Atrial fibrillation from the pathologist's perspective

Pathophysiology and clinical relevance of atrial myopathy

Atrial myopathy is a condition that consists of electrical, structural, contractile, and autonomic remodeling of the atria and is the substrate for development of atrial fibrillation, the most common arrhythmia. Pathophysiologic mechanisms driving atrial myopathy are inflammation, oxidative stress, atrial stretch, and neurohormonal signals, e.g., angiotensin-II and aldosterone. These mechanisms initiate the structural and functional remodeling of the atrial myocardium. Novel therapeutic strategies are being developed that target the pathophysiologic mechanisms of atrial myopathy. In this review, we will discuss the pathophysiology of atrial myopathy, as well as diagnostic and therapeutic strategies.

Atrial myopathy

This paper delves into the progressive concept of atrial myopathy, shedding light on its development and its impact on atrial characteristics. It extensively explores the intricate connections between atrial myopathy, atrial fibrillation (AF), and strokes. Researchers have sought additional contributors to AF-related strokes due to the absence of a clear timing correlation between paroxysmal AF episodes and strokes in patients with cardiac implantable electronic devices. Through various animal models and human investigations, a close interrelation among aging, inflammation, oxidative stress, and stretching mechanisms has been identified. These mechanisms contribute to fibrosis, alterations in electrical properties, autonomic remodeling, and a heightened pro-thrombotic state. These interconnected factors establish a detrimental cycle, exacerbating atrial myopathy and elevating the risk of sustained AF and strokes. By emphasizing the significance of atrial myopathy and the risk of strokes that are distinct from AF, the paper also discusses methods for identifying patients with atrial myopathy. Moreover, it proposes an approach to incorporate the concept of atrial myopathy into clinical practice to guide anticoagulation decisions in individuals with AF.

Atrial fibrillation in human patients is associated with increased collagen type V and TGFbeta1

Background and aim

Atrial fibrosis is an important factor in initiating and maintaining atrial fibrillation (AF). Collagen V belongs to fibrillar collagens. There are, however no data on collagen V in AF. The aim of this work was to study the quantity of collagen V and its relationship with the number of fibroblasts and TGF- b 1 expression in patients in sinus rhythm (SR) and in patients with atrial fibrillation (AF).

Methods

We used quantitative immuhistochemistry to study collagen V in right and left atrial biopsies obtained from 35 patients in SR, 35 patients with paroxysmal AF (pAF) and 27 patients with chronic, long-standing persistent AF (cAF). In addition, we have quantified the number of vimentin-positive fibroblasts and expression levels of TGF-β1.

Results

Compared to patients in SR, collagen V was increased 1.8- and 3.1-fold in patients with pAF and cAF, respectively. In comparison with SR patients, the number of vimentin-positive cells increased significantly 1.46- and 1.8-fold in pAF and cAF patients, respectively.Compared to SR patients, expression levels of TGF-ß1, expressed as fluorescence units per tissue area, was significantly increased by 77 % and 300 % in patients with pAF and cAF, respectively. Similar to intensity measurements, the number of TGFß1-positive cells per 1 mm2 atrial tissue increased significantly from 35.5 ± 5.5 cells in SR patients to 61.9 ± 12.4 cells in pAF and 131.5 ± 23.5 cells in cAF. In both types of measurements, there was a statistically significant difference between pAF and cAF groups.

Conclusions

This is the first study to show that AF is associated with increased expression levels of collagen V and TGF-ß1indicating its role in the pathogenesis of atrial fibrosis. In addition, increases in collagen V correlate with increased number of fibroblasts and TGF-β1 and are more pronounced in cAF patients than those in pAF patients.

Drug-induced atrial fibrillation. A narrative review of a forgotten adverse effect

Atrial fibrillation (AF) is the most common cardiac arrhythmia and is associated with an increased morbidity and mortality. There is clinical evidence that an increasing number of cardiovascular and non-cardiovascular drugs, mainly anticancer drugs, can induce AF either in patients with or without pre-existing cardiac disorders, but drug-induced AF (DIAF) has not received the attention that it might deserve. In many cases DIAF is asymptomatic and paroxysmal and patients recover sinus rhythm spontaneously, but sometimes, DIAF persists, and it is necessary to perform a cardioversion. Furthermore, DIAF is not mentioned in clinical guidelines on the treatment of AF. The risk of DIAF increases in elderly and in patients treated with polypharmacy and with risk factors and comorbidities that commonly coexist with AF. This is the case of cancer patients. Under these circumstances ascribing causality of DIAF to a given drug often represents a clinical challenge. We review the incidence, the pathophysiological mechanisms, risk factors, clinical relevance, and treatment of DIAF. Because of the limited information presently available, further research is needed to obtain a deeper insight into DIAF. Meanwhile, it is important that clinicians are aware of the problem that DIAF represents, recognize which drugs may cause DIAF, and consider the possibility that a drug may be responsible for a new-onset AF episode.

hiPSC-derived cardiomyocytes as a model to study the role of small-conductance Ca2+-activated K+ (SK) ion channel variants associated with atrial fibrillation

Atrial fibrillation (AF), the most common arrhythmia, has been associated with different electrophysiological, molecular, and structural alterations in atrial cardiomyocytes. Therefore, more studies are required to elucidate the genetic and molecular basis of AF. Various genome-wide association studies (GWAS) have strongly associated different single nucleotide polymorphisms (SNPs) with AF. One of these GWAS identified the rs13376333 risk SNP as the most significant one from the 1q21 chromosomal region. The rs13376333 risk SNP is intronic to the KCNN3 gene that encodes for small conductance calcium-activated potassium channels type 3 (SK3). However, the functional electrophysiological effects of this variant are not known. SK channels represent a unique family of K+ channels, primarily regulated by cytosolic Ca2+ concentration, and different studies support their critical role in the regulation of atrial excitability and consequently in the development of arrhythmias like AF. Since different studies have shown that both upregulation and downregulation of SK3 channels can lead to arrhythmias by different mechanisms, an important goal is to elucidate whether the rs13376333 risk SNP is a gain-of-function (GoF) or a loss-of-function (LoF) variant. A better understanding of the functional consequences associated with these SNPs could influence clinical practice guidelines by improving genotype-based risk stratification and personalized treatment. Although research using native human atrial cardiomyocytes and animal models has provided useful insights, each model has its limitations. Therefore, there is a critical need to develop a human-derived model that represents human physiology more accurately than existing animal models. In this context, research with human induced pluripotent stem cells (hiPSC) and subsequent generation of cardiomyocytes derived from hiPSC (hiPSC-CMs) has revealed the underlying causes of various cardiovascular diseases and identified treatment opportunities that were not possible using in vitro or in vivo studies with animal models. Thus, the ability to generate atrial cardiomyocytes and atrial tissue derived from hiPSCs from human/patients with specific genetic diseases, incorporating novel genetic editing tools to generate isogenic controls and organelle-specific reporters, and 3D bioprinting of atrial tissue could be essential to study AF pathophysiological mechanisms. In this review, we will first give an overview of SK-channel function, its role in atrial fibrillation and outline pathophysiological mechanisms of KCNN3 risk SNPs. We will then highlight the advantages of using the hiPSC-CM model to investigate SNPs associated with AF, while addressing limitations and best practices for rigorous hiPSC studies.

New-onset atrial fibrillation among COVID-19 patients: A narrative review

Over the last three years, research has focused on examining cardiac issues arising from coronavirus disease 2019 (COVID-19) infection, including the emergence of new-onset atrial fibrillation (NOAF). Still, no clinical study was conducted on the persistence of this arrhythmia after COVID-19 recovery. Our objective was to compose a narrative review that investigates COVID-19-associated NOAF, emphasizing the evolving pathophysiological mechanisms akin to those suggested for sustaining AF. Given the distinct strategies involved in the persistence of atrial AF and the crucial burden of persistent AF, we aim to underscore the importance of extended follow-up for COVID-19-associated NOAF. A comprehensive search was conducted for articles published between December 2019 and February 11, 2023, focusing on similarities in the pathophysiology of NOAF after COVID-19 and those persisting AF. Also, the latest data on incidence, morbidity-mortality, and management of NOAF in COVID-19 were investigated. Considerable overlaps between the mechanisms of emerging NOAF after COVID-19 infection and persistent AF were observed, mostly involving reactive oxygen pathways. With potential atrial remodeling associated with NOAF in COVID-19 patients, this group of patients might benefit from long-term follow-up and different management. Future cohort studies could help determine long-term outcomes of NOAF after COVID-19.

Imaging in atrial fibrillation: A way to assess atrial fibrosis and remodeling to assist decision-making

The 2020 ESC atrial fibrillation (AF) guidelines suggest the novel 4S-AF scheme for the characterization of AF. Imaging techniques could be helpful for this objective in everyday clinical practice, and information derived from these techniques reflects basic aspects of the pathophysiology of AF, which may facilitate treatment decision-making, and optimal management of AF patients. The aim of this review is to provide an overview of the mechanisms associated with atrial fibrosis and to describe imaging techniques that may help the management of AF patients in clinical practice. Transthoracic echocardiography is the most common procedure given its versatility, safety, and simplicity. Transesophageal echocardiography provides higher resolution exploration, and speckle tracking echocardiography can provide incremental functional and prognostic information over conventional echocardiographic parameters. In addition, LA deformation imaging, including LA strain and strain rate, are related to the extent of fibrosis. On the other hand, multidetector-row computed tomography and cardiac magnetic resonance provide higher resolution data and more accurate assessment of the dimensions, structure, and spatial relationships of the LA. Imaging is central when deciding on catheter ablation or cardioversion, and helps in selecting those patients who will really benefit from these procedures. Moreover, imaging enhances the understanding of the underlying mechanisms of atrial remodeling and might assists in refining the risk of stroke, which help to select the best medical therapies/interventions. In summary, evaluation of LA enlargement, LA remodeling and fibrosis with imaging techniques adds clinical and prognostic information and should be assessed as a part of routine comprehensive AF evaluation.

Screening and Bioinformatics Analysis of Crucial Gene of Heart Failure and Atrial Fibrillation Based on GEO Database

Background and objectives: In clinical practice, we observed that the prognoses of patients with heart failure and atrial fibrillation were worse than those of patients with only heart failure or atrial fibrillation. The study aims to get a better understanding of the common pathogenesis of the two diseases and find new therapeutic targets. Materials and Methods: We downloaded heart failure datasets and atrial fibrillation datasets from the gene expression omnibus database. The common DEGs (differentially expressed genes) in heart failure and atrial fibrillation were identified by a series of bioinformatics methods. To better understand the functions and possible pathways of DEGs, we performed Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analyses. Results: We identified 22 up-regulated genes and 14 down-regulated genes in two datasets of heart failure and 475 up-regulated and 110 down-regulated genes in atrial fibrillation datasets. In addition, two co-upregulated (FRZB, SFRP4) and three co-downregulated genes (ENTPPL, AQP4, C1orf105) were identified. GO enrichment results showed that these common differentially expressed genes were mainly concentrated in the signal regulation of the Wnt pathway. Conclusions: We found five crucial genes in heart failure and atrial fibrillation, which may be potential therapeutic targets for patients with heart failure and atrial fibrillation.

Prednisone Ameliorates Atrial Inflammation and Fibrosis in Atrial Tachypacing Dogs

Atrial inflammation and fibrosis have long been considered culprits in the development of atrial fibrillation (AF). Prior clinical studies showed that corticosteroid therapy is beneficial in patients with AF. Here we sought to determine whether prednisone treatment prevents atrial tachypacing (ATP) induced atrial fibrosis.Dogs were randomized into the sham, ATP, ATP + low-dose prednisone (ALP), and ATP + high-dose prednisone (AHP) groups. After 6 days of recovery from surgery, dogs were subjected to ATP at 400 beats per minute for 4 weeks while being treated with prednisone (15 or 40 mg/day) or a placebo. Pacemakers were not activated in the sham group.Compared with the ATP group, the expression of collagen I, collagen III, α-smooth muscle actin, transforming growth factor-β1 and connective tissue growth factor were significantly reduced in the ALP and AHP groups. Fluorescence assays showed that reactive oxygen species formation in the right atrium was suppressed in the ALP and AHP groups compared with the ATP group. The protein level of NADPH oxidase 2 was reduced in the ALP and AHP groups' versus ATP group, while NOX4 and NOX5 were unchanged. ATP-induced downregulation of BH4 and eNOS uncoupling in the atria was partially restored in the prednisone-treated groups.Our study demonstrated that atrial fibrosis induced by ATP were suppressed by prednisone. Low-dose prednisone was also effective in suppressing the development of atrial fibrosis.

Electrical Remodeling of Left Atrium Is a Better Predictor for Recurrence Than Structural Remodeling in Atrial Fibrillation Patients Undergoing Radiofrequency Catheter Ablation

We demonstrated that the electrical remodeling represented by low voltage zone is a better marker for the prediction of recurrence after radiofrequency catheter ablation as compared with structural remodeling measured by left atrium (LA) diameter. The study provides important clue that further deep dive into LA substrate research will be important to improve success rate of non-paroxysmal atrial fibrillation ablation.

Background and Objectives

Recurrence rates after radiofrequency catheter ablation (RFCA) in atrial fibrillation (AF) patients are not low especially in non-paroxysmal AF. The diameter of left atrium (LA) has been widely used to predict the recurrence after RFCA for decades. However, LA diameter represents structural remodeling of LA and does not reflect electrical remodeling. We aimed to determine the predictive value of electrical remodeling of LA which is represented by the amount of low voltage zone (LVZ).

Methods

We performed a retrospective cohort analysis of AF patients who underwent de novo RFCA in a single-center.

Results

A total of 3,120 AF patients with de novo RFCA were analyzed. Among these patients, 537 patients underwent an electroanatomic mapping with bipolar voltage measurement of LA. The diameter of LA and flow velocity of LA appendage (LAA) differed significantly according to quartile group of LVZ area and percentage: patients with high LVZ had large LA diameter and low LAA flow velocity (p<0.001). Freedom from late recurrence (LR) was significantly lower in patients with high LVZ area and percentage (p<0.001). The diameter and surface area of LA had area under curve (AUC) of 0.592 and 0.593, respectively (p=0.002 for both). The predictive value of LVZ area (AUC, 0.676) and percentage (AUC, 0.671) were both superior compared with LA diameter (p=0.011 and 0.027 for each comparison).

Conclusions

In conclusion, LVZ can predict freedom from LR after RFCA in AF patients. Predictive value was higher in parameters reflecting electrical rather than structural remodeling of LA.

Exosomes and Exosomal Non-coding RNAs Are Novel Promises for the Mechanism-Based Diagnosis and Treatments of Atrial Fibrillation

Atrial fibrillation (AF) is the most common arrhythmia worldwide and has a significant impact on human health and substantial costs. Currently, there is a lack of accurate biomarkers for the diagnosis and prognosis of AF. Moreover, the long-term efficacy of the catheter ablation in the AF is unsatisfactory. Therefore, it is necessary to explore new biomarkers and treatment strategies for the mechanism-based AF. Exosomes are nano-sized biovesicles released by nearly all types of cells. Since the AF would be linked to the changes of the atrial cells and their microenvironment, and the AF would strictly influence the exosomal non-coding RNAs (exo-ncRNAs) expression, which makes them as attractive diagnostic and prognostic biomarkers for the AF. Simultaneously, the exo-ncRNAs have been found to play an important role in the mechanisms of the AF and have potential therapeutic prospects. Although the role of the exo-ncRNAs in the AF is being actively investigated, the evidence is still limited. Furthermore, there is a lack of consensus regarding the most appropriate approach for exosome isolation and characterization. In this article, we reviewed the new methodologies available for exosomes biogenesis, isolation, and characterization, and then discussed the mechanism of the AF and various levels and types of exosomes relevant to the AF, with the special emphasis on the exo-ncRNAs in the diagnosis, prognosis, and treatment of the mechanism-based AF.

Atrial fibrillation and atrial cardiomyopathies

Atrial fibrillation (AF) is the most common arrhythmia among adults. While there have been incredible advances in the management of AF and its clinical sequelae, investigation of atrial cardiomyopathies (ACMs) is becoming increasingly more prominent. ACM refers to the electromechanical changes-appreciated subclinically and/or clinically-that underlie atrial dysfunction and create an environment ripe for the development of clinically apparent AF. There are several subtypes of ACM, distinguished by histologic features. Recent progress in cardiovascular imaging, including echocardiography with speckle-tracking (e.g., strain analysis), cardiovascular magnetic resonance imaging (CMR), and atrial 4-D flow CMR, has enabled increased recognition of ACM. Identification of ACM and its features carry clinical implications, including elevating a patient's risk for development of AF, as well as associations with outcomes related to catheter-based and surgical AF ablation. In this review, we explore the definition and classifications of ACM, its complex relationship with clinical AF, imaging modalities, and clinical implications. We propose next steps for a more unified approach to ACM recognition that can direct further research into this complex field.

Blood-brain barrier disruption in atrial fibrillation: a potential contributor to the increased risk of dementia and worsening of stroke outcomes?

Atrial fibrillation (AF) has become one of the most significant health problems worldwide, warranting urgent answers to currently pending questions on the effects of AF on brain function. Recent evidence has emerged to show an association between AF and an increased risk of developing dementia and worsening of stroke outcomes. A healthy brain is protected by the blood–brain barrier (BBB), which is formed by the endothelial cells that line cerebral capillaries. These endothelial cells are continuously exposed to shear stress (the frictional force generated by blood flow), which affects endothelial cell structure and function. Flow disturbances as experienced during AF can disrupt the BBB and leave the brain vulnerable to damage. Investigating the plausible mechanisms in detail, linking AF to cerebrovascular damage is difficult in humans, leading to paucity of available clinical data. Here, we discuss the available evidence for BBB disruption during AF due to altered cerebral blood flow, and how this may contribute to an increased risk of dementia and worsening of stroke outcomes.

LncRNA Nuclear-Enriched Abundant Transcript 1 Regulates Atrial Fibrosis via the miR-320/NPAS2 Axis in Atrial Fibrillation

Atrial fibrosis is a key contributor to atrial fibrillation (AF). Long non-coding ribonucleic acids (lncRNAs) were demonstrated to exhibit a key role in fibrotic remodeling; however, the function of nuclear-enriched abundant transcript 1 (NEAT1) in atrial fibrosis remains unclear. In the present study, we showed that NEAT1 was upregulated in atrial tissues of AF patients and was positively related to collagen I (coll I) and collagen III (coll III) expressions. Furthermore, the deletion of NEAT1 attenuated angiotensin II (Ang II)-caused atrial fibroblast proliferation, migration, and collagen production. We further observed that NEAT1 knockdown improved Ang II caused mouse atrial fibrosis in in vivo experiments. Moreover, we demonstrated that NEAT1 could negatively regulate miR-320 expression by acting as a competitive endogenous RNA (ceRNA). miR-320 directly targeted neuronal per arnt sim domain protein 2 (NPAS2) and suppressed its expression. We observed that NEAT1 exerted its function via the miR-320–NPAS2 axis in cardiac fibroblasts. These findings indicate that NEAT1 exerts a significant effect on atrial fibrosis and that this lncRNA is a new potential molecular target for AF treatment.

P-wave indices in Japanese patients with ischemic stroke: Implication of atrial myopathy in subtype of ischemic stroke

BACKGROUND

P-wave indices have been not fully studied in subtypes of ischemic stroke. We compared P-wave indices among embolic stroke, lacunar stroke and the control.

METHODS

P-wave duration, advanced interatrial block (aIAB) defined as P-wave duration ≥120 ms and biphasic (positive negative) morphology in inferior leads, and P-terminal force in lead V1 (PTFV1) were measured at the time of the first episode of cardioembolic stroke in 81 patients with paroxysmal atrial fibrillation (PAF), and in 64 patients with lacunar stroke, and compared with 100 control subjects. The latter two groups had no episode of PAF.

RESULTS

The age of participants was 76 ± 11 years. Age, sex distribution, body mass index and CHADS2 score were comparable among three groups. Maximum P-wave duration, the longest across 12 leads, was significantly prolonged in cardioembolic and lacuna stroke compared to the control; 118 ± 12 ms and 118 ± 11 ms vs. 110 ± 11 ms, respectively (P < 0.0001). P-wave duration ≥120 ms and aIAB were more prevalent in ischemic stroke groups than the control, and associated with a higher Odds ratio for stroke, more so in cardioembolic stroke. However, PTFV1 value and the prevalence of PTFV1 ≥ 4.0 ms·mV were significantly not different among the three groups. Abnormal P-wave duration and aIAB indicating the presence of atrial myopathy were present in cardioembolic and lacuna stroke.

CONCLUSION

Atrial myopathy was present in cardioembolic and lacunar stroke, but it can't be the direct cause of small vessel occlusion in lacunar stroke. Roles of atrial myopathy in each subtype of ischemic stroke should be studied.

Identification of microRNAs enriched in exosomes in human pericardial fluid of patients with atrial fibrillation based on bioinformatic analysis

Background

Atrial fibrillation (AF) is related to structural and electrical atria remodeling. Atrial fibrosis development and progression is characteristic of structural remodeling and is taken as the AF perpetuation substrate. Increasing evidence has confirmed that microRNAs (miRNAs) are associated with AF, including cardiac fibrosis.

Methods

Pericardial fluid (PF) samples were collected from nine adult patients who had congenital heart disease with persistent AF or sinus rhythm (SR) undergoing surgery. Abnormally expressed miRNAs were acquired, and P<0.05 and fold change >2 were taken as the thresholds of differentially expressed miRNAs (DE-miRNAs). The predicted target genes were obtained by miRTarBase. The Database for Annotation, Visualization and Integrated Discovery was used to annotate functions and analyze pathway abundance for latent targets of DE-miRNAs. STRING database was applied to construct a protein–protein interplay (PPI) network, and Cytoscape software was used to visualize the miRNA-hub gene-Kyoto Encyclopedia of Genes and Genomes (KEGG) network. DE-miRNA expressions were evaluated by quantitative polymerase chain reaction (qPCR).

Results

Fifty-five exosomal DE-miRNAs were found between the AF and SR samples; these included 24 miRNAs that were upregulated and 31 that were downregulated. For the top 3 downregulated miRNAs (miR-382-3p, miR-3126-5p, and miR-450a-2-3p) 283 predicted target genes were identified, and were implicated in cardiac fibrosis-related pathways, including the hypoxia-inducible factor-1 (HIF1), mitogen-activated protein kinase (MAPK), and adrenergic and insulin pathways. The top 10 hub genes in the PPI network, including mitogen-activated protein kinase 1 (MAPK1) and AKT serine/threonine kinase 1 (AKT1), were identified as hub genes. By establishing the miRNA-hub gene-KEGG network, we observed that these hub genes, which were regulated by miR-382-3p, miR-3126-5p, and miR-450a-2-3p, were involved in many KEGG pathways associated with cardiac fibrosis, such as the AKT1/glycogen synthase kinsase-3β (GSK-3β) and transforming growth factor-β (TGF-β)/MAPK1 pathways.

Conclusions

The findings of the present study suggest that miR-382-3p, miR-450a-2-3p, and miR-3126-5p contained in exosomes in human PF are pivotal in the progression of AF. The results of qPCR showed that miR-382-3p was consistent with our sequencing data, which indicates its potential value as a therapeutic target for AF.

Galectin-3, N-terminal Propeptides of Type I and III Procollagen in Patients with Atrial Fibrillation and Metabolic Syndrome

The aim of this study was to determine the concentration of galectin-3, PINP and PIIINP in patients with metabolic syndrome (MS) and atrial fibrillation (AF) with an assessment of the relationship with severity of left atrium fibrosis. A total of 480 subjects were included in the case-control study: MS patients (n = 337), 176 of whom had AF, 72 patients with AF without MS and 71 healthy subjects. Galectin-3, PINP and PIIINP blood concentrations and metabolic parameters were compared with the severity of left atrium fibrosis, measured by CARTO3. Galectin-3 in AF and MS patients is higher than in MS without AF and in healthy subjects (10.3 (4.8–15.4), 5.1 (4.3–8.8), 3.2 (2.4–4.2) ng/mL, p < 0.0001). Galectin-3 serum concentration in AF patients with MS is higher than in patients without MS: 10.3 (4.8–15.4), 6.8 (5.2–8.1) ng/mL, p = 0.0001. PINP and PIIINP concentration were higher in patients with AF and MS than in MS without AF: 3499.1 (2299.2–4567.3), 2130.9 (1425.3–2861.8) pg/mL, p < 0.0001, 94.9 (64.8–123.5), 57.6 (40.5–86.9) ng/mL, p < 0.0001. Galectin-3 correlates with PINP (r = 0.496, p < 0.001) and PIIINP concentration (r = 0.451, p < 0.0001). The correlation between galectin-3, PINP and the severity of left atrium fibrosis was found (r = 0.410, p < 0.001; r = 0.623, p < 0.001). Galectin-3 higher than 12.6 ng/mL increased the risk of AF more than five-fold. High galectin-3, PINP and PIIINP concentrations were associated with heart remodeling in MS patients and increased the risk of AF.

Prospective Evaluation of Clinico-Pathological Predictors of Postoperative Atrial Fibrillation: An Ancillary Study From the OPERA Trial

BACKGROUND

Postoperative atrial fibrillation (POAF) occurs in 30% to 50% of patients undergoing cardiac surgery and is associated with increased morbidity and mortality. Prospective identification of structural/molecular changes in atrial myocardium that correlate with myocardial injury and precede and predict risk of POAF may identify new molecular pathways and targets for prevention of this common morbid complication.

METHODS

Right atrial appendage samples were prospectively collected during cardiac surgery from 239 patients enrolled in the OPERA trial (Omega-3 Fatty Acids for Prevention of Post-Operative Atrial Fibrillation), fixed in 10% buffered formalin, and embedded in paraffin for histology. We assessed general tissue morphology, cardiomyocyte diameters, myocytolysis (perinuclear myofibril loss), accumulation of perinuclear glycogen, interstitial fibrosis, and myocardial gap junction distribution. We also assayed NT-proBNP (N-terminal pro-B-type natriuretic peptide), hs-cTnT, CRP (C-reactive protein), and circulating oxidative stress biomarkers (F2-isoprostanes, F3-isoprostanes, isofurans) in plasma collected before, during, and 48 hours after surgery. POAF was defined as occurrence of postcardiac surgery atrial fibrillation or flutter of at least 30 seconds duration confirmed by rhythm strip or 12-lead ECG. The follow-up period for all arrhythmias was from surgery until hospital discharge or postoperative day 10.

RESULTS

Thirty-five percent of patients experienced POAF. Compared with the non-POAF group, they were slightly older and more likely to have chronic obstructive pulmonary disease or heart failure. They also had a higher European System for Cardiac Operative Risk Evaluation and more often underwent valve surgery. No differences in left atrial size were observed between patients with POAF and patients without POAF. The extent of atrial interstitial fibrosis, cardiomyocyte myocytolysis, cardiomyocyte diameter, glycogen score or Cx43 distribution at the time of surgery was not significantly associated with incidence of POAF. None of these histopathologic abnormalities were correlated with levels of NT-proBNP, hs-cTnT, CRP, or oxidative stress biomarkers.

CONCLUSIONS

In sinus rhythm patients undergoing cardiac surgery, histopathologic changes in the right atrial appendage do not predict POAF. They also do not correlate with biomarkers of cardiac function, inflammation, and oxidative stress. Graphic Abstract: A graphic abstract is available for this article.

Heart Failure in Atrial Fibrillation - An Update on Clinical and Echocardiographic Implications

Atrial fibrillation (AF) is the most common sustained arrhythmia in adults and has unfavorable consequences such as stroke, heart failure (HF), and death. HF is the most common adverse event following AF and the leading cause of death. Therefore, identifying the association between AF and HF is important to establish risk stratification for HF in AF. Recent studies suggested that left atrial and ventricular fibrosis is an important link between AF and HF, and the prognostic impact may differ with respect to HF subtype, stratified with left ventricular ejection fraction (EF). Mortality risk in patients with concurrent AF and HF with reduced EF (HFrEF) appears slightly higher compared with those with concurrent AF and HF with preserved EF (HFpEF). On the other hand, the prognostic impact of HF in AF is similar between HFrEF and HFpEF. Further, left atrial size, as well as left atrial and left ventricular functional assessment, are reported to be useful for the prediction of HF in AF, incremental to the conventional risk factors. In this review, we focus on the epidemiological, pathophysiological, and prognostic associations between AF and HF, and review the clinical and echocardiographic predictors for HF in AF.

Clinicopathological Bird's-Eye View of Left Atrial Myocardial Fibrosis in 121 Patients With Persistent Atrial Fibrillation: Developing Architecture and Main Cellular Players

BACKGROUND

Scientific research on atrial fibrosis in atrial fibrillation (AF) has mainly focused on quantitative or molecular features. The purpose of this study was to perform a clinicoarchitectural/structural investigation of fibrosis to provide one key to understanding the electrophysiological/clinical aspects of AF.

METHODS

We characterized the fibrosis (amount, architecture, cellular components, and ultrastructure) in left atrial biopsies from 121 patients with persistent/long-lasting persistent AF (group 1; 59 males; 60±11 years; 91 mitral disease-related AF, 30 nonmitral disease-related AF) and from 39 patients in sinus rhythm with mitral valve regurgitation (group 2; 32 males; 59±12 years). Ten autopsy hearts served as controls.

RESULTS

Qualitatively, the fibrosis exhibited the same characteristics in all cases and displayed particular architectural scenarios (which we arbitrarily subdivided into 4 stages) ranging from isolated foci to confluent sclerotic areas. The percentage of fibrosis was larger and at a more advanced stage in group 1 versus group 2 and, within group 1, in patients with rheumatic disease versus nonrheumatic cases. In patients with AF with mitral disease and no rheumatic disease, the percentage of fibrosis and the fibrosis stages correlated with both left atrial volume index and AF duration. The fibrotic areas mainly consisted of type I collagen with only a minor cellular component (especially fibroblasts/myofibroblasts; average value range 69-150 cells/mm², depending on the areas in AF biopsies). A few fibrocytes-circulating and bone marrow-derived mesenchymal cells-were also detectable. The fibrosis-entrapped cardiomyocytes showed sarcolemmal damage and connexin 43 redistribution/internalization.

CONCLUSIONS

Atrial fibrosis is an evolving and inhomogeneous histological/architectural change that progresses through different stages ranging from isolated foci to confluent sclerotic zones which-seemingly-constrain impulse conduction across restricted regions of electrotonically coupled cardiomyocytes. The fibrotic areas mainly consist of type I collagen extracellular matrix and, only to a lesser extent, mesenchymal cells.

Catheter Ablation in the Treatment of Atrial Fibrillation

Catheter ablation (CA) of the pulmonary veins for atrial fibrillation (AF) is growing exponentially and is the most commonly performed electrophysiologic procedure. Initial descriptions focused on CA for paroxysmal AF, and now more recently expanded in application to persistent AF and those with comorbid heart failure. Efforts to improve success have and continue to address issues such as pulmonary vein "reconnection" following ablation through different ablative energy modalities, and the use of a "hybrid" surgical/endocardial combined approach in persistent forms of AF. Technologic advances as well are concurrently seeking to improve safety, particularly regarding the incidence of atrio-esophageal fistula in this seemingly ever-growing ablation population.

Serum N-Acetylneuraminic Acid Is Associated with Atrial Fibrillation and Left Atrial Enlargement

Purpose

Recent studies have indicated that N-acetylneuraminic acid (Neu5Ac) plays a key role in severe coronary artery diseases, involving RhoA signaling pathway activation, which is critically involved in cardiac fibrosis. There is convincing evidence from many studies that left atrium fibrosis is involved in the pathophysiology of AF. Therefore, we speculated that Neu5Ac may be associated with atrial fibrillation (AF) and involved in the development of AF. This study aims to investigate the clinical relationship between Neu5Ac and AF and left atrial enlargement.

Methods

Forty-five patients with AF (AF group) and forty-five patients with non-AF (control group) matched for age, sex, and hospitalization date were recruited for our study. Plasma concentrations of Neu5Ac from peripheral venous blood were analyzed using enzyme-linked immunosorbent assay (ELISA). The baseline characteristics, plasma level of Neu5Ac, and echocardiographic characteristics were evaluated.

Results

The plasma level of Neu5Ac was significantly higher in the AF group than in the control group (107.66 ± 47.50 vs 77.87 ± 39.09  ng/ml; P < 0.05); the left atrial diameters were positively correlated with the plasma Neu5Ac level (R = 0.255; P < 0.05). The plasma Neu5Ac level (R = 0.368; P < 0.05) and the left atrial diameters (R = 0.402; P < 0.05) were positively correlated with AF history times. Neu5Ac (odds ratio 1.018, 95% CI 1.003–1.032; P < 0.05) and the left atrial diameter (odds ratio 1.142, 95% CI 1.020–1.280; P < 0.05) were independent risk factors for AF in multivariate regression analysis.

Conclusions

Serum Neu5Ac is associated with atrial fibrillation, and the mechanism may involve left atrial enlargement.

Development of endomyocardial fibrosis model using a cell patterning technique: In vitro interaction of cell coculture of 3T3 fibroblasts and RL-14 cardiomyocytes

Cardiac functions can be altered by changes in the microstructure of the heart, i.e., remodeling of the cardiac tissue, which may activate pathologies such as hypertrophy, dilation, or cardiac fibrosis. Cardiac fibrosis can develop due to an excessive deposition of extracellular matrix proteins, which are products of the activation of fibroblasts. In this context, the anatomical-histological change may interfere with the functioning of the cardiac tissue, which requires specialized cells for its operation. The purpose of the present study was to determine the cellular interactions and morphological changes in cocultures of 3T3 fibroblasts and RL-14 cardiomyocytes via the generation of a platform an in vitro model. For this purpose, a platform emulating the biological characteristics of endomyocardial fibrosis was generated using a cell patterning technique to study morphological cellular changes in compact and irregular patterns of fibrosis. It was found that cellular patterns emulating the geometrical distributions of endomyocardial fibrosis generated morphological changes after interaction of the RL-14 cardiomyocytes with the 3T3 fibroblasts. Through this study, it was possible to evaluate biological characteristics such as cell proliferation, adhesion, and spatial distribution, which are directly related to the type of emulated endomyocardial fibrosis. This research concluded that fibroblasts inhibited the proliferation of cardiomyocytes via their interaction with specific microarchitectures. This behavior is consistent with the histopathological distribution of cardiac fibrosis; therefore, the platform developed in this research could be useful for the in vitro assessment of cellular microdomains. This would allow for the experimental determination of interactions with drugs, substrates, or biomaterials within the engineering of cardiac tissues.

Atrial fibrosis and decreased connexin 43 in rat hearts after exposure to high-intensity infrasound

BACKGROUND

Noise is an important environmental risk factor. Industrial environments are rich in high-intensity infrasound (hi-IFS), which we have found to induce myocardial and coronary perivascular fibrosis in rats. The effects of exposure to IFS on the ventricles have been studied, but not on the atria. We hypothesized that rats exposed to hi-IFS develop atrial remodeling involving fibrosis and connexin 43, which we sought to evaluate.

MATERIAL AND METHODS

Seventy-two Wistar rats, half exposed to hi-IFS (120 dB, <20 Hz) during a maximum period of 12 weeks and half age-matched controls, were studied. Atrial fibrosis was analyzed by Chromotrope-aniline blue staining. The immunohistochemical evaluation of Cx43 was performed using the polyclonal antibody connexin-43 m diluted 1:1000 at 4 °C overnight. Digitized images were obtained with an optical microscope using 400× magnifications. The measurements were performed using image J software. A two-way ANOVA model was used to compare the groups.

RESULTS

The mean values of the ratio "atrial fibrosis / cardiomyocytes" increased to a maximum of 0.1095 ± 0,04 and 0.5408 ± 0,01, and of the ratio "CX43 / cardiomyocytes" decreased to 0.0834 ± 0,03 and 0.0966 ± 0,03, respectively in IFS-exposed rats and controls. IFS-exposed rats exhibited a significantly higher ratio of fibrosis (p < .001) and lower ratio of Cx43 (p = .009).

CONCLUSION

High-intensity infrasound exposure leads to an increase in atrial interstitial fibrosis and a decrease in connexin 43 in rat hearts. This finding reinforces the need for further experimental and clinical studies concerning the effects of exposure to infrasound.

Fibrosis independent atrial fibrillation in older patients is driven by substrate leukocyte infiltration: diagnostic and prognostic implications to patients undergoing cardiac surgery

Background

The objectives of the study were to characterize and quantify cellular inflammation and structural remodeling of human atria and correlate findings with molecular markers of inflammation and patient surrogate outcome.

Methods

Voluntary participants undergoing heart surgery were enrolled in the study and blood samples were collected prior to surgery, and right atrium samples were harvested intraoperatively. Blood samples were analyzed by flow cytometry and complete blood counts. Atrial samples were divided for fixed fibrosis analysis, homogenized for cytokine analysis and digested for single cell suspension flow cytometry.

Results

A total of 18 patients were enrolled and samples assessed. Isolated cells from the atria revealed a CD45+ population of ~ 20%, confirming a large number of leukocytes. Further characterization revealed this population as 57% lymphocytes and 26% monocyte/macrophages (MoΦ), with the majority of the latter cells being classical (CD14++/CD16−). Interstitial fibrosis was present in 87% of samples and correlated significantly with patient age. Older patients (> 65) had significantly more atrial fibrosis and cellular inflammation. AFib patients had no distinguishing feature of atrial fibrosis and had significantly greater CD45+ MoΦ, increased expression of MMP9 and presented with a significant correlation in length of stay to CCL-2/MCP-1 and NLR (neutrophil-to-lymphocyte ratio).

Conclusion

Atrial fibrosis is correlated with age and not determinate to AFib. However, severity of atrial leukocyte infiltration and markers of matrix degradation are determinant to AFib. This also correlated with CCL2 (or MCP-1) and NLR-indicative of marked inflammation. These data show the potential importance of diagnostic and prognostic assessments that could inform clinical decision making in regard to the intensity of AFib patient management.

Atrial Myopathy

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The authors discuss the concept of atrial myopathy; its relationship to aging, electrophysiological remodeling, and autonomic remodeling; the interplay between atrial myopathy, AF, and stroke; and suggest how to identify patients with atrial myopathy and how to incorporate atrial myopathy into decisions about anticoagulation.

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Atrial myopathy seen in animal models of AF and in patients with AF is the result of a combination of factors that lead to electrical and structural remodeling in the atrium. Although AF may lead to the initiation and/or progression of this myopathy, the presence of AF is by no means essential to the development or the maintenance of the atrial myopathic state.

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Methods to identify atrial myopathy include atrial electrograms, tissue biopsy, cardiac imaging, and certain serum biomarkers. A promising modality is 4-dimensional flow cardiac magnetic resonance. The concept of atrial myopathy may help guide oral anticoagulant therapy in selected groups of patients with AF, particularly those with low to intermediate risk of strokes and those who have undergone successful AF ablation. This review highlights the need for prospective randomized trials to test these hypotheses.

This paper discusses the evolving concept of atrial myopathy by presenting how it develops and how it affects the properties of the atria. It also reviews the complex relationships among atrial myopathy, atrial fibrillation (AF), and stroke. Finally, it discusses how to apply the concept of atrial myopathy in the clinical setting—to identify patients with atrial myopathy and to be more selective in anticoagulation in a subset of patients with AF. An apparent lack of a temporal relationship between episodes of paroxysmal AF and stroke in patients with cardiac implantable electronic devices has led investigators to search for additional factors that are responsible for AF-related strokes. Multiple animal models and human studies have revealed a close interplay of atrial myopathy, AF, and stroke via various mechanisms (e.g., aging, inflammation, oxidative stress, and stretch), which, in turn, lead to fibrosis, electrical and autonomic remodeling, and a pro-thrombotic state. The complex interplay among these mechanisms creates a vicious cycle of ever-worsening atrial myopathy and a higher risk of more sustained AF and strokes. By highlighting the importance of atrial myopathy and the risk of strokes independent of AF, this paper reviews the methods to identify patients with atrial myopathy and proposes a way to incorporate the concept of atrial myopathy to guide anticoagulation in patients with AF.

Thromboembolism in the Absence of Atrial Fibrillation

Atrial fibrillation (AF) is associated with thrombus formation in the left atrial appendage and systemic embolic events including ischemic stroke. Cardiogenic thromboembolism can also occur in the absence of clinical AF as a result of various pathological conditions affecting the endocardium. The inconsistent temporal relation between AF and ischemic events has stimulated exploration for factors other than clinical AF that contribute to thromboembolism. These include subclinical AF, a thrombogenic atrial cardiomyopathy, and left atrial appendage dysfunction and embolism from other sources. In conclusion, thromboembolism during normal sinus rhythm is likely multifactorial, involving intertwined pathologic processes. Patients at risk, if accurately identified, could theoretically benefit from anticoagulation.

Biomarkers Associated with Atrial Fibrosis and Remodeling

Atrial fibrillation is the most common rhythm disturbance encountered in clinical practice. Although often considered as solely arrhythmic in nature, current evidence has established that atrial myopathy constitutes both the substrate and the outcome of atrial fibrillation, thus initiating a vicious, self-perpetuating cycle. This myopathy is triggered by stress-induced (including pressure/volume overload, inflammation, oxidative stress) responses of atrial tissue, which in the long term become maladaptive, and combine elements of both structural, especially fibrosis, and electrical remodeling, with contemporary approaches yielding potentially useful biomarkers of these processes. Biomarker value becomes greater given the fact that they can both predict atrial fibrillation occurrence and treatment outcome. This mini-review will focus on the biomarkers of atrial remodeling (both electrical and structural) and fibrosis that have been validated in human studies, including biochemical, histological and imaging approaches.

Atrial contractility and fibrotic biomarkers are associated with atrial fibrillation after elective coronary artery bypass grafting

OBJECTIVE

New-onset postoperative atrial fibrillation is common after cardiac surgery. Less has been reported about the relationship among fibrosis, inflammation, calcium-induced left atrial and right atrial contractile forces, and postoperative atrial fibrillation. We sought to identify predictors of postoperative atrial fibrillation.

METHODS

From August 2016 to February 2018, we evaluated 229 patients who had preoperative sinus rhythm before elective primary coronary artery bypass grafting. Of 229 patients, 191 maintained sinus rhythm postoperatively, whereas 38 patients developed atrial fibrillation. Preoperative tissue inhibitor of metalloproteinase-1, pentraxin-3, matrix metallopeptidase-9, galectin-3, high-sensitivity C-reactive protein, growth differentiation factor 15, and transforming growth factor-ß were measured. Clinical and echocardiographic findings (tricuspid annular plane systolic excursion for right heart function) and calcium-induced force measurements from left atrial and right atrial-derived skinned myocardial fibers were recorded.

RESULTS

Patients with atrial fibrillation were older (P = .001), had enlarged left atrial (P = .0001) and right atrial areas (P = .0001), and had decreased tricuspid annular plane systolic excursion (P = .001). Levels of matrix metallopeptidase-9 and pentraxin-3 were decreased (P < .05), whereas growth differentiation factor 15 was increased (P = .001). We detected lower left atrial force values at calcium-induced force measurements 5.5 (P < .05), 5.4 (P < .01), and 5.3 to 4.52 (P = .0001) and right atrial force values at calcium-induced force measurements 5.0 to 4.52 (P < .05) in patients with postoperative atrial fibrillation. Multivariable analysis showed that advanced age (P = .033), decreased left atrial force value at calcium-induced force measurement of 5.5 (P = .033), enlarged left atrial (P = .013) and right atrial (P = .081) areas, and reduced tricuspid annular plane systolic excursion (P = .010) independently predicted postoperative atrial fibrillation.

CONCLUSIONS

Advanced age, decreased left atrial force value at calcium-induced force measurement of 5.5, enlarged left atrial and right atrial areas, and reduced tricuspid annular plane systolic excursion were identified as independent predictors for postoperative atrial fibrillation.

Entropy Mapping Approach for Functional Reentry Detection in Atrial Fibrillation: An In-Silico Study

Catheter ablation of critical electrical propagation sites is a promising tool for reducing the recurrence of atrial fibrillation (AF). The spatial identification of the arrhythmogenic mechanisms sustaining AF requires the evaluation of electrograms (EGMs) recorded over the atrial surface. This work aims to characterize functional reentries using measures of entropy to track and detect a reentry core. To this end, different AF episodes are simulated using a 2D model of atrial tissue. Modified Courtemanche human action potential and Fenton–Karma models are implemented. Action potential propagation is modeled by a fractional diffusion equation, and virtual unipolar EGM are calculated. Episodes with stable and meandering rotors, figure-of-eight reentry, and disorganized propagation with multiple reentries are generated. Shannon entropy (ShEn), approximate entropy (ApEn), and sample entropy (SampEn) are computed from the virtual EGM, and entropy maps are built. Phase singularity maps are implemented as references. The results show that ApEn and SampEn maps are able to detect and track the reentry core of rotors and figure-of-eight reentry, while the ShEn results are not satisfactory. Moreover, ApEn and SampEn consistently highlight a reentry core by high entropy values for all of the studied cases, while the ability of ShEn to characterize the reentry core depends on the propagation dynamics. Such features make the ApEn and SampEn maps attractive tools for the study of AF reentries that persist for a period of time that is similar to the length of the observation window, and reentries could be interpreted as AF-sustaining mechanisms. Further research is needed to determine and fully understand the relation of these entropy measures with fibrillation mechanisms other than reentries.

Genetics of Atrial Fibrilation: In Search of Novel Therapeutic Targets

Atrial fibrillation (AF) is the most frequent arrhythmogenic disease in humans, ranging from 2% in the general population and rising up to 10-12% in 80+ years. Genetic analyses of AF familiar cases have identified a series of point mutations in distinct ion channels, supporting a causative link. However, these genetic defects only explain a minority of AF patients. Genomewide association studies identified single nucleotide polymorphisms (SNPs), close to PITX2 on 4q25 chromosome, that are highly associated to AF. Subsequent GWAS studies have identified several new loci, involving additional transcription and growth factors. Furthermore, these risk 4q25 SNPs serve as surrogate biomarkers to identify AF recurrence in distinct surgical and pharmacological interventions. Experimental studies have demonstrated an intricate signalling pathway supporting a key role of the homeobox transcription factor PITX2 as a transcriptional regulator. Furthermore, cardiovascular risk factors such as hyperthyroidism, hypertension and redox homeostasis have been identified to modulate PITX2 driven gene regulatory networks. We provide herein a state-of-the-art review of the genetic bases of atrial fibrillation, our current understanding of the genetic regulatory networks involved in AF and its plausible usage for searching novel therapeutic targets.

The effect of complex intramural microstructure caused by structural remodeling on the stability of atrial fibrillation: Insights from a three-dimensional multi-layer modeling study

BACKGROUND

Recent researches have suggested that the complex three-dimensional structures caused by structural remodeling play a key role in atrial fibrillation (AF) substrates. Here we aimed to investigate this hypothesis using a multi-layer model representing intramural microstructural features.

METHODS

The proposed multi-layer model was composed of the endocardium, connection wall, and epicardium. In the connection wall, intramural fibrosis was simulated using fibrotic patches randomly scattered in the myocardial tissue of fibrotic layers, while endo-epicardial dissociation was simulated using myocardial patches randomly scattered in the fibrotic tissue of isolation layers. Multiple simulation groups were generated to quantitatively analyze the effects of endo-epicardial dissociation and intramural fibrosis on AF stability, including a stochastic group, interrelated groups, fibrosis-degree-controlled groups, and dissociation-degree-controlled groups.

RESULTS

1. Stable intramural re-entries were observed to move along complete re-entrant circuits inside the transmural wall in four of 65 simulations in the stochastic group. 2. About 21 of 23 stable simulations in the stochastic group were distributed in the areas with high endo-epicardial dissociation and intramural fibrosis. 3. The difference between fibrosis-degree-controlled groups and dissociation-degree-controlled groups suggested that some distributions of connection areas may affect AF episodes despite low intramural fibrosis and endo-epicardial dissociation. 4. The overview of tracking phase singularities revealed that endo-epicardial dissociation played a visible role in AF substrates.

CONCLUSION

The complex intramural microstructure is positively correlated with critical components of AF maintenance mechanisms. The occurrence of intramural re-entry further indicates the complexity of AF wave-dynamics.

Chronic obstructive pulmonary disease and the development of atrial fibrillation

BACKGROUND

Chronic obstructive pulmonary disease (COPD) has been associated with atrial fibrillation (AF). More insight into the epidemiology and underlying mechanisms is required to optimize management.

METHODS

The Rotterdam Study is a large, population-based cohort study with long-term follow-up. Time dependent Cox proportional hazard models were constructed to study the effect of COPD on incident AF, adjusted for age, sex and pack years of cigarette smoking, and additionally stratified according to exacerbation frequency, left atrial size and baseline systemic inflammatory levels.

RESULTS

1369 of 10,943 subjects had COPD, of whom 804 developed AF. The AF incidence rate was 14 per 1000 person years in COPD and 8 per 1000 person years in subjects without COPD. The adjusted hazard ratio (HR) for COPD subjects to develop AF as compared to subjects without COPD was 1.28 (95%CI [1.04, 1.57]). COPD subjects with frequent exacerbations had a twofold increased AF risk (HR 1.99 [1.42, 2.79]) and COPD subjects with a left atrial size ≥40 mm also had an elevated AF risk (HR 1.77 [1.07, 2.94]). COPD subjects with baseline systemic inflammatory levels above the median had significantly increased AF risks (hsCRP≥1.83 mg/L: HR 1.51 [1.13, 2.03] and IL6 ≥ 1.91 ng/L: HR 2.49 [1.18, 5.28]), whereas COPD subjects below the median had in both analyses no significantly increased AF risk.

CONCLUSIONS

COPD subjects had a 28% increased AF risk, which further increased with frequent exacerbations and an enlarged left atrium. The risk was driven by COPD subjects having elevated systemic inflammatory levels.

Left Atrium Wall-mapping Application for Wall Thickness Visualisation

The measurement method for the LA wall thickness (WT) using cardiac computed tomography (CT) is observer dependent and cannot provide a rapid and comprehensive visualisation of the global LA WT. We aim to develop a LA wall-mapping application to display the global LA WT on a coplanar plane. The accuracy, intra-observer, and inter-observer reproducibility of the application were validated using digital/physical phantoms, and CT images of eight patients. This application on CT-based LA WT measures were further validated by testing six pig cardiac specimens. To evaluate its accuracy, the expanded maps of the physical phantom and pig LA were generated from the CT images and compared with the expanded map of the digital phantom and LA wall of pig heart. No significant differences (p > 0.05) were found between physical phantom and digital phantom as well as pig heart specimen and CT images using our application. Moreover, the analysis was based on the LA physical phantom or images of clinical patients; the results consistently demonstrated high intra-observer reproducibility (ICC > 0.9) and inter-observer reproducibility (ICC > 0.8) and showed good correlation between measures of pig heart specimen and CT data (r = 0.96, p < 0.001). The application can process and analyse the LA architecture for further visualisation and quantification.

Atrial thrombogenesis in atrial fibrillation : Results from atrial fibrillation models and AF-patients

Atrial fibrillation (AF) is the most common cause of thromboembolic complications. The risk of suffering a thromboembolic complication depends on the accompanying cardiac risk factors and the patient's age. For patients who have an increased risk, which is now classified using the CHA2DS2-VASc score, initiation of long-term oral anticoagulation is the first-line treatment. In AF, thrombi arise in the left atrial appendage. The present review will summarize the basic pathophysiology of thrombogenesis in AF and will provide the molecular basis of a process called prothrombotic endocardial remodeling. Despite oral anticoagulation being a central component of therapy, the present results can be used to support concomitant therapy with statins, angiotensin II blockers, etc. to inhibit atrial thromogenesis.

Integrating new approaches to atrial fibrillation management: the 6th AFNET/EHRA Consensus Conference

There are major challenges ahead for clinicians treating patients with atrial fibrillation (AF). The population with AF is expected to expand considerably and yet, apart from anticoagulation, therapies used in AF have not been shown to consistently impact on mortality or reduce adverse cardiovascular events. New approaches to AF management, including the use of novel technologies and structured, integrated care, have the potential to enhance clinical phenotyping or result in better treatment selection and stratified therapy. Here, we report the outcomes of the 6th Consensus Conference of the Atrial Fibrillation Network (AFNET) and the European Heart Rhythm Association (EHRA), held at the European Society of Cardiology Heart House in Sophia Antipolis, France, 17-19 January 2017. Sixty-two global specialists in AF and 13 industry partners met to develop innovative solutions based on new approaches to screening and diagnosis, enhancing integration of AF care, developing clinical pathways for treating complex patients, improving stroke prevention strategies, and better patient selection for heart rate and rhythm control. Ultimately, these approaches can lead to better outcomes for patients with AF.

Preferential myofibroblast differentiation of cardiac mesenchymal progenitor cells in the presence of atrial fibrillation

Atrial fibrillation (AF) is characterized by electrical, contractile, and structural remodeling mediated by interstitial fibrosis. It has been shown that human cardiac mesenchymal progenitor cells (CMPCs) can be differentiated into endothelial, smooth muscle, and fibroblast cells. Here, we have investigated, for the first time, the contribution of CMPCs in the fibrotic process occurring in AF. As expected, right auricolae samples displayed significantly higher fibrosis in AF vs control (CTR) patients. In tissue samples of AF patients only, double staining for c-kit and the myofibroblast marker α-smooth muscle actin (α-SMA) was detected. The number of c-kit-positive CMPC was higher in atrial subepicardial regions of CTR than AF cells. AF-derived CMPC (AF-CMPC) and CTR-derived CMPC (Ctr-CMPC) were phenotypically similar, except for CD90 and c-kit, which were significantly more present in AF and CTR cells, respectively. Moreover, AF showed a lower rate of population doubling and fold enrichment vs Ctr-CMPC. When exogenously challenged with the profibrotic transforming growth factor-β1 (TGF-β1), AF-CMPC showed a significantly higher nuclear translocation of SMAD2 than Ctr-CMPC. In addition, TGF-β1 treatment induced the upregulation of COL1A1 and COL1A2 in AF-CMPC only. Further, both a marked production of soluble collagen and α-SMA upregulation have been observed in AF-CMPC only. Finally, electrophysiological studies showed that the inwardly rectifying potassium current (I_K1) was evenly present in AF- and Ctr-CMPC in basal conditions and similarly disappeared after TGF-β1 exposure. All together, these data suggest that AF steers the resident atrial CMPC compartment toward an electrically inert profibrotic phenotype.

Premature senescence of cardiac fibroblasts and atrial fibrosis in patients with atrial fibrillation

Premature senescence is associated with atrial fibrosis and has an antifibrotic effect in mice. However, the role of senescence in atrial fibrillation (AF) remains unclear. Here, we investigated the association of premature senescence with fibrosis and also determined the role of senescence in the recurrence of AF after surgery ablation. Western blot, Sirius red staining, SA-β-gal staining and immunohistochemistry were performed to detect the degree of atrial fibrosis ,the expression of TGF-β and collagens, and also the senescence markers in 72 tissue specimens of left atrial appendage in this study. Then the patients undergoing successful surgical ablation were followed up for 12 months. The expression of collagens and TGF-β was paralleled by a high level of atrial fibrosis and were increased in AF group, especially in the persistent AF group. Western blotting of P16 and SA-β-gal staining showed an increased premature senescence in the sinus rhythm, paroxysmal AF and persistent AF groups. In addition, positive area of senescence markers, SA-β-gal and P16, was correlated positively with fibrotic lesions. We also found a lower ratio of P16/TGF-β in patients with recurrence of AF than in patients without recurrent AF. In conclusion, premature senescence is associated with atrial fibrosis in AF, and may have an antifibrotic role in AF.

Left atrial remodeling, hypertrophy, and fibrosis in mouse models of heart failure

Left ventricular dysfunction increases left atrial pressures and causes atrial remodeling. In human subjects, increased left atrial size is a powerful predictor of mortality and adverse events in a broad range of cardiac pathologic conditions. Moreover, structural remodeling of the atrium plays an important role in the pathogenesis of atrial tachyarrhythmias. Despite the potential value of the atrium in assessment of functional endpoints in myocardial disease, atrial pathologic alterations in mouse models of left ventricular disease have not been systematically investigated. Our study describes the geometric, morphologic, and structural changes in experimental mouse models of cardiac pressure overload (induced through transverse aortic constriction), myocardial infarction, and diabetes. Morphometric and histological analysis showed that pressure overload was associated with left atrial dilation, increased left atrial mass, loss of myofibrillar content in a subset of atrial cardiomyocytes, atrial cardiomyocyte hypertrophy, and atrial fibrosis. In mice undergoing nonreperfused myocardial infarction protocols, marked left ventricular systolic dysfunction was associated with left atrial enlargement, atrial cardiomyocyte hypertrophy, and atrial fibrosis. Both infarcted animals and pressure overloaded mice exhibited attenuation and perturbed localization of atrial connexin-43 immunoreactivity, suggesting gap junctional remodeling. In the absence of injury, obese diabetic db/db mice had diastolic dysfunction associated with atrial dilation, atrial cardiomyocyte hypertrophy, and mild atrial fibrosis. Considering the challenges in assessment of clinically relevant functional endpoints in mouse models of heart disease, study of atrial geometry and morphology may serve as an important new tool for evaluation of ventricular function.

How to detect atrial fibrosis

In the last twenty years, new imaging techniques to assess atrial function and to predict the risk of recurrence of atrial fibrillation after treatment have been developed. The present review deals with the role of these techniques in the detection of structural and functional changes of the atrium and diagnosis of atrial remodeling, particularly atrial fibrosis. Echocardiography allows the detection of anatomical, functional changes and deformation of the atrial wall during the phases of the cardiac cycle. For this, adequate acquisition of atrial images is necessary using speckle tracking imaging and interpretation of the resulting strain and strain rate curves. This allows to predict new-onset atrial fibrillation and recurrences. Its main limitations are inter-observer variability, the existence of different software manufacturers, and the fact that the software used were originally developed for the evaluation of the ventricular function and are now applied to the atria. Cardiac magnetic resonance, using contrast enhancement with gadolinium, plays a key role in the visualization and quantification of atrial fibrosis. This is the established method for in vivo visualization of myocardial fibrotic tissue. The non-invasive evaluation of atrial fibrosis is associated with the risk of recurrence of atrial fibrillation and with electro-anatomical endocardial mapping. We discuss the limitations of these techniques, derived from the difficulty of demonstrating the correlation between fibrosis imaging and histology, and poor intra- and inter-observer reproducibility. The sources of discordance are described, mainly due to image acquisition and processing, and the challenges ahead in an attempt to eliminate differences between operators.

Oncostatin M was associated with thrombosis in patients with atrial fibrillation

The mechanism underlying thrombosis in atrial fibrillation (AF) is not yet clearly understood. Oncostatin M (OSM), as a member of IL-6 family, is involved in atherosclerosis-mediated thrombosis. The present study hypothesizes that OSM and its downstream factors play a role in thrombogenesis in AF.The specimens of left atrial appendages collected from patients with rheumatic mitral stenosis who underwent valve replacement were divided into 3 groups: sinus rhythm, AF(+)/thrombus(-), and AF(+)/thrombus(+) group. The macrophage infiltration in atrial tissue was assessed by immunohistochemistry, and the amount of OSM, tissue factor (TF), and tissue factor pathway inhibitors (TFPIs) was detected by Western blot.The infiltration of the M1 macrophages was significantly increased in the AF with thrombus group compared with the sinus rhythm group (P = .03). Moreover, the expression of OSM and TF was much higher in the AF with thrombus group compared with the sinus rhythm group (P = .02, .009, respectively) while the TFPI was decreased in the AF with thrombus group (P = .04).OSM might be correlated with thrombosis in patients with AF mediated by TF and TFPI.

Analysis of immune cell populations in atrial myocardium of patients with atrial fibrillation or sinus rhythm

Background

Atrial fibrillation (AF) is the most common arrhythmia and despite obvious clinical importance remains its pathogenesis only partially explained. A relation between inflammation and AF has been suggested by findings of increased inflammatory markers in AF patients.

Objective

The goal of this study was to characterize morphologically and functionally CD45-positive inflammatory cell populations in atrial myocardium of patients with AF as compared to sinus rhythm (SR).

Methods

We examined 46 subjects (19 with AF, and 27 in SR) undergoing coronary bypass or valve surgery. Peroperative bioptic samples of the left and the right atrial tissue were examined using immunohistochemistry.

Results

The number of CD3+ T-lymphocytes and CD68-KP1+ cells were elevated in the left atrial myocardium of patients with AF compared to those in SR. Immune cell infiltration of LA was related to the rhythm, but not to age, body size, LA size, mitral regurgitation grade, type of surgery, systemic markers of inflammation or presence of diabetes or hypertension. Most of CD68-KP1+ cells corresponded to dendritic cell population based on their morphology and immunoreactivity for DC-SIGN. The numbers of mast cells and CD20+ B-lymphocytes did not differ between AF and SR patients. No foci of inflammation were detected in any sample.

Conclusions

An immunohistochemical analysis of samples from patients undergoing open heart surgery showed moderate and site-specific increase of inflammatory cells in the atrial myocardium of patients with AF compared to those in SR, with prevailing population of monocyte-macrophage lineage. These cells and their cytokine products may play a role in atrial remodeling and AF persistence.

Early Cardioversion in Atrial Fibrillation: Earlier Is Better, but Not Always and (Maybe) Not Immediately

Atrial fibrillation (AF) is the most common cardiac arrhythmia in humans. One of its important features is the tendency to become more persistent over time, even in the absence of underlying progressive heart disease. Conversion and maintenance of sinus rhythm by pharmacological or electrical methods become increasingly difficult the longer the arrhythmia persists. Electrical, mechanical, structural, and autonomic remodeling processes have been implicated in the mechanisms of AF initiation, perpetuation, and progression. Prevention or reversal of these remodeling processes can halt the progression of the disease. Cardioversion is a powerful tool and rhythm control is a widely used strategy in the management of AF. However, important questions remain unanswered regarding not only if, but also when to perform cardioversion. There are observations from past trials and clinical situations that support attempting to restore sinus rhythm, but further prospective randomized clinical trials are needed. Optimal timing of cardioversion remains somewhat uncertain, but it appears to be some time after the first few hours and before the first few months: the earlier, the better, but not always, and maybe not immediately, and it has to be tailored to the clinical situation and its many variables. This review is intended to summarize the evidence supporting early intervention for the prevention of remodeling in patients with AF.