Amiodarone -- waxed and waned and waxed again

Structural modeling of hERG channel-drug interactions using Rosetta

The human ether-a-go-go-related gene (hERG) not only encodes a potassium-selective voltage-gated ion channel essential for normal electrical activity in the heart but is also a major drug anti-target. Genetic hERG mutations and blockage of the channel pore by drugs can cause long QT syndrome, which predisposes individuals to potentially deadly arrhythmias. However, not all hERG-blocking drugs are proarrhythmic, and their differential affinities to discrete channel conformational states have been suggested to contribute to arrhythmogenicity. We used Rosetta electron density refinement and homology modeling to build structural models of open-state hERG channel wild-type and mutant variants (Y652A, F656A, and Y652A/F656 A) and a closed-state wild-type channel based on cryo-electron microscopy structures of hERG and EAG1 channels. These models were used as protein targets for molecular docking of charged and neutral forms of amiodarone, nifekalant, dofetilide, d/l-sotalol, flecainide, and moxifloxacin. We selected these drugs based on their different arrhythmogenic potentials and abilities to facilitate hERG current. Our docking studies and clustering provided atomistic structural insights into state-dependent drug-channel interactions that play a key role in differentiating safe and harmful hERG blockers and can explain hERG channel facilitation through drug interactions with its open-state hydrophobic pockets.

Effects of Antiarrhythmic Drugs on Antiepileptic Drug Action-A Critical Review of Experimental Findings

Severe cardiac arrhythmias developing in the course of seizures increase the risk of SUDEP (sudden unexpected death in epilepsy). Hence, epilepsy patients with pre-existing arrhythmias should receive appropriate pharmacotherapy. Concomitant treatment with antiarrhythmic and antiseizure medications creates, however, the possibility of drug–drug interactions. This is due, among other reasons, to a similar mechanism of action. Both groups of drugs inhibit the conduction of electrical impulses in excitable tissues. The aim of this review was the analysis of such interactions in animal seizure models, including the maximal electroshock (MES) test in mice, a widely accepted screening test for antiepileptic drugs.

Cardioprotective effects of amiodarone in a rat model of epilepsy-induced cardiac dysfunction

Cardiac dysfunction is one of the leading causes of death in epilepsy. The anti-arrhythmic drug, amiodarone, is under investigation for its therapeutic effects in epilepsy. We aimed to evaluate the possible effects of amiodarone on cardiac injury during status epilepticus, as it can cause prolongation of the QT interval. Five rat groups were enrolled in the study; three control groups (1) Control, (2) Control-lithium and (3) Control-Amio, treated with 150 mg/kg/intraperitoneal amiodarone, (4) Epilepsy model, induced by sequential lithium/pilocarpine administration, and (5) the epilepsy-Amio group. The model group expressed a typical clinical picture of epileptiform activity confirmed by the augmented electroencephalogram alpha and beta spikes. The anticonvulsive effect of amiodarone was prominent, it diminished (p < 0.001) the severity of seizures and hence, deaths and reduced serum noradrenaline levels. In the model group, the electrocardiogram findings revealed tachycardia, prolongation of the corrected QT (QTc) interval, depressed ST segments and increased myocardial oxidative stress. The in-vitro myocardial performance (contraction force and - (df/dt)_max ) was also reduced. Amiodarone decreased (p < 0.001) the heart rate, improved ST segment depression, and myocardial contractility with no significant change in the duration of the QTc interval. Amiodarone preserved the cardiac histological structure and reduced the myocardial injury markers represented by serum Troponin-I, oxidative stress and IL-1. Amiodarone pretreatment prevented the anticipated cardiac injury induced during epilepsy. Amiodarone possessed an anticonvulsive potential, protected the cardiac muscle and preserved its histological architecture. Therefore, amiodarone could be recommended as a protective therapy against cardiac dysfunction during epileptic seizures with favourable effect on seizure activity.

Amiodarone Enhances Anticonvulsive Effect of Oxcarbazepine and Pregabalin in the Mouse Maximal Electroshock Model

Accumulating experimental studies show that antiarrhythmic and antiepileptic drugs share some molecular mechanisms of action and can interact with each other. In this study, the influence of amiodarone (a class III antiarrhythmic drug) on the antiseizure action of four second-generation antiepileptic drugs was evaluated in the maximal electroshock model in mice. Amiodarone, although ineffective in the electroconvulsive threshold test, significantly potentiated the antielectroshock activity of oxcarbazepine and pregabalin. Amiodarone, given alone or in combination with oxcarbazepine, lamotrigine, or topiramate, significantly disturbed long-term memory in the passive-avoidance task in mice. Brain concentrations of antiepileptic drugs were not affected by amiodarone. However, the brain concentration of amiodarone was significantly elevated by oxcarbazepine, topiramate, and pregabalin. Additionally, oxcarbazepine and pregabalin elevated the brain concentration of desethylamiodarone, the main metabolite of amiodarone. In conclusion, potentially beneficial action of amiodarone in epilepsy patients seems to be limited by neurotoxic effects of amiodarone. Although results of this study should still be confirmed in chronic protocols of treatment, special precautions are recommended in clinical conditions. Coadministration of amiodarone, even at low therapeutic doses, with antiepileptic drugs should be carefully monitored to exclude undesired effects related to accumulation of the antiarrhythmic drug and its main metabolite, desethylamiodarone.

Effectiveness of drug interventions to prevent sudden cardiac death in patients with heart failure and reduced ejection fraction: an overview of systematic reviews

OBJECTIVES

To summarise and synthesise the current evidence regarding the effectiveness of drug interventions to prevent sudden cardiac death (SCD) and all-cause mortality in patients with heart failure with reduced ejection fraction (HFrEF).

DESIGN

Overview of systematic reviews.

DATA SOURCES

MEDLINE, Embase, ISI Web of Science and Cochrane Library from inception to May 2017; manual search of references of included studies for potentially relevant reviews.

ELIGIBILITY CRITERIA FOR STUDY SELECTION

We reviewed the effectiveness of drug interventions for SCD and all-cause mortality prevention in patients with HFrEF. We included overviews, systematic reviews and meta-analyses of randomised controlled trials of beta-blockers, angiotensin-converting enzyme inhibitors (ACE-i), angiotensin receptor blockers (ARBs), antialdosterones or mineralocorticoid-receptor antagonists, amiodarone, other antiarrhythmic drugs, combined ARB/neprilysin inhibitors, statins and fish oil supplementation.

REVIEW METHODS

Two independent reviewers extracted data and assessed the methodological quality of the reviews and the quality of evidence for the primary studies for each drug intervention, using Assessing the Methodological Quality of Systematic Reviews (AMSTAR) and Grading of Recommendations, Assessment, Development and Evaluation(GRADE), respectively.

RESULTS

We identified 41 reviews. Beta-blockers, antialdosterones and combined ARB/neprilysin inhibitors appeared effective to prevent SCD and all-cause mortality. ACE-i significantly reduced all-cause mortality but not SCD events. ARBs and statins were ineffective where antiarrhythmic drugs and omega-3 fatty acids had unclear evidence of effectiveness for prevention of SCD and all-cause mortality.

CONCLUSIONS

This comprehensive overview of systematic reviews confirms that beta-blockers, antialdosterone agents and combined ARB/neprilysin inhibitors are effective on SCD prevention but not ACE-i or ARBs. In patients with high risk of SCD, an alternative therapeutic strategy should be explored in future research.

SYSTEMATIC REVIEW REGISTRATION

PROSPERO 2017: CRD42017067442.

Amiodarone, a multi-channel blocker, enhances anticonvulsive effect of carbamazepine in the mouse maximal electroshock model

Cardiac arrhythmia may occur in the course of epilepsy. Simultaneous therapy of the two diseases might be complicated by drug interactions since antiarrhythmic and antiepileptic agents share some molecular targets. The aim of this study was to evaluate the influence of amiodarone, an antiarrhythmic drug working as a multi-channel blocker, on the protective activity of four classical antiepileptic drugs in the maximal electroshock test in mice. Amiodarone at doses up to 75 mg/kg did not affect the electroconvulsive threshold in mice. Acute amiodarone at the dose of 75 mg/kg significantly potentiated the anticonvulsive effect of carbamazepine, but not that of valproate, phenytoin or phenobarbital in the maximal electroshock-induced seizures in mice. The antiarrhythmic agent and its combinations with antiepileptic drugs did not impair motor performance or long-term memory in mice, except for the combination of amiodarone and phenobarbital. Brain concentrations of antiepileptic drugs were not changed. Despite favourable impact of amiodarone on the anticonvulsive action of carbamazepine in the maximal electroshock, co-administration of the two drugs should be carefully monitored in clinical conditions. Further studies are necessary to evaluate effects of chronic treatment with amiodarone on seizure activity and the action of antiepileptic drugs.

Diltiazem versus Amiodarone to Prevent Atrial Fibrillation in Coronary Surgery

The prophylactic effect of amiodarone on atrial fibrillation after coronary bypass grafting with extracorporeal circulation was compared with that of diltiazem in two groups of 60 patients each. Patients were monitored continuously for 8 days. The incidence of atrial fibrillation was recorded retrospectively in a control group of 60 patients who received our standard prophylactic regimen of an oral beta blocker. The incidence of postoperative atrial fibrillation was not significantly different in the two test groups: 11.7% for the amiodarone group and 10% for the diltiazem group. The incidence of atrial fibrillation in the control group was 23.3% and the differences were marginally significant when compared to the amiodarone ( p = 0.093) and diltiazem groups ( p = 0.050). The prophylactic use of diltiazem or amiodarone is feasible and safe for patients undergoing coronary bypass, with similar rates of atrial fibrillation.

Interactions between amiodarone and the hERG potassium channel pore determined with mutagenesis and in silico docking

The antiarrhythmic drug amiodarone delays cardiac repolarisation through inhibition of hERG-encoded potassium channels responsible for the rapid delayed rectifier potassium current (I_Kr). This study aimed to elucidate molecular determinants of amiodarone binding to the hERG channel. Whole-cell patch-clamp recordings were made at 37 °C of ionic current (I_hERG) carried by wild-type (WT) or mutant hERG channels expressed in HEK293 cells. Alanine mutagenesis and ligand docking were used to investigate the roles of pore cavity amino-acid residues in amiodarone binding. Amiodarone inhibited WT outward I_hERG tails with a half-maximal inhibitory concentration (IC₅₀) of ∼45 nM, whilst inward I_hERG tails in a high K⁺ external solution ([K⁺]_e) of 94 mM were blocked with an IC₅₀ of 117.8 nM. Amiodarone’s inhibitory action was contingent upon channel gating. Alanine-mutagenesis identified multiple residues directly or indirectly involved in amiodarone binding. The IC₅₀ for the S6 aromatic Y652A mutation was increased to ∼20-fold that of WT I_hERG, similar to the pore helical mutant S624A (∼22-fold WT control). The IC₅₀ for F656A mutant I_hERG was ∼17-fold its corresponding WT control. Computational docking using a MthK-based hERG model differentiated residues likely to interact directly with drug and those whose Ala mutation may affect drug block allosterically. The requirements for amiodarone block of aromatic residues F656 and Y652 within the hERG pore cavity are smaller than for other high affinity I_hERG inhibitors, with relative importance to amiodarone binding of the residues investigated being S624A ∼ Y652A > F656A > V659A > G648A > T623A.

Amiodarone-induced bone marrow granulomas: an unusual cause of reversible pancytopenia

Bone marrow infiltration by granulomas rarely presents with cytopenias and is usually a result of atypical infections, lymphomas, or sarcoidosis. Drugs are also an important but often overlooked causal agent of bone marrow granulomas. Although rare, amiodarone has been associated with bone marrow granuloma formation. This case report describes a 73-year-old male who presented with pancytopenia during a preoperative evaluation. Amiodarone therapy was suspected to be the causal agent after diagnostic evaluation and exclusion of other causes. After cessation of amiodarone, the patient's pancytopenia gradually resolved over a period of several months. Our report illustrates an often overlooked yet important cause of reversible pancytopenia owing to suspected amiodarone-induced bone marrow granuloma formation, and guides clinicians in an expected timeline for blood count improvement after cessation of this drug.

Amiodarone for the emergency care of children

Amiodarone is a class 3 antiarrhythmic agent used for a broad range of arrhythmias including adenosine-resistant supraventricular tachycardia, junctional ectopic tachycardia, and ventricular tachycardia. Compared with adults, there are few data on its use in children with arrhythmias resistant to conventional therapy. National and international guidelines for cardiopulmonary resuscitation and emergency cardiovascular care recommend its use for a variety of arrhythmias based on case reports, cohort studies, and extrapolation from adult data. This article will review the historical development, chemical properties, metabolism, indications and contraindications, and adverse effects of amiodarone in infants and children. After completing this CME activity, the reader should be able to utilize amiodarone in the pediatric population for arrhythmias and identify complications associated with its use.

The hERG potassium channel and hERG screening for drug-induced torsades de pointes

Drug-induced torsades de pointes (TdP) arrhythmia is a major safety concern in the process of drug design and development. The incidence of TdP tends to be low, so early pre-clinical screens rely on surrogate markers of TdP to highlight potential problems with new drugs. hERG (human ether-à-go-go-related gene, alternative nomenclature KCNH2) is responsible for channels mediating the 'rapid' delayed rectifier K+ current (IKr) which plays an important role in ventricular repolarization. Pharmacological inhibition of native IKr and of recombinant hERG channels is a shared feature of diverse drugs associated with TdP. In vitro hERG assays therefore form a key element of an integrated assessment of TdP liability, with patch-clamp electrophysiology offering a 'gold standard'. However, whilst clearly necessary, hERG assays cannot be assumed automatically to provide sufficient information, when considered in isolation, to differentiate 'safe' from 'dangerous' drugs. Other relevant factors include therapeutic plasma concentration, drug metabolism and active metabolites, severity of target condition and drug effects on other cardiac ion channels that may mitigate or exacerbate effects of hERG blockade. Increased understanding of the nature of drug-hERG channel interactions may ultimately help eliminate potential hERG blockade early in the design and development process. Currently, for promising drug candidates integration of data from hERG assays with information from other pre-clinical safety screens remains essential.

Fungicidal activity of amiodarone is tightly coupled to calcium influx

The antiarrhythmic drug amiodarone has microbicidal activity against fungi, bacteria and protozoa. In Saccharomyces cerevisiae, amiodarone triggers an immediate burst of cytosolic Ca2+, followed by cell death markers. Ca2+ transients are a common response to many forms of environmental insults and toxic compounds, including osmotic and pH shock, endoplasmic reticulum stress, and high levels of mating pheromone. Downstream signaling events involving calmodulin, calcineurin and the transcription factor Crz1 are critical in mediating cell survival in response to stress. In this study we asked whether amiodarone induced Ca2+ influx was beneficial, toxic or a bystander effect unrelated to the fungicidal effect of the drug. We show that downregulation of Ca2+ channel activity in stationary phase cells correlates with increased resistance to amiodarone. In actively growing cells, extracellular Ca2+ modulated the size and shape of the Ca2+ transient and directly influenced amiodarone toxicity. Paradoxically, protection was achieved both by removal of external Ca2+ or by adding high levels of CaCl2 (10 mM) to block the drug induced Ca2+ burst. Our results support a model in which the fungicidal activity of amiodarone is mediated by Ca2+ stress, and highlight the pathway of Ca2+ mediated cell death as a promising target for antifungal drug development.

Intravenous and oral amiodarone for the prevention of postoperative atrial fibrillation in patients undergoing off-pump coronary artery bypass surgery

BACKGROUND

Atrial fibrillation is still a frequent complication that increases morbidity after coronary artery bypass grafting. This prospective randomized study is designed to define efficacy of postoperative amiodarone prophylaxis in preventing atrial fibrillation after off-pump coronary artery bypass grafting.

METHODS

One hundred forty-four patients who underwent elective off-pump coronary artery bypass grafting were enrolled for the study. Seventy-six patients (amiodarone group) received 5 mg/kg loading amiodarone infusion in the first postoperative hour, followed by 10 mg/kg for the first 24 hours. After 24 hours, patients received 600 mg/day amiodarone orally for 7 days and 200 mg/day until the end of the postoperative first month. Sixty-eight patients received placebo (control group).

RESULTS

Preoperative characteristics and operative variables of the patients were similar in both groups. Incidence of new-onset atrial fibrillation and maximal ventricular rate response were recorded. The incidence of new-onset atrial fibrillation (11.8% versus 26.5%) (P = .025) and maximal ventricular rate response (109 +/- 13.8 beats/min versus 124.5 +/- 13.9 beats/min) (P = .011) were significantly lower in the amiodarone group. Duration of atrial fibrillation was 17.5 +/- 8.1 hours for the amiodarone group compared with 32.7 +/- 12 hours for the control group (P = .002).

CONCLUSION

Postoperative intravenous amiodarone prophylaxis followed by oral amiodarone significantly reduces the incidence of atrial fibrillation after off-pump coronary artery bypass grafting and the ventricular rate during atrial fibrillation.

The Effect of Levosimendan during Long-Term Amiodarone Treatment in Dogs

The haemodynamic and electrophysiological effects of levosimendan were studied in conscious dogs receiving long-term oral amiodarone treatment. Instrumented dogs were administered increasing doses of levosimendan (up to 0.9 microg/kg/min. intravenously) in three successive 30 min. infusions. This schedule was repeated on the 21st day of treatment with oral amiodarone 100 mg/kg/day. The extent of increase in left ventricular systolic pressure (LVSP) and the decrease in left ventricular end-diastolic pressure (LVEDP) seen with levosimendan were similar before and after long-term treatment with amiodarone. The levosimendan-induced increases in isovolumic contraction (+dP/dt) and in left ventricular contractility (dP/dt/P) seen prior to amiodarone administration were augmented during amiodarone treatment, an effect that was statistically significant (P<0.05) at the highest doses of levosimendan. A tendency towards a shortening of the QT interval and a rise in heart rate was observed for levosimendan alone but they did not exceed the physiological range when the drug was given in combination with amiodarone. QTc value was unaffected by levosimendan either alone or with amiodarone. These effects were apparent in animals with therapeutically meaningful plasma levels of levosimendan, amiodarone and desethylamiodarone levels. The results of this study show that the improvement in ventricular contractile performance usually associated with administration of levosimendan was somewhat enhanced by chronic oral treatment with amiodarone. It seems reasonable to infer that the inotropic potency and electrophysiological safety of parenteral levosimendan will be maintained in patients with heart failure during long-term treatment with oral amiodarone.

Efficacy and safety of intermittent, long-term, concomitant dobutamine and levosimendan infusions in severe heart failure refractory to dobutamine alone

Thirty-six consecutive patients in New York Heart Association functional class IV, who were resistant to 24-hour continuous dobutamine infusion, were treated with continuous infusions of dobutamine 10 microg/kg/min for > or =48 hours (group I, n = 18), followed by weekly intermittent 8-hour infusions or more often if needed. In group II (n = 18), after the initial 24-hour infusion of dobutamine, a 24-hour levosimendan infusion was added followed by biweekly 24-hour infusions. The addition of intermittent levosimendan infusions prolonged the survival of patients with advanced heart failure refractory to intermittent dobutamine infusions (45-day survival rates were 6% and 61% in groups I and II, respectively; p = 0.0002, log-rank test).

Dronedarone: an amiodarone analogue

Of the antiarrhythmic drugs in current use, amiodarone is one of the most effective and is associated with a comparatively low risk of drug-induced pro-arrhythmia, probably due to its multiple pharmacological actions on cardiac ion channels and receptors. However, amiodarone is associated with significant extra-cardiac side effects and this has driven development of amiodarone analogues. These analogues include short acting analogues (e.g., AT-2001) with similar acute effects to amiodarone, the thyroid receptor antagonist KB-130015 and dronedarone. Dronedarone, (SR-33589; Sanofi-Synthelabo), is a non-iodinated amiodarone derivative that inhibits Na +, K + and Ca 2+ currents. It is a potent inhibitor of the acetylcholine-activated K + current from atrial and sinoatrial nodal tissue, and inhibits the rapid delayed rectifier more potently than slow and inward rectifier K + currents and inhibits L-type calcium current. Dronedarone is an antagonist at alpha- and beta-adrenoceptors and unlike amiodarone, has little effect at thyroid receptors. Dronedarone is more potent than amiodarone in inhibiting arrhythmias and death in animal models of ischaemia- and reperfusion-induced arrhythmias. In the Dronedarone Atrial Fibrillation Study After Electrical Cardioversion (DAFNE) clinical trial, dronedarone 800 mg/day appeared to be effective and safe for the prevention of atrial fibrillation relapses after cardioversion. The Antiarrhythmic Trial with Dronedarone in Moderate-to-Severe Congestive Heart Failure Evaluating Morbidity Decrease (ANDROMEDA) trial was stopped due to a potential increased risk of death in the dronedarone group. Trials of dronedarone in the maintenance of sinus rhythm in patients with atrial fibrillation and a safety and tolerability study in patients with an implantable cardioverter defibrillator are ongoing. Further experimental and clinical studies are required before we have a definitive answer to whether dronedarone has advantages over amiodarone and other amiodarone analogues.

A review of the pharmacokinetics, electrophysiology and clinical efficacy of dronedarone

The results of major clinical trials and advances in pharmacologic and nonpharmacologic therapies are continuing to alter treatment approaches for both atrial and ventricular arrhythmias. Originally developed as an antianginal medication, amiodarone serves as the most effective antiarrhythmic drug in the treatment of both atrial and life-threatening ventricular arrhythmias. However, amiodarone has complex pharmacokinetics and is associated with serious extracardiac side effects, partially due to the presence of an iodine moiety. With a better understanding of the mechanisms of arrhythmias and antiarrhythmic drugs, new antiarrhythmic agents are currently under development with the hope that they will be more effective and safer than currently available drugs. One such drug that might potentially fulfill this hope is dronedarone. This amiodarone-like compound lacks the iodine moiety, and is similar in structure and electrophysiologic mechanisms of action to amiodarone, to date no evidence of liver, thyroid or pulmonary toxicity has been reported. Three clinical trials demonstrate efficacy in suppressing recurrences of atrial fibrillation and there is also evidence of a rate-slowing benefit during atrial fibrillation/flutter. However, the ANtiarrhythmic trial with DROnedarone in Moderate-to-severe congestive heart failure Evaluating morbidity Decrease (ANDROMEDA) study, performed in patients with left ventricular dysfunction, demonstrated excess noncardiac mortality in patients treated with dronedarone. Although effective in the treatment of atrial fibrillation, the future of this novel amiodarone-like drug remains uncertain until further clarification of the excess mortality in heart failure patients is better studied.

High affinity HERG K(+) channel blockade by the antiarrhythmic agent dronedarone: resistance to mutations of the S6 residues Y652 and F656

Pharmacological inhibition of human-ether-a-go-go-related gene (HERG) K(+) channels by structurally and therapeutically diverse drugs is associated with the 'acquired' form of long QT syndrome and with potentially lethal cardiac arrhythmias. Two aromatic amino-acid residues (Y652 and F656) on the inner (S6) helices are considered to be key constituents of a high affinity drug binding site within the HERG channel pore cavity. Using wild-type (WT) and mutant HERG channels expressed in mammalian cell lines, we have investigated HERG channel current (I(HERG)) blockade at 37+/-1 degrees C by dronedarone (DRONED), a non-iodinated analogue of the Class III antiarrhythmic agent amiodarone (AMIOD). Under our conditions WT I(HERG) tails, measured at -40 mV following activating pulses to +30 mV, were blocked with IC(50) values of approximately 59 and 70 nM for DRONED and AMIOD, respectively. I(HERG) inhibition by DRONED was contingent upon channel gating, with block developing rapidly on membrane depolarization, but with no preference for activated over inactivated channels. High external [K(+)] (94 mM) reduced the potency of I(HERG) inhibition by both DRONED and AMIOD. Strikingly, mutagenesis to alanine of the S6 residue F656 (F656A) failed to eliminate blockade by both DRONED and AMIOD, whilst Y652A had comparatively little effect on DRONED but some effect on AMIOD. These findings demonstrate that high affinity drug blockade of I(HERG) can occur without a strong dependence on the Y652 and F656 aromatic amino-acid residues.

Repetitive paroxysms of supraventricular tachyarrhythmias triggered during pediatric cardiac interventions: suppression after short infusion of amiodarone

Arrhythmias are the most common major complications encountered during pediatric cardiac catheterizations. This report describes the management of repetitive paroxysms of supraventricular tachyarrhythmias triggered by catheter manipulation during interventional procedures in two children. After 15 minutes, amiodarone infusion (25 microg/kg/min) eliminated further paroxysms in both patients, allowing both interventions to be completed safely and effectively.

L-thyroxine increases susceptibility of adult rats to low K+-induced ventricular fibrillation, and sinus rhythm restoration in old rats

Hypokalaemia increases the risk for life-threatening arrhythmias; however, data about interaction with thyroid status are lacking. The aim of this study was to investigate vulnerability of l-thyroxine (T(4))-treated adult and old rats to low K(+)-induced ventricular fibrillation (VF) as well as the ability of the heart to recover sinus rhythm. The experiments were performed on isolated heart preparations using the heart of 4- and 20-month-old female Wistar rats without and with feeding with T(4) 50 microg (100 g day)(-1) over a period of 2 weeks. Perfusion of the isolated heart with oxygenated Krebs-Henseleit solution at constant pressure was followed by perfusion with K(+)-deficient solution until occurrence of VF (< 10 min). After 2 min of sustained VF, the heart was perfused with normal solution for 10 min, during which sinus rhythm was restored. ECG, left ventricular pressure (LVP) and coronary flow were continuously monitored. The results showed that compared with untreated rats, the onset of low K(+)-induced ventricular premature beats was delayed and their number was significantly decreased in both T(4)-treated groups. Nevertheless, VF occurred earlier in T(4)-treated than in non-treated adult rats (6.78 +/- 0.28 vs. 9.59 +/- 0.55 min, P < 0.05), whereas the difference was not significant in aged animals. Furthermore, sinus rhythm appeared earlier in old T(4)-treated rats compared with non-treated rats (7.18 +/- 0.57 vs. 8.94 +/- 0.64 min, P < 0.05), whereas in adult hearts it set in at practically the same time regardless of treatment. In conclusion, our results indicate that administration of a pharmacological dose of T(4) can increase the risk of low K(+)-induced VF in adult but not in old animals; in the latter it even facilitated restoration of sinus rhythm. Moreover, enhanced mechanical function was observed in both adult and old T(4)-treated hearts.

Impact of long-term administration of amiodarone on the thyroid function of patients with Chagas' disease

The effect of long-term treatment with amiodarone on patients with Chagas' disease has seldom been reported. This nonrandomized observational study attempted to analyze the follow-up of patients with Chagas' disease regarding their clinical evolution, thyroid dysfunction, and goiter. We compared 72 patients with long-term use (11 +/- 5 years) of amiodarone, including 22 patients who developed goiter, to 33 patients who did not use amiodarone, followed-up for 2 to 20 years (7 +/- 11 years). Follow-up of 72 patients for 9 +/- 5.4 years with periodic cardiac and thyroid function evaluations showed that only 26 maintained normal serum thyrotropin (TSH) levels; 24 presented with elevated levels; 4 had low levels, and 18 patients presented with fluctuations of TSH level. Among the 22 patients with goiter, only 3 (14%) patients maintained normal TSH, 8 (36%) had elevated TSH, 2 (9%) had low TSH, and 9 (41%) patients presented with fluctuating serum TSH levels. Most individuals remained clinically euthyroid with no evidence of cardiac impairment that could be attributed to thyroid dysfunction and the arrhythmias were adequately controlled by amiodarone. We suggest that amiodarone treatment may be continued for patients with Chagas' disease with arrhythmias, even in those who develop thyroid function abnormalities or goiter.

KB130015, a new amiodarone derivative with multiple effects on cardiac ion channels

KB130015 (KB015), a new drug structurally related to amiodarone, has been proposed to have antiarrhythmic properties. In contrast to amiodarone, KB015 markedly slows the kinetics of inactivation of Na(+) channels by enhancing concentration-dependently (K(0.5) asymptotically equal to 2 microM) a slow-inactivating I(Na) component (tau(slow) asymptotically equal to 50 ms) at the expense of the normal, fast-inactivating component (tau(fast) asymptotically equal to 2 to 3 ms). However, like amiodarone, KB015 slows the recovery from inactivation and causes a shift (K(0.5) asymptotically equal to 6.9 microM) of the steady-state voltage-dependent inactivation to more negative potentials. Despite prolonging the opening of Na(+) channels KB015 does not lengthen but often shortens the action potential duration (APD) in pig myocytes or in multicellular preparations. Only short APDs in mouse are markedly prolonged by KB015, which frequently induces early afterdepolarizations. KB015 has also an effect on other ion channels. It decreases the amplitude of the L-type Ca(2+) current (I(Ca-L)) without changing its time course, and it inhibits G-protein gated and ATP-gated K(+) channels. Both the receptor-activated I(K(ACh)) (induced in atrial myocytes by either ACh, adenosine or sphingosylphosphorylcholine) and the receptor-independent (GTPgammaS-induced or background) I(K(ACh)) are concentration-dependently (K(0.5) asymptotically equal to 0.6 - 0.9 microM) inhibited by KB015. I(K(ATP)), induced in atrial myocytes during metabolic inhibition with 2,4-dinitrophenol (DNP), is equally suppressed. However, KB015 has no effect on I(K1) or on I(to). Consistent with the effects in K(+) currents, KB015 does not depolarize the resting potential but antagonizes the APD shortening by muscarinic receptor activation or by DNP. Intracellular cell dialysis with KB015 has marginal or no effect on Na(+) or K(+) channels and does not prevent the effect of extracellularly applied drug, suggesting that KB015 interacts directly with channels at sites more easily accessible from the extracellular than the intracellular side of the membrane. At high concentrations KB015 exerts a positive inotropic action. It also interacts with thyroid hormone nuclear receptors. Its toxic effects remain largely unexplored, but it is well tolerated during chronic administration.

Amiodarone reduces the incidence of atrial fibrillation after coronary artery bypass grafting

OBJECTIVE

The purpose of this study was to evaluate the safety and efficacy of postoperative administration of prophylactic amiodarone in the prevention of new-onset postoperative atrial fibrillation in patients undergoing coronary artery bypass grafting.

METHODS

In this prospective study 157 patients were randomly divided into two groups: 77 patients (amiodarone group) received intravenous amiodarone in a dose of 10 mg/kg/d for postoperative 48 hours. On postoperative day 2 oral amiodarone was started with a dose of 600 mg/d for 5 days, 400 mg/d for the following 5 days, and 200 mg/d for 20 days, and 80 patients received placebo (control group).

RESULTS

Preoperative patient characteristics and operative variables were similar in the two groups. Postoperative atrial fibrillation occurred in 8 patients (10.4%) receiving amiodarone and in 20 (25.0%) patients receiving placebo (P =.017). Duration of atrial fibrillation was 12.8 +/- 4.8 hours for the amiodarone group compared with 34.7 +/- 28.7 hours for the control group (P =.003). The maximum ventricular rate during atrial fibrillation was slower in the amiodarone group than in the control group (105.9 +/- 19.1 beats per minute and 126.0 +/- 18.5 beats per minute, respectively, P =.016). The two groups had a similar incidence of complication other than rhythm disturbances (20.8% vs 20.0%, P =.904). Amiodarone group patients had shorter hospital stays than that of control group patients (6.8 +/- 1.7 days vs 7.8 +/- 2.9 days, P =.014). The in-hospital mortality was not different between two groups (1.3% vs 3.8, P =.620).

CONCLUSIONS

Postoperative intravenous amiodarone, followed by oral amiodarone, appears to be effective in the prevention of new-onset postoperative atrial fibrillation. It also reduces ventricular rate and duration of atrial fibrillation after coronary artery bypass grafting. It is well tolerated and decreases the length of hospital stay.

Present and future pharmacotherapy for heart failure

The pharmacotherapy currently recommended by the American College of Cardiology and the American Heart Association for heart failure (HF) is a diuretic, an angiotensin-converting enzyme inhibitor (ACEI), a beta-adrenoceptor antagonist and (usually) digitalis. This current treatment of HF may be improved by optimising the dose of ACEI used, as increasing the dose of lisinopril increases its benefits in HF. Selective angiotensin receptor-1 (AT(1)) antagonists are effective alternatives for those who cannot tolerate ACEIs. AT(1) antagonists may also be used in combination with ACEIs, as some studies have shown cumulative benefits for the combination. In addition to being used in Stage IV HF patients, in whom it has a marked benefit, spironolactone should be studied in less severe HF and in the presence of beta-blockers. The use of carvedilol, extended-release metoprolol and bisoprolol should be extended to severe HF patients as these agents have been shown to decrease mortality in this group. The ancillary properties of carvedilol, particularly antagonism at prejunctional beta -adrenoceptors, may give it additional benefits to selective beta(1)-adrenoceptor antagonists. Celiprolol and bucindolol are not the beta-blockers of choice in HF, as they do not decrease mortality. Although digitalis does not reduce mortality, it remains the only option for a long-term positive inotropic effect, as the long-term use of the phosphodiesterase inhibitors is associated with increased mortality. The calcium sensitising drug levosimendan may be useful in the hospital treatment of decompensated HF to increase cardiac output and improve dyspnoea and fatigue. The antiarrhythmic drug amiodarone should probably be used in patients at high risk of arrhythmic or sudden death, although this treatment may soon be superseded by the more expensive implanted cardioverter defibrillators, which are probably more effective and have fewer side effects. The natriuretic peptide nesiritide has recently been introduced for the hospital treatment of decompensated HF. Novel drugs that may be beneficial in the treatment of HF include the vasopeptidase inhibitors and the selective endothelin-A receptor antagonists but these require much more investigation. However, disappointing results have been obtained in a large clinical trial of the tumour necrosis factor alpha antagonist etanercept, where no likelihood of a difference between placebo and etanercept was observed. Small clinical trials with recombinant growth hormone to thicken ventricles in dilated cardiomyopathy have given variable results.