Substrate For Atrial Fibrillation Research Articles

Myofibroblast-Derived Exosomes Contribute to Development of a Susceptible Substrate for Atrial Fibrillation

Objective: Atrial fibrosis plays a critical role in atrial fibrillation (AF). A key event in the pathogenesis of fibrosis is the activation of fibroblasts (FBs) into myofibroblasts (MFBs). Paracrine factors released from MFBs lead to ion channel expression changes in cardiomyocytes (CMs). Downregulation of L-type calcium channel Ca_v1.2 expression is a hallmark of AF-associated ionic remodeling. However, whether exosome (Exo)-mediated crosstalk between MFBs and CMs regulates Ca_v1.2 expression remains unknown. Methods: Atrial FBs and CMs were isolated and cultured from neonatal rats by enzymatic digestion. The activation of FBs into MFBs was induced by angiotensin II. Co-culture assay and in vitro Exo treatment were used to determine the effect of MFB-derived Exos on Ca_v1.2 expression. Confocal Ca²⁺ imaging was performed to examine the adrenergic stimulation-elicited Ca²⁺ influx signals. The levels of potential Ca_v1.2-inhibitory microRNAs (miRNAs) were measured by qRT-PCR. Results: Untreated FBs expressed limited amounts of alpha smooth muscle actin (α-SMA), while angiotensin II induced a significant upregulation of α-SMA-expressing MFBs. Co-cultures of MFBs and CMs resulted in downregulation of Ca_v1.2 expression in CMs, which was largely abolished by pretreatment of MFBs with exosomal inhibitor GW4869. More importantly, treatment with MFB-derived Exos caused repression of Ca_v1.2 expression in CMs. Additionally, the adrenergic receptor agonist-elicited Ca²⁺ influx signals in CMs were remarkably attenuated by pretreatment with MFB-derived Exos, corresponding to the paralleled change in Ca_v1.2 expression. Finally, miR-21-3p, a potential Ca_v1.2-inhibitory miRNA, was enriched in MFB-derived Exos and upregulated in CMs in response to MFB-derived Exos. Conclusion: We uncover an Exo-mediated crosstalk between MFBs and CMs, contributing to increased vulnerability to AF by reducing the expression of Ca_v1.2 in CMs.

Atrial fibrillation and cardiac fibrosis: A review on the potential of extracellular matrix proteins as biomarkers

The involvement of fibrosis as an underlying pathology in heart diseases is becoming increasingly clear. In recent years, fibrosis has been granted a causative role in heart diseases and is now emerging as a major contributor to Atrial Fibrillation (AF) pathogenesis. AF is the most common arrhythmia encountered in the clinic, but the substrate for AF is still being debated. Consensus in the field is a combination of cardiac tissue remodeling, inflammation and genetic predisposition. The extracellular matrix (ECM) is subject of growing investigation, since measuring circulatory biomarkers of ECM formation and degradation provides both diagnostic and prognostic information. However, fibrosis is not just fibrosis. Each specific collagen biomarker holds information on regulatory mechanisms, as well as information about which section of the ECM is being remodeled, providing a detailed description of cardiac tissue homeostasis. This review entails an overview of the implication of fibrosis in AF, the different collagens and their significance, and the potential of using biomarkers of ECM remodeling as tools for understanding AF pathogenesis and identifying patients at risk for further disease progression.

Reactivation of the Epicardium at the Origin of Myocardial Fibro-Fatty Infiltration During the Atrial Cardiomyopathy.

Fibro-fatty infiltration of subepicardial layers of the atrial wall has been shown to contribute to the substrate of atrial fibrillation. Here, we examined if the epicardium that contains multipotent cells is involved in this remodeling process. One hundred nine human surgical right atrial specimens were evaluated. There was a relatively greater extent of epicardial thickening and dense fibro-fatty infiltrates in atrial tissue sections from patients aged over 70 years who had mitral valve disease or atrial fibrillation when compared with patients aged less than 70 years with ischemic cardiomyopathy as indicated using logistic regression adjusted for age and gender. Cells coexpressing markers of epicardial progenitors and fibroblasts were detected in fibro-fatty infiltrates. Such epicardial remodeling was reproduced in an experimental model of atrial cardiomyopathy in rat and in Wilms tumor 1 (WT1)CreERT2/+;ROSA-tdT+/- mice. In the latter, genetic lineage tracing demonstrated the epicardial origin of fibroblasts within fibro-fatty infiltrates. A subpopulation of human adult epicardial-derived cells expressing PDGFR (platelet-derived growth factor receptor)-α were isolated and differentiated into myofibroblasts in the presence of Ang II (angiotensin II). Furthermore, single-cell RNA-sequencing analysis identified several clusters of adult epicardial-derived cells and revealed their specification from adipogenic to fibrogenic cells in the rat model of atrial cardiomyopathy. Epicardium is reactivated during the formation of the atrial cardiomyopathy. Subsets of adult epicardial-derived cells, preprogrammed towards a specific cell fate, contribute to fibro-fatty infiltration of subepicardium of diseased atria. Our study reveals the biological basis for chronic atrial myocardial remodeling that paves the way of atrial fibrillation.

Obesity and atrial fibrillation: making inroads through fat.

The global prevalence of obesity has reached epidemic proportions, paralleled by a rise in cases of atrial fibrillation (AF). Data from epidemiological cohorts support the role of obesity as an independent risk factor for AF. Increasing evidence indicates that obesity may contribute to the AF substrate through a number of pathways including by altering epicardial adipose tissue biology, inflammatory pathways, structural cardiac remodelling, and inducing atrial fibrosis. Due to changes in pharmacokinetics and pharmacodynamics, specific therapeutic considerations are required to guide management of patients with AF including anticoagulation and rhythm control. Also, weight loss in patients with AF has been associated with reduced progression from paroxysmal to persistent AF and indeed regression from persistent to proximal AF. However, the role of dietary intervention in AF control remains to be fully elucidated and hard prospective outcome data to support weight loss are required in AF to determine its role as part of a comprehensive risk factor management strategy for AF in obese patients.

Building a Career in Cardiovascular Research: A Conversation With Barbara Casadei, MD, DPhil.

Building a Career in Cardiovascular Research: A Conversation With Barbara Casadei, MD, DPhil.

Regional and Temporal Changes in Atrial Electrophysiology Contribute to Atrial Fibrillation in Angiotensin II Induced Hypertension

Atrial fibrillation (AF) is highly prevalent in hypertensive heart disease and is associated with altered angiotensin II (Ang II) signaling. We have recently demonstrated that chronic hypertension (3 weeks of Ang II infusion) in mice increases AF susceptibility in association with distinct patterns of structural and electrical remodelling of the right and left atrium. However, the progressive effects of Ang II infusion on atrial electrophysiology have not been investigated. Accordingly, the goal of this study was to characterize the effects of Ang II infusion on mouse atrial electrophysiology at three different timepoints (3, 10, 21 days). AF susceptibility was increased to 35.7% following 10 days and 53.8% after 21 days of Ang II infusion. This occurred in association with progressive increases in P wave duration and AERP measurements at 3, 10, and 21 days of Ang II infusion. In isolated right atrial myocytes, action potential (AP) morphology and potassium currents (IK) were not altered after 10 days of Ang II infusion whereas AP duration was prolonged and potassium currents (IK) were reduced following 21 days of Ang II infusion. In contrast, AP morphology was differentially altered in the left atrium at all timepoints investigated. Specifically, AP upstroke velocity was reduced after 10 and 21 days of Ang II infusion with a corresponding reduction in sodium current at these timepoints. In addition, AP duration was similarly prolonged following 3, 10, and 21 days of Ang II infusion and IK was reduced to a similar extent at each of these timepoints. Collectively, these data demonstrate that Ang II infusion is associated with distinct regional and temporal alterations in atrial electrophysiology. These alterations provide insight into the changes in atrial electrophysiology that create a substrate for AF.

Commentary: Looking beyond the atrial wall in AF-a review of 2019 and into the next decade

•Significant advances this year in CT, MRI & PET imaging of atrial fibrillation (AF) substrates. •Epicardial Adipose Tissue (EAT) & autonomic activity may interact in driving AF events. •Future studies should focus on inflammatory & autonomic mechanisms for tailored therapies.

An implantable system for long-term assessment of atrial fibrillation substrate in unanesthetized rats exposed to underlying pathological conditions

Atrial fibrillation (AF) is a progressive arrhythmia with underlying mechanisms that are not fully elucidated, partially due to lack of reliable and affordable animal models. Here, we introduce a system for long-term assessment of AF susceptibility (substrate) in ambulatory rats implanted with miniature electrodes on the atrium. Rats were subjected to excessive aldosterone (Aldo) or solvent only (Sham). An additional group was exposed to myocardial infarction (MI). AF substrate was tested two- and four-weeks post implantation and was also compared with implanted rats early post-implantation (Base). Aldo and MI increased the AF substrate and atrial fibrosis. In the MI group only, AF duration was correlated with the level of atrial fibrosis and was inversely correlated with systolic function. Unexpectedly, Shams also developed progressive AF substrate relative to Base individuals. Further studies indicated that serum inflammatory markers (IL-6, TNF-alpha) were not elevated in the shams. In addition, we excluded anxiety\\depression due to social-isolation as an AF promoting factor. Finally, enhanced biocompatibility of the atrial electrode did not inhibit the gradual development of AF substrate over a testing period of up to 8 weeks. Overall, we successfully validated the first system for long-term AF substrate testing in ambulatory rats.

Characterising the Stable and Dynamic Left Atrial Substrate in Atrial Fibrillation

Characterising the Stable and Dynamic Left Atrial Substrate in Atrial Fibrillation

005 Impact of Continuous Positive Airway Pressure on the Atrial Substrate in Patients With Obstructive Sleep Apnoea and Atrial Fibrillation: The SLEEP-AF Substrate Sub-Study

Obstructive sleep apnoea (OSA) is associated with an increasingly remodeled atrial substrate in atrial fibrillation (AF). Management of OSA has also been linked with improved management outcomes of AF. However, the impact of OSA management on the electrophysiologic atrial substrate has not been evaluated. To determine the impact of OSA management on the atrial substrate in AF. We recruited 24 consecutive patients having catheter ablation for AF with at least moderate OSA (AHI ≥15). Participants were randomised in a 1:1 ratio to receive continuous positive airway pressure (CPAP) or no therapy. At baseline, all participants underwent invasive electrophysiologic study comprising high density right atrial mapping and evaluation of effective refractory periods (ERP). After minimum of 6 months, the electrophysiologic protocol was repeated. Data was blinded and analysed offline. Outcome variables were atrial voltage (mV), conduction velocity (m/s), atrial surface area <1.5mV (%), atrial surface area <0.5mV (%), complex points (%) and atrial ERP (ms). There were no differences in baseline characteristics between groups and electrophysiologic parameters were comparable at baseline. Participants having CPAP were highly compliant (device usage: 79±19%, usage time: 268±91mins) resulting in significant AHI reduction (mean reduction: 31±23). There were no differences in blood pressure or body mass index between groups over time. The table presents data showing that CPAP results in marked reverse atrial remodelling. CPAP therapy results in reversal of atrial remodelling, providing mechanistic evidence advocating for management of OSA in AF.

Clinical characteristics of patients with atrial flutter before radiofrequency ablation

Introduction. Radiofrequency ablation (RFA) is today the method of choice for the ineffective medical treatment of atrial fibrillation (AF), but its course is often complicated by comorbid pathology. The predicted great impact of these nosologies on the effectiveness of radiofrequency ablation of the arrhythmia substrate requires additional study before RFA. Objectives – to analyze the clinical characteristics of patients with isolated atrial fibrillation and combination with of atrial fibrillation with atrial flutter (AF + AFib) that underwent radiofrequency ablation of the arrhythmia substrate. Materials and methods. 84 patients aged 65 ± 9 (82.3 % of men) were examined, who underwent RFA of the arrhythmia substrate: cavo-tricuspid isthmus (CTI) or combined with pulmonary veins isolation (CTI + PV) strategy for patients with AFib. Before radiofrequency ablation, the following clinical indicators were assessed: forms of AF + AFib, the presence of chronic heart failure (CHF) and functional classes (FC) according to NYHA classification, the forms of chronic coronary syndromes (CCS): postinfarction cardiosclerosis, syndrome-X, functional classes of stable angina (SA), stages of arterial hypertension (AH), the presence of type 2 diabetes or stroke in the anamnesis. Results. Radiofrequency ablation of isolated atrial fibrillation was more often performed for persistent arrhythmia in patients with stable angina III FC, arterial hypertension stage 2 and 3, radiofrequency ablation of combination of atrial fibrillation with atrial flutter – equally often for persistent or paroxysmal form in patients with SA I and II class, AH stage 2 and 3; in both cases patients with chronic heart failure II and III FC more often needed radiofrequency ablation of the arrhythmia substrate. Conclusions. Given the lack of correlation between clinical and demographic characteristics, it is advisable to continue studying their prognostic effect on the course of comorbid pathology and treatment of patients after radiofrequency ablation of the arrhythmia substrate of atrial fibrillation and combination of atrial fibrillation with atrial flutter.

Impairment of left atrial function and cryptogenic stroke: Potential insights in the pathophysiology of stroke in the young

BackgroundStroke is one of the leading causes of morbidity and mortality with a significant percentage classified as cryptogenic. Left atrial (LA) remodelling, a substrate for atrial fibrillation (AF) and stroke development, may play a role in identification of the aetiology of cryptogenic stroke. We aimed to examine LA function to gain mechanistic insights into the pathophysiology of cryptogenic stroke in young patients otherwise at low risk for cardiovascular disease. MethodsPatients aged <60 years without traditional cardiovascular risk factors and who were diagnosed with ischaemic cryptogenic stroke or TIA were evaluated and compared to healthy controls and patients with paroxysmal AF with a CHA2DS2-VA score of 0. Conventional and novel left ventricular (LV) and LA echocardiographic parameters between the three groups were assessed. ResultsEach group consisted of thirty patients. There were no significant differences in LV parameters (LVEF, LV endoGLS) between groups. LA strain in stroke patients was significantly lower compared to the controls (median 33%; interquartile range (IQ) [32/39] vs 31 [27/34]; p = 0.008). LA strain was significantly lower in AF patients compared to stroke patients (median 21% [19/22] vs 31% [27/34]; p < 0.0001). ConclusionA stepwise reduction in measures of LA function was appreciated between controls, young stroke and paroxysmal AF groups. This may indicate dynamic LA remodelling occurring in the young stroke population and suggest a shared causal mechanism for stroke development in this group. LA strain may further refine the risk for cardioembolic stroke.

Isolating the entire pulmonary venous component versus isolating the pulmonary veins for persistent atrial fibrillation: A propensity-matched analysis.

The outcomes of pulmonary vein isolation (PVI) for persistent atrial fibrillation (AF) are suboptimal. The entire pulmonary venous component (PV-Comp), consisting of the pulmonary veins, their antra, and the area between the antra, provides triggers and substrate for AF. PV-Comp isolation is an alternative strategy for persistent AF ablation. Among 328 patients with persistent AF who underwent a first radiofrequency ablation procedure, 200 patients (PVI, n=100; PV-Comp isolation, n=100) were selected by propensity score matching. Both groups were followed up for 1 year. At 6- and 12-month follow-up, atrial tachyarrhythmia (AF/atrial tachycardia) recurred in 41 and 61 patients in PVI group and 22 (P=.006) and 33 patients (P<.001) in PV-Comp isolation group, respectively. PV-Comp isolation was associated with longer mean time to recurrence (PVI: 8 months, PV-Comp isolation: 10 months, log-rank P<.001) and a lower probability of recurrence (odds ratio [OR]=0.32; 95% confidence of interval [CI]=0.18-0.56, P<.001), with no increase in procedural complications (PVI: 5 of 100, PV-Comp isolation: 6 of 100, P=.76). Procedure duration was longer in PV-Comp isolation group (PVI: 186 ± 42min, PV-Comp isolation: 238 ± 44min, P<.001), as well as fluoroscopy time (PVI: 22 ± 16min, PV-Comp isolation: 31 ± 21min, P=.001). PV-Comp isolation for persistent AF reduced atrial tachyarrhythmia recurrence up to 1 year compared with PVI alone. While procedure and fluoroscopy time increased, there was no difference in procedural complications.

New Findings in Atrial Fibrillation Mechanisms.

This review focusses on novel findings in atrial fibrillation mechanisms derived from mapping studies. Recent panoramic mapping techniques have identified 2 arrhythmic mechanisms of interest, namely, rotational (rotors) and ectopic focal activations as drivers of atrial fibrillation. Epicardial adipose tissue and fatty infiltration into the myocardium have been described as novel substrates for atrial fibrillation. There is increasing appreciation that the thin atrial walls harbor a complex 3-dimensional electrostructural substrate to contribute to atrial fibrillation sustenance. Further research is warranted to advance the field toward more targeted therapy.

The association of low voltage atrial electrograms and the myocardial substrate for atrial fibrillation

The association of low voltage atrial electrograms and the myocardial substrate for atrial fibrillation

The Effects of Valvular Heart Disease on Atrial Conduction During Sinus Rhythm

Different arrhythmogenic substrates for atrial fibrillation (AF) may underlie aortic valve (AV) and mitral valve (MV) disease. We located conduction disorders during sinus rhythm by high-resolution epicardial mapping in patients undergoing AV (n = 85) or MV (n = 54) surgery. Extent and distribution of conduction delay (CD) and block (CD) across the entire right and left atrial surface was determined from circa 1880 unipolar electrogram recordings per patient. CD and CB were most pronounced at the superior intercaval area (2.5% of surface, maximal degree 6.6%/cm2). MV patients had a higher maximal degree of CD at the lateral left atrium than AV patients (4.2 vs 2.3%/cm2, p = 0.001). A history of AF was most strongly correlated to CD/CB at Bachmann’s bundle and age. Although MV patients have more conduction disorders at the lateral left atrium, disturbed conduction at Bachmann’s bundle during sinus rhythm indicates the presence of atrial remodeling which is related to AF episodes.

Metastable Atrial State Underlies the Primary Genetic Substrate for MYL4 Mutation-Associated Atrial Fibrillation.

Atrial fibrillation (AF) is the most common clinical arrhythmia and is associated with heart failure, stroke, and increased mortality. The myocardial substrate for AF is poorly understood because of limited access to primary human tissue and mechanistic questions around existing in vitro or in vivo models. Using an MYH6:mCherry knock-in reporter line, we developed a protocol to generate and highly purify human pluripotent stem cell-derived cardiomyocytes displaying physiological and molecular characteristics of atrial cells. We modeled human MYL4 mutants, one of the few definitive genetic causes of AF. To explore non-cell-autonomous components of AF substrate, we also created a zebrafish Myl4 knockout model, which exhibited molecular, cellular, and physiologic abnormalities that parallel those in humans bearing the cognate mutations. There was evidence of increased retinoic acid signaling in both human embryonic stem cells and zebrafish mutant models, as well as abnormal expression and localization of cytoskeletal proteins, and loss of intracellular nicotinamide adenine dinucleotide and nicotinamide adenine dinucleotide + hydrogen. To identify potentially druggable proximate mechanisms, we performed a chemical suppressor screen integrating multiple human cellular and zebrafish in vivo endpoints. This screen identified Cx43 (connexin 43) hemichannel blockade as a robust suppressor of the abnormal phenotypes in both models of MYL4 (myosin light chain 4)-related atrial cardiomyopathy. Immunofluorescence and coimmunoprecipitation studies revealed an interaction between MYL4 and Cx43 with altered localization of Cx43 hemichannels to the lateral membrane in MYL4 mutants, as well as in atrial biopsies from unselected forms of human AF. The membrane fraction from MYL4-/- human embryonic stem cell derived atrial cells demonstrated increased phospho-Cx43, which was further accentuated by retinoic acid treatment and by the presence of risk alleles at the Pitx2 locus. PKC (protein kinase C) was induced by retinoic acid, and PKC inhibition also rescued the abnormal phenotypes in the atrial cardiomyopathy models. These data establish a mechanistic link between the transcriptional, metabolic and electrical pathways previously implicated in AF substrate and suggest novel avenues for the prevention or therapy of this common arrhythmia.

Region-specific parasympathetic nerve remodeling in the left atrium contributes to creation of a vulnerable substrate for atrial fibrillation.

Atrial fibrillation (AF) is the most common heart rhythm disorder and a major cause of stroke. Unfortunately, current therapies for AF are suboptimal, largely because the molecular mechanisms underlying AF are poorly understood. Since the autonomic nervous system is thought to increase vulnerability to AF, we used a rapid atrial pacing (RAP) canine model to investigate the anatomic and electrophysiological characteristics of autonomic remodeling in different regions of the left atrium. RAP led to marked hypertrophy of parent nerve bundles in the posterior left atrium (PLA), resulting in a global increase in parasympathetic and sympathetic innervation throughout the left atrium. Parasympathetic fibers were more heterogeneously distributed in the PLA when compared with other left atrial regions; this led to greater fractionation and disorganization of AF electrograms in the PLA. Computational modeling revealed that heterogeneously distributed parasympathetic activity exacerbates sympathetic substrate for wave break and reentry. We further discovered that levels of nerve growth factor (NGF) were greatest in the left atrial appendage (LAA), where AF was most organized. Preferential NGF release by the LAA - likely a direct function of frequency and regularity of atrial stimulation - may have important implications for creation of a vulnerable AF substrate.

P5651Association of left atrial fibrosis extent with left ventricular geometric remodeling and diastolic dysfunction in patients with paroxysmal atrial fibrillation

Abstract Introduction Whether left atrial fibrosis (LAf) in patients with atrial fibrillation (AF) is a consequence of left ventricular (LV) diastolic dysfunction or primary atrial pathology continues to be a debatable issue. Electroanatomical mapping (EAM) allows to image and to define LAf as a substrate of AF. Purpose To study the relationship of LAf extent with LV diastolic function and geometric remodeling in patients (pts) with paroxysmal AF. Methods 56 pts with paroxysmal AF (mean age 57.1±8.4 years, 31 males), undergone catheter ablation, were enrolled in the study, including 30 pts with arterial hypertension (AH), 15 – with coronary artery disease (CAD) and AH. Comprehensive transthoracic echocardiography was carried out in all pts to assess chamber volumes, systolic and LV diastolic functions and geometry patterns according to Recommendations of ASE and EACVI. Before ablation, EAM was performed in sinus rhythm. The bipolar low voltage areas of LAf were identified with the cut-off &lt;0.5 mV. For the LAf quantification following indicators were calculated: total square of LAf (Sf, cm2) and LAf degree, estimated as an analog of the UTAH staging system, by selection of UTAH I: &lt;5% fibrosis; II: 5–19%; III: 20–35% and IV: &gt;35%. Results All patients had preserved systolic LV function. To assess the influence of LV geometry on LAf extent all pts were distributed in accordance to LV geometry patterns (p): normal geometry (pI) – 27 pts, concentric remodeling (pII) – 13, eccentric hypertrophy (pIII) – 10, concentric hypertrophy (pIV) – 6. Pts with pIII were older than pI pts: 60.8±6.4 vs 53.9±10.4 (p=0.048). All pts with pIII and pIV had AH. From 11 pts without AH, 10 had pI of LV geometry. PIII was revealed more often in CAD pts compared to those without CAD: 29.2 vs 10.5% (p=0.04). PIII pts had bigger LA volume compared to pI pts (74.3±22.5 vs 58.8±19.4 ml, p=0.019) and pII pts (61.9±14.9, p=0.05), but LA volume of pIII pts didn't differ from pIV pts (71.9±14.5, p=0.78). PIII pts had more extent Sf than pI pts (28.32±8.9 vs 13.4±6.5, p=0.05), while Sf of pII (17.3±8.7, p=0.495) and pIV pts (16.4±9.5, p=0.699) didn't differ significantly from Sf of pI pts. As for the degree of LAf, UTAH I was absent in pts with pIII and UTAH IV was revealed in 40% of these pts, while in pts with pI UTAH I was in 26% and UTAH IV - in 14.8% (p=0.049). However, Sf and UTAH degree did not depend on age, CAD and heart failure presence. As for diastolic dysfunction, in pIII and pIV pts e∼septal and e∼lateral were lower compared to pI pts: 6.3±1.9, 5.5±2.4 vs 8.5±2.2 (p&lt;0.01) and 8.2±2.7, 8.0±3.8 vs 11.3±2.9 (p&lt;0.01), respectively, while E/e∼ in pIII pts didn't differ from pI pts (8.0±1.6 vs 7.2±1.6, p=0.17), but in pIV was more than in pI pts (10.4±2.8, p=0.003). Conclusion LAf extent in paroxysmal AF is associated more with such LV geometry pattern as eccentric hypertrophy, than with diastolic disorders, which accompany both eccentric and concentric hypertrophy.

P1628Angiopoietin-like protein (Angptl) 2 secreted from epicardial adipose tissue induces atrial myocardial fibrosis

Abstract Background Using excised human left atrial appendage samples, we previously demonstrated that epicardial adipose tissue (EAT) are highly associated with atrial myocardial fibrosis as a substrate of atrial fibrillation (AF). We also reported the relationship between Angptl2 in EAT and atrial fibrosis. However, the mechanism is not clear. The purpose is to clarify the mechanisms underlying the effect of EAT on the atrial myocardium. Methods Human peri-left atrial EAT and abdominal subcutaneous adipose tissue (SAT) samples were obtained from 6 cases (2 females, 70.2±13.2 years). 50 mg of EAT and SAT were quickly washed with PBS and centrifuged 1min at 1200rpm. After 3 times this procedures, adipose tissues were cultured in DMEM F12 medium with Fetal bovine Serum (FBS) overnight. After pre-incubation, EAT and SAT tissues were washed and centrifuge d three times and cultured in medium without FBS for 24hours. Finally, we collected oozed medium (conditioned medium) and used for experiments. Concentrations of Angptl2 in conditioned medium were measured by ELISA. To study the effects of conditioned medium, we used “organo-culture” system. Isolated atrium from 8week old male Sprague-Dawley rats were placed on the porous membrane with the endothelial face toward the membrane. After that, loading medium (conditioned medium:culture medium = 1:4), culture medium (control), or recombinant Angptl2 were dropped onto the epicardial face of the atrium once a day and incubated for 7 days (37°C, 5% CO2). Then, histological and immunohistochemical analysis were performed. We also performed quantitative reverse transcription–polymerase chain reaction (RT–PCR) analysis. Next, we isolated and cultured neonatal rat fibroblast and loaded Angptl2 for 24 hours.After collected these cells, we performed western blotting analysis. Results Atria organo-culture incubated for 7 days with conditioned medium showed global fibrosis. At epicardial side, fibrotic area of EAT group was significantly greater compared to that of SAT and control group (P&lt;0.05). mRNA of Col1a1, col3a1 and TGFβ1 were significantly increased in EAT group compared with the SAT and control group. And, the concentration of conditioned medium created from EAT was significant higher than that from SAT (P&lt;0.05). Then, we dropped 500 ng/ml of recombinant Angptl2 onto the rat atria. Fibrotic area of Angptl22 group significantly greater than that of control with increasing number of α-SMA positive cells, and mRNA of col3a1 and TGFβ1 were significantly increased in Angptl2 group compared with control group. In cultured fibroblasts, α-SMA and p-ERK expression were increased in Angptl2 group measured by western blotting analysis. Conclusions Our results demonstrated that EAT rather than SAT induces atrial myocardial fibrosis. There is a possibility that Angptl2 effused from EAT plays a part in atrial fibrosis thought EAT paracrine effect. Acknowledgement/Funding ONO PHARMACEUTICAL CO