Stroke rates in non-anticoagulated individuals with and without atrial fibrillation and one non-sex CHA2DS2-VASc risk factor: a nationwide registry-based cohort (Atrial Fibrillation in Norway – AFNOR)

Background

Stroke prevention is fundamental in the management of atrial fibrillation (AF). However, in patients with intermediate risk of stroke (CHA2DS2-VASc score 2 in women; 1 in men) the net clinical benefit of oral anticoagulant (OAC) treatment is uncertain, as the treatment effect must be carefully balanced against the potential bleeding risk. Moreover, multiple risk factors included in the CHA2DS2-VASc score increase the risk of stroke independent of AF.

Purpose

We aimed to compare rates of ischemic and haemorrhagic stroke between non-anticoagulated individuals with and without AF in a nationwide cohort of individuals at intermediate risk of stroke.

Method

We identified a cohort of non-anticoagulated Norwegian individuals with and without non-valvular AF aged ≥18 years, with one non-sex CHA2DS2-VASc risk factor linking data from the Norwegian Population Registry, Patient Registry, Prescription Database and Cause of Death Registry. AF and comorbidities were identified with minimum three-year look-back period at study start and successively during follow up. Individuals without AF entered the study at date of first registered non-sex CHA2DS2-VASc risk factor while individuals with AF entered at the first date when both AF and first CHA2DS2-VASc risk factor were registered. Individuals with and without AF were followed from study start in 2011 until occurrence of stroke, death, emigration, OAC claim, increased CHA2DS2-VASc score or end of follow-up on December 31, 2018. Rates of ischemic and haemorrhagic stroke were calculated as the number of stroke cases per 100 person-years with 95% confidence intervals (CI).

Results

During 2011–2018, a total of 61,762 individuals with AF at intermediate risk of stroke and no previous OAC use were identified (mean age 63.2±7.6 years (SD); 37% women). In the AF population, a total of 1,304 ischemic strokes were registered during 109,881 person-years, and 127 haemorrhagic strokes during 109,559 person-years. In the corresponding intermediate risk non-AF population, 1,099,655 individuals (mean age 59.5±10.2 years (SD); 49.5% women) were identified, with a total of 6,081 ischemic strokes during 4,037,940 person-years and 3,037 haemorrhagic strokes during 4,022,952 person-years.

The rate of ischemic stroke was 1.19 (95% CI, 1.12–1.25) in AF-patients and 0.15 (95% CI, 0.15–0.15) in non-AF individuals per 100 person-years, corresponding to a rate difference of 1.04 excess stroke cases per 100 person-years in AF patients. The haemorrhagic stroke rate was 0.12 (95% CI, 0.10–0.14) in AF-patients and 0.08 (95% CI, 0.07–0.08) per 100 person-years in non-AF individuals. Similar rate differences were seen in both men and women.

Conclusion

In a nationwide population with one non-sex CHA2DS2-VASc risk factor and without OAC treatment, we found higher stroke rate in AF patients compared to the rest of the population without AF, with a stroke rate difference of ∼1% per year. Haemorrhagic stroke rates were generally low.

Funding Acknowledgement

Type of funding sources: Public Institution(s). Main funding source(s): South-Eastern Norway Regional Health Authority

Integration of Scandinavian genetic data with UK biobank data implicates the RBM20 gene with atrial fibrillation pathogenesis

Purpose

Atrial fibrillation (AF) is the most common sustained arrhythmia. It carries a large healthcare burden and is associated with serious complications. The arrhythmia has a substantial genetic component and is associated with several structural genes, including the gene TTN. A recent large genome-wide association study on AF found an association to RBM20. The RBM20 gene is a splicing factor targeting TTN, RYR2 and CAMK2D among other cardiac genes. Using Next-Generation Sequencing and data derived from the UK Biobank, we aimed to reveal the role of RBM20 in AF.

Methods and results

We examined the burden of rare (Minor allele frequency (MAF)<0.01%) RBM20 loss-of-function (LOF) variants in whole-exome sequencing data from the UK Biobank (n=175,280). AF was defined by ICD9/10, while individuals without AF were used as controls. Association tests aggregating rare variants in RBM20 using the Efficient Variant-Set Mixed Model Association Test (SMMAT) were performed to assess the effect of LOF RBM20 variants, adjusted for age, sex and principal components. We identified 33 LOF variants in RBM20, which were significantly enriched in AF (P=0.0087).

To examine the effect of rare missense RBM20 variants in the splicing of TTN, we screened an in-house cohort of 531 Scandinavian early-onset AF patients using targeted sequencing. We filtered for rare (MAF<0.1%) and deleterious (defined as combined annotation dependent depletion score >20) variants and identified nine missense variants and three novel LOF variants in RBM20. To evaluate the effect of these RBM20 variants, we constructed a series of human RBM20 single nucleotide base exchange mutants. The splicing activity of the variants was measured with RT-qPCR on HEK293 cells transfected with a TTN241–3 splicing reporter. Four of these variants resulted in a significantly altered splicing activity in TTN, with the largest effect observed for LOF variants.

In order to examine the biological effect of RBM20 variants on structural changes in atrial tissue, we used a Norwegian Brown rat animal model with loss of RBM20. In this model, Transmission Electron Microscopy revealed altered sarcomere and mitochondrial structure in its atrial cardiomyocytes. Furthermore, nanopore RNA sequencing of atrial tissue from the aforementioned animal model indicated altered expression in several key cardiac genes, including TTN and PITX2.

Conclusion

Rare RBM20 LOF variants are significantly enriched in AF cases, seen in a large population of 175,000 individuals. We demonstrated that the effect of LOF RBM20 on alternative TTN splicing can be detected on an individual level in patients with AF. Studies using an animal model indicates that LOF in RBM20 may affect atrial function through altered expression of several genes in the atria, and may cause structural changes in the atrial cardiomyocytes. This suggests that RBM20 may be involved in AF pathogenesis mediated through an atrial cardiomyopathy.

Funding Acknowledgement

Type of funding sources: Foundation. Main funding source(s): Novo Nordisk Foundation Pre-Graduate Scholarships (NNF18OC0053094)The Hallas Møller Emerging Investigator grant (Novo Nordisk Foundation (NNF17OC0031204))

P6563Time trends in incidence rates of atrial fibrillation in Norway 2004–2014. A CVDNOR project

Background

The reported incidence and prevalence of atrial fibrillation (AF) has been inconsistent among studies.

Purpose

We aimed to study time trends in incidence (first time) of AF hospitalizations or AF deaths in Norway in the period 2004–2014 by age and sex.

Methods

Nationwide hospital discharge diagnoses in the Cardiovascular Disease in Norway (CVDNOR) database and in the National Patient Registry were linked to the National Cause of Death Registry. All hospitalizations with AF as primary or secondary diagnosis and out-of-hospital deaths with AF as underlying cause (ICD-9: 427.3 or ICD 10: I48; AF or atrial flutter) in individuals ≥18 years were obtained during 1994–2014. Incident AF was defined as first hospitalization or out-of-hospital death due to AF with no previous hospitalization for AF the past 10 years. Age-standardized incidence rates with 95% confidence intervals (CIs) were calculated using direct standardization to the age-distribution in the Norwegian population per Jan 1st 2004. Age-adjusted average yearly incidence rate ratios (IRR) with 95% CIs were estimated by Poisson regression analyses. Accumulated prevalence during 1994–2014 was assessed in Norwegian residents 18 years and older per Dec 31st 2014.

Results

During 39,865,498 person years of follow up from 2004 to 2014 we identified 175,979 incident AF cases of which 30% were registered with AF as primary diagnosis, 69% as secondary diagnosis and 1% as out-of-hospital cause of death. The age-standardized incidence rate of AF hospitalization or out-of-hospital death per 100,000 person years was stable at 433 (426–440) in 2004 and 440 (433–447) in 2014. IRR were stable or declining across age groups of both sexes, except for the youngest age group 18–44 years, where incidence rates of AF hospitalization or out-of-hospital death increased by 2% per year, IRR 1.02 (1.01, 1.03). By 2014, the prevalence of AF assessed from hospital or death records was 2.9% in the adult population 18 years and older.

Conclusion

We found overall stable incidence rates of AF from 2004 to 2014 in the adult Norwegian population. Increased incidence rates of AF in the population 18–44 years are worrying and need further investigation.

Acknowledgement/Funding

The Norwegian Atrial Fibrillation Reseach Network

P1231Loss of function in cytoskeletal genes associates with early onset atrial fibrillation

Introduction

Atrial fibrillation (AF) is the most common cardiac arrhythmia. It carries an increased risk of serious complications and an increased mortality. Genome Wide Association Studies have demonstrated that variants in several structural genes are associated with AF, and recently two landmark papers have implicated loss of function (LoF) variants in titin (TTN), a gene associated with dilated cardiomyopathy (DCM), in patients with early onset AF. An atrial cardiomyopathy syndrome has been proposed as a mechanism in the development of AF.

Purpose

We hypothesized that genes encoding structural proteins that were associated with DCM, could also be involved in atrial cardiomyopathy and contribute to AF.

Materials and methods

We performed targeted deep sequencing of structural genes associated with DCM. The genes were grouped by cellular function, and the burden of LoF variants was examined in a cohort of 540 early onset AF patients and compared to a control group (n=383). The patients were below age 49 with normal echo, and no other cardiovascular disease at onset of AF. Patient inclusion in the cohort is still ongoing, and we are working on obtaining a CRISPR/CAS9 modified zebra fish model with LoF variants in cytoskeletal proteins.

Results

We identified a total of 6 carriers of LoF variants in 3 genes thought to encode cytoskeletal proteins (DMD, PDLIM3 and FKTN). The burden of variants in cytoskeletal genes was significantly increased in patients with early onset AF compared with controls (p=0.0385). Four carriers had LoF variants in the dystrophin gene (DMD), while there was 1 carrier of LoF variants in PDLIM3 and FKTN respectively. All carriers with LoF variants in DMD developed persistent AF before age 30.

Conclusion

Our data suggest that rare mutations in cytoskeletal genes previously associated with DCM, may also play a role in the development of early onset AF. The data supports that AF is a part of an atrial cardiomyopathy syndrome.

Acknowledgement/Funding

Novo Nordisk Fonden Pre-Graduate Scholarships