Risk factors and genetics of atrial fibrillation. Cardiol Clin. 2014;32:485-494. [PMID: 25443231 DOI: 10.1016/j.ccl.2014.07.007]

Polygenic risk scores in atrial fibrillation: Associations and clinical utility in disease prediction

Atrial fibrillation (AF) is a common heart arrhythmia and a major cause of cardioembolic stroke. Therefore, accurate prediction is desirable to allow high-risk individuals to be identified early and their risk lowered before complications arise. Polygenic risk scores (PRSs) have become a popular method of quantifying aggregated genetic risk from common variants, but their clinical value in AF remains uncertain. This literature review summarizes the associations between PRS and AF risk and discusses the evidence for the clinical utility of PRS for AF prediction. Stroke risk in patients with AF is also considered. Despite consistent associations between PRS and AF risk, the performance of PRS as a stand-alone tool for AF prediction was poor. However, addition of PRS to the existing AF prediction models commonly improved the predictive performance above that of the clinical models alone, including in cohorts with comorbid cardiovascular disease. Associations between PRS and cardioembolic stroke risk in patients with AF have also been reported, but improvements in stroke prediction models from PRS have been minimal. PRS are likely to add value to the existing clinical AF prediction models; however, standardization of PRS across studies and populations will likely be required before they can be meaningfully adopted into routine clinical practice.

A New Player in the Game: Can Exergame Be of Support in the Management of Atrial Fibrillation?

Atrial fibrillation (AF) is the most common form of cardiac arrhythmia, currently affecting 2-3% of the world's population. Traditional exercise and physical activity interventions have been successfully implemented in the management of AF, with the aim of improving patients' quality of life and their exercise capacity, as well as reducing their mortality rate. Currently, new technology-mediated approaches to exercise, defined as exergame, have been shown to be successful in the delivery of exercise home-based interventions in patients with cardiovascular diseases. However, data on the effects of exergame on AF are not yet available. In this paper, we summarise the current literature on the role of traditional exercise in AF and how it affects the pathophysiology of this condition. We also review the current literature on exergame and its employment in cardiac rehabilitation and suggest its potential role in the management of AF patients. A review of the evidence suggests that traditional exercise (of light-to-moderate intensity) is beneficial in patients with AF. Additionally, exergame seems to be a promising approach for delivering exercise interventions in patients with cardiovascular diseases. Exergame may be a promising tool to improve the quality of life and exercise capacity in patients with AF, with the additional advantage of being remotely delivered, and the potential to increase patients' engagement. Proper guidelines are required to prescribe exergame interventions, considering the principles of traditional exercise prescription and applying them to this new e-health approach. Further studies are needed to validate the use of exergame in patients with AF.

At the heart of the matter: how mental stress and negative emotions affect atrial fibrillation

Atrial fibrillation (AF) is the most common form of cardiac arrhythmia, affecting 2%-3% of the world's population. Mental and emotional stress, as well as some mental health conditions (e.g., depression) have been shown to significantly impact the heart and have been suggested to act both as independent risk factors and triggers in the onset of AF. In this paper, we review the current literature to examine the role that mental and emotional stress have in the onset of AF and summarise the current knowledge on the interaction between the brain and heart, and the cortical and subcortical pathways involved in the response to stress. Review of the evidence suggests that mental and emotional stress negatively affect the cardiac system, potentially increasing the risk for developing and/or triggering AF. Further studies are required to further understand the cortical and sub-cortical structures involved in the mental stress response and how these interact with the cardiac system, which may help in defining new strategies and interventions to prevent the development of, and improve the management of AF.

Long non-coding RNA and circular RNA: new perspectives for molecular pathophysiology of atrial fibrillation

Many studies have demonstrated the association of atrial fibrillation (AF) with endogenous genetic regulatory mechanisms. These interactions could advance the understanding of the AF pathophysiological process, supporting the search for early biomarkers to improve diagnosis and disease monitoring. Among the endogenous genetic regulatory mechanisms, long non-coding RNAs (lncRNAs) and circular RNAs (circRNAs) have gained special attention, and studies have demonstrated their involvement in AF development and other AF-related diseases such as coronary artery disease and cardiomyopathy. This review describes the main experimental results reported by studies that analyzed the expression of lncRNAs and circRNAs in AF associated with miRNA or mRNA. The search was conducted in PubMed public database using the terms "lncRNA and atrial fibrillation" or "long ncRNA and atrial fibrillation" or "long non-coding RNA and atrial fibrillation" or "circular RNA and atrial fibrillation" or "circRNA and atrial fibrillation". There was no overlapping of lncRNA or circRNA among the studies, attributed to the different sample types, methods, species, and patient classification evaluated in these studies. Although the regulatory mechanisms in which these molecules are involved are not yet well understood, the studies analyzed show their importance in the pathophysiological process of AF, supporting the idea that lncRNAs and circRNAs are involved in miRNA or mRNA regulation in the molecular mechanism of this disease.

Genetic Basis of Early Onset Atrial Fibrillation in Patients without Risk Factors

BACKGROUND

Atrial fibrillation (AF) is the most common arrhythmia and typically occurs in elderly patients with other cardiovascular and extracardiac diseases. However, up to 15% of AF develops without any related risk factors. Recently, the role of genetic factors has been highlighted in this particular form of AF.

AIMS

The aims of this study were to determine the prevalence of pathogenic variants in early-onset AF in patients without known disease-related risk factors and to identify any structural cardiac abnormalities in these patients.

MATERIALS AND METHODS

We conducted exome sequencing and interpretation in 54 risk factor-free early-onset AF patients and further validated our findings in a similar AF patient cohort from the UK Biobank.

RESULTS

Pathogenic/likely pathogenic variants were found in 13/54 (24%) patients. The variants were identified in cardiomyopathy-related and not arrhythmia-related genes. The majority of the identified variants were TTN gene truncating variants (TTNtvs) (9/13 (69%) patients). We also observed two TTNtvs founder variants in the analysed population-c.13696C>T p.(Gln4566Ter) and c.82240C>T p.(Arg27414Ter). Pathogenic/likely pathogenic variants were found in 9/107 (8%) individuals from an independent similar AF patient cohort from the UK Biobank. In correspondence with our Latvian patients, only variants in cardiomyopathy-associated genes were identified. In five (38%) of the thirteen Latvian patients with pathogenic/likely pathogenic variants, dilation of one or both ventricles was identified on a follow-up cardiac magnetic resonance scan.

CONCLUSIONS

We observed a high prevalence of pathogenic/likely pathogenic variants in cardiomyopathy-associated genes in patients with risk factor-free early-onset AF. Moreover, our follow-up imaging data indicate that these types of patients are at risk of developing ventricular dilation. Furthermore, we identified two TTNtvs founder variants in our Latvian study population.

Identification of atrial-enriched lncRNA Walras linked to cardiomyocyte cytoarchitecture and atrial fibrillation

Atrial fibrillation (AF) is the most prevalent cardiac arrhythmia in humans. Genetic and genomic analyses have recently demonstrated that the homeobox transcription factor Pitx2 plays a fundamental role regulating expression of distinct growth factors, microRNAs and ion channels leading to morphological and molecular alterations that promote the onset of AF. Here we address the plausible contribution of long non-coding (lnc)RNAs within the Pitx2>Wnt>miRNA signaling pathway. In silico analyses of annotated lncRNAs in the vicinity of the Pitx2, Wnt8 and Wnt11 chromosomal loci identified five novel lncRNAs with differential expression during cardiac development. Importantly, three of them, Walaa, Walras, and Wallrd, are evolutionarily conserved in humans and displayed preferential atrial expression during embryogenesis. In addition, Walrad displayed moderate expression during embryogenesis but was more abundant in the right atrium. Walaa, Walras and Wallrd were distinctly regulated by Pitx2, Wnt8, and Wnt11, and Wallrd was severely elevated in conditional atrium-specific Pitx2-deficient mice. Furthermore, pro-arrhythmogenic and pro-hypertrophic substrate administration to primary cardiomyocyte cell cultures consistently modulate expression of these lncRNAs, supporting distinct modulatory roles of the AF cardiovascular risk factors in the regulation of these lncRNAs. Walras affinity pulldown assays revealed its association with distinct cytoplasmic and nuclear proteins previously involved in cardiac pathophysiology, while loss-of-function assays further support a pivotal role of this lncRNA in cytoskeletal organization. We propose that lncRNAs Walaa, Walras and Wallrd, distinctly regulated by Pitx2>Wnt>miRNA signaling and pro-arrhythmogenic and pro-hypertrophic factors, are implicated in atrial arrhythmogenesis, and Walras additionally in cardiomyocyte cytoarchitecture.

Possible key microRNAs and corresponding molecular mechanisms for atrial fibrillation

Objective:

We aimed to find crucial microRNAs (miRNAs) associated with the development of atrial fibrillation (AF), and then try to elucidate the possible molecular mechanisms of miRNAs in AF.

Methods:

The miRNA microarray, GSE68475, which included 10 right atrial appendage samples from patients with persistent AF and 11 samples from patients with normal sinus rhythm, was used for the analysis. After data preprocessing, differentially expressed miRNAs were screened using limma. Target genes of miRNAs were predicted using miRWalk2.0. We then conducted functional enrichment analyses for miRNA and target genes. Protein-protein interaction (PPI) network and module analyses for target genes were performed. Finally, transcription factors (TFs)-target genes regulatory network was predicted and constructed.

Results:

Seven genes, including CAMK2D, IGF2R, PPP2R2A, PAX6, POU3F2, YWHAE, and AP2A2, were targeted by TFs. Among these seven genes, CAMK2D (targeted by miR-31-5p), IGF2R (targeted by miR-204-5p), PAX6 (targeted by miR-223-3p), POU3F2 (targeted by miR-204-5p), YWHAE (targeted by miR-31-5p), and AP2A2 (targeted by miR-204-5p) belonged to the top 10 degree genes in the PPI network. Notably, MiR-204-5p, miR-31-5p, and miR-223-3p had more target genes. Besides, CAMK2D was enriched in some pathways, such as adrenergic signaling in cardiomyocytes pathway and cAMP signaling pathway. YWHAE was enriched in the Hippo signaling pathway.

Conclusion:

miR-31-5p played a crucial role in cardiomyocytes by targeting CAMK2D and YWHAE via cAMP and Hippo signaling pathways. miR-204 was involved in the progression of AF by regulating its target genes IGF2R, POU3F2, and AP2A2. On the other hand, miR-223-3p functioned in AF by targeting PAX6, which was associated with the regulation of apoptosis in AF. This study would provide a theoretical basis and potential therapeutic targets for the treatment of AF.

BIRC5, GAJ5, and lncRNA NPHP3-AS1 Are Correlated with the Development of Atrial Fibrillation-Valvular Heart Disease

The aim of this study was to explore the pivotal genes or lncRNAs involved in the progression of atrial fibrillation (AF) -valvular heart disease (VHD). The mRNA profiling GSE113013 was obtained from the Gene Expression Omnibus database. The identification of differentially expressed genes (DEGs) and differentially expressed long non-coding RNAs (DElncRNAs) was performed. Gene Ontology and Kyoto Encyclopedia of Genes and Genomes pathway enrichment analyses were carried out for DEGs. Then, the construction of the protein-protein interaction (PPI) network was conducted. An lncRNA-miRNA-target ceRNA network was constructed after obtaining microRNAs (miRNA) related to DElncRNAs. Ultimately, key disease-related genes were screened. A total of 399 DEGs and 145 DElncRNAs were obtained. There were 283 nodes and 588 interaction pairs in the PPI network, and synaptosome-associated protein 25 (SNAP25) had higher degrees (degree = 22) in the PPI network. There were 65 interaction pairs in the ceRNA network. Here, Baculoviral IAP Repeat Containing 5 (BIRC5) was regulated by hsa-miR-1285-3p, which was regulated by lncRNA NPHP3-AS1. Gap Junction Protein Alpha 5 (GAJ5) was regulated by hsa-miR-4505, hsa-miR-1972, and hsa-miR-1199-5p. In particular, GAJ5 was enriched in the function of ion transmembrane transport regulation, whereas BIRC5 was enriched in the function of apoptosis-multiple species pathway. Similarly, Potassium Inwardly Rectifying Channel Subfamily J Member 6 (KCNJ6) was enriched in the function of an ion channel complex. VENN analysis identified BIRC5 and GJA5 as key AF-related genes. KCNJ6, SNAP25, GJA5, BIRC5, hsa-miR-1285-3p, and lncRNA NPHP3-AS1 were likely to be associated with AF-VHD development.

MR-proANP level predicts new onset atrial fibrillation in patients with acute myocardial infarction

OBJECTIVE

MR-pro ANP is a novel peptide with multiple biological functions, especially within the cardiovascular system. It plays an important role in physiological and pathological processes in the human body and its level may be clinically relevant in new onset atrial fibrillation. The aim of this study was to determine whether elevated MR-proANP level is a predictor of new-onset atrial fibrillation in patients with acute myocardial infarction.

METHODS AND RESULTS

The study included 96 patients with their first diagnosis of acute myocardial infarction hospitalized in the Department of Interventional Cardiology within one year. The plasma levels of MR-proANP were determined on admission, and on the first and fifth day of hospitalisation by BRAHMS MRproANP KRYPTOR. New onset AF was diagnosed in 9.4% of patients during hospitalisation; the level of MR proANP was also found to be significantly higher in this group of patients compared to those without arrhythmia (p = 0.017). ROC curve analysis indicates that the concentration of MR-proANP is a good predictor of AF diagnosed during the hospitalisation in patients with acute myocardial infarction (AUC = 0.738, p = 0.0011).

CONCLUSIONS

MR-proANP might be a good predictor of new-onset atrial fibrillation in patients with acute myocardial infarction.

Analysis of mitochondrial m1A/G RNA modification reveals links to nuclear genetic variants and associated disease processes

RNA modifications affect the stability and function of RNA species, regulating important downstream processes. Modification levels are often dynamic, varying between tissues and individuals, although it is not always clear what modulates this or what impact it has on biological systems. Here, we quantify variation in m1A/G RNA modification levels at functionally important positions in the human mitochondrial genome across 11,552 samples from 39 tissue/cell types and find that modification levels are associated with mitochondrial transcript processing. We identify links between mitochondrial RNA modification levels and genetic variants in the nuclear genome, including a missense mutation in LONP1, and find that genetic variants within MRPP3 and TRMT61B are associated with RNA modification levels across a large number of tissues. Genetic variants linked to RNA modification levels are associated with multiple disease/disease-related phenotypes, including blood pressure, breast cancer and psoriasis, suggesting a role for mitochondrial RNA modification in complex disease.

Ali et al. analyze publicly available RNA-seq data from different tissues to quantify variation in m1A/G methylation levels in mitochondrial RNAs. They show a link between mitochondrial m1A/G modification levels and nuclear genetic variants, many of which are associated with disease.

A Case of an Acute Attack of Atrial Fibrillation following Intake of Etoricoxib for Pain Relief

Atrial fibrillation (AF) is one of the most common rhythm disorders observed in clinical practice and is predominantly associated with coronary heart disease and hypertension. However, different classes of drugs may induce AF as a side effect in patients without apparent heart disease or they may precipitate the onset of AF in patients with preexisting heart disease. This case report includes etoricoxib-induced acute AF in a patient with hypertension.

Genetics of Atrial Fibrilation: In Search of Novel Therapeutic Targets

Atrial fibrillation (AF) is the most frequent arrhythmogenic disease in humans, ranging from 2% in the general population and rising up to 10-12% in 80+ years. Genetic analyses of AF familiar cases have identified a series of point mutations in distinct ion channels, supporting a causative link. However, these genetic defects only explain a minority of AF patients. Genomewide association studies identified single nucleotide polymorphisms (SNPs), close to PITX2 on 4q25 chromosome, that are highly associated to AF. Subsequent GWAS studies have identified several new loci, involving additional transcription and growth factors. Furthermore, these risk 4q25 SNPs serve as surrogate biomarkers to identify AF recurrence in distinct surgical and pharmacological interventions. Experimental studies have demonstrated an intricate signalling pathway supporting a key role of the homeobox transcription factor PITX2 as a transcriptional regulator. Furthermore, cardiovascular risk factors such as hyperthyroidism, hypertension and redox homeostasis have been identified to modulate PITX2 driven gene regulatory networks. We provide herein a state-of-the-art review of the genetic bases of atrial fibrillation, our current understanding of the genetic regulatory networks involved in AF and its plausible usage for searching novel therapeutic targets.

Genomic Variants in NEURL, GJA1 and CUX2 Significantly Increase Genetic Susceptibility to Atrial Fibrillation

Atrial fibrillation (AF) is the most common arrhythmia. In 2014, two new meta-GWAS identified 5 AF loci, including the NEURL locus, GJA1 locus, CAND2 locus, and TBX5 locus in the European ancestry populations and the NEURL locus and CUX2 locus in a Japanese population. The TBX5 locus for AF was reported by us in 2013 in the Chinese population. Here we assessed the association between AF and SNPs in the NEURL, GJA1, CAND2 and CUX2 loci in the Chinese Han population. We carried out a large case-control association study with 1,164 AF patients and 1,460 controls. Significant allelic and genotypic associations were identified between NEURL variant rs6584555 and GJA1 variant rs13216675 and AF. Significant genotypic association was found between CUX2 SNP rs6490029 and AF. No association was found between CAND2 variant rs4642101 and AF, which may be due to an insufficient power of the sample size for rs4642101. Together with our previous findings, seven of fifteen AF loci (<50%) identified by GWAS in the European ancestry populations conferred susceptibility to AF in the Chinese population, and explained approximately 14.5% of AF heritability. On the other hand, two AF loci identified in the Japanese population were both replicated in the Chinese population.

Hyperthyroidism, but not hypertension, impairs PITX2 expression leading to Wnt-microRNA-ion channel remodeling

PITX2 is a homeobox transcription factor involved in embryonic left/right signaling and more recently has been associated to cardiac arrhythmias. Genome wide association studies have pinpointed PITX2 as a major player underlying atrial fibrillation (AF). We have previously described that PITX2 expression is impaired in AF patients. Furthermore, distinct studies demonstrate that Pitx2 insufficiency leads to complex gene regulatory network remodeling, i.e. Wnt>microRNAs, leading to ion channel impairment and thus to arrhythmogenic events in mice. Whereas large body of evidences has been provided in recent years on PITX2 downstream signaling pathways, scarce information is available on upstream pathways influencing PITX2 in the context of AF. Multiple risk factors are associated to the onset of AF, such as e.g. hypertension (HTN), hyperthyroidism (HTD) and redox homeostasis impairment. In this study we have analyzed whether HTN, HTD and/or redox homeostasis impact on PITX2 and its downstream signaling pathways. Using rat models for spontaneous HTN (SHR) and experimentally-induced HTD we have observed that both cardiovascular risk factors lead to severe Pitx2 downregulation. Interesting HTD, but not SHR, leads to up-regulation of Wnt signaling as well as deregulation of multiple microRNAs and ion channels as previously described in Pitx2 insufficiency models. In addition, redox signaling is impaired in HTD but not SHR, in line with similar findings in atrial-specific Pitx2 deficient mice. In vitro cell culture analyses using gain- and loss-of-function strategies demonstrate that Pitx2, Zfhx3 and Wnt signaling influence redox homeostasis in cardiomyocytes. Thus, redox homeostasis seems to play a pivotal role in this setting, providing a regulatory feedback loop. Overall these data demonstrate that HTD, but not HTN, can impair Pitx2>>Wnt pathway providing thus a molecular link to AF.

Effects of Atorvastatin on Serum High-Sensitive C-Reactive Protein and Total Cholesterol Levels in Asian Patients With Atrial Fibrillation

Elevated serum levels of high-sensitive C-reactive protein (hs-CRP) and total cholesterol (TC) correlate with atherosclerotic vascular disease and increased frequency of vascular events. In this study, we investigated the effect of atorvastatin treatment on serum hs-CRP and TC levels, and the recurrence rate of atrial fibrillation (AF) in patients. Furthermore, a meta-analysis was performed to confirm the findings in this study. A total of 105 patients with AF were recruited to this study, including 55 patients with AF who were treated with amiodarone and atorvastatin (the treatment group) and 50 patients with AF who were treated with only amiodarone (the control group). Patients were treated for 12 months and followed up regularly for 1 year. Serum hs-CRP and TC levels in patients before and after treatment were recorded, and AF recurrence rate at 3, 6, and 12 months of treatment was obtained. Statistical analyses were performed with R 3.1.0 software and STATA 12.0 software. For patients in both treatment and control groups, serum hs-CRP and TC levels were high before the treatments began (both P < 0.05). However, after 12 months of treatment, serum hs-CRP and TC levels in the treatment group was dramatically reduced compared with the control group (hs-CRP: 3.63 ± 2.14 mg/L vs. 2.75 ± 1.89 mg/L, t = 2.24, P = 0.027; TC: 4.66 ± 1.13 mmol/L vs. 4.20 ± 1.06 mmol/L, t = 2.15, P = 0.034). After 12 months of treatment, the AF recurrence rate in the treatment group was significantly lower than the control group (16.4% vs. 34.0%; χ = 4.37; P = 0.037). In addition, 13 studies were selected for meta-analysis. Pooled results of the meta-analysis showed that serum hs-CRP and TC levels decreased significantly in the treatment group compared with the case group [hs-CRP: SMD = 0.95, 95% confidence interval (CI) = 0.62-1.29, and P < 0.001; TC: SMD = 1.39, 95% CI = 0.65-2.13, and P < 0.001]. Our study presents compelling evidence that atorvastatin is highly effective in reducing serum hs-CRP and TC levels and lowering the recurrence rate of AF.

Gene regulatory networks in atrial fibrillation

Atrial fibrillation (AF) is the most frequent arrhythmogenic syndrome in humans. With an estimate incidence of 1%-2% in the general population, AF raises up to almost 10%-12% in 80+ years. Thus, AF represents nowadays a highly prevalent medical problem generating a large economic burden. At the electrophysiological level, distinct mechanisms have been elucidated. Yet, despite its prevalence, the genetic and molecular culprits of this pandemic cardiac electrophysiological abnormality have remained largely obscure. Molecular genetics of AF familiar cases have demonstrated that single nucleotide mutations in distinct genes encoding for ion channels underlie the onset of AF, albeit such alterations only explain a minor subset of patients with AF. In recent years, analyses by means of genome-wide association studies have unraveled a more complex picture of the etiology of AF, pointing out to distinct cardiac-enriched transcription factors, as well as to other regulatory genes. Furthermore a new layer of regulatory mechanisms have emerged, i.e., post-transcriptional regulation mediated by non-coding RNA, which have been demonstrated to exert pivotal roles in cardiac electrophysiology. In this manuscript, we aim to provide a comprehensive review of the genetic regulatory networks that if impaired exert electrophysiological abnormalities that contribute to the onset, and subsequently, on self-perpetuation of AF.

Cardiac Fibrosis in Patients With Atrial Fibrillation: Mechanisms and Clinical Implications

Atrial fibrillation (AF) is associated with structural, electrical, and contractile remodeling of the atria. Development and progression of atrial fibrosis is the hallmark of structural remodeling in AF and is considered the substrate for AF perpetuation. In contrast, experimental and clinical data on the effect of ventricular fibrotic processes in the pathogenesis of AF and its complications are controversial. Ventricular fibrosis seems to contribute to abnormalities in cardiac relaxation and contractility and to the development of heart failure, a common finding in AF. Given that AF and heart failure frequently coexist and that both conditions affect patient prognosis, a better understanding of the mutual effect of fibrosis in AF and heart failure is of particular interest. In this review paper, we provide an overview of the general mechanisms of cardiac fibrosis in AF, differences between fibrotic processes in atria and ventricles, and the clinical and prognostic significance of cardiac fibrosis in AF.