Acute regional left atrial ischemia causes acceleration of atrial drivers during atrial fibrillation

Attenuating persistent sodium current-induced atrial myopathy and fibrillation by preventing mitochondrial oxidative stress

Mechanistically driven therapies for atrial fibrillation (AF), the most common cardiac arrhythmia, are urgently needed, the development of which requires improved understanding of the cellular signaling pathways that facilitate the structural and electrophysiological remodeling that occurs in the atria. Similar to humans, increased persistent Na+ current leads to the development of an atrial myopathy and spontaneous and long-lasting episodes of AF in mice. How increased persistent Na+ current causes both structural and electrophysiological remodeling in the atria is unknown. We crossbred mice expressing human F1759A-NaV1.5 channels with mice expressing human mitochondrial catalase (mCAT). Increased expression of mCAT attenuated mitochondrial and cellular reactive oxygen species (ROS) and the structural remodeling that was induced by persistent F1759A-Na+ current. Despite the heterogeneously prolonged atrial action potential, which was unaffected by the reduction in ROS, the incidences of spontaneous AF, pacing-induced after-depolarizations, and AF were substantially reduced. Expression of mCAT markedly reduced persistent Na+ current-induced ryanodine receptor oxidation and dysfunction. In summary, increased persistent Na+ current in atrial cardiomyocytes, which is observed in patients with AF, induced atrial enlargement, fibrosis, mitochondrial dysmorphology, early after-depolarizations, and AF, all of which can be attenuated by resolving mitochondrial oxidative stress.

Acute atrial ischemia associates with early but not late new-onset atrial fibrillation in STEMI patients treated with primary PCI: relationship with in-hospital outcomes

BACKGROUND

New-onset atrial fibrillation (NOAF), both early (EAF) or late (LAF), may complicate ST-segment elevation myocardial infarction (STEMI). The mechanisms underlying EAF or LAF are poorly described. We investigated atrial branch occlusion and EAF or LAF onset in STEMI patients undergoing primary percutaneous coronary intervention.

METHODS

This was a retrospective cohort study including 155 STEMI patients. Patients were divided into 3 groups: sinus rhythm (SR), EAF, or LAF. Clinical characteristics, angiographic features including occlusion of atrial branches, namely ramus ostia cavae superioris (ROCS), atrio-ventricular node artery (AVNA), right intermediate atrial artery (RIAA), and left intermediate atrial artery, were assessed. We also investigated in-hospital adverse events (AEs) and death.

RESULTS

Mean age was 63.8±11.9 years; 78.7% were men. NOAF was detected in 22 (14.2%) patients: 10 (6.4%) EAF and 12 LAF (7.7%). Compared to EAF, LAF patients were older (p=0.013), with higher GRACE risk score (p=0.014) and Killip class (p=0.015), depressed ejection fraction (p=0.007), elevated filling pressures (p=0.029), higher C-reactive protein (p=0.014) and more with thrombolysis in myocardial infarction flow <3 (p=0.015). Compared to SR, EAF was associated with higher prevalence of occluded ROCS (p=0.010), AVNA (p=0.005), and RIAA (p<0.001). Moreover, EAF patients had more frequently ≥2 diseased atrial branches than SR (19.5%, p<0.001) and LAF (25%, p<0.030) patients. LAF patients had a higher in-hospital AEs (p=0.019 vs SR; p=0.029 vs EAF) and death (p=0.004 vs SR).

CONCLUSIONS

The occlusion of atrial branches is associated with EAF but not LAF following STEMI. LAF patients had worse in-hospital AEs and mortality.

Theoretical Models and Computational Analysis of Action Potential Dispersion for Cardiac Arrhythmia Risk Stratification

Reentrant cardiac arrhythmias such as atrial fibrillation (AF) and ventricular fibrillation (VF) are common cardiac arrhythmias that account for substantial morbidity and mortality throughout the world. However, the mechanisms and optimal ablation treatment strategies for such arrhythmias are still unclear. Using 2D optical mapping of a mouse model with AF and VF, we have identified regional heterogeneity of the action potential duration (APD) in the atria and ventricles of the heart as key drivers for the initiation and persistence of reentry. The purpose of this paper is to discuss theoretical patterns of dispersion, demonstrate patterns of dispersion seen in our mouse model and discuss the computational analysis of APD dispersion patterns. These analyses and discussions may lead to better understanding of dispersion patterns in patients with these arrhythmias, as well as help comprehend whether and how reducing dispersion can lead to arrhythmia risk stratification and treatment strategies for arrhythmias.

Fibroblast growth factor homologous factors tune arrhythmogenic late NaV1.5 current in calmodulin binding-deficient channels

The Ca2+-binding protein calmodulin has emerged as a pivotal player in tuning Na+ channel function, although its impact in vivo remains to be resolved. Here, we identify the role of calmodulin and the NaV1.5 interactome in regulating late Na+ current in cardiomyocytes. We created transgenic mice with cardiac-specific expression of human NaV1.5 channels with alanine substitutions for the IQ motif (IQ/AA). The mutations rendered the channels incapable of binding calmodulin to the C-terminus. The IQ/AA transgenic mice exhibited normal ventricular repolarization without arrhythmias and an absence of increased late Na+ current. In comparison, transgenic mice expressing a lidocaine-resistant (F1759A) human NaV1.5 demonstrated increased late Na+ current and prolonged repolarization in cardiomyocytes, with spontaneous arrhythmias. To determine regulatory factors that prevent late Na+ current for the IQ/AA mutant channel, we considered fibroblast growth factor homologous factors (FHFs), which are within the NaV1.5 proteomic subdomain shown by proximity labeling in transgenic mice expressing NaV1.5 conjugated to ascorbate peroxidase. We found that FGF13 diminished late current of the IQ/AA but not F1759A mutant cardiomyocytes, suggesting that endogenous FHFs may serve to prevent late Na+ current in mouse cardiomyocytes. Leveraging endogenous mechanisms may furnish an alternative avenue for developing novel pharmacology that selectively blunts late Na+ current.

Cardiac arrhythmias in patients with COVID-19

The emergence of coronavirus disease 2019 (COVID-19), caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has become a major global public health concern. Although SARS-CoV-2 causes primarily respiratory problems, concurrent cardiac injury cannot be ignored since it may be an independent predictor for adverse outcomes. Cardiac arrhythmias are often observed in patients with COVID-19, especially in severe cases, and more likely contribute to the high risk of adverse outcomes. Arrhythmias should be regarded as one of the main complications of COVID-19. Mechanistically, a number of ion channels can be adversely affected in COVID-19, leading to alterations in cardiac conduction and/or repolarization properties, as well as calcium handling, which can predispose to cardiac arrhythmogenesis. In addition, several antimicrobials that are currently used as potential therapeutic agents for COVID-19, such as chloroquine, hydroxychloroquine and azithromycin, have uncertain benefit, and yet may induce electrocardiographic QT prolongation with potential ventricular pro-arrhythmic effects. Continuous electrocardiogram monitoring, accurate and prompt recognition of arrhythmias are important. The present review focuses on cardiac arrhythmias in patients with COVID-19, its underlying mechanisms, and proposed preventive and therapeutic strategies.

Dietary Saturated Fat Promotes Arrhythmia by Activating NOX2 (NADPH Oxidase 2)

BACKGROUND

Obesity and diets high in saturated fat increase the risk of arrhythmias and sudden cardiac death. However, the molecular mechanisms are not well understood. We hypothesized that an increase in dietary saturated fat could lead to abnormalities of calcium homeostasis and heart rhythm by a NOX2 (NADPH oxidase 2)-dependent mechanism.

METHODS

We investigated this hypothesis by feeding mice high-fat diets. In vivo heart rhythm telemetry, optical mapping, and isolated cardiac myocyte imaging were used to quantify arrhythmias, repolarization, calcium transients, and intracellular calcium sparks.

RESULTS

We found that saturated fat activates NOX (NADPH oxidase), whereas polyunsaturated fat does not. The high saturated fat diet increased repolarization heterogeneity and ventricular tachycardia inducibility in perfused hearts. Pharmacological inhibition or genetic deletion of NOX2 prevented arrhythmogenic abnormalities in vivo during high statured fat diet and resulted in less inducible ventricular tachycardia. High saturated fat diet activates CaMK (Ca2+/calmodulin-dependent protein kinase) in the heart, which contributes to abnormal calcium handling, promoting arrhythmia.

CONCLUSIONS

We conclude that NOX2 deletion or pharmacological inhibition prevents the arrhythmogenic effects of a high saturated fat diet, in part mediated by activation of CaMK. This work reveals a molecular mechanism linking cardiac metabolism to arrhythmia and suggests that NOX2 inhibitors could be a novel therapy for heart rhythm abnormalities caused by cardiac lipid overload.

Association of of Atrial Fibrillation Clinical Phenotypes With Treatment Patterns and Outcomes: A Multicenter Registry Study

Importance

Atrial fibrillation (AF) is usually classified on the basis of the disease subtype. However, this characterization does not capture the full heterogeneity of AF, and a data-driven cluster analysis reveals different possible classifications of patients.

Objective

To characterize patients with AF based on a cluster analysis and to evaluate the association between these phenotypes, treatment, and clinical outcomes.

Design, Setting, and Participants

This cluster analysis used data from an observational cohort that included 9749 patients with AF who had been admitted to 174 US sites participating in the Outcomes Registry for Better Informed Treatment of Atrial Fibrillation (ORBIT-AF) registry. Data analysis was completed from January 2017 to October 2017.

Exposure

Patients with diagnosed AF who were included in the registry.

Main Outcomes and Measures

Composite of major adverse cardiovascular or neurological events and major bleeding, as defined by the International Society of Thrombosis and Hemostasis criteria.

Results

Of 9749 total patients, 4150 (42.6%) were female; 8719 (89.4%) were white and 477 (4.9%) were African American. A cluster analysis was performed using 60 baseline clinical characteristics, and it classified patients with AF into 4 statistically driven clusters: (1) those with considerably lower rates of risk factors and comorbidities than all other clusters (n = 4673); (2) those with AF at younger ages and/or with comorbid behavioral disorders (n = 963); (3) those with AF who had similarities to patients with tachycardia-brachycardia and had device implantation owing to sinus node dysfunction (n = 1651); and (4) those with AF and prior coronary artery disease, myocardial infarction, and/or atherosclerotic comorbidities (n = 2462). Conventional classifications, such as AF subtype and left atrial size, did not drive cluster formation. Compared with the low comorbidity AF cluster, adjusted risks of major adverse cardiovascular or neurological events were significantly higher in the other 3 clusters (behavioral comorbidity cluster: hazard ratio [HR], 1.49; 95% CI, 1.10-2.00; device implantation cluster: HR, 1.39; 95% CI, 1.15-1.68; and atherosclerotic comorbidity cluster: HR, 1.59; 95% CI, 1.31-1.92). For major bleeding, adjusted risks were higher in the behavioral disorder comorbidity cluster (HR, 1.35; 95% CI, 1.05-1.73), those with device implantation (HR, 1.24; 95% CI, 1.05-1.47), and those with atherosclerotic comorbidities (HR, 1.13; 95% CI, 0.96-1.33) compared with the low comorbidity cluster. The same clusters were identified in an external validation in the ORBIT AF II registry.

Conclusions and Relevance

Cluster analysis identified 4 clinically relevant phenotypes of AF that each have distinct associations with clinical outcomes, underscoring the heterogeneity of AF and importance of comorbidities and substrates.

Heterogeneity of the action potential duration is required for sustained atrial fibrillation

Atrial fibrillation (AF) is the most common cardiac arrhythmia and accounts for substantial morbidity and mortality. Recently, we created a mouse model with spontaneous and sustained AF caused by a mutation in the NaV1.5 channel (F1759A) that enhances persistent Na+ current, thereby enabling the investigation of molecular mechanisms that cause AF and the identification of novel treatment strategies. The mice have regional heterogeneity of action potential duration of the atria similar to observations in patients with AF. In these mice, we found that the initiation and persistence of the rotational reentrant AF arrhythmias, known as spiral waves or rotors, were dependent upon action potential duration heterogeneity. The centers of the rotors were localized to regions of greatest heterogeneity of the action potential duration. Pharmacologically attenuating the action potential duration heterogeneity reduced both spontaneous and pacing-induced AF. Computer-based simulations also demonstrated that the action potential duration heterogeneity is sufficient to generate rotors that manifest as AF. Taken together, these findings suggest that action potential duration heterogeneity in mice and humans is one mechanism by which AF is initiated and that reducing action potential duration heterogeneity can lessen the burden of AF.

Atrial Infarction and Ischemic Mitral Regurgitation Contribute to Post-MI Remodeling of the Left Atrium

BACKGROUND

Left atrial (LA) remodeling after an acute myocardial infarction (MI) is poorly characterized regarding its determinants or its effect on ischemic mitral regurgitation (MR) development.

OBJECTIVES

The purpose of this study was: 1) to compare LA structural remodeling in experimental MI swine models recapitulating the effects of left ventricular (LV) dysfunction, ischemic MR, and left atrial infarction (LAI); and 2) to analyze how LA remodeling influences ischemic MR development.

METHODS

Three models of MI were generated: 1) proximal left circumflex (LCx) coronary artery occlusion involving the LA branch (LAI group); 2) proximal LCx occlusion not involving the LA branch (LCx group); and 3) left anterior descending (LAD) occlusion (LAD group). Serial cardiac magnetic resonance scans were performed to define LA and LV remodeling and ischemic MR, and were correlated with histology.

RESULTS

Occlusion of the LA branch (LAI group) induced a greater degree of LA dilation at 1 and 8 weeks post-MI than the LCx and LAD groups, along with early and severe impairment of LA function. In the LCx and LAD groups, LA dysfunction was less pronounced and not consistent. Development of ischemic MR was more pronounced in the LAI group than in the LCx group. Histology confirmed atrial infarction with extensive fibrosis in the LAI group and interstitial fibrosis in the LCx group. In the LAD group, LA remodeling was not observed by cardiac magnetic resonance or histology.

CONCLUSIONS

We provide the first experimental evidence of the deleterious effect of acute LAI on atrial structural remodeling, characterized by early LA dilation, dysfunction, and fibrosis, and early occurrence of ischemic MR.

Cell-selective arrhythmia ablation for photomodulation of heart rhythm

Heart disease, a leading cause of death in the developed world, is overwhelmingly correlated with arrhythmias, where heart muscle cells, myocytes, beat abnormally. Cardiac arrhythmias are usually managed by electric shock intervention, antiarrhythmic drugs, surgery, and/or catheter ablation. Despite recent improvements in techniques, ablation procedures are still limited by the risk of complications from unwanted cellular damage, caused by the nonspecific delivery of ablative energy to all heart cell types. We describe an engineered nanoparticle containing a cardiac-targeting peptide (CTP) and a photosensitizer, chlorin e6 (Ce6), for specific delivery to myocytes. Specificity was confirmed in vitro using adult rat heart cell and human stem cell-derived cardiomyocyte and fibroblast cocultures. In vivo, the CTP-Ce6 nanoparticles were injected intravenously into rats and, upon laser illumination of the heart, induced localized, myocyte-specific ablation with 85% efficiency, restoring sinus rhythm without collateral damage to other cell types in the heart, such as fibroblasts. In both sheep and rat hearts ex vivo, upon perfusion of CTP-Ce6 particles, laser illumination led to the formation of a complete electrical block at the ablated region and restored the physiological rhythm of the heart. This nano-based, cell-targeted approach could improve ablative technologies for patients with arrhythmias by reducing currently encountered complications.

Electrochemical degradation of trichloroethylene in aqueous solution by bipolar graphite electrodes

In this study, we tested the use of the bipolar electrodes to enhance electrochemical degradation of trichloroethylene (TCE) in an undivided, flow-through electrochemical reactor. The bipolar electrode forms when an electrically conductive material polarizes between feeder electrodes that are connected to a direct current source and, therefore, creates an additional anode/cathode pair in the system. We hypothesize that bipolar electrodes will generate additional oxidation/reduction zones to enhance TCE degradation. The graphite cathode followed by graphite anode sequence were operated without a bipolar electrode as well as with one and two bipolar graphite electrodes. The system without bipolar electrodes degraded 29% of TCE while the system with one and two bipolar electrodes degraded 38% and 66% of TCE, respectively. It was found that the removal mechanism for TCE in bipolar mode includes hydrodechlorination at the feeder cathode, and oxidation through reaction with peroxide. The results show that the bipolar electrodes presence enhance TCE removal efficiency and rate and imply that they can be used to improve electrochemical treatment of contaminated groundwater.

Risk factors and genetics of atrial fibrillation

Atrial fibrillation (AF) is by far the most common sustained tachyarrhythmia, affecting 1% to 2% of the general population. AF prevalence and the total annual cost for treatment are alarming, emphasizing the need for an urgent attention to the problem. Thus, having up-to-date information on AF risk factors and appreciating how they promote maintenance of AF maintenance are essential. This article presents a simplified examination of AF risk factors, including emerging genetic risks.

Digital resolution enhancement of intracardiac excitation maps during atrial fibrillation

Atrial fibrillation (AF) is often successfully treated by catheter ablation. Those cases of AF that do not readily succumb to ablation therapy would benefit from improved methods for mapping the complex spatial patterns of tissue activation that typify recalcitrant AF. To this end, the purpose of our study was to investigate the use of numerical deconvolution to improve the spatial resolution of activation maps provided by 2-D arrays of intra-cardiac recording electrodes. We simulated tissue activation patterns and their corresponding electric potential maps using a computational model of cardiac electrophysiology, and sampled the maps over a grid of locations to generate a mapping data set. Following cubic spline interpolation, followed by edge-extension and windowing, we deconvolved the data and compared the results to the model current density fields. We performed a similar analysis on voltage-sensitive dye maps obtained in isolated sheep hearts. For both the synthetic data and the voltage-sensitive dye maps, we found that deconvolution led to visually improved map resolution for arrays of 10×10 up to 30×30 electrodes placed within a few mm of the atrial surface when the activation patterns included 3-4 features that spanned the recording area. Root mean square error was also reduced by deconvolution. Deconvolution of arrays of intracardiac potentials, preceded by appropriate interpolation and edge processing, leads to potentially useful improvements in map resolution that may allow more effective assessment of the spatiotemporal dynamics of tissue excitation during AF.

Cardiac Events Theoretically Cannot Be Produced By Non-Ischemic And/Or Iso-Ischemic Myocardium: Challenging Postulations And Vitality Of The Concept Of "Ischemia-Dependent Conflictogenic Arrhythmias"

Ischemia plays a key role in cardiac arrhythmogenesis, particularly in elderly patients. Healthy, non-ischemic and structurally normal myocardium is universally free from dysrhythmias. Thereby intact coronary blood flow prevents potential cardiac events. Hypothetically, ischemia-related electrophysiological differences are responsible for the supraventricular and/or ventricular rhythm irregularities. The goal of this review is to determine the role of systemic and coronary circulatory peculiarities and their association with heart rhythm abnormalities. The current analytical review extends and enriches previous knowledge about the influence of these peculiarities on the genesis of ischemia-dependent conflictogenic arrhythmias. Different intensity of coronary blood flow resulting from stenotic obstacles or vasospasm potentially leads to the non-uniform perfusion of myocites thus creating albeit subtle but vulnerable and powerful electrophysiologic substrate impending cardiac rhythm disturbances. Apparently, the behavior of both non-ischemic and iso-ischemic myocardium in respect to electric cardiac activity is very similar, at least theoretically. Some different clinical entities, e.g. arterial hypotension and/or anemia containing ischemic component, in most cases are free from arrhythmias. This postulation may be helpful in furthering arrhythmogenicity insights which have been generated previously. On the contrary, increased blood pressure often concurs with the supraventricular and/or ventricular arrhythmias; this pattern also favorably reflects our previous hypothetical assumptions associated with the mechanisms of arrhythmogenesis. Conclusively, both non-ischemic and iso-ischemic myocardium may be attributed to nonarrhythmogenic milieu. Nevertheless, the inventive analysis and more explorative data are required to support the suggested postulations.