Mechanism of and therapeutic strategy for atrial fibrillation associated with diabetes mellitus

Impact of Diabetes Mellitus on Stroke and Survival in Patients With Atrial Fibrillation

Although diabetes mellitus (DM) has been established as a risk factor for developing atrial fibrillation (AF) and is a known risk factor for stroke, it is unclear whether the presence or duration of DM is the primary adverse influence on the clinical course of AF. We retrospectively analyzed patients diagnosed with incident AF to examine the impact of DM on ischemic stroke and all-cause mortality. The diagnosis of DM was established by ICD-9 codes and review of medical records. To account for the significant differences in baseline characteristics of patients with and without diabetes, we matched 909 AF patients with DM with 909 AF patients without DM using propensity score matching based on 26 baseline variables. Cox regression analysis was used to identify independent factors associated with ischemic stroke and mortality. The mean age of the propensity matched cohort was 74 ± 11.5 years and 55.4% were male. Over a median follow-up period of 5.4 years (maximum 23.9 years), cumulative survival was significantly lower for patients with DM than those without DM; Log-rank p <0.001. In the propensity-matched comparison, the risk of mortality was significantly higher in the DM group compared with the non-DM group (hazard ratio 1.25; 95% confidence interval 1.12 to 1.69; p <0.001). Likewise, patients with DM had a higher risk of stroke (hazard ratio 1.32; 95% confidence interval 1.02 to 1.69; p = 0.03). Duration of DM was not associated with increased risk for stroke or mortality. In conclusion, the co-morbidity of DM represents an independent predictor of reduced survival and further highlights the excess risk of thromboembolism in patients with AF.

Insulin Treatment Reduces Susceptibility to Atrial Fibrillation in Type 1 Diabetic Mice

Diabetes has been identified as an independent risk factor for atrial fibrillation (AF), the most common chronic cardiac arrhythmia. Whether or not glucose and insulin disturbances observed during diabetes enhance arrhythmogenicity of the atria, potentially leading to AF, is not well-known. We hypothesized that insulin deficiency and impaired glucose transport provide a metabolic substrate for the development and maintenance of AF during diabetes. Transesophageal atrial pacing was used to induce AF in healthy, streptozotocin-induced insulin-deficient type 1 diabetic, and insulin-treated diabetic mice. Translocation of insulin-sensitive glucose transporters (GLUTs) to the atrial cell surface was measured using a biotinylated photolabeling assay in the perfused heart. Fibrosis and glycogen accumulation in the atrium were measured using histological analysis. Diabetic mice displayed mild hyperglycemia, increased duration and frequency of AF episodes vs. age-matched controls (e.g., AF duration: 19.7 ± 6.8 s vs. 1.8 ± 1.1 s, respectively, p = 0.032), whereas insulin-treated diabetic animals did not. The translocation of insulin-sensitive GLUT-4 and -8 to the atrial cell surface was significantly downregulated in the diabetic mice (by 67 and 79%, respectively; p ≤ 0.001), and rescued by insulin treatment. We did not observe fibrosis or glycogen accumulation in the atria of diabetic mice. Therefore, these data suggest that insulin and glucose disturbances were sufficient to induce AF susceptibility during mild diabetes.

The association between SGLT2 inhibitors and new-onset arrhythmias: a nationwide population-based longitudinal cohort study

BACKGROUND

Clinical trials have shown the cardiovascular protective effect of sodium-glucose cotransporter-2 (SGLT2) inhibitors and reduced hospitalization for heart failure. However, no study has investigated the association between SGLT2 inhibitors and the risk of arrhythmias. This study aimed to evaluate the risk of new-onset arrhythmias (NOA) and all-cause mortality with the use of SGLT2 inhibitors.

METHODS

This was a population-based cohort study utilizing Taiwan's National Health Insurance Research Database. Each patient aged 20 years and older who took SGLT2 inhibitors was assigned to the SGLT2 inhibitor group, whereas sex-, age-, diabetes mellitus duration-, drug index date-, and propensity score-matched randomly selected patients without SGLT2 inhibitors were assigned to the non-SGLT2 inhibitor group. The study outcome was all-cause mortality and NOA.

RESULTS

A total of 399,810 patients newly diagnosed with type 2 DM were enrolled. A 1:1 matching propensity method was used to match 79,150 patients to 79,150 controls in the non-SGLT2 inhibitors group for analysis. The SGLT2 inhibitor group was associated with a lower risk of all-cause mortality [adjusted hazard ratio (aHR) 0.547; 95% confidence interval (CI) 0.482-0.621; P = 0.0001] and NOA (aHR 0.830; 95% CI 0.751-0.916; P = 0.0002).

CONCLUSIONS

Patients with type 2 DM prescribed with SGLT2 inhibitors were associated with a lower risk of all-cause mortality and NOA compared with those not taking SGLT2 inhibitors in real-world practice.

Loss of insulin signaling may contribute to atrial fibrillation and atrial electrical remodeling in type 1 diabetes

Atrial fibrillation (AF) is prevalent in diabetes mellitus (DM); however, the basis for this is unknown. This study investigated AF susceptibility and atrial electrophysiology in type 1 diabetic Akita mice using in vivo intracardiac electrophysiology, high-resolution optical mapping in atrial preparations, and patch clamping in isolated atrial myocytes. qPCR and western blotting were used to assess ion channel expression. Akita mice were highly susceptible to AF in association with increased P-wave duration and slowed atrial conduction velocity. In a second model of type 1 DM, mice treated with streptozotocin (STZ) showed a similar increase in susceptibility to AF. Chronic insulin treatment reduced susceptibility and duration of AF and shortened P-wave duration in Akita mice. Atrial action potential (AP) morphology was altered in Akita mice due to a reduction in upstroke velocity and increases in AP duration. In Akita mice, atrial Na⁺ current (I_Na) and repolarizing K⁺ current (I_K) carried by voltage gated K⁺ (K_v1.5) channels were reduced. The reduction in I_Na occurred in association with reduced expression of SCN5a and voltage gated Na⁺ (Na_V1.5) channels as well as a shift in I_Na activation kinetics. Insulin potently and selectively increased I_Na in Akita mice without affecting I_K Chronic insulin treatment increased I_Na in association with increased expression of Na_V1.5. Acute insulin also increased I_Na, although to a smaller extent, due to enhanced insulin signaling via phosphatidylinositol 3,4,5-triphosphate (PIP₃). Our study reveals a critical, selective role for insulin in regulating atrial I_Na, which impacts susceptibility to AF in type 1 DM.

Cardiometabolic-Based Chronic Disease, Addressing Knowledge and Clinical Practice Gaps: JACC State-of-the-Art Review

In the second part of this JACC State-of-the-Art Review, an early and sustainable preventive care plan is described for cardiometabolic-based chronic disease. This plan can improve cardiometabolic health by targeting early mechanistic events to decrease the risk for certain cardiovascular diseases (e.g., coronary heart disease, heart failure, and atrial fibrillation). Included are various prevention modalities, intensive lifestyle interventions, pharmacotherapy and cardiovascular outcome trial evidence, and bariatric/metabolic procedures. A tactical approach of implementing published clinical practice guidelines/algorithms for early behavioral, adiposity, and dysglycemia targeting is emphasized, as well as relevant educational and research implications.

Diabetes mellitus and atrial remodelling in patients with paroxysmal atrial fibrillation: Role of electroanatomical mapping and catheter ablation

Complex fractionated atrial electrograms (CFAEs) are related to atrial fibrosis, but their ablation has not yet shown superiority. The aim of the study was to compare, in terms of clinical outcome, two strategies of paroxysmal atrial fibrillation (AF) ablation in patients with type 1 diabetes mellitus (DM): pulmonary vein isolation (PVI) vs. PVI + CFAEs. Compared to an historical population of patient with paroxysmal AF and without DM, a higher percentage of patients with DM showed more than 25% of atrial area interested by CFAEs (study population, 58% vs historical group, 15%; p < 0.05). In PVI group, recurrences rate was similar in patients with HbA1c ⩽ 7.5% vs HbA1c > 7.5% (30% vs 22%; p = not significant), but a greater AF burden was observed in patients with HbA1c > 7.5% (6 ± 2 vs 1 ± 2; p < 0.05). In hazard ratios analysis PVI+CFAEs seems more effective than PVI alone in patients with HbA1c > 7.5% (hazard ratio, 1.28; p < 0.05), more than 25 years from DM diagnosis (hazard ratio, 1.25; p < 0.05) and more than five AF episodes/year (hazard ratio, 1.2; p < 0.05). Type 1 DM patients had complex atrial 'substrate', as documented by wider CFAEs areas. Despite this, 1-year follow-up recurrence rate was similar between two ablation approaches (PVI 27% vs. PVI+CFAEs 21%; p = not significant). In our study, only specific subgroups, like patients with disglycaemic state (HbA1c > 7.5%), long diabetes mellitus history and high AF burden, benefit from PVI+ CFAEs approach.

Dysregulation of insulin-sensitive glucose transporters during insulin resistance-induced atrial fibrillation

Diabetes has been identified as major risk factor for atrial fibrillation (AF). Although glucose and insulin disturbances during diabetes may affect atrial function, little is known about the potential pathogenic role of glucose metabolism during AF. Glucose transport into the cell via glucose transporters (GLUTs) is the rate-limiting step of glucose utilization. Although GLUT4 is the major isoform, GLUT8 has emerged as a novel insulin-sensitive cardiac isoform. We hypothesized that atrial glucose homeostasis will be impaired during insulin resistance-induced AF. AF was induced by transesophageal atrial pacing in healthy mice and following a long-term high-fat-diet-induced insulin resistance. Active cell surface GLUT content was measured using the biotinylated photolabeling assay in the intact perfused heart. Atrial fibrosis, advanced glycation end products (AGEs) and glycogen were measured in the atria using histological analyses. Animals fed a high-fat-diet were obese and mildly hyperglycemic, and developed insulin resistance compared to controls. Insulin-resistant (IR) animals demonstrated an increased vulnerability to induced AF, as well as spontaneous AF. Insulin-stimulated translocation of GLUT4 and GLUT8 was down-regulated in the atria of IR animals, as well as their total protein expression. We also reported the absence of fibrosis, glycogen and AGE accumulation in the atria of IR animals. In the absence of structural remodeling and atrial fibrosis, these data suggest that insulin signaling dysregulation, resulting in impaired glucose transport in the atria, could provide a metabolic arrhythmogenic substrate and be a novel early pathogenic factor of AF.

Alogliptin, a Dipeptidyl Peptidase-4 Inhibitor, Alleviates Atrial Remodeling and Improves Mitochondrial Function and Biogenesis in Diabetic Rabbits

BACKGROUND

There is increasing evidence implicating atrial mitochondrial dysfunction in the pathogenesis of atrial fibrillation. In this study, we explored whether alogliptin, a dipeptidyl peptidase-4 inhibitor, can prevent mitochondrial dysfunction and atrial remodeling in a diabetic rabbit model.

METHODS AND RESULTS

A total of 90 rabbits were randomized into 3 groups as follows: control group (n=30), alloxan-induced diabetes mellitus group (n=30), and alogliptin-treated (12.5 mg/kg per day for 8 weeks) diabetes mellitus group (n=30). Echocardiographic and hemodynamic assessments were performed in vivo. The serum concentrations of glucagon-like peptide-1, insulin, and inflammatory and oxidative stress markers were measured. Electrophysiological properties of Langendorff-perfused rabbit hearts were assessed. Mitochondrial morphology, respiratory function, membrane potential, and reactive oxygen species generation rate were assessed. The protein expression of transforming growth factor β1, nuclear factor κB p65, and mitochondrial biogenesis-related proteins were measured by Western blot analysis. Diabetic rabbits exhibited left ventricular hypertrophy and left atrial dilation without obvious hemodynamic abnormalities, and all of these changes were attenuated by alogliptin. Compared with the control group, higher atrial fibrillation inducibility in the diabetes mellitus group was observed, and markedly reduced by alogliptin. Alogliptin decreased mitochondrial reactive oxygen species production rate, prevented mitochondrial membrane depolarization, and alleviated mitochondrial swelling in diabetic rabbits. It also improved mitochondrial biogenesis by peroxisome proliferator-activated receptor-γ coactivator 1α/nuclear respiratory factor-1/mitochondrial transcription factor A signaling regulated by adiponectin/AMP-activated protein kinase.

CONCLUSIONS

Dipeptidyl peptidase-4 inhibitors can prevent atrial fibrillation by reversing electrophysiological abnormalities, improving mitochondrial function, and promoting mitochondrial biogenesis.

Temporal trends in ischemic stroke and anticoagulation therapy for non-valvular atrial fibrillation: effect of diabetes

BACKGROUND

Diabetes is an important risk factor for ischemic stroke in non-valvular atrial fibrillation (AF). The aim of the present study was to evaluate temporal trends in ischemic stroke and warfarin use among US Medicare patients with and without diabetes.

METHODS

In this retrospective cohort study, 1-year cohorts of patients with Medicare as the primary payer over the period 1992-2010 were created using the Medicare 5% sample (excluding patients with valvular disease and end-stage renal disease). International Classification of Diseases, Ninth Revision, Clinical Modification (ICD-9-CM) codes were used to identify AF, ischemic and hemorrhagic stroke, and diabetes; three or more consecutive prothrombin time claims were used to identify warfarin use.

RESULTS

Demographic characteristics of subjects in 1992 (n = 40 255) and 2010 (n = 80 314), respectively, were as follows: age 65-74 years, 37% and 32%; age >85 years, 20% and 25%; White, 94% and 93%; hypertension, 46% and 80%; diabetes, 20% and 32%; and chronic kidney disease, 5% and 18%. Among Medicare AF patients with diabetes, ischemic stroke decreased by 71% (1992-2010) from 65 to 19 per 1000 patient-years; warfarin use increased from 28% to 62%. Among patients without diabetes, ischemic stroke decreased by 68% from 44 to 14 per 1000 patient-years, whereas warfarin use increased from 26% to 59%. Approximately 38% of Medicare AF patients with diabetes did not receive anticoagulation in 2010.

CONCLUSIONS

Ischemic stroke declined and warfarin use increased similarly in Medicare patients with and without diabetes. Ischemic stroke rates were consistently higher in diabetes patients, validating the inclusion of diabetes in risk calculators. The population of Medicare patients with diabetes who did not receive warfarin deserves future attention.

Pathophysiology of cancer therapy-provoked atrial fibrillation

Atrial fibrillation (AF) occurs with increased frequency in cancer patients, especially in patients who undergo surgery or chemotherapy. AF disturbs the prognosis of cancer patients and challenges therapeutic outcomes of cancer treatment. Elucidating the mechanisms of cancer-induced AF would help identify specific strategies for preventing AF occurrence. In addition to concurrent risk factors of cancer and AF, cancer surgery, side effects of anticancer agents, and cancer-associated immune responses play critical roles in the genesis of AF. In this review, we provide succinct potential mechanisms of AF genesis in cancer patients.

Diabetes Alters the Expression and Translocation of the Insulin-Sensitive Glucose Transporters 4 and 8 in the Atria

Although diabetes has been identified as a major risk factor for atrial fibrillation, little is known about glucose metabolism in the healthy and diabetic atria. Glucose transport into the cell, the rate-limiting step of glucose utilization, is regulated by the Glucose Transporters (GLUTs). Although GLUT4 is the major isoform in the heart, GLUT8 has recently emerged as a novel cardiac isoform. We hypothesized that GLUT-4 and -8 translocation to the atrial cell surface will be regulated by insulin and impaired during insulin-dependent diabetes. GLUT protein content was measured by Western blotting in healthy cardiac myocytes and type 1 (streptozotocin-induced, T1Dx) diabetic rodents. Active cell surface GLUT content was measured using a biotinylated photolabeled assay in the perfused heart. In the healthy atria, insulin stimulation increased both GLUT-4 and -8 translocation to the cell surface (by 100% and 240%, respectively, P<0.05). Upon insulin stimulation, we reported an increase in Akt (Th308 and s473 sites) and AS160 phosphorylation, which was positively (P<0.05) correlated with GLUT4 protein content in the healthy atria. During diabetes, active cell surface GLUT-4 and -8 content was downregulated in the atria (by 70% and 90%, respectively, P<0.05). Akt and AS160 phosphorylation was not impaired in the diabetic atria, suggesting the presence of an intact insulin signaling pathway. This was confirmed by the rescued translocation of GLUT-4 and -8 to the atrial cell surface upon insulin stimulation in the atria of type 1 diabetic subjects. In conclusion, our data suggest that: 1) both GLUT-4 and -8 are insulin-sensitive in the healthy atria through an Akt/AS160 dependent pathway; 2) GLUT-4 and -8 trafficking is impaired in the diabetic atria and rescued by insulin treatment. Alterations in atrial glucose transport may induce perturbations in energy production, which may provide a metabolic substrate for atrial fibrillation during diabetes.

Changes of Virtual Planar QRS and T Vectors Derived from Holter in the Populations with and without Diabetes Mellitus

Aims

Research related to type 2 diabetes mellitus (DM) and parameters of electrocardiography (ECG) was limited. Patients with and without DM (NDM) were randomly enrolled in a study to exploit the influence of DM on planar QRS and T vectors derived from the Virtual Holter process.

Methods

A total of 216 (NDM) and 127 DM patients were consecutively and randomly recruited. We selected a 1‐minute length of ECG, which was scheduled for analysis at 4 AM. After a series of calculating algorisms, we received the virtual planar vector parameters.

Results

Patients with DM were elderly (65.61 ± 12.08 vs 59.41 ± 16.86 years, P < 0.001); higher morbidity of hypertension (76.38% vs 58.14%, P < 0.001) and coronary artery disease (44.09% vs 32.41%, P = 0.03); thicker interventricular septum (10.92 ± 1.77 vs 10.08 ± 1.96 mm, P < 0.001) and left ventricular posterior wall (9.84 ± 1.38 vs 9.39 ± 1.66 mm, P = 0.03); higher lipid levels and average heart rate (66.67 ± 12.04 vs 61.87 ± 13.36 bpm, P < 0.01); higher angle of horizontal QRS vector (HQRSA, –2.87 ± 48.48 vs –19.00 ± 40.18 degrees, P < 0.01); lower maximal magnitude of horizontal T vector (HTV, 2.33 ± 1.47 vs 2.88 ± 1.89 mm, P = 0.01) and maximal magnitude of right side T vector (2.77 ± 1.55 vs 3.27 ± 1.92 mm, P = 0.03), and no difference in angle of frontal QRS‐T vector (FQRSTA, 32.77 ± 54.20 vs 28.39 ± 52.87 degrees, P = 0.74) compared with patients having NDM. After adjusting for confounding factors, DM was significantly effective on FQRSTA (regression coefficient –40.0, 95%CI –66.4 to –13.6, P < 0.01), HQRSA (regression coefficient 22.6, 95%CI 2.5 to 42.8, P = 0.03), and HTV (regression coefficient 0.9, 95%CI 0.2 to 1.7, P = 0.01). Confounding factors included: sex, 2‐hour postprandial blood glucose, smoking, triglyceride, apolipoprotein A, creatinine, left ventricular ejection fraction, and average heart rate.

Conclusions

The risk factors of DM and lipid metabolism abnormality particularly apolipoprotein A significantly modified parameters of virtual planar QRS and T vector, including frontal QRS‐T angle.

Diabetes mellitus and atrial fibrillation: Pathophysiological mechanisms and potential upstream therapies

Diabetes mellitus (DM) represents one of the most important risk factors for atrial fibrillation (AF) while AF is a strong and independent marker of overall mortality and cardiovascular morbidity in diabetic patients. Autonomic, electrical, electromechanical, and structural remodeling, including oxidative stress, connexin remodeling and glycemic fluctuations seem to be implicated in AF pathophysiology in the setting of DM. The present review highlights the association between DM and AF, provides a comprehensive overview of the responsible pathophysiological mechanisms and briefly discusses potential upstream therapies for DM-related atrial remodeling.

Clinical characteristics and impact of diabetes mellitus on outcomes in patients with nonvalvular atrial fibrillation

PURPOSE

Studies have shown that diabetes mellitus (DM) is a risk factor for cardiovascular disease, including atrial fibrillation (AF); however, the clinical characteristics and prognostic impact of DM in patients with nonvalvular AF have not been well understood in China.

MATERIALS AND METHODS

Included were 1644 consecutive patients with nonvalvular AF. Endpoints included all-cause mortality, cardiovascular mortality, stroke, major bleeding, and combined endpoint events (CEE) during a 1-year follow-up.

RESULTS

The prevalence of DM was 16.8% in nonvalvular AF patients. Compared with non-diabetic AF patients, diabetic AF patients were older and tended to coexist with other cardiovascular diseases. Most patients with DM (93.5%) were eligible for anticoagulation, as determined by CHADS2 scores. However, only 11.2% of patients received anticoagulation. During a 1-year follow-up, the all-cause mortality and CEE rate in the DM group were significantly higher than those of the non-DM group, while the incidence of stroke was comparable. After multivariate adjustments, DM was still an independent risk factor for 1-year all-cause mortality [hazard ratio (HR)=1.558; 95% confidence interval (CI) 1.126-2.156; p=0.007], cardiovascular mortality (HR=1.615; 95% CI 1.052-2.479; p=0.028), and CEE (HR=1.523; 95% CI 1.098-2.112; p=0.012), yet not for stroke (HR=1.119; 95% CI 0.724-1.728; p=0.614).

CONCLUSION

DM is a common morbidity coexisting with nonvalvular AF and is associated with an increased risk of 1-year all-cause mortality, cardiovascular mortality, and CEE. However, no increased risk of stroke was found during a 1-year follow-up in patients with AF and DM.

Impact of intensive glycemic control on the incidence of atrial fibrillation and associated cardiovascular outcomes in patients with type 2 diabetes mellitus (from the Action to Control Cardiovascular Risk in Diabetes Study)

Atrial fibrillation (AF) is prevalent in patients with type 2 diabetes mellitus (DM) and is associated with markers of poor glycemic control; however, the impact of glycemic control on incident AF and outcomes is unknown. The aims of this study were to prospectively evaluate if intensive glycemic control in patients with DM affects incident AF and to evaluate morbidity and mortality in patients with DM and incident AF. A total of 10,082 patients with DM from the Action to Control Cardiovascular Risk in Diabetes (ACCORD) cohort were studied in a randomized, double-blind fashion. Participants were randomized to an intensive therapeutic strategy targeting a glycated hemoglobin level of <6.0% or a standard strategy targeting a glycated hemoglobin level of 7.0% to 7.9%. Incident AF occurred in 159 patients (1.58%) over the follow-up period, at a rate of 5.9 per 1,000 patient-years in the intensive-therapy group and a rate of 6.37 per 1,000 patient-years in the standard-therapy group (p = 0.52). In a multivariate model, predictors of incident AF were age, weight, diastolic blood pressure, heart rate, and heart failure history. Patients with DM and new-onset AF had a hazard ratio of 2.65 for all-cause mortality (95% confidence interval 1.8 to 3.86, p <0.0001), a hazard ratio of 2.1 for myocardial infarction (95% confidence interval 1.33 to 3.31, p = 0.0015), and a hazard ratio of 3.80 for the development of heart failure (95% confidence interval 2.48 to 5.84, p <0.0001). In conclusion, intensive glycemic control did not affect the rate of new-onset AF. Patients with DM and incident AF had an increased risk for morbidity and mortality compared with those without AF.

Diabetes mellitus and atrial remodeling: mechanisms and potential upstream therapies

Atrial fibrillation (AF) is the most common cardiac arrhythmia in clinical practice, and its prevalence has increasing substantially over the last decades. Recent data suggest that there is an increased risk of AF among the patients with diabetes mellitus (DM). However, the potential molecular mechanisms regarding DM-related AF and diabetic atrial remodeling are not fully understood. In this comprehensive review, we would like to summarize the potential relationship between diabetes and atrial remodeling, including structural, electrical, and autonomic remodeling. Also, some upstream therapies, such as thiazolidinediones, probucol, ACEI/ARBs, may play an important role in the prevention and treatment of AF. Therefore, large prospective randomized, controlled trials and further experimental studies should be challengingly continued.

Atrial fibrillation from the pathologist's perspective

Atrial fibrillation (AF), the most common sustained cardiac arrhythmia encountered in clinical practice, is associated with increased morbidity and mortality. Electrophysiologically, it is characterized by a high rate of asynchronous atrial cell depolarization causing a loss of atrial contractile function and irregular ventricular rates. For a long time, AF was considered as a pure functional disorder without any structural background. Only in recent years, have new mapping and imaging techniques identified atrial locations, which are very often involved in the initiation and maintenance of this supraventricular arrhythmia (i.e. the distal portion of the pulmonary veins and the surrounding atrial myocardium). Morphological analysis of these myocardial sites has demonstrated significant structural remodeling as well as paved the way for further knowledge of AF natural history, pathogenesis, and treatment. This architectural myocardial disarrangement is induced by the arrhythmia itself and the very frequently associated cardiovascular disorders. At the same time, the structural remodeling is also capable of sustaining AF, thereby creating a sort of pathogenetic vicious circle. This review focuses on current understanding about the structural and genetic bases of AF with reference to their classification, pathogenesis, and clinical implications.