Antiarrhythmic and Proarrhythmic Properties of QT-Prolonging Antianginal Drugs

Ranolazine: An Old Drug with Emerging Potential; Lessons from Pre-Clinical and Clinical Investigations for Possible Repositioning

Ischemic heart disease is a significant public health problem with high mortality and morbidity. Extensive scientific investigations from basic sciences to clinics revealed multilevel alterations from metabolic imbalance, altered electrophysiology, and defective Ca²⁺/Na⁺ homeostasis leading to lethal arrhythmias. Despite the recent identification of numerous molecular targets with potential therapeutic interest, a pragmatic observation on the current pharmacological R&D output confirms the lack of new therapeutic offers to patients. By contrast, from recent trials, molecules initially developed for other fields of application have shown cardiovascular benefits, as illustrated with some anti-diabetic agents, regardless of the presence or absence of diabetes, emphasizing the clear advantage of “old” drug repositioning. Ranolazine is approved as an antianginal agent and has a favorable overall safety profile. This drug, developed initially as a metabolic modulator, was also identified as an inhibitor of the cardiac late Na⁺ current, although it also blocks other ionic currents, including the hERG/Ikr K⁺ current. The latter actions have been involved in this drug’s antiarrhythmic effects, both on supraventricular and ventricular arrhythmias (VA). However, despite initial enthusiasm and promising development in the cardiovascular field, ranolazine is only authorized as a second-line treatment in patients with chronic angina pectoris, notwithstanding its antiarrhythmic properties. A plausible reason for this is the apparent difficulty in linking the clinical benefits to the multiple molecular actions of this drug. Here, we review ranolazine’s experimental and clinical knowledge on cardiac metabolism and arrhythmias. We also highlight advances in understanding novel effects on neurons, the vascular system, skeletal muscles, blood sugar control, and cancer, which may open the way to reposition this “old” drug alone or in combination with other medications.

A predictive in vitro risk assessment platform for pro-arrhythmic toxicity using human 3D cardiac microtissues

Cardiotoxicity of pharmaceutical drugs, industrial chemicals, and environmental toxicants can be severe, even life threatening, which necessitates a thorough evaluation of the human response to chemical compounds. Predicting risks for arrhythmia and sudden cardiac death accurately is critical for defining safety profiles. Currently available approaches have limitations including a focus on single select ion channels, the use of non-human species in vitro and in vivo, and limited direct physiological translation. We have advanced the robustness and reproducibility of in vitro platforms for assessing pro-arrhythmic cardiotoxicity using human induced pluripotent stem cell-derived cardiomyocytes and human cardiac fibroblasts in 3-dimensional microtissues. Using automated algorithms and statistical analyses of eight comprehensive evaluation metrics of cardiac action potentials, we demonstrate that tissue-engineered human cardiac microtissues respond appropriately to physiological stimuli and effectively differentiate between high-risk and low-risk compounds exhibiting blockade of the hERG channel (E4031 and ranolazine, respectively). Further, we show that the environmental endocrine disrupting chemical bisphenol-A (BPA) causes acute and sensitive disruption of human action potentials in the nanomolar range. Thus, this novel human 3D in vitro pro-arrhythmic risk assessment platform addresses critical needs in cardiotoxicity testing for both environmental and pharmaceutical compounds and can be leveraged to establish safe human exposure levels.

Trimetazidine and Other Metabolic Modifiers

Treatment goals for people with chronic angina should focus on the relief of symptoms and improving mortality rates so the patient can feel better and live longer. The traditional haemodynamic approach to ischaemic heart disease was based on the assumption that increasing oxygen supply and decreasing oxygen demand would improve symptoms. However, data from clinical trials, show that about one third of people continue to have angina despite a successful percutaneous coronary intervention and medical therapy. Moreover, several trials on chronic stable angina therapy and revascularisation have failed to show benefits in terms of primary outcome (survival, cardiovascular death, all-cause mortality), symptom relief or echocardiographic parameters. Failure to significantly improve quality of life and prognosis may be attributed in part to a limited understanding of ischaemic heart disease, by neglecting the fact that ischaemia is a metabolic disorder. Shifting cardiac metabolism from free fatty acids towards glucose is a promising approach for the treatment of patients with stable angina, independent of the underlying disease (macrovascular and/or microvascular disease). Cardiac metabolic modulators open the way to a greater understanding of ischaemic heart disease and its common clinical manifestations as an energetic disorder rather than an imbalance between the demand and supply of oxygen and metabolites.

Efficacy and Safety of a Metabolic Modulator Drug in Chronic Stable Angina: Review of Evidence from Clinical Trials

A number of newer antianginal agents, including nicorandil, trimetazidine, and ivabradine, have been synthesized in recent years, but ranolazine, a piperazine derivative that partially inhibits fatty acid oxidation and the late INa current in animal models, is of particular interest mechanistically. Earlier clinical trials with immediate-release ranolazine led to the current sustained-release version tested in the Monotherapy Assessment of Ranolazine In Stable Angina (MARISA) (n = 193) and Combination Assessment of Ranolazine In Stable Angina (CARISA) trials (n = 823) of patients with chronic angina and severe limitation of exercise capacity (ie, < 5 metabolic equivalents). MARISA was a placebo-controlled, randomized trial that compared ranolazine monotherapy (500 mg, 1000 mg, and 1500 mg, twice daily) to placebo. CARISA was a placebo-controlled trial that randomized patients on background 1-blocker or calcium antagonist therapy to placebo or ranolazine (750 mg or 1000 mg, twice daily). Both studies showed a significant increase in total exercise duration, time to angina onset, and time to 1 mm ST segment depression. The average magnitude of increase in exercise duration over placebo was 29 to 56 seconds at peak and 24 to 46 seconds at trough with the 3 doses tested in MARISA, and 24 to 34 seconds greater than placebo with the 2 doses used in CARISA. The beneficial effect was achieved without clinically important changes in rest or exercise heart rate or blood pressure. Weekly angina attack frequency and nitroglycerin usage were significantly reduced in a dose-dependent manner in the 12-week CARISA trial. Reported adverse effects were similar in MARISA and CARISA and consisted of asthenia, nausea, constipation, and dizziness. Syncope, reported in 8 patients at doses of 1000 mg twice daily or more may be related to attenuation of α-1 receptor activity. The mean QTc interval increased with dose and was less than 10 msec on ranolazine at 1000 mg twice daily. The mortality rates at 1 and 2 years in MARISA and CARISA open-label run-on studies were 2% and less than 5%, acceptable for this high-risk population with limited exercise capacity. In conclusion, clinical trial evidence with ranolazine to date is consistent with its proposed mechanism of action and demonstrates an effective antianginal profile that may benefit patients with severe chronic angina.

Effects of allocryptopine on outward potassium current and slow delayed rectifier potassium current in rabbit myocardium

Objective

Allocryptopine (ALL) is an effective alkaloid of Corydalis decumbens (Thunb.) Pers. Papaveraceae and has proved to be anti-arrhythmic. The purpose of our study is to investigate the effects of ALL on transmural repolarizing ionic ingredients of outward potassium current (I_to) and slow delayed rectifier potassium current (I_Ks).

Methods

The monophasic action potential (MAP) technique was used to record the MAP duration of the epicardium (Epi), myocardium (M) and endocardium (Endo) of the rabbit heart and the whole cell patch clamp was used to record I_to and I_Ks in cardiomyocytes of Epi, M and Endo layers that were isolated from rabbit ventricles.

Results

The effects of ALL on MAP of Epi, M and Endo layers were disequilibrium. ALL could effectively reduce the transmural dispersion of repolarization (TDR) in rabbit transmural ventricular wall. ALL decreased the current densities of I_to and I_Ks in a voltage and concentration dependent way and narrowed the repolarizing differences among three layers. The analysis of gating kinetics showed ALL accelerated the channel activation of I_to in M layers and partly inhibit the channel openings of I_to in Epi, M and Endo cells. On the other hand, ALL mainly slowed channel deactivation of I_Ks channel in Epi and Endo layers without affecting its activation.

Conclusions

Our study gives partially explanation about the mechanisms of transmural inhibition of I_to and I_Ks channels by ALL in rabbit myocardium. These findings provide novel perspective regarding the anti-arrhythmogenesis application of ALL in clinical settings.

SKF-96365 blocks human ether-à-go-go-related gene potassium channels stably expressed in HEK 293 cells

SKF-96365 is a TRPC channel antagonist commonly used to characterize the potential functions of TRPC channels in different systems, which was recently reported to induce QTc prolongation on ECG by inhibiting TRPC channels. The present study investigates whether the blockade of cardiac repolarization currents would be involved in the increase of QTc interval. Cardiac repolarization currents were recorded in HEK 293 cells stably expressing human ether-à-go-go-related gene potassium (hERG or hKv11.1) channels, hKCNQ1/hKCNE1 channels (IKs) or hKir2.1 channels and cardiac action potentials were recorded in guinea pig ventricular myocytes using a whole-cell patch technique. The potential effect of SKF-96365 on QT interval was evaluated in ex vivo guinea pig hearts. It was found that SKF-96365 inhibited hERG current in a concentration-dependent manner (IC50, 3.4μM). The hERG mutants S631A in the pore helix and F656V of the S6 region reduced the inhibitory sensitivity with IC50s of 27.4μM and 11.0μM, suggesting a channel pore blocker. In addition, this compound inhibited IKs and hKir2.1currents with IC50s of 10.8 and 8.7μM. SKF-96365 (10μM) significantly prolonged ventricular APD90 in guinea pig ventricular myocytes and QTc interval in ex vivo guinea pig hearts. These results indicate that the TRPC channel antagonist SKF-96365 exerts blocking effects on hERG, IKs, and hKir2.1 channels. Prolongation of ventricular APD and QT interval is related to the inhibition of multiple repolarization potassium currents, especially hERG channels.

A new antiarrhythmic drug in the treatment of recent-onset atrial fibrillation: vernakalant

Vernakalant is a new antiarrhythmic agent recently approved in Europe for the rapid cardioversion of recent-onset atrial fibrillation. It works by blocking early-activating K+ atrial channels and frequency-dependent atrial Na+ channels, prolonging atrial refractory periods and rate-dependent slowing atrial conduction, without promoting ventricular arrhythmia. Preclinical and clinical trials showed good toleration of this drug. The main purpose of our review is to describe all the trials that led to the incorporation of vernakalant into the current European atrial fibrillation guidelines.

Ranolazine inhibition of hERG potassium channels: drug-pore interactions and reduced potency against inactivation mutants

The antianginal drug ranolazine, which combines inhibitory actions on rapid and sustained sodium currents with inhibition of the hERG/I_Kr potassium channel, shows promise as an antiarrhythmic agent. This study investigated the structural basis of hERG block by ranolazine, with lidocaine used as a low potency, structurally similar comparator. Recordings of hERG current (I_hERG) were made from cell lines expressing wild-type (WT) or mutant hERG channels. Docking simulations were performed using homology models built on MthK and KvAP templates. In conventional voltage clamp, ranolazine inhibited I_hERG with an IC₅₀ of 8.03 μM; peak I_hERG during ventricular action potential clamp was inhibited ~ 62% at 10 μM. The IC₅₀ values for ranolazine inhibition of the S620T inactivation deficient and N588K attenuated inactivation mutants were respectively ~ 73-fold and ~ 15-fold that for WT I_hERG. Mutations near the bottom of the selectivity filter (V625A, S624A, T623A) exhibited IC₅₀s between ~ 8 and 19-fold that for WT I_hERG, whilst the Y652A and F656A S6 mutations had IC₅₀s ~ 22-fold and 53-fold WT controls. Low potency lidocaine was comparatively insensitive to both pore helix and S6 mutations, but was sensitive to direction of K⁺ flux and particularly to loss of inactivation, with an IC₅₀ for S620T-hERG ~ 49-fold that for WT I_hERG. Docking simulations indicated that the larger size of ranolazine gives it potential for a greater range of interactions with hERG pore side chains compared to lidocaine, in particular enabling interaction of its two aromatic groups with side chains of both Y652 and F656. The N588K mutation is responsible for the SQT1 variant of short QT syndrome and our data suggest that ranolazine is unlikely to be effective against I_Kr/hERG in SQT1 patients.

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hERG K⁺ channels regulate cardiac action potential repolarization.

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The molecular basis of hERG block by ranolazine and structurally related lidocaine was studied.

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S6 Y652A and F656A mutations affected greatly ranolazine but not lidocaine binding.

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T623 and S624 residues may directly interact with ranolazine but not lidocaine.

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N588K and S620T attenuated inactivation mutants had reduced sensitivity to both drugs.

[Cardiovascular risk assessment for the use of ADHD drugs in children]

BACKGROUND

Drug therapy for ADHD (Attention Deficit Hyperactivity Disorder) has generally been regarded as safe. ECG screening of healthy children and adolescents before initiating this type of treatment appears to be usual in Norway, despite recommendations that ECGs should only be undertaken in individuals who are at risk. The purpose of this article is to clarify relevant guidelines for cardiovascular risk assessment for the use of ADHD drugs in children and adolescents, as well as to propose practical recommendations.

METHOD

The article is based on a literature search in PubMed completed on 1 October 2013, and on the author's own clinical experience and discretionary assessments.

RESULTS

The use of CNS stimulants and atomoxetine is associated with a slight rise in blood pressure and pulse rate, as well as small changes in QT interval. A small percentage of patients (5-10%) experience a clinically significant rise in blood pressure and pulse rate. Sudden death does not appear to occur more frequently in children and adolescents taking ADHD drugs in therapeutic doses than in children and adolescents who do not use such drugs. There is little knowledge available on the long-term effects of ADHD drugs on the cardiovascular system of otherwise healthy individuals, or on the risk related to the use of ADHD drugs in children and adolescents with cardiac disease. The drugs are thought to increase the risk of sudden cardiac death in some arrhythmia syndromes.

INTERPRETATION

Our assessment is that caution should be exercised in the use of ADHD drugs in children with potentially dangerous cardiac arrhythmias. We recommend clinical examination and a thorough medical history review in order to identify individuals at risk before initiating drug therapy, and also suggest that it is not necessary for healthy children to be given an ECG examination before introducing ADHD drugs. In children with known cardiac disease, arrhythmia or risk factors for cardiac disease, ADHD treatment should be undertaken in consultation with a medical specialist with competence in pediatric cardiology.

Estimating the risk of drug-induced proarrhythmia using human induced pluripotent stem cell-derived cardiomyocytes

Improved in vitro systems for predicting drug-induced toxicity are needed in the pharmaceutical and biotechnology industries to decrease late-stage drug attrition. One unmet need is an early screen for cardiotoxicity, which accounts for about one third of safety-based withdrawn pharmaceuticals. Herein, the first published report of a high-throughput functional assay employing a monolayer of beating human induced pluripotent stem cell-derived cardiomyocytes (iPSC-CMs) is described, detailing a model that accurately detects drug-induced cardiac abnormalities. Using 96-well plates with interdigitated electrode arrays that assess impedance, the rhythmic, synchronous contractions of the iPSC-CMs were detected. Treatment of the iPSC-CMs with 28 different compounds with known cardiac effects resulted in compound-specific changes in the beat rate and/or the amplitude of the impedance measurement. Changes in impedance for the compounds tested were comparable with the results from a related technology, electric field potential assessment obtained from microelectrode arrays. Using the results from the set of compounds, an index of drug-induced arrhythmias was calculated, enabling the determination of a drug's proarrhythmic potential. This system of interrogating human cardiac function in vitro opens new opportunities for predicting cardiac toxicity and studying cardiac biology.

Electrophysiological properties of HBI-3000: a new antiarrhythmic agent with multiple-channel blocking properties in human ventricular myocytes

HBI-3000 (sulcardine sulfate) has been shown to suppress various ventricular arrhythmias in animal models. The electrophysiological properties of HBI-3000 were investigated using standard microelectrode and patch-clamp techniques in single human ventricular myocytes. HBI-3000 led to concentration-dependent suppression of dofetilide-induced early afterdepolarizations in single nonfailing human ventricular myocytes and early afterdepolarizations seen in failing ventricular myocytes. The concentration-dependent prolongation of action potential duration (APD) by HBI-3000 was bell shaped with maximum response occurring around 10 μM. Interestingly, HBI-3000 at the concentration of 10 μM modestly prolonged the APD at all 3 basic cycle lengths. The slope of APD-cycle length curve of HBI-3000 was only slightly steeper than that of control (88.8 ± 7.7 ms/s vs. 78.9 ± 5.2 ms/s in control, n = 8, P > 0.05). HBI-3000 only showed a minimal use-dependent prolongation of the APD in human ventricular myocytes. HBI-3000 inhibited fast sodium current (INa-F), late sodium channel (INa-L), L-type calcium current (ICa-L), and rapidly activating delayed rectifier K current (IKr) in single human ventricular myocytes. The estimated half-maximal inhibitory concentration values of INa-F, INa-L, ICa-L, and IKr were 48.3 ± 3.8, 16.5 ± 1.4, 32.2 ± 2.9, and 22.7 ± 2.5 μM, respectively. The ion channel profile and electrophysiological properties of HBI-3000 are similar to those of ranolazine and chronic amiodarone (reduced INa-F, INa-L, ICa-L, and IKr). HBI-3000 may be a promising antiarrhythmic agent with low proarrhythmic risk.

New drugs vs. old concepts: a fresh look at antiarrhythmics

Common arrhythmias, particularly atrial fibrillation (AF) and ventricular tachycardia/fibrillation (VT/VF) are a major public health concern. Classic antiarrhythmic (AA) drugs for AF are of limited effectiveness, and pose the risk of life-threatening VT/VF. For VT/VF, implantable cardiac defibrillators appear to be the unique, yet unsatisfactory, solution. Very few AA drugs have been successful in the last few decades, due to safety concerns or limited benefits in comparison to existing therapy. The Vaughan-Williams classification (one drug for one molecular target) appears too restrictive in light of current knowledge of molecular and cellular mechanisms. New AA drugs such as atrial-specific and/or multichannel blockers, upstream therapy and anti-remodeling drugs, are emerging. We focus on the cellular mechanisms related to abnormal Na⁺ and Ca²⁺ handling in AF, heart failure, and inherited arrhythmias, and on novel strategies aimed at normalizing ionic homeostasis. Drugs that prevent excessive Na⁺ entry (ranolazine) and aberrant diastolic Ca²⁺ release via the ryanodine receptor RyR2 (rycals, dantrolene, and flecainide) exhibit very interesting antiarrhythmic properties. These drugs act by normalizing, rather than blocking, channel activity. Ranolazine preferentially blocks abnormal persistent (vs. normal peak) Na⁺ currents, with minimal effects on normal channel function (cell excitability, and conduction). A similar "normalization" concept also applies to RyR2 stabilizers, which only prevent aberrant opening and diastolic Ca²⁺ leakage in diseased tissues, with no effect on normal function during systole. The different mechanisms of action of AA drugs may increase the therapeutic options available for the safe treatment of arrhythmias in a wide variety of pathophysiological situations.

Cardiovascular safety of stimulant medications for pediatric attention-deficit hyperactivity disorder

Attention-deficit hyperactivity disorder (ADHD) is a common neurobehavioral disorder that is often treated with stimulants such as methylphenidate and mixed amphetamine salts. Despite their efficacy and long history of use, there is concern about their potential for adverse cardiovascular effects in children and adolescents. Data from placebo-controlled and open-label extension trials published after 2000 were reviewed, and cardiovascular adverse event data were compared. Both placebo-controlled and open-label extension trials have repeatedly shown stimulant-induced increases in mean blood pressure, heart rate, and QT interval in children, adolescents, and adults. Although these increases seem relatively minor, their existence raises questions regarding whether stimulants could influence the likelihood of sudden death or other serious cardiovascular consequences, especially in patients with underlying heart problems. Moreover, questions have been raised regarding the necessity of screening patients for occult or unrecognized heart problems that are felt to be adversely affected by stimulant use. Obtaining a baseline electrocardiogram for any patient starting stimulant treatment is reasonable if access to such screening is readily available and not too costly.

Multipolar QRST isointegral maps and QT dispersion in old myocardial infarction

Chronic myocardial infarction (CMI) may create, due to structural heterogeneity, abnormal electrophysiological substrates which trigger re-entrant life-threatening ventricular arrhythmias.

METHODS

Electrical instability is assessed using body surface mapping (BSM) [multipolar isointegral QRST maps (mp I(QRST))] and 12-lead ECG (QT dispersion: QTd: the difference between maximal and minimal QT interval). The aim was to find the relation between mp I(QRST) and QTd in CMI patients.

RESULTS

The 32 CMI patients, underwent 12-lead ECG and 64-lead BSM. The 80% (25) of the patients had mp I(QRST) maps. QTd was larger in patients with mp than those with dipolar maps (dp): 170 +/- 20 ms in mp vs 94 +/- 19 ms in dp, respectively. The latter, mp I(QRST) was associated with a decrease of maximum and a stronger minimum.

CONCLUSIONS

Multipolar I(QRST) is associated with a loss of maximum values and increased absolute values of the minimum in CMI patients. I(QRST) and QTd provide similar information in predicting postinfarction arrhythmia risk.

Biological therapies for cardiac arrhythmias: can genes and cells replace drugs and devices?

Cardiac rhythm disorders reflect failures of impulse generation and/or conduction. With the exception of ablation methods that yield selective endocardial destruction, present therapies are nonspecific and/or palliative. Progress in understanding the underlying biology opens up prospects for new alternatives. This article reviews the present state of the art in gene- and cell-based therapies to correct cardiac rhythm disturbances. We begin with the rationale for such approaches, briefly discuss efforts to address aspects of tachyarrhythmia, and review advances in creating a biological pacemaker to cure bradyarrhythmia. Insights gained bring the field closer to a paradigm shift away from devices and drugs, and toward biologics, in the treatment of rhythm disorders.

Screen for chemical modulators of autophagy reveals novel therapeutic inhibitors of mTORC1 signaling

Background

Mammalian target of rapamycin complex 1 (mTORC1) is a protein kinase that relays nutrient availability signals to control numerous cellular functions including autophagy, a process of cellular self-eating activated by nutrient depletion. Addressing the therapeutic potential of modulating mTORC1 signaling and autophagy in human disease requires active chemicals with pharmacologically desirable properties.

Methodology/Principal Findings

Using an automated cell-based assay, we screened a collection of >3,500 chemicals and identified three approved drugs (perhexiline, niclosamide, amiodarone) and one pharmacological reagent (rottlerin) capable of rapidly increasing autophagosome content. Biochemical assays showed that the four compounds stimulate autophagy and inhibit mTORC1 signaling in cells maintained in nutrient-rich conditions. The compounds did not inhibit mTORC2, which also contains mTOR as a catalytic subunit, suggesting that they do not inhibit mTOR catalytic activity but rather inhibit signaling to mTORC1. mTORC1 inhibition and autophagosome accumulation induced by perhexiline, niclosamide or rottlerin were rapidly reversed upon drug withdrawal whereas amiodarone inhibited mTORC1 essentially irreversibly. TSC2, a negative regulator of mTORC1, was required for inhibition of mTORC1 signaling by rottlerin but not for mTORC1 inhibition by perhexiline, niclosamide and amiodarone. Transient exposure of immortalized mouse embryo fibroblasts to these drugs was not toxic in nutrient-rich conditions but led to rapid cell death by apoptosis in starvation conditions, by a mechanism determined in large part by the tuberous sclerosis complex protein TSC2, an upstream regulator of mTORC1. By contrast, transient exposure to the mTORC1 inhibitor rapamycin caused essentially irreversible mTORC1 inhibition, sustained inhibition of cell growth and no selective cell killing in starvation.

Conclusion/Significance

The observation that drugs already approved for human use can reversibly inhibit mTORC1 and stimulate autophagy should greatly facilitate the preclinical and clinical testing of mTORC1 inhibition for indications such as tuberous sclerosis, diabetes, cardiovascular disease and cancer.

Adverse drug reactions in patients with cardiovascular disease

Adverse drug reactions (ADRs) occur frequently in modern medical practice, increasing morbidity and mortality and inflating the cost of care. Patients with cardiovascular disease are particularly vulnerable to ADRs due to their advanced age, polypharmacy, and the influence of heart disease on drug metabolism. The ADR potential for a particular cardiovascular drug varies with the individual, the disease being treated, and the extent of exposure to other drugs. Knowledge of this complex interplay between patient, drug, and disease is a critical component of safe and effective cardiovascular disease management. The majority of significant ADRs involving cardiovascular drugs are predictable and therefore preventable. Better patient education, avoidance of polypharmacy, and clear communication between physicians, pharmacists, and patients, particularly during the transition between the inpatient to outpatient settings, can substantially reduce ADR risk.

Antiplatelet agents sarpogrelate and cilostazol affect experimentally-induced ventricular arrhythmias and mortality

Antiplatelet agents, sarpogrelate (SAR), a 5-hydroxy tryptamine 2A receptor antagonist and cilostazol (CIL), a phosphodiesterase-III inhibitor, were observed to be beneficial in attenuating cardiac remodeling and improving cardiac function in congestive heart failure due to myocardial infarction in rats; however, CIL increased ventricular tachycardia and mortality. In order to study the effects of these antiplatelet agents on arrhythmias, Sprague-Dawley rats were pretreated with either SAR or CIL (5 mg/kg/day) for 2 weeks and were then either injected cumulative doses of epinephrine (Epi) or subjected to coronary occlusion. Saline-treated animals served as controls. Electrocardiographic analysis revealed that SAR pretreatment decreased the incidence and severity of ventricular arrhythmias (time of onset of arrhythmias as well as the occurrence of premature ventricular contractions, salvos, tachycardia, and fibrillations), whereas CIL treatment augmented the incidence of cardiac arrhythmias due to both Epi and coronary occlusion. None of the drugs affected the corrected QT interval significantly. Furthermore, the levels of cyclic adenosine monophosphate (cAMP) in left ventricle were markedly higher in CIL-pretreated rats when compared to SAR-pretreated or control rats. It is suggested that an excessive level of cAMP may contribute to increase incidence of ventricular arrhythmias and mortality in animals pretreated with CIL, unlike the SAR-pretreated rats.

International Life Sciences Institute (Health and Environmental Sciences Institute, HESI) initiative on moving towards better predictors of drug-induced torsades de pointes

Knowledge of the cardiac safety of emerging new drugs is an important aspect of assuring the expeditious advancement of the best candidates targeted at unmet medical needs while also assuring the safety of clinical trial subjects or patients. Present methodologies for assessing drug-induced torsades de pointes (TdP) are woefully inadequate in terms of their specificity to select pharmaceutical agents, which are human arrhythmia toxicants. Thus, the critical challenge in the pharmaceutical industry today is to identify experimental models, composite strategies, or biomarkers of cardiac risk that can distinguish a drug, which prolongs cardiac ventricular repolarization, but is not proarrhythmic, from one that prolongs the QT interval and leads to TdP. To that end, the HESI Proarrhythmia Models Project Committee recognized that there was little practical understanding of the relationship between drug effects on cardiac ventricular repolarization and the rare clinical event of TdP. It was on that basis that a workshop was convened in Virginia, USA at which four topics were introduced by invited subject matter experts in the following fields: Molecular and Cellular Biology Underlying TdP, Dynamics of Periodicity, Models of TdP Proarrhythmia, and Key Considerations for Demonstrating Utility of Pre-Clinical Models. Contained in this special issue of the British Journal of Pharmacology are reports from each of the presenters that set out the background and key areas of discussion in each of these topic areas. Based on this information, the scientific community is encouraged to consider the ideas advanced in this workshop and to contribute to these important areas of investigations over the next several years.

Medication-related complications in the trauma patient

Trauma patients are twice as likely to have adverse reactions to medication as nontrauma patients. The need for medication in trauma patients is high. Surgery is often necessary, and immunosuppression and hypercoagulability may be present. Adverse drug events can be caused in part by altered pharmacokinetics, drug interactions, and polypharmacy. Medications may also have serious long-term adverse effects, which must be considered. It is not the purpose of this review article to discuss all adverse effects of all medications. This article will discuss the more common adverse effects of medications for trauma patients in the acute care setting, in the following categories: pain control, sedation, antibiotics, seizure prophylaxis in head trauma, atrial fibrillation, deep vein thrombosis and pulmonary embolism prophylaxis, hemodynamic support, adrenal insufficiency, factor VIIa.

Augmentation of late sodium current unmasks the proarrhythmic effects of amiodarone

AIM

Clinical use of amiodarone is associated with occasional development of torsade de pointes (TdP). However, preclinical models have failed to demonstrate the proarrhythmic potential of amiodarone. The objective of this study was to reveal and explain the pro- and anti-arrhythmic effects of acute exposure to amiodarone in an animal model.

METHODS AND RESULTS

Endo- and epicardial monophasic action potentials (MAPs) and 12-lead electrocardiogram were recorded in female rabbit isolated hearts. Ion channel currents were measured in human embryonic kidney cells expressing SCN5A Na+ and HERG K+ channels. Acute amiodarone alone caused an insignificant increase in duration of MAP (MAPD90) without causing TdP. In the presence of 3 nM sea anemone toxin (ATX-II), amiodarone (1-30 nM) prolonged MAPD90 from 217 +/- 5 to 250 +/- 8 ms (n = 16, P < 0.01), increased transmural dispersion of repolarization (TDR) from 59 +/- 9 to 70 +/- 10 ms and beat-to-beat variability (BVR) of MAPD(90) from 0.75 +/- 0.03 to 1.06 +/- 0.13 ms (P < 0.05). At 30-300 nM, amiodarone induced TdP in 16 out of 17 hearts. A further increase of amiodarone concentration to 1-10 microM abbreviated MAPD(90) to 211 +/- 9 ms, decreased BVR to 0.5 +/- 0.01 ms, decreased TDR (n = 7, P < 0.05), and suppressed TdP. Amiodarone inhibited HERG K+ and late Na+ currents with IC50s of 0.8 +/- 0.1 and 3.0 +/- 0.9 microM, respectively.

CONCLUSION

In hearts in which late INa is augmented to mimic congenital or acquired pathological conditions, amiodarone has a concentration-dependent biphasic effect to induce and then suppress arrhythmic activity, secondary to inhibition of HERG K+ and late Na+ currents. This is the first preclinical model demonstrating the potential for amiodarone to induce TdP.

Dronedarone for maintenance of sinus rhythm in atrial fibrillation or flutter

BACKGROUND

Amiodarone is effective in maintaining sinus rhythm in atrial fibrillation but is associated with potentially serious toxic effects. Dronedarone is a new antiarrhythmic agent pharmacologically related to amiodarone but developed to reduce the risk of side effects.

METHODS

In two identical multicenter, double-blind, randomized trials, one conducted in Europe (ClinicalTrials.gov number, NCT00259428 [ClinicalTrials.gov] ) and one conducted in the United States, Canada, Australia, South Africa, and Argentina (termed the non-European trial, NCT00259376 [ClinicalTrials.gov] ), we evaluated the efficacy of dronedarone, with 828 patients receiving 400 mg of the drug twice daily and 409 patients receiving placebo. Rhythm was monitored transtelephonically on days 2, 3, and 5; at 3, 5, 7, and 10 months; during recurrence of arrhythmia; and at nine scheduled visits during a 12-month period. The primary end point was the time to the first recurrence of atrial fibrillation or flutter.

RESULTS

In the European trial, the median times to the recurrence of arrhythmia were 41 days in the placebo group and 96 days in the dronedarone group (P=0.01). The corresponding durations in the non-European trial were 59 and 158 days (P=0.002). At the recurrence of arrhythmia in the European trial, the mean (+/-SD) ventricular rate was 117.5+/-29.1 beats per minute in the placebo group and 102.3+/-24.7 beats per minute in the dronedarone group (P<0.001); the corresponding rates in the non-European trial were 116.6+/-31.9 and 104.6+/-27.1 beats per minute (P<0.001). Rates of pulmonary toxic effects and of thyroid and liver dysfunction were not significantly increased in the dronedarone group.

CONCLUSIONS

Dronedarone was significantly more effective than placebo in maintaining sinus rhythm and in reducing the ventricular rate during recurrence of arrhythmia.

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.

Marked QT prolongation and torsades de pointes secondary to acute ischemia in an elderly man taking dofetilide for atrial fibrillation: a cautionary tale

Dofetilide has been shown to be effective and safe in maintaining sinus rhythm in patients with persistent atrial fibrillation and congestive heart failure. Because of serious side effects of an increase in the QT interval causing torsades de pointes, dofetilide must be initiated with close monitoring of the QT interval in an inpatient setting. However, little has been reported about conditions surrounding the change in QT interval after the steady state is achieved that may have implications in the safety and efficacy of the drug. We report marked QT prolongation and torsades de pointes in a setting of flash pulmonary edema resulting from acute myocardial ischemia in a patient who was being treated with dofetilide for atrial fibrillation. Our case reminds the clinicians that the adverse and proarrhythmic effects of dofetilide can occur due to changes in the arrhythmic substrate during acute severe ischemia.

Refining detection of drug-induced proarrhythmia: QT interval and TRIaD

QT interval prolongation is so frequently associated with torsades de pointes (TdP) that it has come to be recognized as a surrogate marker of this unique tachyarrhythmia. However, not only does TdP not always follow QT interval prolongation, but TdP can occur even in the absence of a prolonged QT interval. Worse still, even shortening of the QT interval may be associated with serious arrhythmias (particularly ventricular tachycardia [VT] and ventricular fibrillation [VF]). It appears increasingly probable that the distinction between various ventricular tachyarrhythmias may be arbitrary, and drug-induced TdP, polymorphic VT, VT, catecholaminergic polymorphic VT, and VF may represent discrete entities within a spectrum of drug-induced proarrhythmia. Although they are differentiated by the coupling interval and the duration of QT interval, they appear to share a common substrate: a set of disturbances of repolarization characterized by Triangulation, Reverse use dependency, electrical Instability of the action potential, and Dispersion (TRIaD). It is becoming increasingly evident that augmentation of TRIaD, rather than changes in the duration of QT interval, provides the proarrhythmic substrate. In contrast, when not associated with an increase of TRIaD, QT interval prolongation can be an antiarrhythmic property. Electrophysiologically, augmentation of TRIaD can be explained by inhibition of hERG (human ether-a-go-go related gene) channel. Because drug-induced disturbances in repolarization commonly result from inhibition of hERG channels or I(Kr), hERG blockade and the resulting prolongation of QT interval are important properties of a drug to be studied. However, these need only be a concern if associated with TRIaD. More significantly, TRIaD so often precedes prolongation of action potential duration or QT interval and ventricular tachyarrhythmias that it should be considered a marker of proarrhythmia until proven otherwise, even in the absence of QT interval prolongation. Detecting drug-induced augmentation of TRIaD may offer an additional, more sensitive, and accurate indicator of the broader proarrhythmic potential of a drug than may QT interval prolongation alone.