Effects of angiotensin-converting enzyme inhibition on the development of the atrial fibrillation substrate in dogs with ventricular tachypacing-induced congestive heart failure

Atrial fibrillation in heart failure with preserved ejection fraction: Insights into mechanisms and therapeutics

Atrial fibrillation (AF) and heart failure (HF) often coexist, and the outcomes of patients who have both AF and HF are considerably worse than those with either condition in isolation. Heart failure with preserved ejection fraction (HFpEF) is a heterogeneous clinical entity and accounts for approximately one-half of current HF. At least one-third of patients with HFpEF are burdened by comorbid AF. The current understanding of the relationship between AF and HFpEF is limited, but the clinical implications are potentially important. In this review, we explore 1) the pathogenesis that drives AF and HFpEF to coexist; 2) pharmacologic therapies that may attenuate the impact of AF in HFpEF; and 3) future directions in the management of this complex syndrome.

Class I Histone Deacetylase Inhibition for the Treatment of Sustained Atrial Fibrillation

Current therapies are less effective for treating sustained/permanent versus paroxysmal atrial fibrillation (AF). We and others have previously shown that histone deacetylase (HDAC) inhibition reverses structural and electrical atrial remodeling in mice with inducible, paroxysmal-like AF. Here, we hypothesize an important, specific role for class I HDACs in determining structural atrial alterations during sustained AF. The class I HDAC inhibitor N-acetyldinaline [4-(acetylamino)-N-(2-amino-phenyl) benzamide] (CI-994) was administered for 2 weeks (1 mg/kg/day) to Hopx transgenic mice with atrial remodeling and inducible AF and to dogs with atrial tachypacing-induced sustained AF. Class I HDAC inhibition prevented atrial fibrosis and arrhythmia inducibility in mice. Dogs were divided into three groups: 1) sinus rhythm, 2) sustained AF plus vehicle, and 3) sustained AF plus CI-994. In group 3, the time in AF over 2 weeks was reduced by 30% compared with group 2, along with attenuated atrial fibrosis and intra-atrial adipocyte infiltration. Moreover, group 2 dogs had higher atrial and serum inflammatory cytokines, adipokines, and atrial immune cells and adipocytes compared with groups 1 and 3. On the other hand, groups 2 and 3 displayed similar left atrial size, ventricular function, and mitral regurgitation. Importantly, the same histologic alterations found in dogs with sustained AF and reversed by CI-994 were also present in atrial tissue from transplanted patients with chronic AF. This is the first evidence that, in sustained AF, class I HDAC inhibition can reduce the total time of fibrillation, atrial fibrosis, intra-atrial adipocytes, and immune cell infiltration without significant effects on cardiac function.

Association of cardiac cachexia and atrial fibrillation in heart failure patients

BACKGROUND

Cachexia is a common complication in patients with advanced heart failure (HF) associated with inflammatory response activation. Atrial fibrillation (AF) is the most frequent arrhythmia (26%), probably both exacerbate the cardiac cachexia (CC).

OBJECTIVES

Evaluate the association of cardiac cachexia and atrial fibrillation in heart failure patients.

MATERIAL AND METHODS

In a case control study, CC was diagnosed by electrical bioimpedance with vectorial analysis (BIVA). Subjects with congenital heart disease, cancer, HIV, drug use and other causes than HF were excluded.

RESULTS

Of the 359 subjects analyzed (men: 52.9%) median age 65years (55-74). Those with CC were older [72 (61-67)] vs. without [62 (52-70) years old, p<0.01]. During follow-up 47.8% of subjects developed CC and 17.27% AF, this was significantly more frequent in cachectic patients CC (23% vs 12.11%, OR: 2.17, 95% CI: 1.19-4.01, p=0.006). Subjects, with AF had lower left ventricular ejection fraction (25.49±12.96 vs. 32.01±15.02, p=0.08), lower posterior wall thickness (10.03±2.12 vs. 11.00±2.47, p=0.007), larger diameter of the left atrium (49.87±9.84 vs. 42.66±7.56, p<0.001), and a higher prevalence of CC (85.42% vs. 69.77%, p=0.028). The 50.58% of was in NYHA class I. In NYHA III, 22.95% were in AF vs. 12.10% with not AF (p=0.027).

CONCLUSION

The frequent coexistence of CC and AF as HF complications indicate greater severity of HF, regardless of its type of HF.

Cilostazol Prevents Atrial Structural Remodeling through the MEK/ERK Pathway in a Canine Model of Atrial Tachycardia

OBJECTIVES

Atrial fibrillation (AF) is the most common sustained arrhythmia in clinical practice. Atrial structural remodeling (ASR), particularly atrial fibrosis, is an important contributor to the AF substrate. This study aimed to investigate the preventive effects of the phosphodiesterase 3 inhibitor cilostazol on ASR and its potential molecular mechanisms in a canine model of rapid atrial pacing (RAP).

METHODS

Thirty dogs were assigned to sham (Sham), paced/ no treatment (Paced) and paced + cilostazol 5 mg/kg/day (Paced + cilo) groups, with 10 dogs in each group. RAP at 500 beats/min was maintained for 2 weeks, while the Sham group was instrumented without pacing. Cilostazol was provided orally during pacing. Western blotting, RT-PCR and pathology were used to assess ASR.

RESULTS

Cilostazol attenuated atrial interstitial fibrosis and structural remodeling in canines with RAP. MEK/ERK transduction pathway gene expression was upregulated in the Paced group compared with the Sham group. Cilostazol markedly alleviated these changes in the MEK/ERK pathway. Transforming growth factor-β1 protein expression in the Paced group was significantly higher than in the Sham group (p < 0.01), and was significantly reduced by cilostazol (p < 0.01).

CONCLUSIONS

Our findings suggest that cilostazol is beneficial for prevention and treatment in atrial tachycardia-induced ASR in a canine model of RAP.

Current Perspectives of Electrical Remodeling and Its Therapeutic Implications

Electrical remodeling involves alterations in the electrophysiologic milieu of myocardium in various disease states, such as ventricular hypertrophy, heart failure, atrial tachyarrhythmias, myocardial ischemia, and infarction that are associated with cardiac arrhythmias. Although research in this area dates back to early part of the 19th century, we still lack the exact knowledge of ionic remodeling, the role of various genes and channel proteins, and their relevance for the newer antiarrhythmic therapies. Structural remodeling may also have an impact on the electrical remodeling process, although differences in both structural and electrical remodeling are associated with different disease states. Various electrophysiologic, cellular, and structural alterations, including anisotropic conduction, increased intracellular calcium levels, and gap junction remodeling predispose to increased dispersion of action potential duration and refractoriness. This constitutes a favorable substrate for early and late afterdepolarizations and reentrant arrhythmias. Studying the role of ionic remodeling in the initiation and propagation of cardiac arrhythmias has significant relevance for developing newer antiarrhythmic therapies, for identifying patients at risk of developing fatal arrhythmias, and for implementing effective preventive measures. Further research is required to understand the specific effects of individual ion channel remodeling, to understand the signal transduction mechanisms, and to address whether detrimental effects of electrical remodeling can be altered.

Effect of RAAS blockers on adverse clinical outcomes in high CVD risk subjects with atrial fibrillation: A meta-analysis and systematic review of randomized controlled trials

Recent studies have demonstrated that atrial fibrillation significantly increases the risk of adverse clinical outcomes in high cardiovascular disease risk subjects. Application of renin-angiotensin-aldosterone system blockers for prevention of recurrence of atrial fibrillation and adverse clinical outcomes in subjects with atrial fibrillation is a theoretically appealing concept. However, results of clinical trials evaluating the effect of renin-angiotensin-aldosterone blockers on adverse clinical outcomes in high cardiovascular disease risk subjects with atrial fibrillation remain inconclusive.A pooled study of 6 randomized controlled trials assessing the efficacy of renin-angiotensin-aldosterone blockers on subjects with atrial fibrillation was performed.A total of 6 randomized controlled trials enrolled a total of 53,510 patients followed for 1 to 5 years. RAAS blockade therapy was associated with 14% reduction in the incidence of heart failure (OR: 0.86, [95%CI: 0.76- 0.97], P=0.018) and 17% reduction in the incidence of CVE (OR: 0.83, [95%CI: 0.70-0.99], P = 0.038). The corresponding decline in absolute risk against heart failure (ARR: 1.4%, [95%CI: 0.2-2.6%], P = 0.018) and CVE (ARR: 3.5%, [95%CI: 0.0-6.9%], P = 0.045) in the AF group was much higher than the non-AF group for heart failure (ARR: 0.4%, [95%CI: 0.0-0.7%], P = 0.057) and CVE (ARR: 1.6%, [95%CI: -0.1% to 3.3%], P = 0.071). No significant effect was noted on all-cause or cardiovascular mortality, stroke, or myocardial infarction.This study suggests that RAAS blockade offers protection against heart failure and cardiovascular events in high cardiovascular disease risk subjects with atrial fibrillation.

Effect of irbesartan on development of atrial fibrosis and atrial fibrillation in a canine atrial tachycardia model with left ventricular dysfunction, association with p53

Effects of an angiotensin II receptor blocker, irbesartan (IRB), on the development of atrial fibrosis and atrial fibrillation (AF) were assessed in a canine model of atrial tachycardia remodeling (ATR) with left ventricular dysfunction, together with its possible association with involvement of p53. Atrial tachypacing (400 bpm for 4 weeks) was used to induce ATR in beagles treated with placebo (ATR-dogs, n = 6) or irbesartan (IRB-dogs, n = 5). Non-paced sham dogs served as control (Control-dogs, n = 4). ATR- and IRB-dogs developed tachycardia-induced left ventricular dysfunction. Atrial effective refractory period (AERP) shortened (83 ± 5 ms, p < 0.05), inter-atrial conduction time prolonged (72 ± 2 ms, p < 0.05), and AF duration increased (29 ± 5 s, p < 0.05 vs. baseline) after 4 weeks in ATR-dogs. ATR-dogs also had a larger area of atrial fibrous tissue (5.2 ± 0.5 %, p < 0.05 vs. Control). All these changes, except for AERP, were attenuated in IRB-dogs (92 ± 3 ms, 56 ± 3 ms, 9 ± 5 s, and 2.5 ± 0.7 %, respectively; p < 0.05 vs. ATR for each). In ATR-dogs, p53 expression in the left atrium decreased by 42 % compared with Control-dogs (p < 0.05); however, it was highly expressed in IRB-dogs (+89 % vs. ATR). Transforming growth factor (TGF)-β1 expression was enhanced in ATR-dogs (p < 0.05 vs. Control) but reduced in IRB-dogs (p < 0.05 vs. ATR). Irbesartan suppresses atrial fibrosis and AF development in a canine ATR model with left ventricular dysfunction in association with p53.

Association between Postoperatively Developed Atrial Fibrillation and Long-Term Mortality after Esophagectomy in Esophageal Cancer Patients: An Observational Study

Background

Newly developed atrial fibrillation (AF) in patients who have undergone an esophagectomy increases the incidence of postoperative complications. However, the clinical implications of AF have not been fully elucidated in these patients. This retrospective observational study investigated the predictors for AF and the effect of AF on the mortality in esophageal cancer patients undergoing esophagectomy.

Methods

This study evaluated 583 patients undergoing esophagectomy, from January 2005 to April 2012. AF was defined as newly developed postoperative AF requiring treatment. The risk factors for AF and the association between AF and mortality were evaluated. The long-term mortality was the all-cause mortality, for which the cutoff date was May 31, 2014.

Results

AF developed in 63 patients (10.8%). Advanced age (odds ratio [OR] 1.099, 95% confidence interval [CI] 1.056–1.144, P < 0.001), preoperative calcium channel blocker (CCB) (OR 2.339, 95% CI 1.143–4.786, P = 0.020), and angiotensin-converting enzyme inhibitor (ACEI) or angiotensin receptor blocker (ARB) (OR 0.206, 95% CI 0.067–0.635, P = 0.006) were associated with the incidence of AF. The Kaplan-Meier curve showed a significantly lower survival rate in the AF group compared to the non-AF group (P = 0.045), during a median follow-up of 50.7 months. The multivariable analysis revealed associations between AF and the 1-year mortality (hazard ratio [HR] 2.556, 95% CI 1.430–4.570, P = 0.002) and between AF and the long-term mortality (HR 1.507, 95% CI 1.003–2.266, P = 0.049).

Conclusions

In esophageal cancer patients, the advanced age and the preoperative medications (CCB, ACEI or ARB) were associated with the incidence of AF. Furthermore, postoperatively developed AF was associated with mortality in esophageal cancer patients after esophagectomy, suggesting that a close surveillance might be required in patients who showed AF during postoperative period.

Impact of genetic variants on the upstream efficacy of renin-angiotensin system inhibitors for the prevention of atrial fibrillation

BACKGROUND

Renin-angiotensin system (RAS) inhibition via angiotensin-converting enzyme inhibitors and angiotensin II receptor blockers may reduce the risk of developing atrial fibrillation (AF) in certain populations, but the evidence is conflicting. Recent genome-wide association studies have identified several single nucleotide polymorphisms (SNPs) associated with AF, potentially identifying clinically relevant subtypes of the disease. We sought to investigate the impact of carrier status of 9 AF-associated SNPs on the efficacy of RAS inhibition for the primary prevention of AF.

METHODS

We performed SNP-RAS inhibitor interaction testing with unadjusted and adjusted Cox proportional hazards models using a discovery (Cardiovascular Health Study) and a replication (Atherosclerosis Risk in Communities) cohort. Additive genetic models were used for the SNP analyses, and 2-tailed P values <.05 were considered statistically significant.

RESULTS

Among 2,796 Cardiovascular Health Study participants, none of the 9 a priori identified candidate SNPs exhibited a significant SNP-drug interaction. Two of the 9 SNPs, rs2106261 (16q22) and rs6666258 (1q21), revealed interaction relationships that neared statistical significance (with point estimates in the same direction for angiotensin-converting enzyme inhibitor only and angiotensin II receptor blocker only analyses), but neither association could be replicated among 8,604 participants in Atherosclerosis Risk in Communities.

CONCLUSIONS

Our study failed to identify AF-associated SNP genetic subtypes of AF that derive increased benefit from upstream RAS inhibition for AF prevention. Future studies should continue to investigate the impact of genotype on the response to AF treatment strategies in an effort to develop personalized approaches to therapy and prevention.

Effects of Angiotensin-II Receptor Blocker on Inhibition of Thrombogenicity in a Canine Atrial Fibrillation Model

Background and Objectives

Angiotensin-II receptor blockers (ARBs) are known to reduce the development of atrial fibrillation (AF) through reverse-remodeling. However, the effect of ARBs on thrombogenicity in AF remains unknown.

Materials and Methods

Twelve dogs were assigned to control (n=4), ARB (candesartan cilexitil 10 mg/kg/day p.o., 12 weeks; n=4), or sham (n=4) groups. Sustained AF was induced by rapid atrial pacing. Both arterial and venous serum levels of tissue inhibitor of matrix metalloproteinase-1, von Willebrand factor, P-selectin, and vascular cell adhesion molecule-1 (VCAM-1) were measured at baseline and during AF (0, 4, and 12 weeks) with enzyme-linked immunosorbent assay. Biopsies from both atria including the appendages were performed to semi-quantitatively assess endocardial and myocardial fibrosis after 12 weeks.

Results

The serum levels of bio-markers were not significantly different at baseline or during AF between the control and the candesartan groups. The levels were not significantly different over time, but there was a trend toward a decrease in arterial VCAM-1 from 4 to 12 weeks in the candesartan group compared to the control group. The grades of endocardial fibrosis after 12 weeks but not those of myocardial fibrosis were slightly reduced in the candesartan group compared to the control group.

Conclusion

This study did not show that the ARB candesartan significantly reverses thrombogenicity or fibrosis during AF. Future studies using a larger number of subjects are warranted to determine the therapeutic effect of renin-angiotensin-aldosterone system blockade on prothrombogenic processes in AF.

The potential role of atrial natriuretic peptide in the effects of Angiotensin-(1-7) in a chronic atrial tachycardia canine model

Objective:

The objective of this article is to investigate the possible role of atrial natriuretic peptide (ANP) in Angiotensin-(1–7) (Ang-(1–7)) signaling pathway on atrial electrical and structural remodeling in a chronic rapid atrial pacing canine model.

Methods:

Twenty-four dogs were randomly assigned to four groups: a sham group, paced control group, a paced + Ang-(1–7) group and a paced + Ang-(1–7) + A-71915 group. Atrial rapid pacing (ARP) at 600 bpm was maintained for 14 days except in the animals from the sham group. During the pacing, Ang-(1–7) (6 μg•kg-1•h-1) or Ang-(1–7) (6 μg•kg-1•h-1) + A-71915 (ANP receptor antagonist, 0.30 μg•kg-1•h-1) were given intravenously, respectively. After pacing, it was measured that electrophysiological parameters including atrial effective refractory periods (ERPs), inducibility and duration of atrial fibrillation (AF), I_CaL and I_Na changed, where I_CaL refers to voltage-dependent L-type Ca²⁺ current and I_Na refers to cardiac sodium current. Then, the fibrosis and the expression of Cav1.2, I_Nav1.5α subunit, TGF-β₁ and ANP in atria were assessed.

Results:

After ARP, compared with the sham group, the atrial ERPs at six sites in each dog were shortened with the increasing in inducibility and duration of AF in the paced control group. The density of I_CaL, I_Na and the expression of Cav1.2, I_Nav1.5α subunit mRNA were decreased. Atrial tissue from the paced dogs showed significant interstitial fibrosis. The expression of TGF-β₁ and ANP in mRNA and protein levels were increased. Compared with the paced control group, the shortening of atrial ERPs, and the increasing of inducibility and duration of AF induced by ARP were alleviated by Ang-(1–7) treatment (p < 0.05). The density of I_CaL and I_Na and the expression of Cav1.2 and I_Nav1.5α subunit mRNA were slightly decreased. Atrial tissue showed less interstitial fibrosis after Ang-(1–7) treatment. The increasing of ANP expression was improved by Ang-(1–7), while the increasing of TGF-β₁ expression was alleviated by Ang-(1–7) (p < 0.05). A-71915 treatment blocked the beneficial effects of Ang-(1–7) on the aforementioned electrophysiological parameters and atrial fibrosis. And A-71915 treatment blocked Ang-(1–7), improving the expression of TGF-β₁.

Conclusion:

Ang-(1–7) prevented atrial structural and electrical remodeling induced by ARP. Furthermore, Ang-(1–7) promoted ANP secretion, and ANP played a crucial role in the cardiac protection of the former.

Effects of RAAS Blockers on Atrial Fibrillation Prophylaxis

Background:

Impact of atrial fibrillation on clinical outcomes is well recognized, and application of renin–angiotensin–aldosterone system (RAAS) blockers for the prevention of atrial fibrillation (AF) is a theoretically appealing concept. However, clinical trials have yielded inconsistent results.

Methods:

A pooled study of 26 randomized controlled trials (RCTs) assessing the efficacy of RAAS blockers on AF prophylaxis was performed.

Results:

A total of 28 reports from 26 randomized controlled trials enrolled 165 387 patients, with an overall 24% reduction in the incidence of AF (odds ratio [OR]: 0.76, 95% confidence interval [CI]: 0.68-0.85], P = .000). Forty-nine percent reduction in the incidence of AF (OR: 0.51, 95% CI: 0.30-0.85, P = .010) in systolic heart failure was observed, whereas no significant effect was observed in patients with diastolic heart failure, postmyocardial infarction, and high cardiovascular disease risk. There was a 19% (OR: 0.81, 95% CI: 0.67-1.00, P = .037) reduction in new-onset and 54% (OR: 0.46, 95% CI: 0.33-0.62, P = .000) reduction in recurrent AF in hypertensive patients with 39% (OR: 0.61, 95% CI: 0.44-0.84, P = .003) risk reduction against calcium blockers and 41% (OR: 0.59, 95% CI: 0.44-0.80, P = .001) risk reduction against β blockers. Angiotensin-receptor blocker appeared marginally superior to angiotensin-converting enzyme inhibitor in primary and secondary prevention.

Conclusion:

This study suggests that RAAS blockade effectively suppresses AF in systolic heart failure, and hypertensives derive greater benefit against new-onset and recurrent AF compared to β blockers, calcium channel blockers, and diuretics.

Atrial fibrillation: mechanisms, therapeutics, and future directions

Atrial fibrillation (AF) is the most prevalent cardiac arrhythmia, affecting 1% to 2% of the general population. It is characterized by rapid and disorganized atrial activation leading to impaired atrial function, which can be diagnosed on an EKG by lack of a P-wave and irregular QRS complexes. AF is associated with increased morbidity and mortality and is a risk factor for embolic stroke and worsening heart failure. Current research on AF support and explore the hypothesis that initiation and maintenance of AF require pathophysiological remodeling of the atria, either specifically as in lone AF or secondary to other heart disease as in heart failure-associated AF. Remodeling in AF can be grouped into three categories that include: (i) electrical remodeling, which includes modulation of L-type Ca(2+) current, various K(+) currents and gap junction function; (ii) structural remodeling, which includes changes in tissues properties, size, and ultrastructure; and (iii) autonomic remodeling, including altered sympathovagal activity and hyperinnervation. Electrical, structural, and autonomic remodeling all contribute to creating an AF-prone substrate which is able to produce AF-associated electrical phenomena including a rapidly firing focus, complex multiple reentrant circuit or rotors. Although various remodeling events occur in AF, current AF therapies focus on ventricular rate and rhythm control strategies using pharmacotherapy and surgical interventions. Recent progress in the field has started to focus on the underlying substrate that drives and maintains AF (termed upstream therapies); however, much work is needed in this area. Here, we review current knowledge of AF mechanisms, therapies, and new areas of investigation.

The Stress-Response MAP Kinase Signaling in Cardiac Arrhythmias

Stress-response kinases, the mitogen-activated protein kinases (MAPKs) are activated in response to the challenge of a myriad of stressors. c-Jun N-terminal kinase (JNK), extracellular signal-regulated kinases (ERKs), and p38 MAPKs are the predominant members of the MAPK family in the heart. Extensive studies have revealed critical roles of activated MAPKs in the processes of cardiac injury and heart failure and many other cardiovascular diseases. Recently, emerging evidence suggests that MAPKs also promote the development of cardiac arrhythmias. Thus, understanding the functional impact of MAPKs in the heart could shed new light on the development of novel therapeutic approaches to improve cardiac function and prevent arrhythmia development in the patients. This review will summarize the recent findings on the role of MAPKs in cardiac remodeling and arrhythmia development and point to the critical need of future studies to further elucidate the fundamental mechanisms of MAPK activation and arrhythmia development in the heart.

Comorbidity of atrial fibrillation and heart failure

Atrial fibrillation (AF) and heart failure (HF) are evolving epidemics, together responsible for substantial human suffering and health-care expenditure. Ageing, improved cardiovascular survival, and epidemiological transition form the basis for their increasing global prevalence. Although we now have a clear picture of how HF promotes AF, gaps remain in our knowledge of how AF exacerbates or even causes HF, and how the development of HF affects the outcome of patients with AF. New data regarding HF with preserved ejection fraction and its unique relationship with AF suggest a possible role for AF in its aetiology, possibly as a trigger for ventricular fibrosis. Deciding on optimal treatment strategies for patients with both AF and HF is increasingly difficult, given that results from trials of pharmacological rhythm control are arguably obsolete in the age of catheter ablation. Restoring sinus rhythm by catheter ablation seems successful in the medium term and improves HF symptoms, functional capacity, and left ventricular function. Long-term studies to examine the effect on rates of stroke and death are ongoing. Guidelines continue to evolve to keep pace with this rapidly changing field.

Keeping up the balance: role of HDACs in cardiac proteostasis and therapeutic implications for atrial fibrillation

Cardiomyocytes are long-lived post-mitotic cells with limited regenerative capacity. Proper cardiomyocyte function depends critically on the maintenance of a healthy homeostasis of protein expression, folding, assembly, trafficking, function, and degradation, together commonly referred to as proteostasis. Impairment of proteostasis has a prominent role in the pathophysiology of ageing-related neurodegenerative diseases including Huntington's, Parkinson's, and Alzheimer's disease. Emerging evidence reveals also a role for impaired proteostasis in the pathophysiology of common human cardiac diseases such as cardiac hypertrophy, dilated and ischaemic cardiomyopathies, and atrial fibrillation (AF). Histone deacetylases (HDACs) have recently been recognized as key modulators which control cardiac proteostasis by deacetylating various proteins. By deacetylating chromatin proteins, including histones, HDACs modulate epigenetic regulation of pathological gene expression. Also, HDACs exert a broad range of functions outside the nucleus by deacetylating structural and contractile proteins. The cytosolic actions of HDACs result in changed protein function through post-translational modifications and/or modulation of their degradation. This review describes the mechanisms underlying the derailment of proteostasis in AF and subsequently focuses on the role of HDACs herein. In addition, the therapeutic potential of HDAC inhibition to maintain a healthy proteostasis resulting in a delay in AF onset and progression is discussed.

Atrial fibrillation in heart failure: what should we do?

Heart failure (HF) and atrial fibrillation (AF) are two conditions that are likely to dominate the next 50 years of cardiovascular (CV) care. Both are increasingly prevalent and associated with high morbidity, mortality, and healthcare cost. They are closely inter-related with similar risk factors and shared pathophysiology. Patients with concomitant HF and AF suffer from even worse symptoms and poorer prognosis, yet evidence-based evaluation and management of this group of patients is lacking. In this review, we evaluate the common mechanisms for the development of AF in HF patients and vice versa, focusing on the evidence for potential treatment strategies. Recent data have suggested that these patients may respond differently than those with HF or AF alone. These results highlight the clear clinical need to identify and treat according to best evidence, in order to prevent adverse outcomes and reduce the huge burden that HF and AF are expected to have on global healthcare systems in the future. We propose an easy-to-use clinical mnemonic to aid the initial management of newly discovered concomitant HF and AF, the CAN-TREAT HFrEF + AF algorithm (Cardioversion if compromised; Anticoagulation unless contraindication; Normalize fluid balance; Target initial heart rate <110 b.p.m.; Renin-angiotensin-aldosterone modification; Early consideration of rhythm control; Advanced HF therapies; Treatment of other CV disease).

Angiotensin II activates signal transducers and activators of transcription 3 via Rac1 in the atrial tissue in permanent atrial fibrillation patients with rheumatic heart disease

Patients with rheumatic heart disease (RHD) often experience persistent atrial fibrillation (AF) associated with adverse atrial structural remodeling (ASR) manifested by atrial fibrosis and left atrial enlargement. The aim of this study was to explore the potential molecular signaling mechanisms for atrial fibrosis and ASR. Twenty RHD patients with persistent AF and 10 RHD patients with sinus rhythm (Group A) were recruited in our study, which all underwent transthoracic echocardiography. Right atrial appendage (RAA) tissue samples were obtained from these patients during mitral/aortic valve replacement operation. The AF patients were further divided into two groups according to left atrial diameter (LAD): Group B with LAD ranging 50-65 mm and Group C with LAD >65 mm. Histological examinations were performed with hematoxylin-eosin staining and Masson's trichrome staining. Atrial angiotensin II (AngII) content was measured by ELISA. Rac1 and STAT3 protein levels were determined by Western blot analysis. Hematoxylin-eosin staining demonstrated highly organized arrangement of atrial muscles in control Group A and significant derangement in both Group B and C AF patients with reduced cell density and increased cell size. Moreover, Masson's trichrome staining showed that atrial myocytes were surrounded by large trunks of collagen fibers in both Group B and C, but not in Group A. There was a positive correlation between atrial tissue fibrosis and LAD. AngII content was markedly higher in Group C than in Group B than in Group A, which was positively correlated with LAD. Similarly, Rac1 and STAT3 protein levels were found considerably higher in Group C and B than in Group A with excellent correlation to LAD. Our study unraveled for the first time the AngII/Rac1/STAT3 signaling as a mechanism for ASR thereby AF in a particular clinical setting-RHD patients with persistent AF and indicated inhibition of this pathway may help ameliorating adverse ASR.

Atrial fibrillation and heart failure: update 2015

Heart failure (HF) and atrial fibrillation (AF) commonly coexist, adversely affect mortality, and impose a significant burden on healthcare resources. The presence of AF and HF portends a poor prognosis as well as an increased thromboembolic risk. In patients whose AF is symptomatic, rhythm restoration with either antiarrhythmic drugs or procedural therapies (e.g., pulmonary vein isolation, either catheter-based or surgical) should be considered for symptom improvement, though a mortality benefit has yet to be demonstrated. Emerging evidence suggests that non-pharmacological treatment for AF (including catheter based ablation, hybrid surgical techniques, and atrioventricular node ablation with biventricular pacing) may be of value in improving HF patients' quality of life.

Atrial overexpression of angiotensin-converting enzyme 2 improves the canine rapid atrial pacing-induced structural and electrical remodeling. Fan, ACE2 improves atrial substrate remodeling

The purpose of this study was to investigate whether atrial overexpression of angiotensin-converting enzyme 2 (ACE2) by homogeneous transmural atrial gene transfer can reverse atrial remodeling and its mechanisms in a canine atrial-pacing model. Twenty-eight mongrel dogs were randomly divided into four groups: Sham-operated, AF-control, gene therapy with adenovirus-enhanced green fluorescent protein (Ad-EGFP) and gene therapy with Ad-ACE2 (Ad-ACE2) (n = 7 per subgroup). AF was induced in all dogs except the Sham-operated group by rapid atrial pacing at 450 beats/min for 2 weeks. Ad-EGFP and Ad-ACE2 group then received epicardial gene painting. Three weeks after gene transfer, all animals except the Sham group underwent rapid atrial pacing for another 3 weeks and then invasive electrophysiological, histological and molecular studies. The Ad-ACE2 group showed an increased ACE2 and Angiotensin-(1–7) expression, and decreased Angiotensin II expression in comparison with Ad-EGFP and AF-control group. ACE2 overexpression attenuated rapid atrial pacing-induced increase in activated extracellular signal-regulated kinases and mitogen-activated protein kinases (MAPKs) levels, and decrease in MAPK phosphatase 1(MKP-1) level, resulting in attenuation of atrial fibrosis collagen protein markers and transforming growth factor-β1. Additionally, ACE2 overexpression also modulated the tachypacing-induced up-regulation of connexin 40, down-regulation of connexin 43 and Kv4.2, and significantly decreased the inducibility and duration of AF. ACE2 overexpression could shift the renin–angiotensin system balance towards the protective axis, attenuate cardiac fibrosis remodeling associated with up-regulation of MKP-1 and reduction of MAPKs activities, modulate tachypacing-induced ion channels and connexin remodeling, and subsequently reduce the inducibility and duration of AF.

Atrial fibrillation in heart failure: drug therapies for rate and rhythm control

Pharmacological treatment of atrial fibrillation in the context of heart failure poses numerous challenges. Management decisions are limited by contraindications to several drugs and the paucity of robust clinical trials that provide evidence-based guidance. This review proposes a structured action plan for managing atrial fibrillation coexisting with heart failure that considers published clinical guidelines and integrates recent data derived from substudies of randomized trials, including the atrial fibrillation and congestive heart failure (AF-CHF) trial. Areas of uncertainty, such as target heart rates in atrial fibrillation and upstream therapies, are also discussed.

Atrial fibrillation in heart failure: catheter and surgical interventional therapies

Atrial fibrillation and heart failure commonly coexist in the same patient. Each may adversely affect the other. Atrial fibrillation leads to heart failure exacerbation, left ventricular function deterioration and an increase in thrombo-embolic risk. Therapeutic options targeting atrial fibrillation in heart failure patients include pharmacological and non-pharmacological means. Pharmacological therapy is directed at either rate control using nodal blocking agents or rhythm control using anti-arrhythmic agents, of which the options are limited in patients with heart failure. The landmark AF-CHF trial did not show any benefit of rhythm control strategy as opposed to rate control in patients with heart failure and atrial fibrillation. However, patients in this trial as well as in others used mostly amiodarone for rhythm control. This might have negated any positive effects of achieving normal sinus rhythm. Non-pharmacological therapy both for rate and rhythm control is appealing. This includes AV node ablation for rate control, catheter ablation of atrial fibrillation and surgical therapy of atrial fibrillation. This review will address non-pharmacologic treatment of AF in heart failure patients.

SR calcium handling dysfunction, stress-response signaling pathways, and atrial fibrillation

Atrial fibrillation (AF) is the most common sustained arrhythmia. It is associated with a markedly increased risk of premature death due to embolic stroke and also complicates co-existing cardiovascular diseases such as heart failure. The prevalence of AF increases dramatically with age, and aging has been shown to be an independent risk of AF. Due to an aging population in the world, a growing body of AF patients are suffering a diminished quality of life and causing an associated economic burden. However, effective pharmacologic treatments and prevention strategies are lacking due to a poor understanding of the molecular and electrophysiologic mechanisms of AF in the failing and/or aged heart. Recent studies suggest that altered atrial calcium handling contributes to the onset and maintenance of AF. Here we review the role of stress-response kinases and calcium handling dysfunction in AF genesis in the aged and failing heart.

Wnt signalling suppresses voltage-dependent Na⁺ channel expression in postnatal rat cardiomyocytes

Wnt signalling plays crucial roles in heart development, but is normally suppressed postnatally. In arrhythmogenic conditions, such as cardiac hypertrophy and heart failure, Wnt signalling is reactivated. To explore the potential role of Wnt signalling in arrhythmogenic electrical remodelling, we examined voltage-dependent ion channels in cardiomyocytes. Treatment of neonatal rat ventricular myocytes with either recombinant Wnt3a protein or CHIR-99021 (CHIR, a glycogen synthase kinase-3β inhibitor) caused a dose-dependent increase in Wnt target gene expression (Axin2 and Lef1), indicating activation of the Wnt/β-catenin pathway. Cardiac Na(+) current (INa) density was reduced by Wnt3a (-20 ± 4 vs. control -59 ± 7 pA pF(-1) , at -30 mV) or CHIR (-22 ± 5 pA pF(-1) ), without changes in steady-state activation, inactivation or repriming kinetics. Wnt3a and CHIR also produced dose-dependent reductions in the mRNA level of Scn5a (the cardiac Na(+) channel α subunit gene), as well as a 56% reduction (by Wnt3a) in the Nav 1.5 protein level. Consistent with INa reduction, action potentials in Wnt3a-treated neonatal rat ventricular myocytes had a lower upstroke amplitude (91 ± 3 vs. control 137 ± 2 mV) and decreased maximum upstroke velocity (70 ± 10 vs. control 163 ± 15 V s(-1)). In contrast, inward rectifier K(+) current and L-type Ca(2+) channels were not affected by Wnt3a treatment. Taken together, our data indicate that the Wnt/β-catenin pathway suppresses INa in postnatal cardiomyocytes and may contribute to ion channel remodelling in heart disease.

Effects of candesartan, an angiotensin II receptor type I blocker, on atrial remodeling in spontaneously hypertensive rats

Hypertension‐induced structural remodeling of the left atrium (LA) has been suggested to involve the renin–angiotensin system. This study investigated whether treatment with an angiotensin receptor blocker, candesartan, regresses atrial remodeling in spontaneously hypertensive rats (SHR). Effects of treatment with candesartan were compared to treatment with a nonspecific vasodilatator, hydralazine. Thirty to 32‐week‐old adult male SHR were either untreated (n = 15) or received one of either candesartan cilexetil (n = 9; 3 mg/kg/day) or hydralazine (n = 10; 14 mg/kg/day) via their drinking water for 14 weeks prior to experiments. Untreated age‐ and sex‐matched Wistar‐Kyoto rats (WKY; n = 13) represented a normotensive control group. Untreated SHR were hypertensive, with left ventricular hypertrophy (LVH) compared to WKY, but there were no differences in systolic pressures in excised, perfused hearts. LA from SHR were hypertrophied and showed increased fibrosis compared to those from WKY, but there was no change in connexin‐43 expression or phosphorylation. Treatment with candesartan reduced systolic tail artery pressures of conscious SHR below those of normotensive WKY and caused regression of both LVH and LA hypertrophy. Although hydralazine reduced SHR arterial pressures to those of WKY and led to regression of LA hypertrophy, it had no significant effect on LVH. Notably, LA fibrosis was unaffected by treatment with either agent. These data show that candesartan, at a dose sufficient to reduce blood pressure and LVH, did not cause regression of LA fibrosis in hypertensive rats. On the other hand, the data also suggest that normalization of arterial pressure can lead to the regression of LA hypertrophy.

Structural remodeling of the atria, involving atria enlargement and fibrosis, in hypertension increases the risk of atrial fibrillation (AF). Treatment of spontaneously hypertensive rats with the angiotensin receptor blocker, candesartan, reduced arterial pressure and myocardial hypertrophy to the level of normotensive rats but had no effect on atrial fibrosis. The resistance of hypertension‐associated atrial fibrosis to the AT1 receptor antagonist may provide insight into the basis to the ineffectiveness of drugs targeting the renin–angiotensin system in reducing incidence of AF in hypertensive patients.

Novel therapeutic targets in the management of atrial fibrillation

Atrial fibrillation (AF) is the most common cardiac arrhythmia, contributing to increased morbidity and reduced survival through its associations with stroke and heart failure. AF contributes to a four- to fivefold increase in the risk of stroke in the general population and is responsible for 10-15 % of all ischemic strokes. Diagnosis and treatment of AF require considerable health care resources. Current therapies to restore sinus rhythm in AF are suboptimal and are limited either by their pro-arrhythmic effects or by their procedure-related complications. These limitations have necessitated identification of newer therapeutic targets to expand the treatment options. There has been a considerable amount of research interest in investigating the mechanisms of initiation and propagation of AF. Despite extensive research focused on the pathogenesis of AF, a thorough understanding of various pathways mediating initiation and propagation of AF still remains limited. Research efforts focused on the identification of these pathways and molecular mediators have generated a great degree of interest for developing more targeted therapies. This review discusses the potential therapeutic targets and the results from experimental and clinical research investigating these targets.

Myocardial remodeling and bioelectric changes in tachycardia-induced heart failure in dogs

In this study, electrical and structural remodeling of ventricles was examined in tachycardia-induced heart failure (HF). We studied two groups of weight-matched adult male mongrel dogs: a sham-operated control group (n=5) and a pacing group (n=5) that underwent ventricular pacing at 230 bpm for 3 weeks. Clinical symptoms of congestive HF were observed in both groups. Their hemodynamic parameters were determined and the severity of the HF was evaluated by M-mode echocardiography. Changes in heart morphology were observed by scanning electron and light microscopy. Ventricular action potential duration (APD), as well as the 50 and 90% APD were measured in both groups. All dogs exhibited clinical symptoms of congestive HF after rapid right ventricular pacing for 3 weeks. These data indicate that rapid, right ventricular pacing produces a useful experimental model of low-output HF in dogs, characterized by biventricular pump dysfunction, biventricular cardiac dilation, and non-ischemic impairment of left ventricular contractility. Electrical and structural myocardial remodeling play an essential role in congestive HF progression, and should thus be prevented.

Rhythm control in heart failure patients with atrial fibrillation: contemporary challenges including the role of ablation

Because nonpharmacological interventions likely alter the risks and benefits associated with rhythm control, this paper reviews the role of current rhythm control strategies in atrial fibrillation. This report also focuses on the specific limitations of pharmacological interventions and the utility of percutaneous ablation in this growing population of patients with concomitant atrial fibrillation and heart failure.

Role of the MAPKs/TGF-β1/TRAF6 signaling pathway in atrial fibrosis of patients with chronic atrial fibrillation and rheumatic mitral valve disease

OBJECTIVE

Atrial remodeling is involved in atrial fibrillation (AF), and atrial fibrosis is an important marker of atrial remodeling. On the basis of our previous animal studies of the mitogen-activated protein kinases (MAPKs)/transforming growth factor β1 (TGF-β1)/tumor necrosis factor pathway in atrial fibrosis, we undertook investigation of this signaling pathway in atrial fibrosis of patients with chronic AF (CAF) and rheumatic mitral valve disease.

METHODS

Fifty-six rheumatic mitral valve disease patients were divided into CAF (course of AF >12 months) and sinus rhythm (SR) groups. Left atrial appendage tissue was collected during heart surgery, and pathological examination was done to evaluate atrial fibrosis. Protein and mRNA expression of TGF-β1, TRAF6 and connective tissue growth factor (CTGF) and protein expression of phosphorylated MAPKs and TGF-β-activated kinase 1 (TAK1) were measured.

RESULTS

Histological examination revealed that the severity of atrial fibrosis in CAF patients was significantly higher, mRNA and protein expression of TGF-β1, TRAF6 and CTGF in CAF were significantly increased, and the protein expression of phosphorylated MAPKs and TAK1 was significantly increased in CAF compared to SR patients.

CONCLUSION

The MAPKs/TGF-β1/TRAF6 signaling pathway is involved in atrial fibrosis of CAF patients, and TRAF6 may become a new target for the treatment of atrial fibrosis.

Significance of hypoxia-inducible factor-1α expression with atrial fibrosis in rats induced with isoproterenol

Atrial interstitial fibrosis plays a dual role in inducing and maintaining atrial fibrillation (AF). Hypoxia-inducible factor-1α (HIF-1α) has been reported as closely associated with renal, liver and pulmonary fibrosis diseases. However, whether HIF-1α is involved in myocardial fibrosis, and the associations between HIF-1α, transforming growth factor-β₁ (TGF-β₁) and matrix metalloproteinase-9 (MMP-9) remain unknown. Therefore, this area warrants studying for the significance of AF diagnosis and treatment. The present study investigated the expression of HIF-1α in atrial fibrosis and its possible mechanism in isoproterenol (ISO)-induced rats. The three groups of rats; control, ISO and ISO plus sirolimus [also known as rapamycin (Rapa)], were treated for 15 days and sacrificed to remove the myocardial tissues. The expression levels of HIF-1α, TGF-β₁ and MMP-9 and their associations with atrial fibrosis were examined through histomorphology and protein and mRNA levels. The protein and mRNA levels of HIF-1α, TGF-β₁ and MMP-9 in the ISO group were increased markedly (P<0.01) compared with the control group, while those in the Rapa group were clearly decreased (P<0.01) compared with the ISO group. The protein and mRNA levels of HIF-1α, TGF-β₁ and MMP-9 were positively correlated (P<0.01) with atrial fibrosis (collagen volume fraction index), as were the HIF-1α, TGF-β₁ and MMP-9 mRNA levels (P<0.01) and the mRNA levels between MMP-9 and TGF-β₁ (P<0.01). During the process of atrial fibrosis in ISO-induced rats, HIF-1α promotes the expression of TGF-β₁ and MMP-9 protein, and thus is involved in in atrial fibrosis.

Effects of the angiotensin-(1-7)/Mas/PI3K/Akt/nitric oxide axis and the possible role of atrial natriuretic peptide in an acute atrial tachycardia canine model

OBJECTIVE

To investigate the effects of the angiotensin-(1-7) signaling pathway and the possible role of atrial natriuretic peptide (ANP) on atrial electrical remodeling in canines with acute atrial tachycardia.

METHODS

Forty dogs were randomly assigned to eight groups (five dogs/group): sham, paced control, paced + angiotensin-(1-7), paced + angiotensin-(1-7) + Mas inhibitor, paced + angiotensin-(1-7) + Akt inhibitor, paced + angiotensin-(1-7) + PI3K inhibitor, paced + angiotensin-(1-7) + nitric oxide (NO) inhibitor, and paced + angiotensin-(1-7) + A-71915 (ANP receptor antagonist). Rapid atrial pacing was maintained at 600 bpm for 2 h for all groups, except the sham group, and angiotensin-(1-7) (6 μg kg(-1) h(-1)), Mas inhibitor (5.83 μg kg(-1) h(-1)), Akt inhibitor (2.14 μg kg(-1) h(-1)), PI3K inhibitor (2.86 μg kg(-1) h(-1)), NO synthase inhibitor (180 μg kg(-1)h(-1)), or A-71915 (0.30 μg kg(-1) h(-1)) were administered intravenously. Atrial effective refractory periods, inducibility, and duration of atrial fibrillation (pacing cycle lengths: 300, 250, and 200 ms), and left atrial ANP concentrations were measured.

RESULTS

After pacing, the atrial effective refractory periods at the six sites shortened with increased inducibility and duration of atrial fibrillation, which was attenuated by angiotensin-(1-7), and increased ANP concentrations, which was promoted by angiotensin-(1-7) (paced control vs. sham; P < 0.05). All inhibitors and A-71915 blocked the electrophysiological effects of angiotensin-(1-7). ANP secretion induced by angiotensin-(1-7) was also blocked by all inhibitors.

CONCLUSION

Angiotensin-(1-7) prevented acute electrical remodeling in canines with acute atrial tachycardia via the angiotensin-(1-7)/Mas/PI3K/Akt/NO signaling pathway. ANP was related to the anti-arrhythmic effects of angiotensin-(1-7).

AdipoR1/APPL1 potentiates the protective effects of globular adiponectin on angiotensin II-induced cardiac hypertrophy and fibrosis in neonatal rat atrial myocytes and fibroblasts

Atrial hypertrophy and fibrosis are essential pathological features of atrial fibrillation. Recently, adiponectin has become a protein of interest due to its beneficial effects on cardiovascular diseases. However, the molecular mechanism of atrial structural remodeling and signaling pathways evoked by adiponectin remain unclear. In the present study, we investigated the cardioprotective effect of globular adiponectin (gAcrp) on angiotensin II-induced atrial hypertrophy and fibrosis in neonatal Sprague-Dawley rat. To further investigate the molecular mechanisms underlying the preventive effect of gAcrp, transfection of cells with siRNA was used to suppress the mRNA expression of adiponectin receptor 1 (AdipoR1) and its downstream adaptor protein APPL1. Non-silencing-Cy-3 labelled siRNA was used to determine transfection efficiency using fluorescence microscopy. The expression of atrial natriuretic peptide and procollagen type1 α-1, hypertrophy marker and fibrosis one, respectively, was detected by real-time PCR. Furthermore, the expression of adenosine monophosphate-activated protein kinase (AMPK), phosphatidylinositol 3-kinase (PI3K) and Akt was detected by western blotting. In addition, nuclear p65 translocation activity was analyzed by EMSA supershift assay. Our results showed that AdipoR1 and the adaptor protein APPL1 mediated the protective effects of gAcrp. In addition, the function of adiponectin and phosphorylation of AMPK were prominently diminished by inhibition of PI3K. Furthermore, nuclear factor-κB (NF-κB) transcription was diminished by the specific inhibition of AMPK. Taken together, AMPK pivotally interacts with NF-κB and PI3K, mediating the cardioprotective effect of adiponectin, and may serve as a therapeutic target for preventing atrial hypertrophy and fibrosis. Our present study suggests that gAcrp could ameliorate AngII-induced cardiac hypertrophy and fibrosis in rat atrial cells, which is mediated by the activation of AMPK signaling pathways. APPL1 and AdipoR1 are the key factors involved in the downstream of gAcrp approach.

Renin-angiotensin system inhibitors prevent the recurrence of atrial fibrillation: a meta-analysis of randomized controlled trials

OBJECTIVE

This study was designed to assess whether angiotensin-converting enzyme inhibitors (ACEIs) and angiotensin receptor blockers (ARBs) could prevent the recurrence of atrial fibrillation (AF).

METHODS

A systemic literature search of PubMed, EMBASE, and Cochrane Controlled Trials Register till 2012 was performed to identify randomized controlled trials involving the prevention of recurrence of AF with renin-angiotensin system blockade therapy. Subgroup analysis and meta-regression were performed. Publication bias was checked through funnel plot and Egger's test.

RESULTS

Twenty-one randomized controlled trials including 13,184 patients with AF were identified. Overall, the recurrence of AF was significantly reduced in patients using ACEI/ARBs [odds ratio (OR), 0.43; 95% confidence interval (CI), 0.32-0.56; P < 0.00001], especially both in irbesartan subgroup (OR, 0.38; 95% CI, 0.21-0.68; P = 0.001) and in patients receiving antiarrhythmic drug (AAD) (OR, 0.37; 95% CI, 0.29-0.48; P < 0.00001), and there was no significant difference between ACEIs and ARBs (ACEIs: OR, 0.42; 95% CI, 0.31-0.57 and ARBs: OR, 0.42; 95% CI, 0.31-0.57). Moreover, it was found that the benefits of ACEI/ARBs revealed positive correlation to systolic blood pressure (regression coefficient: -0.0700257, P = 0.000) in no-AAD users.

CONCLUSIONS

ACEI/ARBs are effective on the secondary prevention of AF, especially in patients receiving AAD and suffering from hypertension.

Angiotensin-(1-7) prevent atrial tachycardia induced sodium channel remodeling

BACKGROUND

Activation of the renin-angiotensin system plays an important role in atrial electrical remodeling; angiotensin-(1-7) (Ang-(1-7)) counterbalances the actions of angiotensin II. The aim of this study was to determine the effects of Ang-(1-7) on cardiac sodium current (INa ) in a canine model of atrial tachycardia.

METHODS

Eighteen dogs were randomly assigned to sham, pacing, or pacing + Ang-(1-7) groups (n = 6 in each group). Rapid atrial pacing (500 beats/min) was maintained for 2 weeks, while the dogs in the sham group were not paced. Ang-(1-7) (6 μg/kg/h) was administered intravenously during pacing. Whole-cell patch clamp techniques were utilized to record INa from canine atrial myocytes. Reverse transcription-polymerase chain reaction was used to assess possible underlying changes in cardiac Na(+) channels (Nav1.5).

RESULTS

Our results showed that INa density and expression of the Nav1.5 mRNA significantly decreased following pacing (P < 0.05 vs sham); however, the half-activation voltage (V1/2act ) and half-inactivation voltage (V1/2inact ) of INa were not significantly altered (P > 0.05 vs sham). Ang-(1-7) treatment significantly increased INa densities and hyperpolarized V1/2act without concomitant changes in V1/2inact but have no effect on the expression of the Nav1.5 gene.

CONCLUSIONS

Ang-(1-7) significantly increased INa densities, which contributed to improving intraatrial conduction and decreasing the likelihood of atrial fibrillation maintenance.

Stroke prevention in atrial fibrillation in heart failure

Heart failure and atrial fibrillation are major problems of modern cardiology with important clinical, prognostic, and socioeconomic implications. The risks are high morbidity, impaired quality of life, poor outcome, and increased risk of stroke. Oral anticoagulation with vitamin K antagonists or novel licensed medicines should be considered unless contraindicated. Possible benefits of sinus rhythm maintenance are not entirely clear and need to be explored further. Relatively scarce data are available on stroke prevention in atrial fibrillation in heart failure with preserved ejection fraction; this requires further research.

Mkk4 is a negative regulator of the transforming growth factor beta 1 signaling associated with atrial remodeling and arrhythmogenesis with age

BACKGROUND

Atrial fibrillation (AF), often associated with structural, fibrotic change in cardiac tissues involving regulatory signaling mediators, becomes increasingly common with age. In the present study, we explored the role of mitogen-activated protein kinase kinase 4 (Mkk4), a critical component of the stress-activated mitogen-activated protein kinase family, in age-associated AF.

METHODS AND RESULTS

We developed a novel mouse model with a selective inactivation of atrial cardiomyocyte Mkk4 (Mkk4(ACKO)). We characterized and compared electrophysiological, histological, and molecular features of young (3- to 4-month), adult (6-month), and old (1-year) Mkk4(ACKO) mice with age-matched control littermates (Mkk4(F/F)). Aging Mkk4(ACKO) mice were more susceptible to atrial tachyarrhythmias than the corresponding Mkk4(F/F) mice, showing characteristic slow and dispersed atrial conduction, for which modeling studies demonstrated potential arrhythmic effects. These differences paralleled increased interstitial fibrosis, upregulated transforming growth factor beta 1 (TGF-β1) signaling and dysregulation of matrix metalloproteinases in Mkk4(ACKO), compared to Mkk4(F/F), atria. Mkk4 inactivation increased the sensitivity of cultured cardiomyocytes to angiotensin II-induced activation of TGF-β1 signaling. This, in turn, enhanced expression of profibrotic molecules in cultured cardiac fibroblasts, suggesting cross-talk between these two cell types in profibrotic signaling. Finally, human atrial tissues in AF showed a Mkk4 downregulation associated with increased production of profibrotic molecules, compared to findings in tissue from control subjects in sinus rhythm.

CONCLUSIONS

These findings together demonstrate, for the first time, that Mkk4 is a negative regulator of the TGF-β1 signaling associated with atrial remodeling and arrhythmogenesis with age, establishing Mkk4 as a new potential therapeutic target for treating AF.

Epicardial adipose tissue and atrial fibrillation

Atrial fibrillation (AF) is the most frequent cardiac arrhythmia in clinical practice. AF is often associated with profound functional and structural alterations of the atrial myocardium that compose its substrate. Recently, a relationship between the thickness of epicardial adipose tissue (EAT) and the incidence and severity of AF has been reported. Adipose tissue is a biologically active organ regulating the metabolism of neighbouring organs. It is also a major source of cytokines. In the heart, EAT is contiguous with the myocardium without fascia boundaries resulting in paracrine effects through the release of adipokines. Indeed, Activin A, which is produced in abundance by EAT during heart failure or diabetes, shows a marked fibrotic effect on the atrial myocardium. The infiltration of adipocytes into the atrial myocardium could also disorganize the depolarization wave front favouring micro re-entry circuits and local conduction block. Finally, EAT contains progenitor cells in abundance and therefore could be a source of myofibroblasts producing extracellular matrix. The study on the role played by adipose tissue in the pathogenesis of AF is just starting and is highly likely to uncover new biomarkers and therapeutic targets for AF.

[Upstream therapy for atrial fibrillation]

In recent years a tremendous amount has been learned about the pathophysiology of atrial fibrillation (AF) which induces electrophysiological changes in the right and left atrium. Besides calcium-dependent tissue changes which are induced by activation of proteases and phosphatases, such as calpain and calcineurin, concomitant cardiac diseases activate the atrial angiotensin II system. Experiments have shown positive effects of statins in AF models. In contrast, clinical studies have provided heterogeneous results. Of note, several studies have shown that therapy with angiotensin II receptor blockers or statins does not influence the recurrence of AF.

Atrial fibrillation and congestive heart failure

Heart failure (HF) and atrial fibrillation (AF) commonly coexist and adversely affect mortality when found together. AF begets HF and HF begets AF. Rhythm restoration with antiarrhythmic drugs failed to show a mortality benefit but can be effective in improving symptoms. Nonpharmacologic treatment of AF may be of value in the HF population.