Stretch-activated channel activation promotes early afterdepolarizations in rat ventricular myocytes under oxidative stress

Pregnancy Arrhythmias: Management in the Emergency Department and Critical Care

Pregnancy is closely associated with an elevated risk of arrhythmias, constituting the predominant cardiovascular complication during this period. Pregnancy may induce the exacerbation of previously controlled arrhythmias and, in some instances, arrhythmias may present for the first time in pregnancy. The most important proarrhythmic mechanisms during pregnancy are the atrial and ventricular stretching, coupled with increased sympathetic activity. Notably, arrhythmias, particularly those originating in the ventricles, heighten the likelihood of syncope, increasing the potential for sudden cardiac death. The effective management of arrhythmias during the peripartum period requires a comprehensive, multidisciplinary approach from the prepartum to the postpartum period. The administration of antiarrhythmic drugs during pregnancy necessitates meticulous attention to potential alterations in pharmacokinetics attributable to maternal physiological changes, as well as the potential for fetal adverse effects. Electric cardioversion is a safe and effective intervention during pregnancy and should be performed immediately in patients with hemodynamic instability. This review discusses the pathophysiology of arrythmias in pregnancy and their management.

2023 HRS expert consensus statement on the management of arrhythmias during pregnancy

This international multidisciplinary expert consensus statement is intended to provide comprehensive guidance that can be referenced at the point of care to cardiac electrophysiologists, cardiologists, and other health care professionals, on the management of cardiac arrhythmias in pregnant patients and in fetuses. This document covers general concepts related to arrhythmias, including both brady- and tachyarrhythmias, in both the patient and the fetus during pregnancy. Recommendations are provided for optimal approaches to diagnosis and evaluation of arrhythmias; selection of invasive and noninvasive options for treatment of arrhythmias; and disease- and patient-specific considerations when risk stratifying, diagnosing, and treating arrhythmias in pregnant patients and fetuses. Gaps in knowledge and new directions for future research are also identified.

Treatment of Arrhythmias During Pregnancy

Cardiac disease is the most common cause of maternal mortality in developed nations. Cardiac arrhythmias are frequent among patients with structural heart disease and may require immediate treatment to prevent hemodynamic instability leading to acute maternal and fetal decompensation. Antiarrhythmic therapy during pregnancy should follow the same principles recommended for nonpregnant individuals. Although multidisciplinary management is recommended, obstetricians, and maternal-fetal medicine specialists may sometimes need to emergently recognize and treat rhythm anomalies before support services become available.

COPD maintenance medication is linked to left atrial size: Results from the COSYCONET cohort

BACKGROUND

Lung function impairment in COPD is known to be related to reductions of left heart size, while short-term interventional trials with bronchodilators showed positive effects on cardiac parameters. We investigated whether COPD maintenance therapy has analogous long-term effects.

METHODS

Pooled data of GOLD grade 1-4 patients from visits 1 and 3 (1.5 y apart) of the COSYCONET cohort were used. Medication was categorized as use of ICS, LABA + ICS, LABA + LAMA and triple therapy (LABA + LAMA + ICS), contrasting "always" versus "never". Echocardiographic parameters comprised left ventricular end-diastolic and -systolic diameter (LVEDD, LVESD), ejection fraction (LVEF) and left atrial diameter (LA). Associations were identified by multiple regression analysis, as well as propensity score analysis.

RESULTS

Overall, 846 patients (mean age 64.5 y; 41% female) were included, 53% using ICS at both visits, 51% LABA + ICS, 56% LABA + LAMA, 40% LABA + LAMA + ICS (triple) therapy. Conversely, 30%, 32%, 28% and 42% had no ICS, LABA + ICS, LABA + LAMA or triple therapy, respectively, at both visits. Among echocardiographic measures, only LA showed statistically significant associations (increases) with medication, whereby significant effects were linked to ICS, LABA + ICS and LABA + LAMA (p < 0.05 each, "always" versus "never") and propensity score analyses underlined the role of LABA + LAMA.

CONCLUSIONS

In this observational study, COPD maintenance therapy, especially LABA + LAMA, was linked to left atrial size, consistent with the results of short-term interventional trials. These findings suggest that maintenance medication for COPD does not only improve lung function and patient reported outcomes but may also have an impact on the cardiovascular system.

TRIAL REGISTRATION

NCT01245933.

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.

Left ventricular volume and wall stress are linked to lung function impairment in COPD

BACKGROUND

Cardiovascular comorbidities are common in chronic obstructive pulmonary disease (COPD). We examined the association between airflow limitation, hyperinflation and the left ventricle (LV).

METHODS

Patients from the COPD cohort COSYCONET underwent evaluations including forced expiratory volume in 1 s (FEV₁), forced vital capacity (FVC), effective airway resistance (R_eff), intrathoracic gas volume (ITGV), and echocardiographic LV end-diastolic volume (LVEDV), stroke volume (LVSV), end-systolic volume (LVESV), and end-diastolic and end-systolic LV wall stress. Data from Visit 1 (baseline) and Visit 3 (18 months later) were used. In addition to comparisons of both visits, multivariate regression analysis was conducted, followed by structural equation modelling (SEM) with latent variables "Lung" and "Left heart".

RESULTS

A total of 641 participants were included in this analysis. From Visit 1 to Visit 3, there were significant declines in FEV₁ and FEV₁/FVC, and increases in R_eff, ITGV and LV end-diastolic wall stress, and a borderline significant decrease in LV mass. There were significant correlations of: FEV₁% predicted with LVEDV and LVSV; R_eff with LVSV; and ITGV with LV mass and LV end-diastolic wall stress. The SEM fitted the data of both visits well (comparative fit index: 0.978, 0.962), with strong correlation between "Lung" and "Left heart".

CONCLUSIONS

We demonstrated a relationship between lung function impairment and LV wall stress in patients with COPD. This supports the hypothesis that LV impairment in COPD could be initiated or promoted, at least partly, by mechanical factors exerted by the lung disorder.

Bioactive nanoparticles improve calcium handling in failing cardiac myocytes

AIMS

To evaluate the ability of N-acetylglucosamine (GlcNAc) decorated nanoparticles and their cargo to modulate calcium handling in failing cardiac myocytes (CMs).

MATERIALS & METHODS

Primary CMs isolated from normal and failing hearts were treated with GlcNAc nanoparticles in order to assess the ability of the nanoparticles and their cargo to correct dysfunctional calcium handling in failing myocytes.

RESULTS & CONCLUSION

GlcNAc particles reduced aberrant calcium release in failing CMs and restored sarcomere function. Additionally, encapsulation of a small calcium-modulating protein, S100A1, in GlcNAc nanoparticles also showed improved calcium regulation. Thus, the development of our bioactive nanoparticle allows for a 'two-hit' treatment, by which the cargo and also the nanoparticle itself can modulate intracellular protein activity.

The early stage of the atrial electroanatomic remodeling as substrates for atrial fibrillation in hypertensive patients

BACKGROUND

Hypertension is one of the most important risk factors for atrial fibrillation (AF). Recent studies suggest right atrial remodeling in hypertensive patients may be associated with increased inducibility of AF. This study sought to characterize the electroanatomic features of left and right atria and pulmonary veins (PVs) in hypertensive patients.

METHODS AND RESULTS

A prospective observational study was conducted on patients who underwent ablation for paroxysmal supraventricular tachycardia or paroxysmal AF. Electrophysiological features of the PVs and atria, including event-related potentials, conduction time, and inducibility and vulnerability of AF, were characterized during cardiac catheterization. Anatomic and hemodynamic features were assessed by using echocardiographic and computer tomography imaging. When 15 hypertensive patients with paroxysmal supraventricular tachycardia were compared with 17 normotensive patients with paroxysmal supraventricular tachycardia, the hypertensive patients had significantly shortened PV event-related potentials with increased dispersions (P<0.001) but slightly prolonged atrial event-related potentials (P=NS) and had prolonged interatrial and intra-atrial conduction times (P<0.001). Additionally, the hypertensive patients had increased vulnerability and inducibility of AF and prolonged duration of induced AF (P<0.01). All of these changes were more pronounced in hypertensive patients with paroxysmal AF. Anatomically, compared with the normotensive patients, the diameters of 4 PVs in the hypertensive patients with paroxysmal supraventricular tachycardia were significantly enlarged (P<0.01) and became more remarkable in hypertensive patients with paroxysmal AF (P<0.0001), although the diameter and volume index of the left atrium among 3 groups were similar.

CONCLUSIONS

The hypertensive patients showed electroanatomic changes associated with increased vulnerability to AF, including shortened event-related potentials with increased dispersion, prolonged conduction time, and increased PV diameter, but these changes were not appreciated in the atria. Additionally, these changes became more dramatic in hypertensive patients with paroxysmal AF.

Spatial correlation of action potential duration and diastolic dysfunction in transgenic and drug-induced LQT2 rabbits

BACKGROUND

Enhanced dispersion of action potential duration (APD) is a major contributor to long QT syndrome (LQTS)-related arrhythmias.

OBJECTIVE

To investigate spatial correlations of regional heterogeneities in cardiac repolarization and mechanical function in LQTS.

METHODS

Female transgenic LQTS type 2 (LQT2; n = 11) and wild-type littermate control (LMC) rabbits (n = 9 without E4031 and n = 10 with E4031) were subjected to phase contrast magnetic resonance imaging to assess regional myocardial velocities. In the same rabbits' hearts, monophasic APDs were assessed in corresponding segments.

RESULTS

In LQT2 and E4031-treated rabbits, APD was longer in all left ventricular segments (P < .01) and APD dispersion was greater than that in LMC rabbits (P < .01). In diastole, peak radial velocities (Vr) were reduced in LQT2 and E4031-treated compared to LMC rabbits in LV base and mid (LQT2: -3.36 ± 0.4 cm/s, P < .01; E4031-treated: -3.24 ± 0.6 cm/s, P < .0001; LMC: -4.42 ± 0.5 cm/s), indicating an impaired diastolic function. Regionally heterogeneous diastolic Vr correlated with APD (LQT2: correlation coefficient [CC] 0.38, P = .01; E4031-treated: CC 0.42, P < .05). Time-to-diastolic peak Vr were prolonged in LQT2 rabbits (LQT2: 196.8 ± 2.9 ms, P < .001; E4031-treated: 199.5 ± 2.2 ms, P < .0001, LMC 183.1 ± 1.5), indicating a prolonged contraction duration. Moreover, in transgenic LQT2 rabbits, diastolic time-to-diastolic peak Vr correlated with APD (CC 0.47, P = .001). In systole, peak Vr were reduced in LQT2 and E4031-treated rabbits (P < .01) but longitudinal velocities or ejection fraction did not differ. Finally, random forest machine learning algorithms enabled a differentiation between LQT2, E4031-treated, and LMC rabbits solely based on "mechanical" magnetic resonance imaging data.

CONCLUSIONS

The prolongation of APD led to impaired diastolic and systolic function in transgenic and drug-induced LQT2 rabbits. APD correlated with regional diastolic dysfunction, indicating that LQTS is not purely an electrical but an electromechanical disorder.

Stretch current-induced abnormal impulses in CaMKIIδ knockout mouse ventricular myocytes

BACKGROUND

CaMKII activation is proarrhythmic in heart failure where myocardium is stretched. However, the arrhythmogenic role of CaMKII in stretched ventricle has not been well understood.

OBJECTIVE

We tested abnormal impulse inducibility by stretch current in myocytes isolated from CaMKIIδ knockout (KO) mouse left ventricle (LV) where CaMKII activity is reduced by ≈ 62%.

METHODS AND RESULTS

Action potentials were recorded by whole-cell patch clamp, and abnormal impulses were induced in LV myocytes by a simulation of stretch-activated channel (SAC) current. SAC activation failed to induce abnormal impulses in wild type (WT) myocytes but steadily produced early after-depolarizations and automaticity in KO myocytes in which an increase in L-type calcium channel (LTCC) current (I(Ca)) and a reduction of sarcoplasmic reticulum Ca(2+) leak and action potential duration (APD) were observed. The abnormal impulses were not suppressed by CaMKII inhibitor AIP whereas a low concentration of nifedipine eliminated abnormal impulses without shortening APD, implicating I(Ca) in promoting stretch-induced abnormal impulses. In addition, APD prolongation by LTCC opener S(-)Bay K 8644 or isoproterenol facilitated abnormal impulse induction in WT ventricular myocytes even in the presence of CaMKII inhibitor AIP, whereas APD prolongation by K(+) channel blocker 4-aminopyridine promoted abnormal impulses in KO myocytes but not in WT myocytes.

CONCLUSION

I(Ca) activation plays a central role in stretch-induced abnormal impulses and APD prolongation is arrhythmogenic only when I(Ca) is highly activated. At increased I(Ca) activation, CaMKII inhibition cannot suppress abnormal impulse induction.

Cardioprotection from oxidative stress in the newborn heart by activation of PPARγ is mediated by catalase

Regulation of catalase (CAT) by peroxisome proliferator-activated receptor-γ (PPARγ) was investigated to determine if PPARγ activation provides cardioprotection from oxidative stress caused by hydrogen peroxide (H(2)O(2)) in an age-dependent manner. Left ventricular developed pressure (LVDP) was measured in Langendorff perfused newborn or adult rabbit hearts, exposed to 200μM H(2)O(2), with perfusion of rosiglitazone (RGZ) or pioglitazone (PGZ), PPARγ agonists. We found: (1) H(2)O(2) significantly decreased sarcomere shortening in newborn ventricular cells but not in adult cells. Lactate dehydrogenase (LDH) release occurred earlier in newborn than in adult heart, which may be due, in part, to the lower expression of CAT in newborn heart. (2) RGZ increased CAT mRNA and protein as well as activity in newborn but not in adult heart. GW9662 (PPARγ blocker) eliminated the increased CAT mRNA by RGZ. (3) In newborn heart, RGZ and PGZ treatment inhibited release of LDH in response to H(2)O(2) compared to H(2)O(2) alone. GW9662 decreased this inhibition. (4) LVDP was significantly higher in both RGZ+H(2)O(2) and PGZ+H(2)O(2) groups than in the H(2)O(2) group. Block of PPARγ abolished this effect. In contrast, there was no effect of RGZ in adult. (5) The cardioprotective effects of RGZ were abolished by inhibition of CAT. In conclusion, PPARγ activation is cardioprotective to H(2)O(2)-induced stress in the newborn heart by upregulation of catalase. These data suggest that PPARγ activation may be an effective therapy for the young cardiac patient.

The kinase Pyk2 is involved in renal fibrosis by means of mechanical stretch-induced growth factor expression in renal tubules

Unilateral ureteral obstruction is a well-established experimental model of progressive renal fibrosis. We tested whether mechanical stretch and subsequent renal tubular distension might lead to renal fibrosis by first studying renal tubular epithelial cells in culture. We found that mechanical stretch induced reactive oxygen species that in turn activated the cytoplasmic proline-rich tyrosine kinase-2 (Pyk2). This kinase is abundantly expressed in tubular epithelial cells where it is activated by several stimuli. Using mice with deletion of Pyk2 we found that the expression of transforming growth factor-β1 induced by mechanical stretch in renal tubular epithelial cells was significantly reduced. The expression of connective tissue growth factor was also reduced in the Pyk2(-/-) mice. We also found that expression of connective tissue growth factor was independent of transforming growth factor-β1, but dependent on the Rho-associated coiled-coil forming protein kinase pathway. Thus, Pyk2 may be an important initiating factor in renal fibrosis and might be a new therapeutic target for ameliorating renal fibrosis.

Electromechanical feedback with reduced cellular connectivity alters electrical activity in an infarct injured left ventricle: a finite element model study

Myocardial infarction (MI) significantly alters the structure and function of the heart. As abnormal strain may drive heart failure and the generation of arrhythmias, we used computational methods to simulate a left ventricle with an MI over the course of a heartbeat to investigate strains and their potential implications to electrophysiology. We created a fully coupled finite element model of myocardial electromechanics consisting of a cellular physiological model, a bidomain electrical diffusion solver, and a nonlinear mechanics solver. A geometric mesh built from magnetic resonance imaging (MRI) measurements of an ovine left ventricle suffering from a surgically induced anteroapical infarct was used in the model, cycled through the cardiac loop of inflation, isovolumic contraction, ejection, and isovolumic relaxation. Stretch-activated currents were added as a mechanism of mechanoelectric feedback. Elevated fiber and cross fiber strains were observed in the area immediately adjacent to the aneurysm throughout the cardiac cycle, with a more dramatic increase in cross fiber strain than fiber strain. Stretch-activated channels decreased action potential (AP) dispersion in the remote myocardium while increasing it in the border zone. Decreases in electrical connectivity dramatically increased the changes in AP dispersion. The role of cross fiber strain in MI-injured hearts should be investigated more closely, since results indicate that these are more highly elevated than fiber strain in the border of the infarct. Decreases in connectivity may play an important role in the development of altered electrophysiology in the high-stretch regions of the heart.

Metabolic stress, reactive oxygen species, and arrhythmia

Cardiac arrhythmias can cause sudden cardiac death (SCD) and add to the current heart failure (HF) health crisis. Nevertheless, the pathological processes underlying arrhythmias are unclear. Arrhythmic conditions are associated with systemic and cardiac oxidative stress caused by reactive oxygen species (ROS). In excitable cardiac cells, ROS regulate both cellular metabolism and ion homeostasis. Increasing evidence suggests that elevated cellular ROS can cause alterations of the cardiac sodium channel (Na(v)1.5), abnormal Ca(2+) handling, changes of mitochondrial function, and gap junction remodeling, leading to arrhythmogenesis. This review summarizes our knowledge of the mechanisms by which ROS may cause arrhythmias and discusses potential therapeutic strategies to prevent arrhythmias by targeting ROS and its consequences. This article is part of a Special Issue entitled "Local Signaling in Myocytes".

CARDIAC ARRHYTHMIAS DURING PREGNANCY: A CLINICAL APPROACH

Physiologic changes in maternal haemodynamics, hormones and autonomic properties contribute to arrhythmias in pregnancy. While arrhythmias most commonly occur in pregnant women with structural heart disease or those with a history of cardiac arrhythmias, they can also occur de novo in women with no documented cardiac disease.

Computational models reduce complexity and accelerate insight into cardiac signaling networks

Cardiac signaling networks exhibit considerable complexity in size and connectivity. The intrinsic complexity of these networks complicates the interpretation of experimental findings. This motivates new methods for investigating the mechanisms regulating cardiac signaling networks and the consequences these networks have on cardiac physiology and disease. Next-generation experimental techniques are also generating a wealth of genomic and proteomic data that can be difficult to analyze or interpret. Computational models are poised to play a key role in addressing these challenges. Computational models have a long history in contributing to the understanding of cardiac physiology and are useful for identifying biological mechanisms, inferring multiscale consequences to cell signaling activities and reducing the complexity of large data sets. Models also integrate well with experimental studies to explain experimental observations and generate new hypotheses. Here, we review the contributions computational modeling approaches have made to the analysis of cardiac signaling networks and forecast opportunities for computational models to accelerate cardiac signaling research.

Electrophysiological remodeling in heart failure

Heart failure affects nearly 6 million Americans, with a half-million new cases emerging each year. Whereas up to 50% of heart failure patients die of arrhythmia, the diverse mechanisms underlying heart failure-associated arrhythmia are poorly understood. As a consequence, effectiveness of antiarrhythmic pharmacotherapy remains elusive. Here, we review recent advances in our understanding of heart failure-associated molecular events impacting the electrical function of the myocardium. We approach this from an anatomical standpoint, summarizing recent insights gleaned from pre-clinical models and discussing their relevance to human heart failure.