Update on atrial fibrillation

Salidroside attenuates atrial fibrosis and atrial fibrillation vulnerability induced by angiotensin-II through inhibition of LOXL2-TGF-β1-Smad2/3 pathway

Aims and objectives

Salidroside (SAL), an active component isolated from the Chinese plant Rose Rhodiola, has anti-inflammatory, antioxidant, anti-cancer, neuroprotective, and renal protective properties. Atrial fibrosis developed due to angiotensin II (Ang II) plays a crucial function in developing atrial fibrillation (AF). This research investigates the involvement of SAL in AF, its vulnerability to AF, and Ang II-induced inflammatory atrial fibrosis.

Methods

Ang II (2 mg/kg/day) was infused underneath the skin into male C57BL/6 mice (8-10 weeks old, n = 40) for four weeks to create the AF model. SAL (50 mg/kg/day) was given intraperitoneally once per day for 28 days. Analyses of morphology, histology, and biochemical were carried out. Transesophageal burst pacing was used in vivo to induce AF.

Results

Ang II injection increased mice's heart rate and systolic blood pressure (SBP), whereas SAL treatment was significantly reduced. Ang II infusion increased left atrial diameter (LAD) in mice, which was attenuated after SAL treatment. SAL alone did not affect AF inducibility, but SAL therapy markedly decreased Ang II-induced AF inducibility. Additionally, the expression levels of interleukin-1 beta (IL-1β), interleukin-6 (IL-6) and tumor necrosis factor-alpha (TNF-α) were inhibited with SAL therapy in mice. Compared to the Ang II group, Ang II infusion raised malondialdehyde (MDA) levels and reduced superoxide dismutase (SOD) and catalase (CAT) activity, but SAL therapy altered all of these effects. SAL treatment significantly reduced LOXL2, TGF-β1, p-Smad2 and p-Smad3 protein expression than the Ang II group mice.

Conclusion

SAL inhibits atrial fibrosis and potentially attenuates increased susceptibility to AF by suppressing the LOXL2-TGF-β1-Smad2/3 pathway.

Atrial fibrillation and peripheral arterial disease define MPN patients with very high risk of thrombosis

Myeloproliferative neoplasms (MPNs) are associated with a high risk of thrombotic and hemorrhagic complications, especially in elderly patients. Atrial fibrillation (AF) and peripheral arterial disease (PAD), also frequently discovered in aging patients, are associated with similar complications. We analysed the incidence and complication rates of AF and PAD in a large cohort of MPN patients. In total, 289/1113 patients (26 %) suffered at least one of these diseases as follows: 179 (16.1 %) with AF alone, 81 with PAD alone (7.3 %) and 29 (2.6 %) with both conditions. Postdiagnosis thrombotic events were observed in 31.3 % of AF patients (p = 0.002, OR = 1.80 [1.23;2.61]), 35.8 % of PAD patients (p = 0.002, OR = 2.21[1.31;3.67]) and 62.1 % of AF/PAD patients (p < 0.0001, OR = 6.47 [2.83;15.46]) compared to 20.1 % of no-AF/no-PAD patients. Postdiagnosis hemorrhagic events were also identified in 17.9 %, 16 %, 24.1 % and 10.1 % of AF, PAD, AF/PAD, and no-AF/no-PAD patients, respectively (p = 0.003). This significantly higher risk of thrombosis/bleeding was also observed in patients <60 years old. AF and PAD were significant risk factors for both thrombotic and hemorrhagic risks in multivariate analysis. We identified AF and PAD as criteria for high risk of thrombosis, hemorrhage, and death, emphasizing the interest in early detection and efficient treatment of these conditions.

An Untargeted LC-MS based approach for identification of altered metabolites in blood plasma of rheumatic heart disease patients

Rheumatic heart disease (RHD) is often considered as a disease of developing countries and India is the home of about 40% of RHD patients. Environment seems to play a major role in its causation. Since gene environment interactions can lead to alterations of various metabolic pathways, identification of altered metabolites can help in understanding the various pathways leading to RHD. Blood plasma samples from 51 RHD and 49 healthy controls were collected for the study. Untargeted metabolomics approach was used to identify the metabolites that are altered in RHD patients. Data showed 25 altered metabolites among RHD patients. These altered metabolites were those involved in Purine, Glutamine, Glutamate, Pyrimidine, Arginine, Proline and Linoleic metabolism. Thus, the present study illuminates metabolic alterations among RHD patients which can help in determining the potential therapeutic targets.

LOXL2 Inhibitor Attenuates Angiotensin II-Induced Atrial Fibrosis and Vulnerability to Atrial Fibrillation through Inhibition of Transforming Growth Factor Beta-1 Smad2/3 Pathway

OBJECTIVES

Angiotensin II (Ang II)-induced atrial fibrosis plays a vital role in the development of atrial fibrillation (AF). Lysyl oxidase-like 2 (LOXL2) plays an essential role in matrix remodeling and fibrogenesis, indicating it may involve fibrosis-associated diseases. This study aims to elucidate the role of LOXL2 in AF, and its specific inhibitor can suppress Ang II-induced inflammatory atrial fibrosis and attenuate the enhanced vulnerability to AF.

METHODS

Male mice C57BL/6 were subcutaneously infused with either saline or Ang II (2 mg/kg/day) for 4 weeks. DMSO or LOXL2 inhibitor LOXL2-IN-1 hydrochloride (LOXL2-IN-1) at a dose of 100 μg/kg/day were intraperitoneally injected once daily for 4 weeks. Morphological, histological, and biochemical analyses were performed. AF was induced by transesophageal burst pacing in vivo.

RESULTS

Expression of LOXL2 was increased in serum of AF patients and Ang II-treated mice. LOXL2-IN-1 significantly attenuated Ang II-induced AF vulnerability, cardiac hypertrophy, atrial inflammation, and fibrosis. LOXL2-IN-1 suppressed Ang II-induced expression of transforming growth factor beta-1 (TGF-β1) and collagen I and phosphorylation of Smad2/3 in atrial tissue.

CONCLUSIONS

LOXL2 is a target of AF, and its inhibitor prevents atrial fibrosis and attenuated enhanced vulnerability to AF potentially through the TGF-β/Smad pathway.

PU.1 inhibition attenuates atrial fibrosis and atrial fibrillation vulnerability induced by angiotensin-II by reducing TGF-β1/Smads pathway activation

Fibrosis serves a critical role in driving atrial remodelling‐mediated atrial fibrillation (AF). Abnormal levels of the transcription factor PU.1, a key regulator of fibrosis, are associated with cardiac injury and dysfunction following acute viral myocarditis. However, the role of PU.1 in atrial fibrosis and vulnerability to AF remain unclear. Here, an in vivo atrial fibrosis model was developed by the continuous infusion of C57 mice with subcutaneous Ang‐II, while the in vitro model comprised atrial fibroblasts that were isolated and cultured. The expression of PU.1 was significantly up‐regulated in the Ang‐II‐induced group compared with the sham/control group in vivo and in vitro. Moreover, protein expression along the TGF‐β1/Smads pathway and the proliferation and differentiation of atrial fibroblasts induced by Ang‐II were significantly higher in the Ang‐II‐induced group than in the sham/control group. These effects were attenuated by exposure to DB1976, a PU.1 inhibitor, both in vivo and in vitro. Importantly, in vitro treatment with small interfering RNA against Smad3 (key protein of TGF‐β1/Smads signalling pathway) diminished these Ang‐II‐mediated effects, and the si‐Smad3‐mediated effects were, in turn, antagonized by the addition of a PU.1‐overexpression adenoviral vector. Finally, PU.1 inhibition reduced the atrial fibrosis induced by Ang‐II and attenuated vulnerability to AF, at least in part through the TGF‐β1/Smads pathway. Overall, the study implicates PU.1 as a potential therapeutic target to inhibit Ang‐II‐induced atrial fibrosis and vulnerability to AF.

The rs2236609 Polymorphism Is Related to Increased Risk Susceptibility of Atrial Fibrillation

INTRODUCTION

Genetic variations in the slow component of the delayed rectifier potassium channels (IKs) are reported to contribute to an increased susceptibility to arrhythmias. This study aims to investigate the frequency and the possible association of the rs2236609 polymorphism in the KCNE1 gene and the risk of atrial fibrillation (AF).

METHODS

This was a case-control study that recruited 100 patients suffering from AF (mean age 49.4 ± 15.1 years), and a control group of 95 healthy participants older than 55 years (mean age 59.8 ± 4.1 years) with no history of cardiovascular disease, hypertension, or diabetes. Genomic DNA was extracted from whole peripheral blood, and the desired fragment was amplified using polymerase chain reaction followed by restriction digestion with the NspI restriction enzyme.

RESULTS

The results showed a significant difference between the single-nucle-otide polymorphism variations in AF patients and controls (p < 0.022). The risk of AF in the GG genotype was significantly decreased (odds ratio [OR] 0.42; 95% confidence interval [Cl] 0.23-0.79). The risk of AF in the GA (OR 2.12; 95% Cl 1.11-4.06) and AA (OR 2.28, 95% Cl 0.57-9.1) genotypes was significantly increased. The odds of developing AF according to A allele counting was significantly increased (OR 2.1; 95% Cl 1.2608-3.638; p = 0.0048).

CONCLUSION

Our results showed a significant increase in AF risk in people carrying the A allele, while the G allele might be considered as a protective allele.

Atrial fibrillation among Russian men and women aged 55 years and older: prevalence, mortality, and associations with biomarkers in a population-based study

Objective

To examine the prevalence of atrial fibrillation (AF), its impacts on cardiovascular disease (CVD) and all-cause mortality, and the associations between AF and inflammatory and serum biomarkers in a population-based sample of Muscovites.

Methods

The study is a secondary analysis of data from the Stress, Aging and Health in Russia (SAHR) survey that includes information on 1800 individuals with an average age of 68.5 years at baseline, and on their subsequent mortality during 7.4 years on average. AF is detected by 12-lead electrocardiogram (ECG) and 24-hour Holter monitoring. The statistical analysis includes proportional hazard and logistic regression models.

Results

Of the 1732 participants with relevant Holter data, AF was detected in 100 (74 by ECG and Holter, 26 by Holter only). The prevalence of AF was 5.8% for men and 7.4% for women. The fully adjusted model showed strongly elevated hazard of CVD and all-cause mortality in men and women with long non-self-limiting AF (LAF). LAF was found to be negatively associated with elevated total and low-density lipoprotein cholesterol and to be positively associated with elevated markers of inflammation in women.

Conclusions

The study assessed for the first time the prevalence and the risks of death related to AF among older Russians. LAF was shown to be a strong and independent predictor of CVD and all-cause mortality. AF is unlikely to contribute to the large excess male mortality in Russia. The finding that one-quarter of AF cases were detected only by Holter monitoring demonstrates the usefulness of diagnostics with prolonged ECG registration.

Mechanisms by Which Ranolazine Terminates Paroxysmal but Not Persistent Atrial Fibrillation

BACKGROUND

Ranolazine inhibits Na⁺ current (I_Na), but whether it can convert atrial fibrillation (AF) to sinus rhythm remains unclear. We investigated antiarrhythmic mechanisms of ranolazine in sheep models of paroxysmal (PxAF) and persistent AF (PsAF).

METHODS

PxAF was maintained during acute stretch (N=8), and PsAF was induced by long-term atrial tachypacing (N=9). Isolated, Langendorff-perfused sheep hearts were optically mapped.

RESULTS

In PxAF ranolazine (10 μmol/L) reduced dominant frequency from 8.3±0.4 to 6.2±0.5 Hz (P<0.01) before converting to sinus rhythm, decreased singularity point density from 0.070±0.007 to 0.039±0.005 cm^-2 s^-1 (P<0.001) in left atrial epicardium (LA_epi), and prolonged AF cycle length (AFCL); rotor duration, tip trajectory, and variance of AFCL were unaltered. In PsAF, ranolazine reduced dominant frequency (8.3±0.5 to 6.5±0.4 Hz; P<0.01), prolonged AFCL, increased the variance of AFCL, had no effect on singularity point density (0.048±0.011 to 0.042±0.016 cm^-2 s^-1; P=ns) and failed to convert AF to sinus rhythm. Doubling the ranolazine concentration (20 μmol/L) or supplementing with dofetilide (1 μmol/L) failed to convert PsAF to sinus rhythm. In computer simulations of rotors, reducing I_Na decreased dominant frequency, increased tip meandering and produced vortex shedding on wave interaction with unexcitable regions.

CONCLUSIONS

PxAF and PsAF respond differently to ranolazine. Cardioversion in the former can be attributed partly to decreased dominant frequency and singularity point density, and prolongation of AFCL. In the latter, increased dispersion of AFCL and likely vortex shedding contributes to rotor formation, compensating for any rotor loss, and may underlie the inefficacy of ranolazine to terminate PsAF.

Cognitive Function and Atrial Fibrillation: From the Strength of Relationship to the Dark Side of Prevention. Is There a Contribution from Sinus Rhythm Restoration and Maintenance?

Atrial fibrillation (AF) is the most common chronic cardiac arrhythmia with an increasing prevalence over time mainly because of population aging. It is well established that the presence of AF increases the risk of stroke, heart failure, sudden death, and cardiovascular morbidity. In the last two decades several reports have shown an association between AF and cognitive function, ranging from impairment to dementia. Ischemic stroke linked to AF is a well-known risk factor and predictor of cognitive decline. In this clinical scenario, the risk of stroke might be reduced by oral anticoagulation. However, recent data suggest that AF may be a predictor of cognitive impairment and dementia also in the absence of stroke. Cerebral hypoperfusion, reduced brain volume, microbleeds, white matter hyperintensity, neuroinflammation, and genetic factors have been considered as potential mechanisms involved in the pathogenesis of AF-related cognitive dysfunction. However, a cause-effect relationship remains still controversial. Consequently, no therapeutic strategies are available to prevent AF-related cognitive decline in stroke-free patients. This review will analyze the potential mechanisms leading to cognitive dysfunction in AF patients and examine the available data on the impact of a sinus rhythm restoration and maintenance strategy in reducing the risk of cognitive decline.

GWAS contribution to atrial fibrillation and atrial fibrillation-related stroke: pathophysiological implications

Atrial fibrillation (AF) and stroke are included in a group of complex traits that have been approached regarding of their study by susceptibility genetic determinants. Since 2007, several genome-wide association studies (GWAS) aiming to identify genetic variants modulating AF risk have been conducted. Thus, 11 GWAS have identified 26 SNPs (p < 5 × 10^-2), of which 19 reached genome-wide significance (p < 5 × 10^-8). From those variants, seven were also associated with cardioembolic stroke and three reached genome-wide significance in stroke GWAS. These associations may shed a light on putative shared etiologic mechanisms between AF and cardioembolic stroke. Additionally, some of these identified variants have been incorporated in genetic risk scores in order to elucidate new approaches of stroke prediction, prevention and treatment.

Circular RNA expression profiles of persistent atrial fibrillation in patients with rheumatic heart disease

Objective:

To investigate the expression profile of circular RNAs (circRNAs) and proposed circRNA–microRNA (miRNA) regulatory network in atrial fibrillation (AF).

Methods:

Atrial tissues from patients with persistent AF with rheumatic heart disease and non-AF myocardium with normal hearts were collected for circRNA differential expression analyses by high-throughput sequencing. The Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analyses were performed to predict the potential functions of the differentially expressed genes and AF-related pathways. Co-expression networks of circRNA–miRNA were constructed based on the correlation analyses between the differentially expressed RNAs. Quantitative reverse transcription polymerase chain reaction (PCR) was performed to validate the results.

Results:

A total of 108 circRNAs were found to be differentially expressed in AF. Among them, 51 were up-regulated, and 57 were down-regulated. Dysregulated circRNAs were validated by quantitative real-time PCR. The GO and KEGG pathway enrichment analyses were executed to determine the principal functions of the significantly deregulated genes. Furthermore, we constructed correlated expression networks between circRNAs and miRNAs. circRNA19591, circRNA19596, and circRNA16175 interacted with 36, 28, and 18 miRNAs, respectively; miR-29b-1-5p and miR-29b-2-5p were related to 12 down-regulated circRNAs, respectively.

Conclusion:

Our findings provide a novel perspective on circRNAs involved in AF due to rheumatic heart disease and establish the foundation for future research of the potential roles of circRNAs in AF.

Systematic Evaluation of Efficacy and Safety of Acupuncture Treatment for Patients with Atrial Fibrillation

BACKGROUND:

Atrial fibrillation (AF) is one of the most common types of arrhythmia diagnosed in clinical practice. Due to its negative effects on people’s physical and mental health, it is necessary to prevent and treat AF. Recently, scholars have found that acupuncture can be used to treat AF, but some scholars have questioned its therapeutic efficacy.

AIM:

Therefore, this study was performed to assess the efficacy and safety of acupuncture treatment for AF patients.

METHODS:

Previously published research articles were retrieved from six databases, and the data was analysed using RevMan5.3 software with a statistically significant difference defined as P < 0.05.

RESULTS:

A total of 8 relevant kinds of literature were retrieved containing 633 AF patients (323 in the treatment group and 310 in the control group). Acupuncture treatment increased the total efficacy and the rate of AF cardioversion to sinus rhythm (RR: 1.38; 95% CI: 1.25 to 1.53 vs RR: 1.40;95% CI: 1.16 to 1.69; each P < 0.05), and decreased the time of AF cardioversion to sinus rhythm, the heart rate and incidence of adverse effects (RR: -3.95; 95% CI: -4.98 to -2.91 vs RR: -14.54; 95% CI: -24.09 to -5.00 vs RR: 0.48; 95% CI: 0.21 to 1.11, each P < 0.05). There was difference between retention time more and less than 30 minutes (I2 = 74.9%, P = 0.05). The funnel plot displayed a symmetrical and funnel-form shape, indicating low bias.

CONCLUSION:

Acupuncture has a good therapeutic effect and safety profile on patients with AF, and its application in clinical practice should be considered.

Combinational Biomarkers for Atrial Fibrillation Derived from Atrial Appendage and Plasma Metabolomics Analysis

Atrial fibrillation (AF) is one of the most common types of arrhythmias and often leads to clinical complications. The objectives of this study were to offer insights into the metabolites of AF and to determine biomarkers for AF diagnosis or prediction. Sixty atrial appendage samples (AF group: 30; non-AF group: 30) and 163 plasma samples (AF group: 48; non-AF group: 115) from 49 AF patients and 116 non-AF patients were subjected to liquid chromatography positive ion electrospray ionization tandem mass spectrometry (LC-ESI-MS/MS) metabolomics analysis. Consequently, 24 metabolites in atrial appendage samples and 24 metabolites in plasma samples were found to reflect metabolic differences between AF and non-AF patients (variable importance in projection (VIP) ≥ 1, P ≤ 0.05). Five identical metabolites including creatinine, D-glutamic acid, choline, hypoxanthine, and niacinamide (VIP ≥ 1.5, P < 0.01, FDR < 0.05) in atrial appendage and plasma samples were considered prominent features of AF patients, and the D-glutamine and D-glutamate metabolic pathway was also identified as a feature of AF patients. Finally, in plasma samples, the combination of D-glutamic acid, creatinine, and choline had an AUC value of 0.927 (95% CI: 0.875-0.979, P < 0.001) and displayed 90.5% sensitivity and 83.3% specificity; this group of metabolites was thus defined as a combinational biomarker for the recognition of AF and non-AF patients.

Incidence and impact of atrial arrhythmias on thrombotic events in MPNs

Atrial arrhythmias (AA) induce a high rate of thromboses and require vitamin K antagonists (VKA) or direct anticoagulants (DOAC) prescriptions. Essential thrombocythemia (ET) and polycythemia vera (PV) are also pro-thrombotic diseases. The prevention of thromboses is based on the association of cytoreductive drug and low-dose aspirin (LDA). We studied the incidence and complications of AA among patients with ET or PV. We identified 96/713 patients (13.5%) carrying AA. These patients were older (median 72.1 vs. 61.3 years old, p < 0.0001). In a case-control analysis, we observed that patients with AA had a higher frequency of cardiovascular risk factors (77/96, 80% vs. 61/96, 61%; p = 0.01). A higher incidence of thromboses before and after myeloproliferative neoplasm (MPN) diagnosis was seen in this group: 26/96, 27.1% vs. 14/96, 14.6% (p = 0.03) and 34/96, 35% vs. 18/96, 18.8% (p = 0.009). Most of the events were arterial (82 vs. 61%, p = 0.09). This translates into a shorter thrombosis-free survival (11.0 vs. 21.6 years, p = 0.01). Continuation of LDA in this situation exposed patients to more thrombotic events (p = 0.04) but VKA did not seem to be good anticoagulant drugs either. The association of AA and MPN is more frequent than expected. AA clearly increased the thrombotic risk of these patients. Anticoagulant drugs should be carefully managed between cardiologists and hematologists. Association of LDA and VKA or the role of DOAC in such population should be rapidly discussed to reduce the thrombotic rate.

The crucial role of activin A/ALK4 pathway in the pathogenesis of Ang-II-induced atrial fibrosis and vulnerability to atrial fibrillation

Atrial fibrosis, the hallmark of structural remodeling associated with atrial fibrillation (AF), is characterized by abnormal proliferation of atrial fibroblasts and excessive deposition of extracellular matrix. Transforming growth factor-β1 (TGF-β1)/activin receptor-like kinase 5 (ALK5)/Smad2/3/4 pathway has been reported to be involved in the process. Recent studies have implicated both activin A and its specific downstream component activin receptor-like kinase 4 (ALK4) in stimulating fibrosis in non-cardiac organs. We recently reported that ALK4 haplodeficiency attenuated the pressure overload- and myocardial infarction-induced ventricular fibrosis. However, the role of activin A/ALK4 in the pathogenesis of atrial fibrosis and vulnerability to AF remains unknown. Our study provided experimental and clinical evidence for the involvement of activin A and ALK4 in the pathophysiology of atrial fibrosis and AF. Patients with AF had higher activin A and ALK4 expression in atriums as compared to individuals devoid of AF. After angiotensin-II (Ang-II) stimulation which mimicked atrial fibrosis progression, ALK4-deficient mice showed lower expression of ALK4 in atriums, reduced activation of atrial fibroblasts, blunted atrial enlargement and atrial fibrosis, and further reduced AF vulnerability upon right atrial electrophysiological studies as compared to wild-type littermates. Moreover, we found that apart from the well-known TGF-β1/ALK5 pathway, the activation of activin A/ALK4/smad2/3 pathway played an important role in the pathogenesis of Ang-II-mediated atrial fibrosis and inducibility of AF, suggesting that targeting ALK4 might be a potential therapy for atrial fibrosis and AF.

Causes of death in atrial fibrillation: Challenges and opportunities

Atrial fibrillation (AF) is an age-related arrhythmia associated with several co-morbidities and significant mortality. Most AF patients are in need of anticoagulation due to increased risk of stroke. Despite anticoagulation, AF patients still have a significant risk of death (about 5%/y). Approximately half of deaths in AF are due to heart-related causes (i.e., sudden death, heart failure, and myocardial infarction), one-third of deaths are due to non-vascular causes (i.e., cancer, respiratory diseases, and infections) and the remaining AF patients die from stroke or hemorrhage (about 6% each), or other causes. This review describes current situations related to causes of death in AF, the challenges in the management of AF (e.g., frequent presence of cardiovascular risk factors and co-morbidities, physicians adherence to clinical guidelines and patients adherence to cardiovascular medications in AF) as well as the opportunities for intervention.