Antiarrhythmic actions of amiodarone: a profile of a paradoxical agent

Amiodarone prevents wave front-tail interactions in patients with heart failure: an in silico study

Amiodarone (AM) is an antiarrhythmic drug whose chronic use has proved effective in preventing ventricular arrhythmias in a variety of patient populations, including those with heart failure (HF). AM has both class III [i.e., it prolongs the action potential duration (APD) via blocking potassium channels) and class I (i.e., it affects the rapid sodium channel) properties; however, the specific mechanism(s) by which it prevents reentry formation in patients with HF remains unknown. We tested the hypothesis that AM prevents reentry induction in HF during programmed electrical stimulation (PES) via its ability to induce postrepolarization refractoriness (PRR) via its class I effects on sodium channels. Here we extend our previous human action potential model to represent the effects of both HF and AM separately by calibrating to human tissue and clinical PES data, respectively. We then combine these models (HF + AM) to test our hypothesis. Results from simulations in cells and cables suggest that AM acts to increase PRR and decrease the elevation of takeoff potential. The ability of AM to prevent reentry was studied in silico in two-dimensional sheets in which a variety of APD gradients (ΔAPD) were imposed. Reentrant activity was induced in all HF simulations but was prevented in 23 of 24 HF + AM models. Eliminating the AM-induced slowing of the recovery of inactivation of the sodium channel restored the ability to induce reentry. In conclusion, in silico testing suggests that chronic AM treatment prevents reentry induction in patients with HF during PES via its class I effect to induce PRR.NEW & NOTEWORTHY This work presents a new model of the action potential of the human, which reproduces the complex dynamics during premature stimulation in heart failure patients with and without amiodarone. A specific mechanism of the ability of amiodarone to prevent reentrant arrhythmias is presented.

Current Drug Treatment Strategies for Atrial Fibrillation and TASK-1 Inhibition as an Emerging Novel Therapy Option

Atrial fibrillation (AF) is the most common sustained arrhythmia with a prevalence of up to 4% and an upwards trend due to demographic changes. It is associated with an increase in mortality and stroke incidences. While stroke risk can be significantly reduced through anticoagulant therapy, adequate treatment of other AF related symptoms remains an unmet medical need in many cases. Two main treatment strategies are available: rate control that modulates ventricular heart rate and prevents tachymyopathy as well as rhythm control that aims to restore and sustain sinus rhythm. Rate control can be achieved through drugs or ablation of the atrioventricular node, rendering the patient pacemaker-dependent. For rhythm control electrical cardioversion and pharmacological cardioversion can be used. While electrical cardioversion requires fasting and sedation of the patient, antiarrhythmic drugs have other limitations. Most antiarrhythmic drugs carry a risk for pro-arrhythmic effects and are contraindicated in patients with structural heart diseases. Furthermore, catheter ablation of pulmonary veins can be performed with its risk of intraprocedural complications and varying success. In recent years TASK-1 has been introduced as a new target for AF therapy. Upregulation of TASK-1 in AF patients contributes to prolongation of the action potential duration. In a porcine model of AF, TASK-1 inhibition by gene therapy or pharmacological compounds induced cardioversion to sinus rhythm. The DOxapram Conversion TO Sinus rhythm (DOCTOS)-Trial will reveal whether doxapram, a potent TASK-1 inhibitor, can be used for acute cardioversion of persistent and paroxysmal AF in patients, potentially leading to a new treatment option for AF.

β-Adrenergic Blockers as Antiarrhythmic and Antifibrillatory Compounds: An Overview

β-Adrenergic blockers have a wide spectrum of action for controlling cardiac arrhythmias that is larger than initially thought. Data from the past several decades indicate that, as an antiarrhythmic class, β-blockers remain among the very few pharmacologic agents that reduce the incidence of sudden cardiac death, prolong survival, and ameliorate symptoms caused by arrhythmias in patients with cardiac disease. As a class of compounds, β-blockers have a fundamental pharmacologic property that attenuates the effects of competitive adrenergic receptors. However, the net clinical effects of the different β-receptor blockers may vary quantitatively because of variations in associated intrinsic sympathomimetic agonism and in their intrinsic potency for binding to β-receptors. These individual compounds also differ in their selectivity for β1- and β2-receptors. Metoprolol is a β1-selective blocker, whereas carvedilol is a nonselective β1- and β2-blocker, an antioxidant, and has a propensity to inhibit α1-receptors and endothelin. Evolving data from controlled and uncontrolled clinical trials suggest that there are clinically significant differences among this class of drugs. Recent evidence also suggests that the antiarrhythmic actions of certain β-receptor blockers such as carvedilol and metoprolol extend beyond the ventricular tissue to encompass atrial cells and help maintain sinus rhythm in patients with atrial fibrillation, especially in combination with potent antifibrillatory agents such as amiodarone. This introduction provides a current perspective on these newer developments in the understanding of the antiarrhythmic and antifibrillatory actions of β-blockers.

Investigation of the antifibrillatory drug interactions between Amiodarone and Ibutilide in isolated, perfused Rabbit hearts

In view of the reliability of the serial-shock method of measuring ventricular fibrillation threshold (VFT) in quantitatively assessing the antifibrillatory potency of many anti-arrhythmic drugs and the alarming reports of the proarrhythmic effects of several anti-arrhythmic agents, it was decided to use the above technique to study the possible interactions that may occur when anti-arrhythmic drugs from different classes are combined. Hearts isolated from New Zealand white rabbits of either sex weighing 1.5-2 kg were perfused by the Langendorff method with McEwen's solution. In six hearts, measurement of VFT was made in the absence of any drug throughout the experiments. Perfusion with either amiodarone or ibutilide produced significant, dose-dependent increase in VFT. In addition, there was no significant difference in the increase in VFT produced by the combined infusion of 1 μmol of amiodarone and 0.01 μmol of ibutilide and the summation of the increases produced by the separate infusion of these two concentrations. This is in contrast to a significant synergistic antifibrillatory effect of the combined use of lidocaine and propranolol that was reported previously. The lack of antifibrillatory interactions between amiodarone and Ibutilide may suggest the safety of combining the two drugs in the treatment of cardiac arrhythmias. However, further studies are required to establish this in the clinical setup.

CHronic use of Amiodarone aGAinSt Implantable cardioverter-defibrillator therapy for primary prevention of death in patients with Chagas cardiomyopathy Study: rationale and design of a randomized clinical trial

BACKGROUND

The implantable cardioverter defibrillator (ICD) is better than antiarrhythmic drug therapy for the primary and secondary prevention of all-cause mortality and sudden cardiac death in patients with either coronary artery disease or idiopathic dilated cardiomyopathy. This study aims to assess whether the ICD also has this effect for primary prevention in chronic Chagas cardiomyopathy (CCC).

METHODS

In this randomized (concealed allocation) open-label trial, we aim to enroll up to 1,100 patients with CCC, a Rassi risk score for death prediction of ≥10 points, and at least 1 episode of nonsustained ventricular tachycardia on a 24-hour Holter monitoring. Patients from 28 centers in Brazil will be randomly assigned in a 1:1 ratio to receive an ICD or amiodarone (600 mg/d for 10 days, then 200-400 mg/d until the end of the study). The randomization sequence will be generated by computer, and the members of the committees responsible for end point validation and data analysis will be blinded to study assignment. The primary end point is all-cause death, and enrolment will continue until 256 patients have reached this end point. Key secondary end points include cardiovascular death, sudden cardiac death, hospitalization for heart failure, and quality of life. We expect follow-up to last 3 to 6 years, and data analysis will be done on an intention-to-treat basis. This trial is registered with ClinicalTrials.gov number NCT01722942.

CONCLUSION

CHAGASICS is the first large-scale trial to assess the benefit of ICD therapy for the primary prevention of death in patients with CCC and nonsustained ventricular tachycardia, who have a moderate to high risk of death.

Tumor necrosis factor-alpha potentiates the cytotoxicity of amiodarone in Hepa1c1c7 cells: roles of caspase activation and oxidative stress

Amiodarone (AMD), a class III antiarrhythmic drug, causes idiosyncratic hepatotoxicity in human patients. We demonstrated previously that tumor necrosis factor-alpha (TNF-α) plays an important role in a rat model of AMD-induced hepatotoxicity under inflammatory stress. In this study, we developed a model in vitro to study the roles of caspase activation and oxidative stress in TNF potentiation of AMD cytotoxicity. AMD caused cell death in Hepa1c1c7 cells, and TNF cotreatment potentiated its toxicity. Activation of caspases 9 and 3/7 was observed in AMD/TNF-cotreated cells, and caspase inhibitors provided minor protection from cytotoxicity. Intracellular reactive oxygen species (ROS) generation and lipid peroxidation were observed after treatment with AMD and were further elevated by TNF cotreatment. Adding water-soluble antioxidants (trolox, N-acetylcysteine, glutathione, or ascorbate) produced only minor attenuation of AMD/TNF-induced cytotoxicity and did not influence the effect of AMD alone. On the other hand, α-tocopherol (TOCO), which reduced lipid peroxidation and ROS generation, prevented AMD toxicity and caused pronounced reduction in cytotoxicity from AMD/TNF cotreatment. α-TOCO plus a pancaspase inhibitor completely abolished AMD/TNF-induced cytotoxicity. In summary, activation of caspases and oxidative stress were observed after AMD/TNF cotreatment, and caspase inhibitors and a lipid-soluble free-radical scavenger attenuated AMD/TNF-induced cytotoxicity.

Amiodarone exposure during modest inflammation induces idiosyncrasy-like liver injury in rats: role of tumor necrosis factor-alpha

Amiodarone [2-butyl-3-(3′,5′-diiodo-4’α-diethylaminoethoxybenzoyl)-benzofuran] (AMD), a class III antiarrhythmic drug, is known to cause idiosyncratic hepatotoxic reactions in human patients. One hypothesis for the etiology of idiosyncratic adverse drug reactions is that a concurrent inflammatory stress results in decreased threshold for drug toxicity. To explore this hypothesis in an animal model, male Sprague-Dawley rats were treated with nonhepatotoxic doses of AMD or its vehicle and with saline vehicle or lipopolysaccharide (LPS) to induce low-level inflammation. Elevated alanine aminotransferase (ALT), aspartate aminotransferase, alkaline phosphatase, and gamma-glutamyltransferase activities as well as increased total bile acid concentrations in serum and midzonal hepatocellular necrosis were observed only in AMD/LPS-cotreated rats. The time interval between AMD and LPS administration was critical: AMD injected 16 h before LPS led to liver injury, whereas AMD injected 2–12 h before LPS failed to cause this response. The increase in ALT activity in AMD/LPS cotreatment showed a clear dose-response relationship with AMD as well as LPS. The metabolism and hepatic accumulation of AMD were not affected by LPS coexposure. Serum concentration of tumor necrosis factor-alpha (TNF) was significantly increased by LPS and was slightly prolonged by AMD. In Hepac1c7 cells, addition of TNF potentiated the cytotoxicity of both AMD and its primary metabolite, mono-N-desethylamiodarone. In vivo inhibition of TNF signaling by etanercept attenuated the AMD/LPS-induced liver injury in rats. In summary, AMD treatment during modest inflammation induced severe hepatotoxicity in rats, and TNF contributed to the induction of liver injury in this animal model of idiosyncratic AMD-induced liver injury.

Augmenting Maintenance of Sinus Rhythm in the Control of Atrial Fibrillation by Antiarrhythmic Drug Combinations

In recent years, a major development in the treatment of atrial fibrillation (AF) is the use of catheter ablation, and a significant number of patients may benefit from this mode of therapy. On a global scale, it may not be feasible to deal with most patients solely on the basis of ablation. Therefore, it is likely that much of the therapy for AF will continue to rely on antiarrhythmic agents for maintaining sinus rhythm. For many years, amiodarone and sotalol have been the dominant antiarrhythmic agents, with amiodarone being the most effective antiarrhythmic in suppressing AF; however, amiodarone use is limited due to concerns of end-organ toxicity. Upstream therapies, such as statins, fish oil, angiotensin converting enzyme (ACE) inhibitors, and angiotensin receptor blockers may also provide additive efficacy to these and other membrane-active antiarrhythmics. In recent years, a number of new agents are being developed and the first successful congener of amiodarone, dronedarone, has been shown to be effective in controlling AF and reducing cardiovascular hospitalization. This paper explores the possibility of augmenting the extent of controlling AF by combining multiple potent antiarrhythmic agents old and new.

Aggravation of Arrhythmia by Antiarrhythmic Drugs (Proarrhythmia)

Arrhythmia aggravation by antiarrhythmic drugs (proarrhythmia) can be caused by worsening or a change of a preexisting arrhythmia, development of a new arrhythmia, or development of a bradyarrhythmia. Aggravation of arrhythmia usually occurs within several days of beginning an antiarrhythmic drug or increasing the dose of the drug. The time of occurrence is based on the particular drug and its pharmacokinetic properties. Although there are no ways to predict the patient at risk for developing arrhythmia aggravation with any specific agents, risk factors include QT interval prolongation, elevated serum levels of the drug, electrolyte abnormalities, presence of heart failure, a history of a sustained ventricular tachyarrhythmia, and underlying myocardial ischemia.

Comparative study between the protective effects of Saudi and Egyptian antivenoms, alone or in combination with ion channel modulators, against deleterious actions of Leiurus quinquestriatus scorpion venom

This study compared efficacy of two polyvalent antivenoms (Saudi Arabian and Egyptian), against lethality and pathophysiological changes of Leiurus quinquestriatus quinquestriatus (LQQ) scorpion venom in mice. Additionally, the study examined whether treatment with selected ion channel modulators, lidocaine, nimodipine or amiodarone would be effective, alone or combined with the antivenoms. The protein concentration of the Saudi antivenom was 1/3 of Egyptian, indicating lesser immunogenicity, while both preservative contents were within limits. In immunodiffusion experiments, both exhibited prominent precipitin bands indicating high concentrations of specific antibodies. Neutralizing capacities (60-70 LD(50)) stated on labels were confirmed. Both antivenoms significantly (P < 0.001) prolonged survival time (from 26.9 +/- 1.18 min, 100% dead with venom to 224-300 min, 0-30% dead) of envenomed mice, whether injected iv before or 5 min after venom. Injection of either antivenom plus ion channel modulators, gave comparable results to that observed in mice treated with antivenoms alone. The Na(+) channel blocker lidocaine and the Ca(2+) channel blocker nimodipine on their own significantly protected the animals (P < 0.05), but to a lesser extent. The two antivenoms, significantly ameliorated the venom-evoked changes in serum LDH (P < 0.001) and CKMB (P < 0.01) plus cardiac TNFalpha and nitrate/nitrite levels (P < 0.001). When combined with lidocaine or nimodipine, the effects were not greater than antivenom alone. Moreover, the antivenoms ameliorated characteristic venom-evoked changes in the isolated perfused Langendorff hearts. Lidocaine and amiodarone were more effective than nimodipine. In Conclusion both Saudi and Egyptian antivenoms protected mice from the pathological and lethal effects of LQQ scorpion. Sodium and calcium channel blockers, lidocaine and nimodipine, may be useful when antivenoms are not available.

Amiodarone induces stress responses and calcium flux mediated by the cell wall in Saccharomyces cerevisiae

We used a proteomic approach to study effects of amiodarone on cells of the yeast Saccharomyces cerevisiae. Amiodarone has been shown to have antifungal activity in vitro and causes a massive increase in cytoplasmic calcium levels ([Ca2+]cyt). Proteomic analysis of cells exposed to amiodarone show that this drug elicits stress responses and points to involvement of proteins associated with the cell wall. We tested several of those proteins for involvement in the Ca2+ flux. In particular, the amiodarone-induced Ca2+ flux was decreased in bgl2Delta cells, which have altered levels of beta-glucan and chitin. The involvement of the cell wall in the Ca2+ flux induced by amiodarone treatment was tested by addition of yeast cell-wall components. While mannan inhibited the rise in [Ca2+]cyt, beta-glucan potentiated the Ca2+ flux by 4.5-fold, providing evidence that the cell wall is directly involved in controlling this Ca2+ flux. This conclusion is corroborated by the inhibition of the Ca2+ flux by calcofluor, which is known to bind to cell-wall chitin and inhibit cell growth. Zymolyase treatment altered the kinetics of amiodarone-induced calcium flux and uncoupled the inhibitory effect of calcofluor. These effects demonstrate that the cell-wall beta-glucan regulates calcium flux elicited by amiodarone.

Interaction with the hERG channel and cytotoxicity of amiodarone and amiodarone analogues

BACKGROUND AND PURPOSE

Amiodarone (2-n-butyl-3-[3,5 diiodo-4-diethylaminoethoxybenzoyl]-benzofuran, B2-O-CH(2)CH(2)-N-diethyl) is an effective class III antiarrhythmic drug demonstrating potentially life-threatening organ toxicity. The principal aim of the study was to find amiodarone analogues that retained human ether-a-go-go-related protein (hERG) channel inhibition but with reduced cytotoxicity.

EXPERIMENTAL APPROACH

We synthesized amiodarone analogues with or without a positively ionizable nitrogen in the phenolic side chain. The cytotoxic properties of the compounds were evaluated using HepG2 (a hepatocyte cell line) and A549 cells (a pneumocyte line). Interactions of all compounds with the hERG channel were measured using pharmacological and in silico methods.

KEY RESULTS

Compared with amiodarone, which displayed only a weak cytotoxicity, the mono- and bis-desethylated metabolites, the further degraded alcohol (B2-O-CH(2)-CH(2)-OH), the corresponding acid (B2-O-CH(2)-COOH) and, finally, the newly synthesized B2-O-CH(2)-CH(2)-N-pyrrolidine were equally or more toxic. Conversely, structural analogues such as the B2-O-CH(2)-CH(2)-N-diisopropyl and the B2-O-CH(2)-CH(2)-N-piperidine were significantly less toxic than amiodarone. Cytotoxicity was associated with a drop in the mitochondrial membrane potential, suggesting mitochondrial involvement. Pharmacological and in silico investigations concerning the interactions of these compounds with the hERG channel revealed that compounds carrying a basic nitrogen in the side chain display a much higher affinity than those lacking such a group. Specifically, B2-O-CH(2)-CH(2)-N-piperidine and B2-O-CH(2)-CH(2)-N-pyrrolidine revealed a higher affinity towards hERG channels than amiodarone.

CONCLUSIONS AND IMPLICATIONS

Amiodarone analogues with better hERG channel inhibition and cytotoxicity profiles than the parent compound have been identified, demonstrating that cytotoxicity and hERG channel interaction are mechanistically distinct and separable properties of the compounds.

Clinical review: treatment of new-onset atrial fibrillation in medical intensive care patients--a clinical framework

Atrial fibrillation occurs frequently in medical intensive care unit patients. Most intensivists tend to treat this rhythm disorder because they believe it is detrimental. Whether atrial fibrillation contributes to morbidity and/or mortality and whether atrial fibrillation is an epiphenomenon of severe disease, however, are not clear. As a consequence, it is unknown whether treatment of the arrhythmia affects the outcome. Furthermore, if treatment is deemed necessary, it is not known what the best treatment is. We developed a treatment protocol by searching for the best evidence. Because studies in medical intensive care unit patients are scarce, the evidence comes mainly from extrapolation of data derived from other patient groups. We propose a treatment strategy with magnesium infusion followed by amiodarone in case of failure. Although this strategy seems to be effective in both rhythm control and rate control, the mortality remained high. A randomised controlled trial in medical intensive care unit patients with placebo treatment in the control arm is therefore still defendable.

Dose-dependent effects of oral dronedarone on the circadian variation of RR and QT intervals in healthy subjects: implications for antiarrhythmic actions

Dronedarone, a non-iodinated benzofuran derivative, was developed as a potentially less toxic alternative to amiodarone. This study describes Holter data of dronedarone in humans. Five groups of healthy subjects were given 1 of 5 oral doses of dronedarone in a twice-daily regimen or placebo. Holter recordings of circadian rhythmicity of RR and QT intervals were evaluated. Dronedarone prolonged RR and QT intervals as a function of dose, without effect on circadian patterns. The relative prolongation of QT, QTc, and RR by dronedarone was significant. The QTc interval did not exhibit a clearly recognizable circadian pattern, suggesting that the circadian pattern of the QT interval was mostly a reflection of circadian changes in the RR interval in the study population. Dronedarone resembled amiodarone in class III and sympatholytic effects, indicating its potential as a unique antiarrhythmic compound seemingly devoid of the side effects mediated by iodine in amiodarone.

[Acquired long QT syndrome: a dominant problem?]

QT prolongation is essentially of pharmacologic origin. It is principally linked to a block of the outward potassium current Ikr, with as a consequence a prolongation of the repolarisation causing early after potentials and re-entry. The term "repolarisation reserve" expresses the variable risk of arrhythmia among individuals under the same drug blocking Ikr. This reserve can be altered under various pathologic or genetic conditions. A series of risk factors (bradycar-Torsades de pointes} were described in 1966 by Dessertenne. They are due to a perturbation of ventricular repolarisation causing QT prolongation on surface ECG. Acquired dia, electrolytic disorders, cardiac disease, neurologic disorders, nutrition troubles, female gender) can play a role as well as the metabolic processing of pharmacological agents by Cytochrome P450 and various inhibitors or inductors of this system which can influence the half life of drugs. The list of drugs involved is continuously increasing: antiarrhythmics, antihistamines, psychotropics, anti-infectious are the main categories involved. Risk prediction is difficult particularly for non cardiovascular drugs and a low risk incidence. An other risk is to exclude patients from the benefit of an efficient drug for a serious but not frequent risk, at last an industrial risk for the manufacturer when a drug is withdrawn lately when important quantities of money have already been invested for its development. The diagnosis of torsades is easy on standard ECG although QT measurement and its heart rate variation remain uneasy. The treatment of the arrhythmias is based on heart rate acceleration by Isoprenaline or intravenous pacing and on intravenous administration of magnesium.

K201, a multi-channel blocker, inhibits clofilium-induced torsades de pointes and attenuates an increase in repolarization

K201 (JTV519) is a 1,4-benzothiazepine derivative that exhibits a strong cardioprotective action and acts as a multiple-channel blocker, including as a K+ channel blocker. An experimental model of prolongation of the QT interval and torsades de pointes can be induced in rabbits by treatment with clofilium in the presence of the alpha1-adrenoreceptor agonist methoxamine. In this study we examined the effects of K201 with and without methoxamine on the QT and QTc intervals, and determined whether K201 inhibits clofilium-induced torsades de pointes in the presence of methoxamine (15 microg/kg/min) in rabbits (n=74). Administration of K201 (0, 40, 100, 200 and 400 microg/kg/min) with and without methoxamine prolonged the QT interval in a dose-dependent manner, and torsades de pointes did not occur in any animals. However, clofilium (50 microg/kg/min) with methoxamine induced torsades de pointes in all animals (6/6). Torsades de pointes occurred at rates of 100%, 67%, 40% and 0% at K201 concentrations of 0, 50, 200 and 400 microg/kg/min, respectively, in the clofilium-infused torsades de pointes model. Therefore, 400 microg/kg/min of K201 completely inhibited clofilium-induced torsades de pointes and attenuated the increase of repolarization caused by clofilium; the inhibitory effects of K201 may be related to its pharmacological properties as an alpha1-adrenoceptor blocker. Overall, our results show that K201 causes prolongation of the QT and QTc intervals, but does not induce torsades de pointes, with and without alpha1-adrenoceptor stimulation. Furthermore, K201 inhibits clofilium-induced torsades de pointes, despite QT prolongation, suggesting that QT prolongation alone is not a proarrhythmic signal.

Amiodarone: A multifaceted antiarrhythmic drug

Synthesized as an antianginal compound 40 years ago, amiodarone has emerged as a uniquely effective antiarrhythmic compound in recent years. It has numerous properties, the most prominent being the ability to lengthen repolarization in the atria and ventricles associated with bradycardia without the significant potential for torsades de pointes. Amiodarone effectively controls a wide spectrum of atrial and ventricular antiarrhythmic disorders, but its limiting side effects, such as thyroid dysfunction, pulmonary fibrosis, and dermatologic changes, may limit its long-term use in some patients. What aspects of the multiplicity of the properties of amiodarone are relevant to its unusual efficacy is not known. Deiodination and other structural changes in the amiodarone molecule have has led to a the loss of thyroid and pulmonary effects in the resulting derivative, dronedarone, which is in advanced clinical development.

Pharmacotherapy for atrial fibrillation: is rhythm control achievable?

As the most common sustained cardiac arrhythmia, the health burden presented by atrial fibrillation (AF) continues to grow. One of the current dilemmas in managing AF lies in the decision of whether to pursue a rate or rhythm control strategy. Current antiarrhythmic drugs have many limitations in terms of efficacy and adverse effects, and the availability of better antiarrhythmic drugs that are effective and safe would probably improve outcomes in AF. Enthusiasm for pulmonary vein ablation procedures has been tempered by the relatively high frequency of recurrences of AF, which are often asymptomatic. Ablation also frequently converts symptomatic episodes to asymptomatic recurrences. Irrespective of whether a rate control or a rhythm control strategy is adopted in patients with persistent AF, appropriate antithrombotic therapy should be used.

Unilateral amiodarone keratopathy

Vortex keratopathy is characterized by bilateral symmetrical superficial corneal deposits in a vortex pattern. It is the most common ocular finding among patients being treated with amiodarone. An unusual case of unilateral amiodarone vortex keratopathy in an elderly woman with corneal dysplasia in the second eye is presented. The pathophysiology of amiodarone keratopathy is explored, and a cause for the unilateral keratopathy in this patient proposed.

Amiodarone Is Poorly Effective for the Acute Termination of Ventricular Tachycardia

STUDY OBJECTIVE

It is hypothesized that intravenous (IV) amiodarone is poorly effective for the acute termination of sustained monomorphic ventricular tachycardia because of the relatively slow onset of its Vaughn-Williams class III effect to prolong myocardial depolarization and the refractory period. This study is designed to determine the effectiveness and safety of IV amiodarone for the termination of sustained monomorphic ventricular tachycardia.

METHODS

A retrospective case series was collected at 4 urban university-affiliated hospitals from September 1996 to April 2005 after institutional review board approval with waiver of informed consent. Emergency department (ED) patients treated with IV amiodarone for ventricular tachycardia were identified by ED treatment and hospital pharmacy billing records, International Classification of Diseases, Ninth Revision discharge codes, and ECG characteristics. All consecutive patients who received at least 150 mg amiodarone in 15 minutes or less for spontaneous sustained monomorphic ventricular tachycardia were eligible for inclusion. Sustained monomorphic ventricular tachycardia was defined as a tachycardia with uninterrupted duration or rapid recurrence despite automatic internal cardiac defibrillator therapy for at least 5 minutes before amiodarone treatment, monomorphic morphology, rate greater than 120 beats/min, QRS duration greater than 120 ms, and subsequently determined to be ventricular tachycardia by ECG criteria (eg, atrioventricular dissociation), implanted device interrogation, or formal electrophysiology study. Measured outcomes included sustained termination of ventricular tachycardia within 20 minutes of initiation of amiodarone infusion and any documented adverse effects. Rates of successful termination and adverse effects and their 95% confidence intervals (CIs) were calculated. The presence or average values of potentially confounding predictors in patients with and without ventricular tachycardia termination after amiodarone were also calculated and compared.

RESULTS

Thirty-three patients were identified and included. Five patients received electrical therapy within 20 minutes of initiation of amiodarone infusion, and the response to amiodarone was unknown. Twenty-seven of the remaining 28 patients received 150 mg amiodarone, and the rate of successful ventricular tachycardia termination was 8 of 28, 29% (95% CI 13 to 49). Two of 33 patients, 6% (95% CI 1 to 20), required direct current cardioversion for presyncope or hypotension temporally associated with amiodarone treatment.

CONCLUSION

IV amiodarone, as currently administered, is relatively safe but ineffective for the acute termination of sustained ventricular tachycardia.

Tolvaptan administration does not affect steady state amiodarone concentrations in patients with cardiac arrhythmias

BACKGROUND

Tolvaptan, a nonpeptide selective vasopressin receptor (V2) antagonist, is in development for the treatment of congestive heart failure and hyponatremia. Tolvaptan is primarily metabolized via CYP3A4. This study was conducted to determine the extent of the pharmacokinetic interaction between tolvaptan and steady state amiodarone, an antiarrhythmic drug commonly prescribed for patients with congestive heart failure and a known inhibitor of other drugs metabolized by CYP3A4.

METHODS

This was a multicenter, open-label, 1-arm, 3-period, sequential treatment study conducted in 11 men (10) and women aged 49 to 80 years. They were primarily Caucasian (20) subjects, with a history of cardiac arrhythmias who were otherwise healthy. Subjects were to have been on oral amiodarone maintenance therapy of 200 mg/day for at least 10 months. All subjects took 200 mg amiodarone once daily on each study day; on days 3 and 4, they were also coadministered 30 and 90 mg of tolvaptan, respectively. The plasma concentrations of amiodarone and its metabolite desethylamiodarone were determined for 24 hours postdose on days 2, 3, and 4, tolvaptan concentrations were determined for 24 hours postdose on days 3 and 4.

RESULTS

As determined by the ratio of the geometric means and 90% confidence intervals (0.5 to 2.0) for the maximal plasma concentration and the area under the curve during the dosing interval for both amiodarone and desethylamiodarone, tolvaptan coadministration had no effect on either amiodarone and desethylamiodarone disposition, as all the geometric mean ratios (amiodarone + tolvaptan [30 or 90 mg] vs amiodarone alone) were approximately 1.

CONCLUSION

Tolvaptan coadministration does not alter steady-state amiodarone or desethylamiodarone concentrations. Tolvaptan concentrations did not appear to be different from historical controls. The most frequently reported adverse event was polyuria (15 of 21 subjects for amiodarone + 30 mg tolvaptan); an expected outcome due to the known potent aquaretic action of tolvaptan. The combination of amiodarone and tolvaptan was well tolerated.

Effects of High- and Low-Dose Amiodarone on Mortality, Left Ventricular Remodeling, and Hemodynamics in Rats with Experimental Myocardial Infarction

We examined the effect of high- (AHD) and low-dose (ALD) amiodarone on survival, hemodynamics, and left ventricular remodeling in rats with experimental myocardial infarction (MI). Thirty minutes after coronary artery ligation or sham operation, amiodarone (100 or 20 mg/kg/d) or placebo was given by gavages daily for 8 weeks. Eight weeks later, hemodynamic measurements were performed and left ventricular (LV) volume was determined after KCl-induced cardiac arrest. Early after MI, mortality was lower after both doses of amiodarone. However, excess mortality beginning 15 days after MI outweighed reduced early mortality in rats treated with AHD. Body weight and heart rate were reduced significantly and maximal stroke volume index improved by AHD. In rats with MI, AHD significantly shifted LV pressure-volume curves to the right and increased LV operating volume (2.84 +/- 0.10 versus 2.20 +/- 0.07 mL/kg, P < 0.05). In conclusion, high-dose amiodarone aggravated LV remodeling in rats with large experimental chronic MI probably by lowering heart rate. An early beneficial effect on mortality was probably also lost later by this mechanism. Low-dose amiodarone improved survival without effect on LV remodeling.

Predictors of in-hospital ventricular fibrillation or torsades de pointes in patients with acute symptomatic bradycardia

Severe bradyarrythmias remain as an important cause for hospital urgent admission and these patients can suffer potentially lethal complications (such as ventricular fibrillation [VF] and torsades de pointes [TdP]) between hospital admission and final therapy. Incidence and predictors of these tachyarrhythmias have not been well established. We retrospectively studied all consecutive patients (N = 243, age 75 +/- 10 years; 47% men) admitted to the emergency department of a general hospital between January 1998 and July 2000 for symptomatic bradyarrhythmia. Concomitant therapy included diuretics (25%), digitalis (10%), beta-blockers (10%), amiodarone (2%), and verapamil or diltiazem (8%). Syncope was the most frequent symptom at admission (54%). The most prevalent inclusion bradyarrhythmia was > or =second-degree AV block (82%). Eleven patients (4.5%) presented VF or TdP. Univariate predictors for these complications were previous amiodarone or diuretic intake, presentation as syncope, low serum potassium level, and longer QTc at admission. Multivariate analysis with logistic regression showed only therapy with diuretics and/or amiodarone and QTc at admission as significant predictors for TdP or VF development. Incidence of VF or TdP in patients admitted for symptomatic bradyarrhythmia is relatively important. A prolonged QTc interval and/or therapy with amiodarone or diuretics can predict their presentation.

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.

Cardiovascular collapse after amiodarone administration in neonatal supraventicular tachycardia

Amiodarone is recommended by the International Liaison Committee on Resuscitation and has been adapted by the Resuscitation Council (UK) and the Advanced Life Support Group for use in paediatric advanced life support and advanced paediatric life support for the treatment of refractory supraventricular tachycardia. The International Liaison Committee on Resuscitation has stated that resuscitation guidelines should be evidence based. We present a case report of a cardiovascularly stable infant with supraventricular tachycardia who had a variety of arrthymias requiring cardiopulmonary resucitation for a prolonged period of time after loading with intravenous amiodarone. We believe that this report, together with other evidence, may suggest caution with the use of amiodarone.

Effects of amiodarone and dronedarone on voltage-dependent sodium current in human cardiomyocytes

Effect of Dronedarone on Cardiac Na Current.

INTRODUCTION

Amiodarone (AM) is a highly effective antiarrhythmic agent used in the management of both atrial and ventricular arrhythmias. Its noniodinated analogue dronedarone (SR) may have fewer side effects than AM. In this study, we compared the effects of AM and SR on the sodium current I(Na) in human atrial myocytes.

METHODS AND RESULTS

INa was studied with the whole-cell, patch clamp technique. Both AM and SR induced a dose-dependent inhibition of I(Na) recorded at -40 mV from a holding potential of -100 mV. AM inhibited I(Na) by 41%+/- 11% (n = 4) at 3 microM, and by 80%+/- 7% (n = 5) at 30 microM. SR produced more potent block, inhibiting INa significantly at only 0.3 microM (23%+/- 10%, n = 4) and completely (97%+/- 4%, n = 4) at 3 microM. Both AM and SR had only moderate effects on voltage-dependent properties of I(Na) (current-voltage relationship, availability for activation) and had no effect on the current decay kinetics.

CONCLUSION

Both AM and SR inhibit I(Na) significantly in single human atrial cells, showing that the two drugs have Class I antiarrhythmic properties. The acute effects of SR are more potent than those of AM. The study supports the idea that the iodinated form of the molecule has no part in the acute effect of AM on Na+ channels.

Detection of proarrhythmia in the female rabbit heart: blinded validation

INTRODUCTION

Reliable detection of drug-induced proarrhythmia, especially the potential for polymorphic ventricular tachycardia, is of great importance in the development of new compounds that are safe for the heart and was evaluated in a blinded study.

METHODS AND RESULTS

In 142 female rabbits, the monophasic action potential was used to determine intraventricular conduction, action potential duration (APD), triangulation (APD30 to APD90), reverse use-dependence, instability and presence of chaotic behavior, early afterdepolarizations, torsades de pointes (TdP), and ventricular fibrillation. In addition, 31 coded drugs were tested in a blinded fashion in another 150 hearts. Prototype cardiovascular agents [quinidine (IA), lidocaine (IB), flecainide (IC), propranolol (II), sotalol (IIIB), amiodarone (IIIAB) and verapamil (IV)] were correctly characterized in terms of their effects upon conduction and APD. Agents documented in clinical practice to have proarrhythmic potential (droperidol, sotalol, mibefradil, bepridil, lidoflazine, ketanserin, sertindole, terfenadine, haloperidol, astemizole, cisapride, ziprasidone, lubeluzole, dofetilide, quinidine, ibutilide) were identified as such. Pimozide is reported to rarely produce TdP and was also found to elicit Class III action with few adverse effects. Equally important, agents believed not to be proarrhythmic (two solvents, atenolol, propranolol, fenoximone, cetirizine, verapamil, sildenafil, lidocaine, diltiazem) were identified as having no proarrhythmic activity.

CONCLUSION

The SCREENIT method properly characterized and quantified prototype cardiovascular drugs and correctly identified proarrhythmic noncardiovascular agents of various mechanisms, but it did not produce false-positive results.

Comparison of amiodarone versus ibutilide for the prevention of immediate recurrences of atrial fibrillation during pulmonary vein isolation

During segmental ostial ablation for pulmonary vein isolation, pulmonary vein potentials are easily identified during sinus rhythm or left atrial pacing. Therefore, maintenance of atrial fibrillation (AF) during the procedure is desirable. However, cardioversion is occasionally followed by an immediate recurrence of AF. This study compared the efficacy of ibutilide and amiodarone in preventing immediate recurrences of AF in patients who underwent pulmonary vein isolation. The subjects of this study were 25 patients (mean age 56 +/- 10 years) who underwent pulmonary vein isolation for AF who had an immediate recurrence of AF within 60 seconds after 2 transthoracic cardioversions. The patients were randomized to receive an infusion of either 300 mg of amiodarone over 10 minutes or 1 mg of ibutilide over 5 minutes. Cardioversion was repeated 15 minutes after the drug infusion. If immediate recurrences of AF occurred 2 more times, the alternative study drug was administered, and cardioversion was repeated. Immediate recurrences of AF were suppressed by amiodarone in 8 of 10 patients (80%), and by ibutilide in 9 of 15 patients (60%, p = 0.4). After crossover, immediate recurrence of AF was suppressed in 2 of 6 patients (33%) by amiodarone, and in 1 of 2 patients (50%) by ibutilide (p = 0.6). Ibutilide and amiodarone, when used alone or in combination, prevented immediate recurrences of AF in 20 of 25 patients (80%). There were no adverse drug effects. Ibutilide and amiodarone were equally effective in suppressing immediate recurrences of AF. Overall, immediate recurrences of AF can be prevented by amiodarone and/or ibutilide in 80% of patients.

Chronic administration of amiodarone does not affect Na+/Ca2+ exchange current in guinea pig cardiac ventricular myocytes

We investigated chronic effects of amiodarone on Na+/Ca2+ exchange current (INCX) and on the level of Na+/Ca2+ exchanger (NCX1) mRNA in guinea pig ventricular myocytes using the whole-cell clamp technique and RT-PCR analysis, respectively. Guinea pigs were intraperitoneally injected with 80 mg/kg per day of amiodarone or the vehicle (saline) for 1 or 4 weeks. Single ventricular cells were isolated from the hearts of both groups of animals. Action potential duration at 90% repolarization level was prolonged to 143% and 165% of the control values by treatment with amiodarone for 1 and 4 weeks, respectively. INCX density and the level of NCX1 mRNA were not significantly changed by chronic treatment with amiodarone. The level of thyroid hormone (T4) within the blood was not changed by the treatments. These results suggest that chronic treatment with amiodarone does not affect the Na+/Ca2+ exchanger, with respect to the level of its mRNA and current density in guinea pig ventricular myocytes.

Mechanisms of antiarrhythmic drug actions and their clinical relevance for controlling disorders of cardiac rhythm

This review on antiarrhythmic drugs traces the evolution of the fundamental mechanisms of action of drugs that have been used to control disorders of cardiac rhythm. It describes the very earliest data from experimental studies that dealt with the effects of acute and chronic administration of drugs in whole animals combined with the measurements of the action potential duration and the effective refractory period in isolated tissues. Antiarrhythmic drugs were found to have properties consistent with the block of fast sodium channel conduction, adrenergic blockade, repolarization block, and the block of slow-channel mediated conduction especially in the atrioventricular node. Over the past 15 years, the attention has focused on atrial tissue with atrial fibrillation emerging as the most common arrhythmia in clinical practice. Drug-induced increases in refractoriness as a function rate and in wavelength (product of refractoriness and conduction velocity), and a reduction in numbers of wavelets have been found to be critical in the conversion of atrial fibrillation and maintenance of sinus rhythm. The continued development of newer pharmacologic agents is likely to lead to the resolution of the controversy regarding rhythm versus rate control in various clinical subsets of the arrhythmia by controlled clinical trials.

The effects of acute and chronic amiodarone on activation patterns and defibrillation threshold during ventricular fibrillation in dogs

OBJECTIVES

The goal of this study was to evaluate the effects of acute and chronic amiodarone on activation patterns during ventricular fibrillation (VF), ventricular effective refractory period (VERP) and defibrillation threshold (DFT).

BACKGROUND

Acute and chronic amiodarone may act through different mechanisms.

METHODS

The VERP, VF activation patterns and DFT were determined in 24 dogs. Twelve dogs received acute intravenous amiodarone (10 mg/kg, n = 6) or saline (n = 6), and 12 dogs received chronic oral amiodarone (20 mg/kg/day, n = 6) or placebo (n = 6). Epicardial VF activation patterns were recorded with 504 electrodes. Quantitative descriptors of VF were calculated.

RESULTS

The DFT was unchanged by acute or chronic amiodarone. Although chronic amiodarone significantly extended the VERP, acute amiodarone did not. In the mapped region, acute and chronic amiodarone decreased the number of VF wavefronts by 42% and 60%. Acute amiodarone decreased conduction block by 22%, while chronic amiodarone increased block by 41% but decreased wave fractionation by 50%. Both chronic and acute amiodarone increased the size of the core of re-entrant circuits and decreased the incidence of re-entry by 44% and 57%; however, chronic amiodarone increased wavelength, while acute amiodarone did not.

CONCLUSIONS

Neither acute nor chronic amiodarone change the DFT. While both acute and chronic amiodarone decrease the number of wavefronts, decrease the incidence of re-entry and increase the size of re-entrant cores in the mapped region during VF, they achieve these antiarrhythmic effects through different electrophysiologic mechanisms. Chronic amiodarone prolonged the VF cycle length and slowed conduction velocity, indicating it increased the wavelength and/or the excitable gap.

Significance and control of cardiac arrhythmias in patients with congestive cardiac failure

A wide spectrum of ventricular and supraventricular tachyarrhythmias occurs in the setting of congestive cardiac failure. However, the two most clinically significant are atrial fibrillation and ventricular tachycardia and fibrillation. In the past there has been much emphasis on premature ventricular contractions and more recently, on nonsustained ventricular tachycardia. For the most part, these arrhythmias are asymptomatic in heart failure. They are markers of sudden arrhythmic death but their suppression by antiarrhythmic drugs have not resulted in a reduction of total mortality. Two approaches have been used to this end. The first is the use of beta-adrenergic blocking drugs and antiarrhythmic agents such as amiodarone. Beta-blockers have been shown to significantly reduce sudden death as well as total mortality, while the effects of amiodarone have been less decisive. The prospective role of the implantable cardioverter defibrillator (ICD) is undergoing critical evaluation in patients with cardiac failure at high risk for sudden death. The elective role of the ICD is well established as first-line therapy in patients with heart failure resuscitated from sudden death and in those with sustained ventricular tachycardia in conjunction with conventional therapies for cardiac decompensation. The prevalence of atrial fibrillation rises as a function of severity of cardiac failure, but it is also in known that persistent atrial fibrillation with an uncontrolled ventricular response may induce heart failure. Controlled ventricular response may prevent congestive heart failure and improve left ventricular function. The two most common causes of atrial fibrillation in cardiac failure in Europe and America are ischemic heart disease and hypertension, while mitral valve disease remains the prevalent cause elsewhere. The choice of antiarrhythmic drugs for maintaining sinus rhythm is critical in the prevention of heart failure aggravation and proarrhythmic reactions of antiarrhythmic drugs. Amiodarone and dofetilide are most widely used in this context.

Chronic and acute effects of dronedarone on the action potential of rabbit atrial muscle preparations: comparison with amiodarone

Dronedarone, a noniodinated derivative of amiodarone, is under evaluation as a potentially less toxic anti-arrhythmic alternative to amiodarone. The acute and chronic electrophysiologic effects of dronedarone and amiodarone were compared in isolated rabbit atrial muscle by microelectrode techniques. Four-week PO treatment with dronedarone or amiodarone increased action potential duration (APD90) (58 +/- 4 ms control versus 69 +/- 2 ms dronedarone, p < 0.01; 68 +/- 3 ms amiodarone, p < 0.01 for a 100-mg/kg/d dose) and effective refractory period (49 +/- 6 ms control versus 68 +/- 4 ms dronedarone, p < 0.01; 63 +/- 3 ms amiodarone, p < 0.01). The APD90 prolonged reverse rate-dependency. In contrast, acute superfusion with 10 microM dronedarone or amiodarone decreased APD90 (61 +/- 6 ms control versus 53 +/- 4 ms dronedarone, p < 0.05; 52 +/- 6 ms amiodarone, p < 0.05), effective refractory period (50 +/- 5 ms control versus 44 +/- 4 ms dronedarone, p < 0.05; 43 +/- 6 ms amiodarone, p < 0.05), and the maximum upstroke slope of the action potential (Vmax) (188 +/- 9 V/s control versus 182 +/- 11 V/s dronedarone p < 0.05; 182 +/- 11 V/s amiodarone, p < 0.05). Thus, chronic and acute electrophysiologic effects of dronedarone on rabbit atrial muscle are similar to those of amiodarone, suggesting a similar potential against atrial arrhythmias.

Proarrhythmic effects of intravenous quinidine, amiodarone, D-sotalol, and almokalant in the anesthetized rabbit model of torsade de pointes

The proarrhythmic effects of four antiarrhythmic agents were examined during alpha1-adrenoceptor stimulation in chloralose-anesthetized rabbits. Each dose of almokalant (26, 88, and 260 microg/kg), D-sotalol, quinidine, or amiodarone (each 3, 10, and 30 mg/kg) was infused i.v. over 5 min and there was a 20-min interval between each infusion. D-sotalol and almokalant evoked torsade de pointes (TdP) and other arrhythmics, frequently. The incidences of TdP were 0, 50, and 40% after administering the first, second, and third doses of the nonselective I(Kr) inhibitor D-sotalol, respectively. Similarly, these values were 20, 40, and 33% after administering the first, second, and third doses, respectively, of the selective I(Kr) inhibitor almokalant. Quinidine elicited only a few arrhythmics, but not TdP. Quinidine, D-sotalol, and almokalant evoked conduction blocks in a dose-related manner (p < 0.05) and prolonged QT and QT(c) intervals (p < 0.05). Amiodarone neither prolonged QT and QT(c) nor evoked ventricular tachyarrhythmias, blocks, or other proarrhythmias. In conclusion, these results show no direct correlation between the occurrence of TdP and the infusion rate or dose of anti-arrhythmics. Furthermore, the lack of TdP with quinidine warns of false-negative results in the applied model.

A Benefit-Risk Assessment of Class III Antiarrhythmic Agents

With beta-blockers as the exception, increasing doubt is emerging on the value of antiarrhythmic drug therapy following a series of trials that have either shown no mortality benefit or even an excess mortality. Vaughan Williams class I drugs are generally avoided in patients with structural heart disease, and class IV drugs are avoided in heart failure. Unfortunately, arrhythmias are a growing problem due to an increase in the incidence of atrial fibrillation and sudden death. The population is becoming older and more patients survive for a longer time period with congestive heart failure, which again increases the frequency of both supraventricular as well as ventricular arrhythmias. Class III antiarrhythmic drugs act by blocking repolarising currents and thereby prolong the effective refractory period of the myocardium. This is believed to facilitate termination of re-entry tachyarrhythmias. This class of drugs is developed for treatment of both supraventricular and ventricular arrhythmias. Amiodarone, sotalol, dofetilide, and ibutilide are examples of class III drugs that are currently available. Amiodarone and sotalol have other antiarrhythmic properties in addition to pure class III action, which differentiates them from the others. However, all have potential serious adverse events. Proarrhythmia, especially torsade de pointes, is a common problem making the benefit-risk ratio of these drugs a key question. Class III drugs have been evaluated in different settings: primary and secondary prevention of ventricular arrhythmias and in treatment of atrial fibrillation or flutter. Based on existing evidence there is no routine indication for antiarrhythmic drug therapy other than beta-blockers in patients at high risk of sudden death. Subgroup analyses of trials with amiodarone and dofetilide suggest that patients with atrial fibrillation may have a mortality reduction with these drugs. However, this needs to be tested in a prospective trial. Similarly, subgroups that will benefit from prophylactic treatment with class III antiarrhythmic drugs may be found based on QT-intervals or - in the future - from genetic testing. Class III drugs are effective in converting atrial fibrillation to sinus rhythm and for the maintenance of sinus rhythm after conversion. This is currently by far the most important indication for this class of drugs. As defined by recent guidelines, amiodarone and dofetilide have their place as second-line therapy except for patients with heart failure where they are first line therapy being the only drugs where the safety has been documented for this group of high risk patients.