Electrical and structural remodeling contribute to atrial fibrillation in type 2 diabetic db/db mice

Chronic angiotensin converting enzyme inhibition attenuates frailty and protects against atrial fibrillation in aging mice

BACKGROUND

Aging is a major risk factor for atrial fibrillation (AF); however, not all individuals age at the same rate. Frailty, which is a measure of susceptibility to adverse health outcomes, can be quantified using a frailty index (FI).

OBJECTIVE

To determine the effects of angiotensin converting enzyme (ACE) inhibitors on AF and atrial remodeling in aging and frail mice.

METHODS

Aging mice were treated with the ACE inhibitor enalapril for 6 months beginning at 16.5 months of age and frailty was quantified. AF susceptibility as well as atrial structure and function were assessed using intracardiac electrophysiology in anesthetized mice, high-resolution optical mapping in intact atrial preparations, patch-clamping in isolated atrial myocytes, and histology and molecular biology in atrial tissues.

RESULTS

Enalapril attenuated frailty in aging mice with larger effects in females. AF susceptibility was increased in aging mice, but attenuated by enalapril. AF susceptibility and duration also increased as a function of FI score. P wave duration was increased and atrial conduction velocity was reduced in aging mice and improved after enalapril treatment. Furthermore, P wave duration and atrial conduction velocity were strongly correlated with FI score. Atrial action potential upstroke velocity (Vmax) and Na+ current (INa) were reduced while atrial fibrosis was increased in aging mice. Action potential Vmax, INa, and fibrosis were improved by enalapril and also correlated with FI scores.

CONCLUSIONS

ACE inhibition with enalapril attenuates frailty and reduces AF susceptibility in aging mice by attenuating atrial electrical and structural remodeling.

Inhibition of the P2X7 receptor prevents atrial proarrhythmic remodeling in experimental post-operative atrial fibrillation

BACKGROUND

Post-operative atrial fibrillation (POAF) is a common complication in patients undergoing cardiac surgery. The purinergic receptor P2X7 (P2X7R) is involved in some cardiovascular diseases, whereas its effects on atrial fibrillation (AF) are unclear.

OBJECTIVE

This study was to assess the effect of P2X7R on atrial arrhythmogenic remodeling in the rat model of sterile pericarditis (SP).

METHODS

Male Sprague-Dawley (SD) rats were used to induce the SP model. Electrocardiogram, atrial electrophysiological protocol, histology, mRNA sequencing, real-time quantitative PCR, western blot, and Elisa assay were performed.

RESULTS

SP significantly up-regulated P2X7R expression; increased AF susceptibility; reduced the protein expression of ion channels including Nav1.5, Cav1.2, Kv4.2, Kv4.3, and Kv1.5; caused atrial fibrosis; increased norepinephrine (NE) level in plasma; promoted the production of inflammatory cytokines such as TNF-α, IL-1β, and IL-6; increased the accumulation of immune cells (CD68- and MPO- positive cells); and activated NLRP3 inflammasome signaling pathway. P2X7R antagonist Brilliant Blue G (BBG) mitigated SP-induced alterations. The mRNA sequencing demonstrated that BBG prevented POAF mainly by regulating the immune system. In addition, another selective P2X7R antagonist A740003, and IL-1R antagonist anakinra also reduced AF inducibility in the SP model.

CONCLUSIONS

P2X7R inhibition prevents SP-induced atrial proarrhythmic remodeling, which is closely associated with the improvement of inflammatory changes, ion channel expression, atrial fibrosis, and sympathetic activation. The findings point to P2X7R inhibition as a promising target for AF (particularly POAF) and perhaps other conditions.

Zbtb16 increases susceptibility of atrial fibrillation in type 2 diabetic mice via Txnip-Trx2 signaling

Atrial fibrillation (AF) is the most prevalent sustained cardiac arrhythmia, and recent epidemiological studies suggested type 2 diabetes mellitus (T2DM) is an independent risk factor for the development of AF. Zinc finger and BTB (broad-complex, tram-track and bric-a-brac) domain containing 16 (Zbtb16) serve as transcriptional factors to regulate many biological processes. However, the potential effects of Zbtb16 in AF under T2DM condition remain unclear. Here, we reported that db/db mice displayed higher AF vulnerability and Zbtb16 was identified as the most significantly enriched gene by RNA sequencing (RNA-seq) analysis in atrium. In addition, thioredoxin interacting protein (Txnip) was distinguished as the key downstream gene of Zbtb16 by Cleavage Under Targets and Tagmentation (CUT&Tag) assay. Mechanistically, increased Txnip combined with thioredoxin 2 (Trx2) in mitochondrion induced excess reactive oxygen species (ROS) release, calcium/calmodulin-dependent protein kinase II (CaMKII) overactivation, and spontaneous Ca2+ waves (SCWs) occurrence, which could be inhibited through atrial-specific knockdown (KD) of Zbtb16 or Txnip by adeno-associated virus 9 (AAV9) or Mito-TEMPO treatment. High glucose (HG)-treated HL-1 cells were used to mimic the setting of diabetic in vitro. Zbtb16-Txnip-Trx2 signaling-induced excess ROS release and CaMKII activation were also verified in HL-1 cells under HG condition. Furthermore, atrial-specific Zbtb16 or Txnip-KD reduced incidence and duration of AF in db/db mice. Altogether, we demonstrated that interrupting Zbtb16-Txnip-Trx2 signaling in atrium could decrease AF susceptibility via reducing ROS release and CaMKII activation in the setting of T2DM.

Natriuretic Peptide Receptor B Protects Against Atrial Fibrillation by Controlling Atrial cAMP Via Phosphodiesterase 2

BACKGROUND

β-AR (β-adrenergic receptor) stimulation regulates atrial electrophysiology and Ca2+ homeostasis via cAMP-dependent mechanisms; however, enhanced β-AR signaling can promote atrial fibrillation (AF). CNP (C-type natriuretic peptide) can also regulate atrial electrophysiology through the activation of NPR-B (natriuretic peptide receptor B) and cGMP-dependent signaling. Nevertheless, the role of NPR-B in regulating atrial electrophysiology, Ca2+ homeostasis, and atrial arrhythmogenesis is incompletely understood.

METHODS

Studies were performed using atrial samples from human patients with AF or sinus rhythm and in wild-type and NPR-B-deficient (NPR-B+/-) mice. Studies were conducted in anesthetized mice by intracardiac electrophysiology, in isolated mouse atrial preparations using high-resolution optical mapping, in isolated mouse and human atrial myocytes using patch-clamping and Ca2+ imaging, and in mouse and human atrial tissues using molecular biology.

RESULTS

Atrial NPR-B protein levels were reduced in patients with AF, and NPR-B+/- mice were more susceptible to AF. Atrial cGMP levels and PDE2 (phosphodiesterase 2) activity were reduced in NPR-B+/- mice leading to larger increases in atrial cAMP in the presence of the β-AR agonist isoproterenol. NPR-B+/- mice displayed larger increases in action potential duration and L-type Ca2+ current in the presence of isoproterenol. This resulted in the occurrence of spontaneous sarcoplasmic reticulum Ca2+ release events and delayed afterdepolarizations in NPR-B+/- atrial myocytes. Phosphorylation of the RyR2 (ryanodine receptor) and phospholamban was increased in NPR-B+/- atria in the presence of isoproterenol compared with the wildtypes. C-type natriuretic peptide inhibited isoproterenol-stimulated L-type Ca2+ current through PDE2 in mouse and human atrial myocytes.

CONCLUSIONS

NPR-B protects against AF by preventing enhanced atrial responses to β-adrenergic receptor agonists.

Glucagon-Like Peptide-1 Protects Against Atrial Fibrillation and Atrial Remodeling in Type 2 Diabetic Mice

Atrial fibrillation (AF) is highly prevalent in type 2 diabetes where it increases morbidity and mortality. Glucagon-like peptide (GLP)-1 receptor agonists are used in the treatment of type 2 diabetes (T2DM), but their effects on AF in T2DM are poorly understood. The present study demonstrates type 2 diabetic db/db mice are highly susceptible to AF in association with atrial electrical and structural remodeling. GLP-1, as well as the long-acting GLP-1 analogue liraglutide, reduced AF and prevented atrial remodeling in db/db mice. These data suggest that GLP-1 and related analogues could protect against AF in patients with T2DM.

Shensong Yangxin Capsule Reduces the Susceptibility of Arrhythmia in db/db Mice via Inhibiting the Inflammatory Response Induced by Endothelium Dysfunction

Purpose

The aim of our study was to investigate the mechanism by which the Chinese compound Shensong Yangxin Capsule (SSYX) reduces susceptibility to arrhythmia in db/db mice.

Methods

The db/db mice without drug treatment served as the model group. Other-treated db/db mice were administered SSYX for 8 weeks. Electrocardiogram (ECG), electrical mapping, pathological changes, immunofluorescence staining, real-time quantitative PCR, and Western blot analyses were then conducted.

Results

SSYX decreased arrhythmia susceptibility and shortened the abnormal ECG parameters of db/db mice. Meanwhile, SSYX restored irregular conduction direction and shortened the conduction time of the isolated heart. HE and Masson staining showed that SSYX alleviated inflammatory infiltration and collagen fiber deposition. Western blot showed that SSYX decreased the protein expression of ICAM-1, VCAM-1, and MCP-1 and increased the protein expression of occludin, ZO-1, eNOS, and Cx43. SSYX also increased the content of NO, decreased ET-1, TNF-α, IL-1β, IL-6, MCP-1, and CCR-2 mRNA expression, and increased Kv 4.2, Kv 4.3, Cav 1.2, and Nav 1.5 mRNA expression. Furthermore, SSYX decreased the fluorescence intensity of F4/80 and iNOS, increased the fluorescence intensity of CD31 and eNOS, and improved the Cx43 and α-actinin connection structure in cardiac tissues. The above therapeutic effects of SSYX were inhibited by L-NAME.

Conclusion

SSYX reduced the susceptibility of db/db mice to arrhythmia by inhibiting the inflammatory response and macrophage polarization, and this effect of SSYX occurred through protection of endothelial cell function.

Overview of programmed electrical stimulation to assess atrial fibrillation susceptibility in mice

Atrial fibrillation (AF) is the most common human arrhythmia and is associated with increased risk of stroke, dementia, heart failure, and death. Among several animal models that have been used to investigate the molecular determinants of AF, mouse models have become the most prevalent due to low cost, ease of genetic manipulation, and similarity to human disease. Programmed electrical stimulation (PES) using intracardiac or transesophageal atrial pacing is used to induce AF as most mouse models do not develop spontaneous AF. However, there is a lack of standardized methodology resulting in numerous PES protocols in the literature that differ with respect to multiple parameters, including pacing protocol and duration, stimulus amplitude, pulse width, and even the definition of AF. Given this complexity, the selection of the appropriate atrial pacing protocol for a specific model has been arbitrary. Herein we review the development of intracardiac and transesophageal PES, including commonly used protocols, selected experimental models, and advantages and disadvantages of both techniques. We also emphasize detection of artifactual AF induction due to unintended parasympathetic stimulation, which should be excluded from results. We recommend that the optimal pacing protocol to elicit an AF phenotype should be individualized to the specific model of genetic or acquired risk factors, with an analysis using several definitions of AF as an endpoint.

Regional and temporal progression of atrial remodeling in angiotensin II mediated atrial fibrillation

Atrial fibrillation (AF) is associated with electrical and structural remodeling in the atria; however, the regional and temporal progression of atrial remodeling is incompletely understood. The objective of this study was to investigate the regional and temporal progression of atrial remodeling leading to changes in AF susceptibility in angiotensin II (Ang II) mediated hypertension. Mice were infused with Ang II for 3, 10 or 21 days. AF susceptibility and atrial electrophysiology were studied in vivo using intracardiac electrophysiology. Right and left atrial myocyte electrophysiology was studied using patch-clamping. Atrial fibrosis was assessed histologically. P wave duration and atrial effective refractory period increased progressively from 3 to 21 days of Ang II. AF susceptibility tended to be increased at 10 days of Ang II and was elevated at 21 days of Ang II. Left, but not right, atrial AP upstroke velocity and Na+ current were reduced at 10 and 21 days of Ang II. Left atrial action potential (AP) duration increased progressively from 3 to 21 days of Ang II due to reductions in repolarizing K+ current. Right atrial AP prolongation was increased only after 21 days of Ang II. Left and right atrial fibrosis developed progressively from 3 to 21 days, but increases were larger in the left atrium. In conclusion, Ang II mediated atrial electrical and structural remodeling develop earlier and more extensively in the left atrium compared to the right atrium, providing insight into how atrial remodeling leads to enhanced AF susceptibility in Ang II mediated hypertension.

Modelling Diabetic Cardiomyopathy: Using Human Stem Cell-Derived Cardiomyocytes to Complement Animal Models

Diabetes is a global epidemic, with cardiovascular disease being the leading cause of death in diabetic patients. There is a pressing need for an in vitro model to aid understanding of the mechanisms driving diabetic heart disease, and to provide an accurate, reliable tool for drug testing. Human induced-pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) have potential as a disease modelling tool. There are several factors that drive molecular changes inside cardiomyocytes contributing to diabetic cardiomyopathy, including hyperglycaemia, lipotoxicity and hyperinsulinemia. Here we discuss these factors and how they can be seen in animal models and utilised in cell culture to mimic the diabetic heart. The use of human iPSC-CMs will allow for a greater understanding of disease pathogenesis and open up new avenues for drug testing.

Time series RNA-seq analysis identifies MAPK10 as a critical gene in diabetes mellitus-induced atrial fibrillation in mice

Atrial fibrillation (AF) is a major complication of type 2 diabetes mellitus (T2DM) and plays critical roles in the pathogenesis of atrial remodeling. However, the differentially expressed genes in atria during the development of AF induced by hyperglycemia have rarely been reported. Here, we showed time-dependent increased AF incidence and duration, atrial enlargement, inflammation, fibrosis, conduction time and action potential duration in db/db mice, a model of T2DM. RNA sequencing analysis showed that 2256 genes were differentially expressed in the atria at 12, 14 and 16 weeks. Gene Ontology analysis showed that these genes participate primarily in cell adhesion, cellular response to interferon-beta, immune system process, positive regulation of cell migration, ion transport and cellular response to interferon-gamma. Analysis of significant pathways revealed the IL-17 signaling pathway, TNF signaling pathway, MAPK signaling pathway, chemokine signaling pathway, and cAMP receptor signaling. Additionally, these differentially expressed genes were classified into 50 profiles by hierarchical clustering analysis. Twelve of these profiles were significant and comprised 1115 genes. Gene coexpression network analysis identified that mitogen-activated protein kinase 10 (MAPK10) was localized in the core of the gene network and was the most highly expressed gene at different time points. Knockdown of MAPK10 markedly attenuated DM-induced AF incidence, atrial inflammation, fibrosis, electrical disorder and apoptosis in db/db mice. In summary, the present findings revealed that many genes are involved in DM-induced AF and that MAPK10 plays a central role in this disease, indicating that strategies targeting MAPK10 may represent a potential therapeutic approach to treat DM-induced AF.

The Connubium among diabetes, chronic kidney disease and atrial fibrillation

The burden of cardiovascular comorbid conditions was significantly higher in patients with Atrial Fibrillation (AF); most of them are affected by hypertension, Chronic Kidney Disease (CKD) and/or Diabetes Mellitus (DM). DM represents a well-known risk factor for the development and maintenance of AF; the coexistence of DM and AF is also associated with an increased risk of mortality and stroke. Moreover, DM is currently the main cause of renal impairment and the leading cause of dialysis in the world. The hyperglycemia is responsible for inducing redox imbalance and both systemic and intrarenal inflammation, playing a critical role in the pathogenesis of diabetic kidney disease. Long-term thromboembolic preventive therapy in AF patients with DM and CKD may be more challenging because both DM and CKD have been independently associated with an increased thromboembolic and bleeding risk, which results from the prothrombotic and pro-inflammatory status. Vitamin K Antagonists (VKAs) are characterized by numerous critical issues such as a narrow therapeutic window, increased tissue calcification and an unfavourable risk/benefit ratio with low stroke prevention effect and augmented risk of major bleeding. On the other hand, Direct Oral Anticoagulants (DOACs) are currently contraindicated in dialysis patients even if mounting evidence suggests that they may have a nephroprotective role in AF patients with DM and CKD. Consequently, the choice of anticoagulant therapy in this setting of patient seems to be very challenging. The aim of this review is to investigate the role of DOACs in diabetic patients and its nephroprotective role by reviewing the current literature.

Effectiveness of the use of a high-flow nasal cannula to treat COVID-19 patients and risk factors for failure: a meta-analysis

Background:

Coronavirus disease 2019 (COVID-19) has spread globally, and many patients with severe cases have received oxygen therapy through a high-flow nasal cannula (HFNC).

Objectives:

We assessed the efficacy of HFNC for treating patients with COVID-19 and risk factors for HFNC failure.

Methods:

We searched PubMed, Embase, and the Cochrane Central Register of randomized controlled trials (RCTs) and observational studies of HFNC in patients with COVID-19 published in English from January 1st, 2020 to August 15th, 2021. The primary aim was to assess intubation, mortality, and failure rates in COVID-19 patients supported by HFNC. Secondary aims were to compare HFNC success and failure groups and to describe the risk factors for HFNC failure.

Results:

A total of 25 studies fulfilled selection criteria and included 2851 patients. The intubation, mortality, and failure rates were 0.44 (95% confidence interval (CI): 0.38–0.51, I² = 84%), 0.23 (95% CI: 0.19–0.29, I² = 88%), and 0.47 (95% CI: 0.42–0.51, I² = 56%), respectively. Compared to the success group, age, body mass index (BMI), Sequential Organ Failure Assessment (SOFA) score, Acute Physiology and Chronic Health Evaluation (APACHE) II score, D-dimer, lactate, heart rate, and respiratory rate were higher and PaO₂, PaO₂/FiO₂, ROX index (the ratio of SpO₂/FiO₂ to respiratory rate), ROX index after the initiation of HFNC, and duration of HFNC were lower in the failure group (all Ps < 0.05). There were also more smokers and more comorbidities in the failure group (all Ps < 0.05). Pooled odds ratios (ORs) revealed that older age (OR: 1.04, 95% CI: 1.01–1.07, P = 0.02, I² = 88%), a higher white blood cell (WBC) count (OR: 1.06, 95% CI: 1.01–1.12, P = 0.02, I² = 0%), a higher heart rate (OR: 1.42, 95% CI: 1.15–1.76, P < 0.01, I² = 0%), and a lower ROX index(OR: 0.61, 95% CI: 0.39–0.95, P = 0.03, I² = 93%) after the initiation of HFNC were all significant risk factors for HFNC failure.

Conclusions:

HFNC is an effective way of providing respiratory support in the treatment of COVID-19 patients. Older age, a higher WBC count, a higher heart rate, and a lower ROX index after the initiation of HFNC are associated with an increased risk of HFNC failure.

Loss of natriuretic peptide receptor C enhances sinoatrial node dysfunction in aging and frail mice

Heart rate is controlled by the sinoatrial node (SAN). SAN dysfunction is highly prevalent in aging; however, not all individuals age at the same rate. Rather, health status during aging is affected by frailty. Natriuretic peptides regulate SAN function in part by activating natriuretic peptide receptor C (NPR-C). The impacts of NPR-C on HR and SAN function in aging and as a function of frailty are unknown. Frailty was measured in aging wildtype (WT) and NPR-C knockout (NPR-C -/-) mice using a mouse clinical frailty index (FI). HR and SAN structure and function were investigated using intracardiac electrophysiology in anesthetized mice, high-resolution optical mapping in intact atrial preparations, histology and molecular biology. NPR-C -/- mice rapidly became frail leading to shortened lifespan. HR and SAN recovery time were increased in older vs. younger mice and this was exacerbated in NPR-C -/- mice; however, there was substantial variability among age groups and genotypes. HR and SAN recovery time were correlated with FI score and fell along a continuum regardless of age or genotype. Optical mapping demonstrates impairments in SAN function that were also strongly correlated with FI score. SAN fibrosis was increased in aged and NPR-C -/- mice and was graded by FI score. Loss of NPR-C results in accelerated aging due to a rapid decline in health status in association with impairments in HR and SAN function. Frailty assessment was effective and often better able to distinguish aging-dependent changes in SAN function in the setting of shorted lifespan due to loss of NPR-C.

Distinct Effects of Ibrutinib and Acalabrutinib on Mouse Atrial and Sinoatrial Node Electrophysiology and Arrhythmogenesis

Background

Ibrutinib and acalabrutinib are Bruton tyrosine kinase inhibitors used in the treatment of B‐cell lymphoproliferative disorders. Ibrutinib is associated with new‐onset atrial fibrillation. Cases of sinus bradycardia and sinus arrest have also been reported following ibrutinib treatment. Conversely, acalabrutinib is less arrhythmogenic. The basis for these different effects is unclear.

Methods and Results

The effects of ibrutinib and acalabrutinib on atrial electrophysiology were investigated in anesthetized mice using intracardiac electrophysiology, in isolated atrial preparations using high‐resolution optical mapping, and in isolated atrial and sinoatrial node (SAN) myocytes using patch‐clamping. Acute delivery of acalabrutinib did not affect atrial fibrillation susceptibility or other measures of atrial electrophysiology in mice in vivo. Optical mapping demonstrates that ibrutinib dose‐dependently impaired atrial and SAN conduction and slowed beating rate. Acalabrutinib had no effect on atrial and SAN conduction or beating rate. In isolated atrial myocytes, ibrutinib reduced action potential upstroke velocity and Na⁺ current. In contrast, acalabrutinib had no effects on atrial myocyte upstroke velocity or Na⁺ current. Both drugs increased action potential duration, but these effects were smaller for acalabrutinib compared with ibrutinib and occurred by different mechanisms. In SAN myocytes, ibrutinib impaired spontaneous action potential firing by inhibiting the delayed rectifier K⁺ current, while acalabrutinib had no effects on SAN myocyte action potential firing.

Conclusions

Ibrutinib and acalabrutinib have distinct effects on atrial electrophysiology and ion channel function that provide insight into the basis for increased atrial fibrillation susceptibility and SAN dysfunction with ibrutinib, but not with acalabrutinib.

Atrial Fibrillation in Aging and Frail Mice: Modulation by Natriuretic Peptide Receptor C

[Figure: see text].

Impacts of frailty on heart rate variability in aging mice: Roles of the autonomic nervous system and sinoatrial node

BACKGROUND

Heart rate variability (HRV) is determined by intrinsic sinoatrial node (SAN) activity and the autonomic nervous system (ANS). HRV is reduced in aging; however, aging is heterogeneous. Frailty, which can be measured using a frailty index (FI), can quantify health status in aging separately from chronological age.

OBJECTIVE

The purpose of this study was to investigate the impacts of age and frailty on HRV in mice.

METHODS

Frailty was measured in aging mice between 10 and 130 weeks of age. HRV was assessed using time domain, frequency domain, and Poincaré plot analyses in anesthetized mice at baseline and after ANS blockade, as well as in isolated atrial preparations.

RESULTS

HRV was reduced in aged mice (90-130 weeks and 50-80 weeks old) compared to younger mice (10-30 weeks old); however, there was substantial variability within age groups. In contrast, HRV was strongly correlated with FI score regardless of chronological age. ANS blockade resulted in reductions in heart rate that were largest in 90- to 130-week-old mice and were correlated with FI score. HRV after ANS blockade or in isolated atrial preparations was increased in aged mice but again showed high variability among age groups. HRV was correlated with FI score after ANS blockade and in isolated atrial preparations.

CONCLUSION

HRV is reduced in aging mice in association with a shift in sympathovagal balance and increased intrinsic SAN beating variability; however, HRV is highly variable within age groups. HRV was strongly correlated with frailty, which was able to detect differences in HRV separately from chronological age.

Higher long-term visit-to-visit glycemic variability predicts new-onset atrial fibrillation in patients with diabetes mellitus

Background

Atrial fibrillation (AF) is prevalent in patients with type 2 diabetes mellitus (T2DM). Glycemic variability (GV) is associated with risk of micro- and macrovascular diseases. However, whether the GV can increase the risk of AF remains unknown.

Methods

The cohort study used a database from National Taiwan University Hospital, a tertiary medical center in Taiwan. Between 2014 and 2019, a total of 27,246 adult patients with T2DM were enrolled for analysis. Each individual was assessed to determine the coefficients of variability of fasting glucose (FGCV) and HbA1c variability score (HVS). The GV parameters were categorized into quartiles. Multivariate Cox regression models were employed to estimate the relationship between the GV parameters and the risk of AF, transient ischemic accident (TIA)/ischemic stroke and mortality in patients with T2DM.

Results

The incidence rates of AF and TIA/ischemic stroke were 21.31 and 13.71 per 1000 person-year respectively. The medium follow-up period was 70.7 months. In Cox regression model with full adjustment, the highest quartile of FGCV was not associated with increased risk of AF [Hazard ratio (HR): 1.12, 95% confidence interval (CI) 0.96–1.29, p = 0.148] or TIA/ischemic stroke (HR: 1.04, 95% CI 0.83–1.31, p = 0.736), but was associated with increased risk of total mortality (HR: 1.33, 95% CI 1.12–1.58, p < 0.001) and non-cardiac mortality (HR: 1.41, 95% CI 1.15–1.71, p < 0.001). The highest HVS was significantly associated with increased risk of AF (HR: 1.29, 95% CI 1.12–1.50, p < 0.001), total mortality (HR: 2.43, 95% CI 2.03–2.90, p < 0.001), cardiac mortality (HR: 1.50, 95% CI 1.06–2.14, p = 0.024) and non-cardiac mortality (HR: 2.80, 95% CI 2.28–3.44, p < 0.001) but was not associated with TIA/ischemic stroke (HR: 0.98, 95% CI 0.78–1.23, p = 0.846). The Kaplan–Meier analysis showed significantly higher risk of AF, cardiac and non-cardiac mortality according to the magnitude of GV (log-rank test, p < 0.001).

Conclusions

Our data demonstrate that high GV is independently associated with the development of new-onset AF in patients with T2DM. The benefit of maintaining stable glycemic levels to improve clinical outcomes warrants further studies.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12933-021-01341-3.

A novel system for mapping regional electrical properties and characterizing arrhythmia in isolated intact rat atria

Detailed global maps of atrial electrical activity are needed to understand mechanisms of atrial rhythm disturbance in small animal models of heart disease. To date, optical mapping systems have not provided enough spatial resolution across sufficiently extensive regions of intact atrial preparations to achieve this goal. The aim of this study was to develop an integrated platform for quantifying regional electrical properties and analyzing reentrant arrhythmia in a biatrial preparation. Intact atria from 6/7-mo-old female spontaneously hypertensive rats (SHRs; n = 6) were isolated and secured in a constant flow superfusion chamber at 37°C. Optical mapping was performed with the membrane-voltage dye di-4-ANEPPS using LED excitation and a scientific complementary metal-oxide semiconductor (sCMOS) camera. Programmed stimulus trains were applied from right atrial (RA) and left atrial (LA) sites to assess rate-dependent electrical behavior and to induce atrial arrhythmia. Signal-to-noise ratio was improved by sequential processing steps that included spatial smoothing, temporal filtering, and, in stable rhythms, ensemble-averaging. Activation time, repolarization time, and action potential duration (APD) maps were constructed at high spatial resolution for a wide range of coupling intervals. These data were highly consistent within and between experiments. They confirmed preferential atrial conduction pathways and demonstrated distinct medial-to-lateral APD gradients. We also showed that reentrant arrhythmias induced in this preparation were explained by the spatial variation of these electrical properties. Our new methodology provides a robust means of 1) quantifying regional electrical properties in the intact rat atria at higher spatiotemporal resolution than previously reported, and 2) characterizing reentrant arrhythmia and analyzing mechanisms that give rise to it.NEW & NOTEWORTHY Despite wide-ranging optical mapping studies, detailed information on regional atrial electrical properties in small animal models of heart disease and how these contribute to reentrant arrhythmia remains limited. We have developed a novel experimental platform that enables both to be achieved in a geometrically intact isolated rat bi-atrial preparation.

Impaired regulation of heart rate and sinoatrial node function by the parasympathetic nervous system in type 2 diabetic mice

Heart rate (HR) and sinoatrial node (SAN) function are modulated by the autonomic nervous system. HR regulation by the parasympathetic nervous system (PNS) is impaired in diabetes mellitus (DM), which is denoted cardiovascular autonomic neuropathy. Whether blunted PNS effects on HR in type 2 DM are related to impaired responsiveness of the SAN to PNS agonists is unknown. This was investigated in type 2 diabetic db/db mice in vivo and in isolated SAN myocytes. The PNS agonist carbachol (CCh) had a smaller inhibitory effect on HR, while HR recovery time after CCh removal was accelerated in db/db mice. In isolated SAN myocytes CCh reduced spontaneous action potential firing frequency but this effect was reduced in db/db mice due to blunted effects on diastolic depolarization slope and maximum diastolic potential. Impaired effects of CCh occurred due to enhanced desensitization of the acetylcholine-activated K⁺ current (I_KACh) and faster I_KACh deactivation. I_KACh alterations were reversed by inhibition of regulator of G-protein signaling 4 (RGS4) and by the phospholipid PIP₃. SAN expression of RGS4 was increased in db/db mice. Impaired PNS regulation of HR in db/db mice occurs due to reduced responsiveness of SAN myocytes to PNS agonists in association with enhanced RGS4 activity.

New aspects of endocrine control of atrial fibrillation and possibilities for clinical translation

Hormones are potent endo-, para-, and autocrine endogenous regulators of the function of multiple organs, including the heart. Endocrine dysfunction promotes a number of cardiovascular diseases, including atrial fibrillation (AF). While the heart is a target for endocrine regulation, it is also an active endocrine organ itself, secreting a number of important bioactive hormones that convey significant endocrine effects, but also through para-/autocrine actions, actively participate in cardiac self-regulation. The hormones regulating heart-function work in concert to support myocardial performance. AF is a serious clinical problem associated with increased morbidity and mortality, mainly due to stroke and heart failure. Current therapies for AF remain inadequate. AF is characterized by altered atrial function and structure, including electrical and profibrotic remodelling in the atria and ventricles, which facilitates AF progression and hampers its treatment. Although features of this remodelling are well-established and its mechanisms are partly understood, important pathways pertinent to AF arrhythmogenesis are still unidentified. The discovery of these missing pathways has the potential to lead to therapeutic breakthroughs. Endocrine dysfunction is well-recognized to lead to AF. In this review, we discuss endocrine and cardiocrine signalling systems that directly, or as a consequence of an underlying cardiac pathology, contribute to AF pathogenesis. More specifically, we consider the roles of products from the hypothalamic-pituitary axis, the adrenal glands, adipose tissue, the renin–angiotensin system, atrial cardiomyocytes, and the thyroid gland in controlling atrial electrical and structural properties. The influence of endocrine/paracrine dysfunction on AF risk and mechanisms is evaluated and discussed. We focus on the most recent findings and reflect on the potential of translating them into clinical application.