Effects of simvastatin on the development of the atrial fibrillation substrate in dogs with congestive heart failure☆

Effects of Phenylacetylglutamine on the Susceptibility of Atrial Fibrillation in Overpressure-Induced HF Mice

Phenylacetylglutamine (PAGln), a gut metabolite is substantially elevated in heart failure (HF). The increase of PAGln in plasma is associated with atrial fibrillation (AF), and contributes to AF pathogenesis. However, the role of PAGln in AF with HF remains uncertain. Therefore, this study aimed to determine the effect of PAGln on AF after HF. Thoracic aortic coarctation (TAC) created overpressure-induced HF mice for 4 weeks. Histopathology, biochemical, echocardiographic for assessment of cardiac function, and electrophysiological examination of several electrophysiological indexes (ERP, SNRT, and the occurrence rate of AF) were performed at the end of the HF mice model. We found that plasma PAGln levels were significantly elevated in PAGln-treated HF mice and that PAGln aggravated maladaptive structural remodeling and electrical remodeling, which aggravated the vulnerability of AF, shortened the ERP duration, prolonged the SNRT, increased the occurrence rate of AF in HF mice. Mechanistically, PAGln exacerbated ROS accumulation and increased the levels of phosphorylated PLB and CAMK II. Overall, PAGln played a vital role in promoting the occurrence of AF in HF mice by activating the CAMK II signaling pathway.

Canadian Contributions in Fibroblast Biology

Fibroblasts are stromal cells found in virtually every tissue and organ of the body. For many years, these cells were often considered to be secondary in functional importance to parenchymal cells. Over the past 2 decades, focused research into the roles of fibroblasts has revealed important roles for these cells in the homeostasis of healthy tissue, and has demonstrated that activation of fibroblasts to myofibroblasts is a key step in disease initiation and progression in many tissues, with fibrosis now recognized as not only an outcome of disease, but also a central contributor to tissue dysfunction, particularly in the heart and lungs. With a growing understanding of both fibroblast and myofibroblast heterogeneity, and the deciphering of the humoral and mechanical cues that impact the phenotype of these cells, fibroblast biology is rapidly becoming a major focus in biomedical research. In this review, we provide an overview of fibroblast and myofibroblast biology, particularly in the heart, and including a discussion of pathophysiological processes such as fibrosis and scarring. We then discuss the central role of Canadian researchers in moving this field forwards, particularly in cardiac fibrosis, and highlight some of the major contributions of these individuals to our understanding of fibroblast and myofibroblast biology in health and disease.

A Genotype-Phenotype Analysis of Glutathione Peroxidase 4 in Human Atrial Myocardium and Its Association with Postoperative Atrial Fibrillation

Heterogeneity in the incidence of postoperative atrial fibrillation (POAF) following heart surgery implies that underlying genetic and/or physiological factors impart a higher risk of this complication to certain patients. Glutathione peroxidase-4 (GPx4) is a vital selenoenzyme responsible for neutralizing lipid peroxides, mediators of oxidative stress known to contribute to postoperative arrhythmogenesis. Here, we sought to determine whether GPX4 single nucleotide variants are associated with POAF, and whether any of these variants are linked with altered GPX4 enzyme content or activity in myocardial tissue. Sequencing analysis was performed across the GPX4 coding region within chromosome 19 from a cohort of patients (N = 189) undergoing elective coronary artery bypass graft (−/+ valve) surgery. GPx4 enzyme content and activity were also analyzed in matching samples of atrial myocardium from these patients. Incidence of POAF was 25% in this cohort. Five GPX4 variants were associated with POAF risk (permutated p ≤ 0.05), and eight variants associated with altered myocardial GPx4 content and activity (p < 0.05). One of these variants (rs713041) is a well-known modifier of cardiovascular disease risk. Collectively, these findings suggest GPX4 variants are potential risk modifiers and/or predictors of POAF. Moreover, they illustrate a genotype−phenotype link with this selenoenzyme, which will inform future mechanistic studies.

Degree of Fibrosis in Human Atrial Tissue Is Not the Hallmark Driving AF

Background: The current paradigm is that fibrosis promotes electrophysiological disorders and drives atrial fibrillation (AF). In this current study, we investigated the relation between the degree of fibrosis in human atrial tissue samples of controls and patients in various stages of AF and the degree of electrophysiological abnormalities. Methods: The degree of fibrosis was measured in the atrial tissue and serum of patients in various stages of AF and the controls. Hereto, picrosirius and H&E staining were performed to quantify degree of total, endo-perimysial fibrosis, and cardiomyocyte diameter. Western blot quantified fibrosis markers: neural cell adhesion molecule, tissue inhibitor of metalloproteinase, lysyl oxidase, and α-smooth muscle actin. In serum, the ratio carboxyl-terminal telopeptide of collagen/matrix-metalloproteinase1 was determined. High-resolution epicardial mapping evaluated low-voltage areas and conduction abnormalities. Results: No significant differences were observed in the degree of fibrosis between the groups. Finally, no significant correlation—absolute nor spatial—was observed between all electrophysiological parameters and histological fibrosis markers. Conclusions: No differences in the degree of fibrosis were observed in patients from various stages of AF compared to the controls. Moreover, electrophysiological abnormalities did not correlate with any of the fibrosis markers. The findings indicate that fibrosis is not the hallmark of structural remodeling in AF.

Management of Chronic Congestive Heart Failure Caused by Myxomatous Mitral Valve Disease in Dogs: A Narrative Review from 1970 to 2020

Simple Summary

Myxomatous mitral valve disease (MMVD) is the most common acquired cardiovascular disease in dogs. The progression of the disease and the increasing severity of valvular regurgitation cause a volume overload of the left heart, leading to left atrial and ventricular remodeling and congestive heart failure (CHF). The treatment of chronic CHF secondary to MMVD in dogs has not always been the same over time. In the last fifty years, the drugs utilized have considerably changed, as well as the therapeutic protocols. Some drugs have also changed their intended use. An analysis of the literature concerning the therapy of chronic heart failure in dogs affected by this widespread degenerative disease is not available; a synthesis of the published literature on this topic and a description of its current state of art are needed. To the authors’ knowledge, a review of this topic has never been published in veterinary medicine; therefore, the aim of this study is to overview the treatments of chronic CHF secondary to MMVD in dogs from 1970 to 2020 using the general framework of narrative reviews.

Abstract

The treatment of chronic congestive heart failure (CHF), secondary to myxomatous mitral valve disease (MMVD) in dogs, has considerably changed in the last fifty years. An analysis of the literature concerning the therapy of chronic CHF in dogs affected by MMVD is not available, and it is needed. Narrative reviews (NRs) are aimed at identifying and summarizing what has been previously published, avoiding duplications, and seeking new study areas that have not yet been addressed. The most accessible open-access databases, PubMed, Embase, and Google Scholar, were chosen, and the searching time frame was set in five decades, from 1970 to 2020. The 384 selected studies were classified into categories depending on the aim of the study, the population target, the pathogenesis of MMVD (natural/induced), and the resulting CHF. Over the years, the types of studies have increased considerably in veterinary medicine. In particular, there have been 43 (24.29%) clinical trials, 41 (23.16%) randomized controlled trials, 10 (5.65%) cross-over trials, 40 (22.60%) reviews, 5 (2.82%) comparative studies, 17 (9.60%) case-control studies, 2 (1.13%) cohort studies, 2 (1.13%) experimental studies, 2 (1.13%) questionnaires, 6 (3.40%) case-reports, 7 (3.95%) retrospective studies, and 2 (1.13%) guidelines. The experimental studies on dogs with an induced form of the disease were less numerous (49–27.68%) than the studies on dogs affected by spontaneous MMVD (128–72.32%). The therapy of chronic CHF in dogs has considerably changed in the last fifty years: in the last century, some of the currently prescribed drugs did not exist yet, while others had different indications.

Statins downregulate YAP and TAZ and exert anti-cancer effects in canine mammary tumour cells

Canine mammary tumours (CMTs) are the most common neoplasms in intact bitches, and few chemotherapeutic options are available for highly invasive and metastatic tumours. Recent studies have shown the potential involvement of dysregulated Hippo signalling in CMT development and progression. Statins can activate the Hippo pathway by blocking protein geranylgeranylation (GGylation), resulting in decreased expression and activity of the transcriptional co-activators YAP and TAZ. In this study, we therefore sought to determine if statins could exert anti-cancer effects in CMT cells. Our results demonstrate that Atorvastatin and Fluvastatin are cytotoxic to two CMT cell lines (CMT9 and CMT47), with ED50 values ranging from 0.95 to 23.5 μM. Both statins acted to increase apoptosis and promote cell cycle arrest. Both statins also decreased YAP and TAZ expression and reduced the mRNA levels of key Hippo transcriptional target genes known to be involved in breast cancer progression and chemoresistance (CYR61, CTGF and RHAMM). Moreover, both statins effectively inhibited cell migration and anchorage independent growth, but did not influence matrix invasion. Taken together, our results demonstrate for the first time that statins act upon the Hippo pathway in CMT cells to counteract several molecular and cellular hallmarks of cancer. These findings suggest that targeting the Hippo pathway with statins represents a novel and promising approach for the treatment canine mammary gland cancers.

Atrial fibrosis and substrate based characterization in atrial fibrillation: Time to move forwards

Atrial fibrillation (AF) is the most commonly encountered cardiac arrhythmia in clinical practice. However, current therapeutic interventions for atrial fibrillation have limited clinical efficacy as a consequence of major knowledge gaps in the mechanisms sustaining atrial fibrillation. From a mechanistic perspective, there is increasing evidence that atrial fibrosis plays a central role in the maintenance and perpetuation of atrial fibrillation. Electrophysiologically, atrial fibrosis results in alterations in conduction velocity, cellular refractoriness, and produces conduction block promoting meandering, unstable wavelets and micro-reentrant circuits. Clinically, atrial fibrosis has also linked to poor clinical outcomes including AF-related thromboembolic complications and arrhythmia recurrences post catheter ablation. In this article, we review the pathophysiology behind the formation of fibrosis as AF progresses, the role of fibrosis in arrhythmogenesis, surrogate markers for detection of fibrosis using cardiac magnetic resonance imaging, echocardiography and electroanatomic mapping, along with their respective limitations. We then proceed to review the current evidence behind therapeutic interventions targeting atrial fibrosis, including drugs and substrate-based catheter ablation therapies followed by the potential future use of electro phenotyping for AF characterization to overcome the limitations of contemporary substrate-based methodologies.

Atrial fibrosis underlying atrial fibrillation (Review)

Atrial fibrillation (AF) is one of the most common tachyarrhythmias observed in the clinic and is characterized by structural and electrical remodelling. Atrial fibrosis, an emblem of atrial structural remodelling, is a complex multifactorial and patient-specific process involved in the occurrence and maintenance of AF. Whilst there is already considerable knowledge regarding the association between AF and fibrosis, this process is extremely complex, involving intricate neurohumoral and cellular and molecular interactions, and it is not limited to the atrium. Current technological advances have made the non-invasive evaluation of fibrosis in the atria and ventricles possible, facilitating the selection of patient-specific ablation strategies and upstream treatment regimens. An improved understanding of the mechanisms and roles of fibrosis in the context of AF is of great clinical significance for the development of treatment strategies targeting the fibrous region. In the present review, a focus was placed on the atrial fibrosis underlying AF, outlining its role in the occurrence and perpetuation of AF, by reviewing recent evaluations and potential treatment strategies targeting areas of fibrosis, with the aim of providing a novel perspective on the management and prevention of AF.

The effects of ACEI/ARB, aldosterone receptor antagonists and statins on preventing recurrence of atrial fibrillation: A protocol for systematic review and network meta-analysis

BACKGROUND

Atrial fibrillation (AF) is one of the most common arrhythmias, and is high relative to cardiovascular morbidity and mortality. AF-related complications and treatment costs bring about huge health burden, therefore the prevention recurrence of AF is imperative. "Upstream therapy" refers to the use of non-antiarrhythmic drugs (non-AADs) that modify the atrial substrate or target-specific mechanisms of AF to prevent the occurrence or recurrence of the arrhythmia. RAAS Blockers, aldosterone receptor antagonists and statins have an effect on preventing recurrence of atrial fibrillation. This protocol is designed for systematic review and network meta-analysis, which will assess comparative effects and safety of various non-antiarrhythmic drugs in preventing recurrence of atrial fibrillation.

METHODS

The Cochrane Library, MEDLINE, EMBASE, ClinicalTrials.gov will be searched from inception to Aug 31, 2020 to identify relevant studies. The Cochrane "Risk of bias" tool will be used to assess the methodological quality of eligible studies. The pair-wise meta-analysis will be performed by STATA 14.0 software. The network meta-analysis will be implemented in a Bayesian framework using Win BUGS 1.4.3 and the package "gemtc" V.0.8.1 of R-3.6.2 software. The network plots will be drawn using STATA 14.0 software. A comparison-adjusted funnel plot will be used to assess the publication bias using STATA 14.0 software. Quality of evidence will be assessed using the Grading of Recommendations Assessment, Development and Evaluation (GRADE) approach.

RESULTS

The results of this network meta-analysis will determine the preventive effect and rank ordering of these interventions for recurrence of AF. The report will follow the PRISMA checklist for network meta-analysis.

CONCLUSION

This network meta-analysis will provide comprehensive evidence-based information in clinical practice.

INPLASY REGISTRATION NUMBER

INPLASY202090004.

Cardiac fibrosis: emerging agents in preclinical and clinical development

INTRODUCTION

Myocardial fibrosis is a remarkably dynamic process mediated by different molecular pathways that represent potential targets of novel therapeutic interventions. Transforming Growth Factor-beta (TGF-β), connective Tissue Growth Factor (cTGF) and Galectin-3 (Gal-3) represent the most promising targets on which research has been currently focusing.

AREA COVERED

This review initially discusses those drugs used in clinical practice for their anti-fibrotic properties and later examines emerging pathway-specific agents in preclinical and clinical development [phase I and II-concluded or ongoing trials]. We performed a PubMed, Embase and Google Scholar research including original articles, systematic reviews, ongoing and completed trials using combinations of keywords such as 'myocardial fibrosis', 'reverse remodeling', 'RAAs', 'therapy'.

EXPERT OPINION

A variety of preclinical evidences suggest that new drugs and molecules are potentially useful to target cardiac fibrosis and improve left ventricular function, reduce infarct size and scars, delay incident heart failure and cardiac dysfunction in animal models. However, there are very few clinical trials investigating the effect of such drugs in this setting, as well as a lack of new engineered molecules for specific targets.

Upstream Therapy for Atrial Fibrillation Prevention: The Role of Sacubitril/Valsartan

The therapy or prevention of atrial fibrillation (AF) is defined as upstream therapy when conducted with the use of drugs, e.g., angiotensin-converting enzyme inhibitors (ACEIs), angiotensin receptor antagonists, statins, and omega-3 fatty acids, not included in the classes of antiarrhythmic drugs recognized by the Vaughan Williams classification. In our review, we illustrate the rational bases of upstream AF therapy, which encompasses drugs having the property to reduce hemodynamic congestion and cardiac overload, as in the case of ACEIs or angiotensin receptor blockers, as well as drugs able to prevent atrial fibrosis or reduce oxidative stress, such as statins or omega-3 fatty acids, respectively. In this review, randomized controlled trials (RCTs) conducted with the abovementioned drugs are examined. Really, these RCTs have generated mixed results. In the context of the prevention and therapy of AF, our experience is then presented, relating to a patient with heart failure and reduced left ventricular ejection fraction, with a history of relapsing episodes of paroxysmal AF. In this patient, administration of sacubitril/valsartan at appropriate doses allowed recovery of the sinus rhythm. Therefore this case testifies how the upstream therapy of AF might have good results when conducted with sacubitril/valsartan. Thus, RCTs with adequate statistical power are warranted in order to confirm the preliminary encouraging result of our case report, and validate a useful role of sacubitril/valsartan as an upstream therapy of AF.

AGE-RAGE Stress in the Pathophysiology of Atrial Fibrillation and Its Treatment

Atrial fibrillation (AF) is the most common of cardiac arrhythmias. Mechanisms such as atrial structural remodeling and electrical remodeling have been implicated in the pathogenesis of AF. The data to date suggest that advanced glycation end products (AGEs) and its cell receptor RAGE (receptor for AGE) and soluble receptor (sRAGE) are involved in the pathogenesis of AF. This review focuses on the role of AGE-RAGE axis in the pathogenesis of AF. Interaction of AGE with RAGE generates reactive oxygen species, cytokines, and vascular cell adhesion molecules. sRAGE is a cytoprotective agent. The data show that serum levels of AGE and sRAGE, and expression of RAGE, are elevated in AF patients. Elevated levels of sRAGE did not protect the development of AF. This might be due to greater elevation of AGE than sRAGE. Measurement of AGE-RAGE stress (AGE/sRAGE) would be appropriate as compared with measurement of AGE or RAGE or sRAGE alone in AF patients. AGE and its interaction with RAGE can induce AF through alteration in cellular protein and extracellular matrix. AGE and its interaction with RAGE induce atrial structural and electrical remodeling. The treatment strategy should be directed toward reduction in AGE levels, suppression of RAGE expression, blocking of binding of AGE to RAGE, and elevation of sRAGE and antioxidants. In conclusion, AGE-RAGE axis is involved in the development of AF through atrial structural and electrical remodeling. The treatment modalities for AF should include lowering of AGE, suppression of RAGE, elevation of sRAGE, and use of antioxidants.

Regulation of Atrial Fibrosis by the Bone

MR (mineralocorticoid receptor) antagonists have been demonstrated to provide beneficial effects on preventing atrial fibrosis. However, the underlying cellular and molecular mechanisms remain unclear. We aim to determine the role of osteoblast MR in atrial fibrosis and to explore the underlying mechanism. Using osteoblast MR knockout mouse in combination with mutant TGF (transforming growth factor)-β1 transgenic mouse, we demonstrated that MR deficiency in osteoblasts significantly attenuated atrial fibrosis. Mechanistically, MR directly regulated expression of OCN (osteocalcin) in osteoblasts. Both carboxylated and undercarboxylated OCNs (ucOC) were less secreted in osteoblast MR knockout mice. Mutant TGF-β1 transgenic mice supplemented with recombinant ucOC showed aggravated atrial fibrosis. In cultured atrial fibroblasts, ucOC treatment promoted proliferation and migration of atrial fibroblasts, whereas cotreatment with an antagonist for a GPRC6A (G-protein-coupled receptor, family C, group 6, member A) abolished these effects. Western blotting analysis revealed upregulation of PKA (protein kinase A) and CREB (cAMP-response element-binding protein) phosphorylation after ucOC treatment. Inhibition of PKA with its antagonist reduced ucOC-induced proliferation and migration of atrial fibroblasts. Finally, the impact of osteoblast MR deficiency on atrial fibrosis was abolished by ucOC administration in mutant TGF-β1 transgenic mice. Taken together, MR deficiency in osteoblasts attenuated atrial fibrosis by downregulation of OCN to promote proliferation and migration of atrial fibroblasts.

Molecular identification of HSPA8 as an accessory protein of a hyperpolarization-activated chloride channel from rat pulmonary vein cardiomyocytes

Pulmonary veins (PVs) are the major origin of atrial fibrillation. Recently, we recorded hyperpolarization-activated Cl^- current (I _{Cl, h}) in rat PV cardiomyocytes. Unlike the well-known chloride channel protein 2 (CLCN2) current, the activation curve of I _{Cl, h} was hyperpolarized as the Cl^- ion concentration ([Cl^-] _i ) increased. This current could account for spontaneous activity in PV cardiomyocytes linked to atrial fibrillation. In this study, we aimed to identify the channel underlying I _{Cl, h} Using RT-PCR amplification specific for Clcn2 or its homologs, a chloride channel was cloned from rat PV and detected in rat PV cardiomyocytes using immunocytochemistry. The gene sequence and electrophysiological functions of the protein were identical to those previously reported for Clcn2, with protein activity observed as a hyperpolarization-activated current by the patch-clamp method. However, the [Cl^-] _i dependence of activation was entirely different from the observed I _{Cl, h} of PV cardiomyocytes; the activation curve of the Clcn2-transfected cells shifted toward positive potential with increased [Cl^-] _i , whereas the I _{Cl, h} of PV and left ventricular cardiomyocytes showed a leftward shift. Therefore, we used MS to explore the possibility of additional proteins interacting with CLCN2 and identified an individual 71-kDa protein, HSPA8, that was strongly expressed in rat PV cardiomyocytes. With co-expression of HSPA8 in HEK293 and PC12 cells, the CLCN2 current showed voltage-dependent activation and shifted to negative potential with increasing [Cl^-] _i Molecular docking simulations further support an interaction between CLCN2 and HSPA8. These findings suggest that CLCN2 in rat heart contains HSPA8 as a unique accessory protein.

Biomarkers of Atrial Fibrillation in Metabolic Syndrome

Whether the increased atrial fibrillation (AF) risk in metabolic syndrome (MetS) patients is due to the syndrome as a whole or simply the sum of the risks of its individual component parts is still obscure. These two clinical entities share many pathophysiological links and thus distinction between a casual observation and a significant association is difficult. Biomarkers associated with pathogenesis of AF in the context of MetS have the ability to refine future risk prediction. In the present review we identify circulating substances that could be regarded as potential biomarkers for prediction of incident AF, or of cardiovascular events in the setting of AF in patients with MetS. Cardiac myocyte injury and stress markers (troponin and natriuretic peptides), markers of renal function (glomeral filtration rate, cystatin-C), and inflammation markers/mediators (interleukin- 6, CRP) are promising biomarkers of patients with AF and MetS.

Redox State in Atrial Fibrillation Pathogenesis and Relevant Therapeutic Approaches

BACKGROUND

Myocardial redox state is a critical determinant of atrial biology, regulating cardiomyocyte apoptosis, ion channel function, and cardiac hypertrophy/fibrosis and function. Nevertheless, it remains unclear whether the targeting of atrial redox state is a rational therapeutic strategy for atrial fibrillation prevention.

OBJECTIVE

To review the role of atrial redox state and anti-oxidant therapies in atrial fibrillation.

METHOD

Published literature in Medline was searched for experimental and clinical evidence linking myocardial redox state with atrial fibrillation pathogenesis as well as studies looking into the role of redoxtargeting therapies in the prevention of atrial fibrillation.

RESULTS

Data from animal models have shown that altered myocardial nitroso-redox balance and NADPH oxidases activity are causally involved in the pathogenesis of atrial fibrillation. Similarly experimental animal data supports that increased reactive oxygen / nitrogen species formation in the atrial tissue is associated with altered electrophysiological properties of atrial myocytes and electrical remodeling, favoring atrial fibrillation development. In humans, randomized clinical studies using redox-related therapeutic approaches (e.g. statins or antioxidant agents) have not documented any benefits in the prevention of atrial fibrillation development (mainly post-operative atrial fibrillation risk).

CONCLUSION

Despite strong experimental and translational data supporting the role of atrial redox state in atrial fibrillation pathogenesis, such mechanistic evidence has not been translated to clinical benefits in atrial fibrillation risk in randomized clinical studies using redox-related therapies.

Concise Review: Reduction of Adverse Cardiac Scarring Facilitates Pluripotent Stem Cell-Based Therapy for Myocardial Infarction

Pluripotent stem cells (PSCs) are an attractive, reliable source for generating functional cardiomyocytes for regeneration of infarcted heart. However, inefficient cell engraftment into host tissue remains a notable challenge to therapeutic success due to mechanical damage or relatively inhospitable microenvironment. Evidence has shown that excessively formed scar tissues around cell delivery sites present as mechanical and biological barriers that inhibit migration and engraftment of implanted cells. In this review, we focus on the functional responses of stem cells and cardiomyocytes during the process of cardiac fibrosis and scar formation. Survival, migration, contraction, and coupling function of implanted cells may be affected by matrix remodeling, inflammatory factors, altered tissue stiffness, and presence of electroactive myofibroblasts in the fibrotic microenvironment. Although paracrine factors from implanted cells can improve cardiac fibrosis, the transient effect is insufficient for complete repair of an infarcted heart. Furthermore, investigation of interactions between implanted cells and fibroblasts including myofibroblasts helps the identification of new targets to optimize the host substrate environment for facilitating cell engraftment and functional integration. Several antifibrotic approaches, including the use of pharmacological agents, gene therapies, microRNAs, and modified biomaterials, can prevent progression of heart failure and have been developed as adjunct therapies for stem cell-based regeneration. Investigation and optimization of new biomaterials is also required to enhance cell engraftment of engineered cardiac tissue and move PSCs from a laboratory setting into translational medicine.

Targeting the Substrate in Ablation of Persistent Atrial Fibrillation: Recent Lessons and Future Directions

While isolation of the pulmonary veins is firmly established as effective treatment for the majority of paroxysmal atrial fibrillation (AF) patients, there is recognition that patients with persistent AF have substrate for perpetuation of arrhythmia existing outside of the pulmonary veins. Various computational approaches have been used to identify targets for effective ablation of persistent AF. This paper aims to discuss the clinical aspects of computational approaches that aim to identify critical sites for treatment. Various analyses of electrogram characteristics have been performed with this aim. Leading techniques for electrogram analysis are Complex Fractionated Atrial Electrograms (CFAE) and Dominant Frequency (DF). These techniques have been the subject of clinical trials of which the results are discussed. Evaluation of the activation patterns of atria in AF has been another avenue of research. Focal Impulse and Rotor Modulation (FIRM) mapping and forms of Body Surface Mapping aim to characterize multiple atrial wavelets, macro-reentry and focal sources which have been proposed as basic mechanisms perpetuating AF. Both invasive and non-invasive activation mapping techniques are reviewed. The presence of atrial fibrosis causes non-uniform anisotropic impulse propagation. Therefore, identification of fibrosis by imaging techniques is an avenue of potential research. The leading contender for imaging-based techniques is Cardiac Magnetic Resonance (CMR). As this technology advances, improvements in resolution and scar identification have positioned CMR as the mode of choice for analysis of atrial structure. AF has been demonstrated to be associated with obesity, inactivity and diseases of modern life. An opportunity exists for detailed computational analysis of the impact of risk factor modification on atrial substrate. This ranges from microstructural investigation through to examination at a population level via registries and public health interventions. Computational analysis of atrial substrate has moved from basic science toward clinical application. Future directions and potential limitations of such analyses are examined in this review.

Treatment of Patients With Atrial Fibrillation and Heart Failure With Reduced Ejection Fraction

Atrial fibrillation (AF) and heart failure with reduced ejection fraction (HFrEF) frequently coexist, and each complicates the course and treatment of the other. Recent population-based studies have demonstrated that the 2 conditions together increase the risk of stroke, heart failure hospitalization, and all-cause mortality, especially soon after the clinical onset of AF. Guideline-directed pharmacological therapy for HFrEF is important; however, although there are various treatment modalities for AF, there is no clear consensus on how best to treat AF with concomitant HFrEF. This in-depth review discusses the available data for the treatment of AF in the setting of HFrEF, focuses on areas where more investigation is necessary, examines the clinical implications of randomized and observational clinical trials, and presents suggestions for individualized treatment strategies for specific patient groups.

Pravastatin But Not Simvastatin Improves Survival and Neurofunctional Outcome After Cardiac Arrest and Cardiopulmonary Resuscitation

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In a murine model of CA and CPR, intravenous application of hydrophilic pravastatin resulted in increased survival and neurofunctional outcome.

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In contrast, intravenous application of lipophilic simvastatin did not improve survival or neurofunction following CA/CPR.

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Pravastatin, but not simvastatin, treatment reduced post-resuscitation pulmonary edema and augmented pulmonary function.

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In vitro, pravastatin augmented endothelial cell function, whereas simvastatin induced endothelial cell apoptosis.

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This study supports previous requests for an intravenous formulation of hydrophilic statins for clinical use.

Cardiac arrest (CA) followed by cardiopulmonary resuscitation (CPR) is associated with high mortality and poor neurological outcome. We compared the effects of pravastatin and simvastatin on survival and neurofunction in a murine model of CA/CPR. Pravastatin, a hydrophilic statin, increased survival and neurofunction during a 28-day follow-up period. This therapy was associated with improved pulmonary function, reduced pulmonary edema, and increased endothelial cell function in vitro. In contrast, lipophilic simvastatin did not modulate survival but increased pulmonary edema and impaired endothelial cell function. Although pravastatin may display a therapeutic option for post-CA syndrome, the application of simvastatin may require re-evaluation.

Antiarrhythmic Drug Therapy for Atrial Fibrillation

Atrial fibrillation (AF) is the most frequently encountered arrhythmia. Prevalence increases with advancing age and so as its associated comorbidities, like heart failure. Choice of pharmacologic therapy depends on whether the goal of treatment is maintaining sinus rhythm or tolerating AF with adequate control of ventricular rates. Antiarrhythmic therapy and conversion of AF into sinus rhythm comes with the side effect profile, and we should select best antiarrhythmic therapy, individualized to the patient. New antiarrhythmic drugs are being tested in clinical trials. Drugs that target remodeling and inflammation are being tested for their use as prevention of AF or as upstream therapy.

Atrial Electrophysiological Remodeling and Fibrillation in Heart Failure

Heart failure (HF) causes complex, chronic changes in atrial structure and function, which can cause substantial electrophysiological remodeling and predispose the individual to atrial fibrillation (AF). Pharmacological treatments for preventing AF in patients with HF are limited. Improved understanding of the atrial electrical and ionic/molecular mechanisms that promote AF in these patients could lead to the identification of novel therapeutic targets. Animal models of HF have identified numerous changes in atrial ion currents, intracellular calcium handling, action potential waveform and conduction, as well as expression and signaling of associated proteins. These studies have shown that the pattern of electrophysiological remodeling likely depends on the duration of HF, the underlying cardiac pathology, and the species studied. In atrial myocytes and tissues obtained from patients with HF or left ventricular systolic dysfunction, the data on changes in ion currents and action potentials are largely equivocal, probably owing mainly to difficulties in controlling for the confounding influences of multiple variables, such as patient’s age, sex, disease history, and drug treatments, as well as the technical challenges in obtaining such data. In this review, we provide a summary and comparison of the main animal and human electrophysiological studies to date, with the aim of highlighting the consistencies in some of the remodeling patterns, as well as identifying areas of contention and gaps in the knowledge, which warrant further investigation.

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.

Effects of atorvastatin on atrial remodeling in a rabbit model of atrial fibrillation produced by rapid atrial pacing

Background

Accumulating evidence suggests that myeloperoxidase (MPO) is involved in atrial remodeling of atrial fibrillation (AF). Statins could reduce the MPO levels in patients with cardiovascular diseases. This study evaluated the effects of atorvastatin on MPO level and atrial remodeling in a rabbit model of pacing-induced AF.

Methods

Eighteen rabbits were randomly divided into sham, control and atorvastatin groups. Rabbits in the control and atorvastatin groups were subjected to rapid atrial pacing (RAP) at 600 bpm for 3 weeks, and treated with placebo or atorvastatin (2.5 mg/kg/d), respectively. Rabbits in the sham group did not receive RAP. After 3 weeks of pacing, atrial structural and functional changes were assessed by echocardiography, atrial effective refractory period (AERP) and AF inducibility were measured by atrial electrophysiological examination, and histological changes were evaluated by Masson trichrome-staining. The L-type calcium channel α1c (Cav1.2), collagen I and III, MPO, matrix metalloproteinase (MMP)-2 and MMP-9 were analyzed by real time polymerase chain reaction and/or western blot.

Results

All rabbits were found to have maintained sinus rhythm after 3 weeks of RAP. Atrial burst stimulation induced sustained AF (>30 min) in 5, 4, and no rabbits in the control, atorvastatin, and sham groups, respectively. The AERP shortened and Cav1.2 mRNA level decreased in the control group, but these changes were suppressed in the atorvastatin group. Obvious left atrial enlargement and dysfunction was found in both control and atorvastatin groups. Compared with the control group, these echocardiograhic indices of left atrium did not differ in the atorvastatin group. Prominent atrial fibrosis and increased levels of collagen I and III were observed in the control group but not in the atorvastatin group. The mRNA and protein levels of MPO, MMP-2 and MMP-9 significantly increased in the control group, but these changes were prevented in the atorvastatin group.

Conclusion

Treatment with atorvastatin prevented atrial remodeling in a rabbit model of RAP-induced AF. The reduction of levels of atrial MPO, MMP-2 and MMP-9 may contribute to the prevention of atorvastatin on atrial remodeling.

Novel therapeutic strategies targeting fibroblasts and fibrosis in heart disease

Our understanding of the functions of cardiac fibroblasts has moved beyond their roles in heart structure and extracellular matrix generation and now includes their contributions to paracrine, mechanical and electrical signalling during ontogenesis and normal cardiac activity. Fibroblasts also have central roles in pathogenic remodelling during myocardial ischaemia, hypertension and heart failure. As key contributors to scar formation, they are crucial for tissue repair after interventions including surgery and ablation. Novel experimental approaches targeting cardiac fibroblasts are promising potential therapies for heart disease. Indeed, several existing drugs act, at least partially, through effects on cardiac connective tissue. This Review outlines the origins and roles of fibroblasts in cardiac development, homeostasis and disease; illustrates the involvement of fibroblasts in current and emerging clinical interventions; and identifies future targets for research and development.

Chamber-specific differences in human cardiac fibroblast proliferation and responsiveness toward simvastatin

Fibroblasts, the most abundant cells in the heart, contribute to cardiac fibrosis, the substrate for the development of arrythmogenesis, and therefore are potential targets for preventing arrhythmic cardiac remodeling. A chamber-specific difference in the responsiveness of fibroblasts from the atria and ventricles toward cytokine and growth factors has been described in animal models, but it is unclear whether similar differences exist in human cardiac fibroblasts (HCFs) and whether drugs affect their proliferation differentially. Using cardiac fibroblasts from humans, differences between atrial and ventricular fibroblasts in serum-induced proliferation, DNA synthesis, cell cycle progression, cyclin gene expression, and their inhibition by simvastatin were determined. The serum-induced proliferation rate of human atrial fibroblasts was more than threefold greater than ventricular fibroblasts with faster DNA synthesis and higher mRNA levels of cyclin genes. Simvastatin predominantly decreased the rate of proliferation of atrial fibroblasts, with inhibition of cell cycle progression and an increase in the G0/G1 phase in atrial fibroblasts with a higher sensitivity toward inhibition compared with ventricular fibroblasts. The DNA synthesis and mRNA levels of cyclin A, D, and E were significantly reduced by simvastatin in atrial but not in ventricular fibroblasts. The inhibitory effect of simvastatin on atrial fibroblasts was abrogated by mevalonic acid (500 μM) that bypasses 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibition. Chamber-specific differences exist in the human heart because atrial fibroblasts have a higher proliferative capacity and are more sensitive to simvastatin-mediated inhibition through HMG-CoA reductase pathway. This mechanism may be useful in selectively preventing excessive atrial fibrosis without inhibiting adaptive ventricular remodeling during cardiac injury.

Up-regulation of miR-31 in human atrial fibrillation begets the arrhythmia by depleting dystrophin and neuronal nitric oxide synthase

Atrial fibrillation (AF) is a growing public health burden, and its treatment remains a challenge. AF leads to electrical remodeling of the atria, which in turn promotes AF maintenance and resistance to treatment. Although remodeling has long been a therapeutic target in AF, its causes remain poorly understood. We show that atrial-specific up-regulation of microRNA-31 (miR-31) in goat and human AF depletes neuronal nitric oxide synthase (nNOS) by accelerating mRNA decay and alters nNOS subcellular localization by repressing dystrophin translation. By shortening action potential duration and abolishing rate-dependent adaptation of the action potential duration, miR-31 overexpression and/or disruption of nNOS signaling recapitulates features of AF-induced remodeling and significantly increases AF inducibility in mice in vivo. By contrast, silencing miR-31 in atrial myocytes from patients with AF restores dystrophin and nNOS and normalizes action potential duration and its rate dependency. These findings identify atrial-specific up-regulation of miR-31 in human AF as a key mechanism causing atrial dystrophin and nNOS depletion, which in turn contributes to the atrial phenotype begetting this arrhythmia. miR-31 may therefore represent a potential therapeutic target in AF.

Can heart function lost to disease be regenerated by therapeutic targeting of cardiac scar tissue?

Myocardial infarction results in scar tissue that cannot actively contribute to heart mechanical function and frequently causes lethal arrhythmias. The healing response after infarction involves inflammation, biochemical signaling, changes in cellular phenotype, activity, and organization, and alterations in electrical conduction due to variations in cell and tissue geometry and alterations in protein expression, organization, and function - particularly in membrane channels. The intensive research focus on regeneration of myocardial tissues has, as of yet, only met with modest success, with no near-term prospect of improving standard-of-care for patients with heart disease. An alternative concept for novel therapeutic approach is the rejuvenation of cardiac electrical and mechanical properties through the modification of scar tissue. Several peptide therapeutics, locally applied genetic therapies, or delivery of genetically modified cells have shown promise in improving the characteristics of the fibrous scar and post-myocardial infarction prognosis in experimental models. This review highlights several factors that contribute to arrhythmogenesis in scar formation and how these might be targeted to regenerate some of the electrical and mechanical function of the post-MI scar.

Assessment of the Risk Factors and Outcomes for Postoperative Atrial Fibrillation Patients Undergoing Isolated Coronary Artery Bypass Grafting

BACKGROUND

Atrial fibrillation is the most common complication of cardiac surgery and is associated with significant morbidity and mortality. Recognizing patients at high risk for developing postoperative atrial fibrillation (POAF) may help identify those who could benefit from strategies to prevent POAF. This study was conducted to delineate outcomes and to assess risk factors for POAF among Taiwanese patients undergoing coronary artery bypass grafting (CABG).

METHODS

From January 2009 until February 2012, this prospective study included 266 consecutive patients admitted to our hospital with coronary artery disease. All patients underwent isolated CABG. Patients with preoperative permanent atrial fibrillation and concomitant surgery were excluded. Multiple risk factors associated with the incidence of POAF were collected and evaluated.

RESULTS

POAF occurred in 126 of 226 patients (47.37%). Univariate analysis revealed that significant risk factors for the condition were age, gender, diabetes, dyslipidemia, smoking, impaired renal function, impaired cardiac function, and increased serum electrolytes. Multivariate analysis showed dyslipidemia [hazard ratio (HR): 0.418; 95% confidence interval (Cl): 0.190-0.915, p = 0.029], impaired renal function as indicated by an estimated glomerular filtration rate < 60 mL/min/1.73 m(2) (HR: 3.174; 95% CI: 1.432-7.037, p = 0.004), and serum sodium (HR: 1.112; 95% Cl: 1.047-1.182, p = 0.001) prior to cardiopulmonary bypass as significant. Moreover, POAF was associated with lower 30-day, 1- and 3-year cumulative survival rates and higher early postoperative complications.

CONCLUSIONS

Patients with isolated CABG who were administered β-blockers, angiotensin converting enzyme inhibitor/angiotensin receptor blockers treatment, and lipid therapy before CABG were associated with reduced POAF, while those with impaired renal function and higher serum sodium before CABG predisposed POAF in a Taiwanese population.

KEY WORDS

Atrial fibrillation (AF); Coronary artery bypass grafting (CABG); Coronary artery disease (CAD); Postoperative atrial fibrillation (POAF).

Towards comprehensive cardiac repair and regeneration after myocardial infarction: Aspects to consider and proteins to deliver

Ischemic heart disease is a leading cause of death worldwide. After the onset of myocardial infarction, many pathological changes take place and progress the disease towards heart failure. Pathologies such as ischemia, inflammation, cardiomyocyte death, ventricular remodeling and dilation, and interstitial fibrosis, develop and involve the signaling of many proteins. Proteins can play important roles in limiting or countering pathological changes after infarction. However, they typically have short half-lives in vivo in their free form and can benefit from the advantages offered by controlled release systems to overcome their challenges. The controlled delivery of an optimal combination of proteins per their physiologic spatiotemporal cues to the infarcted myocardium holds great potential to repair and regenerate the heart. The effectiveness of therapeutic interventions depends on the elucidation of the molecular mechanisms of the cargo proteins and the spatiotemporal control of their release. It is likely that multiple proteins will provide a more comprehensive and functional recovery of the heart in a controlled release strategy.

Comorbidity of atrial fibrillation and heart failure

Atrial fibrillation (AF) and heart failure (HF) are evolving epidemics, together responsible for substantial human suffering and health-care expenditure. Ageing, improved cardiovascular survival, and epidemiological transition form the basis for their increasing global prevalence. Although we now have a clear picture of how HF promotes AF, gaps remain in our knowledge of how AF exacerbates or even causes HF, and how the development of HF affects the outcome of patients with AF. New data regarding HF with preserved ejection fraction and its unique relationship with AF suggest a possible role for AF in its aetiology, possibly as a trigger for ventricular fibrosis. Deciding on optimal treatment strategies for patients with both AF and HF is increasingly difficult, given that results from trials of pharmacological rhythm control are arguably obsolete in the age of catheter ablation. Restoring sinus rhythm by catheter ablation seems successful in the medium term and improves HF symptoms, functional capacity, and left ventricular function. Long-term studies to examine the effect on rates of stroke and death are ongoing. Guidelines continue to evolve to keep pace with this rapidly changing field.

Simvastatin alleviates cardiac fibrosis induced by infarction via up-regulation of TGF-β receptor III expression

BACKGROUND AND PURPOSE

Statins decrease heart disease risk, but their mechanisms are not completely understood. We examined the role of the TGF-β receptor III (TGFBR3) in the inhibition of cardiac fibrosis by simvastatin.

EXPERIMENTAL APPROACH

Myocardial infarction (MI) was induced by ligation of the left anterior descending coronary artery in mice given simvastatin orally for 7 days. Cardiac fibrosis was measured by Masson staining and electron microscopy. Heart function was evaluated by echocardiography. Signalling through TGFBR3, ERK1/2, JNK and p38 pathways was measured using Western blotting. Collagen content and cell viability were measured in cultures of neonatal mouse cardiac fibroblasts (NMCFs). Interactions between TGFBR3 and the scaffolding protein, GAIP-interacting protein C-terminus (GIPC) were detected using co-immunoprecipitation (co-IP). In vivo, hearts were injected with lentivirus carrying shRNA for TGFBR3.

KEY RESULTS

Simvastatin prevented fibrosis following MI, improved heart ultrastructure and function, up-regulated TGFBR3 and decreased ERK1/2 and JNK phosphorylation. Simvastatin up-regulated TGFBR3 in NMCFs, whereas silencing TGFBR3 reversed inhibitory effects of simvastatin on cell proliferation and collagen production. Simvastatin inhibited ERK1/2 and JNK signalling while silencing TGFBR3 opposed this effect. Co-IP demonstrated TGFBR3 binding to GIPC. Overexpressing TGFBR3 inhibited ERK1/2 and JNK signalling which was abolished by knock-down of GIPC. In vivo, suppression of cardiac TGFBR3 abolished anti-fibrotic effects, improvement of cardiac function and changes in related proteins after simvastatin.

CONCLUSIONS AND IMPLICATIONS

TGFBR3 mediated the decreased cardiac fibrosis, collagen deposition and fibroblast activity, induced by simvastatin, following MI. These effects involved GIPC inhibition of the ERK1/2/JNK pathway.

Role of the MAPKs/TGF-β1/TRAF6 signaling pathway in atrial fibrosis of patients with chronic atrial fibrillation and rheumatic mitral valve disease

OBJECTIVE

Atrial remodeling is involved in atrial fibrillation (AF), and atrial fibrosis is an important marker of atrial remodeling. On the basis of our previous animal studies of the mitogen-activated protein kinases (MAPKs)/transforming growth factor β1 (TGF-β1)/tumor necrosis factor pathway in atrial fibrosis, we undertook investigation of this signaling pathway in atrial fibrosis of patients with chronic AF (CAF) and rheumatic mitral valve disease.

METHODS

Fifty-six rheumatic mitral valve disease patients were divided into CAF (course of AF >12 months) and sinus rhythm (SR) groups. Left atrial appendage tissue was collected during heart surgery, and pathological examination was done to evaluate atrial fibrosis. Protein and mRNA expression of TGF-β1, TRAF6 and connective tissue growth factor (CTGF) and protein expression of phosphorylated MAPKs and TGF-β-activated kinase 1 (TAK1) were measured.

RESULTS

Histological examination revealed that the severity of atrial fibrosis in CAF patients was significantly higher, mRNA and protein expression of TGF-β1, TRAF6 and CTGF in CAF were significantly increased, and the protein expression of phosphorylated MAPKs and TAK1 was significantly increased in CAF compared to SR patients.

CONCLUSION

The MAPKs/TGF-β1/TRAF6 signaling pathway is involved in atrial fibrosis of CAF patients, and TRAF6 may become a new target for the treatment of atrial fibrosis.

Attenuation of acetylcholine activated potassium current (I KACh) by simvastatin, not pravastatin in mouse atrial cardiomyocyte: possible atrial fibrillation preventing effects of statin

Statins, 3-hydroxy-3-methyl-glutaryl-CoA reductase inhibitors, are associated with the prevention of atrial fibrillation (AF) by pleiotropic effects. Recent clinical trial studies have demonstrated conflicting results on anti-arrhythmia between lipophilic and hydrophilic statins. However, the underlying mechanisms responsible for anti-arrhythmogenic effects of statins are largely unexplored. In this study, we evaluated the different roles of lipophilic and hydrophilic statins (simvastatin and pravastatin, respectively) in acetylcholine (100 µM)-activated K⁺ current (I_KACh, recorded by nystatin-perforated whole cell patch clamp technique) which are important for AF initiation and maintenance in mouse atrial cardiomyocytes. Our results showed that simvastatin (1–10 µM) inhibited both peak and quasi-steady-state I_KACh in a dose-dependent manner. In contrast, pravastatin (10 µM) had no effect on I_KACh. Supplementation of substrates for the synthesis of cholesterol (mevalonate, geranylgeranyl pyrophosphate or farnesyl pyrophosphate) did not reverse the effect of simvastatin on I_KACh, suggesting a cholesterol-independent effect on I_KACh. Furthermore, supplementation of phosphatidylinositol 4,5-bisphosphate, extracellular perfusion of phospholipase C inhibitor or a protein kinase C (PKC) inhibitor had no effect on the inhibitory activity of simvastatin on I_KACh. Simvastatin also inhibits adenosine activated I_KACh, however, simvastatin does not inhibit I_KACh after activated by intracellular loading of GTP gamma S. Importantly, shortening of the action potential duration by acetylcholine was restored by simvastatin but not by pravastatin. Together, these findings demonstrate that lipophilic statins but not hydrophilic statins attenuate I_KACh in atrial cardiomyocytes via a mechanism that is independent of cholesterol synthesis or PKC pathway, but may be via the blockade of acetylcholine binding site. Our results may provide important background information for the use of statins in patients with AF.

Clinical update on the management of atrial fibrillation

Atrial fibrillation (AF) is a cardiac arrhythmia associated with significant morbidity and mortality, affecting more than 3 million people in the United States and 1-2% of the population worldwide. Its estimated prevalence is expected to double within the next 50 years. During the past decade, there have been significant advances in the treatment of AF. Studies have demonstrated that a rate control strategy, with a target resting heart rate between 80 and 100 beats/minute, is recommended over rhythm control in the vast majority of patients. The CHA2 DS2 ≥ (congestive heart failure, hypertension, age ≥ 65 yrs, diabetes mellitus, stroke or transient ischemic attack, vascular disease, female gender) scoring system is a potentially useful stroke risk stratification tool that incorporates additional risk factors to the commonly used CHADS2 (congestive heart failure, hypertension, age ≥ 75 years, diabetes mellitus, stroke transient ischemic attack) scoring tool. Similarly, a convenient scheme, termed HAS-BLED (hypertension, abnormal renal/liver function, stroke, bleeding history or predisposition, labile international normalized ratio, elderly, drugs/alcohol concomitantly), to assess bleeding risk has emerged that may be useful in select patients. Furthermore, new antithrombotic strategies have been developed as potential alternatives to warfarin, including dual-antiplatelet therapy with clopidogrel plus aspirin and the development of new oral anticoagulants such as dabigatran, rivaroxaban, and apixaban. Vernakalant has emerged as another potential option for pharmacologic conversion of AF, whereas recent trials have better defined the role of dronedarone in the maintenance of sinus rhythm. Finally, catheter ablation represents another alternative to manage AF, whereas upstream therapy with inhibitors of the renin-angiotensin-aldosterone system, statins, and polyunsaturated fatty acids could potentially prevent the occurrence of AF. Despite substantial progress in the management of AF, significant uncertainty surrounds the optimal treatment of this condition.

Atrial fibrillation therapy now and in the future: drugs, biologicals, and ablation

Atrial fibrillation (AF) is a complex disease with multiple inter-relating causes culminating in rapid, seemingly disorganized atrial activation. Therapy targeting AF is rapidly changing and improving. The purpose of this review is to summarize current state-of-the-art diagnostic and therapeutic modalities for treatment of AF. The review focuses on reviewing treatment as it relates to the pathophysiological basis of disease and reviews preclinical and clinical evidence for potential new diagnostic and therapeutic modalities, including imaging, biomarkers, pharmacological therapy, and ablative strategies for AF. Current ablation and drug therapy approaches to treating AF are largely based on treating the arrhythmia once the substrate occurs and is more effective in paroxysmal AF rather than persistent or permanent AF. However, there is much research aimed at prevention strategies, targeting AF substrate, so-called upstream therapy. Improved diagnostics, using imaging, genetics, and biomarkers, are needed to better identify subtypes of AF based on underlying substrate/mechanism to allow more directed therapeutic approaches. In addition, novel antiarrhythmics with more atrial specific effects may reduce limiting proarrhythmic side effects. Advances in ablation therapy are aimed at improving technology to reduce procedure time and in mechanism-targeted approaches.

Structural and Functional Remodeling of the Left Atrium: Clinical and Therapeutic Implications for Atrial Fibrillation

Atrial fibrillation (AF) is the most commonly encountered arrhythmia in clinical practice. Despite advances in our understanding of the pathophysiology of this complex arrhythmia, current therapeutic options remain suboptimal. This review aimed to delineate the atrial structural and functional remodeling leading to the perpetuation of AF. We explored the complex changes seen in the atria in various substrates for AF and the therapeutic options available to prevent these changes or for reverse remodeling. Here we also highlighted the emerging role of aggressive risk factor management aimed at the arrhythmogenic atrial substrate to prevent or retard AF progression.

Atrial fibrillation from the pathologist's perspective

Atrial fibrillation (AF), the most common sustained cardiac arrhythmia encountered in clinical practice, is associated with increased morbidity and mortality. Electrophysiologically, it is characterized by a high rate of asynchronous atrial cell depolarization causing a loss of atrial contractile function and irregular ventricular rates. For a long time, AF was considered as a pure functional disorder without any structural background. Only in recent years, have new mapping and imaging techniques identified atrial locations, which are very often involved in the initiation and maintenance of this supraventricular arrhythmia (i.e. the distal portion of the pulmonary veins and the surrounding atrial myocardium). Morphological analysis of these myocardial sites has demonstrated significant structural remodeling as well as paved the way for further knowledge of AF natural history, pathogenesis, and treatment. This architectural myocardial disarrangement is induced by the arrhythmia itself and the very frequently associated cardiovascular disorders. At the same time, the structural remodeling is also capable of sustaining AF, thereby creating a sort of pathogenetic vicious circle. This review focuses on current understanding about the structural and genetic bases of AF with reference to their classification, pathogenesis, and clinical implications.

Prophylactic statin administration may prevent shortening of the fibrillation cycle length in patients with new-onset atrial fibrillation

Patients with recently diagnosed atrial fibrillation (AF) tend to exhibit a longer fibrillation cycle length (FCL) than those having a longer clinical history. However, the electrophysiological properties of new-onset AF may vary because of the clinical background of patients. In this study, we evaluated clinical factors to identify the determinants of FCL in new-onset AF. Electrocardiograms (ECGs) recorded from 2008 through 2011 were analyzed using our digital ECG-profiling system. In the 1,578 AF episodes recorded, 466 new-onset AF episodes were identified using clinical referral history and previous ECGs. After evaluating FCL in these new-onset AF episodes, using a customized fibrillation wave analyzer with fast Fourier transform analysis, we divided the patients into a longer-FCL group and a shorter-FCL group using the median FCL (158 ms). Propensity score matching yielded 135 matched pairs of patients with comparable mean ages between the two groups. Four factors (brain natriuretic peptide levels, and use of angiotensin receptor blockers, calcium channel blockers or statins) exhibited a significant difference between the two groups. Multivariate analysis revealed that statin use was the only significant independent predictor of longer FCL (Odds ratio, 3.86; 95% CI, 1.659.63; P = 0.003). Among various clinical parameters, statin use was related to longer FCL at the time of new-onset AF in patients with AF.

The NO/ONOO-cycle as the central cause of heart failure

The NO/ONOO-cycle is a primarily local, biochemical vicious cycle mechanism, centered on elevated peroxynitrite and oxidative stress, but also involving 10 additional elements: NF-κB, inflammatory cytokines, iNOS, nitric oxide (NO), superoxide, mitochondrial dysfunction (lowered energy charge, ATP), NMDA activity, intracellular Ca(2+), TRP receptors and tetrahydrobiopterin depletion. All 12 of these elements have causal roles in heart failure (HF) and each is linked through a total of 87 studies to specific correlates of HF. Two apparent causal factors of HF, RhoA and endothelin-1, each act as tissue-limited cycle elements. Nineteen stressors that initiate cases of HF, each act to raise multiple cycle elements, potentially initiating the cycle in this way. Different types of HF, left vs. right ventricular HF, with or without arrhythmia, etc., may differ from one another in the regions of the myocardium most impacted by the cycle. None of the elements of the cycle or the mechanisms linking them are original, but they collectively produce the robust nature of the NO/ONOO-cycle which creates a major challenge for treatment of HF or other proposed NO/ONOO-cycle diseases. Elevated peroxynitrite/NO ratio and consequent oxidative stress are essential to both HF and the NO/ONOO-cycle.