Development and validation of the Atri-Risk Conduction Index risk score to predict risk of atrial fibrillation after typical atrial flutter ablation

BACKGROUND

Identification of patients at risk for atrial fibrillation (AF) after typical atrial flutter (tAFL) ablation is important to guide monitoring and treatment.

OBJECTIVE

The purpose of this study was to create and validate a risk score to predict AF after tAFL ablation METHODS: We identified patients who underwent tAFL ablation with no AF history between 2017 and 2022 and randomly allocated to derivation and validation cohorts. We collected clinical variables and measured conduction parameters in sinus rhythm on an electrophysiology recording system (CardioLab, GE Healthcare). Univariate and multivariate logistic regressions (LogR) were used to evaluate association with AF development.

RESULTS

A total of 242 consecutive patients (81% male; mean age 66 ± 11 years) were divided into derivation (n =142) and validation (n = 100) cohorts. Forty-two percent developed AF over median follow-up of 330 days. In multivariate LogR (derivation cohort), proximal to distal coronary sinus time (pCS-dCS) ≥70 ms (odds ratio [OR] 16.7; 95% confidence interval [CI] 5.6-49), pCS time ≥36 ms (OR 4.5; 95% CI 1.5-13), and CHADS2-VASc score ≥3 (OR 4.3; 95% CI 1.6-11.8) were independently associated with new AF during follow-up. The Atri-Risk Conduction Index (ARCI) score was created with 0 as minimal and 4 as high-risk using pCS-dCS ≥70 ms = 2 points; pCS ≥36 ms = 1 point; and CHADS2-VASc score ≥3 = 1 point. In the validation cohort, 0% of patients with ARCI score = 0 developed AF, whereas 89% of patients with ARCI score = 4 developed AF.

CONCLUSION

We developed and validated a risk score using atrial conduction parameters and clinical risk factors to predict AF after tAFL ablation. It stratifies low-, moderate-, and high-risk patients and may be helpful in individualizing approaches to AF monitoring and anticoagulation.

Atrial myopathy

This paper delves into the progressive concept of atrial myopathy, shedding light on its development and its impact on atrial characteristics. It extensively explores the intricate connections between atrial myopathy, atrial fibrillation (AF), and strokes. Researchers have sought additional contributors to AF-related strokes due to the absence of a clear timing correlation between paroxysmal AF episodes and strokes in patients with cardiac implantable electronic devices. Through various animal models and human investigations, a close interrelation among aging, inflammation, oxidative stress, and stretching mechanisms has been identified. These mechanisms contribute to fibrosis, alterations in electrical properties, autonomic remodeling, and a heightened pro-thrombotic state. These interconnected factors establish a detrimental cycle, exacerbating atrial myopathy and elevating the risk of sustained AF and strokes. By emphasizing the significance of atrial myopathy and the risk of strokes that are distinct from AF, the paper also discusses methods for identifying patients with atrial myopathy. Moreover, it proposes an approach to incorporate the concept of atrial myopathy into clinical practice to guide anticoagulation decisions in individuals with AF.

Characterization of cardiac involvement in patients with LMNA splice-site mutation-related dilated cardiomyopathy and sudden cardiac death

Introduction: LMNA splicing mutations occur in 9.1% of cases with cardiac involvement cases, but the phenotype and severity of disease they cause have not yet been systematically studied. The aim of this study was to understand the clinical and pathogenic characteristics of the LMNA splice-site mutation phenotype in patients with LMNA-related dilated cardiomyopathy (DCM) and sudden cardiac death (SCD). Methods and Results: First, we reported a novel family with LMNA-related DCM and SCD, and the clinical characteristics of all current patients with LMNA splicing mutations were further summarized through the ClinVar database. Seventeen families with a total of 134 individuals, containing a total of 15 LMNA splicing mutation sites, were enrolled. A total of 42 subjects (31.3%) had SCD. Compared without with the non-DCM group (n = 56), the patients within the DCM group (n = 78) presented a lower incidence of atrioventricular block (AVB) (p = 0.015) and a higher incidence rates of non-sustained ventricular tachycardia (p = 0.004),) and implantable cardioverter defibrillator (ICD) implantation (p = 0.005). Kaplan‒Meier survival analysis showed that the patients with pacemaker (PM) implantation had a significantly reduced the occurrence of SCD compared to patientswith those without PM implantation (log-rank p < 0.001), while there was no significant difference in ICD implantation between the two groups (log-rank p = 0.73). Second, we identified the family that we reported with a mutation in an LMNA c.513+1 G>A mutation in the reported family, and pathogenic prediction analysis showed that the mutation site was extremely harmful. Next, we conducted gene expression levels and cardiac pathological biopsy studies on the proband of this family. We found that the expression of normal LMNA mRNA from the proband was significantly downregulated in peripheral blood mononuclear cells than incompared with healthy individuals. Finally, we comprehensively summarized the pathological characteristics of LMNA-related DCM, including hypertrophy, atrophy, fibrosis, white blood cell infiltration, intercalated disc remodeling, and downregulation of desmin and connexin 43 (Cx43) expression. Discussion: Above all, Cardiaccardiac involvement in patients with LMNA splice-site mutation presented with a high rate of SCD. Implanting a pacemaker significantly reduced the SCD rate in non-DCM patients with AVB. The pathogenic characterization was not only haveinvolved suppressed the expression of the healthy LMNA allele, but was also associated with abnormal expression and distribution of desmin and Cx43.

Molecular mechanisms of postoperative atrial fibrillation in patients with obstructive sleep apnea

Obstructive sleep apnea (OSA) promotes atrial remodeling and fibrosis, providing a substrate for atrial fibrillation (AF). Herein, we investigate the pathophysiological mechanisms of AF in association with OSA in a cohort of cardiac surgery patients. A prospective study including patients undergoing cardiac surgery. Biomarkers reflective of AF pathophysiology (interleukin [IL-6], C-reactive protein [CRP], von Willebrand factor [vWF], N-terminal pro-brain natriuretic peptide [NT-proBNP], high-sensitivity Troponin T [hs-TnT], and Galectin-3 [Gal-3]) was assessed by functional or immunological assays. miRNAs involved in AF were analyzed by reverse transcription-polymerase chain reaction (RT-PCR). Using atrial tissue samples, fibrosis was assessed by Masson's trichrome. Connexin 40 and 43 (Cx40; Cx43) were evaluated by immunolabeling. Fifty-six patients (15 with OSA and 41 non-OSA) were included in this hypothesis-generating pilot study. OSA group had a higher incidence of postoperative AF (POAF) (46.7% vs. 19.5%; p = .042), presented an increased risk of POAF (OR 3.61, 95% CI 1.01-12.92), and had significantly higher baseline levels of NT-proBNP (p = .044), vWF (p = .049), Gal-3 (p = .009), IL-6 (p = .002), and CRP (p = .003). This group presented lower levels of miR-21 and miR-208 (both p < .05). Also, lower Cx40 levels in POAF and/or OSA patients (50.0% vs. 81.8%, p = .033) were found. The presence of interstitial fibrosis (according to myocardial collagen by Masson's trichrome) was raised in OSA patients (86.7% vs. 53.7%, p = .024). Several biomarkers and miRNAs involved in inflammation and fibrosis were dysregulated in OSA patients, which together with a higher degree of interstitial fibrosis, altered miRNA, and Cxs expression predisposes to the development of a substrate that increases the AF risk.

Deciphering mechanism of the herbal formula WuShen in the treatment of postinfarction heart failure

BACKGROUND

Numerous clinical studies reported the effectiveness of herbal formula WuShen (WS) in treating cardiovascular diseases, yet relevant basic research was rarely conducted.

METHODS AND RESULTS

Twelve main bioactive compounds of WS decoction were identified using the ultra-performance liquid chromatography-LTQ-Orbitrap mass spectrometer. A total of 137 active compounds with 613 targets were predicted by network pharmacology; their bioinformatic annotation and human microarray data suggested that wounding healing, inflammatory response, and gap junction were potentially the major therapeutic modules. A rat model of post-myocardial infarction (MI) heart failure (HF) was used to study the effects of WS on cardiac function, adverse cardiac remodeling, and experimental arrhythmias. Rats treated with WS led to a significantly improved pump function and reduced susceptibility to both ventricular tachycardia and atrial fibrillation, and restricted adverse cardiac remodeling partly via inhibiting TGFβ1/SMADs mediated extracellular matrix deposition and Rac1/NOX2/CTGF/Connexin43 -involved gap junction remodeling.

CONCLUSIONS

The present study highlights that WS can be applied to the treatment of heart failure and the upstream therapy for atrial fibrillation and ventricular tachycardia through its preventive effect on adverse cardiac remodeling.

Xanthine oxidase inhibitor febuxostat reduces atrial fibrillation susceptibility by inhibition of oxidized CaMKII in Dahl salt-sensitive rats

Oxidative stress could be a possible mechanism and a therapeutic target of atrial fibrillation (AF). However, the effects of the xanthine oxidase (XO) inhibition for AF remain to be fully elucidated. We investigated the effects of a novel XO inhibitor febuxostat on AF compared with allopurinol in hypertension rat model. Five-week-old Dahl salt-sensitive rats were fed either low-salt (LS) (0.3% NaCl) or high-salt (HS) (8% NaCl) diet. After 4 weeks of diet, HS diet rats were divided into three groups: orally administered to vehicle (HS-C), febuxostat (5 mg/kg/day) (HS-F), or allopurinol (50 mg/kg/day) (HS-A). After 4 weeks of treatment, systolic blood pressure (SBP) was significantly higher in HS-C than LS, and it was slightly but significantly decreased by treatment with each XO inhibitor. AF duration was significantly prolonged in HS-C compared with LS, and significantly suppressed in both HS-F and HS-A (LS; 5.8 ± 3.5 s, HS-C; 33.9 ± 23.7 s, HS-F; 15.0 ± 14.1 s, HS-A; 20.1 ± 11.9 s: P<0.05). Ca2+ spark frequency was obviously increased in HS-C rats and reduced in the XO inhibitor-treated rats, especially in HS-F group. Western blotting revealed that the atrial expression levels of Met281/282-oxidized Ca2+/Calmodulin-dependent kinase II (CaMKII) and Ser2814-phosphorylated ryanodine receptor 2 were significantly increased in HS-C, and those were suppressed in HS-F and HS-A. Decreased expression of gap junction protein connexin 40 in HS-C was partially restored by treatment with each XO inhibitor. In conclusion, XO inhibitor febuxostat, as well as allopurinol, could reduce hypertension-related increase in AF perpetuation by restoring Ca2+ handling and gap junction.

Linking Electrical Drivers With Atrial Cardiomyopathy for the Targeted Treatment of Atrial Fibrillation

The relationship between atrial fibrillation (AF) and underlying functional and structural abnormalities has received substantial attention in the research literature over the past decade. Significant progress has been made in identifying these changes using non-invasive imaging, voltage mapping, and electrical recordings. Advances in computed tomography and cardiac magnetic resonance imaging can now provide insight regarding the presence and extent of cardiac fibrosis. Additionally, multiple technologies able to identify electrical targets during AF have emerged. However, an organized strategy to employ these resources in the targeted treatment of AF remains elusive. In this work, we will discuss the basis for mechanistic importance of atrial fibrosis and scar as potential sites promoting AF and emerging technologies to identify and target these structural and functional substrates in the electrophysiology laboratory. We also propose an approach to the use of such technologies to serve as a basis for ongoing work in the field.

The ratio of main pulmonary artery to ascending aorta diameter is associated with the right ventricular outflow tract ventriculararrhythmias

BACKGROUND

Although outflow tract (OT) ventricular arrhythmias (VAs) are generally regarded as benign, the relationship between circulation pressure and VAs has received considerable attention in recent years. Previous studies have shown that the ratio of main pulmonary artery (MPA) to ascending aorta (AA) diameter is associated with pulmonary pressure. Here, we investigated whether an elevated MPA/AA ratio is associated with right ventricular OT (RVOT) VAs.

METHODS

A total of 67 patients with OT VAs (47 patients with RVOT and 20 patients with LVOT) who underwent cardiac multidetector computed tomography and radiofrequency ablation were enrolled in this study. MPA and AA diameters were measured at the level of the bifurcation of the pulmonary artery. According to the MPA/AA ratio, patients were further divided into two groups: the MPA/AA ratio abnormal group (n = 19), which is defined as MPA/AA ratio ≥ 0.9, and the MPA/AA ratio normal group (n = 48) consisting of patients with an MPA/AA ratio < 0.9.

RESULTS

Patients with RVOT VAs exhibited an elevated MPA/AA ratio (0.84 ± 0.11 vs. 0.75 ± 0.11, p = 0.006). Furthermore, this MPA/AA ratio was shown to be an independent predictor for RVOT VAs (p = 0.013, 95% confidence interval: 1.016-1.145), with an abnormal MPA/AA ratio increasing the odds of RVOT VAs 5.1-fold in patients with OT VAs.

CONCLUSION

Patients with RVOT VAs exhibited significantly higher MPA/AA ratios compared with those LVOT VAs. The MPA/AA ratio was showed to be an independent predictor RVOT VAs.

Atrial Myopathy

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The authors discuss the concept of atrial myopathy; its relationship to aging, electrophysiological remodeling, and autonomic remodeling; the interplay between atrial myopathy, AF, and stroke; and suggest how to identify patients with atrial myopathy and how to incorporate atrial myopathy into decisions about anticoagulation.

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Atrial myopathy seen in animal models of AF and in patients with AF is the result of a combination of factors that lead to electrical and structural remodeling in the atrium. Although AF may lead to the initiation and/or progression of this myopathy, the presence of AF is by no means essential to the development or the maintenance of the atrial myopathic state.

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Methods to identify atrial myopathy include atrial electrograms, tissue biopsy, cardiac imaging, and certain serum biomarkers. A promising modality is 4-dimensional flow cardiac magnetic resonance. The concept of atrial myopathy may help guide oral anticoagulant therapy in selected groups of patients with AF, particularly those with low to intermediate risk of strokes and those who have undergone successful AF ablation. This review highlights the need for prospective randomized trials to test these hypotheses.

This paper discusses the evolving concept of atrial myopathy by presenting how it develops and how it affects the properties of the atria. It also reviews the complex relationships among atrial myopathy, atrial fibrillation (AF), and stroke. Finally, it discusses how to apply the concept of atrial myopathy in the clinical setting—to identify patients with atrial myopathy and to be more selective in anticoagulation in a subset of patients with AF. An apparent lack of a temporal relationship between episodes of paroxysmal AF and stroke in patients with cardiac implantable electronic devices has led investigators to search for additional factors that are responsible for AF-related strokes. Multiple animal models and human studies have revealed a close interplay of atrial myopathy, AF, and stroke via various mechanisms (e.g., aging, inflammation, oxidative stress, and stretch), which, in turn, lead to fibrosis, electrical and autonomic remodeling, and a pro-thrombotic state. The complex interplay among these mechanisms creates a vicious cycle of ever-worsening atrial myopathy and a higher risk of more sustained AF and strokes. By highlighting the importance of atrial myopathy and the risk of strokes independent of AF, this paper reviews the methods to identify patients with atrial myopathy and proposes a way to incorporate the concept of atrial myopathy to guide anticoagulation in patients with AF.

Biomarkers of Atrial Fibrillation in Hypertension

Background:

Atrial fibrillation (AF) is the most frequently encountered cardiac arrhythmia globally and substantially increases the risk for thromboembolic disease. Albeit, 20% of all cases of AF remain undiagnosed. On the other hand, hypertension amplifies the risk for both AF occurrences through hemodynamic and non-hemodynamic mechanisms and cerebrovascular ischemia. Under this prism, prompt diagnosis of undetected AF in hypertensive patients is of pivotal importance.

Method:

We conducted a review of the literature for studies with biomarkers that could be used in AF diagnosis as well as in predicting the transition of paroxysmal AF to sustained AF, especially in hypertensive patients.

Results:

Potential biomarkers for AF can be broadly categorized into electrophysiological, morphological and molecular markers that reflect the underlying mechanisms of adverse atrial remodeling. We focused on P-wave duration and dispersion as electrophysiological markers, and left atrial (LA) and LA appendage size, atrial fibrosis, left ventricular hypertrophy and aortic stiffness as structural biomarkers, respectively. The heterogeneous group of molecular biomarkers of AF encompasses products of the neurohormonal cascade, including NT-pro BNP, BNP, MR-pro ANP, polymorphisms of the ACE and convertases such as corin and furin. In addition, soluble biomarkers of inflammation (i.e. CRP, IL-6) and fibrosis (i.e. TGF-1 and matrix metalloproteinases) were assessed for predicting AF.

Conclusion:

The reviewed individual biomarkers might be a valuable addition to current diagnostic tools but the ideal candidate is expected to combine multiple indices of atrial remodeling in order to effectively detect both AF and adverse characteristics of high risk patients with hypertension.

Overexpression of miR-27b-3p Targeting Wnt3a Regulates the Signaling Pathway of Wnt/β-Catenin and Attenuates Atrial Fibrosis in Rats with Atrial Fibrillation

MicroRNAs (miRNAs) are regarded as a potential method for the treatment of atrial fibrillation (AF) although its molecular mechanism remains unknown. We found in our previous study that the level of peripheral blood miR-27b-3p and the expression of atrial tissue CX43 were both significantly downregulated in AF patients. In the present study, we propose and test this hypothesis that overexpression of miR-27b-3p attenuates atrial fibrosis, increases CX43 expression, and regulates the signaling pathway of Wnt/β-Catenin by targeting Wnt3a. miR-27b-3p overexpression was induced by rat tail vein injection of adeno-associated virus. Two weeks after transfection of adeno-associated virus, the rat AF model was established by tail vein injection of acetylcholine- (ACh-) CaCl₂ for 7 days, and 1 ml/kg was injected daily. The incidence and duration of AF were recorded with an electrocardiogram. Cardiac function was monitored by cardiac ultrasound. Serum cardiac enzyme was detected by ELISA. The expression of atrial miR-27b-3 and Wnt3a was assayed by quantitative RT-PCR. Atrial fibrosis was determined by Masson's trichrome staining. Expression of atrial Collagen-I and Collagen-III was tested by the immunohistochemical method. Expression of CX43 was measured by immunofluorescence. The expression of Collagen-I, a-SMA, Collagen-III, TGF-β1, CX43, Wnt3a, β-Catenin, and p-β-Catenin was assayed by western blot. Our results showed that miR-27b-3p overexpression could reduce the incidence and duration of AF, alleviate atrial fibrosis, increase atrial CX43 expression, and decrease the expression of Collagen-I, a-SMA, Collagen-III, TGF-β1, Wnt3a, and p-β-Catenin. In addition, the results of luciferase activity assay showed that Wnt3a is a validated miR-27b-3p target in HEK 293T cells. Our results provide a new evidence that miR-27b-3p regulates the signaling pathway of Wnt/β-Catenin by targeting Wnt3a, which may play an important role in the development of atrial fibrosis and AF.

Activin Receptor-Like Kinase 4 Haplodeficiency Mitigates Arrhythmogenic Atrial Remodeling and Vulnerability to Atrial Fibrillation in Cardiac Pathological Hypertrophy

Background Activin receptor-like kinase 4 ( ALK 4) is highly expressed in mammal heart. Atrial fibrillation ( AF ) is closely related to ventricular pressure overload. Because pressure overload increases atrial pressure and leads to atrial remodeling, it would be informative to know whether ALK 4 exerts potential effects on atrial remodeling and AF vulnerability in a pressure-overload model. Methods and Results Wild-type littermates and ALK 4+/- mice were subjected to abdominal aortic constriction or a sham operation. After 4 or 8 weeks, echocardiographic and hemodynamic measurements were performed, and inducibility of AF was tested. The hearts were divided into atria and ventricles and then were fixed in formalin for staining, or they were weighted and snap-frozen for quantitative real-time polymerase chain reaction and Western blot analysis. Compared with wild-type littermates, ALK 4+/- mice demonstrated a similar extent of atrial hypertrophy but significantly suppressed atrial fibrosis at 8 weeks post-abdominal aortic constriction. ALK 4 haplodeficiency partially blocked abdominal aortic constriction-induced upregulation of monocyte chemotactic protein 1 and interleukin-6, and the increased chemotaxin of macrophages. ALK 4 haplodeficiency also blunted a reduction of connexin 40 and redistribution of connexin 43 from the intercalated disk to the lateral membranes, thereby improving localized conduction abnormalities. Meanwhile, ALK 4 haplodeficiency inhibited abdominal aortic constriction-induced decreased INa, ICa-L and IK1 densities as well as the accompanying action potential duration shortening. Mechanistically, ALK 4 haploinsufficiency resulted in the suppression of Smad2/3 activity in this model. Conclusions Our results demonstrate that ALK 4 haplodeficiency ameliorates atrial remodeling and vulnerability to AF in a pressure-overload model through inactivation of the Smad2/3 pathway, suggesting that ALK 4 might be a potential therapeutic target in combating pressure overload-induced AF .

Effects of Pinocembrin Pretreatment on Connexin 43 (Cx43) Protein Expression After Rat Myocardial Ischemia-Reperfusion and Cardiac Arrhythmia

Background

Cardiac infarction frequently leads to arrhythmia and ischemia/reperfusion (I/R) aggravates cardiac injury. Pinocembrin can resist cerebral ischemia and decrease cardiac infarction area. This study thus generated a rat myocardial I/R model to assess the effect on ventricular rhythm and expression of gap junction connexin (Cx43).

Material/Methods

Male SD rats were randomly assigned into sham, model, and pinocembrin (30 mg/kg) pretreatment groups (N=15 each). The I/R model was generated by ligation of the left anterior descending coronary artery for 30 min. The pinocembrin group received intravenous injection 10 min before surgery. Heart rate (HR), mean artery pressure (MAP), rate pressure product (RPP), and arrhythmia were observed at 10 min before ischemia, 30 min after ischemia, and at 30, 60, and 120 min after reperfusion. ELISA was used to assess serum CK-MB and cTnI levels. Na⁺-K⁺ATPase and Ca⁺-Mg²⁺ATPase levels were quantified by spectrometry, followed by HE staining, IHC approach for Cx43 expression, and Western blot for Kir2.1 protein expression.

Results

Model rats had significantly lower HR, MAP, and RPP than in the sham group, and the pinocembrin pretreatment group had higher serum indexes. Arrhythmia index, CK-MB, and cTnI were higher in the model and pinocembrin groups, while Na⁺-K⁺ATPase, Ca⁺-Mg²⁺ATPase, Cx43, and Kir2.1 proteins were lower (p<0.05).

Conclusions

Pinocembrin alleviated ventricular arrhythmia in I/R rats via enhancing Na⁺-K⁺ATPase and Ca⁺-Mg²⁺ATPase activity and upregulating Cx43 and Kir2.1 protein expression.

Shengmai San-derived herbal prevents the development of a vulnerable substrate for atrial fibrillation in a rat model of ischemic heart failure

OBJECTIVE

The study aimed to investigate whether a Shengmai San-derived herbal, Fumai granule (FM), which had a preventive effect on atrial fibrillation (AF) in myocardial infarction (MI)-induced heart failure (HF) rat and to determine the underlying mechanisms.

DESIGN AND METHODS

MI was induced by a ligation of the left anterior descending coronary artery. One week after MI surgery, FM was gavaged for 4 weeks. AF inducibility was detected by transesophageal programmed electrical stimulation technology. Multielectrode array measurements, echocardiogram, histology, and western blotting were performed.

RESULTS

The FM-treated group had lower rates of AF inducibility and shorter AF duration compared to the MI group. FM improved the conduction velocity and homogeneity, decreased left atrial positive fibrosis areas and expression of type I and III collagen, inhibited cardiac fibroblast to myofibroblast differential, and increased the expression of connexin 43 and connexin 40 in the left atrium.

CONCLUSIONS

These results suggest that FM reduced the AF inducibility after MI by improving the left atrial conduction function via inhibiting left atrial fibrosis and increasing the expression of connexin, indicating its benefit in preventing the MI-induced vulnerable substrate for AF.

Cardiac Fibrosis and Arrhythmogenesis

Myocardial injury, mechanical stress, neurohormonal activation, inflammation, and/or aging all lead to cardiac remodeling, which is responsible for cardiac dysfunction and arrhythmogenesis. Of the key histological components of cardiac remodeling, fibrosis either in the form of interstitial, patchy, or dense scars, constitutes a key histological substrate of arrhythmias. Here we discuss current research findings focusing on the role of fibrosis, in arrhythmogenesis. Numerous studies have convincingly shown that patchy or interstitial fibrosis interferes with myocardial electrophysiology by slowing down action potential propagation, initiating reentry, promoting after-depolarizations, and increasing ectopic automaticity. Meanwhile, there has been increasing appreciation of direct involvement of myofibroblasts, the activated form of fibroblasts, in arrhythmogenesis. Myofibroblasts undergo phenotypic changes with expression of gap-junctions and ion channels thereby forming direct electrical coupling with cardiomyocytes, which potentially results in profound disturbances of electrophysiology. There is strong evidence that systemic and regional inflammatory processes contribute to fibrogenesis (i.e., structural remodeling) and dysfunction of ion channels and Ca2+ homeostasis (i.e., electrical remodeling). Recognizing the pivotal role of fibrosis in the arrhythmogenesis has promoted clinical research on characterizing fibrosis by means of cardiac imaging or fibrosis biomarkers for clinical stratification of patients at higher risk of lethal arrhythmia, as well as preclinical research on the development of antifibrotic therapies. At the end of this review, we discuss remaining key questions in this area and propose new research approaches. © 2017 American Physiological Society. Compr Physiol 7:1009-1049, 2017.

α-adrenoceptor-mediated enhanced inducibility of atrial fibrillation in a canine system inflammation model

The exact mechanism associated with inflammation and atrial fibrillation (AF) remains unknown. The aim of the present study was to investigate the roles of connexin 43 (Cx43) and a1‑adrenergic receptor (α1‑AR) activation in the pathogenesis of system inflammation‑induced AF. A canine model of chronic low‑grade system inflammation was established by administrating a low dose of lipopolysaccharide (LPS; 0.1 µg/kg) for 2 weeks. Programmed stimulation was applied on the right atrial appendage to determine the effective refractory periods (ERP) and the window of vulnerability (WOV). Tumor necrosis factor α (TNF‑α) and interleukin 6 (IL‑6) levels in plasma and atrial tissue were measured by ELISA. Cx43, Toll‑like receptor 4 (TLR4) and nuclear factor κB (NF‑κB) proteins were analyzed using western blotting or immunohistochemistry. Administration of LPS for 2 weeks increased the concentration of TNF‑α and IL‑6 in the plasma and right atrium. ERP was markedly shortened and cumulative WOV was significantly widened in the LPS group. Following treatment with LPS, the amount of Cx43 protein in the area of intercalated disk increased. In addition, a high‑density of Cx43 in the lateral connection was identified. LPS also induced the activation of NF‑κB in the canine atrium. Administration with the α1‑AR blocker doxazosin prevented the production of LPS‑induced inflammatory cytokine and reversed the enhanced vulnerability to atrial fibrillation. Doxazosin inhibited the LPS‑induced increase in Cx43 protein and heterogeneous distribution, and prevented the activation of NF‑κB. These results indicated that chronic low‑grade system inflammation may increase the inducibility of AF in a canine model. The underlying mechanism may be involved in the LPS‑induced activation of NF‑κB, and the increase in Cx43 expression and lateral distribution via an α1-AR-dependent pathway.

Propofol attenuated liver transplantation-induced acute lung injury via connexin43 gap junction inhibition

BACKGROUND

Postoperative acute lung injury (ALI) is a severe complication after liver transplantation, which influences patient survival rate obviously. However, its mechanisms are unclear and effective therapies are still lacking. The current study focused on effects of propofol on liver transplantation-induced ALI and whether its underlying mechanism was relative with connexin43 (Cx43) alternation. The authors postulated that endotoxin induced enhancement of Cx43 gap junction (GJ) plays a critical role in mediating post liver transplantation ALI and that pretreatment with the anesthetic propofol, known to inhibit gap junction, can confer effective protection.

METHODS

Male Sprague-Dawley rats underwent autologous orthotopic liver transplantation (AOLT) in the absence or presence of treatments with the selective Cx43 inhibitor, enanthol (0.1 mg/kg) and propofol (50 mg/kg), a commonly used anesthetic in clinical anesthesia. In vitro study, BEAS-2B cells, a kind of lung epithelial cell line expressing Cx43, exposed to lipopolysaccharide (LPS), which mainly contributed to ALI. Function of Cx43 GJ was regulated by Cx43 specific inhibitors, gap26 (300 μM) or enhancer, retinoic acid (10 μM) and two specific siRNAs.

RESULTS

Compared with the sham group, AOLT results in ALI obviously with plasma endotoxin increase. Cx43 inhibition decreased ALI through inflammatory reaction reduction. In vitro studies, LPS-induced BEAS-2B cells damage was attenuated by Cx43 function inhibition, but amplified by enhancement. Another important finding was propofol reduced Cx43 function and protected against LPS-mediated BEAS-2B cells damage or AOLT-induced ALI, mechanisms of which were also associated with inflammatory reaction decrease.

CONCLUSION

Cx43 plays a vital role in liver transplantation-induced ALI. Propofol decreased Cx43 function and protected against ALI in vivo and in vitro. This finding provide a new basis for targeted intervention of organ protection in liver transplantation, even in other kinds of operations.