Negative electro-mechanical windows are required for drug-induced Torsades de Pointes in the anesthetized guinea pig

Predictive Value of Electromechanical Window for Risk of Fatal Ventricular Arrhythmia

BACKGROUND

As an indicator of electro-mechanical coupling, electromechanical window (EMW) can be used to predict fatal ventricular arrhythmias. We investigated the additive effect of EMW on the prediction of fatal ventricular arrhythmias in high-risk patients.

METHODS

We included patients who had implantable cardioverter-defibrillator (ICD) implanted for primary or secondary prevention. The event group was defined as those who received an appropriate ICD therapy. We acquired echocardiograms at ICD implantation and follow-up. The EMW was calculated as the difference between the interval from QRS onset to aortic valve closure and QT interval from the electrocardiogram embedded in the continuous wave doppler image. We evaluated the predictive value of EMW for predicting fatal ventricular arrhythmia.

RESULTS

Of 245 patients (67.2 ± 12.8 years, 63.7% men), the event group was 20.0%. EMW at baseline (EMW-Baseline) and follow-up (EMW-FU) was significantly different between event and control groups. After adjustment, both EMW-Baseline (odds ratio [OR]_adjust 1.02 [1.01-1.03], P = 0.004) and EMW-FU (OR_adjust 1.06 [1.04-1.07], P < 0.001) remained as significant predictors for fatal arrhythmic events. Adding EMW-Baseline significantly improved the discriminating ability of the multivariable model including clinical variables (area under the curve [AUC] 0.77 [0.70-0.84] vs. AUC 0.72 [0.64-0.80], P = 0.004), while a univariable model using EMW-FU alone showed the best performance among models (AUC 0.87 [0.81-0.94], P = 0.060 against model with clinical variables; P = 0.030 against model with clinical variables and EMW-Baseline).

CONCLUSION

The EMW could effectively predict severe ventricular arrhythmia in ICD implanted patients. This finding supports the importance of incorporating the electro-mechanical coupling index into the clinical practice for predicting future fatal arrhythmia events.

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

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

Simultaneous measurement of contractile force and field potential of dynamically beating human iPS cell-derived cardiac cell sheet-tissue with flexible electronics

Human induced pluripotent stem (iPS) cell-derived cardiomyocytes are used for in vitro pharmacological and pathological studies worldwide. In particular, the functional assessment of cardiac tissues created from iPS cell-derived cardiomyocytes is expected to provide precise prediction of drug effects and thus streamline the process of drug development. However, the current format of electrophysiological and contractile assessment of cardiomyocytes on a rigid substrate is not appropriate for cardiac tissues that beat dynamically. Here, we show a novel simultaneous measurement system for contractile force and extracellular field potential of iPS cell-derived cardiac cell sheet-tissues using 500 nm-thick flexible electronic sheets. It was confirmed that the developed system is applicable for pharmacological studies and assessments of excitation-contraction coupling-related parameters, such as the electro-mechanical window. Our results indicate that flexible electronics with cardiac tissue engineering provide an advanced platform for drug development. This system will contribute to gaining new insight in pharmacological study of human cardiac function.

Combining an in silico proarrhythmic risk assay with a tPKPD model to predict QTc interval prolongation in the anesthetized guinea pig assay

Human-based in silico models are emerging as important tools to study the effects of integrating inward and outward ion channel currents to predict clinical proarrhythmic risk. The aims of this study were 2-fold: 1) Evaluate the capacity of an in silico model to predict QTc interval prolongation in the in vivo anesthetized cardiovascular guinea pig (CVGP) assay for new chemical entities (NCEs) and; 2) Determine if a translational pharmacokinetic/pharmacodynamic (tPKPD) model can improve the predictive capacity. In silico simulations for NCEs were performed using a population of human ventricular action potential (AP) models. PatchXpress® (PX) or high throughput screening (HTS) ion channel data from respectively n = 73 and n = 51 NCEs were used as inputs for the in silico population. These NCEs were also tested in the CVGP (n = 73). An M5 pruned decision tree-based regression tPKPD model was used to evaluate the concentration at which an NCE is liable to prolong the QTc interval in the CVGP. In silico results successfully predicted the QTc interval prolongation outcome observed in the CVGP with an accuracy/specificity of 85%/73% and 75%/77%, when using PX and HTS ion channel data, respectively. Considering the tPKPD predicted concentration resulting in QTc prolongation (EC_5%) increased accuracy/specificity to 97%/95% using PX and 88%/97% when using HTS. Our results support that human-based in silico simulations in combination with tPKPD modeling can provide correlative results with a commonly used early in vivo safety assay, suggesting a path toward more rapid NCE assessment with reduced resources, cycle time, and animal use.

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Cardiac electrophysiological in silico model predicts QTc interval prolongation in the guinea pig.

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PKPD model predicts relevant QTc interval prolongation concentration in guinea pig.

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Combining the models improves the accuracy of predicting guinea pig QTc effects.

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Combining models accelerates assessment of QTc with lower resources and animal use.

Drug-induced shortening of the electromechanical window is an effective biomarker for in silico prediction of clinical risk of arrhythmias

BACKGROUND AND PURPOSE

Early identification of drug-induced cardiac adverse events is key in drug development. Human-based computer models are emerging as an effective approach, complementary to in vitro and animal models. Drug-induced shortening of the electromechanical window has been associated with increased risk of arrhythmias. This study investigates the potential of a cellular surrogate for the electromechanical window (EMw) for prediction of pro-arrhythmic cardiotoxicity, and its underlying ionic mechanisms, using human-based computer models.

EXPERIMENTAL APPROACH

In silico drug trials for 40 reference compounds were performed, testing up to 100-fold the therapeutic concentrations (EFTPCmax ) and using a control population of human ventricular action potential (AP) models, optimised to capture pro-arrhythmic ionic profiles. EMw was calculated for each model in the population as the difference between AP and Ca2+ transient durations at 90%. Drug-induced changes in the EMw and occurrence of repolarisation abnormalities (RA) were quantified.

KEY RESULTS

Drugs with clinical risk of Torsade de Pointes arrhythmias induced a concentration-dependent EMw shortening, while safe drugs lead to increase or small change in EMw. Risk predictions based on EMw shortening achieved 90% accuracy at 10× EFTPCmax , whereas RA-based predictions required 100× EFTPCmax to reach the same accuracy. As it is dependent on Ca2+ transient, the EMw was also more sensitive than AP prolongation in distinguishing between pure hERG blockers and multichannel compounds also blocking the calcium current.

CONCLUSION AND IMPLICATIONS

The EMw is an effective biomarker for in silico predictions of drug-induced clinical pro-arrhythmic risk, particularly for compounds with multichannel blocking action.

Reflective lens-free imaging on high-density silicon microelectrode arrays for monitoring and evaluation of in vitro cardiac contractility

The high rate of drug attrition caused by cardiotoxicity is a major challenge for drug development. Here, we developed a reflective lens-free imaging (RLFI) approach to non-invasively record in vitro cell deformation in cardiac monolayers with high temporal (169 fps) and non-reconstructed spatial resolution (352 µm) over a field-of-view of maximally 57 mm². The method is compatible with opaque surfaces and silicon-based devices. Further, we demonstrated that the system can detect the impairment of both contractility and fast excitation waves in cardiac monolayers. Additionally, the RLFI device was implemented on a CMOS-based microelectrode array to retrieve multi-parametric information of cardiac cells, thereby offering more in-depth analysis of drug-induced (cardiomyopathic) effects for preclinical cardiotoxicity screening applications.

Quantitative approach for cardiac risk assessment and interpretation in tuberculosis drug development

Cardiotoxicity is among the top drug safety concerns, and is of specific interest in tuberculosis, where this is a known or potential adverse event of current and emerging treatment regimens. As there is a need for a tool, beyond the QT interval, to quantify cardiotoxicity early in drug development, an empirical decision tree based classifier was developed to predict the risk of Torsades de pointes (TdP). The cardiac risk algorithm was developed using pseudo-electrocardiogram (ECG) outputs derived from cardiac myocyte electromechanical model simulations of increasing concentrations of 96 reference compounds which represented a range of clinical TdP risk. The algorithm correctly classified 89% of reference compounds with moderate sensitivity and high specificity (71 and 96%, respectively) as well as 10 out of 12 external validation compounds and the anti-TB drugs moxifloxacin and bedaquiline. The cardiac risk algorithm is suitable to help inform early drug development decisions in TB and will evolve with the addition of emerging data.

Characteristics of electromechanical window in anesthetized rabbit models of short QT and long QT syndromes

The current regulatory guidelines recommend the use of QT interval to assess the risk of arrhythmogenic potential of new chemical entities. Recently, the electromechanical window (EMW), the difference in duration between electrical and mechanical systole, has been proposed as markers for drug-induced torsades de pointes (TdP); however, data of EMW in short QT model are not available. This study aimed to characterize the EMW as a marker for drug-induced ventricular arrhythmias in anesthetized rabbit model of long QT syndrome type 2 (LQT2) and short QT syndrome (SQTS) infused with reference compounds known to lengthen or shorten QT intervals. After rabbits were anesthetized with isoflurane, body surface electrocardiograms and left ventricular pressure were recorded. The LQT2 was produced by intravenous infusion with dofetilide (n = 6), quinidine (n = 6) and sotalol (n = 6) whereas the SQTS was induced by intravenous escalating concentrations of nicorandil (n = 7), pinacidil (n = 5) and cromakalim (n = 5). The EMW in anesthetized rabbits ranged from 1.3 to 53.3 msec. All three drugs known to lengthen QT intervals prolonged QT and QTcF interval while the EMW was markedly decreased to negative values. Pinacidil significantly produced QT and QTcF shortening and significantly abbreviated the EMW (p < 0.05). This study demonstrated that the EMW is associated with QT intervals (p < 0.001). It is negative in the presence of QT-prolonging drugs while it is more positive in the presence of QT-shortening drugs. The results suggest that the EMW in anesthetized rabbits can be used in drug safety evaluation in addition to the QT interval.

An increasing electromechanical window is a predictive marker of ventricular fibrillation in anesthetized rabbit with ischemic heart

The QTc interval is widely used in Safety Pharmacological studies to predict arrhythmia risk, and the electromechanical window (EMW) and short-term variability of QT intervals (STV_QT) have been studied as new biomarkers for drug-induced Torsades de Pointes (TdP). However, the use of EMW and STV_QT to predict ventricular fibrillation (VF) has not been elucidated. This study aimed to evaluate EMW and STV_QT to predict VF in anesthetized rabbit model of VF. VF was induced by ligation of the left anterior descending and a descending branch of the left circumflex coronary arteries in a sample population of rabbits (n=18). VF was developed 55.6% (10/18). In rabbit with VF, the EMW was significantly higher than in rabbits without VF (96.3 ± 15.6 ms and 49.5 ± 5.6 ms, respectively, P<0.05). STV_QT had significantly increased before the onset of VF in rabbits that experienced VF, but not in rabbits that did not experience VF (11.7 ± 1.8 ms and 3.7 ± 0.4 ms, respectively, P<0.05). The EMW and STV_QT had better predictive power for VF with higher sensitivity and specificity than the QTc measure. The result suggested that the increasing of EMW, as well as the elevation of STV_QT, can potentially be used as biomarkers for predicting of VF.

Effect of butylphthalide intervention on experimental autoimmune myositis in guinea pigs

Idiopathic inflammatory myopathies are a group of rare muscular diseases that are characterized by acute, subacute or chronic proximal and symmetric muscle weakness, muscle fiber necrosis and infiltration of inflammatory cells, particularly activated CD8⁺ cytotoxic T cells and phagocytes. 3-n-butylphthalide (NBP) protects mitochondria and reduces the inflammatory response in multiple disease models. In myositis, it has remained elusive whether NBP can protect muscle cells from muscle fiber injury. Experimental autoimmune myositis (EAM) was induced in a total of 40 guinea pigs by myosin immunization. After 4 weeks, low- or high-dose NBP solution was intraperitoneally injected. Saline solution was used as a negative control. After 10 days, the clinical manifestations were assessed by determining rodent grasping power, histopathological changes, Ca²⁺-adenosinetriphosphatase (ATPase) activity by an ATPase kit, and mRNA expression of interferon (IFN)-γ, retinoic acid receptor-related orphan nuclear receptor (ROR)γt and forkhead box (Fox) p3 in muscle tissue by reverse-transcription quantitative polymerase chain reaction analysis. It was demonstrated that NBP improved the myodynamia of guinea pigs with EAM and reduced the pathological inflammatory cell infiltration in a dose-dependent manner. NBP improved the Ca²⁺-ATPase activity of the muscle mitochondrial membrane and muscle plasma membrane in animals with EAM. It also reduced the mRNA expression of IFN-γ and RORγt, and significantly increased the mRNA expression of Foxp3 in muscle tissue. These results provided a basis for the consideration of NBP as a novel agent for the treatment of myositis and other muscular diseases associated with autoimmunity and inflammation.

Role of abnormal repolarization in the mechanism of cardiac arrhythmia

In cardiac patients, life-threatening tachyarrhythmia is often precipitated by abnormal changes in ventricular repolarization and refractoriness. Repolarization abnormalities typically evolve as a consequence of impaired function of outward K⁺ currents in cardiac myocytes, which may be caused by genetic defects or result from various acquired pathophysiological conditions, including electrical remodelling in cardiac disease, ion channel modulation by clinically used pharmacological agents, and systemic electrolyte disorders seen in heart failure, such as hypokalaemia. Cardiac electrical instability attributed to abnormal repolarization relies on the complex interplay between a provocative arrhythmic trigger and vulnerable arrhythmic substrate, with a central role played by the excessive prolongation of ventricular action potential duration, impaired intracellular Ca²⁺ handling, and slowed impulse conduction. This review outlines the electrical activity of ventricular myocytes in normal conditions and cardiac disease, describes classical electrophysiological mechanisms of cardiac arrhythmia, and provides an update on repolarization-related surrogates currently used to assess arrhythmic propensity, including spatial dispersion of repolarization, activation-repolarization coupling, electrical restitution, TRIaD (triangulation, reverse use dependence, instability, and dispersion), and the electromechanical window. This is followed by a discussion of the mechanisms that account for the dependence of arrhythmic vulnerability on the location of the ventricular pacing site. Finally, the review clarifies the electrophysiological basis for cardiac arrhythmia produced by hypokalaemia, and gives insight into the clinical importance and pathophysiology of drug-induced arrhythmia, with particular focus on class Ia (quinidine, procainamide) and Ic (flecainide) Na⁺ channel blockers, and class III antiarrhythmic agents that block the delayed rectifier K⁺ channel (dofetilide).

Computer-based prediction of the drug proarrhythmic effect: problems, issues, known and suspected challenges

It is likely that computer modelling and simulations will become an element of comprehensive cardiac safety testing. Their role would be primarily the integration and the interpretation of previously gathered data. There are still unanswered questions and issues which we list and describe below. They include sources of data used for the development of the models as well as data utilized as input information, which can come from the in vitro studies and the quantitative structure-activity relationship models. The pharmacokinetics of the drugs in question play a crucial role as their active concentration should be considered, yet the question remains where is the right place to assess it. The pharmacodynamic angle includes complications coming from multiple drugs (i.e. active metabolites) acting in parallel as well as the type of interaction with (potentially) multiple affected channels. Once established, the model and the methodology of its use should be further validated, optimistically against individual data reported at the clinical level as the physiological, anatomical, and genetic parameters play a crucial role in the drug-triggered arrhythmia induction. All the abovementioned issues should be at least considered and-hopefully-resolved, to properly utilize the mathematical models for a cardiac safety assessment.

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.

Impact of hypokalemia on electromechanical window, excitation wavelength and repolarization gradients in guinea-pig and rabbit hearts

Normal hearts exhibit a positive time difference between the end of ventricular contraction and the end of QT interval, which is referred to as the electromechanical (EM) window. Drug-induced prolongation of repolarization may lead to the negative EM window, which was proposed to be a novel proarrhythmic marker. This study examined whether abnormal changes in the EM window may account for arrhythmogenic effects produced by hypokalemia. Left ventricular pressure, electrocardiogram, and epicardial monophasic action potentials were recorded in perfused hearts from guinea-pig and rabbit. Hypokalemia (2.5 mM K(+)) was found to prolong repolarization, reduce the EM window, and promote tachyarrhythmia. Nevertheless, during both regular pacing and extrasystolic excitation, the increased QT interval invariably remained shorter than the duration of mechanical systole, thus yielding positive EM window values. Hypokalemia-induced arrhythmogenicity was associated with slowed ventricular conduction, and shortened effective refractory periods, which translated to a reduced excitation wavelength index. Hypokalemia also evoked non-uniform prolongation of action potential duration in distinct epicardial regions, which resulted in increased spatial variability in the repolarization time. These findings suggest that arrhythmogenic effects of hypokalemia are not accounted for by the negative EM window, and are rather attributed to abnormal changes in ventricular conduction times, refractoriness, excitation wavelength, and spatial repolarization gradients.

Cardiac safety concerns for domperidone, an antiemetic and prokinetic, and galactogogue medicine

INTRODUCTION

Domperidone is a dopamine D2-receptor antagonist developed as an antiemetic and prokinetic agent. Oral domperidone is not approved in the United States, but it is used in many countries to treat nausea and vomiting, gastroparesis and as a galactogogue (to promote lactation). The US Food and Drug Administration (FDA) have issued a warning about the cardiac safety of domperidone.

AREAS COVERED

The authors undertook a review of the cardiac safety of oral domperidone.

EXPERT OPINION

The data from preclinical studies are unambiguous in identifying domperidone as able to produce marked hERG channel inhibition and action potential prolongation at clinically relevant concentrations. The compound's propensity to augment instability of action potential duration and action potential triangulation are also indicative of proarrhythmic potential. Domperidone should not be administered to subjects with pre-existing QT prolongation/LQTS, subjects receiving drugs that inhibit CYP3A4, subjects with electrolyte abnormalities or with other risk factors for QT-prolongation. With these provisos, it is possible that domperidone may be used as a galactogogue without direct risk to healthy breast feeding women, but more safety information should be sought in this situation. Also, more safety information is required regarding risk to breast feeding infants before domperidone is routinely used in gastroparesis or gastroesphageal reflux in children.