Impact of Genetic Discoveries on the Classification of Lone Atrial Fibrillation

Exploring SCN5A variants associated with atrial fibrillation in atrial cardiomyocytes derived from human induced pluripotent stem cells: A characterization study

BACKGROUND

Atrial fibrillation (AF) poses a major risk for heart failure, myocardial infarction, and stroke. Several studies have linked SCN5A variants to AF, but their precise mechanistic contribution remains unclear. Human induced pluripotent stem cells (hiPSCs) provide a promising platform for modeling AF-linked SCN5A variants and their functional alterations.

OBJECTIVE

The purpose of this study was to assess the electrophysiological impact of 3 AF-linked SCN5A variants (K1493R, M1875T, N1986K) identified in 3 unrelated individuals.

METHODS

CRISPR-Cas9 was used to generate a new hiPSC line in which NaV1.5 was knocked out. Following differentiation into specific atrial cardiomyocyte by using retinoic acid, the adult wild-type (WT) and 3 AF variants were introduced into the NaV1.5 knockout (KO) line through transfection. Subsequent analysis including molecular biology, optical mapping, and electrophysiology were performed.

RESULTS

The absence of NaV1.5 channels altered the expression of key cardiac genes. NaV1.5 KO atrial-like cardiomyocytes derived from human induced pluripotent stem cells displayed slower conduction velocities, altered action potential (AP) parameters, and impaired calcium transient propagation. The transfection of the WT channel restored sodium current density, AP characteristics and the expression of several cardiac genes. Among the AF variants, 1 induced a loss of function (N1986K) while the other 2 induced a gain of function in NaV1.5 channel activity. Cellular excitability alterations and early afterdepolarizations were observed in AF variants.

CONCLUSION

Our findings suggest that distinct alterations in NaV1.5 channel properties may trigger altered atrial excitability and arrhythmogenic activity in AF. Our KO model offers an innovative approach for investigating SCN5A variants in an adult human cardiac environment.

Clinical Genetic Testing for Atrial Fibrillation: Are We There Yet?

Important progress has been made toward unravelling the complex genetics underlying atrial fibrillation (AF). Initial studies were aimed to identify monogenic causes; however, it has become increasingly clear that the most common predisposing genetic substrate for AF is polygenic. Despite intensive investigations, there is robust evidence for rare variants for only a limited number of genes and cases. Although the current yield for genetic testing in early onset AF might be modest, there is an increasing appreciation that genetic culprits for potentially life-threatening ventricular cardiomyopathies and channelopathies might initially present with AF. The potential clinical significance of this recognition is highlighted by evidence that suggests that identification of a pathogenic or likely pathogenic rare variant in a patient with early onset AF is associated with an increased risk of death. These findings suggest that it might be warranted to screen patients with early onset AF for these potentially more sinister cardiac conditions. Beyond facilitating the early identification of genetic culprits associated with potentially malignant phenotypes, insight into underlying AF genetic substrates might improve the selection of patients for existing therapies and guide the development of novel ones. Herein, we review the evidence that links genetic factors to AF, then discuss an approach to using genetic testing for early onset AF patients in the present context, and finally consider the potential value of genetic testing in the foreseeable future. Although further work might be necessary before recommending uniform integration of genetic testing in cases of early onset AF, ongoing research increasingly highlights its potential contributions to clinical care.

Two Novel Functional Mutations in Promoter Region of SCN3B Gene Associated with Atrial Fibrillation

The sodium voltage-gated channel beta subunit 3 (SCN3B) plays a crucial role in electrically excitable cells and conduction tissue in the heart. Some previous studies have established that genetic modification in sodium voltage-channel genes encoding for the cardiac β-subunits, such as SCN1B, SCN2B, SCN3B and SCN4B, can result in atrial fibrillation (AF). In the current study, we identified two rare variants in 5′UTR (NM_018400.4: c.-324C>A, rs976125894 and NM_018400.4: c.-303C>T, rs1284768362) of SCN3B in two unrelated lone AF patients. Our further functional studies discovered that one of them, the A allele of c.-324C>A (rs976125894), can improve transcriptional activity and may raise SCN3B expression levels. The A allele of c.-324C>A (rs976125894) has higher transcriptional activity when it interacts with GATA4, as we confirmed transcription factor GATA4 is a regulator of SCN3B. To the best of our knowledge, the current study is the first to demonstrate that the gain-of-function mutation of SCN3B can produce AF and the first to link a mutation occurring in the non-coding 5′UTR region of SCN3B to lone AF. The work also offers empirical proof that GATA4 is a critical regulator of SCN3B gene regulation. Our findings may serve as an encyclopedia for AF susceptibility variants and can also provide insight into the investigation of the functional mechanisms behind AF variants discovered by genetic methods.

Mining of Potential Biomarkers and Pathway in Valvular Atrial Fibrillation (VAF) via Systematic Screening of Gene Coexpression Network

Purpose. We apply the bioinformatics method to excavate the potential genes and therapeutic targets associated with valvular atrial fibrillation (VAF). Methods. The downloaded gene expression files from the gene expression omnibus (GEO) included patients with primary severe mitral regurgitation complicated with sinus or atrial fibrillation rhythm. Subsequently, the differential gene expression in left and right atrium was analyzed by R software. Additionally, weighted correlation network analysis (WGCNA), principal component analysis (PCA), and linear model for microarray data (LIMMA) algorithm were used to determine hub genes. Then, Metascape database, DAVID database, and STRING database were used to annotate and visualize the gene ontology (GO) analysis, KEGG pathway enrichment analysis, and PPI network analysis of differentially expressed genes (DEGs). Finally, the TFs and miRNAs were predicted by using online tools, such as PASTAA and miRDB. Results. 20,484 differentially expressed genes related to atrial fibrillation were obtained through the analysis of left and right atrial tissue samples of GSE115574 gene chip, and 1,009 were with statistical significance, including 45 upregulated genes and 964 downregulated genes. And the hub genes implicated in AF of NPC2, ODC1, SNAP29, LAPTM5, ST8SIA5, and FCGR3B were screened. Finally, the main regulators of targeted candidate biomarkers and microRNAs, EIF5A2, HIF1A, ZIC2, ELF1, and STAT2, were found in this study. Conclusion. These hub genes, NPC2, ODC1, SNAP29, LAPTM5, ST8SIA5, and FCGR3B, are important for the development of VAF, and their enrichment pathways and TFs elucidate the involved molecular mechanisms and assist in the validation of drug targets.

The Atrium in Atrial Fibrillation - A Clinical Review on How to Manage Atrial Fibrotic Substrates

Atrial fibrillation (AF) is the most common sustained arrhythmia in the population and is associated with a significant clinical and economic burden. Rigorous assessment of the presence and degree of an atrial arrhythmic substrate is essential for determining treatment options, predicting long-term success after catheter ablation, and as a substrate critical in the pathophysiology of atrial thrombogenesis. Catheter ablation of AF has developed into an essential rhythm-control strategy. Nowadays is one of the most common cardiac ablation procedures performed worldwide, with its success inversely related to the extent of atrial structural disease. Although atrial substrate evaluation remains complex, several diagnostic resources allow for a more comprehensive assessment and quantification of the extent of left atrial structural remodeling and the presence of atrial fibrosis. In this review, we summarize the current knowledge on the pathophysiology, etiology, and electrophysiological aspects of atrial substrates promoting the development of AF. We also describe the risk factors for its development and how to diagnose its presence using imaging, electrocardiograms, and electroanatomic voltage mapping. Finally, we discuss recent data regarding fibrosis biomarkers that could help diagnose atrial fibrotic substrates.

Genetics of atrial fibrillation-an update of recent findings

Atrial fibrillation (AF) is a common cardiac arrhythmia and a major risk factor for stroke, heart failure, and premature death. AF has a strong genetic predisposition. This review highlights the recent findings on the genetics of AF from genome-wide association studies (GWAS) and high-throughput sequencing studies. The consensus from GWAS implies that AF is both polygenic and pleiotropic in nature. With the advent of whole-genome sequencing and whole-exome sequencing, rare variants associated with AF pathogenesis have been identified. The recent studies have contributed towards better understanding of AF pathogenesis.

Association between ZFHX3 and PRRX1 Polymorphisms and Atrial Fibrillation Susceptibility from Meta-Analysis

Background

Atrial fibrillation (AF) is a common, sustained cardiac arrhythmia. Recent studies have reported an association between ZFHX3/PRRX1 polymorphisms and AF. In this study, a meta-analysis was conducted to confirm these associations. Objective and Methods. The PubMed, Embase, and Wanfang databases were searched, covering all publications before July 20, 2020.

Results

Overall, seven articles including 3,674 cases and 8,990 healthy controls for ZFHX3 rs2106261 and 1045 cases and 1407 controls for PRRX1 rs3903239 were included. The odds ratio (OR) (95% confidence interval (CI)) was used to assess the associations. Publication bias was calculated using Egger's and Begg's tests. We found that the ZFHX3 rs2106261 polymorphism increased AF risk in Asians (for example, allelic contrast: OR [95% CI]: 1.39 [1.31–1.47], P < 0.001). Similarly, strong associations were detected through stratified analysis using source of control and genotype methods (for example, allelic contrast: OR [95% CI]: 1.51 [1.38–1.64], P < 0.001 for HB; OR [95% CI]: 1.31 [1.21–1.41], P < 0.001 for PB; OR [95% CI]: 1.55 [1.33–1.80], P < 0.001 for TaqMan; and OR [95% CI]: 1.31 [1.21–1.41], P < 0.001 for high-resolution melt). In contrast, an inverse relationship was observed between the PRRX1 rs3903239 polymorphism and AF risk (C-allele vs. T-allele: OR [95% CI]: 0.83 [0.77–0.99], P=0.036; CT vs. TT: OR [95% CI]: 0.79 [0.67–0.94], P=0.006). No obvious evidence of publication bias was observed.

Conclusions

In summary, our study suggests that the ZFHX3 rs2106261 and PRRX1 rs3903239 polymorphisms are associated with AF risk, and larger case-controls must be carried out to confirm the abovementioned conclusions.

Connexin45 (GJC1) loss-of-function mutation contributes to familial atrial fibrillation and conduction disease

BACKGROUND

Atrial fibrillation (AF) represents the most common clinical cardiac arrhythmia and substantially increases the risk of cerebral stroke, heart failure, and death. Although causative genes for AF have been identified, the genetic determinants for AF remain largely unclear.

OBJECTIVE

This study aimed to investigate the molecular basis of AF in a Chinese kindred.

METHODS

A 4-generation family with autosomal-dominant AF and other arrhythmias (atrioventricular block, sinus bradycardia, and premature ventricular contractions) was recruited. Genome-wide scan with microsatellite markers and linkage analysis as well as whole-exome sequencing analysis were performed. Electrophysiological characteristics and subcellular localization of the AF-linked mutant were analyzed using dual whole-cell patch clamps and confocal microscopy, respectively.

RESULTS

A novel genetic locus for AF was mapped to chromosome 17q21.3, a 3.23-cM interval between markers D17S951 and D17S931, with a maximum 2-point logarithm of odds score of 4.2144 at marker D17S1868. Sequencing analysis revealed a heterozygous mutation in the mapping region, NM_005497.4:c.703A>T;p.(M235L), in the GJC1 gene encoding connexin45 (Cx45). The mutation cosegregated with AF in the family and was absent in 632 control individuals. The mutation decreased the coupling conductance in cell pairs (M235L/M235L, M235L/Cx45, M235L/Cx43, and M235L/Cx40), likely because of impaired subcellular localization.

CONCLUSION

This study defines a novel genetic locus for AF on chromosome 17q21.3 and reveals a loss-of-function mutation in GJC1 (Cx45) contributing to AF and other cardiac arrhythmias.

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.

Predicting atrial fibrillation using a combination of genetic risk score and clinical risk factors

BACKGROUND

Atrial fibrillation (AF) has a genetic basis, and environmental factors can modify its actual pathogenesis.

OBJECTIVE

The purpose of this study was to construct a combined risk assessment method including both genetic and clinical factors in the Japanese population.

METHODS

We screened a cohort of 540 AF patients and 520 non-AF controls for single nucleotide polymorphisms (SNPs) previously associated with AF by genome-wide association studies. The most strongly associated SNPs after propensity score analysis were then used to calculate a weighted genetic risk score (WGRS). We also enrolled 1018 non-AF Japanese subjects as a validation cohort and monitored AF emergence over several years. Finally, we constructed a logistic model for AF prediction combining WGRS and clinical risk factors.

RESULTS

We identified 5 SNPs (in PRRX1, ZFHX3, PITX2, HAND2, and NEURL1) associated with AF after Bonferroni correction. There was a 4.92-fold difference in AF risk between the highest and lowest WGRS calculated using these 5 SNPs (P = 2.32 × 10^-10). Receiver operating characteristic analysis of WGRS yielded an area under the curve (AUC) of 0.73 for the screening cohort and 0.72 for the validation cohort. The predictive logistic model constructed using a combination of WGRS and AF clinical risk factors (age, body mass index, sex, and hypertension) demonstrated better discrimination of AF than WGRS alone (AUC = 0.84; sensitivity 75.4%; specificity 80.2%).

CONCLUSION

This novel predictive model of combined AF-associated SNPs and known clinical risk factors can accurately stratify AF risk in the Japanese population.

Nocturnal Atrial Fibrillation Caused by Mutation in KCND2, Encoding Pore-Forming (α) Subunit of the Cardiac Kv4.2 Potassium Channel

BACKGROUND

Paroxysmal atrial fibrillation (AF) can be caused by gain-of-function mutations in genes, encoding the cardiac potassium channel subunits KCNJ2, KCNE1, and KCNH2 that mediate the repolarizing potassium currents I_k1, I_ks, and I_kr, respectively.

METHODS

Linkage analysis, whole-exome sequencing, and Xenopus oocyte electrophysiology studies were used in this study.

RESULTS

Through genetic studies, we showed that autosomal dominant early-onset nocturnal paroxysmal AF is caused by p.S447R mutation in KCND2, encoding the pore-forming (α) subunit of the Kv4.2 cardiac potassium channel. Kv4.2, along with Kv4.3, contributes to the cardiac fast transient outward K⁺ current, I_to. I_to underlies the early phase of repolarization in the cardiac action potential, thereby setting the initial potential of the plateau phase and governing its duration and amplitude. In Xenopus oocytes, the mutation increased the channel's inactivation time constant and affected its regulation: p.S447 resides in a protein kinase C (PKC) phosphorylation site, which normally allows attenuation of Kv4.2 membrane expression. The mutant Kv4.2 exhibited impaired response to PKC; hence, Kv4.2 membrane expression was augmented, enhancing potassium currents. Coexpression of mutant and wild-type channels (recapitulating heterozygosity in affected individuals) showed results similar to the mutant channel alone. Finally, in a hybrid channel composed of Kv4.3 and Kv4.2, simulating the mature endogenous heterotetrameric channel underlying I_to, the p.S447R Kv4.2 mutation exerted a gain-of-function effect on Kv4.3.

CONCLUSIONS

The mutation alters Kv4.2's kinetic properties, impairs its inhibitory regulation, and exerts gain-of-function effect on both Kv4.2 homotetramers and Kv4.2-Kv4.3 heterotetramers. These effects presumably increase the repolarizing potassium current I_to, thereby abbreviating action potential duration, creating arrhythmogenic substrate for nocturnal AF. Interestingly, Kv4.2 expression was previously shown to demonstrate circadian variation, with peak expression at daytime in murine hearts (human nighttime), with possible relevance to the nocturnal onset of paroxysmal AF symptoms in our patients. The atrial-specific phenotype suggests that targeting Kv4.2 might be effective in the treatment of nocturnal paroxysmal AF, avoiding adverse ventricular effects.

The research of ion channel-related gene polymorphisms with atrial fibrillation in the Chinese Han population

BACKGROUND

Atrial fibrillation (AF) is one of the common arrhythmia in clinics. Its incidence is high among the elderly. This study aimed to identify a possible connection between ion channel-related gene polymorphisms and the risk of AF.

METHODS

A total of 381 patients with coronary heart disease were recruited. Based on complete cardiac examination, the patients were divided into two subgroups: 185 patients with AF and 196 patients without AF. An association analysis was performed using 13 genotyped SNPs. Odds ratios (ORs) and 95% confidence intervals (95% CIs) were calculated by conditional logistic regression.

RESULTS

In our research, we found that KCNE2 rs8134775 was associated with a decreased AF risk in the allele model (OR = 0.70; 95% CI: 0.50-0.97; p = 0.034). Genetic model analysis shown that the minor allele T of GJA5 rs35594137 was associated with a decreased AF risk under the recessive model (OR = 0.40; 95% CI: 0.19-0.86; p = 0.018) and the minor allele G of KCNJ2 rs8079702 was associated with an increased AF risk in the recessive model (OR = 2.31; 95% CI: 1.20-4.42; p = 0.012).

CONCLUSIONS

Our results suggest that KCNE2, KCNJ2, and GJA5 influence the development of AF.

Genetic, Epigenetic and Transcription Factors in Atrial Fibrillation

Atrial fibrillation (AF) is one of the most common arrhythmia that occurs in patients with cardiovascular diseases. Congenital forms of AF are quite rare. Many studies have shown that genetic, epigenetic and transcription factors may play an important role in the development and the progression of AF. In our review, studies have been conducted on the identification of mutations in ionic and non-ionic channels, possibly associated with AF. These mutations were found only in isolated groups of patients with AF, and in general, monogenic forms of AF are a rare subtype of the disease. Genomic association studies have helped to identify potential links between single nucleotide polymorphisms and AF. The risk of AF in the general population is likely to be determined by the interaction between environmental factors and many alleles. In recent years, the emergence of a genome-wide associative studies has significantly expanded the understanding of the genetic basis for the inheritance of AF and has led to the emergence of new evidence of the important role of genetic factors in the development of AF, in the risk stratification of AF and the recurrence of AF. Epigenetic factors are also important in AF. Epigenetic therapy aimed at treating a disease through exposure to epigenome is currently under development. A newly emerged area of ablatogenomics includes the use of genetic profiles that allow assessing the likelihood of recurrence of AF after catheter ablation. The results of genetic studies in AF show that, in addition to their role in the appearance of congenital heart pathologies, transcription factors play an important role in the pathogenesis of AF.

Atrial Fibrillation Mechanisms and Implications for Catheter Ablation

AF is a heterogeneous rhythm disorder that is related to a wide spectrum of etiologies and has broad clinical presentations. Mechanisms underlying AF are complex and remain incompletely understood despite extensive research. They associate interactions between triggers, substrate and modulators including ionic and anatomic remodeling, genetic predisposition and neuro-humoral contributors. The pulmonary veins play a key role in the pathogenesis of AF and their isolation is associated to high rates of AF freedom in patients with paroxysmal AF. However, ablation of persistent AF remains less effective, mainly limited by the difficulty to identify the sources sustaining AF. Many theories were advanced to explain the perpetuation of this form of AF, ranging from a single localized focal and reentrant source to diffuse bi-atrial multiple wavelets. Translating these mechanisms to the clinical practice remains challenging and limited by the spatio-temporal resolution of the mapping techniques. AF is driven by focal or reentrant activities that are initially clustered in a relatively limited atrial surface then disseminate everywhere in both atria. Evidence for structural remodeling, mainly represented by atrial fibrosis suggests that reentrant activities using anatomical substrate are the key mechanism sustaining AF. These reentries can be endocardial, epicardial, and intramural which makes them less accessible for mapping and for ablation. Subsequently, early interventions before irreversible remodeling are of major importance. Circumferential pulmonary vein isolation remains the cornerstone of the treatment of AF, regardless of the AF form and of the AF duration. No ablation strategy consistently demonstrated superiority to pulmonary vein isolation in preventing long term recurrences of atrial arrhythmias. Further research that allows accurate identification of the mechanisms underlying AF and efficient ablation should improve the results of PsAF ablation.

Lone Pediatric Atrial Fibrillation in the United States: Analysis of Over 1500 Cases

Little is known about lone atrial fibrillation (AF) in pediatrics and its risk factors due to low prevalence. We sought to determine risk factors and estimate recurrence rates in children with lone AF using a large clinical database. Using the Explorys clinical database, we retrospectively identified patients who were below 20 years of age at the time of their AF diagnosis. Patients with congenital heart disease, cardiomyopathy, prior open heart surgery, or thyroid disease were excluded. Out of 7,969,230 children identified, 1910 had AF and 1570 met the definition of lone AF. The prevalence of lone AF was 7.5 per 100,000 children. In comparison to young children (0-4 years), risk for lone AF increased with age (adjusted odds ratio (aOR) 1.2 [95% CI 0.9-1.5, P = 0.21] in those 5-9 years, aOR 1.7 [95% CI 1.3-2.1, P < 0.001] in those 10-14 years, and aOR 10.7 [95% CI 8.7-13.2, P < 0.001] in those 15-19 years). Risk of lone AF was also higher in males than females (aOR 1.7 [95% CI 1.5-1.9, P < 0.001]), and was higher in obese children (BMI ≥ 95th percentile) versus children with normal BMI (aOR 1.3 [95% CI 1.1-1.5], P < 0.001), but there was no difference between overweight (BMI = 85th-94th percentile) and normal (P = 0.14). One-month recurrence rate was 15%, and increased with age. In this large pediatric cohort, the prevalence of lone AF was low, but risk was higher in males and increased with age and obesity. Older children with lone AF had higher rates of recurrence.

Electrocardiographic intervals associated with incident atrial fibrillation: Dissecting the QT interval

BACKGROUND

Prolongation of the QT interval has been associated with an increased risk of developing atrial fibrillation (AF), but the responsible mechanism remains unknown.

OBJECTIVES

The aims of this study were to subdivide the QT interval into its components and identify the resultant electrocardiographic interval(s) responsible for the association with AF.

METHODS

Predefined QT-interval components were assessed for association with incident AF in the Atherosclerosis Risk in Communities study using Cox proportional hazards models. Hazard ratios (HRs) were calculated per 1-SD increase in each component. Among QT-interval components exhibiting significant associations, additional analyses evaluating long extremes, defined as greater than the 95^th percentile, were performed.

RESULTS

Of the 14,625 individuals, 1505 (10.3%) were diagnosed with incident AF during a mean follow-up period of 17.6 years. After multivariable adjustment, QT-interval components involved in repolarization, but not depolarization, exhibited significant associations with incident AF, including a longer ST segment (HR 1.27; 95% confidence interval [CI] 1.14-1.41; P < .001) and a prolonged T-wave onset to T-wave peak (T-onset to T-peak) (HR 1.13; 95% CI 1.07-1.20; P < .001). Marked prolongation of the ST segment (HR 1.31; 95% CI 1.04-1.64; P = .022) and T-onset to T-peak (HR 1.36; 95% CI 1.09-1.69; P = .006) was also associated with an increased risk of incident AF.

CONCLUSION

The association between a prolonged QT interval and incident AF is primarily explained by components involved in ventricular repolarization: prolongation of the ST segment and T-onset to T-peak. These observations suggest that prolongation of phases 2 and 3 of the cardiac action potential drives the association between the QT interval and AF risk.

Genomic Contributors to Rhythm Outcome of Atrial Fibrillation Catheter Ablation - Pathway Enrichment Analysis of GWAS Data

BACKGROUND

Left atrial enlargement and persistent atrial fibrillation (AF) are well-known predictors for arrhythmia recurrence after AF catheter ablation (LRAF). In this study, by using pathway enrichment analysis of GWAS data, we tested the hypothesis that genetic pathways associated with these phenotypes are also associated with LRAF.

METHODS

Samples from 660 patients with paroxysmal (n = 370) or persistent AF (n = 290) undergoing de-novo AF catheter ablation were genotyped for ~1,000,000 SNPs. SNPs found to be significantly associated with left atrial diameter (LAD) or AF type were used for gene-based association tests in a systematic biological Knowledge-based mining system for Genome-wide Genetic studies (KGG). Associated genes were tested for pathway enrichment using WEB-based Gene SeT AnaLysis Toolkit (WebGestalt), the Gene Annotation Tool to Help Explain Relationships (GATHER) and the databases provided by Kyoto Encyclopedia of Genes and Genomes (KEGG). In a second step, the association of consistently enriched pathways and LRAF was tested.

RESULTS

By using sequential 7-day Holter ECGs, LRAF between 3 and 12 months was observed in 48% and was associated with LAD (B = 1.801, 95% CI 0.760-2.841, p = 1.0E-3) and persistent AF (OR = 2.1; 95% CI 1.567-2.931, p = 2.0E-6). WebGestalt (adj. p = 2.7E-22) and GATHER (adj. p = 5.2E-3) identified the calcium signaling pathway (hsa04020) as the only consistently enriched pathway for LAD, while the extracellular matrix (ECM) -receptor interaction pathway (hsa04512) was the only consistently enriched pathway for AF type (adj. p = 2.1E-15 in WebGestalt; adj. p = 9.3E-4 in GATHER). Both calcium signaling (adj. p = 2.2E-17 in WebGestalt; adj. p = 2.9E-2 in GATHER) and ECM-receptor interaction (adj. p = 1.2E-10 in WebGestalt; adj. p = 2.9E-2 in GATHER) were significantly associated with LRAF.

CONCLUSIONS

Calcium signaling and ECM-receptor interaction pathways are associated with LAD and AF type and, in turn, with LRAF. Future and larger studies are necessary to replicate and apply these findings.

Genetic Variants Associated With Susceptibility to Atrial Fibrillation in a Japanese Population

BACKGROUND

Atrial fibrillation (AF) affects millions of individuals worldwide. The genome-wide association studies have identified robust genetic associations with AF.

METHODS

We genotyped 5461 participants of Japanese ancestry for 11 AF-related loci and determined the effects of carrying different numbers of risk alleles on disease development and age at disease onset. The weighted genetic risk score (GRS) was calculated, and its ability to predict AF was determined.

RESULTS

Six single-nucleotide polymorphisms-rs593479 (1q24 in PRRX1), rs1906617 (4q25 near PITX2), rs11773845 (7q31 in CAV1), rs6584555 (10q25 in NEURL), rs6490029 (12q24 in CUX2), and rs12932445 (16q22 in ZFHX3) (P < 1.9 × 10^-5)-were confirmed as being associated with AF. Patients with a high total number of risk alleles (9-12) had a younger median age at onset of AF (58 years; 95% confidence interval [CI], 55-60 years) than those with a low total number (1-4) (63 years; 95% CI, 61-64 years) (P = 0.0015). We observed a 4.38-fold (95% CI, 3.69-5.19) difference in risk of AF between individuals with scores in the top and bottom quartiles of the GRS. Receiver operating characteristic analysis indicated an area under the curve of 0.641 (95% CI, 0.628-0.653; P < 0.0001).

CONCLUSIONS

Six loci were validated as associated with AF in a Japanese population. This study suggests that a combination of common genetic markers modestly facilitates discrimination of AF. This is the first report, to our knowledge, to demonstrate that the age of onset of AF is affected by common risk alleles.

Ablatogenomics: can genotype guide catheter ablation for cardiac arrhythmias?

Previously confined to the management of rare inherited arrhythmia syndromes, a role for genetics within cardiac electrophysiology has begun to emerge for more common arrhythmias, including atrial fibrillation (AF). Catheter ablation for AF is an invasive procedure effective for restoring normal rhythm, however, fails in up to 40% of those undergoing their first procedure and carries a risk for serious adverse events. Recent studies have suggested that a common genetic variant within chromosome 4q25 may be a powerful predictor of procedural success, highlighting the potential of an 'ablatogenomic' strategy. Although still in its infancy, an ablatogenomic approach for AF may facilitate delivery of ablation to those most likely to benefit, while sparing those prone to fail from its risks.

Atrial Fibrillation Associated Genetic Variants and Left Atrial Histology: Evaluation for Molecular Sub-Phenotypes

INTRODUCTION

Genome wide association studies have identified several single nucleotide polymorphisms (SNPs) associated with atrial fibrillation (AF), but the mechanisms underlying these relationships have not yet been elucidated. Inflammation and fibrosis have been posited as important mechanisms responsible for AF. We sought to investigate the impact of SNP carrier status on inflammation and fibrosis in left atrial appendage tissue.

METHODS AND RESULTS

Carrier status of 10 AF-associated SNPs was evaluated on DNA extracted from left atrial appendage tissue in 176 individuals (120 with AF). The presence of inflammation was evaluated through visual quantification of leukocyte infiltration following hematoxylin and eosin staining, while fibrosis was quantified using picrosirius red with fast green staining. Unadjusted and adjusted linear and logistic regression models were utilized to evaluate for an association between SNP carrier status and inflammation and fibrosis. On adjusted logistic regression analysis, the rs7164883 SNP (intronic within HCN4) was associated with a reduced odds of inflammation (odds ratio: 0.42; 95% CI: 0.22-0.81, P = 0.01), and was not associated with fibrosis on adjusted linear regression analysis (β-coefficient: -0.31; 95% CI: -1.03-0.40, P = 0.40). None of the remaining SNPs exhibited significant associations with left atrial inflammation or fibrosis.

CONCLUSIONS

Among 10 AF-associated SNPs, a single genetic variant was associated with reduced left atrial inflammation, while no histologic differences were observed in the remaining 9. The known AF-associated SNPs do not appear to predispose to the development of pro-inflammatory or pro-fibrotic AF sub-phenotypes.

Impact of genetic variants on the upstream efficacy of renin-angiotensin system inhibitors for the prevention of atrial fibrillation

BACKGROUND

Renin-angiotensin system (RAS) inhibition via angiotensin-converting enzyme inhibitors and angiotensin II receptor blockers may reduce the risk of developing atrial fibrillation (AF) in certain populations, but the evidence is conflicting. Recent genome-wide association studies have identified several single nucleotide polymorphisms (SNPs) associated with AF, potentially identifying clinically relevant subtypes of the disease. We sought to investigate the impact of carrier status of 9 AF-associated SNPs on the efficacy of RAS inhibition for the primary prevention of AF.

METHODS

We performed SNP-RAS inhibitor interaction testing with unadjusted and adjusted Cox proportional hazards models using a discovery (Cardiovascular Health Study) and a replication (Atherosclerosis Risk in Communities) cohort. Additive genetic models were used for the SNP analyses, and 2-tailed P values <.05 were considered statistically significant.

RESULTS

Among 2,796 Cardiovascular Health Study participants, none of the 9 a priori identified candidate SNPs exhibited a significant SNP-drug interaction. Two of the 9 SNPs, rs2106261 (16q22) and rs6666258 (1q21), revealed interaction relationships that neared statistical significance (with point estimates in the same direction for angiotensin-converting enzyme inhibitor only and angiotensin II receptor blocker only analyses), but neither association could be replicated among 8,604 participants in Atherosclerosis Risk in Communities.

CONCLUSIONS

Our study failed to identify AF-associated SNP genetic subtypes of AF that derive increased benefit from upstream RAS inhibition for AF prevention. Future studies should continue to investigate the impact of genotype on the response to AF treatment strategies in an effort to develop personalized approaches to therapy and prevention.

A mutation in the atrial-specific myosin light chain gene (MYL4) causes familial atrial fibrillation

Atrial fibrillation (AF), the most common arrhythmia, is a growing epidemic with substantial morbidity and economic burden. Mechanisms underlying vulnerability to AF remain poorly understood, which contributes to the current lack of highly effective therapies. Recognizing mechanistic subtypes of AF may guide an individualized approach to patient management. Here, we describe a family with a previously unreported syndrome characterized by early-onset AF (age <35 years), conduction disease and signs of a primary atrial myopathy. Phenotypic penetrance was complete in all mutation carriers, although complete disease expressivity appears to be age-dependent. We show that this syndrome is caused by a novel, heterozygous p.Glu11Lys mutation in the atrial-specific myosin light chain gene MYL4. In zebrafish, mutant MYL4 leads to disruption of sarcomeric structure, atrial enlargement and electrical abnormalities associated with human AF. These findings describe the cause of a rare subtype of AF due to a primary, atrial-specific sarcomeric defect.

Atrial Fibrillation Genetics: Is There a Practical Clinical Value Now or in the Future?

Atrial fibrillation (AF) is the most common sustained arrhythmia and has significant clinical impact. Over the last decade, our understanding of the genetics of AF has expanded dramatically. After a heritable predisposition for AF was identified, many investigators have in turn identified both common and rare variants associated with AF. Ongoing work is focused on translating these variants into disease pathways and novel therapeutic modalities. In this review, we focus on our understanding of the current concepts behind the genetics of AF and outline a vision for the incorporation of genetic data into clinical practice.

Association between SNP rs13376333 and rs1131820 in the KCNN3 gene and atrial fibrillation in the Chinese Han population

BACKGROUND

The small conductance calcium-activated potassium, subfamily N, member 3 (KCNN3) gene rs13376333 and rs1131820 have been shown to be strongly associated with lone atrial fibrillation (AF), while replication association studies between rs13376333 in KCNN3 gene and risk of AF showed conflicting results. The current study tried to validate the impact of SNP rs13376333 and rs1131820 of KCNN3 gene on the risk of AF in the Chinese Han population.

METHODS

A total of 889 AF patients and 1015 controls were enrolled. Two hundred and seventy-eight cases of AF were lone AF. KCNN3 gene SNP rs13376333 and rs1131820 were genotyped by allele-specific MALDI-TOF mass spectrometry.

RESULTS

The genotype distribution and allele frequency of rs13376333 polymorphism were not different between total AF patients and controls. However, the genotype distribution of rs13376333 polymorphism was significantly different between lone AF and control group (p<0.001); and T allele frequency was significantly higher in lone AF group than that in controls (7.6% vs 3.6%, p<0.001). Multivariable logistic regression analysis showed that T allele carriers of rs13376333 was significantly associated with lone AF (OR=2.31, 95% CI 1.41-3.78, p=0.001). No relationship between rs1131820 polymorphism and total AF or lone AF was found in this study.

CONCLUSIONS

KCNN3 rs13376333 polymorphism was associated with lone AF in the Chinese Han population and the T allele carriers may be an independent predictive factor for lone AF.

A contemporary review on the genetic basis of atrial fibrillation

Atrial fibrillation is the most common sustained cardiac arrhythmia, and affected individuals suffer from increased rates of heart failure, stroke, and death. Despite the enormous clinical burden that it exerts on patients and health care systems, contemporary treatment strategies have only modest efficacy that likely stems from our limited understanding of its underlying pathophysiology. Epidemiological studies have provided unequivocal evidence that the arrhythmia has a substantial heritable component. Subsequent investigations into the genetics underlying atrial fibrillation have suggested that there is considerable interindividual variability in the pathophysiology characterizing the arrhythmia. This heterogeneity may partly account for the poor treatment efficacy of current therapies. Subdividing atrial fibrillation into mechanistic subtypes on the basis of genotype illustrates the heterogeneous nature of the arrhythmia and may ultimately help guide treatment strategies. A pharmacogenetic approach to the management of atrial fibrillation may lead to dramatic improvements in treatment efficacy and improved patient outcomes.

A Comparison of Disease Burden Between Twins and Control Pairs in Medicare: Quantification of Heredity's Role in Human Health

To quantify heredity's effects on the burden of illness in the Medicare population, this study linked information between participants in a research twin registry to a comprehensive set of Medicare claims. To calculate disease categories, the authors used the Centers for Medicare & Medicaid Services Hierarchical Conditions Categories (HCC) model that was developed to risk adjust Medicare's capitation payments to private health care plans based on the health expenditure risk of their enrollees. Using the Medicare database, 2 sets of unrelated but demographically matched control pairs (MCPs) were generated, one specific for the monozygotic twin population and the second specific for the dizygotic twin population. The concordance and correlation rates of the 70 HCC categories for the 2 twin populations, in comparison to their corresponding MCP, was then calculated using Medicare claims data from 1991 through 2011. When indicated, HCCs for which there was a statistically significant difference between the twin and corresponding MCP control group were analyzed by calculating concordance and correlation rates of the International Classification of Diseases, Ninth Revision codes that compose the HCC. Findings reveal that monozygotic twins share 6.5% more HCC disease categories than their MCP while dizygotic twins share 3.8% more HCC disease categories than their MCP. Atrial fibrillation is a highly heritable disease category, a finding consistent with prior literature describing the heritability of the cardiac arrhythmias. These findings are consistent with qualitative assessments of heredity's role found in previous models of population health, and provide both novel methods and quantitative evidence to support future model development.

Telomere length and the risk of atrial fibrillation: insights into the role of biological versus chronological aging

BACKGROUND

Advanced age is the most important risk factor for atrial fibrillation (AF); however, the mechanism remains unknown. Telomeres, regions of DNA that shorten with cell division, are considered reliable markers of biological aging. We sought to examine the association between leukocyte telomere length (LTL) and incident AF in a large population-based cohort using direct LTL measurements and genetic data. To further explore our findings, we compared atrial cell telomere length and LTL in cardiac surgery patients.

METHODS AND RESULTS

Mean LTL and the TERT rs2736100 single nucleotide polymorphism were assessed as predictors of incident AF in the Cardiovascular Health Study (CHS). Among the surgical patients, within subject comparison of atrial cell telomere length versus LTL was assessed. Among 1639 CHS participants, we observed no relationship between mean LTL and incident AF before and after adjustment for potential confounders (adjusted hazard ratio, 1.09; 95% confidence interval: 0.92-1.29; P=0.299); chronologic age remained strongly associated with AF in the same model. No association was observed between the TERT rs2736100 single nucleotide polymorphism and incident AF (adjusted hazard ratio: 0.95; 95% confidence interval: 0.88-1.04; P=0.265). In 35 cardiac surgery patients (26 with AF), atrial cell telomere length was longer than LTL (1.19 ± 0.20 versus 1.02 ± 0.25 [T/S ratio], P<0.001), a finding that remained consistent within the AF subgroup.

CONCLUSIONS

Our study revealed no evidence of an association between LTL and incident AF and no evidence of relative atrial cell telomere shortening in AF. Chronological aging independent of biological markers of aging is the primary risk factor for AF.

Targeted deep sequencing reveals no definitive evidence for somatic mosaicism in atrial fibrillation

BACKGROUND

Studies of ≤15 atrial fibrillation (AF) patients have identified atrial-specific mutations within connexin genes, suggesting that somatic mutations may account for sporadic cases of the arrhythmia. We sought to identify atrial somatic mutations among patients with and without AF using targeted deep next-generation sequencing of 560 genes, including genetic culprits implicated in AF, the Mendelian cardiomyopathies and channelopathies, and all ion channels within the genome.

METHODS AND RESULTS

Targeted gene capture and next-generation sequencing were performed on DNA from lymphocytes and left atrial appendages of 34 patients (25 with AF). Twenty AF patients had undergone cardiac surgery exclusively for pulmonary vein isolation and 17 had no structural heart disease. Sequence alignment and variant calling were performed for each atrial-lymphocyte pair using the Burrows-Wheeler Aligner, the Genome Analysis Toolkit, and MuTect packages. Next-generation sequencing yielded a median 265-fold coverage depth (interquartile range, 64-369). Comparison of the 3 million base pairs from each atrial-lymphocyte pair revealed a single potential somatic missense mutation in 3 AF patients and 2 in a single control (12 versus 11%; P=1). All potential discordant variants had low allelic fractions (range, 2.3%-7.3%) and none were detected with conventional sequencing.

CONCLUSIONS

Using high-depth next-generation sequencing and state-of-the art somatic mutation calling approaches, no pathogenic atrial somatic mutations could be confirmed among 25 AF patients in a comprehensive cardiac arrhythmia genetic panel. These findings indicate that atrial-specific mutations are rare and that somatic mosaicism is unlikely to exert a prominent role in AF pathogenesis.

Assessment of atrial fibrillation and vulnerability in patients with Wolff-Parkinson-White syndrome using two-dimensional speckle tracking echocardiography

Purpose

The aim was to assess atrial fibrillation (AF) and vulnerability in Wolff-Parkinson-White (WPW) syndrome patients using two-dimensional speckle tracking echocardiography (2D-STE).

Methods

All patients were examined via transthoracic echocardiography and 2D-STE in order to assess atrial function 7 days before and 10 days after RF catheter ablation. A postoperative 3-month follow-up was performed via outpatient visit or telephone calls.

Results

Results showed significant differences in both body mass index (BMI) and supraventricular tachycardia (SVT) duration between WPW patients and DAVNP patients (both P<0.05). Echocardiography revealed that the maximum left atrial volume (LAV_max) and the left ventricular mass index (LVMI) in diastole increased noticeably in patients with WPW compared to patients with DAVNP both before and after ablation (all P<0.05). Before ablation, there were obvious differences in the levels of SRs, SRe, and SRa from the 4-chamber view (LA) in the WPW patients group compared with patients in the DAVNP group (all P<0.05). In the AF group, there were significant differences in the levels of systolic strain rate (SRs), early diastolic strain rate (SRe), and late diastolic strain rate (SRa) from the 4-chamber view (LA) both before and after ablation (all P<0.05). In the non-AF group, there were decreased SRe levels from the 4-chamber view (LA/RA) pre-ablation compared to post-ablation (all P<0.05).

Conclusion

Our findings provide convincing evidence that WPW syndrome may result in increased atrial vulnerability and contribute to the development of AF. Further, RF catheter ablation of AAV pathway can potentially improve atrial function in WPW syndrome patients. Two-dimensional speckle tracking echocardiography imaging in WPW patients would be necessary in the evaluation and improvement of the overall function of RF catheter ablation in a long-term follow-up period.

Breed predisposition and heritability of atrial fibrillation in the Standardbred horse: a retrospective case-control study

OBJECTIVES

To assess evidence for genetic contributions to atrial fibrillation (AF) in the Standardbred horse.

ANIMALS

Equine referrals to the Ontario Veterinary College Health Sciences Centre (OVCHSC) for 1985-2009, and age and gait matched breed registry controls.

METHODS

Breeds presenting ≥ 5 times annually were tabulated (admission year and diagnosis; total 40,039; AF 396; no AF 39,643), and breed and year effects examined. Heritability and inbreeding coefficients were determined for Standardbred AF cases and racing contemporaries, and odds ratios for AF were calculated for frequently occurring sires.

RESULTS

Year and breed effects on diagnosis were highly significant (Chi-Square 212.85, p < 0.0001, and 304.25, p < 0.0001, respectively). Year effect on diagnosis by breed was significant from 1997, and due to Standardbred admissions each year. Quarterhorses were significantly less likely to present with AF (OR 0.0578-0.6048), Standardbreds were more likely (OR 4.3874-10.9006). Heritability of AF on the underlying scale (h²(u)) was estimated at 29.6 ± 3.9% and on the observed binomial scale (h²(o)), at 9.6%. For horses born in 1994 or later, h²(u) was 31.1 ± 4.3% and h²(o), 10.1%. Of 22 first generation sires appearing ≥ 10 times in the case/control file, seven pacing and one trotting sire produced affected horses more frequently than expected (OR 2.66-66.32). Inbreeding was not a factor.

CONCLUSIONS

There is genetic liability to AF in Standardbred horses, likely due to more than single genes with simple Mendelian inheritance. Genomic studies are required.

Candidate gene approach to identifying rare genetic variants associated with lone atrial fibrillation

BACKGROUND

Rare variants in candidate atrial fibrillation (AF) genes have been associated with AF in small kindreds. The extent to which such polymorphisms contribute to AF is unknown.

OBJECTIVE

The purpose of this study was to determine the spectrum and prevalence of rare amino acid coding (AAC) variants in candidate AF genes in a large cohort of unrelated lone AF probands.

METHODS

We resequenced 45 candidate genes in 303 European American (EA) lone AF probands (186 lone AF probands screened for each gene on average [range 89-303], 63 screened for all) identified in the Vanderbilt AF Registry (2002-2012). Variants detected were screened against 4300 EAs from the Exome Sequencing Project (ESP) to identify very rare (minor allele frequency ≤0.04%) AAC variants and these were tested for AF co-segregation in affected family members where possible.

RESULTS

Median age at AF onset was 46.0 years [interquartile range 33.0-54.0], and 35.6% had a family history of AF. Overall, 63 very rare AAC variants were identified in 60 of 303 lone AF probands, and 10 of 19 (52.6%) had evidence of co-segregation with AF. Among the 63 lone AF probands who had 45 genes screened, the very rare variant burden was 22%. Compared with the 4300 EA ESP, the proportion of lone AF probands with a very rare AAC variant in CASQ2 and NKX2-5 was increased 3-5-fold (P <.05).

CONCLUSION

No very rare AAC variants were identified in ~80% of lone AF probands. Potential reasons for the lack of very rare AAC variants include a complex pattern of inheritance, variants in as yet unidentified AF genes or in noncoding regions, and environmental factors.

Genetic mechanisms of atrial fibrillation: impact on response to treatment

Atrial fibrillation (AF) is the most-common sustained arrhythmia observed in clinical practice, but response to therapy is highly variable between patients. Current drug therapies to suppress AF are incompletely and unpredictably effective and carry substantial risk of proarrhythmia and noncardiac toxicities. The limited success of therapy for AF is partially the result of heterogeneity of the underlying substrate, interindividual differences in disease mechanisms, and our inability to predict response to therapies in individual patients. In this Review, we discuss the evidence that variability in response to drug therapy is also conditioned by the underlying genetic substrate for AF. Increased susceptibility to AF is mediated through diverse genetic mechanisms, including modulation of the atrial action-potential duration, conduction slowing, and impaired cell-to-cell communication, as well as novel mechanisms, such as regulation of signalling proteins important in the pathogenesis of AF. However, the translation of genetic data to the care of the patients with AF has been limited because of poor understanding of the underlying mechanisms associated with common AF-susceptibility loci, a dearth of prospective, adequately powered studies, and the challenges associated with determining efficacy of antiarrhythmic drugs. What is apparent, however, is the need for appropriately designed, genotype-directed clinical trials.

Lone atrial fibrillation in the young - perhaps not so "lone"?

OBJECTIVE

To determine if pediatric patients with a history of lone atrial fibrillation (AF) have other forms of supraventricular tachycardia (SVT) that may potentially trigger AF.

STUDY DESIGN

A multicenter review of patients with lone AF who underwent electrophysiology (EP) study from 2006-2011 was performed.

INCLUSION CRITERIA

age ≤21 years, normal ventricular function, structurally normal heart, history of AF, and EP study and/or ablation performed.

EXCLUSION CRITERIA

congenital heart disease or cardiomyopathy. Patient demographics, findings at EP study and follow-up data were recorded.

RESULTS

Eighteen patients met inclusion criteria. The mean age was 17.9 ± 2.2 years, weight was 82 ± 21 kg, body mass index was 27 ± 6, and 15 (83%) were males. Eleven (61%) were overweight or obese. Seven (39%) had inducible SVT during EP study: 5 atrioventricular nodal re-entry tachycardia (71%) and 2 concealed accessory pathways with inducible atrioventricular re-entry tachycardia (29%). All 7 patients with inducible SVT underwent radiofrequency ablation. There were no complications during EP study and/or ablation for all 18 patients. The mean follow-up was 1.7 ± 1.5 years and there were no recurrences in the 7 patients who underwent ablation. There were 2 recurrences of AF in patients with no other form of SVT during EP study.

CONCLUSIONS

Inducible SVT was found in 39% of pediatric patients undergoing EP study for lone AF. EP study should be considered for pediatric patients presenting with lone AF.

The developing pulmonary veins and left atrium: implications for ablation strategy for atrial fibrillation

The majority of cases of atrial fibrillation (AF) are the result of triggers originating in the area of the pulmonary veins. The reason for the predilection for that area remains unclear. We sought to examine the different mechanisms responsible for this observation through an extensive search of the medical literature, examining the development of the pulmonary veins, genetics of AF and left to -right cardiac chamber differentiation. Results confirm that the LAA is anatomically and embryologically different from other areas of the atrial walls and develops under distinct genetic and transcriptional pathways. Findings support an ablation strategy whose primary focus should be the creation of a 'box' lesion set, plus additional lines to prevent propagation to the left atrial appendage, the isthmus of the left atrium and the right atrium are likely to be more effective than simple pulmonary vein isolation.

Slower heart rate and altered rate dependence of ventricular repolarization in patients with lone atrial fibrillation

BACKGROUND

Electrophysiological alterations in atrial fibrillation (AF) may be genetically based and may lead to changes in ventricular repolarization. Short QT syndrome is a rare channelopathy with abbreviated ventricular repolarization and a propensity for AF.

AIMS

To determine if minor unrecognized forms of short QT syndrome can explain some cases of lone AF.

METHODS

We prospectively compared QT intervals in 66 patients with idiopathic lone AF and 132 age- and sex-matched controls. QT intervals were measured during sinus rhythm in each of the 12 surface electrocardiogram leads and corrected using Bazett's formula (QTc). QT intervals were also corrected using other formulae. Uncorrected QT and heart rate regression lines were compared between AF patients and controls.

RESULTS

AF patients presented with a slower resting heart rate (64 ± 10 beats per minute [bpm] vs 69 ± 9 bpm; P=0.0006). QTc intervals were shorter in AF patients in 11/12 electrocardiogram leads (significant in 7/12, borderline in 2/12; mean QTc 381 ± 21 ms vs 388 ± 22 ms; P=0.02). QTc intervals were also shorter in AF patients, significantly or not, using other correction formulae. For similar heart rates, uncorrected QT intervals were shorter in patients when heart rates were greater than 70 bpm and longer when heart rates were less than 60 bpm. AF patients displayed steeper QT/heart rate regression line slopes than controls (P=0.009).

CONCLUSION

Heart rate is significantly slower and the rate dependence of ventricular repolarization is significantly altered in patients with lone AF compared with controls. Further study is warranted to determine if AF induces subsequent ventricular repolarization changes or if these modifications are caused by an underlying primary electrical disease.

Personalized medicine and atrial fibrillation: will it ever happen?

Atrial fibrillation (AF) is a common arrhythmia of substantial public health importance. Recent evidence demonstrates a heritable component underlying AF, and genetic discoveries have identified common variants associated with the arrhythmia. Ultimately one hopes that the consideration of genetic variation in clinical practice may enhance care and improve health outcomes. In this review we explore areas of potential clinical utility in AF management including those relating to pharmacogenetics and risk prediction.

Atrial fibrillation in two adolescents

Idiopathic atrial fibrillation (AF) in adolescents is extremely rare and has usually been associated with structural heart disease. We present two cases of symptomatic AF in adolescents without any identifiable etiology. No definitive guidelines are available for management of such patients.

A KCNJ8 mutation associated with early repolarization and atrial fibrillation

AIM

The Kir 6.1 K(atp) channel is believed to play an important role in ventricular repolarization as determined from both functional and genetic studies of the potassium inwardly-rectifying channel, subfamily J, member 8 (KCNJ8)-S422L missense mutation in patients with J-wave syndromes. Although Kir6.1 is also present in atrial tissue, it is unknown whether this channel modulates atrial repolarization and hence whether the S422L mutation portends a greater risk of atrial arrhythmias. This study sought to examine whether there was an increased frequency of the KCNJ8-S422L mutation among patients with atrial fibrillation (AF) and early repolarization (ER) as a possible novel susceptibility gene for AF.

METHODS AND RESULTS

A total of 325 lone AF probands were identified from the Vanderbilt AF Registry, a collection of clinical data and DNA from consented, consecutively enrolled participants. The coding regions of KCNJ8 were sequenced, and the patient's presenting electrocardiogram (ECG) was reviewed by two independent physicians for ER abnormalities. The KCNJ8-S422L mutation was identified in two AF probands while no other candidate gene variants were identified in these cases. Twenty-two (7%) patients were found to have ER on the ECG, including the two probands carrying the S422L variant. In one small AF kindred, the S422L variant co-segregated with AF and ER.

CONCLUSIONS

The KCNJ8-S422L variant is associated with both increased AF susceptibility and ER indicating a role for Kir 6.1 K(atp) channel in both ventricular and atrial repolarization.