PI3K/mTOR inhibitor omipalisib prolongs cardiac repolarization along with a mild proarrhythmic outcome in the AV block dog model.

Background: The phosphoinositide 3-kinase (PI3K) signaling pathway is an interesting target in cancer treatment. The awareness of the proarrhythmic risk of PI3K inhibitors was raised because PI3K is also involved in regulating signaling toward cardiac ion channels. Canine cardiomyocytes treated with PI3K inhibitors show an increased action potential duration and reduced cardiac repolarizing currents. Now, the potential proarrhythmic effect of chronic treatment of PI3K/mTOR inhibitor GSK2126458 (omipalisib) was investigated in the atrioventricular (AV) block dog model. Methods: Purpose-bred Mongrel dogs received complete AV block by ablation of the bundle of His and their hearts were paced in the right ventricular apex at VDD-mode (RVA-VDD). In this way, sinus rhythm was maintained for 15 ± 1 days and thereby bradycardia-induced cardiac remodeling was prevented. Dogs received 1 mg/kg omipalisib once (n = 3) or twice (n = 10) a day via oral administration for 7 days. Under standardized conditions (anesthesia, bradycardia at 60 beats/min, and a dofetilide challenge), potential proarrhythmic effects of omipalisib were investigated. Results: Twice daily dosing of omipalisib increased accumulative plasma levels compared to once daily dosing accompanied with adverse events. Omipalisib prolonged the QT interval at baseline and more strongly after the dofetilide challenge (490 ± 37 to 607 ± 48 ms). The arrhythmic outcome after omipalisib resulted in single ectopic beats in 30% of dogs perpetuating in multiple ectopic beats and TdP arrhythmia in 20% of dogs. Isolated ventricular cardiomyocytes from omipalisib-treated dogs showed a diminished IKs current density. Conclusion: Chronic treatment of PI3K/mTOR inhibitor omipalisib prolonged the QT interval in a preclinical model under standardized proarrhythmic conditions. Furthermore, this study showed that electrical remodeling induced by omipalisib had a mild proarrhythmic outcome.

Istaroxime treatment ameliorates calcium dysregulation in a zebrafish model of phospholamban R14del cardiomyopathy.

The heterozygous Phospholamban p.Arg14del mutation is found in patients with dilated or arrhythmogenic cardiomyopathy. This mutation triggers cardiac contractile dysfunction and arrhythmogenesis by affecting intracellular Ca2+ dynamics. Little is known about the physiological processes preceding induced cardiomyopathy, which is characterized by sub-epicardial accumulation of fibrofatty tissue, and a specific drug treatment is currently lacking. Here, we address these issues using a knock-in Phospholamban p.Arg14del zebrafish model. Hearts from adult zebrafish with this mutation display age-related remodeling with sub-epicardial inflammation and fibrosis. Echocardiography reveals contractile variations before overt structural changes occur, which correlates at the cellular level with action potential duration alternans. These functional alterations are preceded by diminished Ca2+ transient amplitudes in embryonic hearts as well as an increase in diastolic Ca2+ level, slower Ca2+ transient decay and longer Ca2+ transients in cells of adult hearts. We find that istaroxime treatment ameliorates the in vivo Ca2+ dysregulation, rescues the cellular action potential duration alternans, while it improves cardiac relaxation. Thus, we present insight into the pathophysiology of Phospholamban p.Arg14del cardiomyopathy.

How doctors actually (do not) involve families in decisions to continue or discontinue life-sustaining treatment in neonatal, pediatric, and adult intensive care: A qualitative study.

BACKGROUND: Intensive care doctors have to find the right balance between sharing crucial decisions with families of patients on the one hand and not overburdening them on the other hand. This requires a tailored approach instead of a model based approach. AIM: To explore how doctors involve families in the decision-making process regarding life-sustaining treatment on the neonatal, pediatric, and adult intensive care. DESIGN: Exploratory inductive thematic analysis of 101 audio-recorded conversations. SETTING/PARTICIPANTS: One hundred four family members (61% female, 39% male) and 71 doctors (60% female, 40% male) of 36 patients (53% female, 47% male) from the neonatal, pediatric, and adult intensive care of a large university medical center participated. RESULTS: We identified eight relevant and distinct communicative behaviors. Doctors' sequential communicative behaviors either reflected consistent approaches-a shared approach or a physician-driven approach-or reflected vacillating between both approaches. Doctors more often displayed a physician-driven or a vacillating approach than a shared approach, especially in the adult intensive care. Doctors did not verify whether their chosen approach matched the families' decision-making preferences. CONCLUSIONS: Even though tailoring doctors' communication to families' preferences is advocated, it does not seem to be integrated into actual practice. To allow for true tailoring, doctors' awareness regarding the impact of their communicative behaviors is key. Educational initiatives should focus especially on improving doctors' skills in tactfully exploring families' decision-making preferences and in mutually sharing knowledge, values, and treatment preferences.

Involvement of nurses in end-of-life discussions for severely disabled children.

BACKGROUND: In children with profound intellectual and multiple disabilities (PIMD), discussions about end-of-life decisions (EoLDs) are comparatively common. Nurses play a crucial role in the care for these children, yet their involvement in EoLD discussions is largely unknown. The objective of this research was to investigate the involvement in the hospital of nurses in discussions with parents and physicians about EoLDs for children with PIMD. METHOD: In a retrospective, qualitative study, we conducted semi-structured interviews with the nurses of 12 children with PIMD for whom an EoLD was made within the past 2 years. RESULTS: Parents primarily discuss EoLDs with nurses before and after the meeting with the physician. Nurses who were involved in EoL discussions with parents and physicians assisted them by giving factual information about the child and by providing emotional support. Some nurses, especially nurses from ID-care services, were not involved in EoL discussions, even if they had cared for the child for a long period of time. Some of the nurses had moral or religious objections to carrying out the decisions. CONCLUSION: Most nurses were not involved in EoL discussions with parents and physicians in the hospital. Excluding nurses from EoL discussions can cause them moral distress. The involvement of nurses in EoL discussions for children with PIMD should be improved, especially by involving nurses from ID-care services. Because these nurses are usually familiar with the child, they can be valuable sources of information about the child's quality of life.

Considering quality of life in end-of-life decisions for severely disabled children.

BACKGROUND: End-of-life decisions (EoLDs) are very difficult to make. How parents and physicians incorporate quality of life (QoL) considerations into their end-of-life decision making (EoLDM) for children with profound intellectual and multiple disabilities (PIMD) remains unknown. AIMS: To determine which elements contribute to QoL according to parents and physicians, how QoL is incorporated into EoLDM and how parents and physicians discuss QoL considerations in the Netherlands. METHODS: Semi-structured interviews were conducted with the physicians and parents of 14 children with PIMD for whom an EoLD had been made within the past two years. RESULTS: Parents and physicians agreed on the main elements that contribute to QoL in children with PIMD. The way in which QoL was incorporated differed slightly for different types of decisions. Parents and physicians rarely discussed elements contributing to the child's QoL when making EoLDS. CONCLUSIONS: and Implications Although QoL was highly important during EoLDM for children with PIMD, parents and physicians did not fully explore the elements that contribute to the child's QoL when they made EoLDs. We recommend the development of a communication tool that will help parents and physicians discuss elements that contribute to QoL and the consequences these elements have for upcoming decisions.

Deleterious acute and chronic effects of bradycardic right ventricular apex pacing: consequences for arrhythmic outcome.

In the chronic complete atrioventricular (AV) block dog (CAVB) model, both bradycardia and altered ventricular activation due to the uncontrolled idioventricular rhythm contribute to ventricular remodeling and the enhanced susceptibility to Torsade de Pointes (TdP) arrhythmias. We investigated the effect of permanent bradycardic right ventricular apex (RVA) pacing on mechanical and electrical remodeling and TdP. In 23 anesthetized dogs, serial experiments were performed at sinus rhythm (SR), acutely after AV block (AAVB) and 3 weeks of remodeling CAVB at a fixed pacing rate of 60/min. ECG, and left (LV) and right ventricular (RV) monophasic action potentials durations (MAPD) were recorded; activation time (AT) and activation recovery interval (ARI) were determined from ten distinct LV electrograms; interventricular mechanical delay (IVMD) and time-to-peak strain (TTP) of the LV septal and lateral wall (ΔTTP: lateral wall minus septal wall) were obtained echocardiographically. Dofetilide (25 µg/kg/5 min) was infused to study TdP inducibility. In baseline AAVB, in comparison to SR, RVA bradypacing acutely increased QT interval, LV, and RVMAPD. Echocardiographic IVMD and ΔTTP were initially increased, which was partially corrected after 3 weeks of RVA pacing (IVMD: 22 ± 13 vs. 42 ± 11 vs. 31 ± 6 ms; ΔTTP: -2 ± 47 vs. -114 ± 38 vs. -36 ± 22 ms). QT interval (362 ± 23 vs. 373 ± 29 ms), LVMAPD (245 ± 18 vs. 253 ± 22 ms), RVMAPD (226 ± 26 vs. 238 ± 31 ms), and mean LV-ARI (268 ± 5 vs. 267 ± 6 ms) were not significantly changed after 3 weeks of RVA pacing. During AAVB, dofetilide increased mean LV-ARI (381 ± 11 ms) with largest increases in the later activated basal areas (slope AT-ARI: +0.96). In contrast with acute RVA pacing, 3 week pacing increased TdP inducibility (0/13 vs. 11/21) and mean LV-ARI (484 ± 18 ms), while the slope of AT-ARI responded differently on dofetilide (-2.37), with larger APD increases in the early region. The latter was supported at the molecular level: reduced RNA expressions of three repolarization-related ion channel genes in early (KCNQ1, KCNH2, and KCNJ2) versus two in late regions (KNCQ1 and KCNJ2). In conclusion, bradycardic RVA pacing acutely induced LV intra- and interventricular mechanical dyssynchrony, which was partially reversed after 3 weeks of pacing (remodeling). The latter occurred without apparent baseline electrical effects. However, dofetilide clearly unmasked (region-specific) arrhythmic consequences of remodeling.

How parents and physicians experience end-of-life decision-making for children with profound intellectual and multiple disabilities.

BACKGROUND: End-of-life decisions (EoLD) often concern children with profound intellectual and multiple disabilities (PIMD). Yet, little is known about how parents and physicians discuss and make these decisions. AIMS: The objective of this research was to investigate the experiences of the parents and the involved physician during the end-of-life decision-making (EoLDM) process for children with PIMD. METHODS: In a retrospective, qualitative study, we conducted semi-structured interviews with the physicians and parents of 14 children with PIMD for whom an EoLD was made within the past two years. RESULTS: A long-lasting relationship appeared to facilitate the EoLDM process, although previous negative healthcare encounters could also lead to distrust. Parents and physicians encountered disagreements during the EoLDM process, but these disagreements could also improve the decision-making process. Most parents, as well as most physicians, considered the parents to be the experts on their child. In making an EoLD, both parents and physicians preferred a shared decision-making approach, although they differed in what they actually meant by this concept. CONCLUSION: The EoLDM process for children with PIMD can be improved if physicians are more aware of the specific situation and of the roles and expectations of the parents of children with PIMD.

End-of-life decision-making for children with severe developmental disabilities: The parental perspective.

BACKGROUND AND AIMS: The objectives of this integrative review were to understand how parents of children with severe developmental disorders experience their involvement in end-of-life decision-making, how they prefer to be involved and what factors influence their decisions. METHODS AND PROCEDURES: We searched MEDLINE, EMBASE, CINAHL and PsycINFO. The search was limited to articles in English or Dutch published between January 2004 and August 2014. We included qualitative and quantitative original studies that directly investigated the experiences of parents of children aged 0-18 years with severe developmental disorders for whom an end-of-life decision had been considered or made. OUTCOMES AND RESULTS: We identified nine studies that met all inclusion criteria. Reportedly, parental involvement in end-of-life decision-making varied widely, ranging from having no involvement to being the sole decision-maker. Most parents preferred to actively share in the decision-making process regardless of their child's specific diagnosis or comorbidity. The main factors that influenced parents in their decision-making were: their strong urge to advocate for their child's best interests and to make the best (possible) decision. In addition, parents felt influenced by their child's visible suffering, remaining quality of life and the will they perceived in their child to survive. CONCLUSIONS AND IMPLICATIONS: Most parents of children with severe developmental disorders wish to actively share in the end-of-life decision-making process. An important emerging factor in this process is the parents' feeling that they have to stand up for their child's interests in conversations with the medical team.

The risk of ventricular arrhythmias in a Dutch CRT population: CRT-defibrillator versus CRT-pacemaker.

BACKGROUND: Patients eligible for cardiac resynchronisation therapy (CRT) have an indication for primary prophylactic implantable cardioverter defibrillator (ICD) therapy. However, response to CRT might influence processes involved in arrhythmogenesis and therefore change the necessity of ICD therapy in certain patients. METHOD: In 202 CRT-defibrillator patients, the association between baseline variables, 6-month echocardiographic outcome (volume response: left ventricular end-systolic volume decrease < ≥15 % and left ventricular ejection fraction (LVEF) ≤ >35 %) and the risk of first appropriate ICD therapy was analysed retrospectively. RESULTS: Fifty (25 %) patients received appropriate ICD therapy during a median follow-up of 37 (23-52) months. At baseline ischaemic cardiomyopathy (hazard ratio (HR) 2.0, p = 0.019) and a B-type natriuretic peptide level > 163 pmol/l (HR 3.8, p < 0.001) were significantly associated with the risk of appropriate ICD therapy. After 6 months, 105 (52 %) patients showed volume response and 51 (25 %) reached an LVEF > 35 %. Three (6 %) patients with an LVEF > 35 % received appropriate ICD therapy following echocardiography at ± 6 months compared with 43 patients (29 %) with an LVEF ≤ 35 % (p = 0.001). LVEF post-CRT was more strongly associated to the risk of ventricular arrhythmias than volume response (LVEF > 35 %, HR 0.23, p = 0.020). CONCLUSION: Assessing the necessity of an ICD in patients eligible for CRT remains a challenge. Six months post-CRT an LVEF > 35 % identified patients at low risk of ventricular arrhythmias. LVEF might be used at the time of generator replacement to identify patients suitable for downgrading to a CRT-pacemaker.

A 2015 focus on preventing drug-induced arrhythmias.

Drug-induced Torsade de Pointes arrhythmia is a life-threatening adverse effect feared by pharmaceutical companies. For the last decade, the cardiac safety guidelines have imposed human ether-a-go-go-related gene channel blockade and prolongation of QT interval as surrogates for proarrhythmic risk propensity of a new chemical entity. Suffering from a lack of specificity, this assessment strategy led to a great amount of false positive outcomes. Therefore, this review will discuss new pharmaceutical strategies: the cardiac safety proposal that recently emerged, the Comprehensive in vitro Proarrhythmia Assay, combining in vitro assays that integrate effects on main cardiac ion channels, with computational models of human ventricular action potential as well as assays using human stem cell-derived cardiomyocytes for an improved prediction of drug's proarrhythmic liability, alternative pharmacological perspectives as well as the current treatment of drug-induced long QT syndrome.

T-Wave Alternans Is Linked to Microvascular Obstruction and to Recurrent Coronary Ischemia After Myocardial Infarction.

The purpose of this study is to investigate the relationship between T-wave alternans (TWA), infarct size and microvascular obstruction (MVO) and recurrent cardiac morbidity after ST elevation myocardial infarction (STEMI). One hundred six patients underwent TWA testing 1-12 months and 57 patients underwent cardiac magnetic resonance imaging (MRI) in the first 2-4 days after STEMI. During follow-up (3.5 ± 0.5 years), death (n = 2), ventricular tachycardia (n = 3), supraventricular tachycardia (n = 4), heart failure (n = 3) and recurrent coronary ischemia (n = 25) were observed. After multivariate analysis, positive TWA (HR2.59, CI1.10-6.11, p0.024) and larger MVO (HR1.08, CI1.01-1.16, p0.034) were associated with recurrent angina or ACS. Presence of MVO was correlated with TWA (Spearman rho 0.404, p0.002) and the impairment of LVEF (-0.524, p < 0.001). Patients after STEMI remain at a high risk of symptoms of coronary ischemia. The presence of MVO and TWA 1-12 months after STEMI is related to each other and to recurrent angina or ACS.

New antiarrhythmic targets to control intracellular calcium handling.

Sudden cardiac death due to ventricular arrhythmias is a major problem. Drug therapies to prevent SCD do not provide satisfying results, leading to the demand for new antiarrhythmic strategies. New targets include Ca(2+)/Calmodulin-dependent protein kinase II (CaMKII), the Na/Ca exchanger (NCX), the Ryanodine receptor (RyR, and its associated protein FKBP12.6 (Calstabin)) and the late component of the sodium current (I Na-Late ), all related to intracellular calcium (Ca(2+)) handling. In this review, drugs interfering with these targets (SEA-0400, K201, KN-93, W7, ranolazine, sophocarpine, and GS-967) are evaluated and their future as clinical compounds is considered. These new targets prove to be interesting; however more insight into long-term drug effects is necessary before clinical applicability becomes reality.

The electromechanical window is no better than QT prolongation to assess risk of Torsade de Pointes in the complete atrioventricular block model in dogs.

BACKGROUND AND PURPOSE: The electromechanical window (EMW), the interval between the end of the T-wave and the end of the left ventricular pressure (LVP) curve, has recently been proposed as a predictor of risk of Torsade de Pointes (TdP) in healthy animals, whereby a negative EMW (mechanical relaxation earlier than repolarization) after drug administration indicates an increased TdP risk. The aims of this study were to assess (i) the effect of the ventricular remodelling in the canine chronic, complete atrioventricular block (CAVB) model on EMW; (ii) the effect of the I(Kr) -blocker dofetilide on EMW; and (iii) the correlation of EMW with TdP inducibility. EXPERIMENTAL APPROACH: Our 11 year database of experiments of CAVB in dogs under general anaesthesia was reviewed and experiments included if ECG and LVP were recorded simultaneously at spontaneous rhythm. In total, 89 experiments in 44 dogs were appropriate and were analysed. KEY RESULTS: During normally conducted sinus rhythm or acute atrioventricular block, EMW was positive. During CAVB, EMW was decreased to negative values. Dofetilide further reduced EMW before inducing repetitive TdP in 82% of the experiments. However, subclassification into inducible and non-inducible dogs revealed no difference in EMW. Analysis of the components of EMW revealed that the observed changes in EMW were solely caused by QT prolongation. CONCLUSIONS AND IMPLICATIONS: In the canine CAVB model, ventricular remodelling and I(Kr) block by dofetilide are associated with negative EMW values, but this reflects QT prolongation, and implies that the EMW lacks specificity to predict dofetilide-induced TdP.

Structure-activity relationships of pentamidine-affected ion channel trafficking and dofetilide mediated rescue.

BACKGROUND AND PURPOSE: Drug interference with normal hERG protein trafficking substantially reduces the channel density in the plasma membrane and thereby poses an arrhythmic threat. The chemical substructures important for hERG trafficking inhibition were investigated using pentamidine as a model drug. Furthermore, the relationship between acute ion channel block and correction of trafficking by dofetilide was studied. EXPERIMENTAL APPROACH: hERG and K(IR)2.1 trafficking in HEK293 cells was evaluated by Western blot and immunofluorescence microscopy after treatment with pentamidine and six pentamidine analogues, and correction with dofetilide and four dofetilide analogues that displayed different abilities to inhibit IKr . Molecular dynamics simulations were used to address mode, number and type of interactions between hERG and dofetilide analogues. KEY RESULTS: Structural modifications of pentamidine differentially affected plasma membrane levels of hERG and K(IR)2.1. Modification of the phenyl ring or substituents directly attached to it had the largest effect, affirming the importance of these chemical residues in ion channel binding. PA-4 had the mildest effects on both ion channels. Dofetilide corrected pentamidine-induced hERG, but not K(IR)2.1 trafficking defects. Dofetilide analogues that displayed high channel affinity, mediated by pi-pi stacks and hydrophobic interactions, also restored hERG protein levels, whereas analogues with low affinity were ineffective. CONCLUSIONS AND IMPLICATIONS: Drug-induced trafficking defects can be minimized if certain chemical features are avoided or 'synthesized out'; this could influence the design and development of future drugs. Further analysis of such features in hERG trafficking correctors may facilitate the design of a non-blocking corrector for trafficking defective hERG proteins in both congenital and acquired LQTS.

Implementation of guidelines for implantable cardioverter-defibrillator therapy in clinical practice: Which patients do benefit?

PURPOSE: Based on multiple large clinical trials conducted over the last decades guidelines for implantable cardioverter-defibrillator (ICD) implantations have been evolving. The increase in primary prophylactic ICD implantations challenges us to be critical towards the indications in certain patient populations. METHODS: We retrospectively collected patient characteristics and rates of appropriate and inappropriate ICD therapy, appropriate and inappropriate ICD shock and mortality of all patients who received an ICD in the University Medical Center Utrecht (UMCU) over the years 2006-2011. RESULTS: A total of 1075 patients were included in this analysis (74 % male, mean age 61 ± 13 years, left ventricular ejection fraction 30 ± 13 %); 61 % had a primary indication and 58 % had ischaemic heart disease. During a mean follow-up period of 31 ± 17 months, 227 of the patients (21 %) received appropriate ICD therapy (149 (14 %) patients received an appropriate ICD shock). Females, patients with a primary prophylactic indication and patients with non-ischaemic heart disease experienced significantly less ICD therapy. Only a few patients (54, 5 %) received inappropriate ICD therapy; 33 (3 %) patients received an inappropriate ICD shock. Fifty-five patients died within one year after ICD implantation and were therefore, in retrospect, not eligible for ICD implantation. CONCLUSION: Our study confirms the benefit of ICD implantation in clinical practice. Nevertheless, certain patients experience less benefit than others. A more patient-tailored risk stratification based on electrophysiological parameters would be lucrative to improve clinical benefit and cost-effectiveness.

JTV519 (K201) reduces sarcoplasmic reticulum Ca²âº leak and improves diastolic function in vitro in murine and human non-failing myocardium.

BACKGROUND AND PURPOSE: Ca²âº leak from the sarcoplasmic reticulum (SR) via ryanodine receptors (RyR2s) contributes to cardiomyocyte dysfunction. RyR2 Ca²âº leak has been related to RyR2 phosphorylation. In these conditions, JTV519 (K201), a 1,4-benzothiazepine derivative and multi-channel blocker, stabilizes RyR2s and decrease SR Ca²âº leak. We investigated whether JTV519 stabilizes RyR2s without increasing RyR2 phosphorylation in mice and in non-failing human myocardium and explored underlying mechanisms. EXPERIMENTAL APPROACH: SR Ca²âº leak was induced by ouabain in murine cardiomyocytes. [Ca²âº]-transients, SR Ca²âº load and RyR2-mediated Ca²âº leak (sparks/waves) were quantified, with or without JTV519 (1 µmol·L⁻¹). Contribution of Ca²âº -/calmodulin-dependent kinase II (CaMKII) was assessed by KN-93 and Western blot (RyR2-Ser(2814) phosphorylation). Effects of JTV519 on contractile force were investigated in non-failing human ventricular trabeculae. KEY RESULTS: Ouabain increased systolic and diastolic cytosolic [Ca²âº](i) , SR [Ca²âº], and SR Ca²âº leak (Ca²âº spark (SparkF) and Ca²âº wave frequency), independently of CaMKII and RyR-Ser(2814) phosphorylation. JTV519 decreased SparkF but also SR Ca²âº load. At matched SR [Ca²âº], Ca²âº leak was significantly reduced by JTV519, but it had no effect on fractional Ca²âº release or Ca²âº wave propagation velocity. In human muscle, JTV519 was negatively inotropic at baseline but significantly enhanced ouabain-induced force and reduced its deleterious effects on diastolic function. CONCLUSIONS AND IMPLICATIONS: JTV519 was effective in reducing SR Ca²âº leak by specifically regulating RyR2 opening at diastolic [Ca²âº](i) in the absence of increased RyR2 phosphorylation at Ser(2814) , extending the potential use of JTV519 to conditions of acute cellular Ca²âº overload.

Comparison of the IKr blockers moxifloxacin, dofetilide and E-4031 in five screening models of pro-arrhythmia reveals lack of specificity of isolated cardiomyocytes.

BACKGROUND AND PURPOSE: Drug development requires the testing of new chemical entities for adverse effects. For cardiac safety screening, improved assays are urgently needed. Isolated adult cardiomyocytes (CM) and human embryonic stem cell-derived cardiomyocytes (hESC-CM) could be used to identify pro-arrhythmic compounds. In the present study, five assays were employed to investigate their sensitivity and specificity for evaluating the pro-arrhythmic properties of I(Kr) blockers, using moxifloxacin (safe compound) and dofetilide or E-4031 (unsafe compounds). EXPERIMENTAL APPROACH: Assays included the anaesthetized remodelled chronic complete AV block (CAVB) dog, the anaesthetized methoxamine-sensitized unremodelled rabbit, multi-cellular hESC-CM clusters, isolated CM obtained from CAVB dogs and isolated CM obtained from the normal rabbit. Arrhythmic outcome was defined as Torsade de Pointes (TdP) in the animal models and early afterdepolarizations (EADs) in the cell models. KEY RESULTS: At clinically relevant concentrations (5-12 µM), moxifloxacin was free of pro-arrhythmic properties in all assays with the exception of the isolated CM, in which 10 µM induced EADs in 35% of the CAVB CM and in 23% of the rabbit CM. At supra-therapeutic concentrations (≥100 µM), moxifloxacin was pro-arrhythmic in the isolated rabbit CM (33%), in the hESC-CM clusters (18%), and in the methoxamine rabbit (17%). Dofetilide and E-4031 induced EADs or TdP in all assays (50-83%), and the induction correlated with a significant increase in beat-to-beat variability of repolarization. CONCLUSION AND IMPLICATIONS: Isolated cardiomyocytes lack specificity to discriminate between TdP liability of the I(Kr) blocking drugs moxifloxacin and dofetilide or E4031.

Longitudinal arrhythmogenic remodelling in a mouse model of longstanding pressure overload.

INTRODUCTION: Sudden arrhythmogenic cardiac death is a major cause of mortality in patients with congestive heart failure due to adverse electrical remodelling. To establish whether abnormal conduction is responsible for arrhythmogenic remodelling in progressed stages of heart failure, we have monitored functional, structural and electrical remodelling in a murine model of heart failure, induced by longstanding pressure overload. METHODS: Mice were subjected to transverse aortic constriction (TAC; n=18) or sham operated (n=19) and monitored biweekly by echocardiography and electrocardiography. At the 16-week endpoint, electrical mapping was performed to measure epicardial conduction velocity and susceptibility to arrhythmias. Finally, tissue sections were stained for Cx43 and fibrosis. RESULTS: In TAC mice, fractional shortening decreased gradually and was significantly lower compared with sham at 16 weeks. Left ventricular hypertrophy was significant after six weeks. TAC mice developed PQ prolongation after 12 weeks, QT prolongation after 16 weeks and QRS prolongation after two weeks. Right ventricular conduction velocity was slowed parallel to fibre orientation. In 8/18 TAC hearts, polymorphic ventricular tachyarrhythmias were provoked and none in sham hearts. TAC mice had more interstitial fibrosis than sham. Immunohistology showed that Cx43 levels were similar but highly heterogeneous in TAC mice. All parameters were comparable in TAC mice with and without arrhythmias, except for Cx43 heterogeneity, which was significantly higher in arrhythmogenic TAC mice. CONCLUSION.: Chronic pressure overload resulted in rapid structural and electrical remodelling. Arrhythmias were related to heterogeneous expression of Cx43. This may lead to functional block and unstable reentry, giving rise to polymorphic ventricular tachyarrhythmias. (Neth Heart J 2010;18:509-15.).

Robust anti-arrhythmic efficacy of verapamil and flunarizine against dofetilide-induced TdP arrhythmias is based upon a shared and a different mode of action.

BACKGROUND AND PURPOSE: The high predisposition to Torsade de Pointes (TdP) in dogs with chronic AV-block (CAVB) is well documented. The anti-arrhythmic efficacy and mode of action of Ca(2+) channel antagonists, flunarizine and verapamil against TdP were investigated. EXPERIMENTAL APPROACH: Mongrel dogs with CAVB were selected based on the inducibility of TdP with dofetilide. The effects of flunarizine and verapamil were assessed after TdP and in different experiments to prevent dofetilide-induced TdP. Electrocardiogram and ventricular monophasic action potentials were recorded. Electrophysiological parameters and short-term variability of repolarization (STV) were determined. In vitro, flunarizine and verapamil were added to determine their effect on (i) dofetilide-induced early after depolarizations (EADs) in canine ventricular myocytes (VM); (ii) diastolic Ca(2+) sparks in RyR2(R4496+/+) mouse myocytes; and (iii) peak and late I(Na) in SCN5A-HEK 293 cells. KEY RESULTS: Dofetilide increased STV prior to TdP and in VM prior to EADs. Both flunarizine and verapamil completely suppressed TdP and reversed STV to baseline values. Complete prevention of TdP was achieved with both drugs, accompanied by the prevention of an increase in STV. Suppression of EADs was confirmed after flunarizine. Only flunarizine blocked late I(Na). Ca(2+) sparks were reduced with verapamil. CONCLUSIONS AND IMPLICATIONS: Robust anti-arrhythmic efficacy was seen with both Ca(2+) channel antagonists. Their divergent electrophysiological actions may be related to different additional effects of the two drugs.

Gender disparity in cardiac electrophysiology: implications for cardiac safety pharmacology.

BACKGROUND: Gender differences in cardiac electrophysiology were reported for the first time almost a century ago. The importance for safety pharmacology became significant when modern medicine came into use and women appeared to be more susceptible to drug-induced Torsade de Pointes (TdP). To unravel the underlying mechanisms, the effect of sex hormones on cardiac electrophysiology has been studied in humans, animals and cell models. In this review, these data have been summarized and discussed in regard to possible consequences for safety pharmacology testing. RESULTS: In man, electrophysiological differences become apparent during adolescence when the QTc interval shortens in males. This protective effect for long-QT related arrhythmias can be correlated to testosterone levels. Testosterone likely suppresses I(Ca,L) and enhances I(K) which increases the repolarization reserve. Though progesterone may have similar effects in women, these effects are probably balanced out by the small but opposite effects of estrogen. Progesterone levels, however, vary importantly throughout the different phases of the human menstrual cycle, implying that the sensitivity for drug-induced TdP changes too. The consequences for drug safety testing and TdP have not been assessed. CONCLUSION: The testosterone-mediated increase in repolarization reserve in men is a likely cause for their lower susceptibility to drug-induced TdP. For the female population, the shifting balance in estrogen and progesterone creates temporal variation in the lability of repolarization to drug-induced TdP. This is a possible confounding factor in the evaluation and comparison of drugs that has to be further tested.