410 [381-439] ms after applying 100 nmol/L of apamin (P = .01). Apamin induced early afterdepolarizations (EADs) in 6 ventricles, premature ventricular beats (PVBs) in 7 ventricles, and polymorphic ventricular tachycardia consistent with TdP in 4 ventricles. The earliest activation site of EADs and PVBs always occurred at the site with long action potential duration and large amplitude of the secondary rises of Ca(i). Apamin induced secondary rises of Ca(i) in 1 nonfailing ventricle, but no EAD or TdP were observed. CONCLUSIONS In HF ventricles, apamin induces EADs, PVBs, and TdP from areas with secondary rises of Ca(i). I(KAS) is important in maintaining repolarization reserve and preventing TdP in HF ventricles.
Collapse
Affiliation(s)
- Po-Cheng Chang
- Krannert Institute of Cardiology and the Division of Cardiology, Department of Medicine, Indiana University School of Medicine, Indianapolis, Indiana; Second Section of Cardiology, Department of Medicine, Chang Gung Memorial Hospital and Chang Gung University School of Medicine, Taoyuan, Taiwan
| | | | | | | | | | | |
Collapse
|
26
|
CURRAN JERRY, MOHLER PETERJ. Revisiting K +
Channel-Dependent Electrical Remodeling in the Border Zone. J Cardiovasc Electrophysiol 2013; 24:1154-6. [DOI: 10.1111/jce.12189] [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: 11/29/2022]
Affiliation(s)
- JERRY CURRAN
- The Dorothy M. Davis Heart & Lung Research Institute
| | - PETER J. MOHLER
- The Dorothy M. Davis Heart & Lung Research Institute
- Department of Internal Medicine
- Department of Physiology and Cell Biology; The Ohio State University Wexner Medical Center; Columbus Ohio USA
| |
Collapse
|
27
|
Turker I, Yu CC, Chang PC, Chen Z, Sohma Y, Lin SF, Chen PS, Ai T. Amiodarone inhibits apamin-sensitive potassium currents. PLoS One 2013; 8:e70450. [PMID: 23922993 PMCID: PMC3726612 DOI: 10.1371/journal.pone.0070450] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/05/2012] [Accepted: 06/24/2013] [Indexed: 11/18/2022] Open
Abstract
BACKGROUND Apamin sensitive potassium current (I KAS), carried by the type 2 small conductance Ca(2+)-activated potassium (SK2) channels, plays an important role in post-shock action potential duration (APD) shortening and recurrent spontaneous ventricular fibrillation (VF) in failing ventricles. OBJECTIVE To test the hypothesis that amiodarone inhibits I KAS in human embryonic kidney 293 (HEK-293) cells. METHODS We used the patch-clamp technique to study I KAS in HEK-293 cells transiently expressing human SK2 before and after amiodarone administration. RESULTS Amiodarone inhibited IKAS in a dose-dependent manner (IC50, 2.67 ± 0.25 µM with 1 µM intrapipette Ca(2+)). Maximal inhibition was observed with 50 µM amiodarone which inhibited 85.6 ± 3.1% of IKAS induced with 1 µM intrapipette Ca(2+) (n = 3). IKAS inhibition by amiodarone was not voltage-dependent, but was Ca(2+)-dependent: 30 µM amiodarone inhibited 81.5±1.9% of I KAS induced with 1 µM Ca(2+) (n = 4), and 16.4±4.9% with 250 nM Ca(2+) (n = 5). Desethylamiodarone, a major metabolite of amiodarone, also exerts voltage-independent but Ca(2+) dependent inhibition of I KAS. CONCLUSION Both amiodarone and desethylamiodarone inhibit I KAS at therapeutic concentrations. The inhibition is independent of time and voltage, but is dependent on the intracellular Ca(2+) concentration. SK2 current inhibition may in part underlie amiodarone's effects in preventing electrical storm in failing ventricles.
Collapse
Affiliation(s)
- Isik Turker
- Krannert Institute of Cardiology and Division of Cardiology, Department of Medicine, Indiana University School of Medicine, Indianapolis, Indiana
| | - Chih-Chieh Yu
- Krannert Institute of Cardiology and Division of Cardiology, Department of Medicine, Indiana University School of Medicine, Indianapolis, Indiana
- Division of Cardiology, Department of Medicine, National Taiwan University, Taipei, Taiwan
| | - Po-Cheng Chang
- Krannert Institute of Cardiology and Division of Cardiology, Department of Medicine, Indiana University School of Medicine, Indianapolis, Indiana
| | - Zhenhui Chen
- Krannert Institute of Cardiology and Division of Cardiology, Department of Medicine, Indiana University School of Medicine, Indianapolis, Indiana
| | - Yoshiro Sohma
- Department of Pharmacology, Keio University School of Medicine, Shinjuku, Tokyo, Japan
| | - Shien-Fong Lin
- Krannert Institute of Cardiology and Division of Cardiology, Department of Medicine, Indiana University School of Medicine, Indianapolis, Indiana
| | - Peng-Sheng Chen
- Krannert Institute of Cardiology and Division of Cardiology, Department of Medicine, Indiana University School of Medicine, Indianapolis, Indiana
| | - Tomohiko Ai
- Krannert Institute of Cardiology and Division of Cardiology, Department of Medicine, Indiana University School of Medicine, Indianapolis, Indiana
| |
Collapse
|
28
|
Lee YS, Chang PC, Hsueh CH, Maruyama M, Park HW, Rhee KS, Hsieh YC, Shen C, Weiss JN, Chen Z, Lin SF, Chen PS. Apamin-sensitive calcium-activated potassium currents in rabbit ventricles with chronic myocardial infarction. J Cardiovasc Electrophysiol 2013; 24:1144-53. [PMID: 23718850 DOI: 10.1111/jce.12176] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/06/2013] [Revised: 04/13/2013] [Accepted: 04/22/2013] [Indexed: 01/06/2023]
Abstract
INTRODUCTION The apamin-sensitive small-conductance calcium-activated potassium current (IKAS ) is increased in heart failure. It is unknown if myocardial infarction (MI) is also associated with an increase of IKAS . METHODS AND RESULTS We performed Langendorff perfusion and optical mapping in 6 normal hearts and 10 hearts with chronic (5 weeks) MI. An additional 6 normal and 10 MI hearts were used for patch clamp studies. The infarct size was 25% (95% confidence interval, 20-31) and the left ventricular ejection fraction was 50 (46-54). The rabbits did not have symptoms of heart failure. The action potential duration measured to 80% repolarization (APD80 ) in the peri-infarct zone (PZ) was 150 (142-159) milliseconds, significantly (P = 0.01) shorter than that in the normal ventricles (167 [158-177] milliseconds. The intracellular Ca transient duration was also shorter in the PZ (148 [139-157] milliseconds) than that in normal ventricles (168 [157-180] milliseconds; P = 0.017). Apamin prolonged the APD80 in PZ by 9.8 (5.5-14.1)%, which is greater than that in normal ventricles (2.8 [1.3-4.3]%, P = 0.006). Significant shortening of APD80 was observed at the cessation of rapid pacing in MI but not in normal ventricles. Apamin prevented postpacing APD80 shortening. Patch clamp studies showed that IKAS was significantly higher in the PZ cells (2.51 [1.55-3.47] pA/pF, N = 17) than in the normal cells (1.08 [0.36-1.80] pA/pF, N = 15, P = 0.019). CONCLUSION We conclude that IKAS is increased in MI ventricles and contributes significantly to ventricular repolarization especially during tachycardia.
Collapse
Affiliation(s)
- Young Soo Lee
- Krannert Institute of Cardiology and Division of Cardiology, Department of Medicine, Indianapolis, Indiana, USA; Division of Cardiology, Department of Internal Medicine, Catholic University of Daegu School of Medicine, Daegu, Korea
| | | | | | | | | | | | | | | | | | | | | | | |
Collapse
|
29
|
Electrical storm: recent pathophysiological insights and therapeutic consequences. Basic Res Cardiol 2013; 108:336. [DOI: 10.1007/s00395-013-0336-2] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/07/2013] [Revised: 01/29/2013] [Accepted: 02/04/2013] [Indexed: 01/01/2023]
|
30
|
Chang PC, Turker I, Lopshire JC, Masroor S, Nguyen BL, Tao W, Rubart M, Chen PS, Chen Z, Ai T. Heterogeneous upregulation of apamin-sensitive potassium currents in failing human ventricles. J Am Heart Assoc 2013; 2:e004713. [PMID: 23525437 PMCID: PMC3603236 DOI: 10.1161/jaha.112.004713] [Citation(s) in RCA: 68] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
Abstract
Background We previously reported that IKAS are heterogeneously upregulated in failing rabbit ventricles and play an important role in arrhythmogenesis. This study goal is to test the hypothesis that subtype 2 of the small‐conductance Ca2+ activated K+ (SK2) channel and apamin‐sensitive K+ currents (IKAS) are upregulated in failing human ventricles. Methods and Results We studied 12 native hearts from transplant recipients (heart failure [HF] group) and 11 ventricular core biopsies from patients with aortic stenosis and normal systolic function (non‐HF group). IKAS and action potential were recorded with patch‐clamp techniques, and SK2 protein expression was studied by Western blotting. When measured at 1 μmol/L Ca2+ concentration, IKAS was 4.22 (median) (25th and 75th percentiles, 2.86 and 6.96) pA/pF for the HF group (n=11) and 0.98 (0.54 and 1.72) pA/pF for the non‐HF group (n=8, P=0.008). IKAS was lower in the midmyocardial cells than in the epicardial and the endocardial cells. The Ca2+ dependency of IKAS in HF myocytes was shifted leftward compared to non‐HF myocytes (Kd 314 versus 605 nmol/L). Apamin (100 nmol/L) increased the action potential durations by 1.77% (−0.9% and 7.3%) in non‐HF myocytes and by 11.8% (5.7% and 13.9%) in HF myocytes (P=0.02). SK2 protein expression was 3‐fold higher in HF than in non‐HF. Conclusions There is heterogeneous upregulation of IKAS densities in failing human ventricles. The midmyocardial layer shows lower IKAS densities than epicardial and endocardial layers of cells. Increase in both Ca2+ sensitivity and SK2 protein expression contributes to the IKAS upregulation.
Collapse
Affiliation(s)
- Po-Cheng Chang
- Division of Cardiology, Krannert Institute of Cardiology, Indianapolis, IN
| | | | | | | | | | | | | | | | | | | |
Collapse
|
31
|
Chen PS, Ogawa M, Maruyama M, Chua SK, Chang PC, Rubart-von der Lohe M, Chen Z, Ai T, Lin SF. Imaging arrhythmogenic calcium signaling in intact hearts. Pediatr Cardiol 2012; 33:968-74. [PMID: 22349681 PMCID: PMC3586331 DOI: 10.1007/s00246-012-0236-5] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/15/2011] [Accepted: 12/17/2011] [Indexed: 10/28/2022]
Abstract
Protein complex of the cardiac junctional sarcoplasmic reticulum (SR) membrane formed by type 2 ryanodine receptor, junction, triadin, and calsequestrin is responsible for controlling SR calcium (Ca) release. Increased intracellular calcium (Ca(i)) activates the electrogenic sodium-Ca exchanger current, which is known to be important in afterdepolarization and triggered activities (TAs). Using optical-mapping techniques, it is possible to simultaneously map membrane potential (V (m)) and Ca(i) transient in Langendorff-perfused rabbit ventricles to better define the mechanisms by which V (m) and Ca(i) interactions cause early afterdepolarizations (EADs). Phase 3 EAD is dependent on heterogeneously prolonged action potential duration (APD). Electrotonic currents that flow between a persistently depolarized region and its recovered neighbors underlies the mechanisms of phase 3 EADs and TAs. In contrast, "late phase-3 EAD" is induced by APD shortening, not APD prolongation. In failing ventricles, upregulation of apamin-sensitive Ca-activated potassium (K) channels (I(KAS)) causes APD shortening after fibrillation-defibrillation episodes. Shortened APD in the presence of large Ca(i) transients generates late-phase 3 EADs and recurrent spontaneous ventricular fibrillation. The latter findings suggest that I (KAS) may be a novel antiarrhythmic targets in patients with heart failure and electrical storms.
Collapse
Affiliation(s)
- Peng-Sheng Chen
- Krannert Institute of Cardiology, Department of Medicine, Indiana University School of Medicine, 1800 N. Capitol Ave, E475, Indianapolis, IN 46202, USA.
| | | | | | | | | | | | | | | | | |
Collapse
|
32
|
Abstract
Electrical storm (ES), characterized by recurrent ventricular tachycardia/fibrillation, is a serious condition, adversely affecting prognosis in patients with implantable cardioverter/defibrillators. Electrical storm patients often die of progressive heart failure, but the underlying molecular basis is poorly understood. We have recently created an animal model of ES that features repetitive implantable cardioverter/defibrillator firing for recurrent ventricular fibrillation and found that ES events cause striking activation of Ca(2+)/calmodulin-dependent protein kinase II and prominent alteration of Ca(2+)-handling protein phosphorylation, possibly explaining mechanical dysfunction and arrhythmia promotion that characterize ES. Here, the pathophysiology and potential therapeutic strategies for ES, based on experimental and clinical studies by us and others, are described.
Collapse
|
33
|
Kong W, Ideker RE, Fast VG. Intramural optical mapping of V(m) and Ca(i)2+ during long-duration ventricular fibrillation in canine hearts. Am J Physiol Heart Circ Physiol 2012; 302:H1294-305. [PMID: 22268104 DOI: 10.1152/ajpheart.00426.2011] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Intramural gradients of intracellular Ca(2+) (Ca(i)(2+)) Ca(i)(2+) handling, Ca(i)(2+) oscillations, and Ca(i)(2+) transient (CaT) alternans may be important in long-duration ventricular fibrillation (LDVF). However, previous studies of Ca(i)(2+) handling have been limited to recordings from the heart surface during short-duration ventricular fibrillation. To examine whether abnormalities of intramural Ca(i)(2+) handling contribute to LDVF, we measured membrane voltage (V(m)) and Ca(i)(2+) during pacing and LDVF in six perfused canine hearts using five eight-fiber optrodes. Measurements were grouped into epicardial, midwall, and endocardial layers. We found that during pacing at 350-ms cycle length, CaT duration was slightly longer (by ≃10%) in endocardial layers than in epicardial layers, whereas action potential duration (APD) exhibited no difference. Rapid pacing at 150-ms cycle length caused alternans in both APD (APD-ALT) and CaT amplitude (CaA-ALT) without significant transmural differences. For 93% of optrode recordings, CaA-ALT was transmurally concordant, whereas APD-ALT was either concordant (36%) or discordant (54%), suggesting that APD-ALT was not caused by CaA-ALT. During LDVF, V(m) and Ca(i)(2+) progressively desynchronized when not every action potential was followed by a CaT. Such desynchronization developed faster in the epicardium than in the other layers. In addition, CaT duration strongly increased (by ∼240% at 5 min of LDVF), whereas APD shortened (by ∼17%). CaT rises always followed V(m) upstrokes during pacing and LDVF. In conclusion, the fact that V(m) upstrokes always preceded CaTs indicates that spontaneous Ca(i)(2+) oscillations in the working myocardium were not likely the reason for LDVF maintenance. Strong V(m)-Ca(i)(2+) desynchronization and the occurrence of long CaTs during LDVF indicate severely impaired Ca(i)(2+) handling and may potentially contribute to LDVF maintenance.
Collapse
Affiliation(s)
- Wei Kong
- Department of Biomedical Engineering, University of Alabama, Birmingham, 35294, USA
| | | | | |
Collapse
|
34
|
Umar S, Lee JH, de Lange E, Iorga A, Partow-Navid R, Bapat A, van der Laarse A, Saggar R, Saggar R, Ypey DL, Karagueuzian HS, Eghbali M. Spontaneous ventricular fibrillation in right ventricular failure secondary to chronic pulmonary hypertension. Circ Arrhythm Electrophysiol 2011; 5:181-90. [PMID: 22199010 DOI: 10.1161/circep.111.967265] [Citation(s) in RCA: 41] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
BACKGROUND Right ventricular failure (RVF) in pulmonary hypertension (PH) is associated with increased incidence of sudden death by a poorly explored mechanism. We test the hypothesis that PH promotes spontaneous ventricular fibrillation (VF) during a critical post-PH onset period characterized by a sudden increase in mortality. METHODS AND RESULTS Rats received either a single subcutaneous dose of monocrotaline (MCT, 60 mg/kg) to induce PH-associated RVF (PH, n=24) or saline (control, n=17). Activation pattern of the RV-epicardial surface was mapped using voltage-sensitive dye in isolated Langendorff-perfused hearts along with single glass-microelectrode and ECG-recordings. MCT-injected rats developed severe PH by day 21 and progressed to RVF by approximately day 30. Rats manifested increased mortality, and ≈30% rats died suddenly and precipitously during 23-32 days after MCT. This fatal period was associated with the initiation of spontaneous VF by a focal mechanism in the RV, which was subsequently maintained by both focal and incomplete reentrant wave fronts. Microelectrode recordings from the RV-epicardium at the onset of focal activity showed early afterdepolarization-mediated triggered activity that led to VF. The onset of the RV cellular triggered beats preceded left ventricular depolarizations by 23±8 ms. The RV but not the left ventricular cardiomyocytes isolated during this fatal period manifested significant action potential duration prolongation, dispersion, and an increased susceptibility to depolarization-induced repetitive activity. No spontaneous VF was observed in any of the control hearts. RVF was associated with significantly reduced RV ejection fraction (P<0.001), RV hypertrophy (P<0.001), and RV fibrosis (P<0.01). The hemodynamic function of the LV and its structure were preserved. CONCLUSIONS PH-induced RVF is associated with a distinct phase of increased mortality characterized by spontaneous VF arising from the RV by an early afterdepolarization-mediated triggered activity.
Collapse
Affiliation(s)
- Soban Umar
- Department of Anesthesiology, UCLA School of Medicine, BH-160CHS, 650 Charles Young Dr, Los Angeles, CA 90095-7115, USA.
| | | | | | | | | | | | | | | | | | | | | | | |
Collapse
|
35
|
Numata A, Miyauchi Y, Ono N, Fishbein MC, Mandel WJ, Lin SF, Weiss JN, Chen PS, Karagueuzian HS. Spontaneous atrial fibrillation initiated by tyramine in canine atria with increased sympathetic nerve sprouting. J Cardiovasc Electrophysiol 2011; 23:415-22. [PMID: 22034958 DOI: 10.1111/j.1540-8167.2011.02197.x] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
BACKGROUND Chronic left ventricular myocardial infarction (LVMI) promotes atrial and pulmonary veins (PV) sympathetic nerve sprouting. OBJECTIVES To test the hypothesis that sympathetic stimulation with tyramine initiates atrial fibrillation (AF) by early after depolarization (EAD)-mediated triggered activity at the left atrial PV (LAPV) junction. METHODS LVMI was created in 6 dogs and 6 dogs served as controls. Six to 8 weeks later the activation pattern of the isolated LAPV was optically mapped using dual voltage and intracellular Ca(+2) (Ca(i) (2+) )-sensitive epifluorescent dyes before and after tyramine (5 μM) perfusion. RESULTS Tyramine initiated spontaneous AF in 5 of 6 atria but none in the control group (P < 0.01). The AF was initiated by late phase 3 EAD-mediated triggered activity that arose from the LAPV junction causing functional conduction block in LA, reentry, and AF. The AF was subsequently maintained by mixed reentrant and focal mechanisms. The EADs arose during the late phase 3, when the Ca(i) (2+) level was 64 ± 12% of the peak systolic Ca(i) (2+) transient amplitude, a property caused by tyramine's simultaneous shortening of the action potential duration and lengthening of the Ca(i) (2+) transient duration in the LVMI group but not in the control. Tyrosine hydroxylase and growth associated protein 43 positive nerve sprouts were significantly increased in the sinus node, LAA, and the LSPV in the LVMI group compared to control (P < 0.01). CONCLUSIONS Increased atrial sympathetic nerve sprouts after LVMI makes the LAPV junction susceptible to late phase 3 EAD-mediated triggered and AF during sympathetic stimulation with tyramine.
Collapse
Affiliation(s)
- Ayaka Numata
- Division of Cardiovascular Medicine, Ohashi Medical Center, Toho University, Tokyo, Japan
| | | | | | | | | | | | | | | | | |
Collapse
|
36
|
Tsuji Y, Hojo M, Voigt N, El-Armouche A, Inden Y, Murohara T, Dobrev D, Nattel S, Kodama I, Kamiya K. Ca
2+
-Related Signaling and Protein Phosphorylation Abnormalities Play Central Roles in a New Experimental Model of Electrical Storm. Circulation 2011; 123:2192-203. [DOI: 10.1161/circulationaha.110.016683] [Citation(s) in RCA: 51] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Affiliation(s)
- Yukiomi Tsuji
- From the Department of Cardiovascular Research, Research Institute of Environmental Medicine, Nagoya University (Y.T., M.H., I.K., K.K.), and Department of Cardiology, Nagoya Graduate School of Medicine (Y.I., T.M.), Nagoya, Japan; Department of Pharmacology, University Medical Center Göttingen of the Georg-August Universität, Göttingen, Germany (A.E.-A.); Department of Pharmacology and Toxicology, Dresden University of Technology, Dresden, Germany (N.V., D.D.); Division of Experimental Cardiology,
| | - Mayumi Hojo
- From the Department of Cardiovascular Research, Research Institute of Environmental Medicine, Nagoya University (Y.T., M.H., I.K., K.K.), and Department of Cardiology, Nagoya Graduate School of Medicine (Y.I., T.M.), Nagoya, Japan; Department of Pharmacology, University Medical Center Göttingen of the Georg-August Universität, Göttingen, Germany (A.E.-A.); Department of Pharmacology and Toxicology, Dresden University of Technology, Dresden, Germany (N.V., D.D.); Division of Experimental Cardiology,
| | - Niels Voigt
- From the Department of Cardiovascular Research, Research Institute of Environmental Medicine, Nagoya University (Y.T., M.H., I.K., K.K.), and Department of Cardiology, Nagoya Graduate School of Medicine (Y.I., T.M.), Nagoya, Japan; Department of Pharmacology, University Medical Center Göttingen of the Georg-August Universität, Göttingen, Germany (A.E.-A.); Department of Pharmacology and Toxicology, Dresden University of Technology, Dresden, Germany (N.V., D.D.); Division of Experimental Cardiology,
| | - Ali El-Armouche
- From the Department of Cardiovascular Research, Research Institute of Environmental Medicine, Nagoya University (Y.T., M.H., I.K., K.K.), and Department of Cardiology, Nagoya Graduate School of Medicine (Y.I., T.M.), Nagoya, Japan; Department of Pharmacology, University Medical Center Göttingen of the Georg-August Universität, Göttingen, Germany (A.E.-A.); Department of Pharmacology and Toxicology, Dresden University of Technology, Dresden, Germany (N.V., D.D.); Division of Experimental Cardiology,
| | - Yasuya Inden
- From the Department of Cardiovascular Research, Research Institute of Environmental Medicine, Nagoya University (Y.T., M.H., I.K., K.K.), and Department of Cardiology, Nagoya Graduate School of Medicine (Y.I., T.M.), Nagoya, Japan; Department of Pharmacology, University Medical Center Göttingen of the Georg-August Universität, Göttingen, Germany (A.E.-A.); Department of Pharmacology and Toxicology, Dresden University of Technology, Dresden, Germany (N.V., D.D.); Division of Experimental Cardiology,
| | - Toyoaki Murohara
- From the Department of Cardiovascular Research, Research Institute of Environmental Medicine, Nagoya University (Y.T., M.H., I.K., K.K.), and Department of Cardiology, Nagoya Graduate School of Medicine (Y.I., T.M.), Nagoya, Japan; Department of Pharmacology, University Medical Center Göttingen of the Georg-August Universität, Göttingen, Germany (A.E.-A.); Department of Pharmacology and Toxicology, Dresden University of Technology, Dresden, Germany (N.V., D.D.); Division of Experimental Cardiology,
| | - Dobromir Dobrev
- From the Department of Cardiovascular Research, Research Institute of Environmental Medicine, Nagoya University (Y.T., M.H., I.K., K.K.), and Department of Cardiology, Nagoya Graduate School of Medicine (Y.I., T.M.), Nagoya, Japan; Department of Pharmacology, University Medical Center Göttingen of the Georg-August Universität, Göttingen, Germany (A.E.-A.); Department of Pharmacology and Toxicology, Dresden University of Technology, Dresden, Germany (N.V., D.D.); Division of Experimental Cardiology,
| | - Stanley Nattel
- From the Department of Cardiovascular Research, Research Institute of Environmental Medicine, Nagoya University (Y.T., M.H., I.K., K.K.), and Department of Cardiology, Nagoya Graduate School of Medicine (Y.I., T.M.), Nagoya, Japan; Department of Pharmacology, University Medical Center Göttingen of the Georg-August Universität, Göttingen, Germany (A.E.-A.); Department of Pharmacology and Toxicology, Dresden University of Technology, Dresden, Germany (N.V., D.D.); Division of Experimental Cardiology,
| | - Itsuo Kodama
- From the Department of Cardiovascular Research, Research Institute of Environmental Medicine, Nagoya University (Y.T., M.H., I.K., K.K.), and Department of Cardiology, Nagoya Graduate School of Medicine (Y.I., T.M.), Nagoya, Japan; Department of Pharmacology, University Medical Center Göttingen of the Georg-August Universität, Göttingen, Germany (A.E.-A.); Department of Pharmacology and Toxicology, Dresden University of Technology, Dresden, Germany (N.V., D.D.); Division of Experimental Cardiology,
| | - Kaichiro Kamiya
- From the Department of Cardiovascular Research, Research Institute of Environmental Medicine, Nagoya University (Y.T., M.H., I.K., K.K.), and Department of Cardiology, Nagoya Graduate School of Medicine (Y.I., T.M.), Nagoya, Japan; Department of Pharmacology, University Medical Center Göttingen of the Georg-August Universität, Göttingen, Germany (A.E.-A.); Department of Pharmacology and Toxicology, Dresden University of Technology, Dresden, Germany (N.V., D.D.); Division of Experimental Cardiology,
| |
Collapse
|
37
|
Lou Q, Fedorov VV, Glukhov AV, Moazami N, Fast VG, Efimov IR. Transmural heterogeneity and remodeling of ventricular excitation-contraction coupling in human heart failure. Circulation 2011; 123:1881-90. [PMID: 21502574 DOI: 10.1161/circulationaha.110.989707] [Citation(s) in RCA: 123] [Impact Index Per Article: 9.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
BACKGROUND Excitation-contraction (EC) coupling is altered in end-stage heart failure. However, spatial heterogeneity of this remodeling has not been established at the tissue level in failing human heart. The objective of this article was to study functional remodeling of excitation-contraction coupling and calcium handling in failing and nonfailing human hearts. METHODS AND RESULTS We simultaneously optically mapped action potentials and calcium transients in coronary perfused left ventricular wedge preparations from nonfailing (n=6) and failing (n=5) human hearts. Our major findings are the following. First, calcium transient duration minus action potential duration was longer at subendocardium in failing compared with nonfailing hearts during bradycardia (40 bpm). Second, the transmural gradient of calcium transient duration was significantly smaller in failing hearts compared with nonfailing hearts at fast pacing rates (100 bpm). Third, calcium transient in failing hearts had a flattened plateau at the midmyocardium and exhibited a 2-component slow rise at the subendocardium in 3 failing hearts. Fourth, calcium transient relaxation was slower at the subendocardium than at the subepicardium in both groups. Protein expression of sarcoplasmic reticulum Ca(2+)-ATPase 2a was lower at the subendocardium than the subepicardium in both nonfailing and failing hearts. Sarcoplasmic reticulum Ca(2+)-ATPase 2a protein expression at subendocardium was lower in hearts with ischemic cardiomyopathy compared with those with nonischemic cardiomyopathy. CONCLUSIONS For the first time, we present direct experimental evidence of transmural heterogeneity of excitation-contraction coupling and calcium handling in human hearts. End-stage heart failure is associated with the heterogeneous remodeling of excitation-contraction coupling and calcium handling.
Collapse
Affiliation(s)
- Qing Lou
- Department of Biomedical Engineering, Washington University, St. Louis, MO, USA
| | | | | | | | | | | |
Collapse
|
38
|
Wu TJ, Lin SF, Hsieh YC, Lin TC, Lin JC, Ting CT. Pretreatment of BAPTA-AM suppresses the genesis of repetitive endocardial focal discharges and pacing-induced ventricular arrhythmia during global ischemia. J Cardiovasc Electrophysiol 2011; 22:1154-62. [PMID: 21489030 DOI: 10.1111/j.1540-8167.2011.02067.x] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
INTRODUCTION In isolated rabbit hearts, repetitive endocardial focal discharges (REFDs) were consistently observed during ventricular fibrillation (VF) with prolonged (>5 minutes) global ischemia (GI). We hypothesized that BAPTA-AM, a calcium chelator, can suppress these REFDs. METHODS AND RESULTS Using a two-camera optical mapping system, we simultaneously mapped endocardial (left ventricle, LV) and epicardial (both ventricles) activations during ventricular arrhythmia with GI. In 5 hearts (protocol I), we infused Tyrode's solution (no BAPTA-AM) for ≥30 minutes before the onset of no-flow GI. In 7 additional hearts (protocol II), BAPTA-AM (20 μmol/L) was infused for ≥30 minutes before the initiation of GI. In protocol I, sustained VF (>30 seconds) was successfully induced in all 5 hearts with prolonged GI. REFDs were present in >85 % of recording time. In protocol II, however, ventricular arrhythmia was not inducible and REFDs were not observed after 5-minute GI in 5 hearts. Effects of BAPTA-AM on intracellular calcium (Ca(i) ) at the LV endocardium were also evaluated in 5 hearts (protocol III) using dual Ca(i) /membrane potential mapping. GI, both without and with BAPTA-AM pretreatment, caused a decrease of Ca(i) amplitude during S(1) pacing. However, this effect was more pronounced in the hearts with BAPTA-AM pretreatment (P < 0.001). GI, without BAPTA-AM pretreatment, caused broadening of Ca(i) transient. In contrast, GI, with BAPTA-AM pretreatment, caused narrowing of Ca(i) transient. CONCLUSIONS BAPTA-AM pretreatment attenuates Ca(i) transient, suppressing the genesis of REFDs and pacing-induced ventricular arrhythmia during GI. These findings support the notion that Ca(i) dynamics is important in the maintenance of REFDs.
Collapse
Affiliation(s)
- Tsu-Juey Wu
- Cardiovascular Center, Taichung Veterans General Hospital and Department of Internal Medicine, Faculty of Medicine, Institute of Clinical Medicine, Cardiovascular Research Center, National Yang-Ming University School of Medicine, Taipei, Taiwan.
| | | | | | | | | | | |
Collapse
|
39
|
Morita N, Lee JH, Bapat A, Fishbein MC, Mandel WJ, Chen PS, Weiss JN, Karagueuzian HS. Glycolytic inhibition causes spontaneous ventricular fibrillation in aged hearts. Am J Physiol Heart Circ Physiol 2011; 301:H180-91. [PMID: 21478408 DOI: 10.1152/ajpheart.00128.2011] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
Selective glycolytic inhibition (GI) promotes electromechanical alternans and triggered beats in isolated cardiac myocytes. We sought to determine whether GI promotes triggered activity by early afterdepolarization (EAD) or delayed afterdepolarizations in intact hearts isolated from adult and aged rats. Dual voltage and intracellular calcium ion (Ca(i)(2+)) fluorescent optical maps and single cell glass microelectrode recordings were made from the left ventricular (LV) epicardium of isolated Langendorff-perfused adult (∼4 mo) and aged (∼24 mo) rat hearts. GI was induced by replacing glucose with 10 mM pyruvate in oxygenated Tyrode's. Within 20 min, GI slowed Ca(i)(2+) transient decline rate and shortened action potential duration in both groups. These changes were associated with ventricular fibrillation (VF) in the aged hearts (64 out of 66) but not in adult hearts (0 out of 18; P < 0.001). VF was preceded by a transient period of focal ventricular tachycardia caused by EAD-mediated triggered activity leading to VF within seconds. The VF was suppressed by the ATP-sensitive K (K(ATP)) channel blocker glibenclamide (1 μM) but not (0 out of 7) by mitochondrial K(ATP) block. The Ca-calmodulin-dependent protein kinase II (CaMKII) blocker KN-93 (1 μM) prevented GI-mediated VF (P < 0.05). Block of Na-Ca exchanger (NCX) by SEA0400 (2 μM) prevented GI-mediated VF (3 out of 6), provided significant bradycardia did not occur. Aged hearts had significantly greater LV fibrosis and reduced connexin 43 than adult hearts (P < 0.05). We conclude that in aged fibrotic unlike in adult rat hearts, GI promotes EADs, triggered activity, and VF by activation of K(ATP) channels CaMKII and NCX.
Collapse
Affiliation(s)
- Norishige Morita
- Translational Arrhythmia Research Section, Cardiovascular Research Laboratory, David Geffen School of Medicine at UCLA, 675 Charles E. Young Dr. South, MRL 3645 Mail Code: 176022, Los Angeles, CA 90095, USA
| | | | | | | | | | | | | | | |
Collapse
|
40
|
Antzelevitch C, Burashnikov A. Overview of Basic Mechanisms of Cardiac Arrhythmia. Card Electrophysiol Clin 2011; 3:23-45. [PMID: 21892379 DOI: 10.1016/j.ccep.2010.10.012] [Citation(s) in RCA: 203] [Impact Index Per Article: 15.6] [Reference Citation Analysis] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
|
41
|
Chua SK, Chang PC, Maruyama M, Turker I, Shinohara T, Shen MJ, Chen Z, Shen C, Rubart-von der Lohe M, Lopshire JC, Ogawa M, Weiss JN, Lin SF, Ai T, Chen PS. Small-conductance calcium-activated potassium channel and recurrent ventricular fibrillation in failing rabbit ventricles. Circ Res 2011; 108:971-9. [PMID: 21350217 DOI: 10.1161/circresaha.110.238386] [Citation(s) in RCA: 135] [Impact Index Per Article: 10.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
RATIONALE Fibrillation/defibrillation episodes in failing ventricles may be followed by action potential duration (APD) shortening and recurrent spontaneous ventricular fibrillation (SVF). OBJECTIVE We hypothesized that activation of apamin-sensitive small-conductance Ca(2+)-activated K(+) (SK) channels is responsible for the postshock APD shortening in failing ventricles. METHODS AND RESULTS A rabbit model of tachycardia-induced heart failure was used. Simultaneous optical mapping of intracellular Ca(2+) and membrane potential (V(m)) was performed in failing and nonfailing ventricles. Three failing ventricles developed SVF (SVF group); 9 did not (no-SVF group). None of the 10 nonfailing ventricles developed SVF. Increased pacing rate and duration augmented the magnitude of APD shortening. Apamin (1 μmol/L) eliminated recurrent SVF and increased postshock APD(80) in the SVF group from 126±5 to 153±4 ms (P<0.05) and from 147±2 to 162±3 ms (P<0.05) in the no-SVF group but did not change APD(80) in nonfailing group. Whole cell patch-clamp studies at 36°C showed that the apamin-sensitive K(+) current (I(KAS)) density was significantly larger in the failing than in the normal ventricular epicardial myocytes, and epicardial I(KAS) density was significantly higher than midmyocardial and endocardial myocytes. Steady-state Ca(2+) response of I(KAS) was leftward-shifted in the failing cells compared with the normal control cells, indicating increased Ca(2+) sensitivity of I(KAS) in failing ventricles. The K(d) was 232±5 nmol/L for failing myocytes and 553±78 nmol/L for normal myocytes (P=0.002). CONCLUSIONS Heart failure heterogeneously increases the sensitivity of I(KAS) to intracellular Ca(2+), leading to upregulation of I(KAS), postshock APD shortening, and recurrent SVF.
Collapse
Affiliation(s)
- Su-Kiat Chua
- Krannert Institute of Cardiology, Division of Cardiology, Indiana University School of Medicine, Indianapolis, USA
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | |
Collapse
|
42
|
Maruyama M, Lin SF, Xie Y, Chua SK, Joung B, Han S, Shinohara T, Shen MJ, Qu Z, Weiss JN, Chen PS. Genesis of phase 3 early afterdepolarizations and triggered activity in acquired long-QT syndrome. Circ Arrhythm Electrophysiol 2010; 4:103-11. [PMID: 21078812 DOI: 10.1161/circep.110.959064] [Citation(s) in RCA: 81] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
BACKGROUND Both phase 2 and phase 3 early afterdepolarizations (EADs) occur in long-QT syndromes, but their respective roles in generating arrhythmias in intact cardiac tissue are incompletely understood. METHODS AND RESULTS Intracellular Ca (Ca(i)) and membrane voltage (V(m)) were optically mapped in a quasi 2-dimensional model of cryoablated Langendorff-perfused rabbit ventricles (n=16). E-4031 (an I(Kr) blocker) combined with reduced extracellular K ([K(+)](o)) and Mg ([Mg(2+)](o)) prolonged action potential duration heterogeneously and induced phase 2 and phase 3 EADs. Whereas phase 2 EADs were Ca(i)-dependent, phase 3 EADs were not. The origins of 47 triggered activity episodes were attributed to phase 2 EADs in 12 episodes (26%) and phase 3 EADs in 35 episodes (74%). When phase 2 EADs accompanied phase 3 EADs, they accentuated action potential duration heterogeneity, creating a large V(m) gradient across the boundary between long and short action potential duration regions from which triggered activity emerged. The amplitude of phase 3 EADs correlated with the V(m) gradient (r=0.898, P<0.001). Computer simulation studies showed that coupling of cells with heterogeneous repolarization could extrinsically generate phase 3 EADs via electrotonic current flow. Alternatively, reduced I(K1) caused by low [K(+)](o) could generate intrinsic phase 3 EADs capable of inducing triggered activity at the boundary zone. CONCLUSIONS Phase 3 EADs can be extrinsic as the result of electrotonic current across steep repolarization gradients or intrinsic as the result of low I(K1) and do not require spontaneous sarcoplasmic reticulum Ca release. Reduction of I(K1) by low [K(+)](o) strongly promotes ventricular arrhythmias mediated by phase 3 EADs in acquired long-QT syndrome caused by I(Kr) blockade.
Collapse
Affiliation(s)
- Mitsunori Maruyama
- Krannert Institute of Cardiology and the Division of Cardiology, Department of Medicine, Indiana University School of Medicine, Indianapolis, IN, USA
| | | | | | | | | | | | | | | | | | | | | |
Collapse
|
43
|
Maruyama M, Joung B, Tang L, Shinohara T, On YK, Han S, Choi EK, Kim DH, Shen MJ, Weiss JN, Lin SF, Chen PS. Diastolic intracellular calcium-membrane voltage coupling gain and postshock arrhythmias: role of purkinje fibers and triggered activity. Circ Res 2009; 106:399-408. [PMID: 19926871 DOI: 10.1161/circresaha.109.211292] [Citation(s) in RCA: 73] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
RATIONALE Recurrent ventricular arrhythmias after initial successful defibrillation are associated with poor clinical outcome. OBJECTIVE We tested the hypothesis that postshock arrhythmias occur because of spontaneous sarcoplasmic reticulum Ca release, delayed afterdepolarization (DAD), and triggered activity (TA) from tissues with high sensitivity of resting membrane voltage (V(m)) to elevated intracellular calcium (Ca(i)) (high diastolic Ca(i)-voltage coupling gains). METHODS AND RESULTS We simultaneously mapped Ca(i) and V(m) on epicardial (n=14) or endocardial (n=14) surfaces of Langendorff-perfused rabbit ventricles. Spontaneous Ca(i) elevation (SCaE) was noted after defibrillation in 32% of ventricular tachycardia/ventricular fibrillation at baseline and in 81% during isoproterenol infusion (0.01 to 1 micromol/L). SCaE was reproducibly induced by rapid ventricular pacing and inhibited by 3 mumol/L of ryanodine. The SCaE amplitude and slope increased with increasing pacing rate, duration, and dose of isoproterenol. We found TAs originating from 6 of 14 endocardial surfaces but none from epicardial surfaces, despite similar amplitudes and slopes of SCaEs between epicardial and endocardial surfaces. This was because DADs were larger on endocardial surfaces as a result of higher diastolic Ca(i)-voltage coupling gain, compared to those of epicardial surfaces. Purkinje-like potentials preceded TAs in all hearts studied (n=7). I(K1) suppression with CsCl (5 mmol/L, n=3), BaCl(2) (3 micromol/L, n=3), and low extracellular potassium (1 mmol/L, n=2) enhanced diastolic Ca(i)-voltage coupling gain and enabled epicardium to also generate TAs. CONCLUSIONS Higher diastolic Ca(i)-voltage coupling gain is essential for genesis of TAs and may underlie postshock arrhythmias arising from Purkinje fibers. I(K)(1) is a major factor that determines the diastolic Ca(i)-voltage coupling gain.
Collapse
Affiliation(s)
- Mitsunori Maruyama
- Krannert Institute of Cardiology and the Division of Cardiology, Department of Medicine, Indiana University School of Medicine, Indianapolis, USA
| | | | | | | | | | | | | | | | | | | | | | | |
Collapse
|
44
|
Cell calcium, repolarization changes, and spontaneous postshock fibrillation in failing hearts: Causes of refibrillation and electrical storm. Heart Rhythm 2009; 6:793-5. [DOI: 10.1016/j.hrthm.2009.03.019] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/10/2009] [Indexed: 11/20/2022]
|