Inflammatory pathways underlying atrial fibrillation

Chocolate intake and risk of clinically apparent atrial fibrillation: the Danish Diet, Cancer, and Health Study

OBJECTIVE

To evaluate the association between chocolate intake and incident clinically apparent atrial fibrillation or flutter (AF).

METHODS

The Danish Diet, Cancer, and Health Study is a large population-based prospective cohort study. The present study is based on 55 502 participants (26 400 men and 29 102 women) aged 50-64 years who had provided information on chocolate intake at baseline. Incident cases of AF were ascertained by linkage with nationwide registries.

RESULTS

During a median of 13.5 years there were 3346 cases of AF. Compared with chocolate intake less than once per month, the rate of AF was lower for people consuming 1-3 servings/month (hazard ratio (HR) 0.90, 95% confidence interval (CI) 0.82 to 0.98), 1 serving/week (HR 0.83, 95% CI 0.74 to 0.92), 2-6 servings/week (HR 0.80, 95% CI 0.71 to 0.91) and ≥1 servings/day (HR 0.84, 95% CI 0.65 to 1.09; p-linear trend <0.0001), with similar results for men and women.

CONCLUSIONS

Accumulating evidence indicates that moderate chocolate intake may be inversely associated with AF risk, although residual confounding cannot be ruled out.

Multimodality Cardiac Imaging for the Assessment of Left Atrial Function and the Association With Atrial Arrhythmias

Several cardiac imaging modalities are able to visualize the left atrium (LA) and, therefore, allow for quantification of both structural and functional properties of this cardiac chamber. In echocardiography, only the maximal LA volume is included in the assessment of diastolic function at the current moment. Numerous studies, however, have shown that functional measures may be superior to the maximal LA volume in several aspects and to possess clinical value even in the absence of structural abnormalities. Such functional measures could prove particularly useful in the setting of predicting atrial fibrillation, which will be a point of focus in this review. Pivotal cardiac magnetic resonance imaging studies have revealed high correlation between LA fibrosis and risk of atrial fibrillation recurrence after catheter ablation, and subsequent multimodality imaging studies have uncovered an inverse relationship between LA reservoir function and degree of LA fibrosis. This has sparked an increased interest into the application of advanced imaging modalities, including both speckle tracking echocardiography and tissue tracking by cardiac magnetic resonance imaging. Even though increasing evidence has supported the use of functional measures and proven its superiority to the maximal LA volume, they have still not been adopted in clinical guidelines. The reason for this discrepancy may rely on the fact that there is little to no agreement on how to technically perform deformation analysis of the LA. Such technical considerations, limitations, and alternate imaging prospects will be addressed in this review.

Association Between Cataract and Risk of Incident Atrial Fibrillation: A Nationwide Population-Based Retrospective Cohort Study

OBJECTIVE

To identify the association between cataract and the subsequent atrial fibrillation (AF) risk.

PATIENTS AND METHODS

Our retrospective cohort study was designed to analyze the Longitudinal Health Insurance Database 2000 of the Taiwan National Health Insurance program. We established a cataract cohort (n=39,347) and a noncataract cohort (n=39,347) to observe the incidence of AF. The cataract cohort included patients who were newly diagnosed with cataract from January 1, 2000, to December 31, 2010. Propensity score matching was used to form matched sets of participants with cataract and participants without cataract who share a similar value of propensity score. Univariable and multivariable Cox proportional hazards regression models were used to assess the association between having a cataract and AF.

RESULTS

The median (range) follow-up period was 6.52 years (range, 3.76-9.19 years) and 5.88 years (range, 3.12-8.66 years) for the cataract and noncataract cohorts, respectively; the cumulative incidence curves of AF indicated that the cataract cohort had a significantly higher risk of developing AF than did the noncataract cohort (P<.001). Moreover, the risk of AF was 1.32-fold (95% CI, 1.18-1.48) higher in patients with cataract with surgery and was 1.21-fold (95% CI, 1.06-1.37) higher in patients with cataract without surgery than in patients without cataract.

CONCLUSION

The present study is the first to report that cataract is associated with an increased risk of AF.

Significant Increase in C-Reactive Protein and Serum Amyloid A in the Early Hours of Paroxysmal Atrial Fibrillation

Background

A number of data have been accumulated on inflammation in persistent and permanent atrial fibrillation (AF). Our aim was to study the process in paroxysmal AF (PAF) by measuring plasma concentrations of high-sensitivity C-reactive protein (hs-CRP), serum amyloid A (SAA) and fibrinogen in dynamics.

Methods

The markers were investigated in 51 patients (26 males and 25 females; 59.84 ± 1.60 years) at hospital admission (baseline), 24 hours and 28 days after sinus rhythm restoration. Fifty-two controls (26 males and 26 females; 59.50 ± 1.46 years) were selected.

Results

At baseline, hs-CRP and SAA concentrations were higher in patients (8.12 ± 0.82 vs. 5.57 ± 0.21 mg/L, P = 0.003; 16.04 ± 0.93 vs. 5.12 ± 0.23 ng/mL, P < 0.001, respectively) and these changes persisted 24 hours after sinus rhythm restoration (8.16 ± 0.71 vs. 5.57 ± 0.21 mg/L, P < 0.001; 12.99 ± 0.75 vs. 5.12 ± 0.23 ng/mL, P < 0.001, respectively). On the 28th day, no significant difference was measured (5.42 ± 0.29 vs. 5.57 ± 0.21 mg/L, P = 0.68; 5.89 ± 0.38 vs. 5.12 ± 0.23 ng/mL, P = 0.08, respectively). At any measurement, fibrinogen levels did not differ between patients and controls (3.30 ± 0.17 vs. 3.22 ± 0.11 g/L, P = 0.70; 3.32 ± 0.11 vs. 3.22 ± 0.11 g/L, P = 0.52; 3.24 ± 0.13 vs. 3.22 ± 0.11 g/L, P = 0.90, respectively).

Conclusion

PAF is associated with dynamics in hs-CRP and SAA plasma levels. The results suggest that inflammation is closely related to the arrhythmia initiation.

High sensitive C-reactive protein and interleukin 6 in atrial fibrillation with rheumatic mitral stenosis from Indian cohort

Introduction

Presence of chronic low grade inflammation has often been implicated in the etiology of atrial fibrillation (AF). Whether pre-existing inflammatory state promotes AF or initiation of AF activates inflammation is a dilemma among clinicians. This study investigates the role of high sensitive C reactive protein (hs-CRP) and interleukin 6 (IL-6) in AF with rheumatic mitral stenosis (Rh-MS) as markers of chronic inflammation.

Methods

This case control cohort included sixty five (n = 65) Rh-MS patients having other valve lesions as trivial to mild. Out of them twenty nine (n = 29; group C) had baseline AF and rest were normal sinus rhythm (NSR). A 24 h holter recording was done in NSR patients to diagnose paroxysmal AF/tachyarrhythmia forming group B (n = 12) and not having any tachyarrhythmia were designated as NSR; group A (n = 24).

Results

hs-CRP and IL6 showed statistically significant increase in group C (permanent AF) compared to group A (95% CI: 4.2–0.9, p = 0.007; 95% CI: 1.2–0.89; p = 0.05 respectively), while it was non significant between group A and group B (p > 0.05). A weak positive correlation was observed with hs-CRP and left atrial volume index (LAVi) (r = 0.45, p = 0.06) in AF group as compared to NSR group. 68.2% of patients in AF group (27/41) had moderate to severe spontaneous echo contrast (SEC) as compared to 37.5% (10/24) in NSR group.

Conclusion

Increased hs-CRP and IL-6 levels in the paroxysmal and permanent AF group may favour the hypothesis that low grade chronic inflammation could be the cause of atrial fibrillation than a consequence.

Atrial fibrillation in heart failure with preserved ejection fraction: Insights into mechanisms and therapeutics

Atrial fibrillation (AF) and heart failure (HF) often coexist, and the outcomes of patients who have both AF and HF are considerably worse than those with either condition in isolation. Heart failure with preserved ejection fraction (HFpEF) is a heterogeneous clinical entity and accounts for approximately one-half of current HF. At least one-third of patients with HFpEF are burdened by comorbid AF. The current understanding of the relationship between AF and HFpEF is limited, but the clinical implications are potentially important. In this review, we explore 1) the pathogenesis that drives AF and HFpEF to coexist; 2) pharmacologic therapies that may attenuate the impact of AF in HFpEF; and 3) future directions in the management of this complex syndrome.

Atrial Fibrillation and Risk of ESRD in Adults with CKD

BACKGROUND AND OBJECTIVES

Atrial fibrillation frequently complicates CKD and is associated with adverse outcomes. Progression to ESRD is a major complication of CKD, but the link with atrial fibrillation has not been fully delineated. In this study, we examined the association of incident atrial fibrillation with the risk of ESRD in patients with CKD.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

We studied participants in the prospective Chronic Renal Insufficiency Cohort Study without atrial fibrillation at entry. Incident atrial fibrillation was identified by study visit ECGs, self-report, and hospital discharge diagnostic codes, with confirmation by physician adjudication. ESRD through 2012 was ascertained by participant self-report, medical records, and linkage to the US Renal Data System. Data on potential confounders were obtained from self-report, study visits, and laboratory tests. Marginal structural models were used to study the potential association of incident atrial fibrillation with risk of ESRD after adjustment for time-dependent confounding.

RESULTS

Among 3091 participants, 172 (5.6%) developed incident atrial fibrillation during follow-up. During mean follow-up of 5.9 years, 43 patients had ESRD that occurred after development of incident atrial fibrillation (11.8/100 person-years) compared with 581 patients without incident atrial fibrillation (3.4/100 person-years). In marginal structural models with inverse probability weighting, incident atrial fibrillation was associated with a substantially higher rate of ESRD (hazard ratio, 3.2; 95% confidence interval, 1.9 to 5.2). This association was consistent across important subgroups by age, sex, race, diabetes status, and baseline eGFR.

CONCLUSIONS

Incident atrial fibrillation was associated with higher risk of developing ESRD in CKD. Additional study is needed to identify potentially modifiable pathways through which atrial fibrillation was associated with a higher risk of progression to ESRD. More aggressive monitoring and treatment of patients with CKD and atrial fibrillation may improve outcomes in this high-risk population.

Class I Histone Deacetylase Inhibition for the Treatment of Sustained Atrial Fibrillation

Current therapies are less effective for treating sustained/permanent versus paroxysmal atrial fibrillation (AF). We and others have previously shown that histone deacetylase (HDAC) inhibition reverses structural and electrical atrial remodeling in mice with inducible, paroxysmal-like AF. Here, we hypothesize an important, specific role for class I HDACs in determining structural atrial alterations during sustained AF. The class I HDAC inhibitor N-acetyldinaline [4-(acetylamino)-N-(2-amino-phenyl) benzamide] (CI-994) was administered for 2 weeks (1 mg/kg/day) to Hopx transgenic mice with atrial remodeling and inducible AF and to dogs with atrial tachypacing-induced sustained AF. Class I HDAC inhibition prevented atrial fibrosis and arrhythmia inducibility in mice. Dogs were divided into three groups: 1) sinus rhythm, 2) sustained AF plus vehicle, and 3) sustained AF plus CI-994. In group 3, the time in AF over 2 weeks was reduced by 30% compared with group 2, along with attenuated atrial fibrosis and intra-atrial adipocyte infiltration. Moreover, group 2 dogs had higher atrial and serum inflammatory cytokines, adipokines, and atrial immune cells and adipocytes compared with groups 1 and 3. On the other hand, groups 2 and 3 displayed similar left atrial size, ventricular function, and mitral regurgitation. Importantly, the same histologic alterations found in dogs with sustained AF and reversed by CI-994 were also present in atrial tissue from transplanted patients with chronic AF. This is the first evidence that, in sustained AF, class I HDAC inhibition can reduce the total time of fibrillation, atrial fibrosis, intra-atrial adipocytes, and immune cell infiltration without significant effects on cardiac function.

Atrial fibrillation coincides with the advanced glycation end product N(ε)-(carboxymethyl)lysine in the atrium

Presence of advanced glycation end products (AGEs) in the heart induces a proinflammatory phenotype. However, the presence of AGEs within atrial tissue of atrial fibrillation (AF) patients is unknown and was analyzed here. Left atrial appendage tissue from 33 AF patients and 9 controls was analyzed for the presence of the major AGEs N(ε)-(carboxymethyl)lysine (CML), VCAM-1, neutrophilic granulocytes, lymphocytes, and macrophages in both the fat tissue and myocardium separately. The total amount of fibrosis was also analyzed. Presence of CML was significantly higher in blood vessels of the left atrial appendage in AF patients as compared to controls, independent of diabetes mellitus. In AF patients, VCAM-1 expression in blood vessels and the numbers of infiltrated neutrophilic granulocytes, lymphocytes, and macrophages significantly increased compared to controls, and were highest in the fat tissue; there was no significant difference in fibrosis compared to controls. Interestingly, total amount of CML and fibrosis in AF and control patients correlated positively. Finally, there was no difference between AF patients based on AF type or surgical indication in the presence of CML, VCAM-1 expression, inflammatory cells, and fibrosis. Our results indicate that in AF the intramyocardial blood vessels of the left atrial appendage have an increased CML presence and proinflammatory status coinciding with a local increase in the number of inflammatory cells.

Elevated plasma levels of Th17-related cytokines are associated with increased risk of atrial fibrillation

We performed a matched case-control study using a propensity score matching, to assess the association of Th17-related cytokines, including interleukin (IL) 17A (IL-17A), IL-17F, IL-21, IL-22 and IL-6, along with interferon-γ (IFN-γ), IL-10, IL-9, and IL-4, with the risk of AF. A total of 336 patients with AF were matched 1:1 with patients without AF. Plasma levels of cytokines were measured using Luminex xMAP assays. The plasma levels of all examined cytokines were significantly higher in AF patients than controls (P < 0.05), and these cytokines were highly correlated with each other (P < 0.01). A multivariate conditional logistic regression analysis showed that elevated plasma levels of IL-17A, IL-17F, IL-21, IL-22, IFN-γ, IL-10, IL-9 and IL-6 were significantly associated with AF risk independently of potential confounders. There were no significant differences in plasma levels of examined cytokines between paroxysmal and chronic AF patients. IL-17A, IL-21, IL-10 and IL-6 levels were positively correlated with left atrial diameter; IL-17F level was negatively correlated with left ventricle ejection fraction among AF patients (P < 0.05). Elevated plasma levels of Th17-related cytokines were independently associated with increased an risk of AF; hence, Th17-related cytokines may be involved in the pathogenesis of AF.

The Association of Acute Kidney Injury and Atrial Fibrillation after Cardiac Surgery in an Asian Prospective Cohort Study

Acute kidney injury (AKI) and atrial fibrillation (AF) after cardiac surgery are common occurrences and increase patient morbidity and mortality. Inflammation plays a role in increased incidence of AF in patients with chronic kidney disease (CKD); reactive oxygen species and inflammatory markers which are increased in patients with CKD were found to affect the proper functioning of the intracellular ion channels, connexions (transmembrane proteins found in intercellular gap junctions), and electrical homogeneity of the extracellular matrix which are essential for electrical stability and proper conduction of electrical impulses in the atrium. However, it is not known if similar mechanisms are also involved in AKI. We tested the hypothesis that patients with AKI after cardiac surgery have a higher incidence of postoperative AF.Data from 2885 patients, who had undergone cardiac surgery between August 2008 and July 2012 from the Singapore's 2 major heart centers, were obtained prospectively. Postoperative AKI was defined using the Acute Kidney Injury Network criteria. The primary outcome was postoperative AF, and subjects were considered to have postoperative AF if the AF lasted more than an hour, affected hemodynamics, or required medical treatment.The incidence of AKI was 29.7% and the incidence of postoperative AF was 16.8%. A total of 27.7% of AKI patients developed AF. Patients with AKI had a 2-fold increased risk of developing AF (relative risk [RR], 1.716; 95% confidence interval [CI], 1.433-2.055; P < 0.001). The following factors were found to independently increase the risk of AF in patients with AKI: age (RR, 1.011; 95% CI, 1.000-1.022; P = 0.04), low preoperative hemoglobin (RR, 0.942; 95% CI, 0.888-1.000; P = 0.05), low preoperative estimated glomerular filtration rate (eGFR) (RR, 0.987; 95% CI, 0.980-0.994; P < 0.001), and lowest hematocrit during bypass (RR, 0.943; 95% CI, 0.910-0.978; P < 0.001).Patients with AKI are more likely to develop postoperative AF. These patients were older and had lower preoperative hemoglobin, eGFR, and lower nadir hematocrit during bypass. Identification of high-risk AKI patients with early prevention and treatment of AF should reduce the long-term morbidity and mortality among Asian patients undergoing cardiac surgery.

Atrial fibrillation is associated with high levels of monocyte-platelet-aggregates and increased CD11b expression in patients with aortic stenosis

A growing body of evidence suggests a pivotal role of inflammatory processes in AF in a bidirectional manner. Infiltrating leukocytes seem to promote both structural and electrical remodelling processes in patients with AF. Monocyte-platelets-aggregates (MPAs) are sensitive markers of both platelets and monocyte activation. So far it is not clear whether the content of MPAs is affected by AF. The present study examined the content of MPAs and the activation of monocytes in elderly patients with an aortic stenosis in dependence of AF. These patients are known to have a high prevalence of AF. Flow-cytometric quantification analysis demonstrated that patients with AF have an increased content of MPAs (207 ± 13 cells/µl vs 307 ± 21 cells/µl, p< 0.001), and enhanced expression of CD11b on monocytes (p< 0.001), compared to patients in stable sinus rhythm (SR). The number of CD14+/CD16+ monocytes were only slightly elevated in patients with AF. These findings were seen in patients with permanent AF. But also patients with paroxysmal AF, even when presenting in SR, the MPAs were increased by 50 % (p< 0.05) as well as the CD11b expression, which was twice as high (p< 0.05) compared to stable SR. These results demonstrate for the first time a dependency of MPAs and CD11b expression on monocytes in the presence of AF and support the notion of a close relationship between AF, thrombogenesis and inflammation. The content of MPAs and the extent of activation on monocytes appear promising as biomarkers for paroxysmal AF and as possible future targets for developing novel pharmacological therapeutic strategies.

Regulation of SCN3B/scn3b by Interleukin 2 (IL-2): IL-2 modulates SCN3B/scn3b transcript expression and increases sodium current in myocardial cells

BACKGROUND

In the initiation and maintenance of arrhythmia, inflammatory processes play an important role. IL-2 is a pro-inflammatory factor which is associated with the morbidity of arrhythmias, however, how IL-2 affects the cardiac electrophysiology is still unknown.

METHODS

In the present study, we observed the effect of IL-2 by qRT-PCR on the transcription of ion channel genes including SCN2A, SCN3A, SCN4A, SCN5A, SCN9A, SCN10A, SCN1B, SCN2B, SCN3B, KCNN1, KCNJ5, KCNE1, KCNE2, KCNE3, KCND3, KCNQ1, KCNA5, KCNH2 and CACNA1C. Western blot assays and electrophysiological studies were performed to demonstrate the effect of IL-2 on the translation of SCN3B/scn3b and sodium currents.

RESULTS

The results showed that transcriptional level of SCN3B was up-regulated significantly in Hela cells (3.28-fold, p = 0.022 compared with the control group). Consistent results were verified in HL-1 cells (3.73-fold, p = 0.012 compared with the control group). The result of electrophysiological studies showed that sodium current density increased significantly in cells which treated by IL-2 and the effect of IL-2 on sodium currents was independent of SCN3B (1.4 folds, p = 0.023). Western blot analysis showed IL-2 lead to the significantly increasing of p53 and scn3b (2.1 folds, p = 0.021 for p53; 3.1 folds, p = 0.023 for scn3b) in HL-1 cells. Consistent results were showed in HEK293 cells using qRT-PCR analysis (1.43 folds for P53, p = 0.022; 1.57 folds for SCN3B, p = 0.05).

CONCLUSIONS

The present study suggested that IL-2, may play role in the arrhythmia by regulating the expression of SCN3B and sodium current density.

High-fat diet increases vulnerability to atrial arrhythmia by conduction disturbance via miR-27b

BACKGROUND

Lifestyle-related diseases, such as obesity and dyslipidemia are important risk factors for atrial fibrillation (AF). However, the underlying mechanism linking these diseases and AF has not been fully investigated.

METHODS

Adult male mice were fed a high-fat diet (HFD) or vehicle (NC) for 2 months. Electrocardiography and in vivo electrophysiological study were performed. Mice were then sacrificed for quantification of mRNA, microRNA, and protein in atria, in addition to histological analysis. Conduction velocity (CV) in right atrium was measured by optical mapping in Langendorff perfused hearts. Cultured atrial cardiomyocytes were treated with palmitate with or without a specific microRNA inhibitor. Twelve hours after stimulation, cells were lysed, and subjected to analysis with qPCR and Western blotting.

RESULTS

HFD mice showed prolonged P wave duration, increased inducibility of sustained atrial tachycardia, and reduced atrial CV than NC mice. HFD mice also showed increased expression in inflammatory cytokines, whereas fibrotic area and signals relating fibrosis were not changed. HFD mice demonstrated reduced expression of Cx40 in mRNA and protein levels, and its lateralized expression in atria. MicroRNA array analysis revealed that miR-27b expression was up-regulated in HFD mice, and luciferase assay confirmed the direct interaction between miR-27b and Cx40 3'UTR. In palmitate-stimulated atrial cardiomyocytes, miR-27b up-regulation and Cx40 down-regulation were observed, while expression of inflammatory cytokines was not altered. Inhibition of miR-27b with antisense oligonucleotides reversed the alteration caused by palmitate stimulation.

CONCLUSION

HFD may increase the vulnerability to atrial arrhythmia by down-regulation of Cx40 via miR-27b, rather than fibrosis, which is independent of inflammation.

Proinflammatory gene expression in patients undergoing mitral valve surgery and maze ablation for atrial fibrillation

OBJECTIVE

It is difficult to achieve rhythm control in patients with long-standing persistent atrial fibrillation (AF). The radiofrequency maze procedure is an effective means in curing AF with a variable recurrence rate depending on patient characteristics and AF duration. In these patients, the characteristics of the atrial substrate have not been well investigated. Because the inflammatory process has been shown to be important in the pathogenesis of AF, we sought to characterize the proinflammatory gene expression in left atria obtained from patients with AF undergoing mitral valve surgery combined with the maze procedure to distinguish the changes associated with AF and its recurrence after the surgical ablation.

METHODS

Left atrial appendages from 35 patients receiving mitral valve surgery were used for study. Ten patients had sinus rhythm (SR) and 25 patients had persistent AF for more than 1 year and underwent the maze procedure. Among the AF patients, 13 patients remained in SR (AF-SR) and 12 patients had recurrent AF during the 1-year clinical follow-up (AF-AF). The nCounter Human Inflammation Array (NanoString Technologies, Seattle, Wash) was used for evaluating proinflammatory gene expression. Quantitative polymerase chain reaction, Western blot, and immunohistochemistry were applied for studying messenger RNA and protein expression.

RESULTS

Of 144 expressed proinflammatory genes, the inflammation array analysis revealed that 32 genes were differentially expressed between AF (including AF-SR and AF-AF) and SR. Thirteen genes were differentially expressed between AF-SR and AF-AF. The array and quantitative polymerase chain reaction produced parallel results in analyzing the expression of particular genes. Concordant with the gene expression difference between AF and SR patients, rapid pacing increased the expressions of SHC1, RHOA, PDGFA, and TRAF2 in HL-1 myocytes, implicating a causative effect of tachyarrhythmia on these genes. Compared with AF-SR, AF-AF expressed more intense oxidative stress, upregulations of collagen, transforming growth factor beta 1, and intranuclear nuclear factor of activated T-cells. Regression analysis showed that increased left atrial diameter was associated with the expression of RHOA and STAT1.

CONCLUSIONS

Differential expression profiles of proflammatory genes were presented between SR and AF and between maintained SR and recurrent AF after the maze procedure. The identified inflammatory molecules associated with AF and failed surgical ablation may provide clues for developing new potential therapeutic targets to improve AF rhythm control.

Ventricular myocarditis coincides with atrial myocarditis in patients

INTRODUCTION

Atrial fibrillation (AF) is a common complication in myocarditis. Atrial inflammation has been suggested to play an important role in the pathophysiology of AF. However, little is known about the occurrence of atrial inflammation in myocarditis patients. Here, we analyzed inflammatory cell numbers in the atria of myocarditis patients without symptomatic AF.

METHODS

Cardiac tissue was obtained postmortem from lymphocytic myocarditis patients (n=6), catecholamine-induced myocarditis patients (n=5), and control patients without pathological evidence of heart disease (n=5). Tissue sections of left and right ventricle and left and right atrium were stained for myeloperoxidase (neutrophilic granulocytes), CD45 (lymphocytes), and CD68 (macrophages). These cells were subsequently quantified in atrial and ventricular myocardium and atrial adipose tissue.

RESULTS

In lymphocytic myocarditis patients, a significant increase was observed for lymphocytes in the left atrial adipose tissue. In catecholamine-induced myocarditis patients, significant increases were found in the atria for all three inflammatory cell types. Infiltrating inflammatory cell numbers in the atrial myocardium correlated positively with those in the ventricles, especially in catecholamine-induced myocarditis patients.

CONCLUSIONS

To a varying extent, atrial myocarditis occurs concurrently with ventricular myocarditis in patients diagnosed with myocarditis of different etiology. This provides a substrate that potentially predisposes myocarditis patients to the development of AF and subsequent complications such as sudden cardiac death and heart failure.

Association of epicardial adipose tissue thickness and inflammation parameters with CHA2DS2-VASASc score in patients with nonvalvular atrial fibrillation

BACKGROUND

Epicardial adipose tissue (EAT), mean platelet volume (MPV), platelet-to- lymphocyte ratio (PLR), and neutrophil-to-lymphocyte ratio (NLR) have been shown to be helpful in predicting adverse cardiovascular events. However, to date, in the literature, there have been no studies demonstrating the relationship between EAT, MPV, PLR, NLR, and thromboembolism risk in atrial fibrillation (AF). Therefore, we examined the relationship between EAT, MPV, PLR, NLR, and CHA2DS2-VASc score used for the evaluation of thromboembolism risk in patients with AF.

METHODS

The study included 96 consecutive patients with AF and 52 age- and sex-matched control subjects. We calculated CHA2DS2-VASc risk score for each patient and measured baseline EAT thickness, MPV, PLR, NLR, left atrial volume index, and left ventricular ejection fraction.

RESULTS

The group with high CHA2DS2-VASc score had higher EAT (7.2±1.5 vs 5.9±1.2 mm, P<0.001), MPV (9.1±1.1 vs 8.4±1.0 fL, P=0.004), PLR (152.3±28.4 vs 126.7±25.4, P=0.001), and NLR (4.0±1.6 vs 3.2±1.3, P<0.001) compared to group with low-intermediate CHA2DS2-VASc score. Moreover, CHA2DS2-VASc score was found to be positively correlated with EAT (r=0.623, P<0.001), MPV (r=0.350, P=0.004), PLR (r=0.398, P=0.001), and NLR (r=0.518, P<0.001).

CONCLUSION

Our study results demonstrated that EAT thickness, MPV, PLR, and NLR were associated with the thromboembolic risk exhibited by CHA2DS2-VASc score in patients with nonvalvular AF.

Evaluating the Atrial Myopathy Underlying Atrial Fibrillation: Identifying the Arrhythmogenic and Thrombogenic Substrate

Atrial disease or myopathy forms the substrate for atrial fibrillation (AF) and underlies the potential for atrial thrombus formation and subsequent stroke. Current diagnostic approaches in patients with AF focus on identifying clinical predictors with the evaluation of left atrial size by echocardiography serving as the sole measure specifically evaluating the atrium. Although the atrial substrate underlying AF is likely developing for years before the onset of AF, there is no current evaluation to identify the preclinical atrial myopathy. Atrial fibrosis is 1 component of the atrial substrate that has garnered recent attention based on newer MRI techniques that have been applied to visualize atrial fibrosis in humans with prognostic implications regarding the success of treatment. Advanced ECG signal processing, echocardiographic techniques, and MRI imaging of fibrosis and flow provide up-to-date approaches to evaluate the atrial myopathy underlying AF. Although thromboembolic risk is currently defined by clinical scores, their predictive value is mediocre. Evaluation of stasis via imaging and biomarkers associated with thrombogenesis may provide enhanced approaches to assess risk for stroke in patients with AF. Better delineation of the atrial myopathy that serves as the substrate for AF and thromboembolic complications might improve treatment outcomes. Furthermore, better delineation of the pathophysiologic mechanisms underlying the development of the atrial substrate for AF, particularly in its earlier stages, could help identify blood and imaging biomarkers that could be useful to assess risk for developing new-onset AF and suggest specific pathways that could be targeted for prevention.

Monocyte-platelet aggregates and CD11b expression as markers for thrombogenicity in atrial fibrillation

BACKGROUND

A strong interdependence is known between atrial fibrillation (AF), inflammation and thrombogenesis. Monocyte-platelet aggregates (MPAs) are sensitive markers of platelets and monocyte activation. It is not known whether MPAs are associated with thrombogenicity in AF. Therefore, we examined differences in the content of MPAs and CD11b expression in patients with AF in dependence of the presence of atrial thrombus formation.

METHODS

107 patients with symptomatic AF underwent transesophageal echocardiography (TEE) before planned cardioversion or pulmonary vein isolation. Flow-cytometric quantification analysis was done on the day of performed TEE to determine the content of MPAs and the expression of CD11b on monocytes and granulocytes.

RESULTS

Compared to patients without thrombus (n = 80) those with an echocardiographic proven left atrium (LA) thrombus (n = 27) showed an increased extent of the risk factors age, diabetes and heart failure. The content of MPAs (147 ± 12 vs. 311 ± 29 cells/µl, p < 0.001) as well as the CD11b expression on monocytes (p < 0.05) and granulocytes (p < 0.05) were strongly associated with the existence of a LA thrombus. The content of MPAs and the CD11b expression remained independent predictors for LA thrombus after adjustment in logistic regression analysis and negatively correlated with left atrial appendage flow velocity. MPAs above 170 cells/µl (OR 34.2, p = 0.01) had a sensitivity of 96 % and a specificity of 73 % for predicting LA-thrombus.

CONCLUSIONS

The content of MPAs and the CD11b expression on monocytes and granulocytes are increased in AF-patients with proven thrombus formation. They seem to be appropriate biomarkers for stratification of thromboembolic risk in patients with AF.

Role of tumor necrosis factor alpha in the pathogenesis of atrial fibrillation: A novel potential therapeutic target?

Atrial fibrillation (AF) is the most common sustained arrhythmia in clinical practice and a major cause of morbidity and mortality. Although the fundamental mechanisms underlying AF remain incompletely understood, atrial remodeling, including structural, electrical, contractile, and autonomic remodeling, has been demonstrated to contribute to the substrate for AF maintenance. Accumulating evidence shows that tumor necrosis factor alpha (TNF-α) plays exceedingly important roles in atrial remodeling. This article reviews recent advances in the roles of TNF-α in the pathogenesis of AF, elucidates the related mechanisms, and exploits its potential usefulness as a novel therapeutic target.

Low-level transcutaneous electrical vagus nerve stimulation suppresses atrial fibrillation

BACKGROUND

Transcutaneous low-level tragus electrical stimulation (LLTS) suppresses atrial fibrillation (AF) in canines.

OBJECTIVES

This study examined the antiarrhythmic and anti-inflammatory effects of LLTS in humans.

METHODS

Patients with paroxysmal AF who presented for AF ablation were randomized to either 1 h of LLTS (n = 20) or sham control (n = 20). Attaching a flat metal clip onto the tragus produced LLTS (20 Hz) in the right ear (50% lower than the voltage slowing the sinus rate). Under general anesthesia, AF was induced by burst atrial pacing at baseline and after 1 h of LLTS or sham treatment. Blood samples from the coronary sinus and the femoral vein were collected at those time points and then analyzed for inflammatory cytokines, including tumor necrosis factor alpha and C-reactive protein, using a multiplex immunoassay.

RESULTS

There were no differences in baseline characteristics between the 2 groups. Pacing-induced AF duration decreased significantly by 6.3 ± 1.9 min compared with baseline in the LLTS group, but not in the control subjects (p = 0.002 for comparison between groups). AF cycle length increased significantly from baseline by 28.8 ± 6.5 ms in the LLTS group, but not in control subjects (p = 0.0002 for comparison between groups). Systemic (femoral vein) but not coronary sinus tumor necrosis factor (TNF)-alpha and C-reactive protein levels decreased significantly only in the LLTS group.

CONCLUSIONS

LLTS suppresses AF and decreases inflammatory cytokines in patients with paroxysmal AF. Our results support the emerging paradigm of neuromodulation to treat AF.

Serum levels of interleukin-2 predict the recurrence of atrial fibrillation after pulmonary vein ablation

AIMS

Interleukin-2 has a significant antitumor activity in some types of cancer, and has been associated with the development of atrial fibrillation (AF). In addition, IL-2 serum levels in recent onset AF have been related with pharmaceutical cardioversion outcomes. We evaluated the hypothesis that a relationship exists between inflammation and the outcome of catheter ablation of AF.

METHODS

We studied 44 patients with paroxysmal AF who underwent catheter ablation. Patients with structural heart disease, coronary artery or valve disease, active inflammatory disease, known or suspected neoplasm, endocrinopathies, or exposure to anti-inflammatory drugs were excluded. All study participants underwent evaluation with a standardized protocol, including echocardiography, and cytokine levels of interleukin-2, interleukin-4, interleukin-6, interleukin-10, tumour necrosis factor-alpha, and gamma-interferon determination before procedure. Clinical and electrocardiographic follow-up were performed with Holter-ECG at 3, 6 and 12months in order to know if sinus rhythm was maintained.

RESULTS

After catheter ablation of the 44 patients included (53±10years, 27.3% female), all patients returned to sinus rhythm. During the first year of follow-up seven patients (15.9%) experienced recurrence of AF. The demographics, clinical and echocardiographic features, and pharmacological treatments of these patients were similar to those who maintained sinus rhythm. The only independent factor predictive of recurrence of AF was an elevated level of IL-2 (OR 1.18, 95% CI 1.12-1.38).

CONCLUSIONS

High serum levels of interleukin-2, a pro-inflammatory non-vascular cytokine, are associated with the recurrence of AF in patients undergoing catheter ablation.

Sodium tanshinone IIA sulfonate attenuates the transforming growth factor-β1-induced differentiation of atrial fibroblasts into myofibroblasts in vitro

The differentiation of atrial fibroblasts into myofibroblasts is a critical event in atrial fibrosis. One of the most important factors in atrial fibroblast differentiation is transforming growth factor-β1 (TGF-β1). Accumulating evidence indicates that sodium tanshinone IIA sulfonate (STS) possesses antifibrotic properties. In this study, we therefore investigated whether STS attenuates the TGF-β1‑induced differentiation of atrial fibroblasts. TGF-β1 enhanced collagen production, collagen synthesis and the expression of collagen type I and III, as shown by hydroxyproline assay, collagen synthesis assay and western blot analysis, respectively. In addition, as shown by immunohistochemistry and western blot analysis, TGF-β1 enhanced the expression of α-smooth muscle actin (α-SMA), which is the hallmark of myofibroblast differentiation. These responses were attenuated by treatment with STS. In addition, STS suppressed the TGF-β1‑induced expression of phosphorylated (p)Smad/pSmad3 expression and nuclear translocation. Furthermore, STS suppressed extracellular signal-regulated kinase (ERK) phosphorylation. In conclusion, the current study demonstrates that STS exerts antifibrotic effects by modulating atrial fibroblast differentiation through ERK phosphorylation and the Smad pathway.

Relationship of the total atrial conduction time to subclinical atherosclerosis, inflammation and echocardiographic parameters in patients with type 2 diabetes mellitus

OBJECTIVES

The aim of our study was to evaluate the total atrial conduction time and its relationship to subclinical atherosclerosis, inflammation and echocardiographic parameters in patients with type 2 diabetes mellitus.

METHODS

A total of 132 patients with type 2 diabetes mellitus (mean age 54.5 ± 9.6 years; 57.6% male) and 80 age- and gender-matched controls were evaluated. The total atrial conduction time was measured by tissue-Doppler imaging and the carotid intima-media thickness was measured by B-mode ultrasonography.

RESULTS

The total atrial conduction time was significantly longer in the patients with type 2 diabetes mellitus than in the control group (131.7 ± 23.6 vs. 113.1 ± 21.3, p<0.001). The patients with type 2 diabetes mellitus had significantly increased carotid intima-media thicknesses, neutrophil to lymphocyte ratios and high-sensitivity C-reactive protein levels than those of the controls. The total atrial conduction time was positively correlated with the high-sensitivity C-reactive protein level, neutrophil to lymphocyte ratio, carotid intima-media thickness and left atrial volume index and negatively correlated with the early diastolic velocity (Em), Em/late diastolic velocity (Am) ratio and global peak left atrial longitudinal strain. A multiple logistic regression analysis demonstrated that the neutrophil to lymphocyte ratio, carotid intima-media thickness and global peak left atrial longitudinal strain were independent predictors of the total atrial conduction time.

CONCLUSIONS

We suggest that subclinical atherosclerosis and inflammation may represent a mechanism related to prolonged total atrial conduction time and that prolonged total atrial conduction time and impaired left atrial myocardial deformation may be represent early subclinical cardiac involvement in patients with type 2 diabetes mellitus.

Association of epicardial and peri-atrial adiposity with the presence and severity of non-valvular atrial fibrillation

Epicardial adipose tissue (EAT), as an endocrine organ, may serve as a source of pro-inflammatory cytokines. Also, given the strong relationship between atrial fibrillation (AF), obesity and inflammation, the purpose of this study was to investigate the association of non-valvular AF with epicardial and periatrial fat. A total of 618 (192 in sinus rhythm, 169 with paroxysmal AF, 133 with persistent AF and 124 with permanent AF) patients who underwent CT angiography for the evaluation of CAD or pulmonary vein anatomy before catheter ablation were enrolled in this study. Thickness of the EAT and periatrial fat were measured by CT angiography. Together with body mass index, these were examined in relation to the presence and severity of AF and left atrial (LA) diameter. Patients with AF had significantly more total EAT and periatrial fat thickness compared with patients in sinus rhythm (p < 0.001). EAT thickness was significantly higher in permanent, persistent and paroxysmal AF compared with sinus rhythm group (p < 0.001). Multivariable multinomial logistic regression analysis comparing patients with sinus rhythm and subtypes of AF revealed a significant association between periatrial fat and total EAT thickness with all AF subtypes. Correlation analysis demonstrated that both total EAT thickness and periatrial fat thickness were significantly correlated with LA diameter (p < 0.05). Epicardial fat thickness is associated with both the presence and severity of AF independent of all other risk factors including LA diameter. Mediators for the association of EAT with AF pathophysiology requires future large scale prospective studies.

Intersection of cardiovascular disease and kidney disease: atrial fibrillation

PURPOSE OF REVIEW

Atrial fibrillation is the most common sustained arrhythmia in patients with kidney disease. The purpose of this review is to describe the burden of atrial fibrillation in patients with chronic kidney disease (CKD) and end-stage renal disease (ESRD), postulate possible mechanisms to explain this burden of disease, understand the clinical consequences of atrial fibrillation and review the treatment options for atrial fibrillation specific to patients with kidney disease.

RECENT FINDINGS

Recent literature has revealed that the clinical multiorgan impact of atrial fibrillation in patients with CKD and ESRD is substantial. Although novel oral anticoagulants to treat atrial fibrillation and prevent associated complications have been tested in large trials in the general population, there is a paucity of data on the efficacy and safety of these agents in patients with advanced CKD and ESRD.

SUMMARY

Atrial fibrillation is a significant comorbidity in patients with CKD and ESRD with important prognostic implications. More research is needed to understand the mechanisms that contribute to the disproportionate burden of this arrhythmia in patients with kidney disease and in to treatment options specific to this population of high-risk patients.

Novel therapeutic targets in the management of atrial fibrillation

Atrial fibrillation (AF) is the most common cardiac arrhythmia, contributing to increased morbidity and reduced survival through its associations with stroke and heart failure. AF contributes to a four- to fivefold increase in the risk of stroke in the general population and is responsible for 10-15 % of all ischemic strokes. Diagnosis and treatment of AF require considerable health care resources. Current therapies to restore sinus rhythm in AF are suboptimal and are limited either by their pro-arrhythmic effects or by their procedure-related complications. These limitations have necessitated identification of newer therapeutic targets to expand the treatment options. There has been a considerable amount of research interest in investigating the mechanisms of initiation and propagation of AF. Despite extensive research focused on the pathogenesis of AF, a thorough understanding of various pathways mediating initiation and propagation of AF still remains limited. Research efforts focused on the identification of these pathways and molecular mediators have generated a great degree of interest for developing more targeted therapies. This review discusses the potential therapeutic targets and the results from experimental and clinical research investigating these targets.

Mechanisms And Management Of Thrombo-Embolism In Atrial Fibrillation

Atrial fibrillation (AF) is the most common cardiac arrhythmia in the general population and in patients with a history of cardiovascular disease. AF is becoming an outbreak particularly for the western countries as it increases with advancing age; furthermore, AF has a negative social impact because it is associated with stroke and myocardial infarction. Thrombosis generated in the left atrial appendage with ensuing embolism in the cerebral circulation is considered the most important cause of ischemic stroke. In addition to thrombo-embolism, AF is characterized by a constellation of atherosclerotic risk factors, including hypertension, dyslipidaemia and diabetes, which may predispose to serious clinical complications of atherosclerosis such myocardial infarction. Even if interventional trials with oral anticoagulants such as warfarin reduced by about 60% the risk of stroke, AF patients still disclose an elevated residual cardiovascular risk, which may severely complicate the clinical course and management of AF. Recent trials with new oral anticoagulants (NOACs) are opening a new scenario for the treatment of AF, which could improve its management, as NOACs apparently would not require monitoring. However, important caveats are emerging in the real world of AF management, which are questioning the concept that NOACs do not need monitoring. Thus, issues related to compliance and large variability in blood concentration may negatively influence the cost/effectiveness benefit of NOACs. This review will focus on pathophysiology of thrombo-embolism and athero-thrombosis and the impact of old and new anticoagulants in the real world of AF management.

Incident atrial fibrillation and risk of death in adults with chronic kidney disease

Background

Atrial fibrillation (AF) frequently occurs in patients with chronic kidney disease (CKD); however, the long‐term impact of development of AF on the risk of death among patients with CKD is unknown.

Methods and Results

We studied adults with CKD (glomerular filtration rate <60 mL/min per 1.73 m² by the Chronic Kidney Disease Epidemiology Collaboration equation) identified between 2002 and 2010 who were enrolled in Kaiser Permanente Northern California and had no previously documented AF. Incident AF was identified using primary hospital discharge diagnoses or ≥2 outpatient visits for AF. Death was comprehensively ascertained from health plan administrative databases, Social Security Administration vital status files, and the California death certificate registry. Covariates included demographics, comorbidity, ambulatory blood pressure, laboratory values (hemoglobin, proteinuria), and longitudinal medication use. Among 81 088 adults with CKD, 6269 (7.7%) developed clinically recognized incident AF during a mean follow‐up of 4.8±2.7 years. There were 2388 cases of death that occurred after incident AF (145 per 1000 person‐years) compared with 18 865 cases of death during periods without AF (51 per 1000 person‐years, P<0.001). After adjustment for potential confounders, incident AF was associated with a 66% increase in relative rate of death (adjusted hazard ratio 1.66, 95% CI 1.57 to 1.77).

Conclusion

Incident AF is independently associated with an increased risk of death in adults with CKD. Further study is needed to understand the mechanisms by which CKD is associated with AF and to identify potentially modifiable risk factors to decrease the burden of AF and subsequent risk of death in this high‐risk population.

Pioglitazone inhibits angiotensin II-induced atrial fibroblasts proliferation via NF-κB/TGF-β1/TRIF/TRAF6 pathway

The exact mechanisms underlying inhibitory effects of pioglitazone (Pio) on Angiotensin II (AngII)-induced atrial fibrosis are complex and remain largely unknown. In the present study, we examined the effect of Pio on AngII-induced mice atrial fibrosis in vivo and atrial fibroblasts proliferation in vitro. In vivo study showed that AngII infusion induced atrial fibrosis and increased expressions of Toll/IL-1 receptor domain-containing adaptor inducing IFN-β (TRIF) and tumor necrosis factor receptor associated factor 6 (TRAF6) in mice models. However, those effects could be attenuated by Pio (P<0.01). As for in vitro experiment, Pio suppressed AngII-induced atrial fibroblasts proliferation via nuclear factor-κB/transforming growth factor-β1/TRIF/TRAF6 signaling pathway in primary cultured mice atrial fibroblasts (P<0.01). In conclusion, suppression of Pio on AngII-induced atrial fibrosis might be related to its inhibitory effects on above signaling pathway.

Aspirin use and risk of atrial fibrillation in the Physicians' Health Study

Background

Inflammatory processes have been associated with an increased risk of atrial fibrillation (AF), potentially allowing for preventive therapy by anti‐inflammatory agents such as aspirin. However, the effect of chronic aspirin on the incidence of AF has not been evaluated in a prospective cohort followed for an extended period.

Methods and Results

This study was comprised of a prospective cohort of 23 480 male participants of the Physicians' Health Study. Aspirin intake and covariates were estimated using self‐reported questionnaires. Incident AF was ascertained through yearly follow‐up questionnaires. Cox's regression, with adjustment for multiple covariates, was used to estimate relative risk of AF. Average age at baseline was 65.1±8.9 years. During a mean follow‐up of 10.0 years, 2820 cases of AF were reported. Age‐standardized incidence rates were 12.6, 11.1, 12.7, 11.3, 15.8, and 13.8/1000 person‐years for people reporting baseline aspirin intake of 0, <14 days per year, 14 to 30 days per year, 30 to 120 days per year, 121 to 180 days per year, and >180 days per year, respectively. Multivariable adjusted hazard ratios (95% confidence interval) for incident AF were 1.00 (reference), 0.88 (0.76 to 1.02), 0.93 (0.76 to 1.14), 0.96 (0.80 to 1.14), 1.07 (0.80 to 1.14), and 1.04 (0.94 to 1.15) across consecutive categories of aspirin intake. Analysis of the data using time‐varying Cox's regression model to update aspirin intake over time showed similar results.

Conclusions

In a large cohort of males followed for a long period, we did not find any association between aspirin use and incident AF.

Arrhythmic risk in rheumatoid arthritis: the driving role of systemic inflammation

When compared to the general population, patients with rheumatoid arthritis (RA) have an overall standard mortality ratio of approximately two, with more than 50% of premature deaths attributable to cardiovascular disease (CVD). Moreover, RA patients were twice as likely to experience sudden cardiac death (SCD) compared with non-RA subjects, as a putative consequence of an increased incidence of malignant arrhythmias. Accordingly, mounting data indicate that in patients affected with RA the risk of developing rhythm disturbances, particularly tachyarrhythmias, is high. Although a number of papers reviewing the problem of cardiovascular involvement in RA are currently available, the main focus is on the mechanisms of accelerated atherosclerosis and related ischemic consequences in the clinical setting. On the contrary, only little consideration has been specifically given to the arrhythmic risk so far. In the light of this concern, in the present paper we reviewed the topic with the aim to put together the apparently fragmentary existing information, with particular attention to the putative role of chronic systemic inflammation characterizing the disease. In fact, although the underlying mechanisms accounting the arrhythmogenic substrate in RA are probably intricate, the leading role seems to be played by inflammatory activation, able to promote arrhythmias either indirectly, by accelerating the development of structural CVD, and directly by affecting cardiac electrophysiology. In this view, lowering inflammatory burden through an increasingly tight control of disease activity may represent the most effective intervention to reduce arrhythmic risk and prevent life-threatening complications in these patients.

Circulating fibrosis biomarkers and risk of atrial fibrillation: The Cardiovascular Health Study (CHS)

BACKGROUND

Cardiac fibrosis is thought to play a central role in the pathogenesis of atrial fibrillation (AF). Retrospective studies have suggested that circulating fibrosis biomarkers are associated with AF, but prospective studies are limited.

METHODS

We measured circulating levels of 2 fibrosis biomarkers, procollagen type III, N-terminal propeptide (PIIINP) and transforming growth factor β1 among participants of the CHS, a population-based study of older Americans. We used Cox proportional hazards and competing risks models to examine adjusted risk of incident AF over a median follow-up of 8.8 years.

RESULTS

Levels of PIIINP were assessed in 2,935 participants, of whom 767 developed AF. Compared with the median PIIINP level (4.45 μg/L), adjusted hazard ratios (95% CIs) were 0.85 (0.72-1.00) at the 10th percentile, 0.93 (0.88-0.99) at the 25th percentile, 1.04 (0.95-1.04) at the 75th percentile, and 1.07 (0.90-1.26) at the 90th. Transforming growth factor β1 levels, assessed in 1,538 participants with 408 cases of incident AF, were not associated with AF risk.

CONCLUSION

In older adults, PIIINP levels were associated with risk of incident AF in a complex manner, with an association that appeared to be positive up to median levels but with little relationship beyond that. Further studies are required to confirm and possibly delineate the mechanism for this relationship.

Induction of atrial fibrillation by neutrophils critically depends on CD11b/CD18 integrins

Background

Recent observational clinical and ex-vivo studies suggest that inflammation and in particular leukocyte activation predisposes to atrial fibrillation (AF). However, whether local binding and extravasation of leukocytes into atrial myocardium is an essential prerequisite for the initiation and propagation of AF remains elusive. Here we investigated the role of atrial CD11b/CD18 mediated infiltration of polymorphonuclear neutrophils (PMN) for the susceptibility to AF.

Methods and Results

C57bl/6J wildtype (WT) and CD11b/CD18 knock-out (CD11b^−/−) mice were treated for 14 days with subcutaneous infusion of angiotensin II (Ang II), a known stimulus for PMN activation. Atria of Ang II-treated WT mice were characterized by increased PMN infiltration assessed in immunohistochemically stained sections. In contrast, atrial sections of CD11b^−/− mice lacked a significant increase in PMN infiltration upon Ang II infusion. PMN infiltration was accompanied by profoundly enhanced atrial fibrosis in Ang II treated WT as compared to CD11b^−/− mice. Upon in-vivo electrophysiological investigation, Ang II treatment significantly elevated the susceptibility for AF in WT mice if compared to vehicle treated animals given an increased number and increased duration of AF episodes. In contrast, animals deficient of CD11b/CD18 were entirely protected from AF induction. Likewise, epicardial activation mapping revealed decreased electrical conduction velocity in atria of Ang II treated WT mice, which was preserved in CD11b^−/− mice. In addition, atrial PMN infiltration was enhanced in atrial appendage sections of patients with persistent AF as compared to patients without AF.

Conclusions

The current data critically link CD11b-integrin mediated atrial PMN infiltration to the formation of fibrosis, which promotes the initiation and propagation of AF. These findings not only reveal a mechanistic role of leukocytes in AF but also point towards a potential novel avenue of treatment in AF.

Atrial arrhythmia in ageing spontaneously hypertensive rats: unraveling the substrate in hypertension and ageing

Background

Both ageing and hypertension are known risk factors for atrial fibrillation (AF) although the pathophysiological contribution or interaction of the individual factors remains poorly understood. Here we aim to delineate the arrhythmogenic atrial substrate in mature spontaneously hypertensive rats (SHR).

Methods

SHR were studied at 12 and 15 months of age (n = 8 per group) together with equal numbers of age-matched normotensive Wistar-Kyoto control rats (WKY). Electrophysiologic study was performed on superfused isolated right and left atrial preparations using a custom built high-density multiple-electrode array to determine effective refractory periods (ERP), atrial conduction and atrial arrhythmia inducibility. Tissue specimens were harvested for structural analysis.

Results

Compared to WKY controls, the SHR demonstrated: Higher systolic blood pressure (p<0.0001), bi-atrial enlargement (p<0.05), bi-ventricular hypertrophy (p<0.05), lower atrial ERP (p = 0.008), increased atrial conduction heterogeneity (p = 0.001) and increased atrial interstitial fibrosis (p = 0.006) & CD68-positive macrophages infiltration (p<0.0001). These changes resulted in higher atrial arrhythmia inducibility (p = 0.01) and longer induced AF episodes (p = 0.02) in 15-month old SHR. Ageing contributed to incremental bi-atrial hypertrophy (p<0.01) and atrial conduction heterogeneity (p<0.01) without affecting atrial ERP, fibrosis and arrhythmia inducibility. The limited effect of ageing on the atrial substrate may be secondary to the reduction in CD68-positive macrophages.

Conclusions

Significant atrial electrical and structural remodeling is evident in the ageing spontaneously hypertensive rat atria. Concomitant hypertension appears to play a greater pathophysiological role than ageing despite their compounding effect on the atrial substrate. Inflammation is pathophysiologically linked to the pro-fibrotic changes in the hypertensive atria.