Translational Challenges in Atrial Fibrillation

Computational modeling of cardiac electrophysiology and arrhythmogenesis: toward clinical translation

The complexity of cardiac electrophysiology, involving dynamic changes in numerous components across multiple spatial (from ion channel to organ) and temporal (from milliseconds to days) scales, makes an intuitive or empirical analysis of cardiac arrhythmogenesis challenging. Multiscale mechanistic computational models of cardiac electrophysiology provide precise control over individual parameters, and their reproducibility enables a thorough assessment of arrhythmia mechanisms. This review provides a comprehensive analysis of models of cardiac electrophysiology and arrhythmias, from the single cell to the organ level, and how they can be leveraged to better understand rhythm disorders in cardiac disease and to improve heart patient care. Key issues related to model development based on experimental data are discussed, and major families of human cardiomyocyte models and their applications are highlighted. An overview of organ-level computational modeling of cardiac electrophysiology and its clinical applications in personalized arrhythmia risk assessment and patient-specific therapy of atrial and ventricular arrhythmias is provided. The advancements presented here highlight how patient-specific computational models of the heart reconstructed from patient data have achieved success in predicting risk of sudden cardiac death and guiding optimal treatments of heart rhythm disorders. Finally, an outlook toward potential future advances, including the combination of mechanistic modeling and machine learning/artificial intelligence, is provided. As the field of cardiology is embarking on a journey toward precision medicine, personalized modeling of the heart is expected to become a key technology to guide pharmaceutical therapy, deployment of devices, and surgical interventions.

Electrophysiological Effects of the Sodium-Glucose Co-Transporter-2 (SGLT2) Inhibitor Dapagliflozin on Human Cardiac Potassium Channels

The sodium-glucose co-transporter-2 (SGLT2) inhibitor dapagliflozin is increasingly used in the treatment of diabetes and heart failure. Dapagliflozin has been associated with reduced incidence of atrial fibrillation (AF) in clinical trials. We hypothesized that the favorable antiarrhythmic outcome of dapagliflozin use may be caused in part by previously unrecognized effects on atrial repolarizing potassium (K+) channels. This study was designed to assess direct pharmacological effects of dapagliflozin on cloned ion channels Kv11.1, Kv1.5, Kv4.3, Kir2.1, K2P2.1, K2P3.1, and K2P17.1, contributing to IKur, Ito, IKr, IK1, and IK2P K+ currents. Human channels coded by KCNH2, KCNA5, KCND3, KCNJ2, KCNK2, KCNK3, and KCNK17 were heterologously expressed in Xenopus laevis oocytes, and currents were recorded using the voltage clamp technique. Dapagliflozin (100 µM) reduced Kv11.1 and Kv1.5 currents, whereas Kir2.1, K2P2.1, and K2P17.1 currents were enhanced. The drug did not significantly affect peak current amplitudes of Kv4.3 or K2P3.1 K+ channels. Biophysical characterization did not reveal significant effects of dapagliflozin on current-voltage relationships of study channels. In conclusion, dapagliflozin exhibits direct functional interactions with human atrial K+ channels underlying IKur, IKr, IK1, and IK2P currents. Substantial activation of K2P2.1 and K2P17.1 currents could contribute to the beneficial antiarrhythmic outcome associated with the drug. Indirect or chronic effects remain to be investigated in vivo.

Reduced plakoglobin increases the risk of sodium current defects and atrial conduction abnormalities in response to androgenic anabolic steroid abuse

Androgenic anabolic steroids (AAS) are commonly abused by young men. Male sex and increased AAS levels are associated with earlier and more severe manifestation of common cardiac conditions, such as atrial fibrillation, and rare ones, such as arrhythmogenic right ventricular cardiomyopathy (ARVC). Clinical observations suggest a potential atrial involvement in ARVC. Arrhythmogenic right ventricular cardiomyopathy is caused by desmosomal gene defects, including reduced plakoglobin expression. Here, we analysed clinical records from 146 ARVC patients to identify that ARVC is more common in males than females. Patients with ARVC also had an increased incidence of atrial arrhythmias and P wave changes. To study desmosomal vulnerability and the effects of AAS on the atria, young adult male mice, heterozygously deficient for plakoglobin (Plako+/- ), and wild type (WT) littermates were chronically exposed to 5α-dihydrotestosterone (DHT) or placebo. The DHT increased atrial expression of pro-hypertrophic, fibrotic and inflammatory transcripts. In mice with reduced plakoglobin, DHT exaggerated P wave abnormalities, atrial conduction slowing, sodium current depletion, action potential amplitude reduction and the fall in action potential depolarization rate. Super-resolution microscopy revealed a decrease in NaV 1.5 membrane clustering in Plako+/- atrial cardiomyocytes after DHT exposure. In summary, AAS combined with plakoglobin deficiency cause pathological atrial electrical remodelling in young male hearts. Male sex is likely to increase the risk of atrial arrhythmia, particularly in those with desmosomal gene variants. This risk is likely to be exaggerated further by AAS use. KEY POINTS: Androgenic male sex hormones, such as testosterone, might increase the risk of atrial fibrillation in patients with arrhythmogenic right ventricular cardiomyopathy (ARVC), which is often caused by desmosomal gene defects (e.g. reduced plakoglobin expression). In this study, we observed a significantly higher proportion of males who had ARVC compared with females, and atrial arrhythmias and P wave changes represented a common observation in advanced ARVC stages. In mice with reduced plakoglobin expression, chronic administration of 5α-dihydrotestosterone led to P wave abnormalities, atrial conduction slowing, sodium current depletion and a decrease in membrane-localized NaV 1.5 clusters. 5α-Dihydrotestosterone, therefore, represents a stimulus aggravating the pro-arrhythmic phenotype in carriers of desmosomal mutations and can affect atrial electrical function.

Circulating exosome long non-coding RNAs are associated with atrial structural remodeling by increasing systemic inflammation in atrial fibrillation patients

Background

Atrial fibrillation (AF) is the most common cardiac arrhythmia with severe clinical sequelae, but its genetic characteristic implicated in pathogenesis has not been completely clarified. Accumulating evidence has indicated that circulating exosomes and their carried cargoes, such as long non-coding RNAs (lncRNAs), involve in the progress of multiple cardiovascular diseases. However, their potential role as clinical biomarkers in AF diagnosis and prognosis remains unknown.

Methods

Herein, we conducted the sequence and bioinformatic analysis of circulating exosomes harvested from AF and sinus rhythm patients.

Results

A total of 53 differentially expressed lncRNAs were identified, and a total of 6 significantly changed lncRNAs (fold change > 2.0), including NR0046235, NR003045, NONHSAT167247.1, NONHSAT202361.1, NONHSAT205820.1 and NONHSAT200958.1, were verified by qRT-PCR in 215 participants. Moreover, these circulating exosome lncRNA levels were different between paroxysmal and persistent AF patients, which were dramatically associated with abnormal hemodynamics and atrial diameter. Furthermore, we observed that the area under ROC curve (AUC) of six lncRNAs combination for diagnosis of persistent AF was 80.34%. Gene ontology (GO) and Kyoto encyclopedia of genes and genomes (KEGG) enrichment pathway analysis indicated these exosome lncRNAs mainly concerning response to chemokine-chemokine receptor interaction, which induced activated inflammation and structural remodeling. In addition, increased plasma levels of CXCR3 ligands, including CXCL4, CXCL9, CXCL10 and CXCL11, were accumulated in AF patient tissues.

Conclusion

Our study provides the transcriptome profile revealing pattern of circulating exosome lncRNAs in atrial structural remodeling, which bring valuable insights into improving prognosis and therapeutic targets for AF.

A novel ablation strategy for recurrent atrial fibrillation: Fractionated signal area in the atrial muscle ablation 1-year follow-up

INTRODUCTION

Treatment of recurrent atrial fibrillation (AF) is sometimes challenging due to non-pulmonary vein (PV) foci. Fractionated signal area in the atrial muscle (FAAM) is a valid predictor of the location of non-PV foci. FAAM ablation has the potential to decrease the recurrence rate of atrial tachyarrhythmia in patients with recurrent AF. We compared the clinical impact of FAAM ablation for recurrent AF, using 1 year follow up date.

METHODS

A total of 230 consecutive patients with symptomatic recurrent AF who underwent catheter ablation specifically targeting non-PV foci as FAAM-guided ablation (n = 113) and non-FAAM-guided ablation (n = 117) were retrospectively analyzed. FAAM was assigned a parameter (peaks slider, which indicates the number of components of fractionated signals), ranging from 1 to 15, indicating the location of the FAAM (1: largest, 15: smallest). FAAM-guided ablation was performed by ablating FAAM until none inducibility of non-PV foci. On the other hand, non-FAAM-guided ablation was performed via linear ablation, complex fractionated atrial electrogram ablation, superior vena cava isolation, and focal ablation according to the location of the non-PV foci. The RHYTHMIA system was used to perform all the procedures. The primary endpoints were AF recurrence, atrial flutter, and/or atrial tachycardia.

RESULTS

After a 1-year follow up, freedom from atrial tachyarrhythmia was achieved in 90.3% and 75.2% of patients in the FAAM and non-FAAM groups, respectively (hazard ratio = 0.438 [95% confidence interval: 0.243-0.788], p  =  .005).

CONCLUSIONS

FAAM ablation showed a promising decrease in the recurrence rate of atrial tachyarrhythmia in patients with recurrent AF during a 1-year follow-up.

Integrative human atrial modelling unravels interactive protein kinase A and Ca2+/calmodulin-dependent protein kinase II signalling as key determinants of atrial arrhythmogenesis

AIMS

Atrial fibrillation (AF), the most prevalent clinical arrhythmia, is associated with atrial remodelling manifesting as acute and chronic alterations in expression, function, and regulation of atrial electrophysiological and Ca2+-handling processes. These AF-induced modifications crosstalk and propagate across spatial scales creating a complex pathophysiological network, which renders AF resistant to existing pharmacotherapies that predominantly target transmembrane ion channels. Developing innovative therapeutic strategies requires a systems approach to disentangle quantitatively the pro-arrhythmic contributions of individual AF-induced alterations.

METHODS AND RESULTS

Here, we built a novel computational framework for simulating electrophysiology and Ca2+-handling in human atrial cardiomyocytes and tissues, and their regulation by key upstream signalling pathways [i.e. protein kinase A (PKA), and Ca2+/calmodulin-dependent protein kinase II (CaMKII)] involved in AF-pathogenesis. Populations of atrial cardiomyocyte models were constructed to determine the influence of subcellular ionic processes, signalling components, and regulatory networks on atrial arrhythmogenesis. Our results reveal a novel synergistic crosstalk between PKA and CaMKII that promotes atrial cardiomyocyte electrical instability and arrhythmogenic triggered activity. Simulations of heterogeneous tissue demonstrate that this cellular triggered activity is further amplified by CaMKII- and PKA-dependent alterations of tissue properties, further exacerbating atrial arrhythmogenesis.

CONCLUSIONS

Our analysis reveals potential mechanisms by which the stress-associated adaptive changes turn into maladaptive pro-arrhythmic triggers at the cellular and tissue levels and identifies potential anti-AF targets. Collectively, our integrative approach is powerful and instrumental to assemble and reconcile existing knowledge into a systems network for identifying novel anti-AF targets and innovative approaches moving beyond the traditional ion channel-based strategy.

What determines the optimal pharmacological treatment of atrial fibrillation? Insights from in silico trials in 800 virtual atria

The best pharmacological treatment for each atrial fibrillation (AF) patient is unclear. We aim to exploit AF simulations in 800 virtual atria to identify key patient characteristics that guide the optimal selection of anti-arrhythmic drugs. The virtual cohort considered variability in electrophysiology and low voltage areas (LVA) and was developed and validated against experimental and clinical data from ionic currents to ECG. AF sustained in 494 (62%) atria, with large inward rectifier K+ current (IK1 ) and Na+ /K+ pump (INaK ) densities (IK1 0.11 ± 0.03 vs. 0.07 ± 0.03 S mF-1 ; INaK 0.68 ± 0.15 vs. 0.38 ± 26 S mF-1 ; sustained vs. un-sustained AF). In severely remodelled left atrium, with LVA extensions of more than 40% in the posterior wall, higher IK1 (median density 0.12 ± 0.02 S mF-1 ) was required for AF maintenance, and rotors localized in healthy right atrium. For lower LVA extensions, rotors could also anchor to LVA, in atria presenting short refractoriness (median L-type Ca2+ current, ICaL , density 0.08 ± 0.03 S mF-1 ). This atrial refractoriness, modulated by ICaL and fast Na+ current (INa ), determined pharmacological treatment success for both small and large LVA. Vernakalant was effective in atria presenting long refractoriness (median ICaL density 0.13 ± 0.05 S mF-1 ). For short refractoriness, atria with high INa (median density 8.92 ± 2.59 S mF-1 ) responded more favourably to amiodarone than flecainide, and the opposite was found in atria with low INa (median density 5.33 ± 1.41 S mF-1 ). In silico drug trials in 800 human atria identify inward currents as critical for optimal stratification of AF patient to pharmacological treatment and, together with the left atrial LVA extension, for accurately phenotyping AF dynamics. KEY POINTS: Atrial fibrillation (AF) maintenance is facilitated by small L-type Ca2+ current (ICaL ) and large inward rectifier K+ current (IK1 ) and Na+ /K+ pump. In severely remodelled left atrium, with low voltage areas (LVA) covering more than 40% of the posterior wall, sustained AF requires higher IK1 and rotors localize in healthy right atrium. For lower LVA extensions, rotors can also anchor to LVA, if the atria present short refractoriness (low ICaL ) Vernakalant is effective in atria presenting long refractoriness (high ICaL ). For short refractoriness, atria with fast Na+ current (INa ) up-regulation respond more favourably to amiodarone than flecainide, and the opposite is found in atria with low INa . The inward currents (ICaL and INa ) are critical for optimal stratification of AF patient to pharmacological treatment and, together with the left atrial LVA extension, for accurately phenotyping AF dynamics.

In Vitro Models for Improved Therapeutic Interventions in Atrial Fibrillation

Atrial fibrillation is the most common type of cardiac arrhythmias in humans, mostly caused by hyper excitation of specific areas in the atrium resulting in dyssynchronous atrial contractions, leading to severe consequences such as heart failure and stroke. Current therapeutics aim to target this condition through both pharmacological and non-pharmacological approaches. To test and validate any of these treatments, an appropriate preclinical model must be carefully chosen to refine and optimise the therapy features to correctly reverse this condition. A broad range of preclinical models have been developed over the years, with specific features and advantages to closely mimic the pathophysiology of atrial fibrillation. In this review, currently available models are described, from traditional animal models and in vitro cell cultures to state-of-the-art organoids and organs-on-a-chip. The advantages, applications and limitations of each model are discussed, providing the information to select the appropriate model for each research application.

Adiposity-associated atrial fibrillation: molecular determinants, mechanisms, and clinical significance

Obesity is an important contributing factor to the pathophysiology of atrial fibrillation (AF) and its complications by causing systemic changes, such as altered haemodynamic, increased sympathetic tone, and low-grade chronic inflammatory state. In addition, adipose tissue is a metabolically active organ that comprises various types of fat deposits with discrete composition and localization that show distinct functions. Fatty tissue differentially affects the evolution of AF, with highly secretory active visceral fat surrounding the heart generally having a more potent influence than the rather inert subcutaneous fat. A variety of proinflammatory, profibrotic, and vasoconstrictive mediators are secreted by adipose tissue, particularly originating from cardiac fat, that promote atrial remodelling and increase the susceptibility to AF. In this review, we address the role of obesity-related factors and in particular specific adipose tissue depots in driving AF risk. We discuss the distinct effects of key secreted adipokines from different adipose tissue depots and their participation in cardiac remodelling. The possible mechanistic basis and molecular determinants of adiposity-related AF are discussed, and finally, we highlight important gaps in current knowledge, areas requiring future investigation, and implications for clinical management.

An objective tool for quantifying atrial fibrillation substrate in rats

The utility of rodents for research related to atrial fibrillation (AF) is growing exponentially. However, the obtained arrhythmic waveforms are often mixed with ventricular signals and the ability to analyze regularity and complexity of such events is limited. Recently, we introduced an implantable quadripolar electrode adapted for advanced atrial electrophysiology in ambulatory rats. Notably, we have found that the implantation itself leads to progressive atrial remodeling, presumably because of mechanical loading of the atria. In the present study, we developed an algorithm to clean the atrial signals from ventricular mixing and thereafter quantify the AF substrate in an objective manner based on waveform complexity. Rats were sequentially examined 1-, 4-, and 8-wk postelectrode implantation using a standard AF triggering protocol. Preburst ventricular mixing was sampled and automatically subtracted based on QRS detection in the ECG. Thereafter, the "pure" atrial signals were analyzed by Lempel-Ziv complexity algorithm and a complexity ratio (CR) was defined for each signal by normalizing the postburst to the preburst values. Receiver operating characteristic (ROC) curve analysis indicated an optimal CR cutoff of 1.236 that detected irregular arrhythmic events with high sensitivity (94.5%), specificity (93.1%), and area under the curve (AUC) (0.96, 95% confidence interval, 0.945-0.976). Automated and unbiased analysis indicated a gradual increase in signal complexity over time with augmentation of high frequencies in power spectrum analysis. Our findings indicate that CR algorithm detects irregularity in a highly efficient manner and can also detect the atrial remodeling induced by electrode implantation. Thus, CR analysis can strongly facilitate standardized AF research in rodents.NEW & NOTEWORTHY Rodents are increasingly used in AF research. However, because of technical difficulties including atrial waveform mixing by ventricular signals, most studies do not discriminate between irregular (i.e., AF) and regular atrial arrhythmias. Here, we develop an unbiased computerized tool to "pure" the atrial signals from ventricular mixing and thereafter analyze AF substrate based on the level of irregularity in an objective manner. This novel tool can facilitate standardized AF research in rodents.

Heart rate characteristic based modelling of atrial fibrillatory rate using implanted cardiac monitor data

Objective. The objective of the present study is to investigate the feasibility of using heart rate characteristics to estimate atrial fibrillatory rate (AFR) in a cohort of atrial fibrillation (AF) patients continuously monitored with an implantable cardiac monitor. We will use a mixed model approach to investigate population effect and patient specific effects of heart rate characteristics on AFR, and will correct for the effect of previous ablations, episode duration, and onset date and time.Approach. The f-wave signals, from which AFR is estimated, were extracted using a QRST cancellation process of the AF episodes in a cohort of 99 patients (67% male; 57 ± 12 years) monitored for 9.2(0.2-24.3) months as median(min-max). The AFR from 2453 f-wave signals included in the analysis was estimated using a model-based approach. The association between AFR and heart rate characteristics, prior ablations, and episode-related features were modelled using fixed-effect and mixed-effect modelling approaches.Main results. The mixed-effect models had a better fit to the data than fixed-effect models showing h.c. of determination (R2 = 0.49 versusR2 = 0.04) when relating the variations of AFR to the heart rate features. However, when correcting for the other factors, the mixed-effect model showed the best fit (R2 = 0.04). AFR was found to be significantly affected by previous catheter ablations (p< 0.05), episode duration (p< 0.05), and irregularity of theRRinterval series (p< 0.05).Significance. Mixed-effect models are more suitable for AFR modelling. AFR was shown to be faster in episodes with longer duration, less organizedRRintervals and after several ablation procedures.

Inflammatory signalling in atrial cardiomyocytes: a novel unifying principle in atrial fibrillation pathophysiology

Inflammation has been implicated in atrial fibrillation (AF), a very common and clinically significant cardiac rhythm disturbance, but its precise role remains poorly understood. Work performed over the past 5 years suggests that atrial cardiomyocytes have inflammatory signalling machinery - in particular, components of the NLRP3 (NACHT-, LRR- and pyrin domain-containing 3) inflammasome - that is activated in animal models and patients with AF. Furthermore, work in animal models suggests that NLRP3 inflammasome activation in atrial cardiomyocytes might be a sufficient and necessary condition for AF occurrence. In this Review, we evaluate the evidence for the role and pathophysiological significance of cardiomyocyte NLRP3 signalling in AF. We first summarize the evidence for a role of inflammation in AF and review the biochemical properties of the NLRP3 inflammasome, as defined primarily in studies of classic inflammation. We then briefly consider the broader evidence for a role of inflammatory signalling in heart disease, particularly conditions that predispose individuals to develop AF. We provide a detailed discussion of the available information about atrial cardiomyocyte NLRP3 inflammasome signalling in AF and related conditions and evaluate the possibility that similar signalling might be important in non-myocyte cardiac cells. We then review the evidence on the role of active resolution of inflammation and its potential importance in suppressing AF-related inflammatory signalling. Finally, we consider the therapeutic potential and broader implications of this new knowledge and highlight crucial questions to be addressed in future research.

A training pipeline of an arrhythmia classifier for atrial fibrillation detection using Photoplethysmography signal

Photoplethysmography (PPG) signal is potentially suitable in atrial fibrillation (AF) detection for its convenience in use and similarity in physiological origin to electrocardiogram (ECG). There are a few preceding studies that have shown the possibility of using the peak-to-peak interval of the PPG signal (PPIp) in AF detection. However, as a generalized model, the accuracy of an AF detector should be pursued on the one hand; on the other hand, its generalizability should be paid attention to in view of the individual differences in PPG manifestation of even the same arrhythmia and the existence of sub-types. Moreover, a binary classifier for atrial fibrillation and normal sinus rhythm is not convincing enough for the similarity between AF and ectopic beats. In this study, we project the atrial fibrillation detection as a multiple-class classification and try to propose a training pipeline that is advantageous both to the accuracy and generalizability of the classifier by designing and determining the configurable options of the pipeline, in terms of input format, deep learning model (with hyperparameter optimization), and scheme of transfer learning. With a rigorous comparison of the possible combinations of the configurable components in the pipeline, we confirmed that first-order difference of heartbeat sequence as the input format, a 2-layer CNN-1-layer Transformer hybrid^R model as the learning model and the whole model fine-tuning as the implementing scheme of transfer learning is the best combination for the pipeline (F1 value: 0.80, overall accuracy: 0.87)^R.

Novel Pulmonary Delivery of Drugs for the Management of Atrial Fibrillation

Atrial fibrillation (AF) is the most prevalent cardiac arrhythmia, affecting approximately 335 million patients worldwide. Comprehensive pharmacological treatment of AF includes medications for rate or rhythm control and anticoagulants to reduce the risk of thromboembolism; yet, these agents have significant limitations. Oral anti-arrhythmic agents have a slow onset of action, and rapid onset formulations require hospitalization for intravenous therapy. Orally administered drugs also require high doses to attain therapeutic levels, and thus dose-related severe adverse effects are often unavoidable. Given the therapeutic benefits of inhaled drug delivery, including rapid onset of action and very low doses to achieve therapeutic efficacy, this review will discuss the benefits of novel pulmonary delivery of drugs for the management of AF.

Inhibition of EPAC1 signaling pathway alters atrial electrophysiology and prevents atrial fibrillation

Introduction: Atrial fibrillation (AF) is the most common sustained cardiac arrhythmia and is associated with increased mortality and morbidity. The Exchange Protein directly Activated by cAMP (EPAC), has been implicated in pro-arrhythmic signaling pathways in the atria, but the underlying mechanisms remain unknown. Methods: In this study, we investigated the involvement of EPAC1 and EPAC2 isoforms in the genesis of AF in wild type (WT) mice and knockout (KO) mice for EPAC1 or EPAC2. We also employed EPAC pharmacological modulators to selectively activate EPAC proteins (8-CPT-AM; 10 μM), or inhibit either EPAC1 (AM-001; 20 μM) or EPAC2 (ESI-05; 25 μM). Transesophageal stimulation was used to characterize the induction of AF in vivo in mice. Optical mapping experiments were performed on isolated mouse atria and cellular electrophysiology was examined by whole-cell patch-clamp technique. Results: In wild type mice, we found 8-CPT-AM slightly increased AF susceptibility and that this was blocked by the EPAC1 inhibitor AM-001 but not the EPAC2 inhibitor ESI-05. Consistent with this, in EPAC1 KO mice, occurrence of AF was observed in 3/12 (vs. 4/10 WT littermates) and 4/10 in EPAC2 KO (vs. 5/10 WT littermates). In wild type animals, optical mapping experiments revealed that 8-CPT-AM perfusion increased action potential duration even in the presence of AM-001 or ESI-05. Interestingly, 8-CPT-AM perfusion decreased conduction velocity, an effect blunted by AM-001 but not ESI-05. Patch-clamp experiments demonstrated action potential prolongation after 8-CPT-AM perfusion in both wild type and EPAC1 KO mice and this effect was partially prevented by AM-001 in WT. Conclusion: Together, these results indicate that EPAC1 and EPAC2 signaling pathways differentially alter atrial electrophysiology but only the EPAC1 isoform is involved in the genesis of AF. Selective blockade of EPAC1 with AM-001 prevents AF in mice.

Analysis of infiltrated immune cells in left atriums from patients with atrial fibrillation and identification of circRNA biomarkers for postoperative atrial fibrillation

Background: Atrial fibrillation (AF) increases the risk of stroke and heart failure. Postoperative AF (POAF) increases the risk of mortality after cardiac surgery. This study aims to explore mechanisms underlying AF, analyze infiltration of immune cells in left atrium (LA) from patients with AF, and identify potential circular RNA (circRNA) biomarkers for POAF. Methods: Raw data of GSE797689, GSE115574, and GSE97455 were downloaded and processed. AF-related gene co-expression network was constructed using weighted gene correlation network analysis and enrichment analysis of genes in relevant module was conducted. Gene set enrichment analysis (GSEA) and gene set variation analysis (GSVA) were applied to investigate pathways significantly enriched in AF group. Infiltration of immune cells was analyzed using single-sample GSEA. Differentially expressed genes (DEGs) between patients with or without AF were identified and competing endogenous RNA (ceRNA) networks of DEGs were constructed. To screen biomarkers for POAF, differentially expressed circRNAs (DEcircRNAs) between patients with or without POAF were identified. Intersection between DEcircRNAs and circRNAs in ceRNA networks of DEGs were extracted and circRNAs in the intersection were further screened using support vector machine, random forest, and neural network to identify biomarkers for POAF. Results: Three modules were found to be relevant with AF and enrichment analysis indicated that genes in these modules were enriched in synthesis of extracellular matrix and inflammatory response. The results of GSEA and GSVA suggested that inflammatory response-related pathways were significantly enriched in AF group. Immune cells like macrophages, mast cells, and neutrophils were significantly infiltrated in LA tissues from patients with AF. The expression levels of immune genes such as CHGB, HLA-DRA, LYZ, IGKV1-17 and TYROBP were significantly upregulated in patients with AF, which were correlated with infiltration of immune cells. ceRNA networks of DEGs were constructed and has_circ_0006314 and hsa_circ_0055387 were found to have potential predictive values for POAF. Conclusion: Synthesis of extracellular matrix and inflammatory response were main processes involved in development and progression of AF. Infiltration of immune cells was significantly different between patients with or without AF. Has_circ_0006314 and hsa_circ_0055387 were found to have potential predictive values for POAF.

Editorial (Preface) "Cells/Cells of the Cardiovascular System-Editorial Highlights 2020-2021: The Book Selection"

This introduction provides a preface to the section on "Cells of the Cardiovascular System" in the book entitled "Editor's Choice Articles in 2020-2021" [...].

Regions of Highly Recurrent Electrogram Morphology With Low Cycle Length Reflect Substrate for Atrial Fibrillation

Traditional anatomically guided ablation and attempts to perform electrogram-guided atrial fibrillation (AF) ablation (CFAE, DF, and FIRM) have not been shown to be sufficient treatment for persistent AF. Using biatrial high-density electrophysiologic mapping in a canine rapid atrial pacing model of AF, we systematically investigated the relationship of electrogram morphology recurrence (EMR) (Rec% and CL_R) with established AF electrogram parameters and tissue characteristics. Rec% correlates with stability of rotational activity and with the spatial distribution of parasympathetic nerve fibers. These results have indicated that EMR may therefore be a viable therapeutic target in persistent AF.

Adenosine and Adenosine Receptors: Advances in Atrial Fibrillation

Atrial fibrillation (AF) is the most common arrhythmia in the world. Because the key to developing innovative therapies that limit the onset and the progression of AF is to fully understand the underlying molecular mechanisms of AF, the aim of the present narrative review is to report the most recent advances in the potential role of the adenosinergic system in the pathophysiology of AF. After a comprehensive approach describing adenosinergic system signaling and the mechanisms of the initiation and maintenance of AF, we address the interactions of the adenosinergic system's signaling with AF. Indeed, adenosine release can activate four G-coupled membrane receptors, named A₁, A_2A, A_2B and A₃. Activation of the A_2A receptors can promote the occurrence of delayed depolarization, while activation of the A₁ receptors can shorten the action potential's duration and induce the resting membrane's potential hyperpolarization, which promote pulmonary vein firing, stabilize the AF rotors and allow for functional reentry. Moreover, the A_2B receptors have been associated with atrial fibrosis homeostasis. Finally, the adenosinergic system can modulate the autonomous nervous system and is associated with AF risk factors. A question remains regarding adenosine release and the adenosine receptors' activation and whether this would be a cause or consequence of AF.

Hub Genes Identification, Small Molecule Compounds Prediction for Atrial Fibrillation and Diagnostic Model Construction Based on XGBoost Algorithm

Background

Atrial fibrillation (AF) is the most common sustained cardiac arrhythmia and engenders significant global health care burden. The underlying mechanisms of AF is remained to be revealed and current treatment options for AF have limitations. Besides, a detection system can help identify those at risk of developing AF and will enable personalized management.

Materials and Methods

In this study, we utilized the robust rank aggregation method to integrate six AF microarray datasets from the Gene Expression Omnibus database, and identified a set of differentially expressed genes between patients with AF and controls. Potential compounds were identified by mining the Connectivity Map database. Functional modules and closely-interacted clusters were identified using weighted gene co-expression network analysis and protein–protein interaction network, respectively. The overlapped hub genes were further filtered. Subsequent analyses were performed to analyze the function, biological features, and regulatory networks. Moreover, a reliable Machine Learning-based diagnostic model was constructed and visualized to clarify the diagnostic features of these genes.

Results

A total of 156 upregulated and 34 downregulated genes were identified, some of which had not been previously investigated. We showed that mitogen-activated protein kinase and epidermal growth factor receptor inhibitors were likely to mitigate AF based on Connectivity Map analysis. Four genes, including CXCL12, LTBP1, LOXL1, and IGFBP3, were identified as hub genes. CXCL12 was shown to play an important role in regulation of local inflammatory response and immune cell infiltration. Regulation of CXCL12 expression in AF was analyzed by constructing a transcription factor-miRNA-mRNA network. The Machine Learning-based diagnostic model generated in this study showed good efficacy and reliability.

Conclusion

Key genes involving in the pathogenesis of AF and potential therapeutic compounds for AF were identified. The biological features of CXCL12 in AF were investigated using integrative bioinformatics tools. The results suggested that CXCL12 might be a biomarker that could be used for distinguishing subsets of AF, and indicated that CXCL12 might be an important intermediate in the development of AF. A reliable Machine Learning-based diagnostic model was constructed. Our work improved understanding of the mechanisms of AF predisposition and progression, and identified potential therapeutic avenues for treatment of AF.

The Editor’s Choice Articles—Section “Cells of the Cardiovascular System” 2020–2021

Cells is experiencing a rapid increase in attractiveness and impact [...]

Emerging Antiarrhythmic Drugs for Atrial Fibrillation

Atrial fibrillation (AF), the most common cardiac arrhythmia worldwide, is driven by complex mechanisms that differ between subgroups of patients. This complexity is apparent from the different forms in which AF presents itself (post-operative, paroxysmal and persistent), each with heterogeneous patterns and variable progression. Our current understanding of the mechanisms responsible for initiation, maintenance and progression of the different forms of AF has increased significantly in recent years. Nevertheless, antiarrhythmic drugs for the management of AF have not been developed based on the underlying arrhythmia mechanisms and none of the currently used drugs were specifically developed to target AF. With the increased knowledge on the mechanisms underlying different forms of AF, new opportunities for developing more effective and safer AF therapies are emerging. In this review, we provide an overview of potential novel antiarrhythmic approaches based on the underlying mechanisms of AF, focusing both on the development of novel antiarrhythmic agents and on the possibility of repurposing already marketed drugs. In addition, we discuss the opportunity of targeting some of the key players involved in the underlying AF mechanisms, such as ryanodine receptor type-2 (RyR2) channels and atrial-selective K⁺-currents (I_K2P and I_SK) for antiarrhythmic therapy. In addition, we highlight the opportunities for targeting components of inflammatory signaling (e.g., the NLRP3-inflammasome) and upstream mechanisms targeting fibroblast function to prevent structural remodeling and progression of AF. Finally, we critically appraise emerging antiarrhythmic drug principles and future directions for antiarrhythmic drug development, as well as their potential for improving AF management.

Triglyceride-Glucose Index and New-Onset Atrial Fibrillation in ST-Segment Elevation Myocardial Infarction Patients After Percutaneous Coronary Intervention

Background

New-onset atrial fibrillation (NOAF) is associated with worse prognostic outcomes in cases diagnosed with ST-segment elevation myocardial infarction (STEMI) patients after percutaneous coronary intervention (PCI). The triglyceride-glucose (TyG) index, as a credible and convenient marker of insulin resistance, has been shown to be predictive of outcomes for STEMI patients following revascularization. The association between TyG index and NOAF among STEMI patients following PCI, however, has not been established to date.

Objective

To assess the utility of the TyG index as a predictor of NOAF incidence in STEMI patients following PCI, and to assess the relationship between NOAF and long-term all-cause mortality.

Methods

This retrospective cohort research enrolled 549 STEMI patients that had undergone PCI, with these patients being clustered into the NOAF group and sinus rhythm (SR) group. The predictive relevance of TyG index was evaluated through logistic regression analyses and the receiver operating characteristic (ROC) curve. Kaplan-Meier curve was employed to explore differences in the long-term all-cause mortality between the NOAF and SR group.

Results

NOAF occurred in 7.7% of the enrolled STEMI patients after PCI. After multivariate logistic regression analysis, the TyG index was found to be an independent predictor of NOAF [odds ratio (OR): 8.884, 95% confidence interval (CI): 1.570–50.265, P = 0.014], with ROC curve analyses further supporting the predictive value of this parameter, which exhibited an area under ROC curve of 0.758 (95% CI: 0.720–0.793, P < 0.001). All-cause mortality rates were greater for patients in the NOAF group in comparison with the SR group over a median 35-month follow-up period (log-rank P = 0.002).

Conclusions

The TyG index exhibits values as an independent predictor of NOAF during hospitalization, which indicated a poorer prognosis after a relatively long-term follow-up.

Integrative Computational Modeling of Cardiomyocyte Calcium Handling and Cardiac Arrhythmias: Current Status and Future Challenges

Cardiomyocyte calcium-handling is the key mediator of cardiac excitation-contraction coupling. In the healthy heart, calcium controls both electrical impulse propagation and myofilament cross-bridge cycling, providing synchronous and adequate contraction of cardiac muscles. However, calcium-handling abnormalities are increasingly implicated as a cause of cardiac arrhythmias. Due to the complex, dynamic and localized interactions between calcium and other molecules within a cardiomyocyte, it remains experimentally challenging to study the exact contributions of calcium-handling abnormalities to arrhythmogenesis. Therefore, multiscale computational modeling is increasingly being used together with laboratory experiments to unravel the exact mechanisms of calcium-mediated arrhythmogenesis. This article describes various examples of how integrative computational modeling makes it possible to unravel the arrhythmogenic consequences of alterations to cardiac calcium handling at subcellular, cellular and tissue levels, and discusses the future challenges on the integration and interpretation of such computational data.

Pathophysiological aspects of insulin resistance in Atrial Fibrillation: novel therapeutic approaches

Background

Insulin resistance is associated with metabolic disorders including diabetes, obesity, hypertension, and inflammation which are the risk factors for Atrial Fibrillation. Many studies have reported that type 2 diabetes and AF are related and also their prevalence is increasing globally. Moreover, insulin resistance begins the type 2 diabetes.

Main body

This review explains the pathophysiological aspects of insulin resistance in AF patients and discusses the drugs that are used to manage insulin resistance including Biguanides (metformin), thiazolidinediones (TZDs) [Pioglitazone, rosiglitazone], Sodium-glucose cotransporter 2 (SGLT2) inhibitors, Concentrated Insulin Products, Dipeptidyl peptidase-4 (DPP-4) Inhibitors, Glucagon-like peptide 1 (GLP-1) receptor Agonists, Pramlintide, Sulfonylureas, Meglitinides, α-Glucosidase Inhibitors, Colesevelam, Bromocriptine. This review will highlight a few major drugs that played a significant role in AF patients. For this purpose, many databases were used for reviewing the literature and keywords are used such as Insulin Resistance, Pathophysiology, Atrial Fibrillation, and Drugs.

Conclusion

This review article concludes that insulin resistance is related to AF. It also provides an outlook on the recent pathophysiological aspects of insulin resistance in AF; however, more studies are needed to clarify the management of insulin resistance in AF patients to prevent the development of type 2 diabetes.

Use of the Apple Watch iECG in adult congenital heart disease patients

Introduction

This study evaluates the accuracy of iECGs in comparison to the gold standard ECG in adult patients with congenital heart disease and recommends the appropriate iECG derivation based on the patient's characteristics.

Methods

In 106 adults (51 female, 55 male) with congenital heart disease, a gold standard 12-lead ECG was recorded, followed by three iECGs with the Apple Watch series 4, which correspond to Einthoven leads I, II, and III. Two experienced and independent cardiologists analyzed the time intervals, amplitudes, and polarities of the ECG parameters as well as the rhythm type and correlated the patient characteristics with the iECG parameters.

Results

The iECG parameters of all three iECG leads correlate strongly with those of the gold standard ECG, with exception of the P and T wave durations. We demonstrated that the informative value of the individual iECGs was independent of the patient's characteristics, in particular the heart axis, anatomy, and situs, even if the quality of the Einthoven III-like derivation was partially inadequate. The automatic rhythm analysis of the Apple Watch and the heart rhythm classification of a standard ECG analyzed manually by a cardiologist corresponded in 77%.

Conclusion

iECG recordings of adults with congenital heart disease provide comparable results with Einthoven recordings I, II, and III of the 12-lead ECG and current data encourage the use of the Apple Watch not only in patients with structurally normal hearts but also in patients with congenital heart disease.

Aminophylline at clinically relevant concentrations affects inward rectifier potassium current in a dual way

Bronchodilator aminophylline may induce atrial or less often ventricular arrhythmias. The mechanism of this proarrhythmic side effect has not been fully explained. Modifications of inward rectifier potassium (Kir) currents including I_K1 are known to play an important role in arrhythmogenesis; however, no data on the aminophylline effect on these currents have been published. Hence, we tested the effect of aminophylline (3-100 µM) on I_K1 in enzymatically isolated rat ventricular myocytes using the whole-cell patch-clamp technique. A dual steady-state effect of aminophylline was observed; either inhibition or activation was apparent in individual cells during the application of aminophylline at a given concentration. The smaller the magnitude of the control I_K1, the more likely the activation of the current by aminophylline and vice versa. The effect was reversible; the relative changes at -50 and -110 mV did not differ. Using I_K1 channel population model, the dual effect was explained by the interaction of aminophylline with two different channel populations, the first one being inhibited and the second one being activated. Considering various fractions of these two channel populations in individual cells, varying effects observed in the measured cells could be simulated. We propose that the dual aminophylline effect may be related to the direct and indirect effect of the drug on various Kir2.x subunits forming the homo- and heterotetrameric I_K1 channels in a single cell. The observed I_K1 changes induced by clinically relevant concentrations of aminophylline might contribute to arrhythmogenesis related to the use of this bronchodilator in clinical medicine.

Conditional immortalization of human atrial myocytes for the generation of in vitro models of atrial fibrillation

The lack of a scalable and robust source of well-differentiated human atrial myocytes constrains the development of in vitro models of atrial fibrillation (AF). Here we show that fully functional atrial myocytes can be generated and expanded one-quadrillion-fold via a conditional cell-immortalization method relying on lentiviral vectors and the doxycycline-controlled expression of a recombinant viral oncogene in human foetal atrial myocytes, and that the immortalized cells can be used to generate in vitro models of AF. The method generated 15 monoclonal cell lines with molecular, cellular and electrophysiological properties resembling those of primary atrial myocytes. Multicellular in vitro models of AF generated using the immortalized atrial myocytes displayed fibrillatory activity (with activation frequencies of 6-8 Hz, consistent with the clinical manifestation of AF), which could be terminated by the administration of clinically approved antiarrhythmic drugs. The conditional cell-immortalization method could be used to generate functional cell lines from other human parenchymal cells, for the development of in vitro models of human disease.

Left atrial appendage shape impacts on the left atrial flow hemodynamics: A numerical hypothesis generating study on two cases

BACKGROUND AND OBJECTIVES

The left atrial appendage (LAA) is the most common region for thrombus formation in atrial fibrillation (AF). Morphological parameters such as shape, size, and LAA volume can cause insufficient effectiveness of available therapeutic options. This study aimed to examine blood flow inside LAA and its removal effects. Computational fluid dynamic (CFD) simulations were carried out on two patients with different morphologies.

METHODS

Two patients' CT was used to reconstruct the 3D geometries of the left atrium (LA) and left atrial appendage (LAA). Then, the geometries were refined in the mentioned software, and the LAA in some models was removed. Next, in generated 3D volume mesh, sinus rhythm (SR) and atrial fibrillation (AF) outflow velocity were imposed at the mitral valve as boundary conditions. Finally, CFD simulation was conducted to analyzing blood flow within LA with/without LA.

RESULTS

The results confirmed that velocity and vorticity decreased under AF conditions inside the LA domain for both patients. However, removing LAA may cause unpredictable consequences, due to different shape and volume of LAA. LAA removal had insignificant effects on velocity and vorticity within LA in SR-mitral outflow. However, removing LAA increased the blood flow rate by 9.15% and vorticity by 7.27% for patient one under AF rhythm (SR)-outflow. In contrast, for patient two, LAA removal in both AF and SR decreased velocity and vorticity within the LA domain. In SR-mitral outflow, velocity dropped by 18.8 %, and vorticity by 13.2%. Also, under AF velocity and vorticity decreased by 23.33% and 18.6% respectively. Meanwhile, the results indicated that the vorticity magnitude increased inside the LAA under AF associated with the risk of thrombus formation, particularly for patient one under AF. The distal part of LAA in both patients was the most common region for blood stasis because of the lowest velocity magnitude.

CONCLUSION

Overall, the morphology of LAA could be the critical parameter to determine the possibility of thrombosis formation, particularly under AF conditions. High volume, low blood flow velocity and two-lobe-appendage are more likely to have blood stasis. Furthermore, the morphology difference can affect the LAA removal result and make it more complicated. So, it could be challenging to generalize LAA removal as a therapeutic option for different patients. The implication of this CFD observation needs more investigation.

Epigenetic Age and the Risk of Incident Atrial Fibrillation

BACKGROUND

The most prominent risk factor for atrial fibrillation (AF) is chronological age; however, underlying mechanisms are unexplained. Algorithms using epigenetic modifications to the human genome effectively predict chronological age. Chronological and epigenetic predicted ages may diverge in a phenomenon referred to as epigenetic age acceleration (EAA), which may reflect accelerated biological aging. We sought to evaluate for associations between epigenetic age measures and incident AF.

METHODS

Measures for 4 epigenetic clocks (Horvath, Hannum, DNA methylation [DNAm] PhenoAge, and DNAm GrimAge) and an epigenetic predictor of PAI-1 (plasminogen activator inhibitor-1) levels (ie, DNAm PAI-1) were determined for study participants from 3 population-based cohort studies. Cox models evaluated for associations with incident AF and results were combined via random-effects meta-analyses. Two-sample summary-level Mendelian randomization analyses evaluated for associations between genetic instruments of the EAA measures and AF.

RESULTS

Among 5600 participants (mean age, 65.5 years; female, 60.1%; Black, 50.7%), there were 905 incident AF cases during a mean follow-up of 12.9 years. Unadjusted analyses revealed all 4 epigenetic clocks and the DNAm PAI-1 predictor were associated with statistically significant higher hazards of incident AF, though the magnitudes of their point estimates were smaller relative to the associations observed for chronological age. The pooled EAA estimates for each epigenetic measure, with the exception of Horvath EAA, were associated with incident AF in models adjusted for chronological age, race, sex, and smoking variables. After multivariable adjustment for additional known AF risk factors that could also potentially function as mediators, pooled EAA measures for 2 clocks remained statistically significant. Five-year increases in EAA measures for DNAm GrimAge and DNAm PhenoAge were associated with 19% (adjusted hazard ratio [HR], 1.19 [95% CI, 1.09-1.31]; P<0.01) and 15% (adjusted HR, 1.15 [95% CI, 1.05-1.25]; P<0.01) higher hazards of incident AF, respectively. Mendelian randomization analyses for the 5 EAA measures did not reveal statistically significant associations with AF.

CONCLUSIONS

Our study identified adjusted associations between EAA measures and incident AF, suggesting that biological aging plays an important role independent of chronological age, though a potential underlying causal relationship remains unclear. These aging processes may be modifiable and not constrained by the immutable factor of time.

Panoramic Endocardial Optical Mapping Demonstrates Serial Rotors Acceleration and Increasing Complexity of Activity During Onset of Cholinergic Atrial Fibrillation

Background

Activation during onset of atrial fibrillation is poorly understood. We aimed at developing a panoramic optical mapping system for the atria and test the hypothesis that sequential rotors underlie acceleration of atrial fibrillation during onset.

Methods and Results

Five sheep hearts were Langendorff perfused in the presence of 0.25 µmol/L carbachol. Novel optical system recorded activations simultaneously from the entire left and right atrial endocardial surfaces. Twenty sustained (>40 s) atrial fibrillation episodes were induced by a train and premature stimuli protocol. Movies obtained immediately (Initiation stage) and 30 s (Early Stabilization stage) after premature stimulus were analyzed. Serial rotor formation was observed in all sustained inductions and none in nonsustained inductions. In sustained episodes maximal dominant frequency increased from (mean±SD) 11.5±1.74 Hz during Initiation to 14.79±1.30 Hz at Early Stabilization (P<0.0001) and stabilized thereafter. At rotor sites, mean cycle length (CL) during 10 prerotor activations increased every cycle by 0.53% (P=0.0303) during Initiation and 0.34% (P=0.0003) during Early Stabilization. In contrast, CLs at rotor sites showed abrupt decreases after the rotors appearances by a mean of 9.65% (P<0.0001) during both stages. At Initiation, atria‐wide accelerations and decelerations during rotors showed a net acceleration result whereby post‐rotors atria‐wide minimal CL (CLmin) were 95.5±6.8% of the prerotor CLmin (P=0.0042). In contrast, during Early Stabilization, there was no net acceleration in CLmin during accelerating rotors (prerotor=84.9±11.0% versus postrotor=85.8±10.8% of Initiation, P=0.4029). Levels of rotor drift distance and velocity correlated with atria‐wide acceleration. Nonrotor phase singularity points did not accelerate atria‐wide activation but multiplied during Initiation until Early Stabilization. Increasing number of singularity points, indicating increased complexity, correlated with atria‐wide CLmin reduction (P<0.0001).

Conclusions

Novel panoramic optical mapping of the atria demonstrates shortening CL at rotor sites during cholinergic atrial fibrillation onset. Atrial fibrillation acceleration toward Early Stabilization correlates with the net result of atria‐wide accelerations during drifting rotors activity.

Diminished PLK2 Induces Cardiac Fibrosis and Promotes Atrial Fibrillation

[Figure: see text].

Antiarrhythmic drugs for atrial fibrillation: lessons from the past and opportunities for the future

Atrial fibrillation (AF) remains a highly prevalent and troublesome cardiac arrhythmia, associated with substantial morbidity and mortality. Restoration and maintenance of sinus rhythm (rhythm-control therapy) is an important element of AF management in symptomatic patients. Despite significant advances and increasing importance of catheter ablation, antiarrhythmic drugs (AADs) remain a cornerstone of rhythm-control therapy. During the past 50 years, experimental and clinical research has greatly increased our understanding of AADs. As part of the special issue on paradigm shifts in AF, this review summarizes important milestones in AAD research that have shaped their current role in AF management, including (i) awareness of the proarrhythmic potential of AADs; (ii) increasing understanding of the pleiotropic effects of AADs; (iii) the development of dronedarone; and (iv) the search for AF-specific AADs. Finally, we discuss short- and long-term opportunities for better AF management through advances in AAD therapy, including personalization of AAD therapy based on individual AF mechanisms.

Atrial heat shock protein levels are associated with early postoperative and persistence of atrial fibrillation

BACKGROUND

Early detection and staging of atrial fibrillation (AF) is of importance for clinical management. Serum (bio)markers, such as heat shock proteins (HSP), may enable AF staging and identify patients at risk for AF recurrence and postoperative AF (PoAF).

OBJECTIVE

This study evaluates the relation between serum and atrial tissue HSP levels, stages of AF, AF recurrence after treatment, and PoAF from patients undergoing cardiothoracic surgery.

METHODS

Patients without (control) and with paroxysmal, persistent (PerAF), or longstanding persistent (LSPerAF) AF were included. HSPB1, HSPA1, HSPB7, and HSPD1 levels were measured in serum obtained prior to and post intervention. HSPB1, HSPA1, HSPA5, HSPD1, HSPB5, and pHSF1 levels were measured in left and/or right atrial appendages (respectively, LAA and RAA).

RESULTS

In RAA, HSPA5 levels were significantly lower in LSPerAF and HSPD1 levels significantly higher in PerAF patients compared to controls. In RAA of controls who developed PoAF, HSPA1 and HSPA5 levels were significantly higher compared to those without PoAF. Also, HSPB1 RAA levels were lower and HSPA5 LAA levels higher in patients undergoing arrhythmia surgery who developed AF recurrence within 1 week after surgery compared to patients who did not.

CONCLUSION

HSPA5 RAA and HSPD1 RAA and LAA levels are altered in persistent stages of AF. RAA HSPA1 and HSPA5 levels associate with development of PoAF. Additionally, HSPB1 RAA and HSPA5 LAA levels can predict AF recurrence in patients who underwent arrhythmia surgery. Nevertheless, HSP levels in serum cannot discriminate AF stages from controls, nor predict PoAF or AF recurrence after treatment.

Computational models of atrial fibrillation: achievements, challenges, and perspectives for improving clinical care

Despite significant advances in its detection, understanding and management, atrial fibrillation (AF) remains a highly prevalent cardiac arrhythmia with a major impact on morbidity and mortality of millions of patients. AF results from complex, dynamic interactions between risk factors and comorbidities that induce diverse atrial remodelling processes. Atrial remodelling increases AF vulnerability and persistence, while promoting disease progression. The variability in presentation and wide range of mechanisms involved in initiation, maintenance and progression of AF, as well as its associated adverse outcomes, make the early identification of causal factors modifiable with therapeutic interventions challenging, likely contributing to suboptimal efficacy of current AF management. Computational modelling facilitates the multilevel integration of multiple datasets and offers new opportunities for mechanistic understanding, risk prediction and personalized therapy. Mathematical simulations of cardiac electrophysiology have been around for 60 years and are being increasingly used to improve our understanding of AF mechanisms and guide AF therapy. This narrative review focuses on the emerging and future applications of computational modelling in AF management. We summarize clinical challenges that may benefit from computational modelling, provide an overview of the different in silico approaches that are available together with their notable achievements, and discuss the major limitations that hinder the routine clinical application of these approaches. Finally, future perspectives are addressed. With the rapid progress in electronic technologies including computing, clinical applications of computational modelling are advancing rapidly. We expect that their application will progressively increase in prominence, especially if their added value can be demonstrated in clinical trials.

Prevention of Pathological Atrial Remodeling and Atrial Fibrillation: JACC State-of-the-Art Review

Atrial enlargement in response to pathological stimuli (e.g., hypertension, mitral valve disease) and physiological stimuli (exercise, pregnancy) can be comparable in magnitude, but the diseased enlarged atria is associated with complications such as atrial fibrillation (AF), whereas physiological atrial enlargement is not. Pathological atrial enlargement and AF is also observed in a small percentage of athletes undergoing extreme/intense endurance sport and pregnant women with preeclampsia. Differences between physiological and pathological atrial enlargement and underlying mechanisms are poorly understood. This review describes human and animal studies characterizing atrial enlargement under physiological and pathological conditions and highlights key knowledge gaps and clinical challenges, including: 1) the limited ability of atria to reverse remodel; and 2) distinguishing physiological and pathological enlargement via imaging/biomarkers. Finally, this review discusses how targeting distinct molecular mechanisms underlying physiological and pathological atrial enlargement could provide new therapeutic and diagnostic strategies for preventing or reversing atrial enlargement and AF.

Probabilistic domain-knowledge modeling of disorder pathogenesis for dynamics forecasting of acute onset

Disease pathogenesis, a type of domain knowledge about biological mechanisms leading to diseases, has not been adequately encoded in machine-learning-based medical diagnostic models because of the inter-patient variabilities and complex dependencies of the underlying pathogenetic mechanisms. We propose 1) a novel pathogenesis probabilistic graphical model (PPGM) to quantify the dynamics underpinning patient-specific data and pathogenetic domain knowledge, 2) a Bayesian-based inference paradigm to answer the medical queries and forecast acute onsets. The PPGM model consists of two components: a Bayesian network of patient attributes and a temporal model of pathogenetic mechanisms. The model structure was reconstructed from expert knowledge elicitation, and its parameters were estimated using Variational Expectation-Maximization algorithms. We benchmarked our model with two well-established hidden Markov models (HMMs) - Input-output HMM (IO-HMM) and Switching Auto-Regressive HMM (SAR-HMM) - to evaluate the computational costs, forecasting performance, and execution time. Two case studies on Obstructive Sleep Apnea (OSA) and Paroxysmal Atrial Fibrillation (PAF) were used to validate the model. While the performance of the parameter learning step was equivalent to those of IO-HMM and SAR-HMM models, our model forecasting ability was outperforming those two models. The merits of the PPGM model are its representation capability to capture the dynamics of pathogenesis and perform medical inferences and its interpretability for physicians. The model has been used to perform medical queries and forecast the acute onset of OSA and PAF. Additional applications of the model include prognostic healthcare and preventive personalized treatments.

THE ROLE OF PHOSPHORYLATION IN ATRIAL FIBRILLATION: A FOCUS ON MASS SPECTROMETRY APPROACHES

Atrial fibrillation (AF) is the most common arrhythmia worldwide. It is associated with significant increases in morbidity in the form of stroke and heart failure, and a doubling in all-cause mortality. The pathophysiology of AF is incompletely understood, and this has contributed to a lack of effective treatments and disease-modifying therapies. An important cellular process that may explain how risk factors give rise to AF includes post-translational modification (PTM) of proteins. As the most commonly occurring PTM, protein phosphorylation is especially relevant. Although many methods exist for studying protein phosphorylation, a common and highly resolute technique is mass spectrometry (MS). This review will discuss recent evidence surrounding the role of protein phosphorylation in the pathogenesis of AF. MS-based technology to study phosphorylation and uses of MS in other areas of medicine such as oncology will also be presented. Based on these data, future goals and experiments will be outlined that utilize MS technology to better understand the role of phosphorylation in AF and elucidate its role in AF pathophysiology. This may ultimately allow for the development of more effective AF therapies.

New aspects of endocrine control of atrial fibrillation and possibilities for clinical translation

Hormones are potent endo-, para-, and autocrine endogenous regulators of the function of multiple organs, including the heart. Endocrine dysfunction promotes a number of cardiovascular diseases, including atrial fibrillation (AF). While the heart is a target for endocrine regulation, it is also an active endocrine organ itself, secreting a number of important bioactive hormones that convey significant endocrine effects, but also through para-/autocrine actions, actively participate in cardiac self-regulation. The hormones regulating heart-function work in concert to support myocardial performance. AF is a serious clinical problem associated with increased morbidity and mortality, mainly due to stroke and heart failure. Current therapies for AF remain inadequate. AF is characterized by altered atrial function and structure, including electrical and profibrotic remodelling in the atria and ventricles, which facilitates AF progression and hampers its treatment. Although features of this remodelling are well-established and its mechanisms are partly understood, important pathways pertinent to AF arrhythmogenesis are still unidentified. The discovery of these missing pathways has the potential to lead to therapeutic breakthroughs. Endocrine dysfunction is well-recognized to lead to AF. In this review, we discuss endocrine and cardiocrine signalling systems that directly, or as a consequence of an underlying cardiac pathology, contribute to AF pathogenesis. More specifically, we consider the roles of products from the hypothalamic-pituitary axis, the adrenal glands, adipose tissue, the renin–angiotensin system, atrial cardiomyocytes, and the thyroid gland in controlling atrial electrical and structural properties. The influence of endocrine/paracrine dysfunction on AF risk and mechanisms is evaluated and discussed. We focus on the most recent findings and reflect on the potential of translating them into clinical application.

Neutrophil degranulation interconnects over-represented biological processes in atrial fibrillation

Despite our expanding knowledge about the mechanism underlying atrial fibrillation (AF), the interplay between the biological events underlying AF remains incompletely understood. This study aimed to identify the functionally enriched gene-sets in AF and capture their interconnection via pivotal factors, that may drive or be driven by AF. Global abundance of the proteins in the left atrium of AF patients compared to control patients (n = 3/group), and the functionally enriched biological processes in AF were determined by mass-spectrometry and gene set enrichment analysis, respectively. The data were validated in an independent cohort (n = 19-20/group). In AF, the gene-sets of innate immune system, metabolic process, cellular component disassembly and ion homeostasis were up-regulated, while the gene-set of ciliogenesis was down-regulated. The innate immune system was over-represented by neutrophil degranulation, the components of which were extensively shared by other gene-sets altered in AF. In the independent cohort, an activated form of neutrophils was more present in the left atrium of AF patients with the increased gene expression of neutrophil granules. MYH10, required for ciliogenesis, was decreased in the atrial fibroblasts of AF patients. We report the increased neutrophil degranulation appears to play a pivotal role, and affects multiple biological processes altered in AF.

Postoperative atrial fibrillation in pneumonectomy for primary lung cancer

Background

This study assessed the incidence and risk factors (RFs) of postoperative atrial fibrillation (POAF) and its impact on clinical outcomes in patients undergoing pneumonectomy for lung cancer.

Methods

Between 2013 and 2018, this monocentric retrospective study enrolled 324 consecutive pneumonectomy patients for primary lung cancer from our institution and 350 lobectomy and 349 segmentectomy cases matched by age, sex and body mass index (BMI). RF for POAF and postoperative death in pneumonectomy patients were assessed by logistic regression, and long-term outcomes after a median follow-up of 30 (range, 2–61) months by Cox proportional hazard model. Electrophysiology study (EPS) files of 30 AF patients with lung resection history were reviewed.

Results

POAF developed more often after pneumonectomy than lobectomy and segmentectomy (23.2% vs. 6.6% vs. 1.4%, respectively; P<0.001). Among 75 pneumonectomy patients with POAF, POAF was solitary in 55 patients (73.3%) and concurrent with other complications in 3 patients (4%). POAF risk after pneumonectomy was 4 and 22 times that after lobectomy and segmentectomy, respectively, with age >60 years and left atrial diameter (LAd) ≥35 mm as independent predictors. POAF, infection and hemorrhage were independent RFs for perioperative death after pneumonectomy; however, POAF was not RF for long-term death. Pulmonary vein (PV) trigger was identified in 60% (18/30) of AF patients with lung resection history, with stump PVs being more active than non-stump PVs (38.2% vs. 10.5%, P<0.001).

Conclusions

Post-pneumonectomy AF, with remarkable incidence, risk and independent predictors including age >60 years and LAd ≥35 mm, was mostly solitary and possibly secondary to stump and non-stump PV triggers. POAF, along with infection and hemorrhage, was a RF for perioperative death.

A new implantable tool for repeated assessment of supraventricular electrophysiology and atrial fibrillation susceptibility in freely moving rats

The complex pathophysiology of atrial fibrillation (AF) is governed by multiple risk factors in ways that are still elusive. Basic electrophysiological properties, including atrial effective refractory period (AERP) and conduction velocity, are major factors determining the susceptibility of the atrial myocardium to AF. Although there is a great need for affordable animal models in this field of research, in vivo rodent studies are limited by technical challenges. Recently, we introduced an implantable system for long-term assessment of AF susceptibility in ambulatory rats. However, technical considerations did not allow us to perform concomitant supraventricular electrophysiology measurements. Here, we designed a novel quadripolar electrode specifically adapted for comprehensive atrial studies in ambulatory rats. Electrodes were fabricated from medical-grade silicone, four platinum-iridium poles, and stainless-steel fixating pins. Initial quality validation was performed ex vivo, followed by implantation in adult rats and repeated electrophysiological studies 1, 4, and 8 wk postimplantation. Capture threshold was stable. Baseline AERP values (38.1 ± 2.3 and 39.5 ± 2.0 using 70-ms and 120-ms S1-S1 cycle lengths, respectively) confirmed the expected absence of rate adaptation in the unanesthetized state and validated our prediction that markedly higher values reported under anesthesia are nonphysiological. Evaluation of AF substrate in parallel with electrophysiological parameters validated our recent finding of a gradual increase in AF susceptibility over time and demonstrated that this phenomenon is associated with an electrical remodeling process characterized by AERP shortening. Our findings indicate that the miniature quadripolar electrode is a potent new tool, which opens a window of opportunities for better utilization of rats in AF research.NEW & NOTEWORTHY Rodents are increasingly used in AF research. However, technical challenges restrict long-term supraventricular electrophysiology studies in these species. Here, we developed an implantable electrode adapted for such studies in the rat. Our findings indicate that this new tool is effective for long-term follow-up of critical parameters such as atrial refractoriness. Obtained data shed light on the normal electrophysiology and on the increased AF susceptibility that develops in rats with implanted atrial electrodes over time.

Association between routine biomarkers and atrial fibrillation in patients undergoing implantation of a dual-chamber pacemaker

BACKGROUND

Elderly patients having a permanent pacemaker frequently have atrial remodeling. We examined the association between routine biomarkers and atrial fibrillation (AF) in patients receiving a dual-chamber pacemaker for sinus node disease (SND) or second-/third-degree atrioventricular block.

METHODS

We recorded clinical, laboratory, and electrocardiographic parameters as well as pacemaker lead parameters at implantation. The final analysis included 217 patients with SND and 393 patients with atrioventricular block. Notably, 102/217 (47%) of the SND patients (median age: 77 years, 54% men) and 54/393 (14%) of the atrioventricular block patients (median age: 79 years, 54% men) had AF history (paroxysmal or persistent).

RESULTS

Multivariable analysis showed that red blood cell distribution width (RDW) (OR: 1.17; 95% CI: 1.05-1.36; P = .05) and serum γ-glutamyl transferase (γGT) levels (OR: 1.15; 95% CI: 1.03-1.28; P = .04) were independently associated with AF history in patients with SND. In ROC curve analysis, the area under the curve (AUC) was 0.648; P < .01 for RDW, and 0.753; P < .01 for γGT. A RDW cut-off point of 14 was associated with AF with a sensitivity of 67% and a specificity of 68%, while a γGT cut-off point of 21 was associated with AF with a sensitivity of 80% and a specificity of 65%. In patients with second-/third-degree atrioventricular block, there were no significant independent correlations between AF and the parameters studied.

CONCLUSIONS

In elderly patients with SND, RDW and γGT have an independent association with AF history. Our study failed to show any corresponding associations in patients with advanced disorders of atrioventricular conduction.