Expression of angiotensin II receptors in human left and right atrial tissue in atrial fibrillation with and without underlying mitral valve disease

Phenotypes and functions of "aged" neutrophils in cardiovascular diseases

Neutrophils are important effector cells of innate immunity and undergo several phenotypic changes after release from the bone marrow. Neutrophils with a late life cycle phenotype are often referred to as "aged" neutrophils. These neutrophils undergo functional changes that accompany stimuli of inflammation, tissue senescence and injury, inducing their maturation and senescence in the circulation and locally in damaged tissues, forming a unique late-life neutrophil phenotype. "Aged" neutrophils, although attenuated in antibacterial capacity, are more active in aging and age-related diseases, exhibit high levels of mitochondrial ROS and mitochondrial DNA leakage, promote senescence of neighboring cells, and exacerbate cardiac and vascular tissue damage, including vascular inflammation, myocardial infarction, atherosclerosis, stroke, abdominal aortic aneurysm, and SARS-CoV-2 myocarditis. In this review, we outline the phenotypic changes of "aged" neutrophils characterized by CXCR4high/CD62Llow, investigate the mechanisms driving neutrophil aging and functional transformation, and analyze the damage caused by "aged" neutrophils to various types of heart and blood vessels. Tissue injury and senescence promote neutrophil infiltration and induce neutrophil aging both in the circulation and locally in damaged tissues, resulting in an "aged" neutrophil phenotype characterized by CXCR4high/CD62Llow. We also discuss the effects of certain agents, such as neutralizing mitochondrial ROS, scavenging IsoLGs, blocking VDAC oligomers and mPTP channel activity, activating Nrf2 activity, and inhibiting neutrophil PAD4 activity, to inhibit neutrophil NET formation and ameliorate age-associated cardiovascular disease, providing a new perspective for anti-aging therapy in cardiovascular disease.

SNRK regulates TGFβ levels in atria to control cardiac fibrosis

Atrial fibrosis is central to the pathology of heart failure (HF) and atrial fibrillation (AF). Identifying precise mechanisms underlying atrial fibrosis will provide effective strategies for clinical intervention. This study investigates a metabolic serine threonine kinase gene, sucrose non-fermenting related kinase (SNRK), that we previously reported to control cardiac metabolism and function. Conditional knockout of Snrk in mouse cardiomyocytes ( Snrk cmcKO) leads to atrial fibrosis and subsequently HF. The precise mechanism underlying cardiomyocyte SNRK-driven repression of fibrosis is not known. Here, using mouse, rat, and human tissues, we demonstrate that SNRK expression is high in atria, especially in atrial cardiomyocytes. SNRK expression correlates with lower levels of pro-fibrotic protein transforming growth factor-beta 1 (TGFβ1) in the atrial cardiomyocytes. In HL-1 adult immortalized mouse atrial cells, using siRNA approaches, we show that Snrk knockdown cells show more TGFβ1 secretion, which was also observed in heart lysates from Snrk cardiac-specific knockout mice in vivo. These effects were exacerbated upon infusion of Angiotensin II. Results from Snrk knockdown cardiomyocytes co-cultured with cardiac fibroblasts suggest that SNRK represses TGFβ1 signaling (Smad 2/3) in atrial CMs and prevents paracrine cardiac fibroblast activation (α-SMA marker). In conclusion, high SNRK expression in atria regulates cardiac homeostasis, by preventing the release of TGFβ1 secretion to block cardiac fibrosis. These studies will assist in developing heart chamber-specific fibrosis therapy for non-ischemic HF and AF.

Activated factor X stimulates atrial endothelial cells and tissues to promote remodelling responses through AT1R/NADPH oxidases/SGLT1/2

AIMS

Atrial fibrillation (AF), the most common cardiac arrhythmia favouring ischemic stroke and heart failure involves left atrial remodelling, fibrosis and a complex interplay between cardiovascular risk factors. This study examined whether activated factor X (FXa) induces pro-remodelling and pro-fibrotic responses in atrial endothelial cells (AECs) and human atrial tissues and determined the underlying mechanisms.

METHODS AND RESULTS

AECs collected from porcine hearts and human right atrial appendages (RAA) from patients undergoing heart surgery. Protein expression levels were assessed by Western blot and immunofluorescence staining, mRNA levels by RT-qPCR, formation of reactive oxygen species (ROS) and NO using fluorescent probes, thrombin and angiotensin II generation by specific assays, fibrosis by Sirius red staining and senescence by senescence-associated beta-galactosidase (SA-β-gal) activity. In AECs, FXa increased ROS formation, senescence (SA-β-gal activity, p53, p21), angiotensin II generation and the expression of pro-inflammatory (VCAM-1, MCP-1), pro-thrombotic (tissue factor), pro-fibrotic (TGF-β and collagen-1/3a) and pro-remodelling (MMP-2/9) markers whereas eNOS levels and NO formation were reduced. These effects were prevented by inhibitors of FXa but not thrombin, protease-activated receptors antagonists (PAR-1/2) and inhibitors of NADPH oxidases, ACE, AT1R, SGLT1/SGLT2. FXa also increased expression levels of ACE1, AT1R, SGLT1/2 proteins which were prevented by SGLT1/2 inhibitors. Human RAA showed tissue factor mRNA levels that correlated with markers of endothelial activation, pro-remodelling and pro-fibrotic responses and SGLT1/2 mRNA levels. They also showed protein expression levels of ACE1, AT1R, p22phox, SGLT1/2, and immunofluorescence signals of nitrotyrosine and SGLT1/2 colocalized with those of CD31. FXa increased oxidative stress levels which were prevented by inhibitors of the AT1R/NADPH oxidases/SGLT1/2 pathway.

CONCLUSION

FXa promotes oxidative stress triggering premature endothelial senescence and dysfunction associated with pro-thrombotic, pro-remodelling and pro-fibrotic responses in AECs and human RAA involving the AT1R/NADPH oxidases/SGLT1/2 pro-oxidant pathway. Targeting this pathway may be of interest to prevent atrial remodelling and the progression of atrial fibrillation substrate.

Renin-angiotensin-aldosterone system inhibitors and mortality risk in elderly patients with atrial fibrillation. Insights from the nationwide START registry

BACKGROUND

Arterial hypertension is the most common cardiovascular comorbidity in atrial fibrillation (AF). Few studies investigated management strategies of hypertension in AF.

MATERIALS AND METHODS

We included 5769 AF patients on oral anticoagulants from the nationwide ongoing Italian START registry. We investigated the prescription of antihypertensive drugs and mortality risk. Subgroup analyses according to sex and major cardiovascular comorbidities were performed.

RESULTS

Mean age was 80.8 years, 46.1% were women; 80.3% of patients were hypertensive. Furosemide (30.1%) was the most frequent diuretic followed by hydrochlorothiazide (15.4%) and potassium canrenoate (7.9%). 61.1% received β-blockers: 34.2% bisoprolol, 6.2% atenolol. Additionally, 36.9% were on angiotensin converting enzyme inhibitors (ACE-I): ramipril (20.9%), enalapril (5.3%) and perindopril (2.8%); 31.7% were on angiotensin receptors blockers (ARBs): valsartan (7.6%) and irbesartan (6.4%). Amlodipine and lercanidipine were prescribed in 14.0% and 2.3%, respectively. ACE-I (p < 0.001), α-blockers (p = 0.020) and Dihydropyridines calcium channel blockers (p = 0.004) were more common in men, while ARBs (p = 0.008), thiazide diuretics (p < 0.001) and β-blockers (p < 0.001) in women. During 22.61 ± 17.1 months, 512 patients died. Multivariable Cox regression analysis showed that ACE-I (Hazard ratio [HR] 0.758, 95% Confidence Interval [95%CI] 0.612-0.940, p = 0.012) and ARBs (HR 0.623, 95%CI 0.487-0.796, p < 0.001) inversely associated with mortality. ACE-I/ARBs inversely associated with mortality in both sexes and in patients with diabetes. This associastion was evident for ACE-I in patients with previous cardiovascular disease, and for ARBs in HF.

CONCLUSION

A lower mortality risk was found in AF patients on ACE-I/ARBs. Different prescription patterns of antihypertensive drugs between men and women do exist.

Lifestyle changes in atrial fibrillation management and intervention

Atrial fibrillation (AF) is one of the most common arrhythmias in adults, and its continued rise in the United States is complicated by the increased incidence and prevalence of several AF risk factors, such as obesity, physical inactivity, hypertension, obstructive sleep apnea, diabetes mellitus, coronary artery disease, and alcohol, tobacco, or caffeine use. Lifestyle and risk factor modification has been proposed as an additional pillar of AF therapy, added to rhythm control, rate control, and anticoagulation, to reduce AF burden and risk. Although emerging evidence largely supports the integration of lifestyle and risk factor management in clinical practice, randomized clinical trials investigating the long-term sustainability and reproducibility of these benefits remain sparse. The purpose of this review is to discuss potentially reversible risk factors on AF, share evidence for the impact on AF by modification of these risk factors, and then provide an overview of the effects of reversing or managing these risk factors on the success of various AF management strategies, such as antithrombotic, rate control, and rhythm control therapies.

Mechanism and prevention of atrial remodeling and their related genes in cardiovascular disorders

Atrial fibrillation (AF) is associated with profound structural and functional changes in the atrium. Inflammation mediated atrial fibrosis is one of the key mechanisms in the pathogenesis of AF. The collagen deposition in extracellular matrix (ECM) is mainly mediated by transforming growth factor β1 (TGF-β1) which promotes AF via controlling smads mediated-collagen gene transcription and regulating the balance of metalloproteinases (MMPs)/ tissue inhibitor of metalloproteinases (TIMPs). Although many processes can alter atrial properties and promote AF, animal models and clinical studies have provided insights into two major forms of atrial remodeling: Atrial tachycardia remodeling (ATR), which occurs with rapid atrial tachyarrhythmia's such as AF and atrial flutter, and atrial structural remodeling (ASR), which is associated with CHF and other fibrosis-promoting conditions. The mechanism of atrial remodeling such as atrial enlargement, ultra structural changes of atrial muscle tissue and myocardial interstitial fibrosis in AF is still unclear. At present, many studies focus on calcium overload, renin angiotensin aldosterone system and transforming growth factor β1, that effect on atrial structural remodeling. Recent experimental studies and clinical investigations have provided structural remodeling is important contributor to the AF. This paper reviews the current understanding of the progresses about mechanism of atrial structural remodeling, and highlights the potential therapeutic approaches aimed at attenuating structural remodeling to prevent AF. Now some recent advancements of this area are reviewed in this paper.

Psychological factors and risk of atrial fibrillation: A meta-analysis and systematic review

BACKGROUND

Multiple studies have shown that mental disorders are common risk factors for cardiovascular diseases (CVD). However, the relationship between psychological factors and atrial fibrillation (AF) incidence remains unclear. Therefore, we performed a systematic review and meta-analysis to assess the risk of AF due to psychological factors.

METHODS

PubMed, Embase, Web of Science, and Cochrane Library were searched from inception to January 2022. Relevant and eligible cohort studies were included. Random or fixed effect model was used to estimate the pooled hazard ratios (HRs) and 95% confidence intervals (CIs). For non-randomized studies, the risk of bias was assessed using the Newcastle-Ottawa Scale (NOS).

RESULTS

Thirteen publications, including 5,329,908 participants, met our inclusion criteria. The incidence of AF was increased by 10% (HR = 1.10, 95% CI 1.02 to 1.19, I² = 33.6%, P = 0.013, n = 235,599 in 6 studies) for patients with anxiety, by 15% (HR = 1.15, 95% CI 1.04 to 1.26, I² = 40.2%, P = 0.04, n = 21,791 in 3 studies) for patients with anger, by 25% (HR = 1.25, 95% CI 1.12 to 1.39, I² = 57.4%, P < 0.001, n = 5,160,247 in 6 studies) for patients with depression, and by 18% (HR = 1.18, 95% CI 1.05 to 1.32, I² = 19.2%, P = 0.004, n = 51,664 in 4 studies) for people under work stress.

CONCLUSIONS

Adverse psychological factors such as anxiety, anger, depression, and work stress may increase the risk of AF. Interventions to prevent mental disorders may reduce the growing global burden of AF and its associated healthcare costs. Given the current study's limitations, our findings need to be further confirmed by a larger prospective study.

Blood pressure measurements during treadmill exercise testing and the risk for the future development of atrial fibrillation

Hypertension is a well-established risk factor for the onset and progression of atrial fibrillation (AF). Blood pressure (BP) measurements during routine exercise stress testing (EST) may identify subjects at increased risk for developing AF. We performed a retrospective analysis of treadmill EST carried out using the Bruce protocol in patients aged ≥40 years without a history of AF (n = 17,617; 42% women). BP was measured at rest, peak exercise, and 2-min recovery and analyzed for its association with the risk for developing AF. During a mean follow-up of 7 years, AF was documented in 4.5% of the patients. The incidence rate of AF per 1000 person-years increased with the rise in CHA₂DS₂VASc scores (3.26 for a Score=0 to 19.78 for scores ≥6). In a multivariate analysis, adjusting for risk score components and exercise capacity, systolic BP measurements taken at rest (≥130 vs. ≤110 mmHg), peak exercise (>170 vs. ≤150 mmHg), and recovery (>150 vs. ≤130 mmHg) were associated with an increased risk for AF: the hazard ratios (HRs) were 1.56 (95% CI, 1.30-1.87), 1.21 (1.01-1.45), and 1.33 (1.10-1.62), respectively. Similarly, diastolic BP measurements taken at rest (≥90 vs. <80 mmHg), peak exercise (≥100 vs. <90 mmHg), and recovery (>90 vs. ≤80 mmHg) were associated with an increased risk for AF: the HRs were 1.80 (1.36-2.38), 2.08 (1.28-3.37), and 1.56 (0.81-3.02), respectively. The association of exercise BP with AF was further observed when the BPs were analyzed as continuous variables and in subjects without a baseline diagnosis of hypertension. In conclusion, systolic and diastolic BP taken at the rest, peak exercise and recovery phases of EST may provide independent predictive information regarding future risk for developing AF.

Atrial Electrical Remodeling in Mice With Cardiac‐Specific Overexpression of Angiotensin II Type 1 Receptor

Background

Elevated angiotensin II levels are thought to play an important role in atrial electrical and structural remodeling associated with atrial fibrillation. However, the mechanisms by which this remodeling occurs are still unclear. Accordingly, we explored the effects of angiotensin II on atrial remodeling using transgenic mice overexpressing angiotensin II type 1 receptor (AT1R) specifically in cardiomyocytes.

Methods and Results

Voltage‐clamp techniques, surface ECG, programmed electrical stimulations along with quantitative polymerase chain reaction, Western blot, and Picrosirius red staining were used to compare the atrial phenotype of AT1R mice and their controls at 50 days and 6 months. Atrial cell capacitance and fibrosis were increased only in AT1R mice at 6 months, indicating the presence of structural remodeling. Ca 2+ ( I CaL ) and K + currents were not altered by AT1R overexpression (AT1R at 50 days). However, I CaL density and Ca V 1.2 messenger RNA expression were reduced by structural remodeling (AT1R at 6 months). Conversely, Na + current ( I Na ) was reduced (−65%) by AT1R overexpression (AT1R at 50 days) and the presence of structural remodeling (AT1R at 6 months) yields no further effect. The reduced I Na density was not explained by lower Na V 1.5 expression but was rather associated with an increase in sarcolemmal protein kinase C alpha expression in the atria, suggesting that chronic AT1R activation reduced I Na through protein kinase C alpha activation. Furthermore, connexin 40 expression was reduced in AT1R mice at 50 days and 6 months. These changes were associated with delayed atrial conduction time, as evidenced by prolonged P‐wave duration.

Conclusions

Chronic AT1R activation leads to slower atrial conduction caused by reduced I Na density and connexin 40 expression.

A Review of the Molecular Mechanisms Underlying Cardiac Fibrosis and Atrial Fibrillation

The cellular and molecular mechanism involved in the pathogenesis of atrial fibrosis are highly complex. We have reviewed the literature that covers the effectors, signal transduction and physiopathogenesis concerning extracellular matrix (ECM) dysregulation and atrial fibrosis in atrial fibrillation (AF). At the molecular level: angiotensin II, transforming growth factor-β1, inflammation, and oxidative stress are particularly important for ECM dysregulation and atrial fibrotic remodelling in AF. We conclude that the Ang-II-MAPK and TGF-β1-Smad signalling pathways play a major, central role in regulating atrial fibrotic remodelling in AF. The above signalling pathways induce the expression of genes encoding profibrotic molecules (MMP, CTGF, TGF-β1). An important mechanism is also the generation of reactive oxygen species. This pathway induced by the interaction of Ang II with the AT₂R receptor and the activation of NADPH oxidase. Additionally, the interplay between cardiac MMPs and their endogenous tissue inhibitors of MMPs, is thought to be critical in atrial ECM metabolism and fibrosis. We also review recent evidence about the role of changes in the miRNAs expression in AF pathophysiology and their potential as therapeutic targets. Furthermore, keeping the balance between miRNA molecules exerting anti-/profibrotic effects is of key importance for the control of atrial fibrosis in AF.

Remodeling of Cardiac Gap Junctional Cell-Cell Coupling

The heart works as a functional syncytium, which is realized via cell-cell coupling maintained by gap junction channels. These channels connect two adjacent cells, so that action potentials can be transferred. Each cell contributes a hexameric hemichannel (=connexon), formed by protein subuntis named connexins. These hemichannels dock to each other and form the gap junction channel. This channel works as a low ohmic resistor also allowing the passage of small molecules up to 1000 Dalton. Connexins are a protein family comprising of 21 isoforms in humans. In the heart, the main isoforms are Cx43 (the 43 kDa connexin; ubiquitous), Cx40 (mostly in atrium and specific conduction system), and Cx45 (in early developmental states, in the conduction system, and between fibroblasts and cardiomyocytes). These gap junction channels are mainly located at the polar region of the cardiomyocytes and thus contribute to the anisotropic pattern of cardiac electrical conductivity. While in the beginning the cell–cell coupling was considered to be static, similar to an anatomically defined structure, we have learned in the past decades that gap junctions are also subject to cardiac remodeling processes in cardiac disease such as atrial fibrillation, myocardial infarction, or cardiomyopathy. The underlying remodeling processes include the modulation of connexin expression by e.g., angiotensin, endothelin, or catecholamines, as well as the modulation of the localization of the gap junctions e.g., by the direction and strength of local mechanical forces. A reduction in connexin expression can result in a reduced conduction velocity. The alteration of gap junction localization has been shown to result in altered pathways of conduction and altered anisotropy. In particular, it can produce or contribute to non-uniformity of anisotropy, and thereby can pre-form an arrhythmogenic substrate. Interestingly, these remodeling processes seem to be susceptible to certain pharmacological treatment.

Molecular Insights in Atrial Fibrillation Pathogenesis and Therapeutics: A Narrative Review

The prevalence of atrial fibrillation (AF) is bound to increase globally in the following years, affecting the quality of life of millions of people, increasing mortality and morbidity, and beleaguering health care systems. Increasingly effective therapeutic options against AF are the constantly evolving electroanatomic substrate mapping systems of the left atrium (LA) and ablation catheter technologies. Yet, a prerequisite for better long-term success rates is the understanding of AF pathogenesis and maintenance. LA electrical and anatomical remodeling remains in the epicenter of current research for novel diagnostic and treatment modalities. On a molecular level, electrical remodeling lies on impaired calcium handling, enhanced inwardly rectifying potassium currents, and gap junction perturbations. In addition, a wide array of profibrotic stimuli activates fibroblast to an increased extracellular matrix turnover via various intermediaries. Concomitant dysregulation of the autonomic nervous system and the humoral function of increased epicardial adipose tissue (EAT) are established mediators in the pathophysiology of AF. Local atrial lymphomononuclear cells infiltrate and increased inflammasome activity accelerate and perpetuate arrhythmia substrate. Finally, impaired intracellular protein metabolism, excessive oxidative stress, and mitochondrial dysfunction deplete atrial cardiomyocyte ATP and promote arrhythmogenesis. These overlapping cellular and molecular alterations hinder us from distinguishing the cause from the effect in AF pathogenesis. Yet, a plethora of therapeutic modalities target these molecular perturbations and hold promise in combating the AF burden. Namely, atrial selective ion channel inhibitors, AF gene therapy, anti-fibrotic agents, AF drug repurposing, immunomodulators, and indirect cardiac neuromodulation are discussed here.

The Impact of Spironolactone on Markers of Myocardial Oxidative Status, Inflammation and Remodeling in Hyperthyroid Rats

BACKGROUND

Hyperthyroidism promotes the development and progression of cardiovascular diseases (CVD). Aldosterone, a key mediator of myocardial inflammation, oxidative stress and fibrosis, may be activated in hyperthyroidism.

OBJECTIVE

To assess the impact of hyperthyroidism on aldosterone levels and myocardial oxidative status, inflammatory and fibrotic markers in hyperthyroid rats, and to test if the use of spironolactone (an aldosterone antagonist) attenuates these changes.

METHODS

Adult Wistar rats were randomly distributed into 4 groups; controls, spironolactone treated rats (Spir, 50mg/kg/day), hyperthyroid rats (Hyper, daily intraperitoneal levothyroxine 0.3mg/kg/day), and spironolactone treated hyperthyroid rats (Hyper+Spir) for 4 weeks. Blood pressure (Bp), and levels of serum and myocardial aldosterone, oxidants/antioxidants, inflammatory and fibrotic markers were measured.

RESULTS

Levothyroxine increased serum thyroid hormones and increased Bp, heart rate and heart to bodyweight ratio. Relative to control, serum aldosterone levels were increased in Hyper and Hyper+ Spir groups. In parallel, cardiac lipid peroxides and serum endothelin-1 were increased whereas cardiac superoxide dismutase, catalase, glutathione, and matrix metalloproteinase -2 were reduced in the Hyper group. Spironolactone decreased serum thyroid hormones and improved cardiac lipid peroxides and metalloproteinase -2 levels. The use of spironolactone decreased serum nitrite levels and increased cardiac SOD and glutathione. Cardiac levels of aldosterone, endothelin-1, transforming growth factor-beta and nitrite were similar among all groups.

CONCLUSION

Hyperthyroid status was associated with an increase in aldosterone and oxidant/ inflammatory biomarkers. The use of spironolactone enhanced antioxidant defenses. Aldosterone antagonists may serve as potential drugs to attenuate the development of cardiac disease in hyperthyroidism.

The Role of Renin-Angiotensin-Aldosterone System in the Heart and Lung: Focus on COVID-19

The renin-angiotensin-aldosterone system (RAAS) firstly considered as a cardiovascular circulating hormonal system, it is now accepted as a local tissue system that works synergistically or independently with the circulating one. Evidence states that tissue RAAS locally generates mediators with regulatory homeostatic functions, thus contributing, at some extent, to organ dysfunction or disease. Specifically, RAAS can be divided into the traditional RAAS pathway (or classic RAAS) mediated by angiotensin II (AII), and the non-classic RAAS pathway mediated by angiotensin 1–7. Both pathways operate in the heart and lung. In the heart, the classic RAAS plays a role in both hemodynamics and tissue remodeling associated with cardiomyocyte and endothelial dysfunction, leading to progressive functional impairment. Moreover, the local classic RAAS may predispose the onset of atrial fibrillation through different biological mechanisms involving inflammation, accumulation of epicardial adipose tissue, and electrical cardiac remodeling. In the lung, the classic RAAS regulates cell proliferation, immune-inflammatory response, hypoxia, and angiogenesis, contributing to lung injury and different pulmonary diseases (including COVID-19). Instead, the local non-classic RAAS counteracts the classic RAAS effects exerting a protective action on both heart and lung. Moreover, the non-classic RAAS, through the angiotensin-converting enzyme 2 (ACE2), mediates the entry of the etiological agent of COVID-19 (SARS-CoV-2) into cells. This may cause a reduction in ACE2 and an imbalance between angiotensins in favor of AII that may be responsible for the lung and heart damage. Drugs blocking the classic RAAS (angiotensin-converting enzyme inhibitors and angiotensin receptor blockers) are well known to exert a cardiovascular benefit. They are recently under evaluation for COVID-19 for their ability to block AII-induced lung injury altogether with drugs stimulating the non-classic RAAS. Herein, we discuss the available evidence on the role of RAAS in the heart and lung, summarizing all clinical data related to the use of drugs acting either by blocking the classic RAAS or stimulating the non-classic RAAS.

Angiotensin II and angiotensin 1-7: which is their role in atrial fibrillation?

Atrial fibrillation (AF) is a significant cause of morbidity and mortality as well as a public health burden considering the high costs of AF-related hospitalizations. Pre-clinical and clinical evidence showed a potential role of the renin angiotensin system (RAS) in the etiopathogenesis of AF. Among RAS mediators, angiotensin II (AII) and angiotensin 1-7 (A1-7) have been mostly investigated in AF. Specifically, the stimulation of the pathway mediated by AII or the inhibition of the pathway mediated by A1-7 may participate in inducing and sustaining AF. In this review, we summarize the evidence showing that both RAS pathways may balance the onset of AF through different biological mechanisms involving inflammation, epicardial adipose tissue (EAT) accumulation, and electrical cardiac remodeling. EAT is a predictor for AF as it may induce its onset through direct (infiltration of epicardial adipocytes into the underlying atrial myocardium) and indirect (release of inflammatory adipokines, the stimulation of oxidative stress, macrophage phenotype switching, and AF triggers) mechanisms. Classic RAS blockers such as angiotensin converting enzyme inhibitors (ACE-I) and angiotensin receptor blockers (ARB) may prevent AF by affecting the accumulation of the EAT, representing a useful therapeutic strategy for preventing AF especially in patients with heart failure and known left ventricular dysfunction. Further studies are necessary to prove this benefit in patients with other cardiovascular diseases. Finally, the possibility of using the A1-7 or ACE2 analogues, to enlarge current therapeutic options for AF, may represent an important field of research.

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

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

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

RATIONALE

Fibro-fatty infiltration of subepicardial layers of the atrial wall has been shown to contribute to the substrate of atrial fibrillation.

OBJECTIVE

Here, we examined if the epicardium that contains multipotent cells is involved in this remodeling process.

METHODS AND RESULTS

One hundred nine human surgical right atrial specimens were evaluated. There was a relatively greater extent of epicardial thickening and dense fibro-fatty infiltrates in atrial tissue sections from patients aged over 70 years who had mitral valve disease or atrial fibrillation when compared with patients aged less than 70 years with ischemic cardiomyopathy as indicated using logistic regression adjusted for age and gender. Cells coexpressing markers of epicardial progenitors and fibroblasts were detected in fibro-fatty infiltrates. Such epicardial remodeling was reproduced in an experimental model of atrial cardiomyopathy in rat and in Wilms tumor 1 (WT1)^CreERT2/+;ROSA-tdT^+/- mice. In the latter, genetic lineage tracing demonstrated the epicardial origin of fibroblasts within fibro-fatty infiltrates. A subpopulation of human adult epicardial-derived cells expressing PDGFR (platelet-derived growth factor receptor)-α were isolated and differentiated into myofibroblasts in the presence of Ang II (angiotensin II). Furthermore, single-cell RNA-sequencing analysis identified several clusters of adult epicardial-derived cells and revealed their specification from adipogenic to fibrogenic cells in the rat model of atrial cardiomyopathy.

CONCLUSIONS

Epicardium is reactivated during the formation of the atrial cardiomyopathy. Subsets of adult epicardial-derived cells, preprogrammed towards a specific cell fate, contribute to fibro-fatty infiltration of subepicardium of diseased atria. Our study reveals the biological basis for chronic atrial myocardial remodeling that paves the way of atrial fibrillation.

Protective effects of Gαq-RGS2 signalling inhibitor in aminophylline induced cardiac arrhythmia

An over activation of GPCR mediated Gαq dependent signalling pathway is widely associated with the development of cardiovascular abnormalities. The objective of study was to evaluate the effects of (1-(5-chloro-2-hydroxyphenyl)-3-(4-(trifluoromethyl)phenyl)-1H-1,2,4-triazol-5(4H)-one) Gαq-RGS2 signalling inhibitor on aminophylline induced cardiac arrhythmia in rats. Rats were divided into four groups; normal rats, disease control (DC, aminophylline treated 100 mg/kg/d, i.p., 7 days), Gαq-RGS2 signalling inhibitor (1 and 10 mg/kg/d, p.o., 7 days) treated arrhythmic rats. Gαq-RGS2 signalling inhibitor was administered 1 hour prior to the administration of aminophylline from 1st day. At the end of study, heart rate (HR), QRS complex, QT and RR interval were measured by electrocardiogram (ECG) of anesthetized rats. Systolic and diastolic blood pressure (SBP, DBP) by invasive method, cardiac damage markers (CK-MB, LDH) in the serum, antioxidant enzymes (SOD, catalase, glutathione) and cAMP level were measured. The treatment of Gαq-RGS2 signalling inhibitor (10 mg/kg) significantly abolished the aminophylline induced increase of heart rate, prolongation of RR and QT interval as compared to DC rats. Gαq-RGS2 signalling inhibitor (1 and 10 mg/kg) significantly attenuated the prolongation in QRS complex, increase of SBP, DBP and cardiac damage markers as compared to DC. Gαq-RGS2 signalling inhibitor treatment (10 mg/kg) significantly reduced the cAMP level and increased the antioxidant enzyme level as compared to DC. Gαq-RGS2 signalling inhibitor (10 mg/kg) showed the protective effect against the aminophylline induced cardiac arrhythmia and it might be due to improvement in cAMP level and antioxidant enzymes.

Differential Gene Expression Profile of Renin-Angiotensin System in the Left Atrium in Mitral Regurgitation Patients

Background

Left atrial enlargement is a mortality and heart failure risk factor in primary mitral regurgitation (MR) patients. Pig models of MR have shown differential expression of genes linked to the renin-angiotensin system. Therefore, the aim of this study was to investigate the key genes of the renin-angiotensin that are expressed differentially in the left atrial myocardium in MR patients.

Methods

Quantitative RT-PCR was used to compare gene expression in the renin-angiotensin system in the left atrium in MR patients, aortic valve disease patients, and normal subjects.

Results

Plasma angiotensin II concentrations did not significantly differ between MR patients and aortic valve disease patients (P = 0.582). Compared to normal controls, however, MR patients had significantly downregulated expressions of angiotensin-converting enzyme, angiotensin I converting enzyme 2, type 1 angiotensin II receptor, glutamyl aminopeptidase, angiotensinogen, cathepsin A (CTSA), thimet oligopeptidase 1, neurolysin, alanyl aminopeptidase, cathepsin G, leucyl/cystinyl aminopeptidase (LNPEP), neprilysin, and carboxypeptidase A3 in the left atrium. The MR patients also had significantly upregulated expressions of MAS1 oncogene (MAS1) and mineralocorticoid receptor compared to normal controls. Additionally, in comparison with aortic valve disease patients, MR patients had significantly downregulated CTSA and LNPEP expression and significantly upregulated MAS1 expression in the left atrium.

Conclusions

Expressions of genes in the renin-angiotensin system, especially CTSA, LNPEP, and MAS1, in the left atrium in MR patients significantly differed from expressions of these genes in aortic valve disease patients and normal controls. Notably, differences in expression were independent of circulating angiotensin II levels. The results of this study provide a rationale for pharmacological therapies or posttranslational regulation therapies targeting genes expressed differentially in the renin-angiotensin system to remedy structural remodeling associated with atrial enlargement and heart failure progression in patients with MR.

Involvement of Apelin/APJ Axis in Thrombogenesis in Valve Heart Disease Patients with Atrial Fibrillation

The mechanism underlying thrombosis in atrial fibrillation (AF) is not yet clearly understood. The apelin/APJ axis parallel and counter-regulate with the angiotensin system. The present study hypothesizes that apelin/APJ axis exert its anti-thrombus effect in normal left atrial tissue and is disrupted by up-regulated renin-angiotensin-aldosterone system (RAAS) signaling during AF. The specimens of left atrial appendages collected from patients with rheumatic mitral stenosis who underwent valve replacement were divided into 3 groups: sinus rhythm, AF⁺/thrombus^-, and AF⁺/thrombus⁺. The amounts of angiotensin II receptor subtype 1 (AT1), apelin/APJ and its downstream plasminogen activator inhibitor-1 (PAI-1) were detected by western blot. The expression of apelin/APJ was significantly decreased in the AF⁺/thrombus⁺ group compared with the sinus rhythm and AF⁺/thrombus^- groups. Meanwhile the expressions of AT1 and PAI-1 were highest in the AF⁺/thrombus⁺ group compared to the other two groups. Taken together, the present study reveals apelin/APJ axis might be correlated with thrombosis in patients with AF mediated by PAI-1.

Baseline atrial fibrillation is associated with contrast-induced nephropathy after cardiac catheterization in coronary artery disease: Systemic review and meta-analysis

BACKGROUND

Atrial fibrillation (AF) is the most common arrhythmia, independently associated with significant mortality and morbidity. Recent studies suggest that AF is potentially associated with contrast-induced nephropathy (CIN) in patients with coronary artery disease (CAD) undergoing catheterization. However, the association was not conclusive. Thus, we assessed the association between AF in patients with CAD and CIN by a systematic review of the literature and a meta-analysis.

HYPOTHESIS

AF is a predictor of CIN in patients with CAD.

METHODS

We comprehensively searched the databases of MEDLINE and EMBASE from inception to April 2018. Included studies were published observational studies that compared the risk of CIN among CAD patients with AF vs those without AF. Data from each study were combined using the random-effects, generic inverse variance method of DerSimonian and Laird to calculate risk ratios and 95% confidence intervals (CIs).

RESULTS

Eight cohort studies from June 2007 to November 2017 were included in this meta-analysis involving 16,691 subjects with CAD (1,030 with AF and 15,661 without its presence). The presence of AF was associated with CIN (pooled risk ratio = 2.17, 95% CI: 1.50-3.14, P < 0.001, I² = 54.1%). In our subgroup analysis by urgency and multivariable adjustment, both groups still showed substantial association between AF and CIN (P < 0.05).

CONCLUSIONS

AF increased the risk of CIN up to two fold among patients with CAD compared to the absence of it. Our study suggests that the presence of AF in CAD is prognostic for the development of CIN.

Intracellular Angiotensin-II Interacts With Nuclear Angiotensin Receptors in Cardiac Fibroblasts and Regulates RNA Synthesis, Cell Proliferation, and Collagen Secretion

BACKGROUND

Cardiac fibroblasts play important functional and pathophysiological roles. Intracellular ("intracrine") angiotensin-II (Ang-II) signaling regulates intercellular communication, excitability, and gene expression in cardiomyocytes; however, the existence and role of intracrine Ang-II signaling in cardiac fibroblasts is unstudied. Here, we evaluated the localization of Ang-II receptors on atrial fibroblast nuclei and associated intracrine effects of potential functional significance.

METHODS AND RESULTS

Immunoblots of subcellular protein-fractions from isolated canine atrial fibroblasts indicated the presence of nuclear Ang-II type 1 receptors (AT1Rs) and Ang-II type 2 receptors (AT2Rs). Fluorescein isothiocyanate-Ang-II binding displaceable by AT1R- and AT2R-blockers was present on isolated fibroblast nuclei. G-protein subunits, including Gαq/11, Gαi/3, and Gβ, were observed in purified fibroblast nuclear fractions by immunoblotting and intact-fibroblast nuclei by confocal immunocytofluorescence microscopy. Nuclear AT1Rs and AT2Rs regulated de novo RNA synthesis ([α32P]UTP incorporation) via IP3R- and NO-dependent pathways, respectively. In intact cultured fibroblasts, intracellular Ang-II release by photolysis of a membrane-permeable caged Ang-II analog led to IP3R-dependent nucleoplasmic Ca2+-liberation, with IP3R3 being the predominant nuclear isoform. Intracellular Ang-II regulated fibroblast proliferation ([3H]thymidine incorporation), collagen-1A1 mRNA-expression, and collagen secretion. Intracellular Ang-II and nuclear AT1R protein levels were significantly increased in a heart failure model in which atrial fibrosis underlies atrial fibrillation.

CONCLUSIONS

Fibroblast nuclei possess AT1R and AT2R binding sites that are coupled to intranuclear Ca2+-mobilization and NO liberation, respectively. Intracellular Ang-II signaling regulates fibroblast proliferation, collagen gene expression, and collagen secretion. Heart failure upregulates Ang-II intracrine signaling-components in atrial fibroblasts. These results show for the first time that nuclear angiotensin-II receptor activation and intracrine Ang-II signaling control fibroblast function and may have pathophysiological significance.

Role of the MAPKs/TGF-β1/TRAF6 signaling pathway in postoperative atrial fibrillation

Objectives

To explore the relationship between the MAPKs/TGF-β1/TRAF6 signaling pathway and atrial fibrosis in patients with rheumatic heart disease (RHD) and its role in atrial fibrillation (AF) after cardiac surgery on the basis of our previous animal study of the MAPKs/TGF-β1/TRAF6 signaling pathway in atrial fibrosis.

Methods

A total of 57 patients with RHD without a history of AF consented to left atrial biopsy. Histopathology quantified the percentage of fibrosis, and real-time PCR and western blot assessed the mRNA and protein expression of TGF-β1, TRAF6, and connective tissue growth factor (CTGF), respectively. Western blot was also used to measure the protein expression of phosphorylated MAPKs and TGF-β-activated kinase 1 (TAK1). Serum angiotensin II (Ang II) levels were assayed using enzyme-linked immunosorbent assay (ELISA).

Results

Eighteen patients developed AF, whereas 39 remained in sinus rhythm (SR). The severity of atrial fibrosis was significantly higher in patients who developed AF versus those who remained in SR; the mRNA and protein expression of TGF-β1, TRAF6 and CTGF were significantly higher in patients with AF. The protein expression of phosphorylated MAPKs and TAK1 was significantly increased in patients who developed AF compared with the patients who remained in SR. Serum Ang II levels were significantly higher in patients who developed AF versus those who remained in SR.

Conclusion

The MAPKs/TGF-β1/TRAF6 signaling pathway is involved in atrial fibrosis in patients with RHD, which results in the occurrence of AF after cardiac surgery.

Atrial Fibrillation and Hypertension: Mechanistic, Epidemiologic, and Treatment Parallels

Atrial fibrillation (AF) is an increasingly prevalent condition and the most common sustained arrhythmia encountered in ambulatory and hospital practice. Several clinical risk factors for AF include age, sex, valvular heart disease, obesity, sleep apnea, heart failure, and hypertension (HTN). Of all the risk factors, HTN is the most commonly encountered condition in patients with incident AF. Hypertension is associated with a 1.8-fold increase in the risk of developing new-onset AF and a 1.5-fold increase in the risk of progression to permanent AF. Hypertension predisposes to cardiac structural changes that influence the development of AF such as atrial remodeling. The renin angiotensin aldosterone system has been demonstrated to be a common mechanistic link in the pathogenesis of HTN and AF. Importantly, HTN is one of the few modifiable AF risk factors, and guideline-directed management of HTN may reduce the incidence of AF.

Nitrated fatty acids suppress angiotensin II-mediated fibrotic remodelling and atrial fibrillation

AIM

Atrial fibrosis, one of the most striking features in the pathology of atrial fibrillation (AF), is promoted by local and systemic inflammation. Electrophilic fatty acid nitroalkenes, endogenously generated by both metabolic and inflammatory reactions, are anti-inflammatory mediators that in synthetic form may be useful as drug candidates. Herein we investigate whether an exemplary nitro-fatty acid can limit atrial fibrosis and AF.

METHODS AND RESULTS

Wild-type C57BL6/J mice were treated for 2 weeks with angiotensin II (AngII) and vehicle or nitro-oleic acid (10-nitro-octadec-9-enoic acid, OA-NO2, 6 mg/kg body weight) via subcutaneous osmotic minipumps. OA-NO2 significantly inhibited atrial fibrosis and depressed vulnerability for AF during right atrial electrophysiological stimulation to levels observed for AngII-naive animals. Left atrial epicardial mapping studies demonstrated preservation of conduction homogeneity by OA-NO2. The protection from fibrotic remodelling was mediated by suppression of Smad2-dependent myofibroblast transdifferentiation and inhibition of Nox2-dependent atrial superoxide formation.

CONCLUSION

OA-NO2 potently inhibits atrial fibrosis and subsequent AF. Nitro-fatty acids and possibly other lipid electrophiles thus emerge as potential therapeutic agents for AF, either by increasing endogenous levels through dietary modulation or by administration as synthetic drugs.

Is atrial fibrillation a risk factor for contrast-induced nephropathy in patients with ST-elevation myocardial infarction?

BACKGROUND

Contrast-induced nephropathy (CIN) is an iatrogenic problem in patients with ST-elevation myocardial infarction (STEMI) undergoing primary percutaneous coronary intervention (PPCI). Atrial fibrillation (AF) may also contribute to impaired kidney function. Several factors may contribute to the development of CIN. In patients with STEMI, concomitant AF is associated with higher in-hospital/follow-up mortality and morbidity. Therefore, we aimed to investigate the relationship between AF and CIN developments.

METHODS

In this study, 650 consecutive STEMI patients treated with PPCI were enrolled. Patients with AF at admission who did not achieve a sinus rhythm during 48h after hospitalization were defined as AF patients. CIN was defined by an increase in serum creatinine by >25% or 0.5mg/dL within 72h following contrast media exposure.

RESULTS

Our patients were divided into two groups based on whether they had AF, and although warfarin usage was different, the other parameters were similar between the groups. When our patients were grouped according to CIN development [group 1: CIN (+), group 2: CIN (-)], creatinine levels prior to PPCI (p=0.020), estimated glomerular filtration rate (eGFR) prior to PPCI (p<0.001), left ventricular ejection fraction (LVEF) (p=0.011), AF (p<0.001), and warfarin usage (p=0.016) were different between the two groups. We also performed multivariate logistic regression analyses and found that AF [odds ratio (OR), 6.945; 95% confidence interval (CI), 2.789-17.293; p<0.001], eGFR (OR, 0.973; 95% CI, 0.957-0.989; p=0.001), and LVEF (OR, 0.963; 95% CI, 0.935-0.991; p=0.010) independently predicted CIN development in patients with STEMI.

CONCLUSIONS

The risk factors for CIN are multifactorial and identifying high-risk patients is the most important step for prevention. In addition to traditional risk factors, AF can contribute to CIN development in patients with STEMI.

Angiotensin II activates signal transducers and activators of transcription 3 via Rac1 in the atrial tissue in permanent atrial fibrillation patients with rheumatic heart disease

Patients with rheumatic heart disease (RHD) often experience persistent atrial fibrillation (AF) associated with adverse atrial structural remodeling (ASR) manifested by atrial fibrosis and left atrial enlargement. The aim of this study was to explore the potential molecular signaling mechanisms for atrial fibrosis and ASR. Twenty RHD patients with persistent AF and 10 RHD patients with sinus rhythm (Group A) were recruited in our study, which all underwent transthoracic echocardiography. Right atrial appendage (RAA) tissue samples were obtained from these patients during mitral/aortic valve replacement operation. The AF patients were further divided into two groups according to left atrial diameter (LAD): Group B with LAD ranging 50-65 mm and Group C with LAD >65 mm. Histological examinations were performed with hematoxylin-eosin staining and Masson's trichrome staining. Atrial angiotensin II (AngII) content was measured by ELISA. Rac1 and STAT3 protein levels were determined by Western blot analysis. Hematoxylin-eosin staining demonstrated highly organized arrangement of atrial muscles in control Group A and significant derangement in both Group B and C AF patients with reduced cell density and increased cell size. Moreover, Masson's trichrome staining showed that atrial myocytes were surrounded by large trunks of collagen fibers in both Group B and C, but not in Group A. There was a positive correlation between atrial tissue fibrosis and LAD. AngII content was markedly higher in Group C than in Group B than in Group A, which was positively correlated with LAD. Similarly, Rac1 and STAT3 protein levels were found considerably higher in Group C and B than in Group A with excellent correlation to LAD. Our study unraveled for the first time the AngII/Rac1/STAT3 signaling as a mechanism for ASR thereby AF in a particular clinical setting-RHD patients with persistent AF and indicated inhibition of this pathway may help ameliorating adverse ASR.

Age and CHADS2 Score Predict the Effectiveness of Renin-Angiotensin System Blockers on Primary Prevention of Atrial Fibrillation

Renin-angiotensin system (RAS) blockers have potential protective effects against atrial fibrillation (AF). The purpose of this study was to determine if patient characteristics and underlying co-morbidities could predict the efficacy of RAS blockers in AF prevention. Patients aged ≥ 45 years with hypertension were identified from the Taiwan National Health Insurance Research Database. After propensity-score matching, a total of 22,324 patients were included in this study. Risk of new-onset AF in RAS blockers users and non-users was estimated. During up to 10 years of follow-up, 1,475 patients experienced new-onset AF. Overall, RAS blockers reduced the risk of AF by 36% (adjusted HR 0.64; 95% CI 0.58 to 0.71; p < 0.001). Subgroup analysis showed that RAS blockers use was beneficial for AF prevention in patients aged ≥ 55 years or with a CHADS2 score of 1, 2, or 3. The therapy provided no obvious beneficial effect for AF prevention in those aged less than 55 years or with a CHADS2 score ≥ 4. In conclusion, RAS blockers reduced the risk of new-onset AF in patients aged ≥ 55 years or with a CHADS2 score of 1, 2, or 3, but not in patients aged less than 55 years or with a CHADS2 score ≥ 4.

The histology of human right atrial tissue in patients with high-risk Obstructive Sleep Apnea and underlying cardiovascular disease: A pilot study

Background

Obstructive Sleep Apnea (OSA) results in intermittent hypoxia leading to atrial remodeling, which, among other things, facilitates development of atrial fibrillation. While much data exists on the macrostructural changes in cardiac physiology induced by OSA, there is a lack of studies looking for histologic changes in human atrial tissue induced by OSA which might lead to the observed macrostructural changes.

Methods

A case control study was performed. Patients undergoing coronary artery bypass grafting (CABG) were evaluated for OSA and categorized as high-risk or low-risk. The right atrial tissue samples were obtained during CABG and both microscopic histological analysis and Sirius Red staining were performed.

Results

18 patients undergoing CABG were included; 10 high-risk OSA and 8 low-risk OSA in evenly matched populations. No statistically significant difference between the two groups was observed in amount of myocytolysis (p = 0.181), nuclear hypertrophy (p = 0.671), myocardial inflammation (p = n/a), amyloid deposition (p = n/a), or presence of thrombi (p = n/a), as measured through routine H&E staining. As well, no statistically significant difference in interstitial and epicardial collagen was observed, as measured by Sirius Red staining (for total tissue: p = 0.619: for myocardium: p = 0.776).

Conclusions

In this pilot study there were no observable histological differences in human right atrial tissue from individuals at high- and low-risk for OSA. Further investigation would be required for more definitive results.

Upregulation of SERCA2a following short-term ACE inhibition (by enalaprilat) alters contractile performance and arrhythmogenicity of healthy myocardium in rat

Chronic angiotensin-converting enzyme inhibitor (ACEIs) treatment can suppress arrhythmogenesis. To examine whether the effect is more immediate and independent of suppression of pathological remodelling, we tested the antiarrhythmic effect of short-term ACE inhibition in healthy normotensive rats. Wistar rats were administered with enalaprilat (ENA, i.p., 5 mg/kg every 12 h) or vehicle (CON) for 2 weeks. Intraarterial blood pressure in situ was measured in A. carotis. Cellular shortening was measured in isolated, electrically paced cardiomyocytes. Standard 12-lead electrocardiography was performed, and hearts of anaesthetized open-chest rats were subjected to 6-min ischemia followed by 10-min reperfusion to examine susceptibility to ventricular arrhythmias. Expressions of calcium-regulating proteins (SERCA2a, cardiac sarco/endoplasmic reticulum Ca(2+)-ATPase; CSQ, calsequestrin; TRD, triadin; PLB, phospholamban; Thr(17)-PLB-phosphorylated PLB at threonine-17, FKBP12.6, FK506-binding protein, Cav1.2-voltage-dependent L-type calcium channel alpha 1C subunit) were measured by Western blot; mRNA levels of L-type calcium channel (Cacna1c), ryanodine receptor (Ryr2) and potassium channels Kcnh2 and Kcnq1 were measured by qRT-PCR. ENA decreased intraarterial systolic as well as diastolic blood pressure (by 20%, and by 31%, respectively, for both P < 0.05) but enhanced shortening of cardiomyocytes at basal conditions (by 34%, P < 0.05) and under beta-adrenergic stimulation (by 73%, P < 0.05). Enalaprilat shortened QTc interval duration (CON 78 ± 1 ms vs. ENA 72 ± 2 ms; P < 0.05) and significantly decreased the total duration of ventricular fibrillations (VF) and the number of VF episodes (P < 0.05). Reduction in arrhythmogenesis was associated with a pronounced upregulation of SERCA2a (CON 100 ± 20 vs. ENA 304 ± 13; P < 0.05) and complete absence of basal Ca(2+)/calmodulin-dependent phosphorylation of PLB at Thr(17). Short-term ACEI treatment can provide protection against I/R injury-induced ventricular arrhythmias in healthy myocardium, and this effect is associated with increased SERCA2a expression.

Relation of vitamin D deficiency and new-onset atrial fibrillation among hypertensive patients

Vitamin D deficiency is associated with various cardiovascular disorders including hypertension, coronary artery disease, and heart failure. The renin-angiotensin-aldosterone system (RAS) axis is activated in vitamin D deficiency. The RAS axis also plays a role in the pathophysiology of atrial fibrillation (AF). We aimed to investigate whether vitamin D deficiency is a risk factor for the development of new-onset AF in hypertension. A total of 227 hypertensive patients were enrolled, of whom 137 had new-onset AF; 90 patients without AF were included in the control group. The age of the patient, left atrial diameter, and vitamin D deficiency increased the probability of new-onset AF independent from confounding factors (odds ratio [OR], 1.04; 95% confidence interval [CI], 1.01-1.08; P = .03 for age; OR, 1.88; 95% CI, 1.15-3.45; P = .03 for left atrial diameter; OR, 1.68; 95% CI, 1.18-2.64; P = .03 for vitamin D deficiency). Vitamin D deficiency is associated with new-onset AF in hypertension.

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.

Remodeling of cardiac passive electrical properties and susceptibility to ventricular and atrial arrhythmias

Coordinated electrical activation of the heart is essential for the maintenance of a regular cardiac rhythm and effective contractions. Action potentials spread from one cell to the next via gap junction channels. Because of the elongated shape of cardiomyocytes, longitudinal resistivity is lower than transverse resistivity causing electrical anisotropy. Moreover, non-uniformity is created by clustering of gap junction channels at cell poles and by non-excitable structures such as collagenous strands, vessels or fibroblasts. Structural changes in cardiac disease often affect passive electrical properties by increasing non-uniformity and altering anisotropy. This disturbs normal electrical impulse propagation and is, consequently, a substrate for arrhythmia. However, to investigate how these structural changes lead to arrhythmias remains a challenge. One important mechanism, which may both cause and prevent arrhythmia, is the mismatch between current sources and sinks. Propagation of the electrical impulse requires a sufficient source of depolarizing current. In the case of a mismatch, the activated tissue (source) is not able to deliver enough depolarizing current to trigger an action potential in the non-activated tissue (sink). This eventually leads to conduction block. It has been suggested that in this situation a balanced geometrical distribution of gap junctions and reduced gap junction conductance may allow successful propagation. In contrast, source-sink mismatch can prevent spontaneous arrhythmogenic activity in a small number of cells from spreading over the ventricle, especially if gap junction conductance is enhanced. Beside gap junctions, cell geometry and non-cellular structures strongly modulate arrhythmogenic mechanisms. The present review elucidates these and other implications of passive electrical properties for cardiac rhythm and arrhythmogenesis.

Atrial fibrillation in essential hypertension: an issue of concern

Many clinical studies indicate that atrial fibrillation is closely related to hypertension. Atrial fibrillation is not only associated with the level of blood pressure (BP) but also with the circadian rhythms of BP. However, the underlying mechanisms of atrial fibrillation in essential hypertension patients remain largely unknown. Hypertension may facilitate the onset and persistence of atrial fibrillation by stretch-induced changes in the repolarization of atrial myocytes (triggers of atrial fibrillation) and atrial remodeling (structural and electrical remodeling). Importantly, the effects of hypertension on atrial fibrillation are progressive. These progressive anatomic, functional, electrophysiological and structural changes occur at different times. This characterization of the time course of atrial changes presents an intervention window before remodeling progresses to changes that are difficult to reverse. Given that the medium to long-term efficacy of antiarrhythmic drugs has proved poor, it is essential to seek new therapies to prevent the onset of atrial fibrillation and to effectively control recurrences of atrial fibrillation. The study of nonantiarrhythmic drugs that act on the atrial remodeling that constitutes the substrate of the arrhythmia is a new and very interesting field of research. Treatment with angiotensin-converting enzyme inhibitors angiotension-converting enzyme inhibitors (ACEIs) and angiotensin receptor blockers (ARBs) seems more promising. However, from recent trials, only hypertension with structural heart disease, left ventricular dysfunction and left ventricular hypertrophy benefit from ACEIs and ARBs. This article reviews many aspects of atrial fibrillatio in essential hypertension patients to provide the foundation of atrial fibrillatio treatment.

Cross-talk between mineralocorticoid receptor/angiotensin II type 1 receptor and mitogen-activated protein kinase pathways underlies aldosterone-induced atrial fibrotic responses in HL-1 cardiomyocytes

BACKGROUND

Aldosterone is increasingly recognized for its involvement in atrial structural remodeling. However, the precise molecular mechanisms and signal pathways underlying aldosterone-induced atrial fibrosis are unknown.

METHODS

Western blotting was used to investigate the effects of aldosterone on the expression of mineralocorticoid receptor (MR), angiotensin II type I receptor (AT1), mitogen-activated protein kinases (MAPKs), and fibrotic marker proteins in cultured HL-1 cardiomyocytes.

RESULTS

Aldosterone upregulated MR and AT1 expressions in a concentration-dependent and time-dependent manner. Aldosterone (10(-6)M) significantly and time-dependently increased activation of the extracellular signal-regulated protein kinase (ERK), c-Jun N-terminal kinase (JNK), p38MAPK pathways, and the protein expression of collagen 1A and 3A (COL1A and COL3A), transforming growth factor (TGF)-β1, and α-smooth muscle actin (SMA). Pre-treatment with eplerenone (10(-10)M) prevented the increased expression of MR, MAPK signals and the above profibrotic molecules, but amplified the increase in AT1 level stimulated by aldosterone (10(-6)M). Pre-treatment with losartan (10(-10)M) or MAPK pathway inhibitors (U0126 or SP600125) abolished aldosterone-induced MR upregulation and significantly inhibited the expression of the above fibrotic marker proteins, indicating the critical role of MR and the requirement for active AT1 in the development of aldosterone-induced atrial fibrosis.

CONCLUSIONS

Elevated MR activity plays a central role in aldosterone-mediated activation of the MAPK signaling pathway and subsequent profibrotic effects in HL-1 atrial cells. MR/AT1 and the MAPK signaling pathway interact to trigger the molecular mechanism underlying the aldosterone-induced atrial fibrotic response. Our results support the view that MR blockade in conjunction with AT1 blockade can prevent the occurrence of atrial fibrillation.

Atrial remodeling is directly related to end-diastolic left ventricular pressure in a mouse model of ventricular pressure overload

Background

Atrial fibrillation (AF) is often preceded by underlying cardiac diseases causing ventricular pressure overload.

Objective

It was our aim to investigate the progression of atrial remodeling in a small animal model of ventricular pressure overload and its association with induction of AF.

Methods

Male mice were subjected to transverse aortic constriction (TAC) or sham operation. After four or eight weeks, echocardiographic measurements and hemodynamic measurements were made and AF induction was tested. The hearts were either fixed in formalin or ventricles and atria were separated, weighed and snap-frozen for RNA analysis.

Results

Four weeks of pressure overload induced ventricular hypertrophy and minor changes in the atria. After eight weeks a significant reduction in left ventricular function occurred, associated with significant atrial remodeling including increased atrial weight, a trend towards an increased left atrial cell diameter, atrial dilatation and increased expression of markers of hypertrophy and inflammation. Histologically, no fibrosis was found in the left atrium. But atrial gene expression related to fibrosis was increased. Minor changes related to electrical remodeling were observed. AF inducibility was not different between the groups. Left ventricular end diastolic pressures were increased and correlated with the severity of atrial remodeling but not with AF induction.

Conclusion

Permanent ventricular pressure overload by TAC induced atrial remodeling, including hypertrophy, dilatation and inflammation. The extent of atrial remodeling was directly related to LVEDP and not duration of TAC per se.

Effect of renal sympathetic denervation on atrial substrate remodeling in ambulatory canines with prolonged atrial pacing

We have previously demonstrated that catheter-based renal sympathetic denervation (RSD) could suppress atrial fibrillation (AF) in canines with short-time rapid right atrial pacing (RAP). However, the role of renal denervation on atrial remodeling is unclear. The aim of the present study was to explore the long-term effect of RSD on the atrial remodeling during prolonged RAP. Twenty mongrel dogs were implanted with a high-frequency cardiac pacemaker with a transvenous lead inserted into the right atrial appendage. The dogs were divided into three groups: a sham-operated group (n = 6), the chronic RAP (CRAP) group (n = 7), and the CRAP+RSD group (n = 7). In the CRAP+RSD group, a pacemaker was implanted 6 weeks after RSD was performed bilaterally for recovery. RAP was maintained for 5 weeks in CRAP group and CRAP+RSD group. The plasma levels of Angiotensin II and aldosterone were significantly increased in CRAP group compared with sham-operated group, but the increasing trend was inhibited in CRAP+RSD group compared with CRAP group (P<0.05). Similarly, RSD suppressed the increasing trend that prolonged RAP produced in the left atrial levels of ANP, TNF-α and IL-6. Compared with the sham-operated group, the CRAP group had significantly increased levels of caspase-3, bax and Cx40 whereas the level of Bcl-2 decreased (P<0.05). RSD markedly reduced the upregulation of caspase-3, bax and Cx40 and the downregulation of Bcl-2 expression compared with the CRAP group (P<0.05). Picric acid–sirius red staining study suggested that RSD could markedly alleviate the lesion degree of cardic fibrosis induced by CRAP (P<0.05). Immunohistochemistry results showed that the densities of TH- and GAP43- positive nerves were significantly elevated in the CRAP group compared with the sham-operated group, while RSD operation signicantly inhibited the these changes produced by CRAP. These findings suggest that renal denervation could suppress the atrial remodeling after prolonged RAP in ambulatory canines.

Oxidative stress in atrial fibrillation: an emerging role of NADPH oxidase

Atrial fibrillation (AF) is the most common cardiac arrhythmia. Patients with AF have up to seven-fold higher risk of suffering from ischemic stroke. Better understanding of etiologies of AF and its thromboembolic complications are required for improved patient care, as current anti-arrhythmic therapies have limited efficacy and off target effects. Accumulating evidence has implicated a potential role of oxidative stress in the pathogenesis of AF. Excessive production of reactive oxygen species (ROS) is likely involved in the structural and electrical remodeling of the heart, contributing to fibrosis and thrombosis. In particular, NADPH oxidase (NOX) has emerged as a potential enzymatic source for ROS production in AF based on growing evidence from clinical and animal studies. Indeed, NOX can be activated by known upstream triggers of AF such as angiotensin II and atrial stretch. In addition, treatments such as statins, antioxidants, ACEI or AT1RB have been shown to prevent post-operative AF; among which ACEI/AT1RB and statins can attenuate NOX activity. On the other hand, detailed molecular mechanisms by which specific NOX isoform(s) are involved in the pathogenesis of AF and the extent to which activation of NOX plays a causal role in AF development remains to be determined. The current review discusses causes and consequences of oxidative stress in AF with a special focus on the emerging role of NOX pathways.

Elevated pre-operative serum peptides for collagen I and III synthesis result in post-surgical atrial fibrillation

OBJECTIVES

This study sought to determine if serum markers for collagen I and III synthesis, the carboxyl terminal peptide from pro-collagen I (PICP) and the amino terminal peptide from pro-collagen III (PIIINP), correlate with left atrial (LA) fibrosis and post-operative atrial fibrillation (AF).

BACKGROUND

AF after cardiac surgery is associated with adverse outcomes. We recently demonstrated that LA fibrosis is associated with post-operative AF in patients with no previous history of AF.

METHODS

Fifty-four patients having cardiac surgery without a history of AF consented to left and right atrial biopsies and a pre-operative peripheral blood draw. Picrosirius red staining quantified the percentage of fibrosis, and reverse transcriptase polymerase chain reaction assessed atrial tissue messenger ribonucleic acid transcripts involved in the fibrosis pathway. PICP and PIIINP levels were measured using an enzyme immunosorbent assay.

RESULTS

Eighteen patients developed AF, whereas 36 remained in normal sinus rhythm. LA fibrosis was higher in patients who developed AF versus normal sinus rhythm (6.13 ± 2.9% vs. 2.03 ± 1.9%, p = 0.03). LA messenger ribonucleic acid transcripts for collagen I, III, transforming growth factor, and angiotensin were 1.5- to 2.0-fold higher in AF patients. Serum PICP and PIIINP levels were highest in AF versus normal sinus rhythm (PICP: 451.7 ± 200 ng/ml vs. 293.3 ± 114 ng/ml, p = 0.006; PIIINP: 379 ± 286 pg/ml vs. 191.6 ± 162 pg/ml, p = 0.01). Furthermore, there was a linear correlation between LA fibrosis and serum PICP levels (R(2) = 0.2; p = 0.01), and of the markers, only PICP was independently associated with AF.

CONCLUSIONS

This demonstrates that serum PICP and PIIINP levels correlate with the presence of LA fibrosis and may act as predictors for post-operative AF even in the absence of previous history of AF.

Circulating and local renin-angiotensin-aldosterone system express differently in atrial fibrillation patients with different types of mitral valvular disease

Mitral valvular disease is strongly related to atrial fibrillation (AF), but the different types of mitral valvular disease have a different prevalence of AF. In this study we explored the expressions of the circulating and local renin-angiotensin-aldosterone system (RAAS) in order to determine the relationship between circulating and local RAAS expressions and its effects on AF in different types of mitral valvular disease patients. Our study group consisted of 24 mitral valvular disease patients scheduled for mitral valve replacement surgery. Peripheral blood samples and left atrial appendage tissue samples were obtained from all patients. Radioimmunoassay was performed to assess the expression levels of circulating and local renin, angiotensin II and aldosterone. In mitral valvular diseases, linear correlation analyses were done for local and circulating renin, angiotensin II and aldosterone; the p values were 0.979, 0.518 and 0.125, respectively. Expression levels of local angiotensin II, circulating angiotensin II and local aldosterone were significantly increased in the AF group compared with sinus rhythm; the p values were 0.023, 0.042 and 0.035, respectively. In mitral stenosis patients, AF was primarily associated with local angiotensin II (p=0.010), as well as being associated with circulating angiotensin II (p=0.038). In mitral regurgitation patients, AF was only significantly associated with local angiotensin II (p=0.038). Circulating and local RAAS expressions are associated with AF in mitral valvular disease patients. The levels of circulating and local RAAS expressions were different in AF patients with different types of mitral valvular diseases. The differentiation of circulating and local RAAS expression levels in AF patients between different types of mitral valvular disease can potentially improve the specific pharmacological interventions outcomes for these patients.

The effects of radio-frequency ablation on blood pressure control in patients with atrial fibrillation and hypertension

PURPOSE

The effects of radio-frequency ablation (RFA) on blood pressure (BP) regulation in patients with atrial fibrillation (AF) and hypertension remain unknown. We hypothesized that patients with successful ablation had a lower BP and/or lesser utilization of antihypertensive drug therapy during follow-up when compared to patients with failed ablation.

METHODS AND RESULTS

This was a retrospective evaluation of patients with AF and hypertension treated with ablation at the University of Utah between July 2006 and June 2010. BP and use of antihypertensive medications were assessed at baseline and 1 year follow-up. A total of 167 patients were identified. Eight patients were excluded due to the need for AAD therapy beyond the blanking period thus leaving 80 patients in the success group and 79 patients in the failure group. The mean BP and HR at baseline were not significant between the groups. In the success group, the mean systolic BP decreased from a baseline value of 129 ± 17 to 125 ± 14 mmHg at 1 year (p = 0.075). In contrast, in the failure group, the mean systolic BP increased from a baseline value of 124 ± 16 to 127 ± 14 mmHg at 1 year (p = 0.176). Between-group comparison revealed a p value of 0.026. Minimal changes in diastolic BP were noted in both groups. No significant changes in antihypertensive therapy were noted.

CONCLUSION

We have shown that successful catheter ablation in patients with AF and hypertension is associated with a decrease in systolic BP when compared to an increase in patients with failed ablation. Our findings suggest that restoring sinus rhythm could have an antihypertensive effect in patients with AF and hypertension.