Alterations of K+ currents in isolated human ventricular myocytes from patients with terminal heart failure

Propionic Acidemia-Induced Proarrhythmic Electrophysiological Alterations in Human iPSC-Derived Cardiomyocytes

Propionic acidemia (PA) is a metabolic disorder caused by a deficiency of the mitochondrial enzyme propionyl-CoA carboxylase (PCC) due to mutations in the PCCA or PCCB genes, which encode the two PCC subunits. PA may lead to several types of cardiomyopathy and has been linked to cardiac electrical abnormalities such as QT interval prolongation, life-threatening arrhythmias, and sudden cardiac death. To gain insights into the mechanisms underlying PA-induced proarrhythmia, we recorded action potentials (APs) and ion currents using whole-cell patch-clamp in ventricular-like induced pluripotent stem cells-derived cardiomyocytes (hiPSC-CMs) from a PA patient carrying two pathogenic mutations in the PCCA gene (p.Cys616_Val633del and p.Gly477Glufs*9) (PCCA cells) and from a healthy subject (healthy cells). In cells driven at 1 Hz, PCC deficiency increased the latency and prolonged the AP duration (APD) measured at 20% of repolarization, without modifying resting membrane potential or AP amplitude. Moreover, delayed afterdepolarizations appeared at the end of the repolarization phase in unstimulated and paced PCCA cells. PCC deficiency significantly reduced peak sodium current (INa) but increased the late INa (INaL) component. In addition, L-type Ca2+ current (ICaL) density was reduced, while the inward and outward density of the Na+/Ca2+ exchanger current (INCX) was increased in PCCA cells compared to healthy ones. In conclusion, our results demonstrate that at the cellular level, PCC deficiency can modify the ion currents controlling cardiac excitability, APD, and intracellular Ca2+ handling, increasing the risk of arrhythmias independently of the progressive late-onset cardiomyopathy induced by PA disease.

Stellate Ganglia: A Key Therapeutic Target for Malignant Ventricular Arrhythmia in Heart Disease

Malignant ventricular arrhythmias (VAs), such as ventricular tachycardia and ventricular fibrillation, are the cause of approximately half a million deaths per year in the United States, which is a common lethal event in heart disease, such as hypertension, catecholaminergic polymorphic ventricular tachycardia, takotsubo cardiomyopathy, long-QT syndrome, and progressing into advanced heart failure. A common characteristic of these heart diseases, and the subsequent development of VAs, is the overactivation of the sympathetic nervous system. Current treatments for VAs in these heart diseases, such as β-adrenergic receptor blockers and cardiac sympathetic ablation, aim at inhibiting cardiac sympathetic overactivation. However, these treatments do not translate into becoming efficacious as long-term suppressors of ventricular tachycardia/ventricular fibrillation events. As a key regulatory component in the heart, cardiac postganglionic sympathetic neurons residing in the stellate ganglia (SGs) release neurotransmitters (such as norepinephrine and NPY [neuropeptide Y]) to perform their regulatory role in dictating cardiac function. Growing evidence from animal experiments and clinical studies has demonstrated that the remodeling of the SG may be intimately involved in malignant arrhythmogenesis. This identifies the SG as a key potential therapeutic target for the treatment of malignant VAs in heart disease. Therefore, this review summarizes the role of SG in ventricular arrhythmogenesis and updates the novel targeting of SG for clinical treatment of VAs in heart disease.

Rational design, synthesis, and evaluation of novel polypharmacological compounds targeting NaV1.5, KV1.5, and K2P channels for atrial fibrillation

Atrial fibrillation (AF) involves electrical remodeling of the atria, with ion channels such as NaV1.5, KV1.5, and TASK-1 playing crucial roles. This study investigates acetamide-based compounds designed as multi-target inhibitors of these ion channels to address AF. Compound 6f emerged as the most potent in the series, demonstrating a strong inhibition of TASK-1 (IC50 ∼ 0.3 μM), a moderate inhibition of NaV1.5 (IC50 ∼ 21.2 μM) and a subtle inhibition of KV1.5 (IC50 ∼ 81.5 μM), alongside unexpected activation of TASK-4 (∼ 40% at 100 μM). Functional assays on human atrial cardiomyocytes from sinus rhythm (SR) and patients with AF revealed that 6f reduced action potential amplitude in SR (indicating NaV1.5 block), while in AF it increased action potential duration (APD), reflecting high affinity for TASK-1. Additionally, 6f caused hyperpolarization of the resting membrane potential in AF cardiomyocytes, consistent with the observed TASK-4 activation. Mathematical modeling further validated its efficacy in reducing AF burden. Pharmacokinetic analyses suggest favorable absorption and low toxicity. These findings identify 6f as a promising multi-target therapeutic candidate for AF management.

Ventricular arrhythmias in acute heart failure. A clinical consensus statement of the Association for Acute CardioVascular Care (ACVC), the European Heart Rhythm Association (EHRA) and the Heart Failure Association (HFA) of the ESC

Patients presenting with or alerting emergency networks due to acute heart failure (AHF) form a diverse group with a plethora of symptoms, risks, comorbidities, and aetiologies. During AHF, there is an increased risk of destabilizing the functional substrate and modulatory adding to the risk of ventricular arrhythmias (VAs) already created by the structural substrate. New VAs during AHF have previously identified patients with higher in-hospital and 60-day morbidity and mortality. Risk stratification and criteria/best time point for coronary intervention and implantable cardioverter-defibrillator implantation, however, are still controversial topics in this difficult clinical setting. The characteristics and logistics of pre-hospital emergency medicine, as well as the density of centres capable of treating AHF and VAs, differ massively throughout Europe. Scientific guidelines provide clear recommendations for the management of arrhythmias in chronic heart failure patients. However, the incidence, significance, and management of arrhythmias in patients with AHF have been less studied. This consensus paper aimed to address the identification and treatment of VAs that complicate the course of patients who have AHF, including cardiogenic shock.

Rate Versus Rhythm Control for Atrial Fibrillation with Heart Failure

Atrial fibrillation with Heart Failure is a constellation of co-morbid conditions that now constitutes a major cardiovascular epidemic, with HF now the most common complication of AF. Mechanistically, both conditions promote substrate disease in the atrium and ventricle. AF is an independent rixk factor in HF progression and pump failure death. While early studies comparing rhythm control antiarrhythmic drugs and rate control drugs showed no significant benefit in cardiovascular outcomes, AF did promote HF emergence and hospitalizations. Newer rhythm control strategies with present day antiarrhythmic drugs and catheter ablation support benefits in cardiovascular outcomes in AF with HF. Catheter ablation improved HF outcomes in HF with reduced ejection fraction but further and larger studies are needed, especially for AF with HF with preserved ejection fraction.

Multipoint Left Ventricular Pacing as Alternative Approach in Cases of Biventricular Pacing Failure

Cardiac resynchronization therapy (CRT) is a cornerstone in the treatment of dyssynchronous heart failure with reduced ejection fraction. However, the phenomenon of non-response has plagued CRT since its initial application. Notwithstanding issues such as failure to capture the left ventricle, lower-than-required pacing delivery percent, and failure to optimize atrioventricular and interventricular delays, there are patients who fail to exhibit an adequate response to CRT in its classical biventricular pacing (BiVP) form. Several modalities have been proposed as a means to remedy this issue, including pacing the conduction system itself-His or left bundle branch pacing, allowing for intrinsic conduction in some myocardial segments, pacing the left ventricle from multiple points in the coronary sinus (multipoint pacing), or even combining the above (e.g., His/left bundle pacing and BiVP leading to His/left bundle-optimized CRT). In the present review, we present recent evidence for the advantages and disadvantages of each modality and attempt to formulate a pathophysiology and simulation-based strategy to determine the best way forward for delivering CRT in non-responders to BiVP.

Mechanisms and Implications of Electrical Heterogeneity in Cardiac Function in Ischemic Heart Disease

A healthy heart shows intrinsic electrical heterogeneities that play a significant role in cardiac activation and repolarization. However, cardiac diseases may perturb the baseline electrical properties of the healthy cardiac tissue, leading to increased arrhythmic risk and compromised cardiac functions. Moreover, biological variability among patients produces a wide range of clinical symptoms, which complicates the treatment and diagnosis of cardiac diseases. Ischemic heart disease is usually caused by a partial or complete blockage of a coronary artery. The onset of the disease begins with myocardial ischemia, which can develop into myocardial infarction if it persists for an extended period. The progressive regional tissue remodeling leads to increased electrical heterogeneities, with adverse consequences on arrhythmic risk, cardiac mechanics, and mortality. This review aims to summarize the key role of electrical heterogeneities in the heart on cardiac function and diseases. Ischemic heart disease has been chosen as an example to show how adverse electrical remodeling at different stages may lead to variable manifestations in patients. For this, we have reviewed the dynamic electrophysiological and structural remodeling from the onset of acute myocardial ischemia and reperfusion to acute and chronic stages post-myocardial infarction. The arrhythmic mechanisms, patient phenotypes, risk stratification at different stages, and patient management strategies are also discussed. Finally, we provide a brief review on how computational approaches incorporate human electrophysiological heterogeneity to facilitate basic and translational research.

Development of new Kir2.1 channel openers from propafenone analogues

BACKGROUND AND PURPOSES

Reduced inward rectifier potassium channel (Kir2.1) functioning is associated with heart failure and may cause Andersen-Tawil Syndrome, among others characterized by ventricular arrhythmias. Most heart failure or Andersen-Tawil Syndrome patients are treated with β-adrenoceptor antagonists (β-blockers) or sodium channel blockers; however, these do not specifically address the inward rectifier current (IK1) nor aim to improve resting membrane potential stability. Consequently, additional pharmacotherapy for heart failure and Andersen-Tawil Syndrome treatment would be highly desirable. Acute propafenone treatment at low concentrations enhances IK1 current, but it also exerts many off-target effects. Therefore, discovering and exploring new IK1-channel openers is necessary.

EXPERIMENTAL APPROACH

Effects of propafenone and 10 additional propafenone analogues were analysed. Currents were measured by single-cell patch-clamp electrophysiology. Kir2.1 protein expression levels were determined by western blot analysis and action potential characteristics were further validated in human-induced pluripotent stem cells-derived cardiomyocytes (hiPSC-CMCs). Molecular docking was performed to obtain detailed information on drug-channel interactions.

KEY RESULTS

Analogues GPV0019, GPV0057 and GPV0576 strongly increased the outward component of IK1 while not affecting the Kir2.1 channel expression levels. GPV0057 did not block IKr at concentrations below 0.5 μmol L-1 nor NaV1.5 current below 1 μmol L-1. Moreover, hiPSC-CMC action potential duration was also not affected by GPV0057 at 0.5 and 1 μmol L-1. Structure analysis indicates a mechanism by which GPV0057 might enhance Kir2.1 channel activation.

CONCLUSION AND IMPLICATIONS

GPV0057 has a strong efficiency towards increasing IK1, which makes it a good candidate to address IK1 deficiency-associated diseases.

Clinical phenotypes in acute and chronic infarction explained through human ventricular electromechanical modelling and simulations

Sudden death after myocardial infarction (MI) is associated with electrophysiological heterogeneities and ionic current remodelling. Low ejection fraction (EF) is used in risk stratification, but its mechanistic links with pro-arrhythmic heterogeneities are unknown. We aim to provide mechanistic explanations of clinical phenotypes in acute and chronic MI, from ionic current remodelling to ECG and EF, using human electromechanical modelling and simulation to augment experimental and clinical investigations. A human ventricular electromechanical modelling and simulation framework is constructed and validated with rich experimental and clinical datasets, incorporating varying degrees of ionic current remodelling as reported in literature. In acute MI, T-wave inversion and Brugada phenocopy were explained by conduction abnormality and local action potential prolongation in the border zone. In chronic MI, upright tall T-waves highlight large repolarisation dispersion between the border and remote zones, which promoted ectopic propagation at fast pacing. Post-MI EF at resting heart rate was not sensitive to the extent of repolarisation heterogeneity and the risk of repolarisation abnormalities at fast pacing. T-wave and QT abnormalities are better indicators of repolarisation heterogeneities than EF in post-MI.

The Cardiomyocyte in Cirrhosis: Pathogenic Mechanisms Underlying Cirrhotic Cardiomyopathy

Cirrhotic cardiomyopathy is defined as systolic and diastolic dysfunction in patients with cirrhosis, in the absence of any primary heart disease. These changes are mainly due to the malfunction or abnormalities of cardiomyocytes. Similar to non-cirrhotic heart failure, cardiomyocytes in cirrhotic cardiomyopathy demonstrate a variety of abnormalities: from the cell membrane to the cytosol and nucleus. At the cell membrane level, biophysical plasma membrane fluidity, and membrane-bound receptors such as the beta-adrenergic, muscarinic and cannabinoid receptors are abnormal either functionally or structurally. Other changes include ion channels such as L-type calcium channels, potassium channels, and sodium transporters. In the cytosol, calcium release and uptake processes are dysfunctional and the myofilaments such as myosin heavy chain and titin, are either functionally abnormal or have structural alterations. Like the fibrotic liver, the heart in cirrhosis also shows fibrotic changes such as a collagen isoform switch from more compliant collagen III to stiffer collagen I which also impacts diastolic function. Other abnormalities include the secondary messenger cyclic adenosine monophosphate, cyclic guanosine monophosphate, and their downstream effectors such as protein kinase A and G-proteins. Finally, other changes such as excessive apoptosis of cardiomyocytes also play a critical role in the pathogenesis of cirrhotic cardiomyopathy. The present review aims to summarize these changes and review their critical role in the pathogenesis of cirrhotic cardiomyopathy.

Using a Failing Human Ventricular Cardiomyocyte Model to Re-Evaluate Ca2+ Cycling, Voltage Dependence, and Spark Characteristics

Previous studies have observed alterations in excitation-contraction (EC) coupling during end-stage heart failure that include action potential and calcium (Ca2+) transient prolongation and a reduction of the Ca2+ transient amplitude. Underlying these phenomena are the downregulation of potassium (K+) currents, downregulation of the sarcoplasmic reticulum Ca2+ ATPase (SERCA), increase Ca2+ sensitivity of the ryanodine receptor, and the upregulation of the sodium-calcium (Na=-Ca2+) exchanger. However, in human heart failure (HF), debate continues about the relative contributions of the changes in calcium handling vs. the changes in the membrane currents. To understand the consequences of the above changes, they are incorporated into a computational human ventricular myocyte HF model that can explore the contributions of the spontaneous Ca2+ release from the sarcoplasmic reticulum (SR). The reduction of transient outward K+ current (Ito) is the main membrane current contributor to the decrease in RyR2 open probability and L-type calcium channel (LCC) density which emphasizes its importance to phase 1 of the action potential (AP) shape and duration (APD). During current-clamp conditions, RyR2 hyperphosphorylation exhibits the least amount of Ca2+ release from the SR into the cytosol and SR Ca2+ fractional release during a dynamic slow-rapid-slow (0.5-2.5-0.5 Hz) pacing, but it displays the most abundant and more lasting Ca2+ sparks two-fold longer than a normal cell. On the other hand, under voltage-clamp conditions, HF by decreased SERCA and upregulated INCX show the least SR Ca2+ uptake and EC coupling gain, as compared to HF by hyperphosphorylated RyR2s. Overall, this study demonstrates that the (a) combined effect of SERCA and NCX, and the (b) RyR2 dysfunction, along with the downregulation of the cardiomyocyte's potassium currents, could substantially contribute to Ca2+ mishandling at the spark level that leads to heart failure.

Cardiomyocyte Reduction of Hybrid/Complex N-Glycosylation in the Adult Causes Heart Failure With Reduced Ejection Fraction in the Absence of Cellular Remodeling

BACKGROUND

Heart failure (HF) presents a massive burden to health care with a complex pathophysiology that results in HF with reduced left ventricle ejection fraction (EF) or HF with preserved EF. It has been shown that relatively modest changes in protein glycosylation, an essential posttranslational modification, are associated with clinical presentations of HF. We and others previously showed that such aberrant protein glycosylation in animal models can lead to HF.

METHODS AND RESULTS

We develop and characterize a novel, tamoxifen-inducible, cardiomyocyte Mgat1 knockout mouse strain, achieved through deletion of Mgat1, alpha-1,3-mannosyl-glycoproten 2-beta-N-acetlyglucosaminyltransferase, which encodes N-acetylglucosaminyltransferase I. We investigate the role of hybrid/complex N-glycosylation in adult HFrEF pathogenesis at the ion channel, cardiomyocyte, tissue, and gross cardiac level. The data demonstrate successful reduction of N-acetylglucosaminyltransferase I activity and confirm that hybrid/complex N-glycans modulate gating of cardiomyocyte voltage-gated calcium channels. A longitudinal study shows that the tamoxifen-inducible, cardiomyocyte Mgat1 knockout mice present with significantly reduced systolic function by 28 days post induction that progresses into HFrEF by 8 weeks post induction, without significant ventricular dilation or hypertrophy. Further, there was minimal, if any, physiologic or pathophysiologic cardiomyocyte electromechanical remodeling or fibrosis observed before (10-21 days post induction) or after (90-130 days post induction) HFrEF development.

CONCLUSIONS

The tamoxifen-inducible, cardiomyocyte Mgat1 knockout mouse strain created and characterized here provides a model to describe novel mechanisms and causes responsible for HFrEF onset in the adult, likely occurring primarily through tissue-level reductions in electromechanical activity in the absence of (or at least before) cardiomyocyte remodeling and fibrosis.

Ventricular arrhythmias in acute heart failure: a clinical consensus statement of the Association for Acute CardioVascular Care, the European Heart Rhythm Association, and the Heart Failure Association of the European Society of Cardiology

Patients presenting with or alerting emergency networks due to acute heart failure (AHF) form a diverse group with a plethora of symptoms, risks, comorbidities, and aetiologies. During AHF, there is an increased risk of destabilizing the functional substrate and modulatory adding to the risk of ventricular arrhythmias (VAs) already created by the structural substrate. New VAs during AHF have previously identified patients with higher intra-hospital and 60-day morbidity and mortality. Risk stratification and criteria/best time point for coronary intervention and implantable cardioverter defibrillator implantation, however, are still controversial topics in this difficult clinical setting. The characteristics and logistics of pre-hospital emergency medicine, as well as the density of centres capable of treating AHF and VAs, differ massively throughout Europe. Scientific guidelines provide clear recommendations for the management of arrhythmias in patients with chronic heart failure. However, the incidence, significance, and management of arrhythmias in patients with AHF have been less studied. This consensus paper aimed to address the identification and treatment of VAs that complicate the course of patients who have AHF, including cardiogenic shock.

A Comparative Study of the Rapid (IKr) and Slow (IKs) Delayed Rectifier Potassium Currents in Undiseased Human, Dog, Rabbit, and Guinea Pig Cardiac Ventricular Preparations

To understand the large inter-species variations in drug effects on repolarization, the properties of the rapid (IKr) and the slow (IKs) components of the delayed rectifier potassium currents were compared in myocytes isolated from undiseased human donor (HM), dog (DM), rabbit (RM) and guinea pig (GM) ventricles by applying the patch clamp and conventional microelectrode techniques at 37 °C. The amplitude of the E-4031-sensitive IKr tail current measured at -40 mV after a 1 s long test pulse of 20 mV, which was very similar in HM and DM but significant larger in RM and GM. The L-735,821-sensitive IKs tail current was considerably larger in GM than in RM. In HM, the IKs tail was even smaller than in DM. At 30 mV, the IKr component was activated extremely rapidly and monoexponentially in each studied species. The deactivation of the IKr component in HM, DM, and RM measured at -40 mV. After a 30 mV pulse, it was slow and biexponential, while in GM, the IKr tail current was best fitted triexponentially. At 30 mV, the IKs component activated slowly and had an apparent monoxponential time course in HM, DM, and RM. In contrast, in GM, the activation was clearly biexponential. In HM, DM, and RM, IKs component deactivation measured at -40 mV was fast and monoexponential, while in GM, in addition to the fast component, another slower component was also revealed. These results suggest that the IK in HM resembles that measured in DM and RM and considerably differs from that observed in GM. These findings suggest that the dog and rabbit are more appropriate species than the guinea pig for preclinical evaluation of new potential drugs expected to affect cardiac repolarization.

Lower diastolic tension may be indicative of higher proarrhythmic propensity in failing human cardiomyocytes

Chronic heart failure is one of the most common reasons for hospitalization. Current risk stratification is based on ejection fraction, whereas many arrhythmic events occur in patients with relatively preserved ejection fraction. We aim to investigate the mechanistic link between proarrhythmic abnormalities, reduced contractility and diastolic dysfunction in heart failure, using electromechanical modelling and simulations of human failing cardiomyocytes. We constructed, calibrated and validated populations of human electromechanical models of failing cardiomyocytes, that were able to reproduce the prolonged action potential, reduced contractility and diastolic dysfunction as observed in human data, as well as increased propensity to proarrhythmic incidents such as early afterdepolarization and beat-to-beat alternans. Our simulation data reveal that proarrhythmic incidents tend to occur in failing myocytes with lower diastolic tension, rather than with lower contractility, due to the relative preserved SERCA and sodium calcium exchanger current. These results support the inclusion of end-diastolic volume to be potentially beneficial in the risk stratifications of heart failure patients.

Interaction between cardiac resynchronization therapy and cytokines in heart failure patients

Congestive heart failure (CHF) is a complex multistage syndrome that has a great financial burden on human societies. It was known that the damaged myocardium sends a signal to stimulate the immune system and proliferation of leukocytes. In continuous, cytokine storm can be initiated and causes the probability of CHF. Persistent inflammation by increasing the levels of pro-inflammatory cytokines, plays an important role in the pathogenesis of CHF and causes remodeling, which is a progressive processs. Although treatment by drugs can reduce mortality and partially control the symptoms of heart failure patients, but complications and mortality are still high. Therefore, other treatment options such as Cardiac Resynchronization Therapy (CRT) are necessary. Today, it is known that CRT can be an effective treatment for many patients with heart failure. CRT is novel, non-pharmacological, and device-based therapy that would be beneficial to know more about its performance in the management of heart failure. In this study, we have reviewed the immunological processes involved in heart failure and the effect of CRT in controlling of the cytokine storm.

Naphazoline intoxication with transient QT prolongation and acute myocardial injury

A 27-year-old Japanese woman with a history of depression and an eating disorder presented to our emergency department with a chief complaint of generalized weakness. Electrocardiography showed prominent QT prolongation with multiple ventricular contractions. Chest X-ray plain computed tomography revealed pulmonary edema. Echocardiography showed decreased left ventricular systolic function. Suspecting acute myocarditis, we performed a myocardial biopsy from the right ventricular septum. The biopsy histology revealed extensive myocardial fibrosis and a very mild inflammatory cell infiltrate. In an additional detailed medical interview, the patient admitted that she had consumed three bottles of a first-aid liquid containing naphazoline approximately ~12 h before her presentation, in a suicide attempt. Her QTc and left ventricular ejection fraction improved during hospitalization.

Learning objective

Acute drug intoxication can cause QT prolongation and ventricular arrhythmias, cardiomyopathy, and pulmonary edema. When acute QT prolongation, myocardial damage, and pulmonary edema are seen (suggesting acute myocarditis), naphazoline intoxication should be investigated in the differential diagnosis.

Differential Effects of the Betablockers Carvedilol, Metoprolol and Bisoprolol on Cardiac Kv4.3 (Ito) Channel Isoforms

Cardiac Kv4.3 channels contribute to the transient outward K+ current, Ito, during early repolarization of the cardiac action potential. Two different isoforms of Kv4.3 are present in the human ventricle and exhibit differential remodeling in heart failure (HF). Cardioselective betablockers are a cornerstone of HF with reduced ejection fraction therapy as well as ventricular arrhythmia treatment. In this study we examined pharmacological effects of betablockers on both Kv4.3 isoforms to explore their potential for isoform-specific therapy. Kv4.3 isoforms were expressed in Xenopus laevis oocytes and incubated with the respective betablockers. Dose-dependency and biophysical characteristics were examined. HEK 293T-cells were transfected with the two Kv4.3 isoforms and analyzed with Western blots. Carvedilol (100 µM) blocked Kv4.3 L by 77 ± 2% and Kv4.3 S by 67 ± 6%, respectively. Metoprolol (100 µM) was less effective with inhibition of 37 ± 3% (Kv4.3 L) and 35 ± 4% (Kv4.3 S). Bisoprolol showed no inhibitory effect. Current reduction was not caused by changes in Kv4.3 protein expression. Carvedilol inhibited Kv4.3 channels at physiologically relevant concentrations, affecting both isoforms. Metoprolol showed a weaker blocking effect and bisoprolol did not exert an effect on Kv4.3. Blockade of repolarizing Kv4.3 channels by carvedilol and metoprolol extend their pharmacological mechanism of action, potentially contributing beneficial antiarrhythmic effects in normal and failing hearts.

A multiscale predictive digital twin for neurocardiac modulation

Cardiac function is tightly regulated by the autonomic nervous system (ANS). Activation of the sympathetic nervous system increases cardiac output by increasing heart rate and stroke volume, while parasympathetic nerve stimulation instantly slows heart rate. Importantly, imbalance in autonomic control of the heart has been implicated in the development of arrhythmias and heart failure. Understanding of the mechanisms and effects of autonomic stimulation is a major challenge because synapses in different regions of the heart result in multiple changes to heart function. For example, nerve synapses on the sinoatrial node (SAN) impact pacemaking, while synapses on contractile cells alter contraction and arrhythmia vulnerability. Here, we present a multiscale neurocardiac modelling and simulator tool that predicts the effect of efferent stimulation of the sympathetic and parasympathetic branches of the ANS on the cardiac SAN and ventricular myocardium. The model includes a layered representation of the ANS and reproduces firing properties measured experimentally. Model parameters are derived from experiments and atomistic simulations. The model is a first prototype of a digital twin that is applied to make predictions across all system scales, from subcellular signalling to pacemaker frequency to tissue level responses. We predict conditions under which autonomic imbalance induces proarrhythmia and can be modified to prevent or inhibit arrhythmia. In summary, the multiscale model constitutes a predictive digital twin framework to test and guide high-throughput prediction of novel neuromodulatory therapy. KEY POINTS: A multi-layered model representation of the autonomic nervous system that includes sympathetic and parasympathetic branches, each with sparse random intralayer connectivity, synaptic dynamics and conductance based integrate-and-fire neurons generates firing patterns in close agreement with experiment. A key feature of the neurocardiac computational model is the connection between the autonomic nervous system and both pacemaker and contractile cells, where modification to pacemaker frequency drives initiation of electrical signals in the contractile cells. We utilized atomic-scale molecular dynamics simulations to predict the association and dissociation rates of noradrenaline with the β-adrenergic receptor. Multiscale predictions demonstrate how autonomic imbalance may increase proclivity to arrhythmias or be used to terminate arrhythmias. The model serves as a first step towards a digital twin for predicting neuromodulation to prevent or reduce disease.

Changes in cellular Ca2+ and Na+ regulation during the progression towards heart failure

In adapting to disease and loss of tissue, the heart shows great phenotypic plasticity that involves changes to its structure, composition and electrophysiology. Together with parallel whole body cardiovascular adaptations, the initial decline in cardiac function resulting from the insult is compensated. However, in the long term, the heart muscle begins to fail and patients with this condition have a very poor prognosis, with many dying from disturbances of rhythm. The surviving myocytes of these hearts gain Na+ , which is positively inotropic because of alterations to Ca2+ fluxes mediated by the Na+ /Ca2+ exchange, but compromises Ca2+ -dependent energy metabolism in mitochondria. Uptake of Ca2+ into the sarcoplasmic reticulum (SR) is reduced because of diminished function of SR Ca2+ ATPases. The result of increased Ca2+ influx and reduced SR Ca2+ uptake is an increase in the diastolic cytosolic Ca2+ concentration, which promotes spontaneous SR Ca2+ release and induces delayed afterdepolarisations. Action potential duration prolongs because of increased late Na+ current and changes in expression and function of other ion channels and transporters increasing the probability of the formation of early afterdepolarisations. There is a reduction in T-tubule density and so the normal spatial arrangements required for efficient excitation-contraction coupling are compromised and lead to temporal delays in Ca2+ release from the SR. Therefore, the structural and electrophysiological responses that occur to provide compensation do so at the expense of (1) increasing the likelihood of arrhythmogenesis; (2) activating hypertrophic, apoptotic and Ca2+ signalling pathways; and (3) decreasing the efficiency of SR Ca2+ release.

Mechanisms for the α-Adrenoceptor-Mediated Positive Inotropy in Mouse Ventricular Myocardium: Enhancing Effect of Action Potential Prolongation

Mechanisms for the α-adrenoceptor-mediated positive inotropy in neonatal mouse ventricular myocardium were studied with isolated myocardial preparations. The phenylephrine-induced positive inotropy was suppressed by prazosin, nifedipine, and chelerythrine, a protein kinase C inhibitor, but not by SEA0400, a selective Na⁺/Ca²⁺ exchanger inhibitor. Phenylephrine increased the L-type Ca²⁺ channel current and prolonged the action potential duration, while the voltage-dependent K⁺ channel current was not influenced. In the presence of cromakalim, an ATP-sensitive K⁺ channel opener, the phenylephrine-induced prolongation of action potential duration, as well as the positive inotropy, were smaller than in the absence of cromakalim. These results suggest that the α-adrenoceptor-mediated positive inotropy is mediated by an increase in Ca²⁺ influx through the L-type Ca²⁺ channel, and the concomitant increase in action potential duration acts as an enhancing factor.

Electrical Remodelling in Cardiac Disease

The human heart responds to various diseases with structural, mechanical, and electrical remodelling processes [...].

InsP3R-RyR Ca2+ channel crosstalk facilitates arrhythmias in the failing human ventricle

Dysregulated intracellular Ca²⁺ handling involving altered Ca²⁺ release from intracellular stores via RyR channels underlies both arrhythmias and reduced function in heart failure (HF). Mechanisms linking RyR dysregulation and disease are not fully established. Studies in animals support a role for InsP₃ receptor Ca²⁺ channels (InsP₃R) in pathological alterations in cardiomyocyte Ca²⁺ handling but whether these findings translate to the divergent physiology of human cardiomyocytes during heart failure is not determined. Using electrophysiological and Ca²⁺ recordings in human ventricular cardiomyocytes, we uncovered that Ca²⁺ release via InsP₃Rs facilitated Ca²⁺ release from RyR and induced arrhythmogenic delayed after depolarisations and action potentials. InsP₃R-RyR crosstalk was particularly increased in HF at RyR clusters isolated from the T-tubular network. Reduced SERCA activity in HF further facilitated the action of InsP₃. Nanoscale imaging revealed co-localisation of InsP₃Rs with RyRs in the dyad, which was increased in HF, providing a mechanism for augmented Ca²⁺ channel crosstalk. Notably, arrhythmogenic activity dependent on InsP₃Rs was increased in tissue wedges from failing hearts perfused with AngII to promote InsP₃ generation. These data indicate a central role for InsP₃R-RyR Ca²⁺ signalling crosstalk in the pro-arrhythmic action of GPCR agonists elevated in HF and the potential for their therapeutic targeting.

Arrhythmic Sudden Cardiac Death in Heart Failure With Preserved Ejection Fraction: Mechanisms, Genetics, and Future Directions

Heart failure with preserved ejection fraction (HFpEF) is an increasingly recognized disorder. Many clinical trials have failed to demonstrate benefit in patients with HFpEF but have recognized alarming rates of sudden cardiac death (SCD). Genetic testing has become standard in the workup of patients with otherwise unexplained cardiac arrest, but the genetic architecture of HFpEF, and the overlap of a genetic predisposition to HFpEF and arrhythmias, is poorly understood. An understanding of the genetics of HFpEF and related SCD has the potential to redefine and generate novel diagnostic, prognostic, and therapeutic tools. In this review, we examine recent pathophysiological and clinical advancements in our understanding of HFpEF, which reinforce the heterogeneity of the condition. We also discuss data describing SCD events in patients with HFpEF and review the current literature on genetic underpinnings of HFpEF. Mechanisms of arrhythmogenesis which may lead to SCD in this population are also explored. Lastly, we outline several areas of promise for experimentation and clinical trials that have the potential to further advance our understanding of and contribute to improved clinical care of this patient population.

Protein Kinase D1 Regulates Cardiac Hypertrophy, Potassium Channel Remodeling, and Arrhythmias in Heart Failure

Background Structural and electrophysiological remodeling characterize heart failure (HF) enhancing arrhythmias. PKD1 (protein kinase D1) is upregulated in HF and mediates pathological hypertrophic signaling, but its role in K+ channel remodeling and arrhythmogenesis in HF is unknown. Methods and Results We performed echocardiography, electrophysiology, and expression analysis in wild-type and PKD1 cardiomyocyte-specific knockout (cKO) mice following transverse aortic constriction (TAC). PKD1-cKO mice exhibited significantly less cardiac hypertrophy post-TAC and were protected from early decline in cardiac contractile function (3 weeks post-TAC) but not the progression to HF at 7 weeks post-TAC. Wild-type mice exhibited ventricular action potential duration prolongation at 8 weeks post-TAC, which was attenuated in PKD1-cKO, consistent with larger K+ currents via the transient outward current, sustained current, inward rectifier K+ current, and rapid delayed rectifier K+ current and increased expression of corresponding K+ channels. Conversely, reduction of slowly inactivating K+ current was independent of PKD1 in HF. Acute PKD inhibition slightly increased transient outward current in TAC and sham wild-type myocytes but did not alter other K+ currents. Sham PKD1-cKO versus wild-type also exhibited larger transient outward current and faster early action potential repolarization. Tachypacing-induced action potential duration alternans in TAC animals was increased and independent of PKD1, but diastolic arrhythmogenic activities were reduced in PKD1-cKO. Conclusions Our data indicate an important role for PKD1 in the HF-related hypertrophic response and K+ channel downregulation. Therefore, PKD1 inhibition may represent a therapeutic strategy to reduce hypertrophy and arrhythmias; however, PKD1 inhibition may not prevent disease progression and reduced contractility in HF.

Biological noise is a key determinant of the reproducibility and adaptability of cardiac pacemaking and EC coupling

Each heartbeat begins with the generation of an action potential in pacemaking cells in the sinoatrial node. This signal triggers contraction of cardiac muscle through a process termed excitation-contraction (EC) coupling. EC coupling is initiated in dyadic structures of cardiac myocytes, where ryanodine receptors in the junctional sarcoplasmic reticulum come into close apposition with clusters of CaV1.2 channels in invaginations of the sarcolemma. Cooperative activation of CaV1.2 channels within these clusters causes a local increase in intracellular Ca2+ that activates the juxtaposed ryanodine receptors. A salient feature of healthy cardiac function is the reliable and precise beat-to-beat pacemaking and amplitude of Ca2+ transients during EC coupling. In this review, we discuss recent discoveries suggesting that the exquisite reproducibility of this system emerges, paradoxically, from high variability at subcellular, cellular, and network levels. This variability is attributable to stochastic fluctuations in ion channel trafficking, clustering, and gating, as well as dyadic structure, which increase intracellular Ca2+ variance during EC coupling. Although the effects of these large, local fluctuations in function and organization are sometimes negligible at the macroscopic level owing to spatial-temporal summation within and across cells in the tissue, recent work suggests that the "noisiness" of these intracellular Ca2+ events may either enhance or counterintuitively reduce variability in a context-dependent manner. Indeed, these noisy events may represent distinct regulatory features in the tuning of cardiac contractility. Collectively, these observations support the importance of incorporating experimentally determined values of Ca2+ variance in all EC coupling models. The high reproducibility of cardiac contraction is a paradoxical outcome of high Ca2+ signaling variability at subcellular, cellular, and network levels caused by stochastic fluctuations in multiple processes in time and space. This underlying stochasticity, which counterintuitively manifests as reliable, consistent Ca2+ transients during EC coupling, also allows for rapid changes in cardiac rhythmicity and contractility in health and disease.

Effects of the Dectin-2/TNF-α Pathway on Ventricular Arrhythmia after Acute Myocardial Infarction in Mice

Background

Inflammatory responses are involved in ischemic injuries and cardiac repair after acute myocardial infarction (AMI). Dectin-2 is a C-type lectin receptor that induces cytokine production and promotes local inflammatory responses.

Methods

Sixty C57BL/6 mice were randomly assigned to a sham-surgery group, AMI group, or AMI + etanercept group, with 20 mice in each group. Programmed electrical stimulation (PES) was used to anesthetized mice to induce ventricular tachycardia. Real-time polymerase chain reaction (PCR) and western blot analysis were adopted to determine the expression and distribution of dectin-2 in heart tissues. The tumor necrosis factor-α (TNF-α), interferon-gamma (IFN)-γ, interleukin (IL) 4, and IL-5 levels in the serum were determined using ELISAs.

Results

The expression of dectin-2 and TNF-α was increased in the myocardium in AMI, and the susceptibility to ventricular arrhythmia (VA) was increased. The induction rate of VA was significantly decreased by etanercept. Compared with those in the sham-surgery group, the AMI group showed significantly higher serum TNF-α and IFN-γ levels and lower IL-4 and IL-5levels.

Conclusion

Dectin-2 intensifies the activation of the TNF-α immune reaction through the Th1 differentiation, which may increase vulnerability to VA in AMI.

Candesartan Cilexetil Attenuates Arrhythmogenicity Following Pressure Overload in Rats via the Modulation of Cardiac Electrical and Structural Remodeling and Calcium Handling Dysfunction

Background

Cardiac hypertrophy is associated with abnormal electrophysiology and increased arrhythmia risk. This study assessed whether candesartan cilexetil, an angiotensin II type 1 receptor blocker, could suppress arrhythmogenecity by attenuating cardiac electrical remodeling and calcium mishandling in rats with pressure‐overload hypertrophy.

Methods and Results

Male Sprague‐Dawley rats were randomly subjected to abdominal aorta banding or sham procedure and received either candesartan cilexetil (3.0 mg/kg per day) or vehicle by gavage for 5 weeks. Pressure overload was characterized by compensated left ventricular (LV) hypertrophy and fibrosis, increased LV pressure and its decay time, and prolonged corrected QT interval, all of which were attenuated by candesartan cilexetil treatment. Candesartan cilexetil–treated banded rat hearts displayed shorter QT intervals and lower vulnerability to atrial and ventricular tachyarrhythmias than vehicle‐treated banded hearts. Candesartan cilexetil prevented banding‐induced prolonged action potential duration and reduced the occurrence of triggered activity in LV papillary muscles. In addition, the prolonged time to 50% cell relengthening and calcium transient decay time were normalized in LV myocytes from candesartan cilexetil–treated banded rats, along with a normalization of decreased SERCA2a (sarco[endo]plasmic reticulum calcium‐ATPase) expression in LV tissues. Furthermore, candesartan cilexetil normalized depressed transient outward potassium current densities and protein and mRNA levels of both voltage‐gated potassium 4.2 and 4.3 channel subunits (Kv4.2 and Kv4.3) in banded rats.

Conclusions

Candesartan cilexetil protects the heart from pressure overload‐induced adverse electrical remodeling by preserving potassium channel densities. In addition, calcium handling and its molecular regulation also improved after treatment. These beneficial effects may contribute to a lower susceptibility to arrhythmias in hearts from candesartan cilexetil–treated pressure‐overloaded rats.

Indoxyl sulfate reduces Ito,f by activating ROS/MAPK and NF-κB signaling pathways

There is a high prevalence of ventricular arrhythmias related to sudden cardiac death in patients with chronic kidney disease (CKD). To explored the possible mechanism of CKD-related ventricular arrhythmias, a CKD rat model was created, and indoxyl sulfate (IS) was further used in vivo and in vitro. This project used the following methods: patch clamp, electrocardiogram, and some molecular biology experimental techniques. IS was found to be significantly elevated in the serum of CKD rats. Interestingly, the expression levels of the fast transient outward potassium current-related (Ito,f-related) proteins (Kv4.2, Kv4.3, and KChIP2) in the heart of CKD rats and rats treated with IS decreased. IS dose-dependently reduced Ito,f density, accompanied by the decreases in Kv4.2, Kv4.3, and KChIP2 proteins in vitro. IS also prolonged the action potential duration and QT interval, and paroxysmal ventricular tachycardia could be induced by IS. In-depth studies have shown that ROS/p38MAPK, ROS-p44/42 MAPK, and NF-κB signaling pathways play key roles in the reduction of Ito,f density and Ito,f-related proteins caused by IS. These data suggest that IS reduces Ito,f-related proteins and Ito,f density by activating ROS/MAPK and NF-κB signaling pathways, and the action potential duration and QT interval are subsequently prolonged, which contributes to increasing the susceptibility to arrhythmia in CKD.

Ventricular Arrhythmias in Seniors with Heart Failure: Present Dilemmas and Therapeutic Considerations: A Systematic Review

BACKGROUND

Heart Failure (HF) is a global public health problem, which affects over 23 million people worldwide. The prevalence of HF is higher among seniors in the USA and other developed countries. Ventricular Arrhythmias (VAs) account for 50% of deaths among patients with HF. We aim to elucidate the factors associated with VAs among seniors with HF, as well as therapies that may improve the outcomes.

METHODS

PubMed, Web of Science, Scopus, Cochrane Library databases, Science Direct, and Google Scholar were searched using specific keywords. The reference lists of relevant articles were searched for additional studies related to HF and VAs among seniors as well as associated outcomes.

RESULTS

The prevalence of VAs increases with worsening HF. A 24-hour Holter electrocardiogram may be useful in risk stratifying patients for device therapy if they do not meet the criterion of low ventricular ejection fraction. Implantable Cardiac Defibrillators (ICDs) are superior to anti-arrhythmic drugs in reducing mortality in patients with HF. Guideline-Directed Medical Therapy (GDMT) together with device therapy may be required to reduce symptoms. In general, the proportion of seniors on GDMT is low. A combination of ICDs and cardiac resynchronization therapy may improve outcomes in selected patients.

CONCLUSION

Seniors with HF and VAs have high mortality even with the use of device therapy and GDMT. The holistic effect of device therapy on outcomes among seniors with HF is equivocal. More studies focused on seniors with advanced HF as well as therapeutic options are, therefore, required.

A Carvedilol Analogue, VK-II-86, Prevents Hypokalaemia-induced Ventricular Arrhythmia through Novel multi-Channel Effects

BACKGROUND AND PURPOSE

QT prolongation and intracellular Ca²⁺ loading with diastolic Ca²⁺ release via ryanodine receptors (RyR2) are the predominant mechanisms underlying hypokalaemia-induced ventricular arrhythmia. We investigated the antiarrhythmic actions of two RyR2 inhibitors: dantrolene and VK-II-86, a carvedilol analogue with no β-blocking activity, in hypokalaemia.

EXPERIMENTAL APPROACH

Surface ECG and ventricular action potentials (APs) were recorded from whole-heart murine Langendorff preparations. Ventricular arrhythmia incidence was compared in hearts perfused with low [K⁺ ], and those pre-treated with dantrolene or VK-II-86. Whole-cell patch clamping was used in murine and canine ventricular cardiomyocytes to study the effects of dantrolene and VK-II-86 on AP parameters in low [K⁺ ] and the effects of VK-II-86 on the inward rectifier current (I_K1 ), late sodium current (I_{Na_L} ) and the L-type Ca²⁺ current (I_Ca ). Effects of VK-II-86 on I_Kr were investigated in transfected HEK-293 cells. A fluorogenic probe quantified the effects of VK-II-86 on oxidative stress in hypokalaemia.

KEY RESULTS

Dantrolene reduced the incidence of ventricular arrhythmias induced by low [K⁺ ] in explanted murine hearts by 94%, whereas VK-II-86 prevented all arrhythmias. VK-II-86 prevented hypokalaemia-induced AP prolongation and depolarization, but did not alter AP parameters in normokalaemia. Hypokalaemia was associated with a significant reduction of I_K1 and I_Kr , and increase in I_Na-L , and I_Ca . VK-II-86 prevented all hypokalaemia-induced changes in ion channel activity and oxidative stress.

CONCLUSIONS AND IMPLICATIONS

VK-II-86 prevents hypokalaemia-induced arrhythmogenesis by normalising calcium homeostasis and repolarization reserve. VK-II-86 may provide an exciting treatment in hypokalaemia and other arrhythmias caused by delayed repolarization or Ca²⁺ overload.

Effect of ivabradine in heart failure: a meta-analysis of heart failure patients with reduced versus preserved ejection fraction

In clinical trials of heart failure reduced ejection fraction (HFrEF), ivabradine seemed to be an effective heart rate lowering agent associated with lower risk of cardiovascular death. In contrast, ivabradine failed to improve cardiovascular outcomes in heart failure preserved ejection fraction (HFpEF) despite the significant effect on heart rate. This meta-analysis is the first to compare the effects of ivabradine on heart rate and mortality parameters in HFpEF versus HFrEF. We screened three databases: PubMed, Embase, and Cochrane Library. The outcomes of these studies were mortality, reduction in heart rate, and left ventricular function improvement. We compared the efficacy of ivabradine treatment in HFpEF versus HFrEF. Heart rate analysis of pooled data showed decrease in both HFrEF (-17.646 beats/min) and HFpEF (-11.434 beats/min), and a tendency to have stronger bradycardic effect in HFrEF (p = 0.094) in randomized clinical trials. Left ventricular ejection fraction analysis revealed significant improvement in HFrEF (5.936, 95% CI: [4.199-7.672], p < 0.001) when compared with placebo (p < 0.001). We found that ivabradine significantly improves left ventricular performance in HFrEF, at the same time it exerts a tendency to have improved bradycardic effect in HFrEF. These disparate effects of ivabradine and the higher prevalence of non-cardiac comorbidities in HFpEF may explain the observed beneficial effects in HFrEF and the unchanged outcomes in HFpEF patients after ivabradine treatment.

Sensitivity Analysis of Ion Channel Conductance on Myocardial Electromechanical Delay: Computational Study

It is well known that cardiac electromechanical delay (EMD) can cause dyssynchronous heart failure (DHF), a prominent cardiovascular disease (CVD). This work computationally assesses the conductance variation of every ion channel on the cardiac cell to give rise to EMD prolongation. The electrical and mechanical models of human ventricular tissue were simulated, using a population approach with four conductance reductions for each ion channel. Then, EMD was calculated by determining the difference between the onset of action potential and the start of cell shortening. Finally, EMD data were put into the optimized conductance dimensional stacking to show which ion channel has the most influence in elongating the EMD. We found that major ion channels, such as L-type calcium (CaL), slow-delayed rectifier potassium (Ks), rapid-delayed rectifier potassium (Kr), and inward rectifier potassium (K1), can significantly extend the action potential duration (APD) up to 580 ms. Additionally, the maximum intracellular calcium (Cai) concentration is greatly affected by the reduction in channel CaL, Ks, background calcium, and Kr. However, among the aforementioned major ion channels, only the CaL channel can play a superior role in prolonging the EMD up to 83 ms. Furthermore, ventricular cells with long EMD have been shown to inherit insignificant mechanical response (in terms of how strong the tension can grow and how far length shortening can go) compared with that in normal cells. In conclusion, despite all variations in every ion channel conductance, only the CaL channel can play a significant role in extending EMD. In addition, cardiac cells with long EMD tend to have inferior mechanical responses due to a lack of Cai compared with normal conditions, which are highly likely to result in a compromised pump function of the heart.

Genetic basis and molecular biology of cardiac arrhythmias in cardiomyopathies

Cardiac arrhythmias are common, often the first, and sometimes the life-threatening manifestations of hereditary cardiomyopathies. Pathogenic variants in several genes known to cause hereditary cardiac arrhythmias have also been identified in the sporadic cases and small families with cardiomyopathies. These findings suggest a shared genetic aetiology of a subset of hereditary cardiomyopathies and cardiac arrhythmias. The concept of a shared genetic aetiology is in accord with the complex and exquisite interplays that exist between the ion currents and cardiac mechanical function. However, neither the causal role of cardiac arrhythmias genes in cardiomyopathies is well established nor the causal role of cardiomyopathy genes in arrhythmias. On the contrary, secondary changes in ion currents, such as post-translational modifications, are common and contributors to the pathogenesis of arrhythmias in cardiomyopathies through altering biophysical and functional properties of the ion channels. Moreover, structural changes, such as cardiac hypertrophy, dilatation, and fibrosis provide a pro-arrhythmic substrate in hereditary cardiomyopathies. Genetic basis and molecular biology of cardiac arrhythmias in hereditary cardiomyopathies are discussed.

Characterization of the Electrophysiologic Remodeling of Patients With Ischemic Cardiomyopathy by Clinical Measurements and Computer Simulations Coupled With Machine Learning

RATIONALE

Patients with ischemic cardiomyopathy (ICMP) are at high risk for malignant arrhythmias, largely due to electrophysiological remodeling of the non-infarcted myocardium. The electrophysiological properties of the non-infarcted myocardium of patients with ICMP remain largely unknown.

OBJECTIVES

To assess the pro-arrhythmic behavior of non-infarcted myocardium in ICMP patients and couple computational simulations with machine learning to establish a methodology for the development of disease-specific action potential models based on clinically measured action potential duration restitution (APDR) data.

METHODS AND RESULTS

We enrolled 22 patients undergoing left-sided ablation (10 ICMP) and compared APDRs between ICMP and structurally normal left ventricles (SNLVs). APDRs were clinically assessed with a decremental pacing protocol. Using genetic algorithms (GAs), we constructed populations of action potential models that incorporate the cohort-specific APDRs. The variability in the populations of ICMP and SNLV models was captured by clustering models based on their similarity using unsupervised machine learning. The pro-arrhythmic potential of ICMP and SNLV models was assessed in cell- and tissue-level simulations. Clinical measurements established that ICMP patients have a steeper APDR slope compared to SNLV (by 38%, p < 0.01). In cell-level simulations, APD alternans were induced in ICMP models at a longer cycle length compared to SNLV models (385-400 vs 355 ms). In tissue-level simulations, ICMP models were more susceptible for sustained functional re-entry compared to SNLV models.

CONCLUSION

Myocardial remodeling in ICMP patients is manifested as a steeper APDR compared to SNLV, which underlies the greater arrhythmogenic propensity in these patients, as demonstrated by cell- and tissue-level simulations using action potential models developed by GAs from clinical measurements. The methodology presented here captures the uncertainty inherent to GAs model development and provides a blueprint for use in future studies aimed at evaluating electrophysiological remodeling resulting from other cardiac diseases.

Alamandine significantly reduces doxorubicin-induced cardiotoxicity in rats

Doxorubicin (DOX) is an anthracycline antibiotic. Despite its unwanted side effects, it has been successfully used in tumor therapy. Given that oxidative stress and inflammatory factors are essential to cardiotoxicity caused by DOX, we assumed that alamandine, which enhances endogenous antioxidants and has anti-inflammatory effects, may prevent DOX-induced cardiotoxicity. Rats received DOX (3.75 mg/kg) i.p on days 14, 21, 28, and 35 (total cumulative dose = 15 mg/kg) and alamandine (50 μg/kg/day) via mini-osmotic pumps for 42 days. At the end of the 42-day period, we evaluated hemodynamic parameters, electrocardiogram, cardiac troponin I (cTnI), superoxidase dismutase (SOD), total antioxidant capacity (TAC), malondialdehyde (MDA), inflammatory cytokines (tumor necrosis factor-α (TNF-α), IL-1β, NF-κB), apoptosis markers (caspase 3), and histopathology of haemotoxylin- and eosin-stained cardiac muscle fibers were evaluated. DOX significantly increased QT, corrected QT (QTc), and RR intervals. Alamandine co-therapy prevented ECG changes. Alamandine administration restored DOX-induced disruptions in the cardiac muscle architecture and vascular congestion. Alamandine co-therapy also alleviated other effects of DOX, including cardiac contractility, decreased systolic and diastolic blood pressure, and increased left ventricular end-diastolic pressure. Moreover, alamandine co-therapy substantially decreased the elevation of oxidative stress markers, inflammatory cytokines, and caspase 3 in DOX-treated rats. The results suggest that alamandine reduced DOX-induced cardiotoxicity via antioxidant, anti-inflammatory, and anti-apoptotic activities.

Chronic perinatal hypoxia delays cardiac maturation in a mouse model for cyanotic congenital heart disease

Compared with acyanotic congenital heart disease (CHD), cyanotic CHD has an increased risk of lifelong mortality and morbidity. These adverse outcomes may be attributed to delayed cardiomyocyte maturation, since the transition from a hypoxic fetal milieu to oxygen-rich postnatal environment is disrupted. We established a rodent model to replicate hypoxic myocardial conditions spanning perinatal development, and tested the hypothesis that chronic hypoxia impairs cardiac development. Pregnant mice were housed in hypoxia beginning at embryonic day 16. Pups stayed in hypoxia until postnatal day (P)8 when cardiac development is nearly complete. Global gene expression was quantified at P8 and at P30, after recovering in normoxia. Phenotypic testing included electrocardiogram, echocardiogram, and ex vivo electrophysiology study. Hypoxic P8 animals were 47% smaller than controls with preserved heart size. Gene expression was grossly altered by hypoxia at P8 (1,427 genes affected), but normalized after recovery (P30). Electrocardiograms revealed bradycardia and slowed conduction velocity in hypoxic animals at P8, with noticeable resolution after recovery (P30). Notable differences that persisted after recovery (P30) included a 65% prolongation in ventricular effective refractory period, sinus node dysfunction, 23% reduction in ejection fraction, and 16% reduction in fractional shortening in animals exposed to hypoxia. We investigated the impact of chronic hypoxia on the developing heart. Perinatal hypoxia was associated with changes in gene expression and cardiac function. Persistent changes to the electrophysiological substrate and contractile function warrant further investigation and may contribute to adverse outcomes observed in the cyanotic CHD population.NEW & NOTEWORTHY We utilized a new mouse model of chronic perinatal hypoxia to simulate the hypoxic myocardial conditions present in cyanotic congenital heart disease. Hypoxia caused numerous abnormalities in cardiomyocyte gene expression, the electrophysiologic substrate of the heart, and contractile function. Taken together, alterations observed in the neonatal period suggest delayed cardiac development immediately following hypoxia.

Diabetes-induced changes in cardiac voltage-gated ion channels

Diabetes mellitus affects the heart through various mechanisms such as microvascular defects, metabolic abnormalities, autonomic dysfunction and incompatible immune response. Furthermore, it can also cause functional and structural changes in the myocardium by a disease known as diabetic cardiomyopathy (DCM) in the absence of coronary artery disease. As DCM progresses it causes electrical remodeling of the heart, left ventricular dysfunction and heart failure. Electrophysiological changes in the diabetic heart contribute significantly to the incidence of arrhythmias and sudden cardiac death in diabetes mellitus patients. In recent studies, significant changes in repolarizing K+ currents, Na+ currents and L-type Ca2+ currents along with impaired Ca2+ homeostasis and defective contractile function have been identified in the diabetic heart. In addition, insulin levels and other trophic factors change significantly to maintain the ionic channel expression in diabetic patients. There are many diagnostic tools and management options for DCM, but it is difficult to detect its development and to effectively prevent its progress. In this review, diabetes-associated alterations in voltage-sensitive cardiac ion channels are comprehensively assessed to understand their potential role in the pathophysiology and pathogenesis of DCM.

Circadian Pattern of Ion Channel Gene Expression in Failing Human Hearts

BACKGROUND

Ventricular tachyarrhythmias and sudden cardiac death show a circadian pattern of occurrence in patients with heart failure. In the rodent ventricle, a significant portion of genes, including some ion channels, shows a circadian pattern of expression. However, genes that define electrophysiological properties in failing human heart ventricles have not been examined for a circadian expression pattern.

METHODS

Ventricular tissue samples were collected from patients at the time of cardiac transplantation. Two sets of samples (n=37 and 46, one set with a greater arrhythmic history) were selected to generate pseudo-time series according to their collection time. A third set (n=27) of samples was acquired from the nonfailing ventricles of brain-dead donors. The expression of 5 known circadian clock genes and 19 additional ion channel genes plausibly important to electrophysiological properties were analyzed by real-time polymerase chain reaction and then analyzed for the percentage of expression variation attributed to a 24-hour circadian pattern.

RESULTS

The 5 known circadian clock gene transcripts showed a strong circadian expression pattern. Compared with rodent hearts, the human circadian clock gene transcripts showed a similar temporal order of acrophases but with a ≈7.6 hours phase shift. Five of the ion channel genes also showed strong circadian expression. Comparable studies of circadian clock gene expression in samples recovered from nonheart failure brain-dead donors showed acrophase shifts, or weak or complete loss of circadian rhythmicity, suggesting alterations in circadian gene expression.

CONCLUSIONS

Ventricular tissue from failing human hearts display a circadian pattern of circadian clock gene expression but phase-shifted relative to rodent hearts. At least 5 ion channels show a circadian expression pattern in the ventricles of failing human hearts, which may underlie a circadian pattern of ventricular tachyarrhythmia/sudden cardiac death. Nonfailing hearts from brain-dead donors show marked differences in circadian clock gene expression patterns, suggesting fundamental deviations from circadian expression.

Inhibition of cardiac potassium currents by oxidation-activated protein kinase A contributes to early afterdepolarizations in the heart

Reactive oxygen species (ROS) have been shown to prolong cardiac action potential duration resulting in afterdepolarizations, the cellular basis of triggered arrhythmias. As previously shown, protein kinase A type I (PKA I) is readily activated by oxidation of its regulatory subunits. However, the relevance of this mechanism of activation for cardiac pathophysiology is still elusive. In this study, we investigated the effects of oxidation-activated PKA I on cardiac electrophysiology. Ventricular cardiomyocytes were isolated from redox-dead PKA-RI Cys17Ser knock-in (KI) and wild-type (WT) mice and exposed to H₂O₂ (200 µmol/L) or vehicle (Veh) solution. In WT myocytes, exposure to H₂O₂ significantly increased oxidation of the regulatory subunit I (RI) and thus its dimerization (threefold increase in PKA RI dimer). Whole cell current clamp and voltage clamp were used to measure cardiac action potentials (APs), transient outward potassium current (I_to) and inward rectifying potassium current (I_K1), respectively. In WT myocytes, H₂O₂ exposure significantly prolonged AP duration due to significantly decreased I_to and I_K1 resulting in frequent early afterdepolarizations (EADs). Preincubation with the PKA-specific inhibitor Rp-8-Br-cAMPS (10 µmol/L) completely abolished the H₂O₂-dependent decrease in I_to and I_K1 in WT myocytes. Intriguingly, H₂O₂ exposure did not prolong AP duration, nor did it decrease I_to, and only slightly enhanced EAD frequency in KI myocytes. Treatment of WT and KI cardiomyocytes with the late I_Na inhibitor TTX (1 µmol/L) completely abolished EAD formation. Our results suggest that redox-activated PKA may be important for H₂O₂-dependent arrhythmias and could be important for the development of specific antiarrhythmic drugs.NEW & NOTEWORTHY Oxidation-activated PKA type I inhibits transient outward potassium current (I_to) and inward rectifying potassium current (I_K1) and contributes to ROS-induced APD prolongation as well as generation of early afterdepolarizations in murine ventricular cardiomyocytes.

Cardiac transmembrane ion channels and action potentials: cellular physiology and arrhythmogenic behavior

Cardiac arrhythmias are among the leading causes of mortality. They often arise from alterations in the electrophysiological properties of cardiac cells and their underlying ionic mechanisms. It is therefore critical to further unravel the pathophysiology of the ionic basis of human cardiac electrophysiology in health and disease. In the first part of this review, current knowledge on the differences in ion channel expression and properties of the ionic processes that determine the morphology and properties of cardiac action potentials and calcium dynamics from cardiomyocytes in different regions of the heart are described. Then the cellular mechanisms promoting arrhythmias in congenital or acquired conditions of ion channel function (electrical remodeling) are discussed. The focus is on human-relevant findings obtained with clinical, experimental, and computational studies, given that interspecies differences make the extrapolation from animal experiments to human clinical settings difficult. Deepening the understanding of the diverse pathophysiology of human cellular electrophysiology will help in developing novel and effective antiarrhythmic strategies for specific subpopulations and disease conditions.

Cholinergic stimulation improves electrophysiological rate adaptation during pressure overload-induced heart failure in rats

BACKGROUND

Left ventricular (LV) electrical maladaptation to increased heart rate in failing myocardium contributes to morbidity and mortality. Recently, cardiac cholinergic neuron activation reduced loss of contractile function resulting from chronic trans-aortic constriction (TAC) in rats. We hypothesized that chronic activation of cardiac cholinergic neurons would also reduce TAC-induced derangement of cardiac electrical activity.

METHODS

We investigated electrophysiological rate adaptation in TAC rat hearts with and without daily chemogenetic activation of hypothalamic oxytocin neurons for downstream cardiac cholinergic neuron stimulation. Sprague Dawley rat hearts were excised, perfused, and optically mapped under dynamic pacing after 16 weeks of TAC with or without 12 weeks of daily chemogenetic treatment. Action potential duration (APD60) and conduction velocity (CV) maps were analyzed for regional rate adaptation to dynamic pacing.

RESULTS

At lower pacing rates, untreated TAC induced elevated LV epicardial APD60. Fitted APD60 steady state (APDss) was reduced in treated TAC hearts. At higher pacing rates, treatment heterogeneously reduced APD60 compared to untreated TAC hearts. Variance of conduction loss was reduced in treated hearts compared to untreated hearts during fast pacing. However, CV was markedly reduced in both treated and untreated TAC hearts throughout dynamic pacing. At 150msec pacing cycle length, APD60 v. diastolic interval (DI) dispersion was reduced in treated hearts compared to untreated hearts.

CONCLUSIONS

Chronic activation of cardiac cholinergic neurons improved electrophysiological adaptation to increases in pacing rate during development of TAC-induced heart failure. This provides insight into the electrophysiological benefits of cholinergic stimulation as a treatment for heart failure patients.

Exercise training reveals micro-RNAs associated with improved cardiac function and electrophysiology in rats with heart failure after myocardial infarction

AIMS

Endurance training improves aerobic fitness and cardiac function in individuals with heart failure. However, the underlying mechanisms are not well characterized. Exercise training could therefore act as a tool to discover novel targets for heart failure treatment. We aimed to associate changes in Ca²⁺ handling and electrophysiology with micro-RNA (miRNA) profile in exercise trained heart failure rats to establish which miRNAs induce heart failure-like effects in Ca²⁺ handling and electrophysiology.

METHODS AND RESULTS

Post-myocardial infarction (MI) heart failure was induced in Sprague Dawley rats. Rats with MI were randomized to sedentary control (sed), moderate (mod)- or high-intensity (high) endurance training for 8 weeks. Exercise training improved cardiac function, Ca²⁺ handling and electrophysiology including reduced susceptibility to arrhythmia in an exercise intensity-dependent manner where high intensity gave a larger effect. Fifty-five miRNAs were significantly regulated (up or down) in MI-sed, of which 18 and 3 were changed towards Sham-sed in MI-high and MI-mod, respectively. Thereafter we experimentally altered expression of these "exercise-miRNAs" individually in human induced pluripotent stem cell-derived cardiomyocytes (hIPSC-CM) in the same direction as they were changed in MI. Of the "exercise-miRNAs", miR-214-3p prolonged AP duration, whereas miR-140 and miR-208a shortened AP duration. miR-497-5p prolonged Ca²⁺ release whereas miR-214-3p and miR-31a-5p prolonged Ca²⁺ decay.

CONCLUSION

Using exercise training as a tool, we discovered that miR-214-3p, miR-497-5p, miR-31a-5p contribute to heart-failure like behaviour in Ca²⁺ handling and electrophysiology and could be potential treatment targets.

Human Cell Modeling for Cardiovascular Diseases

The availability of appropriate and reliable in vitro cell models recapitulating human cardiovascular diseases has been the aim of numerous researchers, in order to retrace pathologic phenotypes, elucidate molecular mechanisms, and discover therapies using simple and reproducible techniques. In the past years, several human cell types have been utilized for these goals, including heterologous systems, cardiovascular and non-cardiovascular primary cells, and embryonic stem cells. The introduction of induced pluripotent stem cells and their differentiation potential brought new prospects for large-scale cardiovascular experiments, bypassing ethical concerns of embryonic stem cells and providing an advanced tool for disease modeling, diagnosis, and therapy. Each model has its advantages and disadvantages in terms of accessibility, maintenance, throughput, physiological relevance, recapitulation of the disease. A higher level of complexity in diseases modeling has been achieved with multicellular co-cultures. Furthermore, the important progresses reached by bioengineering during the last years, together with the opportunities given by pluripotent stem cells, have allowed the generation of increasingly advanced in vitro three-dimensional tissue-like constructs mimicking in vivo physiology. This review provides an overview of the main cell models used in cardiovascular research, highlighting the pros and cons of each, and describing examples of practical applications in disease modeling.

Towards the Development of AgoKirs: New Pharmacological Activators to Study Kir2.x Channel and Target Cardiac Disease

Inward rectifier potassium ion channels (I_K1-channels) of the K_ir2.x family are responsible for maintaining a stable negative resting membrane potential in excitable cells, but also play a role in processes of non-excitable tissues, such as bone development. I_K1-channel loss-of-function, either congenital or acquired, has been associated with cardiac disease. Currently, basic research and specific treatment are hindered by the absence of specific and efficient K_ir2.x channel activators. However, twelve different compounds, including approved drugs, show off-target I_K1 activation. Therefore, these compounds contain valuable information towards the development of agonists of K_ir channels, AgoKirs. We reviewed the mechanism of I_K1 channel activation of these compounds, which can be classified as direct or indirect activators. Subsequently, we examined the most viable starting points for rationalized drug development and possible safety concerns with emphasis on cardiac and skeletal muscle adverse effects of AgoKirs. Finally, the potential value of AgoKirs is discussed in view of the current clinical applications of potentiators and activators in cystic fibrosis therapy.

Human Cardiac Mesenchymal Stem Cells Remodel in Disease and Can Regulate Arrhythmia Substrates

BACKGROUND

The mesenchymal stem cell (MSC), known to remodel in disease and have an extensive secretome, has recently been isolated from the human heart. However, the effects of normal and diseased cardiac MSCs on myocyte electrophysiology remain unclear. We hypothesize that in disease the inflammatory secretome of cardiac human MSCs (hMSCs) remodels and can regulate arrhythmia substrates.

METHODS

hMSCs were isolated from patients with or without heart failure from tissue attached to extracted device leads and from samples taken from explanted/donor hearts. Failing hMSCs or nonfailing hMSCs were cocultured with normal human cardiac myocytes derived from induced pluripotent stem cells. Using fluorescent indicators, action potential duration, Ca2+ alternans, and spontaneous calcium release (SCR) incidence were determined.

RESULTS

Failing and nonfailing hMSCs from both sources exhibited similar trilineage differentiation potential and cell surface marker expression as bone marrow hMSCs. Compared with nonfailing hMSCs, failing hMSCs prolonged action potential duration by 24% (P<0.001, n=15), increased Ca2+ alternans by 300% (P<0.001, n=18), and promoted spontaneous calcium release activity (n=14, P<0.013) in human cardiac myocytes derived from induced pluripotent stem cells. Failing hMSCs exhibited increased secretion of inflammatory cytokines IL (interleukin)-1β (98%, P<0.0001) and IL-6 (460%, P<0.02) compared with nonfailing hMSCs. IL-1β or IL-6 in the absence of hMSCs prolonged action potential duration but only IL-6 increased Ca2+ alternans and promoted spontaneous calcium release activity in human cardiac myocytes derived from induced pluripotent stem cells, replicating the effects of failing hMSCs. In contrast, nonfailing hMSCs prevented Ca2+ alternans in human cardiac myocytes derived from induced pluripotent stem cells during oxidative stress. Finally, nonfailing hMSCs exhibited >25× higher secretion of IGF (insulin-like growth factor)-1 compared with failing hMSCs. Importantly, IGF-1 supplementation or anti-IL-6 treatment rescued the arrhythmia substrates induced by failing hMSCs.

CONCLUSIONS

We identified device leads as a novel source of cardiac hMSCs. Our findings show that cardiac hMSCs can regulate arrhythmia substrates by remodeling their secretome in disease. Importantly, therapy inhibiting (anti-IL-6) or mimicking (IGF-1) the cardiac hMSC secretome can rescue arrhythmia substrates.

Vernakalant hydrochloride for the treatment of atrial fibrillation: evaluation of its place in clinical practice

Vernakalant is an intravenous anti-arrhythmic drug available in Europe, Canada and some countries in Asia for the restoration of sinus rhythm in acute onset atrial fibrillation. Currently, it is not available in USA because the US FDA have ongoing concerns about its safety. Vernakalant has a unique pharmacological profile of multi-ion channel activity and atrial-specificity that distinguishes it from other anti-arrhythmic drugs. This is thought to enhance efficacy but there are concerns of adverse events stemming from its diverse pharmacology. This ambiguity has prompted a review of the available clinical evidence on efficacy and safety to help re-evaluate its place in clinical practice.

Inhibition of cardiac Kv4.3 (Ito) channel isoforms by class I antiarrhythmic drugs lidocaine and mexiletine

Transient outward K⁺ current, I_to, contributes to cardiac action potential generation and is primarily carried by K_v4.3 (KCND3) channels. Two K_v4.3 isoforms are expressed in human ventricle and show differential remodeling in heart failure (HF). Lidocaine and mexiletine may be applied in selected patients to suppress ventricular arrhythmias, without effects on sudden cardiac death or mortality. Isoform-dependent effects of antiarrhythmic drugs on K_v4.3 channels and potential implications for remodeling-based antiarrhythmic management have not been assessed to date. We sought to test the hypotheses that K_v4.3 channels are targeted by lidocaine and mexiletine, and that drug sensitivity is determined in isoform-specific manner. Expression of KCND3 isoforms was quantified using qRT-PCR in left ventricular samples of patients with HF due to either ischemic or dilated cardiomyopathies (ICM or DCM). Long (K_v4.3-L) and short (K_v4.3-S) isoforms were heterologously expressed in Xenopus laevis oocytes to study drug sensitivity and effects on biophysical characteristics activation, deactivation, inactivation, and recovery from inactivation. In the present HF patient cohort KCND3 isoform expression did not differ between ICM and DCM. In vitro, lidocaine (IC₅₀-K_v4.3-L: 0.8 mM; IC₅₀-K_v4.3-S: 1.2 mM) and mexiletine (IC₅₀-K_v4.3-L: 146 μM; IC₅₀-K_v4.3-S: 160 μM) inhibited K_v4.3 with different sensitivity. Biophysical analyses identified accelerated and enhanced inactivation combined with delayed recovery from inactivation as primary biophysical mechanisms underlying K_v4.3 current reduction. In conclusion, differential effects on K_v4.3 isoforms extend the electropharmacological profile of lidocaine and mexiletine. Patient-specific remodeling of K_v4.3 isoforms may determine individual drug responses and requires consideration during clinical application of compounds targeting K_v4.3.