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YAMABE HIROSHIGE, TANAKA YASUAKI, MORIHISA KENJI, UEMURA TAKASHI, KOYAMA JUNJIROH, KANAZAWA HISANORI, HOSHIYAMA TADASHI, OGAWA HISAO. Electrophysiologic Mechanism of Typical Atrial Flutter Termination by Nifekalant: Effect of a Pure IKr-Selective Blocking Agent. Pacing Clin Electrophysiol 2013; 36:1123-31. [DOI: 10.1111/pace.12147] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/05/2013] [Revised: 01/31/2013] [Accepted: 02/15/2013] [Indexed: 12/12/2022]
Affiliation(s)
- HIROSHIGE YAMABE
- Department of Cardiovascular Medicine; Graduate School of Medical Sciences; Kumamoto University; Kumamoto Japan
| | - YASUAKI TANAKA
- Department of Cardiovascular Medicine; Graduate School of Medical Sciences; Kumamoto University; Kumamoto Japan
| | - KENJI MORIHISA
- Department of Cardiovascular Medicine; Graduate School of Medical Sciences; Kumamoto University; Kumamoto Japan
| | - TAKASHI UEMURA
- Department of Cardiovascular Medicine; Graduate School of Medical Sciences; Kumamoto University; Kumamoto Japan
| | - JUNJIROH KOYAMA
- Department of Cardiovascular Medicine; Graduate School of Medical Sciences; Kumamoto University; Kumamoto Japan
| | - HISANORI KANAZAWA
- Department of Cardiovascular Medicine; Graduate School of Medical Sciences; Kumamoto University; Kumamoto Japan
| | - TADASHI HOSHIYAMA
- Department of Cardiovascular Medicine; Graduate School of Medical Sciences; Kumamoto University; Kumamoto Japan
| | - HISAO OGAWA
- Department of Cardiovascular Medicine; Graduate School of Medical Sciences; Kumamoto University; Kumamoto Japan
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Miake J, Kurata Y, Iizuka K, Furuichi H, Manabe K, Sasaki N, Yamamoto Y, Hoshikawa Y, Taniguchi SI, Yoshida A, Igawa O, Makita N, Shiota G, Nanba E, Ohgi S, Narahashi T, Hisatome I. State-Dependent Blocking Actions of Azimilide Dihydrochlo-ride (NE-10064) on Human Cardiac Na+ Channels. Circ J 2004; 68:703-11. [PMID: 15226638 DOI: 10.1253/circj.68.703] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
BACKGROUND Azimilide reportedly blocks Na(+) channels, although its mechanism remains unclear. METHODS AND RESULTS The kinetic properties of the azimilide block of the wild-type human Na(+) channels (WT: hH1) and mutant DeltaKPQ Na(+) channels (DeltaKPQ) expressed in COS7 cells were investigated using the whole-cell patch clamp technique and a Markovian state model. Azimilide induced tonic block of WT currents by shifting the h infinity curve in the hyperpolarizing direction and caused phasic block of WT currents with intermediate recovery time constant. The peak and steady-state DeltaKPQ currents were blocked by azimilide, although with only a slight shift in the h infinity curve. The phasic block of peak and steady-state DeltaKPQ currents by azimilide was significantly larger than the blocking of the peak WT current. The affinity of azimilide predicted by a Markovian state model was higher for both the activated state (Kd(A) =1.4 micromol/L), and the inactivated state (Kd(I) =1.4 micromol/L), of WT Na(+) channels than that for the resting state (Kd(R) =102.6 micromol/L). CONCLUSIONS These experimental and simulation studies suggest that azimilide blocks the human cardiac Na(+) channel in both the activated and inactivated states.
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Affiliation(s)
- Junichiro Miake
- Department of Cardiovascular Medicine, Tottori University Hospital, Tottori, Japan
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Vereckei A, Zipes DP, Besch H. Combined amiodarone and silymarin treatment, but not amiodarone alone, prevents sustained atrial flutter in dogs. J Cardiovasc Electrophysiol 2003; 14:861-7. [PMID: 12890050 DOI: 10.1046/j.1540-8167.2003.02446.x] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
UNLABELLED Amiodarone/Silymarin Treatment for Sustained Atrial Flutter. INTRODUCTION Because amiodarone generates free radicals that may mediate amiodarone's toxicity, simultaneous therapy with an antioxidant might be beneficial if the antioxidant did not impair amiodarone's antiarrhythmic action. We tested whether simultaneous administration of a flavonoid antioxidant, silymarin, altered the electrophysiologic (EP) actions of amiodarone in 62 open chest dogs with electrically induced atrial flutter created by a Y-shaped right atrial incision. METHODS AND RESULTS Fifteen dogs received oral amiodarone (600 mg/day); 15 dogs received amiodarone (600 mg/day) and silymarin (70 mg bid); and 8 dogs received silymarin (70 mg bid) alone. All dosing was for 8 weeks; 24 control dogs received no drugs prior to induction of atrial flutter. Atrial flutter was induced by rapid right atrial pacing, and EP measurements were made before (presurgical) and after (postsurgical) creation of a Y-shaped right atrial incision. There was no difference in the frequency of induction of atrial flutter lasting >30 minutes among amiodarone-treated (8/15 [53%]), silymarin-treated (4/6 [67%]), and control (15/21 [71%]) groups, whereas the frequency of induction in the amiodarone+silymarin dogs (2/15 [13%]) was significantly reduced (P = 0.008) compared with the other three groups. Both amiodarone and amiodarone+silymarin treatment prolonged the presurgical and postsurgical right atrial effective refractory period (P = 0.012) compared with control; however, there was no significant difference in either parameter between the amiodarone+silymarin-treated and amiodarone-treated groups. The increase in atrial flutter mean cycle length (postsurgical minus presurgical) was significantly (P = 0.005) less in the amiodarone+silymarin-treated and control dogs compared with the amiodarone-treated dogs (16 +/- 11 msec for amiodarone+silymarin; 24 +/- 8 msec for control; and 42 +/- 14 msec for amiodarone treatment). Amiodarone+silymarin treatment resulted in a longer postsurgical right atrial refractory period (155 +/- 13 msec) than atrial flutter mean cycle length (154 +/- 19 msec), consistent with reduction and/or elimination of the excitable gap. Silymarin alone did not exert significant EP or antiarrhythmic action. CONCLUSION Amiodarone exerted no preventative antiarrhythmic action in this atrial flutter model, probably because it could not reduce the excitable gap of atrial flutter. However, an antioxidant, silymarin, without a direct antiarrhythmic action, when administered together with amiodarone, potentiated amiodarone's antiarrhythmic actions and prevented sustained atrial flutter by reduction and/or elimination of the excitable gap.
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Affiliation(s)
- András Vereckei
- Department of Medicine, Indiana University, School of Medicine and the Roudebush Veterans Administration Medical Center, Indianapolis Indiana 46202, USA
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Chen F, Esmailian F, Sun W, Wetzel GT, Sarma JSM, Singh BN, Klitzner TS. Azimilide inhibits multiple cardiac potassium currents in human atrial myocytes. J Cardiovasc Pharmacol Ther 2002; 7:255-64. [PMID: 12490972 DOI: 10.1177/107424840200700409] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
BACKGROUND Studies in animal cell preparations suggest that azimilide may produce a more desirable rate-dependent profile of class III action as a result of its effects on both the slowly (I(Ks)) and rapidly (I(Kr)) activating components of potassium current (I(K)). However, relatively little is known about the effects of azimilide on K(+) currents in human atrial cells. The present study investigated the effect of azimilide on the inward rectifier potassium current (I(K1)), delayed rectifier potassium current (I(K)), ultrarapid delayed rectifier current (I(Kur)), and transient outward potassium current (I(to)) in isolated single human atrial myocytes. METHODS The tight-seal, whole-cell voltage clamp technique was used to investigate the acute effects of azimilide on K(+) currents in single human atrial myocytes. The cells were isolated enzymatically from atrial tissues that were obtained from patients undergoing open-heart surgeries, with the approval of the local Institutional Review Board. RESULTS The average cell capacitance of the human atrial myocytes was 77.5 +/- 2.8 pF (Mean +/- standard error of mean, total 28 cells from 17 patients). We found that 100 microM of azimilide in the extracellular solution significantly inhibited the inward rectifier potassium current (12.3 +/- 3.1 vs 6.7 +/- 2.0 pA/pF, n = 12, P < 0.05) at the testing potential of -100 mV. Superfusion with 100 microM of azimilide for 10 minutes inhibited I(K) by 51.7 +/- 5.1% (from 3.4 +/- 0.5 to 1.6 +/- 0.2 pA/pF, n = 9, P < 0.01) at the clamping membrane potential of +40 mV. Human atrial cell I(Kur) was inhibited with 100 microM of azimilide by 38.6 +/- 4.4% (from 3.9 +/- 0.5 to 2.3 +/- 0.2 pA/pF, n = 9, P < 0.01, test potential = 40 mV). We also found that the average peak current amplitude of I(to) in these cells was significantly inhibited with 100 microM of azimilide by 60.3 +/- 5.9% (from 10.3 +/- 1.5 to 3.6 +/- 0.3 pA/pF, n = 6, P < 0.01, test potential = 50 mV). CONCLUSION The present study provides direct evidence that azimilide inhibits multiple cellular transmembrane K(+) currents in freshly isolated human atrial myocytes. Inhibition of these K(+) currents by azimilide, especially of I(Ks) and I(Kur) is likely to be the electrophysiologic basis for the prolongation of the action potential duration in the human atria which mediates its known antifibrillatory effects in atrial fibrillation and flutter.
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Affiliation(s)
- Fuhua Chen
- Department of Pediatrics, University of California at Los Angeles, School of Medicine, Los Angeles, CA 90095, USA
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Nagasawa H, Fujiki A, Fujikura N, Matsuda T, Yamashita T, Inoue H. Effects of a novel class III antiarrhythmic agent, NIP-142, on canine atrial fibrillation and flutter. Circ J 2002; 66:185-91. [PMID: 11999646 DOI: 10.1253/circj.66.185] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
The effects of a new benzopyran derivative, NIP-142, on atrial fibrillation (AF) and flutter (AFL) and on electrophysiological variables were studied in the dog. NIP-142 (3mg/kg) was administered intravenously to pentobarbital-anesthetized beagles during vagally-induced AF and during AFL induced after placement of an intercaval crush. Isolated canine atrial tissues were studied using standard microelectrode technique. NIP-142 terminated AF in 5 of 6 dogs after an increase in fibrillation cycle length (CL) and prevented reinitiation of AF in all 6 dogs. NIP-142 terminated AFL in all 6 dogs without any appreciable change in flutter CL, and prevented reinitiation of AFL in all 6 dogs. NIP-142 prolonged atrial effective refractory periods (11+/-5%, 3+/-3%, 12+/-3%, and 10+/-5% from the baseline value at basic CLs of 150, 200, 300, and 350ms, respectively) without changes in intraatrial conduction time. The prolongation of the atrial effective refractory period was greater in the presence of vagal stimulation. NIP-142 decreased action potential phase-1 notch and increased phase-2 plateau height without making any changes in the action potential duration, although it did reverse carbachol-induced shortening of the action potential duration. In conclusion, NIP-142 is effective in treating AFL and vagally-induced AF by prolonging atrial refractoriness.
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Affiliation(s)
- Hidehiko Nagasawa
- The Second Department of Internal Medicine, Toyama Medical and Pharmaceutical University, Japan
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Brooks RR, Pong SF, Izzo NJ, Moorehead TJ, Gopalakrishnan M, Triggle DJ. Interaction of azimilide with neurohumoral and channel receptors. Biochem Pharmacol 2001; 62:883-92. [PMID: 11543723 DOI: 10.1016/s0006-2952(01)00737-7] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
Abstract
Binding of the class III antiarrhythmic agent azimilide to brain, heart, and other organ receptors was assessed by standard radioligand binding techniques. In a survey of 60 receptors, azimilide at 10 microM inhibited binding by more than 50% at serotonin uptake (K(i): 0.6 microM), muscarinic (K(i): 0.9 to -3.0 microM), Na(+) channel site 2 (K(i): 4.3 microM), and central sigma (K(i): 6.2 microM) sites. Lesser (20-40%) inhibition was seen at adrenergic, histamine, serotonin, purinergic, angiotensin II, dopamine uptake, and norepinephrine sites and at a voltage-sensitive K(+) channel. In rat ventricle, azimilide inhibited binding to alpha(1)- and beta-adrenergic and muscarinic receptors (K(i): < 5 microM) and to the L-type Ca(2+) channel (K(i): 37.3 microM). In rat brain, azimilide blocked ligand binding to these same receptors and to a serotonin receptor, and the breadth and potency of its interaction pattern differentiated it from ten other class III antiarrhythmics. Azimilide displayed agonist and antagonist action at five muscarinic receptor subtypes in transfected NIH 3T3 cells producing receptor-sensitive mitogenesis and beta-galactosidase activity. Agonist action predominated at M(2) and M(4) subtypes, and antagonist action predominated at M(1), M(3), and M(5) subtypes. The azimilide concentration for 50% maximum stimulation (EC(50)) in M(2)-expressing cells was 1.97 microM (vs 0.14 microM for carbachol). Azimilide's receptor interactions occur at concentrations from one to forty times those required to block cardiac delayed-rectifier channels but could contribute to the efficacy and safety of the drug.
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Affiliation(s)
- R R Brooks
- Procter & Gamble Pharmaceuticals, 11810 E. Miami River Rd., Cincinnati, OH 45252, USA.
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Abstract
Azimilide dihydrochloride (Stedicor) is a new class III anti-arrhythmic agent that is being developed by Proctor & Gamble to treat supraventricular and ventricular arrhythmias. Development of this agent is being undertaken due to the high prevalence of atrial fibrillation and the lack of satisfactory therapy for this arrhythmia, along with the desire to develop therapy to reduce the risk of life-threatening ventricular arrhythmias in patients following myocardial infarction. The mechanism of action of azimilide is to block both the slowly conducting (I(Ks)) and rapidly conducting (I(Kr)) rectifier potassium currents in cardiac cells. This differs from other class III agents that block I(Kr) exclusively or in combination with sodium, calcium, or transient outward (I(to)) potassium current channels. Azimilide is distinguished by a relative lack of reverse use-dependence, excellent oral absorption, no need for dose titration, an option for out-patient initiation, no need for adjustment associated with renal or liver failure and a lack of interaction with warfarin or digoxin. It carries some risk of torsade de pointes and rarely, neutropoenia. Azimilide has shown dose-related efficacy in prolonging the time to recurrence of atrial fibrillation. A large trial examining the impact of azimilide on mortality in high-risk patients following myocardial infarction has completed enrolment and should yield data in the next couple of years and further studies are planned. Even if this trial fails to show a survival benefit, a neutral effect on mortality will make the agent attractive for atrial arrhythmias.
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Affiliation(s)
- R Abrol
- University of Texas Southwestern Medical Center, 5323 Harry Hines Blvd., Dallas, TX 75235-9047, USA
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Abstract
Azimilide is a potassium channel antagonist that, in contrast to existing class III antiarrhythmic agents, blocks both the rapidly (I(Kr)) and slowly (I(Ks)) activating components of the delayed rectifier potassium current. In animal and clinical studies, azimilide prolonged repolarisation by increasing the action potential duration and effective refractory period. In animal models, azimilide was effective in terminating both atrial and ventricular arrhythmias. Azimilide also demonstrated antifibrillatory efficacy in a canine model of sudden cardiac death. In patients with a history of atrial fibrillation/flutter, oral azimilide controlled arrhythmias more effectively than placebo in a 6-month randomised double-blind study. At a dosage of 125 mg once daily, azimilide significantly increased the time to first symptomatic recurrence of atrial fibrillation/flutter. However, no significant difference between placebo and azimilide was found in another study. Oral azimilide 100 mg once daily demonstrated clinically significant treatment effects in patients with paroxysmal supraventricular tachycardia. In clinical trials, azimilide was generally well tolerated and headache was the most commonly occurring adverse event. Azimilide is associated with a low incidence of proarrhythmic events, such as torsades de pointes, and few serious adverse events have been reported.
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Affiliation(s)
- D Clemett
- Adis International Limited, Mairangi Bay, Auckland, New Zealand.
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Tai CT, Chen SA, Feng AN, Yu WC, Chen YJ, Chang MS. Electropharmacologic effects of class I and class III antiarrhythmia drugs on typical atrial flutter: insights into the mechanism of termination. Circulation 1998; 97:1935-45. [PMID: 9609087 DOI: 10.1161/01.cir.97.19.1935] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
BACKGROUND Acute effects of class I and class III antiarrhythmia drugs on the reentrant circuit of typical atrial flutter are not fully studied. Furthermore, the critical electrophysiologic determinants of flutter termination by antiarrhythmia drugs are not clear. METHODS AND RESULTS The study population consisted of 36 patients (mean age, 53+/-17 years) with clinically documented typical atrial flutter. A 20-pole "halo" catheter was positioned around the tricuspid annulus. Incremental pacing was performed to measure the conduction velocity along the isthmus and lateral wall, and extrastimulation was performed to evaluate atrial refractory period in the baseline state and after intravenous infusion of ibutilide, propafenone, and amiodarone. Efficacy of these drugs in conversion of typical atrial flutter and patterns of termination were also determined. Ibutilide significantly increased the atrial refractory period and decreased conduction velocity in the isthmus at short pacing cycle length. It terminated atrial flutter in 8 (67%) of 12 patients after prolongation of flutter cycle length due to increase (86+/-19%) of conduction time in the isthmus. Propafenone predominantly decreased conduction velocity with use dependency and significantly increased atrial refractory period, but it only converted atrial flutter in 4 (33%) of 12 patients. Amiodarone had fewer effects on atrial refractory period and conduction velocity than did ibutilide and propafenone, and it terminated atrial flutter in only 4 (33%) of 12 patients. Termination of typical atrial flutter was due to failure of wave front propagation through the isthmus, which occurred with cycle length oscillation, abruptly without variability of cycle length, or after premature activation of the reentrant circuit. CONCLUSIONS Ibutilide, with a unique increase in atrial refractoriness, was more effective in conversion of atrial flutter than were propafenone and amiodarone.
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Affiliation(s)
- C T Tai
- Department of Medicine, National Yang-Ming University, School of Medicine, Veterans General Hospital-Taipei, Taiwan, ROC
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Abstract
Azimilide, a novel class III antiarrhythmic agent, blocks both the slowly activating (IKs) and rapidly activating (IKr) components of the delayed rectifier potassium current, which distinguishes it from conventional potassium channel blockers such as sotalol and dofetilide, which block only IKr. Azimilide is being developed to prolong the time to recurrence of atrial fibrillation, atrial flutter, and paroxysmal supraventricular tachycardia in patients with and without structural heart disease. Azimilide is also being studied for its role in prevention of sudden cardiac death in high-risk patients after myocardial infarction (MI). Preclinical and clinical studies indicate that azimilide prolongs cardiac refractory period in a dose-dependent manner, as manifested by increases in action potential duration, QTc interval, and effective refractory period. Azimilide does not affect PR or QRS interval and minimally affects hemodynamic properties such as blood pressure and heart rate. Its in vivo effects appear to be rate-independent and are maintained under ischemic or hypoxic conditions, properties of potential clinical significance. Azimilide has shown excellent efficacy (>85%) in suppressing supraventricular arrhythmias in a variety of dog models. It also suppressed complex ventricular arrhythmias in infarcted dogs and, in a sudden death cardiac model, decreased mortality. Azimilide pharmacokinetics are very predictable. The drug is completely absorbed, and the extent of absorption is not affected by food. It can be administered once daily. Clinical data suggest that dose adjustments of azimilide are not required for age, gender, hepatic or renal function, or concomitant use of digoxin or warfarin. Azimilide has a good safety profile in open-label safety studies in >800 supraventricular arrhythmia patients, most with structural heart disease. The incidence of serious adverse events, including torsade de pointes, is low. The rate of patient withdrawal from long-term studies is also encouragingly low. Unlike amiodarone, azimilide has shown no evidence of pulmonary or ocular toxicity. Azimilide is expected to provide a unique new therapy for the prevention of supraventricular arrhythmias and sudden cardiac death when Phase III clinical trials are complete and safety and efficacy are confirmed.
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Affiliation(s)
- R Karam
- Procter & Gamble Pharmaceuticals, Cincinnati, Ohio 45061, USA
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Busch AE, Eigenberger B, Jurkiewicz NK, Salata JJ, Pica A, Suessbrich H, Lang F. Blockade of HERG channels by the class III antiarrhythmic azimilide: mode of action. Br J Pharmacol 1998; 123:23-30. [PMID: 9484850 PMCID: PMC1565134 DOI: 10.1038/sj.bjp.0701575] [Citation(s) in RCA: 43] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
1. The class III antiarrhythmic azimilide has previously been shown to inhibit I(Ks) and I(Kr) in guinea-pig cardiac myocytes and I(Ks) (minK) channels expressed in Xenopus oocytes. Because HERG channels underly the conductance I(Kr), in human heart, the effects of azimilide on HERG channels expressed in Xenopus oocytes were the focus of the present study. 2. In contrast to other well characterized HERG channel blockers, azimilide blockade was reverse use-dependent, i.e., the relative block and apparent affinity of azimilide decreased with an increase in channel activation frequency. Azimilide blocked HERG channels at 0.1 and 1 Hz with IC50s of 1.4 microM and 5.2 microM respectively. 3. In an envelope of tail test, HERG channel blockade increased with increasing channel activation, indicating binding of azimilide to open channels. 4. Azimilide blockade of HERG channels expressed in Xenopus oocytes and I(Kr) in mouse AT-1 cells was decreased under conditions of high [K+]e, whereas block of slowly activating I(Ks) channels was not affected by changes in [K+]e. 5. In summary, azimilide is a blocker of cardiac delayed rectifier channels, I(Ks) and HERG. Because of the distinct effects of stimulation frequency and [K+]e on azimilide block of I(Kr) and I(Ks) channels, we conclude that the relative contribution of block of each of these cardiac delayed rectifier channels depends on heart frequency. [K+]e and regulatory status of the respective channels.
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Affiliation(s)
- A E Busch
- Institute of Physiology I, Eberhard-Karls University of Tübingen, Germany
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Tai CT, Chen SA, Chiang CE, Lee SH, Ueng KC, Wen ZC, Huang JL, Chen YJ, Yu WC, Feng AN, Chiou CW, Chang MS. Characterization of low right atrial isthmus as the slow conduction zone and pharmacological target in typical atrial flutter. Circulation 1997; 96:2601-11. [PMID: 9355900 DOI: 10.1161/01.cir.96.8.2601] [Citation(s) in RCA: 62] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
BACKGROUND Previous electrophysiological studies in patients with typical atrial flutter suggested that the slow conduction zone might be located in the low right atrial isthmus, which is a path formed by orifice of inferior vena cava, eustachian valve/ridge, coronary sinus ostium, and tricuspid annulus. The conduction characteristics during atrial pacing and responses to antiarrhythmic drugs of this anatomic isthmus were unknown. METHODS AND RESULTS Forty-four patients, 20 patients with paroxysmal supraventricular tachycardia (group 1) and 24 patients with clinically documented paroxysmal typical atrial flutter (group 2), were studied. A 20-pole halo catheter was situated around the tricuspid annulus. Incremental pacing from the low right atrium and coronary sinus ostium was performed to measure the conduction time and velocity along the isthmus and lateral wall in the baseline state and after intravenous infusion of procainamide or sotalol. In both groups, conduction velocity in the isthmus during incremental pacing was significantly lower than that in the lateral wall before and after infusion of antiarrhythmic drugs. Furthermore, gradual conduction delay with unidirectional block in the isthmus was relevant to initiation of typical atrial flutter. Compared with group 1, group 2 had a lower conduction velocity in the isthmus and shorter right atrial refractory period. Procainamide significantly decreased the conduction velocity, but sotalol did not change it. In contrast, sotalol significantly prolonged the atrial refractory period with a higher extent than procainamide. After infusion of procainamide, the increase of conduction time in the isthmus accounted for 52+/-19% of the increase in flutter cycle length, and 5 of 12 patients (42%) had spontaneous termination of typical flutter. After infusion of sotalol, typical flutter was induced in only 6 of 12 patients (50%) without significant prolongation of flutter cycle length. CONCLUSIONS The low right atrial isthmus with rate-dependent slow conduction properties is critical to initiation of typical human atrial flutter. It may be the potentially pharmacological target of antiarrhythmic drugs in the future.
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Affiliation(s)
- C T Tai
- Department of Medicine, National Yang-Ming University, School of Medicine, Veterans General Hospital-Taipei and Kaoshiung, Taiwan, ROC
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