Clonal Hematopoiesis of Intermediate Potential in Atrial Fibrillation: A Critical View of Current Knowledge as a Springboard for Future Research

Abstract

Clonal hematopoiesis of intermediate potential (CHIP) is the presence of a clonally expanded hematopoietic stem cell because of a mutation in individuals without evidence of hematologic malignancy, dysplasia, or cytopenia. Interestingly, CHIP is associated with a two-fold increase in cardiovascular risk, independently of traditional risk factors. Recent studies using deep-targeted sequencing have revealed that CHIP mutations, primarily TET2 and DNMT3A, present a higher incidence in patients with AF compared to healthy controls. Moreover, the presence of the aforementioned mutations is positively correlated with the progression and the severity of the AF clinical course. Regarding the predisposition of AF, it has been proven that TET2 and ASXL1 mutations, and not DNMT3A mutation, are associated with higher interleukin-6 (IL-6) levels. IL-6 levels, being indices of cardiac remodeling, predispose to an elevated risk for AF in healthy subjects. Currently conducted research has focused on elaborating the mechanisms driving the association between AF and CHIP and on the evaluation of potential interventions to reduce the risk of AF development. The aims of our review are (i) to summarize published evidence regarding the presence of CHIP mutations as a contributor to AF severity and predisposition, and (ii) to highlight the potential benefits of investigating the correlations between CHIP and AF for AF-diagnosed patients.

1. Introduction

Cardiac arrhythmias represent a substantial health burden and are associated with increased risk of related complications in all age groups, including life-threatening strokes, heart failure, cardiac arrest, and sudden infant death [1,2,3]. Recent evidence suggests that cardiac arrhythmias affect approximately 1–5% of middle-aged populations, with their prevalence increasing by increasing age, especially in chronically ill populations [4,5,6,7,8]. Atrial fibrillation (AF) is the most common supraventricular cardiac arrhythmia, with an incidence of 1% in the general population and up to 10% in the elderly. AF is associated with increased mortality, accounting for up to 50% of cardiovascular deaths [2,9,10], and is considered a multifactorial disease, as its pathogenesis is influenced by several factors, including age, ethnicity, physical activity, and comorbidities (e.g., diabetes, hypertension) [11,12,13]. Chronic systemic and myocardial inflammation enhances structural remodeling and fibrosis of the myocardial tissue, leading to AF pathogenesis, while acute cardiac inflammation after being exposed to a triggering factor (e.g., post-vaccination) also leads to sometimes lethal cardiac arrhythmias, including AF [14,15,16]. AF pathogenesis involves an interaction between several initiating factors, manifesting as multiple rapidly firing ectopic foci within at least one pulmonary vein, along with abnormal atrial myocardial tissue capable of sustaining the arrhythmia [14]. Structural heart disease is the triggering factor behind many AF cases. It was shown that defects in molecular pathways are also involved in AF pathogenesis, leading to electrical conduction dysregulation, while human aging, as a state of chronic inflammation, is a potential contributor to the higher prevalence of AF in the elderly [17,18,19]. Epidemiological studies provide evidence that genetic factors play a crucial role in approximately 30% of patients with AF. Moreover, several studies propose a range of rare gene involvement (including GJA1, GJA5, KCNQ1, LMNA, NUP155, JPH2, SYNE2, and GREM2) associated with ionic channels, calcium-handling protein, fibrosis, conduction, and inflammation, in AF pathogenesis [20,21].

Clonal hematopoiesis of indeterminate potential (CHIP) is defined by the presence of somatic mutations with a variant allele frequency (VAF) of at least 2% in peripheral blood, which leads to the expansion of mutated clones in the absence of cytopenia, dysplastic hematopoiesis, and diagnostic criteria of hematologic malignancy [22,23]. CHIP is a predisposing state of hematological malignancies (13-fold increased risk), including monoclonal gammopathy of unknown significance (MGUS) and myelodysplastic syndrome (MDS), combined or not with other mutations or epigenetic alterations [24,25,26]. The majority of CHIP carriers remain asymptomatic; however, they have a 1.4-fold increased risk of mortality, although the annual risk of malignant development remains low [27]. Prior chemotherapy and radiotherapy are associated with CHIP development, mainly affecting DNA repair genes (e.g., TP53), leading to therapy-related myelodysplasia or leukemia, while bone marrow transplantation-derived CHIP mutations are associated with poor prognosis and higher mortality rates [28]. The expansion of mutant hematopoietic stem cells that lead to CHIP development is age-related, conferring risk for multiple diseases of aging, including not only hematologic cancers, but also cardiac diseases (myocardial infarction, arrhythmias, heart failure) [29,30,31,32]. The development of cardiac disease involves inflammatory cells derived from the cells of erythroid, myeloid, lymphoid, and megakaryocytic lineage, all of which originate from hematopoietic stem cells [33]. CHIP is an independent risk factor for cardiac disease and all-cause mortality [34,35]. Its involvement in cardiovascular disease is mainly suggested for atherosclerosis and heart failure, while individuals with VAF > 10% are at a higher risk of myocardial infarction, calcific aortic disease’s mortality and progression, and, generally, heart-failure related hospitalization [36,37,38,39].

The potential association between somatic mutations and AF pathogenesis has been largely studied within the last two decades, revealing pathogenic mutations in ion channel genes (KCNQ1) [40] and genes encoding junction proteins (GJA5 and GJA1) [41,42]. Emerging evidence suggests that CHIP somatic mutations are a potential contributor to AF development [43,44]. Population-based studies and gene-specific analyses indicate that several CHIP mutations are associated with a higher incidence of AF, while their presence predisposes to AF-related adverse events [40]. However, several gaps regarding the specific role of CHIP in AF remain inadequately studied, as most real-world research has primarily focused on atherosclerosis and heart failure, with limited emphasis on AF. To date, only two reviews [43,44] have specifically addressed the aforementioned relationship, highlighting the lack of in-depth analysis of the shared risk factors at a clinical level, the limited number of in vivo prior studies, and the unexplored role of less common gene-specific subtypes. Given both the complexity in the management of AF [45] and the increasing availability of targeted next-generation sequencing with prediction utility in a variety of pre-neoplastic conditions [46,47], CHIP-direction and intervention strategies should be considered in AF patients. Defining the pathophysiologic correlations between CHIP and AF pathogenesis could significantly reduce the risk of severe complications in patients with AF. Herein, we provide a current state of the field regarding the identification and clinical impact of AF-related CHIP mutations, discussing the potential inclusion of these alterations in AF diagnostic and therapeutic approaches.

2. Pathophysiologic Interconnections Between CHIP and AF

2.1. The Role of Aging

Aging is considered the primary predictor of cardiovascular diseases, surpassing several traditional risk factors (including hypertension, dyslipidemia, and smoking) [48]. Aging leads to a gradual decline in tissue and organ function, along with the accumulation of somatic mutations [48]. A great variety of these somatic mutations, originating mostly in the bone marrow (and less in the heart and blood vessels), affect the cardiovascular system [49]. However, only a small subset of these mutations provides a selective advantage, leading to a clonal expansion and contributing to age-related conditions, including AF [49]. CHIP exhibits a similar age-dependent pattern, affecting 9.5% of people aged 70–79 years, 11.7 of those aged 80–89 years, and 18.4% of those over 90 years, while being rare in individuals under 40 years of age, demonstrating an annual increase of 6.7% and being associated with epigenetic aging [44]. This evidence combined suggests that CHIP is a potential mediator between aging-related biological changes and cardiovascular disease development [50]. As CHIP prevalence rises with age, specific driver mutations show distinct clonal patterns; mutations in DNMT3 and JAK2 tend to occur early, even during fetal development or childhood in some cases, while SF3B1 and SRSF2 mutations typically emerge later in adulthood [51]. Recently published research suggested that CHIP mutations are found more frequently in individuals with AF than in healthy controls, and they tend to increase patients’ vulnerability to AF complications [52]. However, the direct causal relationship between AF and CHIP remains uncertain, with age-related inflammation and telomere shortening in leucocytes being considered as key mediators, as discussed in the next sections of our review [44].

2.2. Inflammation: Macrophage Activity and Cytokine Storm Predisposing to Cardiovascular Risk and Thrombotic Events

The presence of CHIP mutations has been associated with an inflammatory pro-thrombotic state, which includes dysregulation of monocytes and macrophages, resulting in increased risk of cardiovascular complications in AF patients, and high risk of complications and mortality [53,54]. Chronic inflammation, which subsequently leads to endothelial dysfunction and thrombin generation, represents a potential association between AF-related cardiovascular risk and CHIP [55,56,57]. This statement initially stemmed from evidence associating significantly elevated cytokine levels with CHIP mutations, as a part of the investigation on how the inflammatory microenvironment leads to the development of neoplastic or pre-neoplastic conditions [58,59,60]. Cytokine levels are associated with monocyte activity regulation, macrophage formation, and atherosclerosis progression; thus, alterations in cytokine profiles and dysregulated monocytic and macrophage functions may cause vascular deformities [43,55,56,57]. In older individuals, elevated cytokines are significantly linked both to CHIP and AF, and notably, the NLRP3 inflammasome pathway plays a crucial role, activating caspase-1 in macrophages and leading to the conversion of pro-IL-1β and pro-IL-18 into active cytokines, stimulating IL-6 production [61,62] (Figure 1). These cytokines enhance changes in atrial electrophysiology via prolongation of action potentials and promoting calcium dysregulation (which is further dysregulated by inflammasome activation), with promoted arrhythmogenic activity being the final result of these processes [63,64] (Figure 1).

Investigating the role of inflammation as a link between CHIP and AF pathogenesis, the study of Fuster and his colleagues demonstrated a direct causal association between CHIP and atherosclerosis through a persistently inflammatory state, consisting of increased IL-1β levels and atherosclerotic pathogenesis in TET2-mutant mouse models [65]. Inhibition of IL-1β activity resulted in a significant reduction of the atherosclerotic potential, a finding that needs to be further evaluated by in vivo studies [65]. Another study in animal models reported that pharmacological inhibition of NLRP3 inflammasome in TET2-deficient mice resulted in decreasing the inflammatory state, lowering IL-1β, and ameliorating atherosclerosis and heart failure [66]. In the next years, research focused on both the two most common CHIP mutations (TET2 and DNMT3A), demonstrating in vitro and in animal models that TET2 deficiency upregulates the secretion of IL-1β, IL-6, and TNF-α [67,68], while DNMT3A deficiency was strongly associated with elevated cytokine (CXCL1, CXCL2, IL-6, and CCL5) levels in macrophages [69]. Importantly, individuals with germline DNMT3 alterations have shown reduced monocyte IL-10 secretion. DNMT3 activation has recently been considered a stimulator of antiviral responses in macrophages via histone deacetylase 9 [68,70]. Regarding JAK2 mutations, it is suggested that they may influence macrophage functionality as well, inducing DNA replication and activating the inflammasome, subsequently worsening atherosclerosis [71]. These results combined suggest that a clonal hematopoiesis-driven pro-inflammatory state is a potential contributor to AF development.

2.3. Atrial Remodeling: Fibrotic Changes and Altered Calcium Handling

Left atrial enlargement is considered a risk factor and a consequence of AF, at the same time, creating a cycle in which AF promotes further atrial dilation [72,73]. Cardiac fibrotic changes, which increase with increasing age and are associated with extracellular matrix buildup, are also main contributors to atrial remodeling [74,75]. The mechanisms behind cardiac fibrosis are complex and not yet fully elucidated; however, inflammation and shortened leukocyte telomere length are considered as main pathophysiological mechanisms, while disturbances in calcium signaling may contribute to electrical atrial remodeling [76,77]. Chronic inflammation, as indicated by elevated CRP and IL-6 levels, leads to atrial remodeling and fibrosis mediated by macrophage-derived osteopontin (SPP1) [78,79,80]. Shortened leukocyte telomere length has been associated with higher CHIP prevalence, as longer telomeres may promote cell division and increase somatic mutation risk [81]. Conversely, CHIP mutations, especially in genes like TET2 and ASXL1, can accelerate leukocyte telomere length shortening, leading to greater atrial dilation and progression of atrial fibrosis [19,76]. Several signaling pathways may be involved in these processes, mainly EGFR/Akt signaling, which disrupts electrical impulse propagation and fosters re-entrant circuits, finally worsening AF [74].

Dysregulation of calcium signaling is a crucial link between CHIP and AF. In individuals carrying TET2 mutations, impaired calcium handling in heart cells, which occurs due to the activation of NLRP3 inflammasome, has been demonstrated [82,83]. In ΤΕΤ2-deficient mouse models, increased calcium flux in the sarcoplasmic reticulum was observed in one study, leading to abnormal calcium release into the cardiac cells’ cytosol, and further promoting AF [83]. Moreover, cardiomyocytes from TET2-deficient mice have demonstrated prolonged calcium transient and release, contributing to electrical remodeling and increased AF risk [83]. Several other studies support the role of cardiac macrophages in electrical cardiac functionality and arrhythmia development [84,85,86,87], while calcium dysregulation is considered to be worsened by inflammatory molecules (IL-1β and IL-6) in TET2-deficient macrophages [39]. Several in vivo studies confirm that cultures of atrial cardiomyocytes with TET2-deficient macrophages cause reduced serum calcium and impaired calcium transients, along with findings of studies on mouse models [39,83].

2.4. Other Secondary Potential Mechanisms (Thrombophilia, Elevated Red Cell Distribution Width)

Thromboembolism is a common complication of AF, as previously referred to herein [88]. CHIP is strongly associated with pro-thrombotic states, potentially elevating the risk of thromboembolic events in AF patients [89]. CHIP mutations, mainly JAK2, are linked with elevated thrombotic risk, increasing megakaryocyte activity, enhancing platelet reactivity through hypersensitive thrombopoietin (MPL) receptors, and raising levels of procoagulant microvesicles; all these represent mechanisms that enhance coagulation and blood clotting [90,91]. In addition to JAK2, mutations in TET2 and DNMT3A also contribute to CHIP-related hypercoagulability [83]. TET2 mutations lead to increased inflammatory cytokines like IL-1β and IL-6, worsening endothelial dysfunction and thrombin production [92]. This pro-inflammatory environment interacts with coagulation pathways, creating conditions conducive to thromboembolic events [93,94].

Red cell distribution width (RDW) reflects the variability in erythrocyte size and is closely related to hematopoietic dysfunction [95]. Elevated RDW is a strong predictor of increased mortality and poor prognosis in AF patients [96]. In non-valvular AF, RDW levels below 13.9% strongly indicate thromboembolic events, with predictive accuracy increasing at older ages [97]. Additionally, a meta-analysis reported a significant connection between elevated RDW and AF pathogenesis, while, at the same time, RDW is the only hematological parameter that is found consistently elevated in CHIP carriers, potentially indicating underlying disruptions in erythropoiesis or hematopoiesis in general, which both represent characteristic features of CHIP [98,99].

3. Initial Observations Supporting the Association Between CHIP and AF and Shared Risk Factors

Recently reported clinical evidence highlights the significant interplay between CHIP alterations and AF pathogenesis, complications, and risk stratification. A population-based study by UK Biobank on over 200,000 individuals found a modest 1.09-fold increased risk of AF in those with CHIP [100]. Several mutations, mainly in TET2 and ASXL1, are associated with increased AF risk, at percentages 1.18- and 1.33-fold, respectively [53,100,101]. Moreover, CHIP mutations are associated with specific disease subtypes in AF patients, namely postoperative AF (POAF) and in-hospital AF, predisposing individuals of all ages carrying CHIP mutations for undergoing aortic valve replacement to have a 3.5-fold higher risk of POAF [62,101,102]. The prevalence of AF is also significantly higher among CHIP carriers who underwent cardiac surgery and stem cell transplantation, especially those with larger clones (variant allele frequency above 10%). These individuals also tend to experience higher recurrence rates. While a dose–response relationship between CHIP clone size and AF risk has been hypothesized, causality remains uncertain due to potential confounding factors and shared aging-related pathways [103,104]. Moreover, several risk factors that predispose both to CHIP and AF have been identified, including age, lifestyle, and cardiometabolic comorbidities [44].

Increasing aging is the main predisposing factor of cardiovascular disease, surpassing traditional risk factors (e.g., hypertension, smoking), and leading to dysregulation of several mechanisms of myocardial functionality and to the acquisition of somatic mutations, as well [105,106]. A large number of mutations that affect the cardiovascular system originate from the bone marrow, though only a minority of them confer a growth advantage that leads to clonal expansion and accelerates age-related conditions, including AF [96]. A significant increase in AF with age is observed in several population studies, specifically from approximately 2% in the general population to 10–12% in individuals over 80 years of age [107,108]. An association between CHIP and epigenetic aging has been demonstrated, with a potential link with cardiac disease development [43]. Specifically, TET2 mutations that can occur at any year of age but are most common in individuals above 80 years of age, are likely to influence both CHIP and AF pathogenesis, with CHIP mutations becoming more prevalent with age and found more frequently in patients with AF compared to healthy individuals [109,110]. The mechanisms behind these correlations have not been fully identified; however, factors like age-related inflammation and telomere shortening are suggested to play a crucial role [43]. Moreover, lifestyle factors, including smoking, cardiometabolic syndrome (including related comorbidities, e.g., diabetes, PCOS) [111], and a high-fat diet, not only predispose to cardiac disease, but also have a 16% increased risk of CHIP, particularly with ASXL1 mutations, and this risk persists even after quitting [112,113]. Diet similarly influences these conditions. Low vegetable or high meat consumption is linked to a 25% higher risk of CHIP and increased AF susceptibility, indicating that dietary choices may impact both through common mechanisms [112,114].

In more detail regarding cardiometabolic comorbidities, patients with AF and CHIP mutations present a higher prevalence of hypertension, while TET2 deficiency, due to TET2 somatic mutations identified in human tissues via deep-targeted sequencing, has been demonstrated in population-based studies to be an aggravating factor for cardiac dysfunction, NLRP3 inflammasome activation, and sodium retention, effects that can be considered potential therapeutic targets in AF patients [58,115]. Obesity and diabetes are also main contributors to both conditions, while higher body mass index (BMI) and waist-to-hip ratios are associated with increased CHIP prevalence [100,112]. In diabetic patients, CHIP independently increases cardiovascular disease risk by 21% [65]. Conversely, AF patients with CHIP (especially with TET2 and ASXL1 alterations) face a 23% higher diabetes risk [116]. Studies on animal models have reported potential links between obesity, particularly leptin deficiency, and increased CHIP levels and inflammation, underscoring the interplay between metabolic health and CHIP in cardiovascular disease [117].

4. Clinical Studies and Real-World Data

Collectively, several recent population-based studies have demonstrated the potential link between CHIP and AF, highlighting the potential of targeting CHIP mutations as a part of AF therapy and prevention. A study on over a thousand AF individuals reported CHIP mutations in 23.6% of AF patients and 10.7% in controls, using deep-targeted sequencing of 24 CHIP-associated genes with a VAF of ≥2% as a threshold [49]. Specifically, for TET2 mutations, this study showed that they were significantly more frequent in AF patients with an adjusted odds ratio of 1.65. Individuals with AF and CHIP demonstrated worse clinical phenotype, including longer AF duration, increased left atrial size, and higher diastolic dysfunction [49]. Moreover, in this cohort, AF patients with CHIP presented a 1.32-fold risk of severe adverse events (heart failure and stroke), while the presence of CHIP mutations was an independent risk factor of mortality [58]. Another population-based study on TET2 mutations, using evidence from both in vivo studies of a patient cohort (358,000 participants in total) and murine models, showed that CHIP (VAF ≥ 2%) predisposed to AF development with an 11% increased risk, with TET2 mutations conferring the highest risk [83]. Interestingly, TET2-deficient mouse models demonstrated that inflammation via the NLRP3 inflammasome and calcium handling abnormalities in atrial cells contributed to AF susceptibility, findings that were further proved by the decreased arrhythmia incidence after NLRP3 inhibition [74].

CHIP mutations in AF patients were further investigated using the large patient Biobank’s data of over a million AF individuals. To begin with, a large UK Biobank study on over 410,000 middle-aged adults without baseline arrhythmias, reported, by using whole-exome sequencing and identifying CHIP with VAF ≥ 2% (any CHIP) and ≥10% (large CHIP), that CHIP was an independent risk factor for the development of cardiac arrhythmias, especially the large clones [101]. TET2 and ASXL1 mutations are common CHIP mutations predisposing to cardiac arrest, with inflammation and myocardial remodeling proposed as the main pathogenetic mechanisms [101]. Another population-based study using the ARIC and UK Biobank studies reported similar results for TET2 and ASXL1 mutations, specifically suggesting that TET2 mutations were associated with elevated IL-6, indicating systemic inflammation, while ASXL1 mutations correlated with markers of cardiac remodeling, such as increased troponin T levels and left ventricular mass [19]. ASXL1 mutations have also been studied in a high-risk cohort consisting of cardiac catheterized patients and have been shown to be significantly different (2-fold increased) [19]. Screening for the aforementioned CHIP mutations is not yet part of standard AF practice in patients’ cohorts, primarily due to the absence of proven interventions to mitigate the increased cardiovascular risk associated with these mutations. Further research, including animal studies and clinical trials, is essential to convert this expanding knowledge into targeted, personalized strategies for preventing and managing AF.

5. Driver Mutations Involving CHIP and AF: A Brief Sum-Up of Their Potential Distinct Role

The most commonly observed driver mutations are DNMT3A, TET2, and ASXL1, followed by several other mutations, including JAK2, PPM1D, TP53, SF3B1, and SRSF2. Current knowledge on the role of each gene mutation in AF pathogenesis is discussed in the next sections.

5.1. DNMT3A Mutation

DNMT3A is an epigenetic regulator that encodes a methyltransferase controlling gene silencing via CpG methylation, playing a crucial role in hematopoietic stem cell (HSC) self-renewal and differentiation [118,119]. DNMT3A mutations represent over 50% of identified CHIP mutations [110]. In the UK Biobank, over 3.4% of individuals carry these mutations [19,58]. Mechanistically, DNMT3A mutations, mainly detected in peripheral blood, activate monocytes and CD8+ T cells, triggering the NLRP3/IL-1/IL-6 inflammatory axis and promoting resistance to apoptosis via interferon-gamma (IFN-γ) [120,121,122]. They also increase CXCL chemokine expression and activate pathways like RASSF1A-ERK1/2 in hematopoietic stem and progenitor cells, which can contribute to myocardial fibrosis [121,122,123]. The effect of DNMT3A mutations on cardiovascular disease is not yet fully elucidated; however, recent evidence demonstrates its association with many diseases, including atherosclerosis, heart failure, or peripheral artery disease, while in atrial fibrillation, as previously reported herein, it presents a rather limited impact [40]. This lack of correlation is partially related to the absence of associations between DNMT3A mutations and mean leukocyte telomere length [40].

In more detail, clinical studies on stem cell transplant recipients or individuals with familial DNMT3A mutations have demonstrated several correlations with cardiac abnormalities, suggesting that they are explained mainly by secondary factors (transplant-related stress and inflammation) rather than the mutation itself; therefore, although DNMT3A mutations do not directly cause AF, they affect its pathogenesis through inflammatory pathways and signaling pathways [124,125]. A recent study showed that DNMT3A possibly contributes to recurrent AF in elderly populations via the activation of the PI3K-Akt signaling pathway, in combination with the downregulation of miR-200b [126]. These observations, however, present limitations, considering that the abnormal levels of DNMT3A, miRNAs, and PI3K-Akt molecules in circulating serum may be influenced by various factors, making it difficult to establish a direct link to AF [40]. Further in vitro and in vivo evidence is needed to confirm these observations.

5.2. TET2 Mutation

TET2, the second most common CHIP mutation, encodes a dioxygenase involved in DNA methylation, playing an important role in epigenetic regulation and hematopoietic processes [127,128]. In more detail, TET2 mutations are detected in the peripheral blood of 5–10% of adult individuals older than 65 years of age and are associated with myeloid expansion and innate immunity dysregulation, further contributing to several diseases, including leukemia and cardiovascular disease [129,130]. In mouse models, it has been shown that TET2 deficiency enhances myeloid differentiation via enhancing hematopoietic stem cell self-renewal, with bone marrow dysfunction and extramedullary hematopoiesis presenting as further consequences [131]. Epidemiological studies address a link between TET2 mutations and an increased risk of AF, demonstrating associations between accelerated atherosclerosis, myocardial fibrosis, cardiac arrest, and adverse cardiac remodeling, with TET2 alterations [44]. TET2 gene alterations promote AF through structural and electrical atrial remodeling, with the main mechanisms being the decreased refractory periods and the enlarged left atrium, as observed in studies in animal models [83]. The activation of inflammatory pathways by TET2 mutations, specifically the NLRP3/IL-1/IL-6 axis, and the subsequent dysregulated cytokine production in macrophages disrupts calcium signaling and cellular homeostasis, leading to further cardiac dysfunction and predisposing to AF development [83]. Worth noting, a recent study in TET2-mutant patients treated with IL-1β inhibitor canakinumab reports decreased cardiovascular events in these patients, highlighting the potential involvement of TET2 mutations in cardiac disease via inflammatory pathways, as well as the therapeutic role of targeting inflammation [44,132].

5.3. ASLX1 Mutation

ASLX1 is the third most common CHIP mutation, mainly presenting as a frameshift or nonsense variant in the terminal gene exon. It has a crucial role in epigenetic regulation by promoting gene activation through chromatin interactions [133]. ASLX1 mutations are mainly encountered in older individuals with chronic inflammation (e.g., prior HIV infection), where inflammation is considered a main driver of clonal expansion, highly correlated with mortality rates [134,135]. The involvement of ASLX1 mutations in AF has not yet been fully described, with current evidence addressing a 22% elevated risk per 10% increase in the size of clones; however, other studies report no significant correlations, possibly due to the different VAF thresholds [19,83]. At a pathophysiologic level, ASLX1 mutations may be involved in cardiac remodeling via inflammatory pathways, as has been suggested by studies in mouse models correlating ASLX1 with elevated macrophage infiltration and pro-inflammatory cytokine levels [122]. At the clinical level, this generally inflammatory environment is associated with adverse cardiac phenotypes, including increased serum troponin, increased left ventricular mass index, and elevated N-terminal pro-BNP, factors indicating ongoing cardiovascular damage and heart-related pathologies [136].

5.4. Other Driver Mutations (JAK2, TP53, PPM1D, Spliceosome)

JAK2 encodes a tyrosine kinase involved in receptor signaling for hematopoietic cytokines, including growth hormone and prolactin, and also plays a crucial role in TET2 phosphorylation [137,138]. JAK2 mutations can be detected using both peripheral blood and bone marrow samples. The V617F mutation, which represents the most common JAK2 variant, is encountered mostly in individuals of a younger age and is strongly associated with clonal hematopoiesis, with a detection rate of approximately 3% [139]. JAK2 mutations significantly increase the risk of coronary heart disease, mainly via platelet vulnerability enhancement [139]. Although the association between JAK2 mutations and AF has not been much investigated, pathophysiologic mechanisms previously analyzed herein create a potential association: JAK2 mutations may lead to atrial remodeling and fibrosis via activating the inflammasome and NLRP3 pathway, being involved in AF pathogenesis [139,140]. Primary results from animal studies show that JAK2 inhibition decreases atrial fibrosis, preventing electrical and mechanical remodeling; however, real-world data from further cohort studies are needed to confirm this hypothesis [44]. TP53, PPM1D, and spliceosome gene mutations (SF3B1 and SRSF2) are less common CHIP driver mutations, which lead to genomic instability (TP53), regulate hematopoietic stem cell renewal (TP53 and PPM1D), are essential for RNA splicing and gene regulation (SF3B1 and SRSF2), or are associated with high mortality rates and poor chemosensitivity (PPM1D), all being strongly associated with hematologic malignancies [40]. Their role on AF is rather under-investigated; however, UK Biobank suggests that TP53 and PPM1D may elevate arrhythmia, and a recent cohort study on individuals carrying SF3B1 mutations showed a 1.73-fold increased risk of arrhythmia for SF3B1 mutations [141]. Notably, SF3B1 is considered a common genetic alteration among diabetics who exhibit a 2.5-fold increased cardiovascular risk, which highlights the need for further investigation on its roles [142].

A brief sum-up of research findings for the role of the aforementioned CHIP mutations in AF pathogenesis is presented in

Table 1. Driver CHIP mutations with a potential clinical impact on AF pathogenesis. [AF: atrial fibrillation; CHIP: clonal hematopoiesis of intermediate potential].

References	Driver CHIP Mutations	Pathophysiology	Clinical Impact on AF
[124,125,126,127]	DNMT3	CpG methylation, regulates HSC self-renewal and differentiation	No significant correlation. Worsening AF in special patient groups: the elderly, cases of chronic inflammation, and/or post-transplantation.
[129,130,132]	TET2	DNA methylation, regulates HSC self-renewal and differentiation at deficient state, promotes myeloid expansion	Strong correlation with AF development. Increased AF risk.
[19,83,122,136]	ASXL1	Regulates epigenetic processes via chromatin-binding proteins	Limited data for its association with AF pathogenesis.
[139,140]	JAK2	Tyrosine kinase activity	Mildly elevated risk for AF via the inflammasome pathway.
[44,45,46,47,48,49,50,51,52,53,54,55,56,57,58,59,60,61,62,63,64,65,66,67,68,69,70,71,72,73,74,75,76,77,78,79,80,81,82,83,84,85,86,87,88,89,90,91,92,93,94,95,96,97,98,99,100,101,102,103,104,105,106,107,108,109,110,111,112,113,114,115,116,117,118,119,120,121,122,123,124,125,126,127,128,129,130,131]	TP53	Regulates DNA damage repair	May elevate arrhythmias (including AF) in some cases.
[40,130]	PPM1D	Regulates DNA damage repair	May elevate arrhythmias in some cases.
[142]	SF3B1	Regulates mRNA splicing	A study reports increased AF incidence in patients with SF3B1 mutations.

.

6. Discussion and Future Directions

CHIP and AF are two distinct entities sharing common risk factors and pathophysiological mechanisms (Figure 2); however, a direct causal link between them has not yet been confirmed. Chronic inflammatory state is considered to be a central mechanism in oncogenesis and in cardiac disease, dysregulating calcium homeostasis and enhancing abnormal electrical activity, while other mechanisms, mainly atrial enlargement, serve as potential contributors, as well [40,143,144,145,146]. The exact role of the different driver CHIP mutations on AF pathogenesis varies. The strongest association to AF is served by TET2 mutations, while DNMT3A, despite being the most common CHIP mutation, generally presents no significant association with AF, except in conditions of chronic inflammatory disease or post-transplantation stress [43,124,125,126]. The distinct roles of rarer CHIP mutations (ASXL1, JAK2, TP53, PPM1D, and spliceosome components) might also influence AF [19,44,74,122,136,139,140,141]. The emerging effect of inflammation, and especially inflammasome activity, in CHIP-TET2/DNMT3 association, suggests the promising role of targeting the inflammasome in order to reduce inflammation and subsequently decrease AF complications and mortality risk [39,147,148]. Colchicine, canakinumab, and IL-6 blockers are anti-inflammatory drugs being tested in currently conducted clinical trials on individuals carrying CHIP mutations [149]. Hypomethylating agents, mainly JAK2 inhibitors, antifibrotic medication, mainly sodium-glucose co-transporter-2 (SGLT2) inhibitors, and GLP-1 receptor agonists are also potential inhibitors of AF progression; however, further research is needed to confirm their efficacy in CHIP-related AF [139,150]. Regarding SGLT2 inhibitors, their protective effect against cardiovascular disease has been confirmed in recent studies, which indicate a possible pathophysiologic interconnection between AF and heart failure with reduced ejection fraction [150]. However, other studies show contradictory results, suggesting that SGLT2 inhibitors do not decrease the risk of AF occurrence, regardless of other factors (type of therapeutic evaluation, patients’ follow-up, and patients’ demographic and clinical characteristics). Further research is needed to establish an exact correlation [151,152,153].

Despite the significant progress in understanding the complex correlations between CHIP and AF, in vivo investigation faces several limitations, including the variability in sequencing methods (mainly the low sensitivity of whole exome sequencing in detecting low VAF clones and different VAF thresholds in different studies) and the lack of diversity of the studied cohorts, as most studies analyzed herein are predominantly conducted in European populations [19,39,40,74,112,114,115,116,125,128,129,130]. In the near term, clinical application of current knowledge, in terms of applying the aforementioned evidence on further exploring and targeting CHIP mutations (mainly TET2 and JAK2) as diagnostic markers and therapeutic targets of the medication previously described (mainly hypomethylating agents), would be of a great interest for better establishing the role of CHIP mutations in AF patients. While anti-inflammatory therapies targeting NLRP3 mutations show potential in mitigating AF, further research is needed to evaluate their efficacy across various CHIP mutations and to determine the utility of CHIP as a predictive biomarker for classifying AF subtypes and related complications. Furthermore, exploring the dose–response relationship between the size of VAF clones and AF progression could further guide AF clinical management and prevention in individuals carrying CHIP mutations [39]. It would also be of great importance to incorporate translational and epigenomic research techniques—fundamental tools in ongoing investigations of CHIP mutations, leukemia, and other cancers—to uncover the indirect roles of CHIP in AF pathogenesis [154,155,156,157]. Chromatin immunoprecipitation followed by sequencing (ChIP-seq) is a novel technique that allows genome-wide analysis of histone modifications, enhancer activity, and chromatin states, providing evidence into how the epigenome influences cell identity, development, lineage specification, and disease, and could play a role in AF pathogenesis, especially for common CHIP mutations for which data regarding AF pathogenesis are scarce [158,159]. Other advanced genomic techniques, including polygenic risk scores, Mendelian randomization, and PheWAS, are considered promising for covering the aforementioned research gap in establishing optimal VAF thresholds for different populations in the near term. Another issue to be addressed is the identification of the mechanistic pathways linking specific CHIP mutations, particularly those involving the inflammasome, with inflammation and AF, which are currently not fully understood. Overall, integrating mechanistic insights with clinical, translational, and epigenetic research is the key to moving from correlation to causation, enabling personalized treatment strategies for AF in CHIP carriers.

7. Conclusions

In conclusion, emerging evidence strongly indicates CHIP mutations, especially TET2, are a promising risk factor for AF development. Recent findings analyzed herein underscore the potential advantage of CHIP mutation screening in AF patients, as well as the role of cardiovascular surveillance in individuals with CHIP mutations. Despite promising evidence from current studies, CHIP evaluation is not yet a part of standard cardiology practice, mainly due to the absence of established interventions mitigating the elevated CHIP-driven cardiovascular risk. Future research is essential for clarifying shared risk factors and signaling pathways between CHIP and AF, further aiming to develop CHIP-targeted therapeutic options, converting the expanding knowledge described in this review into targeted strategies for preventing and managing AF.