Drug-induced AF: Arrhythmogenic Mechanisms and Management Strategies

AF is a prevalent condition that is associated with various modifiable and unmodifiable risk factors. Drug-induced AF, despite being commonly under-recognised, can be relatively easy to manage. Numerous cardiovascular and non-cardiovascular agents, including catecholaminergic agents, adenosine, anti-tumour agents and others, have been reported to induce AF. However, the mechanisms underlying drug-induced AF are diverse and not fully understood. The complexity of clinical scenarios and insufficient knowledge regarding drug-induced AF have rendered the management of this condition complicated, and current treatment guidelines follow those for other types of AF. Here, we present a review of the epidemiology of drug-induced AF and highlight a range of drugs that can induce or exacerbate AF, along with their molecular and electrophysiological mechanisms. Given the inadequate evidence and lack of attention, further research is crucial to underscore the clinical significance of drug-induced AF, clarify the underlying mechanisms and develop effective treatment strategies for the condition.

[Prediction of Cardiac Toxicity by Anti-cancer Drugs Using iPSC Cardiomyocytes]

Recent advances in cancer therapy have significantly improved the survival rate of patients with cancer. In contrast, anti-cancer drug-induced adverse effects, especially cardiotoxicity, have come to affect patients' prognosis and quality of life. Therefore, there is a growing need to understand the anti-cancer drug-induced cardiotoxicity. Human induced pluripotent stem (iPS) cell-derived cardiomyocytes (hiPSC-CMs) have been used to assess drug-induced cardiotoxicity by improving the predictability of clinical cardiotoxicity and the principles of the 3Rs (replacement, reduction and refinement). To predict the anti-cancer drug-induced cardiotoxicity, we developed a novel method to assess drug-induced proarrhythmia risk using hiPSC-CMs by participating in the international validation. In addition, we established the chronic contractility toxicity assessment by image-based motion analysis. The compound BMS-986094, which was withdrawn from clinical trials, inhibited contractility velocity and relaxation velocity in hiPSC-CMs. Currently, we are trying to investigate the predictability of the contractility assay by comparing the hiPSC-CM data with adverse events reports from real-world database. In this review, we would like to introduce the novel imaging-based contractility method using hiPSC-CMs and future perspectives in anti-cancer drug-induced cardiotoxicity.

Failure of Intrinsic Antitachycardia Pacing to Terminate Ventricular Tachycardia and Potential Proarrhythmic Effects

Intrinsic antitachycardia pacing (iATP) is a novel, automated antitachycardia pacing (ATP) algorithm that provides individualized therapy to terminate ventricular tachycardia (VT). If the first ATP attempt is unsuccessful, the algorithm analyzes the tachycardia cycle length and the postpacing interval and adjusts the subsequent sequence to successfully terminate VT. This algorithm was effective in a single clinical study without a comparator arm. However, iATP failure has not been well-documented in the literature. This publication represents the first case series with episode analysis of iATP failure, including a demonstration of its proarrhythmic effect.

Proarrhythmia Risk Assessment Using Electro-Mechanical Window in Human iPS Cell-Derived Cardiomyocytes

Evaluation of drug-induced cardiotoxicity is still challenging to avoid adverse effects, such as torsade de pointes (TdP), in non-clinical and clinical studies. Numerous studies have suggested that human-induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) are a useful platform for detecting drug-induced TdP risks. Comprehensive in vitro Proarrhythmia Assay (CiPA) validation study suggested that hiPSC-CMs can assess clinical TdP risk more accurately than the human ether-a-go-go-related assay and QT interval prolongation. However, there were still some outliers, such as bepridil, mexiletine, and ranolazine, among the CiPA 28 compounds in the CiPA international multi-site study using hiPSC-CMs. In this study, we assessed the effects of the positive compound dofetilide, the negative compound aspirin, and several CiPA compounds (bepridil, mexiletine, and ranolazine) on the electromechanical window (E-M window), which were evaluated using multi-electrode array assay and motion analysis, in hiPSC-CMs. Similar to previous in vivo studies, dofetilide, which has a high TdP risk, decreased the E-M window in hiPSC-CMs, whereas aspirin, which has a low TdP risk, had little effect. Bepridil, classified in the high TdP-risk group in CiPA, decreased the E-M window in hiPSC-CMs, whereas ranolazine and mexiletine, which are classified in the low TdP-risk group in CiPA, slightly decreased or had little effect on the E-M window of hiPSC-CMs. Thus, the E-M window in hiPSC-CMs can be used to classify drugs into high and low TdP risk.

Systemic immune-inflammation index as a tool for predicting the need for a permanent pacemaker in patients with drug-induced atrioventricular block

BACKGROUND

Drug-induced atrioventricular block (AVB) is generally considered reversible and does not require a permanent pacemaker implantation (PPM). However, some studies have demonstrated a failure of AVB cessation even when the inducing agent has been discontinued. This study has investigated the use of systemic immune-inflammation index (SII) to predict irreversible drug-induced AVB after drug discontinuation.

METHOD

Files of patients with high-degree AVB that required a temporary pacemaker (TPM) were retrospectively analyzed. Sixty-three patients in which AVB was drug-induced were included in the study. The patients were divided into the following two groups: (1) those whose AVB reversed after discontinuation of the related drug, and (2) those in which AVB did not reverse.

RESULTS

AVB reversed in 24 patients (38%) after the inducing agent was discontinued while in the remaining 39 patients (62%) PPM was required. The most common drugs to induce AVB were beta-blockers (n = 46, 73%). Follow-up time with TPM was significantly longer in the irreversible group (2.91 ± 1.05 days vs. 4.94 ± 2.15 days, p < .001). Multivariate logistic regression analysis showed that SII (odds ratio [OR] = 1.002; 95% confidence interval [CI] = 1.000-1.003; p = .01) was an independent predictor of the requirement for a PPM. An SII > 752.05 was found to be a predictor of irreversible AVB requiring PPM with a sensitivity of 64% and specificity of 75% (receiving-operating characteristics [ROC] area under the ROC curve [AUC]: 0.704, 95% CI = 0.570-0.838, p = .007).

CONCLUSION

Approximately 2/3 of drug-induced high-degree AVBs are irreversible. SII is an easily available and cheap inflammatory biomarker that can be used to predict irreversible AVB.

Comprehensive Cardiotoxicity Assessment of COVID-19 Treatments Using Human Induced Pluripotent Stem Cell-derived Cardiomyocytes

Coronavirus disease 2019 (COVID-19) continues to spread across the globe, with numerous clinical trials underway seeking to develop and test effective COVID-19 therapies, including remdesivir. Several ongoing studies have reported hydroxychloroquine-induced cardiotoxicity, including development of torsade de pointes (TdP). Meanwhile, human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) are expected to serve as a tool for assessing drug-induced cardiotoxicity, such as TdP and contraction impairment. However, the cardiotoxicity of COVID-19 treatments has not been fully assessed using hiPSC-CMs. In the present study, we focused on drug repurposing with various modes of actions and examined the TdP risk associated with COVID-19 treatments using field potential using multi-electrode array (MEA) system and motion analysis with hiPSC-CMs. Hydroxychloroquine induced early after depolarization, while remdesivir, favipiravir, camostat and ivermectin had little effect on field potentials. We then analyzed electromechanical window (EMw), which is defined as the difference between field potential and contraction-relaxation durations. Hydroxychloroquine decreased EMw of hiPSC-CMs in a concentration-dependent manner. In contrast, other drugs have little effect. Our data suggest that hydroxychloroquine has proarrhythmic risk and other drugs have low proarrhythmic risk. Thus, hiPSC-CMs represent a useful tool for assessing the comprehensive cardiotoxicity caused by COVID-19 treatments in non-clinical settings.

Role of Pharmacogenetics in Adverse Drug Reactions: An Update towards Personalized Medicine

Adverse drug reactions (ADRs) are an important and frequent cause of morbidity and mortality. ADR can be related to a variety of drugs, including anticonvulsants, anaesthetics, antibiotics, antiretroviral, anticancer, and antiarrhythmics, and can involve every organ or apparatus. The causes of ADRs are still poorly understood due to their clinical heterogeneity and complexity. In this scenario, genetic predisposition toward ADRs is an emerging issue, not only in anticancer chemotherapy, but also in many other fields of medicine, including hemolytic anemia due to glucose-6-phosphate dehydrogenase (G6PD) deficiency, aplastic anemia, porphyria, malignant hyperthermia, epidermal tissue necrosis (Lyell's Syndrome and Stevens-Johnson Syndrome), epilepsy, thyroid diseases, diabetes, Long QT and Brugada Syndromes. The role of genetic mutations in the ADRs pathogenesis has been shown either for dose-dependent or for dose-independent reactions. In this review, we present an update of the genetic background of ADRs, with phenotypic manifestations involving blood, muscles, heart, thyroid, liver, and skin disorders. This review aims to illustrate the growing usefulness of genetics both to prevent ADRs and to optimize the safe therapeutic use of many common drugs. In this prospective, ADRs could become an untoward "stress test," leading to new diagnosis of genetic-determined diseases. Thus, the wider use of pharmacogenetic testing in the work-up of ADRs will lead to new clinical diagnosis of previously unsuspected diseases and to improved safety and efficacy of therapies. Improving the genotype-phenotype correlation through new lab techniques and implementation of artificial intelligence in the future may lead to personalized medicine, able to predict ADR and consequently to choose the appropriate compound and dosage for each patient.

The fatal consequence of inappropriate therapy in a single VF zone primary prevention defibrillator

We report a case of inappropriate implantable cardioverter defibrillator (ICD) therapy due to single ventricular fibrillation (VF) zone programming leading to patient death. A remote transmission was received from a patient with a cardiac resynchronization therapy-defibrillator showing sinus tachycardia in the VF detection zone initiating inappropriate shocks and resulting in shock refractory VF. This case report highlights the importance of manufacturer specific ICD programming. In devices without discrimination in the VF zone, a higher rate single VF detection zone and/or addition of a ventricular tachycardia zone with supraventricular tachycardia discrimination should be considered.

Machine learning-based QSAR models to predict sodium ion channel (Nav 1.5) blockers

Aim: Conventional experimental approaches used for the evaluation of the proarrhythmic potential of compounds in the drug discovery process are expensive and time consuming but an integral element in the safety profile required for a new drug to be approved. The voltage-gated sodium ion channel 1.5 (Na_v 1.5), a target known for arrhythmic drugs, causes adverse cardiac complications when the channel is blocked. Results: Machine learning classification and regression models were built to predict the possibility of blocking these channels by small molecules. The finalized models tested with balanced accuracies of 0.88, 0.93 and 0.94 at three thresholds (1, 10 and 30 µmol, respectively). The regression model built to predict the pIC₅₀ of compounds had q² of 0.84 (root-mean-square error = 0.46). Conclusion: The machine learning models that have been built can act as effective filters to screen out the potentially toxic compounds in the early stages of drug discovery.

Cardiotoxicity Assessment of Drugs Using Human iPS Cell-Derived Cardiomyocytes: Toward Proarrhythmic Risk and Cardio-Oncology

Growing evidence suggests that Human Induced Pluripotent Stem Cell-Derived Cardiomyocytes (hiPSC-CMs) can be used as a new human cell-based platform to assess cardiac toxicity/safety during drug development. Cardiotoxicity assessment is highly challenging due to species differences and various toxicities, such as electrophysiological and contractile toxicities, which can result in proarrhythmia and heart failure. To explore proarrhythmic risk, the Multi-Electrode Array (MEA) platform is widely used to assess QT-interval prolongation and the proarrhythmic potential of drug candidates using hiPSC-CMs. Several consortiums, including the Comprehensive in vitro Proarrhythmia Assay (CiPA) and the Japanese iPS Cardiac Safety Assessment (JiCSA), have demonstrated the applicability of hiPSC-CMs/MEA for assessing the torsadogenic potential of drug candidates. Additionally, contractility is a key safety issue in drug development, and efforts have been undertaken to measure contractility by a variety of imaging-based methods using iPS-CMs. Therefore, hiPSC-CMs might represent a standard testing tool for evaluating the proarrhythmic and contractile potentials. This review provides new insights into the practical application of hiPSC-CMs in early or late-stage nonclinical testing during drug development.

Exercise-induced ventricular tachycardia in a case with hypertrophic cardiomyopathy taking cibenzoline

We report a 17‐year‐old woman with hypertrophic cardiomyopathy (HCM) successfully resuscitated from ventricular fibrillation while taking cibenzoline. During exercise–stress testing before implanting an implantable cardioverter–defibrillator, ventricular tachycardia was induced and thought to be a proarrhythmia due to the use‐dependent effect of the Na channel blockade with cibenzoline. In patients with arrhythmogenic substrates such as HCM, it is critical to pay attention to the proarrhythmic effects of class I antiarrhythmic drugs while increasing heart rate.

Left ventricular pacing induced polymorphic ventricular tachycardia via the adaptive left ventricle pacing algorithm

Providers should be aware of the possibility of cardiac resynchronization therapy-related proarrhythmia which could be life-threatening. His-bundle pacing may serve as an alternative, more physiological, option in the management as it preserves the normal sequence of depolarization from the septum to the lateral wall, and from endocardium to epicardium.

Proarrhythmic effects from competitive atrial pacing and potential programming solutions

BACKGROUND

Programmed long AV delays and intrinsic long first degree AV block may increase risk for competitive atrial pacing (CAP) in devices without CAP avoidance algorithms.

METHODS

Patients identified with CAP-induced mode switch episodes were followed clinically from September 2013 to August 2019. Attempts to avoid CAP included shortening of postventricular atrial refractory period (PVARP) or postventricular atrial blanking period (PVAB), or change to AAI or DDI modes. After observing associations with sensor-driven pacing, rate response was inactivated in a subset.

RESULTS

Among 23 patients identified with CAP (22 St Jude Medical [Abbott]; one Boston Scientific Corporation devices), atrial fibrillation (AF) was induced in 12 (52%), lasting 10 seconds to 28 hours and 32 minutes. In one patient with an ICD CAP-induced AF with rapid ventricular rates that triggered a shock, inducing ventricular fibrillation, syncope, and another shock. Changing AV delays and shortening of PVARP failed to resolve CAP. After noting that all had CAP during sensor-driven pacing, rate response was inactivated in seven, resolving further device-induced AF in the three of seven that had prior CAP-induced AF. In two patients with intact AV conduction, AAI(R) pacing resolved further documentation of CAP.

CONCLUSIONS

CAP predominantly occurs during sensor-driven atrial pacing that competes with intrinsic atrial events falling in PVARP. Inactivation of the activity sensor or change to atrial-based pacing modes (AAI/R) appears to effectively prevent induction of device-induced atrial proarrhythmia. Ultimately, a corrective algorithm is needed to avoid CAP-induced proarrhythmia.

Proarrhythmic effect of automatic threshold testing algorithm in dual chamber devices

BACKGROUND

Operation of auto-threshold testing (ATT) algorithm in current dual chamber cardiac devices require temporary shortening of atrio-ventricular (AV) delay to accurately measure evoked potential (capture) after a pacing pulse. Near simultaneous AV pacing causes atrial pressure elevation and may be associated with atrial arrhythmias.

OBJECTIVE

We evaluated the prevalence of atrial arrhythmias induced by ATT in Abbott devices.

METHODS

Device clinic records were reviewed at a single center for patients with dual chamber Abbott pacemaker/ICD. ATT-induced atrial fibrillation (AF) cases were defined as new appropriate mode switch episodes while the ATT was operating. The auto-capture test trends were defined as unstable if there were deviations >1 V in capture threshold trend events that did not correlate with routine in-office testing.

RESULTS

One hundred and seventy patients were programmed in dual chamber pacing mode. The ventricular ATT was active in 118 patients and of these 78 had true mode switch episodes. Six patients developed AF during ventricular ATT. Three patients had most recorded atrial arrhythmias in close association with ATT (63%, 66%, 100% vs 2%,9%, 33% in other patients with known prior AF). An unstable auto-capture trend curve was seen in 33 patients (6 showing ATT-induced AF) versus 85 patients with stable auto-capture curve and no ATT-induced AF (P = .0001, the χ² test).

CONCLUSION

Ventricular auto-capture algorithm use is associated with induction of AF in dual chamber Abbott devices with a prevalence of over 5%. AF occur more frequently (18%) in patients with erratic ventricular ATT trend results.

Hazard of acquired long QT syndrome during coronavirus pandemic. Focus on hydroxychloroquine

Hydroxychloroquine is an immunomodulatory drug that has been used to treat malaria and autoimmune diseases such as systemic lupus erythematosus and inflammatory arthritis. The authors conclude the proarrhytmic effects of hydroxychloroquine and the most important signs of drug-induced long QT syndrome. This article is especially relevant and timely due to the more frequent (currently not evidence-based) use of the drug during the 2019–2020 coronavirus pandemic. Orv Hetil. 2020; 161(17): 689–691.

Evaluation of Possible Proarrhythmic Potency: Comparison of the Effect of Dofetilide, Cisapride, Sotalol, Terfenadine, and Verapamil on hERG and Native IKr Currents and on Cardiac Action Potential

The proarrhythmic potency of drugs is usually attributed to the IKr current block. During safety pharmacology testing analysis of IKr in cardiomyocytes was replaced by human ether-a-go-go-related gene (hERG) test using automated patch-clamp systems in stable transfected cell lines. Aim of this study was to compare the effect of proarrhythmic compounds on hERG and IKr currents and on cardiac action potential. The hERG current was measured by using both automated and manual patch-clamp methods on HEK293 cells. The native ion currents (IKr, INaL, ICaL) were recorded from rabbit ventricular myocytes by manual patch-clamp technique. Action potentials in rabbit ventricular muscle and undiseased human donor hearts were studied by conventional microelectrode technique. Dofetilide, cisapride, sotalol, terfenadine, and verapamil blocked hERG channels at 37°C with an IC50 of 7 nM, 18 nM, 343 μM, 165 nM, and 214 nM, respectively. Using manual patch-clamp, the IC50 values of sotalol and terfenadine were 78 µM and 31 nM, respectively. The IC50 values calculated from IKr measurements at 37°C were 13 nM, 26 nM, 52 μM, 54 nM, and 268 nM, respectively. Cisapride, dofetilide, and sotalol excessively lengthened, terfenadine, and verapamil did not influence the action potential duration. Terfenadine significantly inhibited INaL and moderately ICaL, verapamil blocked only ICaL. Automated hERG assays may over/underestimate proarrhythmic risk. Manual patch-clamp has substantially higher sensitivity to certain drugs. Action potential studies are also required to analyze complex multichannel effects. Therefore, manual patch-clamp and action potential experiments should be a part of preclinical safety tests.

The Role of the Food and Drug Administration in Drug Development: On the Subject of Proarrhythmia Risk

The Food and Drug Administration (FDA) is responsible for the regulation of the pharmaceutical industry in the interest of protecting public health. The aim of this review was to outline the evolution and current role of the FDA in the development and approval of new drugs. Additionally, we describe current assessments of proarrhythmia risk to illustrate recent FDA initiatives intended to harness information technology to modernize the regulatory process. In order to identify the literature required to produce this review, search tools such as PubMed and Google Scholar were used to locate relevant web pages and articles. The job of the FDA is not only to ensure that high standards for drug efficacy and safety are applied to products available to American consumers and patients but also to balance the lengthy, costly process of maintaining these standards against the pressure to provide access to effective treatments earlier and without surplus expenditures. In order to provide expedited access to the newest effective therapies for critically ill patients in the safest way possible, the FDA has developed several accelerated pathways to fast-track drug approval. Through partnerships with industry and academic institutions, research is being conducted into how information technology can be integrated into the drug development process to improve its cost-effectiveness.

Allocryptopine: A Review of Its Properties and Mechanism of Antiarrhythmic Effect

Abstract：Throughout the last decade, extensive efforts have been devoted to developing a percutaneous catheter ablation and implantable cardioverter-defibrillator technique for patients suffering from ventricular arrhythmia. Antiarrhythmic drug efficacy for preventing arrhythmias remains disappointing because of adverse cardiovascular effects. Allocryptopine is an isoquinoline alkaloid widely present in medicinal herbs. Studies have indicated that allocryptopine exhibits potential anti-arrhythmic actions in various animal models. The potential therapeutic benefit of allocryptopine in arrhythmia diseases is addressed in this study, focusing on multiple ion channel targets and reduced repolarization dispersion. The limitations of allocryptopine research are clear given a lack of parameters regarding toxicology and pharmacokinetics and clinical efficacy in patients with ventricular arrhythmias. Much remains to be revealed about the properties of allocryptopine.

QT Assessment in Early Drug Development: The Long and the Short of It

The QT interval occupies a pivotal role in drug development as a surface biomarker of ventricular repolarization. The electrophysiologic substrate for QT prolongation coupled with reports of non-cardiac drugs producing lethal arrhythmias captured worldwide attention from government regulators eventuating in a series of guidance documents that require virtually all new chemical compounds to undergo rigorous preclinical and clinical testing to profile their QT liability. While prolongation or shortening of the QT interval may herald the appearance of serious cardiac arrhythmias, the positive predictive value of an abnormal QT measurement for these arrhythmias is modest, especially in the absence of confounding clinical features or a congenital predisposition that increases the risk of syncope and sudden death. Consequently, there has been a paradigm shift to assess a compound's cardiac risk of arrhythmias centered on a mechanistic approach to arrhythmogenesis rather than focusing solely on the QT interval. This entails both robust preclinical and clinical assays along with the emergence of concentration QT modeling as a primary analysis tool to determine whether delayed ventricular repolarization is present. The purpose of this review is to provide a comprehensive understanding of the QT interval and highlight its central role in early drug development.

K2p 3.1 protein is expressed as a transmural gradient across the rat left ventricular free wall

Introduction

K_2p3.1, also known as TASK‐1, is a twin‐pore acid‐sensitive repolarizing K⁺ channel, responsible for a background potassium current that significantly contributes to setting the resting membrane potential of cardiac myocytes. Inhibition of I_K2p3.1 alters cardiac repolarization and is proarrhythmogenic. In this study, we have examined the expression of K_2p3.1 and function of this channel in tissue and myocytes from across the left ventricular free wall.

Methods and Results

Using fluorescence immunocytochemistry, the expression of K_2p3.1 protein in myocytes from the subendocardial region was found to be twice (205% ± 13.5%) that found in myocytes from the subepicardial region of the left ventricle (100% ± 5.3%). The left ventricular free wall exhibited a marked transmural gradient of K_2p3.1 protein expression. Western blot analysis confirmed significantly higher K_2p3.1 protein expression in subendocardial tissue (156% ± 2.5%) than subepicardial tissue (100% ± 5.0%). However, there was no difference in K_2p3.1 messenger RNA expression. Whole‐cell patch clamp identified I_K2p3.1 current density to be significantly greater in myocytes isolated from the subendocardium (7.66 ± 0.53 pA/pF) compared with those from the subepicardium (3.47 ± 0.74 pA/pF).

Conclusions

This is the first study to identify a transmural gradient of K_2p3.1 in the left ventricle. This gradient has implications for understanding ventricular arrhythmogenesis under conditions of ischemia but also in response to other modulatory factors, such as adrenergic stimulation and the presence of anesthetics that inhibits or activates this channel.

AV hysteresis causing initiation of recurrent atrial arrhythmias

A 73-year-old male with dual-chamber implantable cardioverter defibrillator (Teligen, Boston Scientific, Marlborough, MA, USA) had multiple episodes of automatic mode switch (AMS) during clinical follow-up. Over 50% of these demonstrated a similar pattern of initiation. AV Search+ in combination with sensor rate pacing can cause short-coupled atrial paced intervals that can be proarrhythmic. After programming changes were made AMS burden has significantly decreased.

Drugs and life-threatening ventricular arrhythmia risk: results from the DARE study cohort

OBJECTIVES

To establish a unique sample of proarrhythmia cases, determine the characteristics of cases and estimate the contribution of individual drugs to the incidence of proarrhythmia within these cases.

SETTING

Suspected proarrhythmia cases were referred by cardiologists across England between 2003 and 2011. Information on demography, symptoms, prior medical and drug histories and data from hospital notes were collected.

PARTICIPANTS

Two expert cardiologists reviewed data for 293 referred cases: 130 were included. Inclusion criteria were new onset or exacerbation of pre-existing ventricular arrhythmias, QTc >500 ms, QTc >450 ms (men) or >470 ms (women) with cardiac syncope, all secondary to drug administration. Exclusion criteria were acute ischaemia and ischaemic polymorphic ventricular tachycardia at presentation, structural heart disease, consent withdrawn or deceased prior to study. Descriptive analysis of Caucasian cases (95% of included cases, n=124) and culpable drug exposures was performed.

RESULTS

Of the 124 Caucasian cases, 95 (77%) were QTc interval prolongation-related; mean age was 62 years (SD 15), and 63% were female. Cardiovascular comorbidities included hypertension (53%) and patient-reported 'heart rhythm problems' (73%). Family history of sudden death (36%) and hypokalaemia at presentation (27%) were common. 165 culpable drug exposures were reported, including antiarrhythmics (42%), of which amiodarone and flecainide were the most common. Sotalol, a beta-blocking agent with antiarrhythmic activity, was also common (15%). 26% reported multiple drugs, of which 84% reported at least one cytochrome (CYP) P450 inhibitor. Potential pharmacodynamics interactions identified were mainly QT prolongation (59%).

CONCLUSIONS

Antiarrhythmics, non-cardiac drugs and drug combinations were found to be culpable in a large cohort of 124 clinically validated proarrhythmia cases. Potential clinical factors that may warn the prescriber of potential proarrhythmia include older women, underlying cardiovascular comorbidity, family history of sudden death and hypokalaemia.

Early drug development: assessment of proarrhythmic risk and cardiovascular safety

INTRODUCTION

hERG assays and thorough ECG trials have been mandated since 2005 to evaluate the QT interval and potential proarrhythmic risk of new chemical entities. The high cost of these studies and the shortcomings inherent in these binary and limited approaches to drug evaluation have prompted regulators to search for more cost effective and mechanistic paradigms to assess drug liability as exemplified by the CiPA initiative and the exposure response ICH E14(R3) guidance document. Areas covered: This review profiles the changing regulatory landscape as it pertains to early drug development and outlines the analyses that can be performed to characterize preclinical and early clinical cardiovascular risk. Expert commentary: It is further acknowledged that the narrow focus on the QT interval needs to be expanded to include a more comprehensive evaluation of cardiovascular risk since unanticipated off target effects have led to the withdrawal of multiple drugs after they had been approved and marketed.

Virtual Clinical Trial Toward Polytherapy Safety Assessment: Combination of Physiologically Based Pharmacokinetic/Pharmacodynamic-Based Modeling and Simulation Approach With Drug-Drug Interactions Involving Terfenadine as an Example

A Quantitative Systems Pharmacology approach was utilized to predict the cardiac consequences of drug-drug interaction (DDI) at the population level. The Simcyp in vitro-in vivo correlation and physiologically based pharmacokinetic platform was used to predict the pharmacokinetic profile of terfenadine following co-administration of the drug. Electrophysiological effects were simulated using the Cardiac Safety Simulator. The modulation of ion channel activity was dependent on the inhibitory potential of drugs on the main cardiac ion channels and a simulated free heart tissue concentration. ten Tusscher's human ventricular cardiomyocyte model was used to simulate the pseudo-ECG traces and further predict the pharmacodynamic consequences of DDI. Consistent with clinical observations, predicted plasma concentration profiles of terfenadine show considerable intra-subject variability with recorded C_max values below 5 ng/mL for most virtual subjects. The pharmacokinetic and pharmacodynamic effects of inhibitors were predicted with reasonable accuracy. In all cases, a combination of the physiologically based pharmacokinetic and physiology-based pharmacodynamic models was able to differentiate between the terfenadine alone and terfenadine + inhibitor scenario. The range of QT prolongation was comparable in the clinical and virtual studies. The results indicate that mechanistic in vitro-in vivo correlation can be applied to predict the clinical effects of DDI even without comprehensive knowledge on all mechanisms contributing to the interaction.

Multielectrode Array (MEA) Assay for Profiling Electrophysiological Drug Effects in Human Stem Cell-Derived Cardiomyocytes

More relevant and reliable preclinical cardiotoxicity tests are required to improve drug safety and reduce the cost of drug development. Human stem cell-derived cardiomyocytes (hSC-CMs) provide a potential model for the development of superior assays for preclinical drug safety screening. One such hSC-CM assay that has shown significant potential for enabling more predictive drug cardiac risk assessment is the MEA assay. The Multi-electrode Array (MEA) assay is an electrophysiology-based technique that uses microelectrodes embedded in the culture surface of each well to measure fluctuations in extracellular field potential (FP) generated from spontaneously beating hSC-CMs. Perturbations to the recorded FP waveform can be used as an unbiased method of predicting the identity of ion channel(s) impacted on drug exposure. Here, a higher throughput MEA assay using hSC-CMs in 48-well MEA plates is described for profiling compound-induced effects on cardiomyocyte electrophysiology. Techniques for preparing hSC-CM monolayers in MEA plates and methods to contextualize MEA assay experimental results are also covered. © 2016 by John Wiley & Sons, Inc.

Proarrhythmia Risk Assessment in Human Induced Pluripotent Stem Cell-Derived Cardiomyocytes Using the Maestro MEA Platform

Evaluation of stem cell-derived cardiomyocytes (SC-CM) using multi-electrode array (MEA) has attracted attention as a novel model to detect drug-induced arrhythmia. An experiment was conducted to determine if MEA recording from human induced pluripotent SC-CM (hiPSC-CM) could assess proarrhythmic risk. Ten hERG blockers, 4 Na(+) blockers, and 1 IKs blocker were evaluated blindly. Eight drugs are associated with Torsades de Pointes (TdP) and 4 are not. Multiple parameters, including field potential duration (FPD), Na(+) slope, Na(+) amplitude, beat rate (BR), and early after-depolarization (EAD) were recorded. Minimum effective concentrations (MEC) that elicited a significant change were calculated. Our results determined that FPD and EAD were unable to distinguish torsadogenic from benign compounds, Na(+) slope and amplitude could not differentiate Na(+) channel blockade from hERG blockade, BR had an inconsistent response to pharmacological treatment, and that hiPSC-CM were, in general, insensitive to IKs inhibition. A ratio was calculated that relates MEC for evoking FPD prolongation, or triggering EAD, to the human therapeutic unbound Cmax (MEC/Cmax). The key finding was that the ratio was sensitive, but specificity was low. Consistently, the ratio had high positive predictive value and low negative predictive value. In conclusion, MEA recordings of hiPSC-CM were sensitive for FPD and EAD detection, but unable to distinguish agents with low- and high-risk for TdPs. Although some published reports suggested great potential for MEA recordings in hSC-CM to assess preclinical cardiac toxicity, the current evaluation implies that this model would have a high false-positive rate in regard to proarrhythmic risk.

Influence of Zoledronic Acid on Atrial Electrophysiological Parameters and Electrocardiographic Measurements

INTRODUCTION

Our objective was to determine effects of zoledronic acid (ZA) on atrial electrophysiological parameters and electrocardiographic measurements.

METHODS AND RESULTS

Ex vivo perfusion study: Isolated guinea pig hearts were perfused with modified Krebs-Henseleit (K-H) buffer with or without ZA 0.07 mg/kg/L (each n = 6). In ZA-perfused hearts, atrial action potential at 90% repolarization (APD90 ) decreased more from baseline than in controls (-23.2% ± -5.1% vs. -2.1% ± -8.1%, P < 0 .0001), as did APD30 (-28.8% ± -3.8% vs. -2.1% ± -2.1%, P < 0.0001). In vivo dose-response study: Guinea pigs underwent intraperitoneal injections every 2 weeks in 1 of 4 groups (each n = 8): ZA 0.007 mg/kg (low-dose), ZA 0.07 mg/kg (medium-dose), ZA 0.7 mg/kg (high-dose), or placebo. Hearts were excised at 8 weeks and perfused with modified K-H. Atrial effective refractory period (ERP) was lower with medium- and high-dose ZA versus placebo (P = 0.004). Atrial APD30 was lower with high-dose ZA versus placebo, low and medium doses (P < 0.001). Canine ECG study: Mature female beagles received intravenous ZA 0.067 mg/kg or saline (placebo; each n = 6) every 2 weeks for 12 weeks. P wave dispersion was greater in the ZA group (7.7 ± 3.7 vs. 3.4 ± 2.6 ms, P = 0.04). There were no significant differences in P wave index, maximum or minimum P wave duration, or PR interval.

CONCLUSION

ZA shortens left atrial APD and ERP and increases P wave dispersion.

Severe iatrogenic bradycardia related to the combined use of beta-blocking agents and sodium channel blockers

Purpose

Drug-induced bradycardia is common during antiarrhythmic therapy; the major culprits are beta-blockers. However, whether other antiarrhythmic drugs are also a significant cause of this, alone or in combination with beta-blockers, is not well known.

Methods

We retrospectively investigated the records of all patients hospitalized at our institution for drug-related bradycardia from the years 2004 to 2012. Patients with cardiac disease and electrolytic or hormonal abnormalities that could cause bradyarrhythmias were excluded.

Results

Eight patients were identified (mean age, 79±5 years; range, 71–85 years; 6 women). Three patients were taking only beta-blockers (hereafter referred to as the BB group), while five patients were on both beta-blockers and Na channel blockers (hereafter referred to as the BB + Na group). Heart rates ranged from 20∼49 beats/minute on arrival. The initial electrocardiogram showed sinus bradycardia (n=6) or sinus arrest with escape beats (n=2). QRS duration was 80–100 ms. The clinical presentation of the BB + Na group was considerably worse than that of the BB group, and included cardiogenic shock and heart failure. Four of the BB + Na patients had been on their medications for over 300 days. The BB group recovered solely with drug discontinuation, while 4 of the 5 patients in the BB + Na group needed additional treatments, such as intravenous administration of atropine or adrenergic agonist and temporary pacing. Bradycardia did not recur during follow-up (median, 687 days).

Conclusion

Although wide QRS ventricular tachyarrhythmia is a better known proarrhythmic effect of Na channel blockers, life-threatening bradycardia may also occur in combination with beta-blockers in the elderly, even months after the start of medication, and at plasma concentrations that do not prolong QRS width.

How in vitro influences in silico utilized for the prediction of in vivo - pilot study of the drug-induced pro-arrhythmic potency prediction

The current drug cardiac safety risk assessment paradigm is about to be changed. The discussed modifications cover clinical as well as pre-clinical sides. As for the latter, the pre-clinical assessment, it is planned to be based on the analysis of the drug-triggered multiple ion currents inhibition. Considering the variability in the in vitro patch clamp studies results, it would be of benefit to assess how these apparatus- and protocol-dependent differences influence the risk prediction and, eventually, the decision making. Four compounds, namely dextromethorphan, ketoconazole, terfenadine, and quinidine were screened for hERG inhibition with an automated patch clamp apparatus (CytoPatch(TM)2). The results were then compared against the literature published data, and after being complemented with information about other current inhibitions and effective therapeutic plasma concentration, utilized for the in silico based safety assessment. Two endpoints were used: (1) the concentration dependent potential to induce early afterdepolarizations in the simulated action potential and (2) the arrhythmia-like disruption in the simulated pseudo-ECG signals. Data analysis results prove that IC50 values, describing the inhibition potential, significantly differ among studies, and the choice of input data can greatly influence the in silico based safety assessment and thus the decision making process.

Pharmacology and Toxicology of Nav1.5-Class 1 anti-arrhythmic drugs

Although cardiac sodium channel blocking drugs can exert antiarrhythmic actions, they can also provoke life-threatening arrhythmias through a variety of mechanisms. This review addresses the way in which drugs interact with the channel, and how these effects translate to clinical beneficial or detrimental effects. A further understanding of the details of channel function and of drug-channel interactions may lead to the development of safer and more effective antiarrhythmic therapies.

High-throughput multi-parameter profiling of electrophysiological drug effects in human embryonic stem cell derived cardiomyocytes using multi-electrode arrays

Human stem cell derived cardiomyocytes (hESC-CM) provide a potential model for development of improved assays for pre-clinical predictive drug safety screening. We have used multi-electrode array (MEA) analysis of hESC-CM to generate multi-parameter data to profile drug impact on cardiomyocyte electrophysiology using a panel of 21 compounds active against key cardiac ion channels. Our study is the first to apply multi-parameter phenotypic profiling and clustering techniques commonly used for high-content imaging and microarray data to the analysis of electrophysiology data obtained by MEA analysis. Our data show good correlations with previous studies in stem cell derived cardiomyocytes and demonstrate improved specificity in compound risk assignment over convention single-parametric approaches. These analyses indicate great potential for multi-parameter MEA data acquired from hESC-CM to enable drug electrophysiological liabilities to be assessed in pre-clinical cardiotoxicity assays, facilitating informed decision making and liability management at the optimum point in drug development.

Feasibility of targeting ischaemia-related ventricular arrhythmias by mimicry of endogenous protection by endocannabinoids

BACKGROUND AND PURPOSE

The hypothesis that endocannabinoids protect hearts against ventricular fibrillation (VF) induced by myocardial ischaemia and reperfusion was examined, and the concept that cannabinoids may represent a new class of anti-VF drug was tested.

EXPERIMENTAL APPROACH

In rat isolated hearts (Langendorff perfusion), VF evoked by reperfusion after 60 min regional ischaemia is known to be exacerbated by inhibitors of endogenous protectants such as nitric oxide. This preparation was used to assay the effects of cannabinoid agonists and antagonists, and the protocols were varied to examine mechanisms.

KEY RESULTS

Reperfusion-induced VF was not facilitated by relatively selective CB1 (1 μM AM251) or CB2 (1 μM AM630) antagonists. VF evoked during early (30 min) acute ischaemia was also unaffected. However, AM251 significantly increased the incidence of VF and the duration of VF episodes occurring during the later stage of acute ischaemia (30-60 min). AM630 had no such effects. In a separate study, cannabinoid perfusion (anandamide or 2-arachidonoylglycerol, both 0.01-1 μM) failed to reduce VF incidence concentration-dependently during 30 min ischaemia. In all these studies, changes in ancillary variables (QT, PR, heart rate) were unrelated to changes in VF.

CONCLUSIONS AND IMPLICATIONS

Endocannabinoids are not endogenous anti-VF mediators during reperfusion, but may have a weak protective effect during the late stages of ischaemia, mediated via CB1 agonism. This does not suggest endocannabinoids are important endogenous protectants in these settings, or that CB1 (or CB2) receptors are useful novel targets for developing drugs for VF.

Ibandronate and ventricular arrhythmia risk

INTRODUCTION

Bisphosphonates, including ibandronate, are used in the prevention and treatment of osteoporosis.

METHODS AND RESULTS

We report a case of suspected ibandronate-associated arrhythmia, following a single dose of ibandronate in a 55-year-old female. ECG at presentation revealed frequent ectopy and QT/QTc interval prolongation; at follow-up 9 months later the QT/QTc intervals were normalized. Proarrhythmic potential of ibandronate was assessed with a combination of in vivo and in vitro approaches in canines and canine ventricular myocytes. We observed late onset in vivo repolarization instability after ibandronate treatment. Myocytes superfused with ibandronate exhibited action potential duration (APD) prolongation and variability, increased early afterdepolarizations (EADs) and reduced Ito (P < 0.05), with no change in IKr . Ibandronate-induced APD changes and EADs were prevented by inhibition of intracellular calcium cycling. Ibandronate increased sarcoplasmic reticulum calcium load; during washout there was an increase in calcium spark frequency and spontaneous calcium waves. Computational modeling was used to examine the observed effects of ibandronate. While reductions in Ito alone had modest effects on APD, when combined with altered RyR inactivation kinetics, the model predicted effects on APD and SR Ca(2+) load consistent with observed experimental results.

CONCLUSION

Ibandronate may increase the susceptibility to ventricular ectopy and arrhythmias. Collectively these data suggest that reduced Ito combined with abnormal RyR calcium handling may result in a previously unrecognized form of drug-induced proarrhythmia.

Usefulness of T-wave alternans in sudden death risk stratification and guiding medical therapy

Visible T-wave alternans (TWA), a beat-to-beat alternation in the morphology and amplitude of the ST segment or T wave, has been observed for over a century to occur in association with life-threatening arrhythmias in patients with acute coronary syndrome, heart failure, and cardiac channelopathies. This compelling linkage prompted development of quantitative techniques leading to FDA-cleared commercial methodologies for measuring nonvisible levels of TWA in the frequency and time domains. The first aim of this review is to summarize evidence from more than a hundred studies enrolling a total of >12,000 patients that support the predictivity of TWA for cardiovascular mortality and sudden cardiac death. The second focus is on the usefulness of TWA in guiding therapy. Until recently, TWA has been used primarily in decision making for cardioverter-defibrillator implantation. Its potential utility in guiding pharmacologic therapy has been underappreciated. We review clinical literature supporting the usefulness of TWA as an index of antiarrhythmic effects and proarrhythmia for different drug classes. Beta-adrenergic and sodium channel-blocking agents are the most widely studied drugs in clinical TWA investigations, with both reducing TWA magnitude; the exception is patients in whom sodium channel blockade discloses the Brugada syndrome and provokes macroscopic TWA. An intriguing possibility is that TWA may help to detect beneficial effects of nonantiarrhythmic agents such as the angiotensin II receptor blocker valsartan, which indirectly protects from arrhythmia through improving myocardial remodeling. We conclude that quantitative analysis of TWA has considerable potential to guide pharmacologic intervention and thereby serve as a therapeutic target.

Proarrhythmia Induced by Propafenone: What is the Mechanism?

Propafenone, a Class IC antiarrhythmic drug, is an orally active sodium channel-blocking agent. It is effective in supraventricular tachyarrhythmias and is particularly useful in converting atrial fibrillation to sinus rhythm. In therapeutic doses, it may cause non-cardiac and cardiac toxicity, including proarrhythmia.

Atrial fibrillation: a review of mechanism, etiology, and therapy

The prevalence of elderly individuals in the populations of developed countries is increasing rapidly, and atrial fibrillation (AF) is quite common in these elderly patients: currently, 11% of the U.S. population is between the ages of 65 and 85 years; 70% of people with AF are between the ages of 65 and 85 years. AF causes symptoms secondary to hemodynamic derangements that are the result of increased ventricular response and loss of atrial booster function. AF can lead to reversible impairment of left ventricular function, cardiac chamber dilatation, clinical heart failure, and thromboembolic events. AF requires treatment in order to prevent these potential complications. Type Ia, Ic, and III antiarrhythmics are capable of converting AF to normal sinus rhythm (NSR). Amiodarone has the greatest efficacy and safety for converting AF and maintaining NSR while digoxin and verapamil are ineffective in restoring NSR. Quinidine, flecainide, disopyramide, and sotalol have also been shown to maintain NSR after conversion of AF. Proarrhythmia is a definite concern with the latter four agents. Alternative therapy for AF includes anticoagulation with warfarin or aspirin for the prevention of thromboembolic events, and a variety of agents to control the ventricular response. All medications used to treat AF carry significant risks in the elderly, whether from proarrhythmia, overdosing because of compliance errors, or hemorrhage secondary to anticoagulation. Treatment of AF must be based on a careful risk-benefit evaluation. The physician must know the capability of the particular patient as well as drug mechanisms and effects in the elderly. The decision to convert patients from AF to NSR or to leave the patient in AF and control the ventricular response represents a complex intellectual challenge. Factors favoring one or the other of these two clinical strategies are discussed. Multicenter clinical trials, for example, the Atrial Fibrillation Follow-up Investigation Rhythm Management (AFFIRM) trial, are currently underway to assess various clinical strategies for maintenance of NSR following conversion from AF. Amiodarone is one of the drugs under investigation.

A practical approach to torsade de pointes

The term torsade de pointes refers to polymorphic ventricular tachycardia that occurs in the setting of an abnormally long QT interval. While the most common cause is treatment with QT prolonging drugs, torsade de pointes also occurs in the congenital long QT syndromes and in the setting of acquired heart block or severe electrolyte disturbance, notably hypokalemia. Among QT prolonging drugs that cause torsade de pointes, both antiarrhythmics and "noncardioactive" drugs have been recognized. The electrocardiographic features of torsade de pointes include labile QT intervals, prominent U waves, and a "pause-dependent" onset of the arrhythmia. Treatment consists of recognition of the syndrome, correction of underlying electrolyte abnormalities, and withdrawal of any offending drugs. Magnesium, isoproterenol, or cardiac pacing provides specific antiarrhythmic therapy in torsade de pointes.

Potential proarrhythmic effects of implantable cardioverter-defibrillators

Implantable cardioverter-defibrillator (ICD) interventions have the potential to be proarrhythmogenic. New arrhythmias can occur in the setting of clinically appropriate therapies, as well as during a cardiac rhythm for which therapy is not intended. Cardioversion/defibrillation therapies, antitachycardia pacing, and antibradycardia pacing are potential triggers for the development of new arrhythmias. Newer ICDs allow better recognition and interpretation of the arrhythmias that are induced by delivered therapies. Two cases of ICD-induced proarrhythmias are described. Based on the course of these patients and review of previous reports, proarrhythmic effects of ICD interventions along with prevention and management strategies are discussed.

In vitro models of proarrhythmia

Proarrhythmia models use electrophysiological markers to predict the risk of torsade de pointes (TdP) in patients. The set of variables used by each model to predict the torsadogenic propensity of a drug has been reported to correlate with clinical outcome; however, these reports should be interpreted cautiously as no model has been independently assessed. Each model is discussed along with its merits and shortcomings; none, as yet, having shown a predictive value that makes it clearly superior to the others. As predictive as these models may become, extrapolation of results directly to the clinic must be exercised with caution. The use of in silico models, from subcellular to whole system, is rapidly beginning to form the first line of screening activity in many drug discovery programmes, indicating that biological experimentation may become secondary to analysis by simulation. In vitro proarrhythmia models challenge current perceptions of appropriate surrogates for TdP in man and question existing non-clinical strategies for assessing proarrhythmic risk. The rapid emergence of such models, compounded by the lack of a clear understanding of the key proarrhythmic mechanisms has resulted in a regulatory reluctance to embrace such models. The wider acceptance of proarrhythmia models is likely to occur when there is a clear understanding and agreement on the key proarrhythmia mechanisms. With greater acceptance and ongoing improvements, these models have the potential to unravel the complex mechanisms underlying TdP.

A rabbit Langendorff heart proarrhythmia model: predictive value for clinical identification of Torsades de Pointes

BACKGROUND AND PURPOSE

The rabbit isolated Langendorff heart model (SCREENIT) was used to investigate the proarrhythmic potential of a range of marketed drugs or drugs intended for market. These data were used to validate the SCREENIT model against clinical outcomes.

EXPERIMENTAL APPROACH

Fifty-five drugs, 3 replicates and 2 controls were tested in a blinded manner. Proarrhythmia variables included a 10% change in MAPD(60), triangulation, instability and reverse frequency-dependence of the MAP. Early after-depolarisations, ventricular tachycardia, TdP and ventricular fibrillation were noted. Data are reported at nominal concentrations relative to EFTPC(max). Proarrhythmic scores were assigned to each drug and each drug category.

KEY RESULTS

Category 1 and 2 drugs have the highest number of proarrhythmia variables and overt proarrhythmia while Category 5 drugs have the lowest, at every margin. At 30-fold the EFTPC(max), the mean proarrhythmic scores are: Category 1, 101+/-24; Category 2, 101+/-14; Category 3, 72+/-20; Category 4, 59+/-16 and Category 5, 22+/-9 points. Only drugs in Category 5 have mean proarrhythmic scores, below 30-fold, that remain within the Safety Zone.

CONCLUSIONS AND IMPLICATIONS

A 30-fold margin between effects and EFTPC(max) is sufficiently stringent to provide confidence to proceed with a new chemical entity, without incurring the risk of eliminating potentially beneficial drugs. The model is particularly useful where compounds have small margins between the hERG IC(50) and predicted EFTPC(max). These data suggest this is a robust and reliable assay that can add value to an integrated QT/TdP risk assessment.

QT interval prolongation related to psychoactive drug treatment: a comparison of monotherapy versus polytherapy

BACKGROUND: Several antipsychotic agents are known to prolong the QT interval in a dose dependent manner. Corrected QT interval (QTc) exceeding a threshold value of 450 ms may be associated with an increased risk of life threatening arrhythmias. Antipsychotic agents are often given in combination with other psychotropic drugs, such as antidepressants, that may also contribute to QT prolongation. This observational study compares the effects observed on QT interval between antipsychotic monotherapy and psychoactive polytherapy, which included an additional antidepressant or lithium treatment. METHOD: We examined two groups of hospitalized women with Schizophrenia, Bipolar Disorder and Schizoaffective Disorder in a naturalistic setting. Group 1 was composed of nineteen hospitalized women treated with antipsychotic monotherapy (either haloperidol, olanzapine, risperidone or clozapine) and Group 2 was composed of nineteen hospitalized women treated with an antipsychotic (either haloperidol, olanzapine, risperidone or quetiapine) with an additional antidepressant (citalopram, escitalopram, sertraline, paroxetine, fluvoxamine, mirtazapine, venlafaxine or clomipramine) or lithium. An Electrocardiogram (ECG) was carried out before the beginning of the treatment for both groups and at a second time after four days of therapy at full dosage, when blood was also drawn for determination of serum levels of the antipsychotic.Statistical analysis included repeated measures ANOVA, Fisher Exact Test and Indipendent T Test. RESULTS: Mean QTc intervals significantly increased in Group 2 (24 +/- 21 ms) however this was not the case in Group 1 (-1 +/- 30 ms) (Repeated measures ANOVA p < 0,01). Furthermore we found a significant difference in the number of patients who exceeded the threshold of borderline QTc interval value (450 ms) between the two groups, with seven patients in Group 2 (38%) compared to one patient in Group 1 (7%) (Fisher Exact Text, p < 0,05). CONCLUSIONS: No significant prolongation of the QT interval was found following monotherapy with an antipsychotic agent, while combination of these drugs with antidepressants caused a significant QT prolongation. Careful monitoring of the QT interval is suggested in patients taking a combined treatment of antipsychotic and antidepressant agents.

Should class III drugs be initiated in hospital to prevent drug-induced torsade de pointes arrhythmias?

OBJECTIVES

In the US, the FDA requires in-hospital institution of class III drugs. This study retrospectively assessed whether these criteria, which differ markedly from the Dutch exclusion criteria, could predict sotalol-induced torsade de pointes arrhythmias (TdP).

METHOD

Oral sotalol effect in a control group (50 patients, 62±12 years, 23 men, 27 women) was compared with five patients developing TdP (75±5years, all women), using known and new (JTU area measured in lead V2) risk parameters. Paroxysmal atrial fibrillation was the most common indication for sotalol treatment.

RESULTS

At baseline the strict US regulations would have identified four of five TdP patients on the basis of individual K⁺ levels, creatinine clearance and QT_c. However, 7 of 49 controls would also have been excluded, although they did not develop documented TdP in the >2 years follow-up. Sotalol slightly increased QT_c (361±34 to 387±33ms) in controls, due to heart rate reduction. In the TdP group, sotalol dramatically increased QT_c (467±33 to 626±52 ms, +35%, p<0.05) accompanied by deep negative TU waves and an increased JTU area and all could be identified as risk patients.

CONCLUSION

Patients developing TdP on oral sotalol can be identified using the FDA risk criteria and hospitalisation may therefore be appropriate. A European prospective study is required to investigate the costs, sensitivity and specificity of this strategy.

Interaction of different potassium channels in cardiac repolarization in dog ventricular preparations: role of repolarization reserve

1 The aim of this study was to investigate the possible role of the interaction of different potassium channels in dog ventricular muscle, by applying the conventional microelectrode and whole cell patch-clamp techniques at 37 degrees C. 2 Complete block of I(Kr) by 1 micro M dofetilide lengthened action potential duration (APD) by 45.6+/-3.6% at 0.2 Hz (n=13). Chromanol 293B applied alone at 10 micro M (a concentration which selectively blocks I(Ks)) did not markedly lengthen APD (<7%), but when repolarization had already been prolonged by complete I(Kr) block with 1 micro M dofetilide, inhibition of I(Ks) with 10 micro M chromanol 293B substantially delayed repolarization by 38.5+/-8.2% at 0.2 Hz (n=6). 3 BaCl(2), at a concentration of 10 micro M which blocks I(Kl) without affecting other currents, lengthened APD by 33.0+/-3.1% (n=11), but when I(Kr) was blocked with 1 micro M dofetilide, 10 micro M BaCl(2) produced a more excessive rate dependent lengthening in APD, frequently (in three out of seven preparations) initiating early afterdepolarizations. 4 These findings indicate that if only one type of potassium channels is inhibited in dog ventricular muscle, excessive APD lengthening is not likely to occur. Dog ventricular myocytes seem to repolarize with a strong safety margin ('repolarization reserve'). However, when this normal 'repolarization reserve' is attenuated, otherwise minimal or moderate potassium current inhibition can result in excessive and potentially proarrhythmic prolongation of the ventricular APD. Therefore, application of drugs which are able to block more than one type of potassium channel is probably more hazardous than the use of a specific inhibitor of one given sort of potassium channel, and when simultaneous blockade of several kinds of potassium channel may be presumed, a detailed study is needed to define the determinants of 'repolarization reserve'.

Proarrhythmic potential of halofantrine, terfenadine and clofilium in a modified in vivo model of torsade de pointes

1. This study was designed to compare the proarrhythmic activity of the antimalarial drug, halofantrine and the antihistamine, terfenadine, with that of clofilium a K(+) channel blocking drug that can induce torsade de pointes. 2. Experiments were performed in pentobarbitone-anaesthetized, open-chest rabbits. Each rabbit received intermittent, rising dose i.v. infusions of the alpha-adrenoceptor agonist phenylephrine. During these infusions rabbits also received increasing i.v. doses of clofilium (20, 60 and 200 nmol kg(-1) min(-1)), terfenadine (75, 250 and 750 nmol kg(-1) min(-1)), halofantrine (6, 20 and 60 micromol kg(-1)) or vehicle. 3. Clofilium and halofantrine caused dose-dependent increases in the rate-corrected QT interval (QTc), whereas terfenadine prolonged PR and QRS intervals rather than prolonging cardiac repolarization. Progressive bradycardia occurred in all groups. After administration of the highest dose of each drug halofantrine caused a modest decrease in blood pressure, but terfenadine had profound hypotensive effects resulting in death of most rabbits. 4. The total number of ventricular premature beats was highest in the clofilium group. Torsade de pointes occurred in 6 out of 8 clofilium-treated rabbits and 4 out of 6 of those which received halofantrine, but was not seen in any of the seven terfenadine-treated rabbits. 5. These results show that, like clofilium, halofantrine can cause torsade de pointes in a modified anaesthetized rabbit model whereas the primary adverse effect of terfenadine was cardiac contractile failure.

Tedisamil and dofetilide-induced torsades de pointes, rate and potassium dependence

1. Tedisamil is a bradycardiac agent that prolongs the QT interval of the ECG and prevents cardiac arrhythmias. Given this profile, tedisamil might be expected to have proarrhythmic actions similar to Class III antiarrhythmic drugs. To address this question, the actions of dofetilide and tedisamil were examined in rabbit isolated hearts in which bradycardia was induced by AV ablation. 2. The QT interval was prolonged in a reverse rate-dependent fashion by dofetilide (3 and 30 nM) and tedisamil (0.3 and 3 microM). 3. Torsades de pointes was observed in 1/7 hearts treated with 3 nM dofetilide and 0/7 hearts treated with 0.3 microM tedisamil. The incidence of torsades de pointes was increased to 5/7 in hearts treated with 30 nM dofetilide and to 7/7 in hearts treated with 3 microM tedisamil (both P < 0.05 vs control). 4. The actions of 30 nM dofetilide and 3 microM tedisamil were also examined in hearts paced at 50, 100, 200 and 50 beats min(-1) successively. Both drugs caused torsades de pointes in 5/5 hearts paced at 50 beats min(-1); however, the incidence was reduced to 0/5 during pacing at 200 beats min(-1). Thus, drug-induced proarrhythmia was bradycardia-dependent. 5. Drug-induced prolongation of the interval between the peak and end of the T-wave (QTa-e) was reverse rate-dependent and was associated with the occurrence of torsades de pointes (r = 0.91, P < 0.01). 6. The results suggest that tedisamil, like dofetilide, presents a risk for development of torsades de pointes.

MS-551 and KCB-328, two class III drugs aggravated adrenaline-induced arrhythmias

We investigated the proarrhythmic effects of MS-551 and KCB-328, class III antiarrhythmic drugs using adrenaline-induced arrhythmia models in halothane anaesthetized, closed-chest dogs. In the control period, adrenaline, starting from a low dose of 0.25 to up to 1.0 microg/kg/50 s i.v., was injected to determine the arrhythmia inducing dose and the non-inducing dose. After MS-551 or KCB-328 administration, the adrenaline injection was repeated and the interval between the injection and the occurrence of arrhythmia (latent interval), the changes in arrhythmic ratio (as calculated by dividing the number of ventricular premature contraction by the number of the total heart rate) and the severity of arrhythmia were observed. MS-551 infusion, 1 mg/kg/30 min, decreased the heart rate (HR) by 16% (P<0.01) and prolonged the QTc interval by 20% (P<0.01). During the 30 min of MS-551 infusion, arrhythmias occurred in three out of seven dogs (torsades de pointes (TdP) type VT in one dog). After these arrhythmias disappeared, MS-551 decreased the latent interval of the adrenaline arrhythmias produced by the inducing dose (30+/-2 s compared with 43+/-3 s of the control interval, P < 0.05), increased the arrhythmic ratio (P<0.05) and induced arrhythmias by non-inducing adrenaline doses (P<0.05). Effect of a new class III drug KCB-328 infusion, 0.3 mg/kg/30 min, was compared witih MS-551 using the same model. KCB-328 decreased the HR by 21% (P<0.01) and prolonged the QTc interval by 25% (P<0.01). During the 30 min of infusion, arrhythmias occurred in five out of seven dogs (TdP in two dogs). KCB-328 also decreased the latent interval of the adrenaline arrhythmias produced by the inducing doses (31+/-3 s compared with 49+/-7 s of the control period, P<0.05), but did not significantly alter the arrhythmic ratio. Adrenaline induced TdP only after MS-551 or KCB-328 was administered, i.e. after MS-551, 1 mg/kg/30 min, 3/7 versus 0/7 in the control; KCB, 0.3 mg/kg/30 min, 3/7 versus 0/7 in the control. To examine the direct arrhythmogenic effect of MS-551 and whether an adrenergic mechanism plays some role on this arrhythmogenesis, a bolus injection of MS-551, 3 mg/kg, was injected either without pre-treatment or after pre-treatment with propranolol 0.3 mg/kg. MS-551 induced arrhythmias in five out of seven dogs (TdP in one dog). Also in the propranolol pre-treated dogs, MS-551 induced arrhythmias in five out of seven dogs (TdP in 1 dog). In conclusion, these observations indicate that MS-551 and KCB-328 induced arrhythmias and intensified proarrhythmic effects of adrenaline, MS-551 being stronger than KCB-328 at the same QTc prolonging doses. The direct arrhythmogenic effect of MS-551 was not influenced by beta-blocker treatment.

Amiodarone: the expanding antiarrhythmic role and how to follow a patient on chronic therapy

Amiodarone was introduced as an antiarrhythmic compound in the early 1970s and was approved in the U.S. for the treatment of refractory ventricular arrhythmias in late 1984. Since that time the drug has become the most widely studied antiarrhythmic compound with expanding potential indications, including maintaining stability of sinus rhythm, secondary prevention in the survivors of myocardial infarction, and prolongation of survival in certain subsets of patients with congestive heart failure. Intravenous amiodarone was introduced in the U.S. in 1995 for the control of recurrent destabilizing ventricular tachycardia or ventricular fibrillation resistant to conventional therapy. The level of comfort in its use has risen considerably in the recent past. This has stemmed from the reasonably decisive evidence that class I agents increase mortality in patients with structural heart disease. In contrast, amiodarone either reduces mortality or its effect is neutral; this is consistent with its low to negligible proarrhythmic actions. The drug does not aggravate heart failure and it may even increase left ventricular ejection fraction and improve exercise capacity. Above all, it is becoming increasingly evident from wider experience and from controlled clinical trials that the side-effect profile of the drug is not as compelling an issue as it appeared to be when first used in much higher doses. Therefore, the overall objective of amiodarone therapy is to use the lowest dose that produces a defined therapeutic end point without causing serious side effects. Careful clinical surveillance in conjunction with monitoring of certain laboratory parameters and indices of efficacy at regular intervals permits the drug to be used effectively in a large number of patients who fail to respond to, or are intolerant of other antiarrhythmic compounds. Many experienced clinicians have begun to consider the use of amiodarone as first-line therapy in certain disorders of rhythm, especially in patients with severely compromised ventricular function.