Effects of MS-551, a new class III antiarrhythmic drug, on action potential and membrane currents in rabbit ventricular myocytes

Facilitation of hERG Activation by Its Blocker: A Mechanism to Reduce Drug-Induced Proarrhythmic Risk

Modulation of the human Ether-à-go-go-Related Gene (hERG) channel, a crucial voltage-gated potassium channel in the repolarization of action potentials in ventricular myocytes of the heart, has significant implications on cardiac electrophysiology and can be either antiarrhythmic or proarrhythmic. For example, hERG channel blockade is a leading cause of long QT syndrome and potentially life-threatening arrhythmias, such as torsades de pointes. Conversely, hERG channel blockade is the mechanism of action of Class III antiarrhythmic agents in terminating ventricular tachycardia and fibrillation. In recent years, it has been recognized that less proarrhythmic hERG blockers with clinical potential or Class III antiarrhythmic agents exhibit, in addition to their hERG-blocking activity, a second action that facilitates the voltage-dependent activation of the hERG channel. This facilitation is believed to reduce the proarrhythmic potential by supporting the final repolarizing of action potentials. This review covers the pharmacological characteristics of hERG blockers/facilitators, the molecular mechanisms underlying facilitation, and their clinical significance, as well as unresolved issues and requirements for research in the fields of ion channel pharmacology and drug-induced arrhythmias.

Nifekalant versus Amiodarone for Out-Of-Hospital Cardiac Arrest with Refractory Shockable Rhythms; a Post Hoc Analysis

INTRODUCTION

It is still unclear that which anti-arrhythmics are adequate for treating refractory dysrhythmia. This study aimed to compare amiodarone and nifekalant in management of out-of-hospital cardiac arrest cases with refractory shockable rhythm.

METHODS

This was a post hoc analysis of cases registered in a nationwide, multicentre, prospective registry that includes 288 critical care medical centres in Japan. From June 2014 to December 2017, we included all out-of-hospital cardiac arrest patients aged ≥18 years who presented with refractory arrhythmia (sustained ventricular fibrillation or ventricular tachycardia following delivery of at least two defibrillator shocks) and treated with nifekalant or amiodarone after arrival to hospital. Overlap weight was performed to address potential confounding factors.

RESULTS

1,317 out-of-hospital cardiac arrest patients with refractory arrhythmia were enrolled and categorized into amiodarone (n = 1,275) and nifekalant (n = 42) groups. After overlap weight was performed, there were no significant intergroup differences in increased the rate of admission after return of spontaneous circulation [-5.9% (95%CI: -7.1 to 22.4); p = 0.57], 30-day favourable neurological outcome [0.1% (95%CI: -14 to 13.9); p = 0.99], and 30-day survival [-3.9% (95% CI: -19.8 to 12.0); p = 0.63].

CONCLUSION

This nationwide study showed that nifekalant was not associated with improved outcomes regarding admission after return of spontaneous circulation, 30-day survival, and 30-day favourable neurological outcome compared with amiodarone.

Hydroxyzine-induced Torsade de Pointes in a Patient with Complete Atrioventricular Block

An 82-year-old woman was admitted to our hospital because of dyspnea and bradycardia during exertion. Electrocardiography revealed complete atrioventricular block. During pacemaker implantation, a small dose (12.5 mg) of hydroxyzine was injected for sedation, and torsade de pointes (Tdp) occurred. The QT interval was prolonged after administration of hydroxyzine, and Tdp was observed after the R on T phenomenon occurred, indicating that hydroxyzine was capable of prolonging the QT interval and causing Tdp. Therefore, we must be cautious when administering hydroxyzine for sedation during surgery, especially in patients with bradycardia.

Drug Therapy for Vagally-Mediated Atrial Fibrillation and Sympatho-Vagal Balance in the Genesis of Atrial Fibrillation: A Review of the Current Literature

Objective

The presence of both sympathetic activation-mediated triggers and parasympathetic activation-mediated substrates are required to initiate and maintain some forms of atrial fibrillation (AF). AF predominantly precipitated by parasympathetic stimulation is known as vagally-mediated AF (VM-AF). The role of novel drugs and molecular targeted gene therapy that modulate the autonomic nervous system are therapeutic options in this unique population with VM-AF. Here, we review the role of the sympatho-vagal balance in the genesis of AF and consider drug therapy for VM-AF.

Methods

In accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses Statement, literature search was conducted using the keywords "vagal", "vagal nerve", "vagus", "vagus nerve", and "atrial fibrillation". Retrieved citations were first screened independently by 2 reviewers for inclusion and exclusion criteria.

Results

A total of 14 studies and 3 practice guidelines from 1986-2017 were included. Only two clinical investigations evaluated the effectiveness of disopyramide and sotalol in human subjects with VM-AF. The potential role of antiarrhythmic drugs has been studied in animal models.

Conclusions

Growing evidence suggests that the autonomic nervous system is integral in the development of VM-AF. Novel medications and genetic targets are undergoing investigation with promising results.

Population pharmacokinetic/pharmacodynamic modelling of nifekalant in healthy Chinese volunteers

Nifekalant is a class III antiarrhythmic drug, and its major adverse effect is prolongation of the QT interval. This study analysed data generated from a pharmacokinetic (PK) study to develop a population PK/pharmacodynamics (PD) model for describing the relationship between plasma concentrations and prolongation of the QT interval over time following intravenous administration of nifekalant. This open-labelled, phase I clinical study comprised two dose level groups of eight healthy Chinese volunteers. Concentrations of nifekalant in plasma samples collected at set time-points were determined using a liquid chromatography-tandem mass spectrometry (LC-MS/MS) method. A PK/PD model was constructed using a non-linear mixed-effects approach (Phoenix NLME 8.1). Furthermore, demographic covariates of the model were investigated and a concentration factor (Conc^Ɵ) was introduced as the only covariate which improved the performance of the model. The final population PK model exhibited one-order elimination with two-compartment distribution and adequately described nifekalant plasma concentrations over time. The QT interval prolongation was best described by an indirect effect model with an inhibition build-up effect, representing the relationship between plasma concentrations and effect. The final population PK/PD model may facilitate more accurate predictions of the drug profile in clinical settings in the future.

Efficacy of Nifekalant in Patients With Wolff-Parkinson-White Syndrome and Atrial Fibrillation: Electrophysiological and Clinical Findings

Background

The efficacy of nifekalant in preexcited atrial fibrillation (AF) has not been assessed.

Methods and Results

The study populations consisted of patients with sustained preexcited AF (n=51), paroxysmal supraventricular tachycardia (n=201), and persistent AF (n=87). Effects of intravenous infusion of nifekalant were assessed on electrophysiological and clinical parameters. Nifekalant prolonged the shortest preexcited R‐R, the average preexcited R‐R, and the average R‐R intervals from 290±35 to 333±44 ms, 353±49 to 443±64 ms, and 356±53 to 467±75 ms, respectively, in patients with preexcited AF (all P<0.001). Nifekalant also decreased the percentage of preexcited QRS complexes, heart rate, and increased systolic pressure (all P<0.001). Nifekalant terminated AF in 33 of 51 patients (65%). Similar effects were also observed in a subgroup of 12 patients with preexcited AF and impaired left ventricular function. In patients with paroxysmal supraventricular tachycardia, nifekalant significantly prolonged the effective refractory period, the block cycle length of the antegrade accessory pathway, and the atrial effective refractory period (all P<0.001). Nifekalant had no effect on the effective refractory period of the antegrade atrioventricular node. Finally, in patients with persistent AF without an accessory pathway, nifekalant did not significantly decrease the ventricular rate of AF. One patient developed Torsades de Pointes. No other adverse effects were observed.

Conclusions

Nifekalant prolongs the effective refractory period of the antegrade accessory pathway and atrium without blocking antegrade conduction through the atrioventricular node, leading to slowing and/or to termination of preexcited AF. Thus, nifekalant might be an effective and a relatively safe drug in patients with preexcited AF.

Facilitation of I Kr current by some hERG channel blockers suppresses early afterdepolarizations

Some hERG channel blockers are clinically safe, but others cause fatal cardiac arrhythmias. Furutani et al. show that safe blockers facilitate channel opening in ventricular myocytes and provide a repolarization reserve at precisely the voltages and times needed to suppress arrhythmias.

Drug-induced block of the cardiac rapid delayed rectifying potassium current (I_Kr), carried by the human ether-a-go-go-related gene (hERG) channel, is the most common cause of acquired long QT syndrome. Indeed, some, but not all, drugs that block hERG channels cause fatal cardiac arrhythmias. However, there is no clear method to distinguish between drugs that cause deadly arrhythmias and those that are clinically safe. Here we propose a mechanism that could explain why certain clinically used hERG blockers are less proarrhythmic than others. We demonstrate that several drugs that block hERG channels, but have favorable cardiac safety profiles, also evoke another effect; they facilitate the hERG current amplitude in response to low-voltage depolarization. To investigate how hERG facilitation impacts cardiac safety, we develop computational models of I_Kr block with and without this facilitation. We constrain the models using data from voltage clamp recordings of hERG block and facilitation by nifekalant, a safe class III antiarrhythmic agent. Human ventricular action potential simulations demonstrate the ability of nifekalant to suppress ectopic excitations, with or without facilitation. Without facilitation, excessive I_Kr block evokes early afterdepolarizations, which cause lethal arrhythmias. When facilitation is introduced, early afterdepolarizations are prevented at the same degree of block. Facilitation appears to prevent early afterdepolarizations by increasing I_Kr during the repolarization phase of action potentials. We empirically test this prediction in isolated rabbit ventricular myocytes and find that action potential prolongation with nifekalant is less likely to induce early afterdepolarization than action potential prolongation with dofetilide, a hERG channel blocker that does not induce facilitation. Our data suggest that hERG channel blockers that induce facilitation increase the repolarization reserve of cardiac myocytes, rendering them less likely to trigger lethal ventricular arrhythmias.

Does Antiarrhythmic Drug During Cardiopulmonary Resuscitation Improve the One-month Survival: The SOS-KANTO 2012 Study

BACKGROUND

Antiarrhythmic drugs (AAD) are often used for fatal ventricular arrhythmias during cardiopulmonary resuscitation (CPR). However, the efficacy of initial AAD administration during CPR in improving long-term prognosis remains unknown. This study retrospectively evaluated the effect of AAD administration during CPR on 1-month prognosis in the SOS-KANTO 2012 study population.

METHODS AND RESULTS

Of the 16,164 out-of-hospital cardiac arrest cases, 1350 shock-refractory patients were included: 747 patients not administered AAD and 603 patients administered AAD. Statistical adjustment for potential selection bias was performed using propensity score matching, yielding 1162 patients of whom 792 patients were matched (396 pairs). The primary outcome was 1-month survival. The secondary outcome was the proportion of patients with favorable neurological outcome at 1 month. Logistic regression with propensity scoring demonstrated an odds ratio (OR) for 1-month survival in the AAD group of 1.92 (P < 0.01), whereas the OR for favorable neurological outcome at 1 month was 1.44 (P = 0.26).

CONCLUSIONS

Significantly greater 1-month survival was observed in the AAD group compared with the non-AAD group. However, the effect of ADD on the likelihood of a favorable neurological outcome remains unclear. The findings of the present study may indicate a requirement for future randomized controlled trials evaluating the effect of ADD administration during CPR on long-term prognosis.

The anaesthetized rabbit with acute atrioventricular block provides a new model for detecting drug-induced Torsade de Pointes

BACKGROUND AND PURPOSE

Several rabbit proarrhythmia models have been developed using genetic or pharmacological methods to suppress the slow component of delayed rectifier K⁺ currents in the ventricle, leading to reduction of the repolarization reserve. Here we have characterized a novel rabbit in vivo proarrhythmia model with severe bradycardia caused by acute atrioventricular block (AVB).

EXPERIMENTAL APPROACH

Bradycardia was induced in isoflurane-anaesthetized rabbits by inducing AVB with catheter ablation, and the ventricle was electrically driven at 60 beats min^-1 throughout the experiment except when extrasystoles appeared. We assessed the effects of two antiarrhythmics, two quinolone antibiotics and one antipsychotic drug, which were chosen as positive drugs (dofetilide, sparfloxacin and haloperidol) and negative drugs (amiodarone and moxifloxacin) for induction of Torsades de Pointes (TdP).

KEY RESULTS

In our model, TdP arrhythmias appeared with high reproducibility after i.v. dofetilide (10-100 μg·kg^-1 ) in five out of six rabbits, sparfloxacin (30 mg·kg^-1 ) in three out of six rabbits and haloperidol (0.3-3 mg·kg^-1 ) in two out of six rabbits. The lethal arrhythmias repeatedly appeared and were accompanied with prolongation of the QT interval and early afterdepolarization-like phenomena. Neither amiodarone (0.3-10 mg·kg^-1 , n = 6) nor moxifloxacin (3-30 mg·kg^-1 , n = 6) induced such arrhythmias, even when QT intervals were prolonged.

CONCLUSIONS AND IMPLICATIONS

These results suggest that our model of the unremodelled and bradycardic heart of the anaesthetized rabbit is a useful test system for the detection of drug-induced TdP arrhythmias.

Antiarrhythmic drugs for out-of-hospital cardiac arrest with refractory ventricular fibrillation

This article is one of ten reviews selected from the Annual Update in Intensive Care and Emergency medicine 2017. Other selected articles can be found online at http://ccforum.com/series/annualupdate2017. Further information about the Annual Update in Intensive Care and Emergency Medicine is available from http://www.springer.com/series/8901.

Electrophysiologic effects of the IK1 inhibitor PA-6 are modulated by extracellular potassium in isolated guinea pig hearts

The pentamidine analog PA-6 was developed as a specific inward rectifier potassium current (IK1) antagonist, because established inhibitors either lack specificity or have side effects that prohibit their use in vivo. We previously demonstrated that BaCl2, an established IK1 inhibitor, could prolong action potential duration (APD) and increase cardiac conduction velocity (CV). However, few studies have addressed whether targeted IK1 inhibition similarly affects ventricular electrophysiology. The aim of this study was to determine the effects of PA-6 on cardiac repolarization and conduction in Langendorff-perfused guinea pig hearts. PA-6 (200 nm) or vehicle was perfused into ex-vivo guinea pig hearts for 60 min. Hearts were optically mapped with di-4-ANEPPS to quantify CV and APD at 90% repolarization (APD90). Ventricular APD90 was significantly prolonged in hearts treated with PA-6 (115 ± 2% of baseline; P < 0.05), but not vehicle (105 ± 2% of baseline). PA-6 slightly, but significantly, increased transverse CV by 7%. PA-6 significantly prolonged APD90 during hypokalemia (2 mmol/L [K+]o), although to a lesser degree than observed at 4.56 mmol/L [K+]o In contrast, the effect of PA-6 on CV was more pronounced during hypokalemia, where transverse CV with PA-6 (24 ± 2 cm/sec) was significantly faster than with vehicle (13 ± 3 cm/sec, P < 0.05). These results show that under normokalemic conditions, PA-6 significantly prolonged APD90, whereas its effect on CV was modest. During hypokalemia, PA-6 prolonged APD90 to a lesser degree, but profoundly increased CV Thus, in intact guinea pig hearts, the electrophysiologic effects of the IK1 inhibitor, PA-6, are [K+]o-dependent.

Amiodarone or nifekalant upon hospital arrival for refractory ventricular fibrillation after out-of-hospital cardiac arrest

BACKGROUND

We evaluated the association between nifekalant or amiodarone on hospital admission and in-hospital mortality for cardiac arrest patients with persistent ventricular fibrillation on hospital arrival.

METHODS

This was a retrospective cohort study using the Japanese Diagnosis Procedure Combination inpatient database. We identified 2961 patients who suffered cardiogenic out-of-hospital cardiac arrest and who had ventricular fibrillation on hospital arrival between July 2007 and March 2013. Patients were categorized into amiodarone (n=2353) and nifekalant (n=608) groups, from which 525 propensity score-matched pairs were generated.

RESULTS

We found a significant difference in the admission rate between the nifekalant and amiodarone groups in propensity score-matched groups (75.6% vs. 69.3%, respectively; difference, 6.3%; 95% confidence interval (CI), 0.9-11.7). An analysis using the hospital nifekalant/amiodarone rate as an instrumental variable found that receiving nifekalant was associated with an improved admission rate (22.2%, 95% CI, 11.9-32.4). We found no significant difference in in-hospital mortality between the nifekalant and amiodarone groups (81.5% vs. 82.1%, respectively; difference, -0.6%; 95% CI, -5.2 to 4.1). Instrumental variable analysis showed that receiving nifekalant was not associated with reduced in-hospital mortality (6.2%, 95% CI, -2.4 to 14.8).

CONCLUSIONS

This nationwide study suggested no significant in-hospital mortality association between nifekalant and amiodarone for cardiogenic out-of-hospital cardiac arrest patients with ventricular fibrillation/persistent ventricular tachycardia on hospital arrival. Although nifekalant may potentially improve hospital admission rates compared with amiodarone for these patients, further studies are required to confirm our results.

A multicenter observational study of the effectiveness of antiarrhythmic agents in ventricular arrhythmias: A propensity-score adjusted analysis

Background

Ventricular tachyarrhythmias (VTs) are life-threatening events that result in hemodynamic compromise. Recurrence is common and may worsen a patient׳s clinical course despite appropriate treatment. This study aimed to examine the effectiveness of antiarrhythmic drugs for suppression of VTs.

Methods

In this cohort study, eligible patients were those who were admitted to one of the nine cardiovascular care centers and treated with continuous infusion of an antiarrhythmic drug for at least 1 h to prevent recurrence of VTs after return of spontaneous circulation. To adjust for differences in baseline characteristics among treatment groups, propensity scores for administered agents were generated and used as covariates in regression analyses.

Results

Seventy-two patients were enrolled and 67 patients were included in the final analysis. Amiodarone (n=21, 31.3%), nifekalant (n=24, 35.8%), and lidocaine (n=22, 32.8%) were administered as first-line therapy for suppression of VTs. In the adjusted analyses, the odds ratio (OR) of switching to a different drug was significantly higher in the lidocaine group (OR 37.6, 95% CI 5.1–279, p<0.001) than in the amiodarone group, but not in the nifekalant group (OR 4.1, 95% CI 0.72–23.2, p=0.11). There was no significant difference in mortality rate in the lidocaine group (OR 1.67, 95% CI 0.40–6.95, p=0.48) or the nifekalant group (OR 1.11, 95% CI 0.15–4.85, p=0.89) compared with the amiodarone group.

Conclusion

Amiodarone and nifekalant are similarly effective in preventing VT recurrence, but their impact on survival rate is minimal. These data indicate that both nifekalant and amiodarone can be used for treatment of refractory VT.

Effect of sophoridine on Ca²⁺ induced Ca²⁺ release during heart failure

Sophoridine is a type of alkaloid extract derived from the Chinese herb Sophora flavescens Ait (kushen) and possess a variety of pharmacological effects including anti-inflammation, anti-anaphylaxis, anti-cancer, anti-arrhythmic and so on. However, the effect of sophoridine on heart failure has not been known yet. In this study, the effect of sophoridine on heart failure was investigated using Sprague-Dawley (SD) rat model of chronic heart failure. Morphological results showed that in medium and high dose group, myofilaments were arranged orderly and closely, intermyofibrillar lysis disappeared and mitochondria contained tightly packed cristae compared with heart failure group. We investigated the Ca(2+) induced Ca(2+) transients and assessed the expression of ryanodine receptor (RyR2) and L-type Ca(2+) channel (dihydropyridine receptor, DHPR). We found that the cytosolic Ca(2+) transients were markedly increased in amplitude in medium (deltaF/F(0)=43.33+/-1.92) and high dose groups (deltaF/F(0)=47.21+/-1.25) compared with heart failure group (deltaF/F(0)=16.7+/-1.29, P<0.01), Moreover, we demonstrated that the expression of cardiac DHPR was significantly increased in medium- and high dose-group compared with heart failure rats. Our results suggest that sophoridine could improve heart failure by ameliorating cardiac Ca(2+) induced Ca(2+) transients, and that this amelioration is associated with upregulation of DHPR.

Comparison of nifekalant and amiodarone for resuscitation of out-of-hospital cardiopulmonary arrest resulting from shock-resistant ventricular fibrillation

Purpose

Nifekalant is a pure potassium channel blocker that has been used to treat ventricular tachyarrhythmias since 1999 in Japan. Intravenous amiodarone was approved later than nifekalant in Japan, and it is still unclear which of the two agents is superior. The aim of this study was to compare the efficacy of nifekalant and amiodarone for resuscitation of out-of-hospital cardiopulmonary arrest caused by shock-resistant ventricular fibrillation.

Methods

From December 2005 to January 2011, ambulance services transported 283 out-of-hospital cardiopulmonary arrest patients to our hospital. Of these, 25 patients were treated with nifekalant or amiodarone in response to ventricular fibrillation that was resistant to two or more shocks. We undertook a retrospective analysis of these 25 patients.

Results

We enrolled 20 men and 5 women with a mean age (± standard deviation) of 61.1 ± 16.4 years. All 25 patients were treated with tracheal intubation and intravenous epinephrine. Fourteen patients received nifekalant and 11 patients received amiodarone. The rates of return of spontaneous circulation (ROSC) (nifekalant, 5/14, versus amiodarone, 4/11; P = 0.97) and survival to discharge (nifekalant, 4/14, versus amiodarone, 2/11; P = 0.89) were not significantly different between the two groups. The time from nifekalant or amiodarone administration to ROSC was 6.0 ± 6.6 and 20.3 ± 10.0 min, respectively, which was significantly different (P < 0.05).

Conclusion

In this small sample size study, nifekalant, compared with amiodarone, is equally effective for ROSC and survival to discharge after shock-resistant ventricular fibrillation and can achieve ROSC more quickly. Further prospective studies are needed to confirm our results.

Rate-dependent electrophysiologic effects of the class III antiarrhythmic drugs nifekalant, amiodarone, and ibutilide on the atrium in patients with persistent atrial fibrillation

Persistent atrial fibrillation (AF) is characterized by electrical remodeling, ie, marked decreases in the atrial effective refractory period (ERP), ERP rate adaptation, and atrial conduction velocity. Little information is available on the effects of class III antiarrhythmic drugs on the remodeled atrium. We studied the effects of the class III antiarrhythmic drugs nifekalant, ibutilide, and amiodarone on rate-dependent changes in atrial action potential duration in patients with persistent AF. Right atrial (RA) monophasic action potential duration (MAPD) and intra-atrial conduction time (IACT) were measured at pacing cycle lengths (CLs) of 800, 700, 600, 500, 400, 350, 300, and 250 ms before and after administration of nifekalant (0.4 mg/kg + 0.3 mg/kg/hr, iv), amiodarone (5 mg/kg, iv), or ibutilide (0.01 mg/kg, iv) in 31 patients after successful internal cardioversion of chronic AF of > 2 months duration. Nifekalant and ibutilide significantly increased RA MAPD and the ERP at each CL in a reverse rate-dependent manner. Amiodarone did not affect RA MAPD. Nifekalant did not affect IACT, whereas amiodarone increased IACT at each CL in a rate-dependent manner, and ibutilide increased IACT at CLs ≤ 350 ms. The atrial electrophysiologic effects of the class III antiarrhythmic drugs nifekalant, amiodarone, and ibutilide differ, depending on the degree of electrical and structural remodeling and the effects of the drugs on the depolarizing and repolarizing currents.

Protective effect of oxymatrine on chronic rat heart failure

Oxymatrine is one of the alkaloids extracted from the Chinese herb Sophora japonica (Sophora flavescens Ait.) with anti-inflammatory, immune reaction inhibiting, antiviral, and hepatocyte and antihepatic fibrosis protective activities. However, the effect of oxymatrine on heart failure is not yet known. In this study, the effect of oxymatrine on heart failure was investigated using a Sprague-Dawley rat model of chronic heart failure. Morphological findings showed that in the group treated with 50 and 100 mg/kg of oxymatrine; intermyofibrillar lysis disappeared, myofilaments were orderly, closely and evenly arranged; and mitochondria contained tightly packed cristae compared with the heart failure group. We investigated the cytosolic Ca(2+) transients and sarcoplasmic reticulum (SR) Ca(2+) content, and assessed the expression of ryanodine receptor (RyR2), SR-Ca(2+) ATPase (SERCA2a), and L-type Ca(2+) channel (dihydropyridine receptor, DHPR). We found that the cytosolic Ca(2+) transients were markedly increased in amplitude in the medium- (ΔF/F (0) = 26.22 ± 2.01) and high-dose groups (ΔF/F (0) = 29.49 ± 1.17) compared to the heart failure group (ΔF/F (0) = 12.12 ± 1.35, P < 0.01), with changes paralleled by a significant increase in the SR Ca(2+) content (medium-dose group: ΔF/F (0) = 32.20 ± 1.67, high-dose group: ΔF/F (0) = 32.57 ± 1.29, HF: ΔF/F (0) = 17.26 ± 1.05, P < 0.01). Moreover, we demonstrated that the expression of SERCA2a and cardiac DHPR was significantly increased in the medium- and high-dose group compared with the heart failure rats. These findings suggest that oxymatrine could improve heart failure by improving the cardiac function and that this amelioration is associated with upregulation of SERCA2a and DHPR.

Nifekalant in the treatment of life-threatening ventricular tachyarrhythmias

The aim of the present study is to review the literature and discuss nifekalant's potential use as a first aid drug in an emergency care setting. The PubMed database was used to identify papers, using keywords nifekalant, MS-551, amiodarone and lidocaine. Nifekalant hydrochloride, formally known as MS-551, is a class III antiarrhythmic agent which acts only by increasing the time course of myocardial repolarization. It was developed and is currently being used only in Japan for the treatment of ventricular tachyarrhythmias. It is a non-selective K(+) channel blocker without any β-blocking actions. Administration of nifekalant suppressed sustained ventricular tachyarrhythmias in acute coronary syndrome patients, and in cardiac arrest victims as well as during or after cardiac surgery. The major adverse effect of nifekalant is QT interval prolongation and occurrence of torsades de pointes which requires frequent monitoring of the QT interval during nifekalant infusion with adequate dose adjustment. Nifekalant is a possible effective antiarrhythmic agent for refractory ventricular tachyarrhythmias. Further clinical studies are required before nifekalant is routinely used in the emergency care setting.

Use of Intravenous Amiodarone in the Treatment of Nifekalant-Resistant Arrhythmia: A Review of 11 Consecutive Cases with Severe Heart Failure

Background: Both nifekalant hydrochloride (NIF), a selective I_Kr blocker, and intravenous amiodarone (AMD), a multi-channel (including I_Kr blocking) blocker, have been reported to be efficacious for refractory arrhythmias. However, the optimal use of those antiarrhythmic drugs for refractory arrhythmia with severe heart failure has not been established. Intravenous AMD might be effective for arrhythmias refractory to NIF in patients with severe heart failure. Here, we report that intravenous amiodarone was effective in the treatment of nifekalant-resistant in a group of arrhythmia patients with severe heart failure. Methods: Eleven severe heart failure patients who had received intravenous AMD for treatment of NIF-resistant arrhythmias were included in this study, and retrospective analysis was performed. Clinical efficacy (terminative and preventive effects on arrhythmia) of intravenous AMD was evaluated. Results: All cases were emergent cases and had depressed left ventricular ejection fraction (30 ± 13%). Clinical arrhythmias were ventricular fibrillation (VF) in four patients, ventricular tachycardia (VT) in six patients, and atrial fibrillation (AF) in one patient. NIF was administered to all patients by intravenous injection. After administration of NIF, VT/VF/AF was terminated in seven of the 10 patients, but a preventive effect was not obtained in any of the patients (NIF-resistance). Intravenous AMD (maintenance dose: 484 ± 166 mg/day) was effective both in termination (80%) and in prevention (80%) of VT/VF events in those patients. It was also effective in termination (80%) and prevention (60%) of AF events refractory to NIF. During continuous AMD administration, no significant adverse effects or proarrhythmic effects were observed in any of the patients. Five patients died within one month, but there was no arrhythmic deaths. Conclusions: Intravenous AMD was effective in NIF-resistant lethal arrhythmias and was relatively safe in emergent cases with severe heart failure.

Defective Ca(2+) handling proteins regulation during heart failure

Abnormal release of Ca(2+) from sarcoplasmic reticulum (SR) via the cardiac ryanodine receptor (RyR2) may contribute to contractile dysfunction in heart failure (HF). We previously demonstrated that RyR2 macromolecular complexes from HF rat were significantly more depleted of FK506 binding protein (FKBP12.6). Here we assessed expression of key Ca(2+) handling proteins and measured SR Ca(2+) content in control and HF rat myocytes. Direct measurements of SR Ca(2+) content in permeabilized cardiac myocytes demonstrated that SR luminal [Ca(2+)] is markedly lowered in HF (HF: DeltaF/F(0) = 26.4+/-1.8, n=12; control: DeltaF/F(0) = 49.2+/-2.9, n=10; P<0.01). Furthermore, we demonstrated that the expression of RyR2 associated proteins (including calmodulin, sorcin, calsequestrin, protein phosphatase 1, protein phosphatase 2A), Ca(2+) ATPase (SERCA2a), PLB phosphorylation at Ser16 (PLB-S16), PLB phosphorylation at Thr17 (PLB-T17), L-type Ca(2+) channel (Cav1.2) and Na(+)- Ca(2+) exchanger (NCX) were significantly reduced in rat HF. Our results suggest that systolic SR reduced Ca(2+) release and diastolic SR Ca(2+) leak (due to defective protein-protein interaction between RyR2 and its associated proteins) along with reduced SR Ca(2+) uptake (due to down-regulation of SERCA2a, PLB-S16 and PLB-T17), abnormal Ca(2+) extrusion (due to down-regulation of NCX) and defective Ca(2+) -induced Ca(2+) release (due to down-regulation of Cav1.2) could contribute to HF.

Comparative study of nifekalant versus amiodarone for shock-resistant ventricular fibrillation in out-of-hospital cardiopulmonary arrest patients

BACKGROUND

In Japan, intravenous nifekalant (NIF) was often used for direct current cardioversion-resistant ventricular fibrillation (VF), until the use of intravenous amiodarone (AMD) was approved in 2007. The defibrillatory efficacy of NIF and AMD has thus far not been compared for resuscitation.

METHODS AND RESULTS

Between August 2007 and April 2009, 403 consecutive out-of-hospital patients with cardiopulmonary arrest were transferred to the Emergency Medical Service of Tokai University. Of these, 30 patients with first defibrillation failure or VF recurrence were enrolled for this NIF/AMD study. The final defibrillation success (and hospital survival rate) was 67% (10/15) in the AMD and 47% (7/15) in the NIF group. The discharge survival rate was 53% (8/15) in the AMD and 21% (4/15) in the NIF group (P = 0.06). Notably, all 4 survivors in the NIF group could take up normal daily life again, whereas this was restricted to only 2 patients from the 11 survivors in the AMD group. The difference is probably partly attributable to longer time from AMD administration to defibrillation success compared with NIF. In the cases of defibrillation failure, VF continued in 4/8 by NIF, however, asystole or pulseless electrical activity occurred in 4/5 patients by AMD.

CONCLUSIONS

AMD may be borderline superior over NIF to facilitate defibrillation in out-of-hospital patients with cardiopulmonary arrest. However, from the view point of preservation of brain function, NIF is not inferior to AMD for CPR.

Comparison of the efficacy of nifekalant and amiodarone in a porcine model of cardiac arrest

OBJECTIVE

To compare the efficacy of nifekalant and amiodarone in the treatment of cardiac arrest in a porcine model.

METHODS

After 4min of untreated ventricular fibrillation, animals were randomly treated with nifekalant (2mgkg(-1)), amiodarone (5mgkg(-1)) or saline placebo (n=12 pigs per group). Precordial compression and ventilation were initiated after drug administration and defibrillation was attempted 2min later. Hemodynamics were continuously measured for 6h after successful resuscitation.

RESULTS

Compared with saline, nifekalant and amiodarone equally decreased the number of electric shocks, defibrillation energy, epinephrine dose, and duration of cardiopulmonary resuscitation required for successful resuscitation (P<0.01). The incidence of restoration of spontaneous circulation (ROSC) and the 24-h survival rate were higher in both antiarrhythmic drug groups (P<0.05) vs. the saline group. Furthermore, post-resuscitation myocardial dysfunction at 4-6h after successful resuscitation was improved in animals given antiarrhythmic drugs as compared with the saline group (P<0.05). There were no differences between nifekalant and amiodarone for any of these parameters.

CONCLUSION

The effect of nifekalant was similar to that of amiodarone for improving defibrillation efficacy and for the treatment of cardiac arrest. Administration of either nifekalant or amiodarone before defibrillation increased the ROSC and 24-h survival rates and improved post-resuscitation cardiac function in this porcine model.

Altered intracellular Ca2+ regulation in chronic rat heart failure

intracellular Ca(2+) handling by the sarcoplasmic reticulum (SR) plays a crucial role in the pathogenesis of heart failure (HF). Despite extensive effort, the underlying causes of abnormal SR Ca(2+) handling in HF have not been clarified. To determine whether the diastolic SR Ca(2+) leak along with reduced Ca(2+) reuptake is required for decreased contractility, we investigated the cytosolic Ca(2+) transients and SR Ca(2+) content and assessed the expression of ryanodine receptor (RyR2), FK506 binding protein (FKBP12.6), SR-Ca(2+) ATPase (SERCA2a), and L-type Ca(2+) channel (LTCC) using an SD-rat model of chronic HF. We found that the cytosolic Ca(2+) transients were markedly reduced in amplitude in HF myocytes (DeltaF/F(0) = 12.3 +/- 0.8) compared with control myocytes (DeltaF/F(0) = 17.7 +/- 1.2, P < 0.01), changes paralleled by a significant reduction in the SR Ca(2+) content (HF: DeltaF/F(0) = 12.4 +/- 1.1, control: DeltaF/F(0) = 32.4 +/- 1.9, P < 0.01). Moreover, we demonstrated that the expression of FKBP12.6 associated with RyR2, SERCA2a, and LTCC was significantly reduced in rat HF. These results provide evidence for phosphorylation-induced detachment of FKBP12.6 from RyRs and down-regulation of SERCA2a and LTCC in HF. We conclude that diastolic SR Ca(2+) leak (due to dissociation of FKBP12.6 from RyR2) along with reduced SR Ca(2+) uptake (due to down-regulation of SERCA2a) and defective E-C coupling (due to down-regulation of LTCC) could contribute to HF.

Nifekalant versus lidocaine for in-hospital shock-resistant ventricular fibrillation or tachycardia

OBJECTIVE

To compare the efficacy and safety of nifekalant, a pure class III anti-arrhythmic drug, and lidocaine in patients with shock-resistant in-hospital ventricular fibrillation (VF) or ventricular tachycardia (VT).

PATIENTS AND METHODS

Between August 2005 and March 2008, we conducted a prospective, two-arm, cluster observational study, in which participating hospitals were pre-registered either to the nifekalant arm or the lidocaine arm. Patients were enrolled if they had in-hospital VF or VT resistant to at least two defibrillation shocks. Congenital or drug-induced long QT syndrome was excluded. The primary end-point was termination of VF or VT with/without additional shock. The secondary end-points were return of spontaneous circulation (ROSC), 1-month survival and survival to hospital discharge. We also assessed the frequency of adverse events, including asystole, pulseless electrical activity and torsade de pointes.

RESULTS

In total, 55 patients were enrolled. After nifekalant, 22 of 27 patients showed termination of VF or VT, as compared with 15 of 28 patients treated with lidocaine with/without additional shock (odds ratio (OR): 3.8; 95% confidence interval (CI): 1.1-13.0; P=0.03). Twenty-three of 27 patients given nifekalant showed ROSC, as compared with 15 of 28 patients given lidocaine (OR: 5.0; 95% CI: 1.4-18.2; P=0.01). There was no difference in 1-month survival or survival to hospital discharge between the nifekalant and lidocaine arms. There was a higher incidence of asystole with lidocaine (7 of 28 patients) than with nifekalant (0 of 27 patients) (P=0.005). Torsade de pointes was not observed.

CONCLUSION

Nifekalant was more effective than lidocaine for termination of arrhythmia and for ROSC in patients with shock-resistant in-hospital VF or VT (umin-CTR No. UMIN 000001781).

Human atrial natriuretic peptide suppresses torsades de pointes in rabbits

BACKGROUND

The increase in inward current, primarily L-type Ca2+ current, facilitates torsades de pointes (TdP). Because human atrial natriuretic peptide (ANP) moderates the L-type Ca2+ current, in our study it was hypothesized that ANP counteracts TdP.

METHODS AND RESULTS

We tested the effect of ANP, guanosine 3', 5'-cyclic monophosphate analogue (8-bromo cGMP) and hydralazine on the occurrence of TdP in a rabbit model. In control rabbits, administration of methoxamine and nifekalant almost invariably caused TdP (14/15). In contrast, ANP (10 microg . kg(-1) . min(-1)) markedly abolished TdP (2/15), whereas hydralazine failed to show a comparable anti-arrhythmic action (10/15). TdP occurred only in 1 of 15 rabbits treated with 8-bromo cGMP. Presence of early afterdepolarization-like hump in the ventricular monophasic action potential was associated with the occurrence of TdP.

CONCLUSION

Results suggest that ANP affects TdP in the rabbit model, and that this anti-arrhythmic effect of ANP is not necessarily shared by other vasodilating agents.

Clinical study of the acute effects of intravenous nifekalant on the defibrillation threshold in patients with persistent and paroxysmal atrial fibrillation

BACKGROUND

Antiarrhythmic agents are considered to have significant effects on the defibrillation energy requirement, so this study investigated the effects of nifekalant on defibrillation.

METHODS AND RESULTS

Forty-two patients with persistent atrial fibrillation (AF) underwent electrical cardioversion via intracardiac electrode catheters prior to and after the intravenous administration of nifekalant. The success rate of the defibrillation and change in the defibrillation threshold using sequential incremental defibrillation energy deliveries was investigated. In addition, the parameters that could predict the beneficial effects of nifekalant were also assessed. Nifekalant significantly decreased the defibrillation energy requirement in 13 of the 42 cases, and nifekalant also converted AF to sinus rhythm with an identical energy to that of the last unsuccessful defibrillation in 21 of 42 cases. The success of defibrillation seemed to be dependent on significant prolongation of the intracardiac atrial electrogram intervals during AF by the nifekalant.

CONCLUSIONS

Intravenous nifekalant significantly improved the electrical defibrillation efficacy in patients with persistent AF that was resistant to defibrillation, without any serious adverse effects.

Effect of nifekalant for acute conversion of atrial flutter: the possible termination mechanism of typical atrial flutter

BACKGROUND

Nifekalant is a class III antiarrhythmic drug, which is usually used for suppression of ventricular tachycardia (VT) and fibrillation. We studied the efficacy of nifekalant for acute conversion of atrial flutter (AFL) in a prospective, open label study in the intensive care unit (ICU) of cardiovascular medicine.

METHODS

This study consisted of 31 patients. Twenty-six patients (84%) suffered from structural heart diseases. AFL was developed in 15 patients (48%) while on antiarrhythmic therapy with class IA or IC drugs (I-AFL group) for suppressing atrial fibrillation (AF) and in the remaining patients without such drugs (S-AFL group). Patients with prolonged QT interval, hypokalemia were excluded. All patients received one dose of 0.3 mg/kg of nifekalant over 10 minutes under continuous ambulatory monitoring. Four patients with common AFL in each group received nifekalant during electrophysiologic (EP) study.

RESULTS

Nifekalant had an overall AFL conversion efficacy of 77.4% within 60 minutes. Eleven patients in S-AFL group (68.8%) and 13 patients in I-AFL group (86.7%) could be converted with mean conversion times of 10.8 +/- 6.2 and 15.0 +/- 8.0 minutes, respectively (n.s.). Conversion rate was significantly higher in patients with a short duration of arrhythmia. The two modes of AFL termination were mainly demonstrated and the preferential mode significantly differed between the two groups. One patient in each group with excessive QT prolongation (6.5%) developed torsade de pointes (TdP), requiring electrical shock in one patient (3.3%).

CONCLUSIONS

Nifekalant can be used for conversion of AFL with a potent efficacy even in patients with structural heart diseases. However, caution should be required for developing TdP.

Analysis of arrhythmogenic profile in a canine model of chronic atrioventricular block by comparing in vitro effects of the class III antiarrhythmic drug nifekalant on the ventricular action potential indices between normal heart and atrioventricular block heart

The chronic atrioventricular block dog is a useful model for predicting the future onset of drug-induced long QT syndrome in clinical practice. To better understand the arrhythmogenic profile of this model, we recorded the action potentials of the isolated ventricular tissues in the presence and absence of the class III antiarrhythmic drug nifekalant. The action potential durations of the Purkinje fiber and free wall of the right ventricle were longer in the chronic atrioventricular block dogs than in the dogs with normal sinus rhythm. Nifekalant in concentrations of 1 and 10 microM prolonged the action potential durations of Purkinje fiber and the free wall in a concentration-dependent manner. The extent of prolongation was greater in the chronic atrioventricular block dogs than in the normal dogs. However, increase of temporal dispersion of ventricular repolarization including early afterdepolarization was not detected by nifekalant in either group of dogs, indicating lack of potential to trigger arrhythmias in vitro. These results suggest that the ventricular repolarization delay in the chronic atrioventricular block model by nifekalant may largely depend on the decreased myocardial repolarization reserve, whereas the trigger for lethal arrhythmia was not generated in the in vitro condition in contrast to the in vivo experiment.

Reduction of repolarization reserve by halothane anaesthesia sensitizes the guinea-pig heart for drug-induced QT interval prolongation

The utility of halothane-anaesthetized guinea-pigs as an in vivo model for predicting the clinical potential of a drug to induce QT interval prolongation was assessed using the electrocardiogram and monophasic action potential (MAP) recordings with electrical ventricular pacing. Intravenous administration of D-sotalol (0.3 mg kg(-1)) and terfenadine (0.3 mg kg(-1)), blockers of a rapid component of delayed rectifier potassium currents, prolonged the QT interval by 32+/-7 and 23+/-6 ms, respectively, whereas chromanol 293B (1 mg kg(-1)), a blocker of a slow component of delayed rectifier potassium currents, lengthened it by 33+/-8 ms. The extent of the QT interval prolongation by these drugs was greater than those in previous reports using pentobarbital-anaesthetized guinea-pigs. The MAP duration at the control was shortened by decreasing the pacing cycle length from 400 to 200 ms, but the MAP duration at each cycle length was prolonged by D-sotalol. The formulas of Van de Water, Matsunaga, Fridericia and Bazett showed good correlation of the repolarization period when compared with the MAP duration at a pacing cycle length of 400 ms. The halothane-anaesthetized guinea-pig model may possess enough sensitivity to detect drug-induced QT interval prolongation, indicating that halothane anaesthesia can reduce the repolarization reserve of the heart in vivo.

Mechanisms of destabilization and early termination of spiral wave reentry in the ventricle by a class III antiarrhythmic agent, nifekalant

Nifekalant (NF) is a novel class III antiarrhythmic agent that is effective in preventing life-threatening ventricular tachycardia/fibrillation (VT/VF). We investigated mechanisms of destabilization and early termination of spiral-type reentrant VT by NF in a two-dimensional subepicardial myocardial layer of Langendorff-perfused rabbit hearts (n = 21) using a high-resolution optical action potential mapping system. During basic stimulation, NF (0.1 microM) caused uniform prolongation of action potential duration (APD) without affecting conduction velocity and an increase of APD restitution slope. VTs induced by direct current stimulation in the presence of NF were of shorter duration (VTs > 30 s: 2/54 NF vs. 19/93 control). During VTs in control (with visible rotors), the wave front chased its own tail with a certain distance (repolarized zone), and they seldom met each other. The average number of phase singularity (PS) points was 1.31 +/- 0.14 per 665 ms (n = 7). In the presence of NF, the wave front frequently encountered its own tail, causing a transient breakup of the spiral wave or sudden movement of the rotation center (spatial jump of PS). The average number of PS was increased to 1.63 +/- 0.22 per 665 ms (n = 7, P < 0.05) after NF. The mode of spontaneous termination of rotors in control was in most cases (9/10, 90.0%) the result of mutual annihilation of counterrotating wave fronts. With NF, rotors frequently terminated by wave front collision with the atrioventricular groove (12/19, 63.2%) or by trapping the spiral tip in a refractory zone (7/19, 36.8%). Destabilization and early termination of spiral wave reentry induced by NF are the result of a limited proportion of excitable tissue after modulation of repolarization.

Comparison of efficacy of sotalol and nifekalant for ventricular tachyarrhythmias

BACKGROUND

Suppression of implantable defibrillator discharges associated with ventricular tachyarrhythmia (VTA) has been reported for sotalol. This study aimed to investigate the efficacy of intravenous nifekalant hydrochloride in predicting the effects of oral sotalol.

METHODS AND RESULTS

The present study included 14 patients who had sustained VTA associated with structural heart disease. All patients also had inducible VTA. To compare the effects of nifekalant and sotalol, programmed electrical stimulation was performed, in the basal state, after nifekalant administration, and after sotalol administration. Nifekalant and sotalol similarly prolonged the corrected QT interval and ventricular effective refractory periods, but the heart rate was slowed by sotalol only. In 4 of 5 patients whose VTA became non-inducible by nifekalant, subsequent treatment with sotalol also suppressed the inducible VTA. In all of the 9 patients non-responding to nifekalant, VTA remained inducible during sotalol treatment. Nifekalant accurately predicted the response to sotalol during electrophysiologic study in 13 of 14 patients. Of 11 patients who remained on sotalol, VTA recurred in 3 non-responders during a follow-up of 46 +/- 11 months.

CONCLUSIONS

Nifekalant and sotalol had similar effects on inducible VTA. The response of inducible VTA to nifekalant may predict the clinical efficacy of sotalol.

Reduced inotropic effect of nifekalant in failing hearts in rats

Class III antiarrhythmic agents have been widely used to suppress ventricular tachyarrhythmias in patients with heart failure because they have been shown to have positive inotropic effects as well. However, it remains to be examined whether those agents also exert positive inotropic effects in failing hearts. We addressed this important issue in a rat model of heart failure. We used Nifekalant as a representative class III antiarrhythmic agent. Four weeks after a s.c. injection of 60 mg/kg monocrotaline (MCT) or vehicle (Ctr) into rats, we obtained trabeculae from right ventricles and measured the developed force and intracellular Ca(2+) ([Ca(2+)](i)) by the fura-2 microinjection method. The sarcoplasmic reticulum (SR) Ca(2+) content was assessed by the rapid-cooling contracture (RCC) technique. MCT rats exhibited right ventricular hypertrophy induced by pressure overload. The protein expression of SR Ca(2+) ATPase type 2 (SERCA2) and the SERCA2/phospholamban ratio in MCT rats was lower with a slower decline of Ca(2+) transients and a reduced amplitude of RCCs. Nifekalant concentration-dependently increased the force, peak [Ca(2+)](i), and the amplitude of RCCs in Ctr rats but not in MCT rats with identical prolongation of the action potential. Under the SR inhibited with cyclopiazonic acid and ryanodine, Nifekalant increased the force in Ctr rats but not in MCT rats. These results indicate that the positive inotropic effects of Nifekalant is reduced in failing hearts, probably due to the depressed SR Ca(2+) uptake and reduced reserve of the trans-sarcolemmal Ca(2+) transport, warranting a caution in the antiarrhythmic therapy with a class III antiarrhythmic agent in heart failure.

Efficacy of nifekalant hydrochloride in the treatment of fatal ventricular arrhythmia in patients with ischemic heart disease

Ventricular tachycardia (VT), which causes hemodynamic instability, and ventricular fibrillation (VF) sometimes occur in patients with severe underlying cardiovascular disease such as myocardial ischemia or infarction, and are associated with high mortality. This report presents the efficacy of nifekalant hydrochloride (nifekalant), a pure class III antiarrhythmic agent, in treating life-threatening ventricular arrhythmia in such patients. From June 2000, when nifekalant became commercially available in Japan, to May 2003, 30 ischemic heart disease (IHD) patients with VT/VF resistant to direct-current (DC) countershock received nifekalant in our hospital. These 30 patients served as the nifekalant group in this study. As a control group, we also included 33 IHD patients with VT/VF that had been resistant to DC countershock upon or during hospitalization between January 1996 and May 2000 before nifekalant became commercially available. No significant differences were observed in patient background factors and treatments between the two groups. The rates of death within 48 hours of occurrence of VT/VF were significantly lower in the nifekalant group (7%, 2/30) than in the control group (27%, 9/33; P < 0.03). The rates of cardiac death during hospitalization were also significantly lower in the nifekalant group (40%, 12/30) than in the control group (67%, 22/33; P < 0.03). The rates of survival until hospital discharge were significantly higher in the nifekalant group (57%, 17/30) than in the control group (30%, 10/33; P < 0.03). Multivariate analysis of all 63 patients revealed nifekalant administration was the factor that significantly improved the mortality (odds ratio for cardiac death, 0.26; 95% confidence interval (CI), 0.07 to 0.95; P = 0.041). Nifekalant improves the prognosis for life-threatening ventricular arrhythmia in IHD patients.

Nifekalant hydrochloride suppresses severe electrical storm in patients with malignant ventricular tachyarrhythmias

BACKGROUND

Some patients with an implantable cardioverter-defibrillator (ICD) suffer from burst of inappropriate multiple discharges (severe electrical storm), and because the current therapeutic options are limited, the effect of nifekalant hydrochloride, a new class III drug, on severe electrical storm was investigated in the present study.

METHODS AND RESULTS

Ninety-one consecutive patients treated with ICD were included in the study (M 70; mean age 58 years; left ventricular ejection fraction 45+/-15%). Severe electrical storm was defined as more than 10 ICD discharges within 1 h. During a mean follow-up period of 30+/-13 months, 41/91 (45%) patients had appropriate ICD therapy for arrhythmias and severe electrical storm occurred in 11 of them (12%) at 20+/-18 months after ICD implantation. The mean number of ICD discharges/h during severe electrical storm was 18+/-12. In 4 of 10 patients, severe electrical storm was successfully suppressed by a combination of deep sedation and beta-blocking agent; 6 other patients were refractory to this treatment, but severe electrical storm was successfully suppressed by intravenous administration of nifekalant hydrochloride with no adverse effects.

CONCLUSIONS

Nifekalant hydrochloride is an effective and safe treatment for severe electrical storm.

Comparison of Four Rate-Correction Algorisms for the Ventricular Repolarization Period in Assessing Net Effects of IKr Blockers in Dogs

The utility of corrected and uncorrected QT interval changes for assessing net repolarization delay by I(Kr) (a rapid component of delayed rectifier K(+) currents) blockers was assessed in halothane-anesthetized dogs using the electrocardiogram and monophasic action potential (MAP) recordings with electrical ventricular pacing. Intravenous administration of dl-sotalol (0.2 - 2 mg/kg) prolonged the MAP duration and RR interval, while terfenadine (3 mg/kg) increased the MAP duration but transiently shortened RR interval. The order of correlation coefficient between the MAP duration at a pacing cycle length of 400 ms and MAP duration itself or that with arithmetical correction was uncorrected > Van de Water = Matsunaga > Fridericia > Bazett. These results suggest that Matsunaga's and Van de Water's formulae would better predict the net repolarization delay in the in vivo canine model. Also, the risk of drug candidates that may prolong the QT interval should be judged by change in uncorrected QT interval as well as corrected QT interval.

Can Nifekalant Hydrochloride be Used as a First-Line Drug for Cardiopulmonary Arrest (CPA)?

BACKGROUND

Early defibrillation of ventricular tachycardia and fibrillation (VT/VF) is an urgent and most important method of resuscitation for survival in cardiopulmonary arrest (CPA). We have previously reported that nifekalant (NIF), a specific I(Kr) blocker developed in Japan, is effective for lidocaine (LID) resistant VT/VF in out-of-hospital CPA (OHCPA). However, little is known about the differences in the effect of NIF on OHCPA with acidosis and in-hospital CPA (IHCPA) without acidosis.

METHODS AND RESULTS

The present study enrolled 91 cases of DC shock resistant VT/VF among 892 cases of CPA that occurred between June 2000 and May 2003. NIF was used (0.15-0.3 mg/kg) after LID according to the cardiopulmonary resuscitation (CPR) algorithm of Tokai University. The defibrillation rate was higher in the NIF group for both OHCPA and IHCPA than for LID alone, and the VT/VF rate reduction effect could be maintained even with acidosis. However, sinus bradycardia in OHCPA, and torsades de pointes in IHCPA were occasionally observed. These differences in adverse effects might be related to the amount of epinephrine, serum potassium levels, serum pH, and interaction with LID.

CONCLUSIONS

NIF had a favorable defibrillating effect in both CPA groups, and it shows promise of becoming a first-line drug for CPR.

Nifekalant Hydrochloride Administration During Cardiopulmonary Resuscitation Improves the Transmural Dispersion of Myocardial Repolarization Experimental Study in a Canine Model of Cardiopulmonary Arrest

BACKGROUND

Because nifekalant hydrochloride (NIF) displayed a superior defibrillating effect on ventricular tachycardia/fibrillation (VT/VF) in cardiopulmonary arrest (CPA) patients, despite some QT prolongation, its effect on transmural dispersion of repolarization (TDR) in the left ventricle (LV) in an animal model of CPA was investigated.

METHODS AND RESULTS

Eight beagle dogs were created with a myocardial infarction under anesthesia, and then VT/VF induction by continuous stimulation and cardiopulmonary resuscitation (CPR) were repeated. NIF (0.3 mg/kg) was administered under acidotic conditions (pH 7.26). The QTc interval measured by Y-lead ECG showed no significant prolongation before and after NIF. The activation recovery interval (ARI) measured by 64-lead LV surface mapping showed minimum ARI prolongation (40%) by NIF without maximum ARI prolongation, and as a result the ARI dispersion decreased by 67%. The repolarization time (RPT) with the plunge electrode showed 13-19% prolongation in the subendocardium and subepicardium with CPR, but NIF prolonged the RPT in the middle layer alone (17%), and as a result Plunge-TDR decreased by 82% (n=8, p<0.05).

CONCLUSIONS

Administration of NIF during CPR decreased the TDR by RPT prolongation selectively in the middle layer. Because the subendocardial and subepicardial RPTs after CPR were already prolonged before NIF administration, it may have been the reason why the QT-prolonging effect of NIF was not reflected in the body surface ECG.

Enhancing electrical cardioversion and preventing immediate reinitiation of hemodynamically deleterious atrial fibrillation with class III drug pretreatment

Nifekalant for shock-resistant atrial fibrillation.

INTRODUCTION

In severely ill patients, the development of atrial fibrillation (AF) may provoke lethal hemodynamic instability requiring immediate electrical defibrillation, which often is unsuccessful. Using the novel potassium channel blocking agent nifekalant, we prospectively assessed the hypothesis that class III antiarrhythmic drugs facilitate electrical cardioversion and suppress the immediate recurrence of hemodynamically deleterious AF.

METHODS AND RESULTS

Among 1896 adults admitted to the intensive care unit for cardiovascular diseases, hemodynamically destabilizing new-onset AF (systolic blood pressure<90 mm Hg) resistant to conventional electrical cardioversion occurred in 27 patients, and of these, 24 patients (70+/-12 years) were enrolled. Twenty-one patients had congestive heart failure and 11 patients had been mechanically ventilated. After three failed transthoracic cardioversions due to failure of conversion to SR (11 patients) or immediate reinitiation (13 patients), nifekalant (0.25+/-0.04 mg/kg) was administered intravenously, and electrical defibrillation was reattempted. In 18 patients (75%), sinus rhythm was restored and maintained after nifekalant infusion (6 patients) or subsequent transthoracic cardioversion (12 patients). Nifekalant administration significantly decreased the heart rate and increased systolic blood pressure during AF (P<0.001), and successful cardioversion rapidly further ameliorated these parameters (P<0.001). Logistic regression analysis showed that atrial defibrillation failure (relative risk [RR] 19.34, P=0.05) and age of >75 years (RR 15.25, P=0.03) were independent predictors of in-hospital death.

CONCLUSION

Nifekalant renders electrical defibrillation and the prevention of the early recurrence of hemodynamically unstable AF more successful without deteriorating hemodynamics, and successful defibrillation is associated with a more favorable patient outcome. Pretreatment with other class III drugs, e.g., ibutilide or dofetilide, would also be efficacious in patients with failed urgent electrical cardioversion.