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

20-Hydroxyeicosatetraenoic acid induces apoptosis in neonatal rat cardiomyocytes through mitochondrial-dependent pathways

OBJECTIVE

20-Hydroxyeicosatetraenoic acid (20-HETE), a [omega]-hydroxylation product of arachidonic acid catalyzed by cytochrome P450 4A, may play a role in the cardiovascular system. It is well known that cytochrome P450 [omega]-hydroxylase inhibitors markedly reduced the cardiac ischemia reperfusion injury. However, the direct effect of 20-HETE on cardiomyocytes is still poorly investigated. Here, we studied the effect of 20-HETE on cardiomyocyte apoptosis and the apoptosis-associated signaling pathways.

METHODS AND RESULTS

The cardiomyocyte apoptosis was measured by fluorescein isothiocyanate conjugated annexin V/propidium iodide double staining cytometry, indicating that the percentage of early apoptotic cells increased from 15.6% +/- 2.6% to 25.5% +/- 2.5% in control and 20-HETE-treated cells, respectively. The mitochondrial membrane potential ([DELTA][PSI]m) was measured by detecting the ratio of JC-1 green/red emission intensity. A significant decrease in the ratio was observed after treatment with 20-HETE for 24 hours in comparison with control group, suggesting the disruptive effect of 20-HETE on mitochondrial [DELTA][PSI]m. In addition, 20-HETE stimulated caspase-3 activity and Bax mRNA expression in cardiomyocytes. In contrast, the Bcl-2 mRNA levels were significantly decreased by 20-HETE treatment.

CONCLUSION

These results demonstrate that 20-HETE induces cardiomyocyte apoptosis by activation of several intrinsic apoptotic pathways. The 20-HETE-induced apoptosis could contribute to the cytochrome P450 [omega]-hydroxylase-dependent cardiac injure during cardiac ischemia-reperfusion.

Upstream therapies for management of atrial fibrillation: review of clinical evidence and implications for European Society of Cardiology guidelines. Part II: secondary prevention

Fundamental research into molecular mechanisms of atrial fibrillation (AF) and improved understanding of processes involved in the initiation and maintenance of AF have transformed the traditional approach to its management by targeting only the electrical aspects, usually with antiarrhythmic drugs and, recently, by ablation. The antiarrhythmic potential of upstream therapies, such as angiotensin-converting enzyme inhibitors, angiotensin receptor blockers (ARBs), statins, and n-3 (ω-3) polyunsaturated fatty acids, extends beyond the benefit of treating underlying heart disease to modifying the atrial substrate and intervening in specific mechanisms of AF. The key target is structural remodelling of the atria, particularly inflammation and fibrosis, although there is evidence to suggest the direct involvement at the ion channel level. Positive clinical reports supported by robust experimental data have suggested that upstream therapies can be valuable strategies for primary prevention of AF in selected patients and have resulted in several class IIA recommendations in the new European guidelines on AF. However, these results have not been consistently replicated in the secondary prevention setting, and several recent randomized controlled studies failed to demonstrate any effect of upstream therapies on AF burden or on major cardiovascular outcomes. Part II of the review summarizes the evidence base for the use of upstream therapies for secondary prevention of AF.

Recent clinical and experimental advances in atrial fibrillation

Atrial fibrillation (AF) is the most common arrhythmia in clinical settings (Fuster et al., 2001), and it is often associated with congestive heart diseases (Issac et al., 2007). Many studies in both laboratory and clinical settings have sought to analyze the mechanisms of AF, develop treatments based on these mechanisms, and examine atrial remodeling in chronic AF. The aim of this paper is to analyze recent findings regarding the atrial remodeling that occurs in AF. In particular, we will describe the electrical and structural changes that involve atrial myocytes and the extracellular matrix. We will also describe the general classification and basic pathophysiology of AF and its surgical treatments.

Mechanisms of termination and prevention of atrial fibrillation by drug therapy

Atrial fibrillation (AF) is a disorder of the rhythm of electrical activation of the cardiac atria. It is the most common cardiac arrhythmia, has multiple aetiologies, and increases the risk of death from stroke. Pharmacological therapy is the mainstay of treatment for AF, but currently available anti-arrhythmic drugs have limited efficacy and safety. An improved understanding of how anti-arrhythmic drugs affect the electrophysiological mechanisms of AF initiation and maintenance, in the setting of the different cardiac diseases that predispose to AF, is therefore required. A variety of animal models of AF has been developed, to represent and control the pathophysiological causes and risk factors of AF, and to permit the measurement of detailed and invasive parameters relating to the associated electrophysiological mechanisms of AF. The purpose of this review is to examine, consolidate and compare available relevant data on in-vivo electrophysiological mechanisms of AF suppression by currently approved and investigational anti-arrhythmic drugs in such models. These include the Vaughan Williams class I-IV drugs, namely Na(+) channel blockers, β-adrenoceptor antagonists, action potential prolonging drugs, and Ca(2+) channel blockers; the "upstream therapies", e.g., angiotensin converting enzyme inhibitors, statins and fish oils; and a variety of investigational drugs such as "atrial-selective" multiple ion channel blockers, gap junction-enhancers, and intracellular Ca(2+)-handling modulators. It is hoped that this will help to clarify the main electrophysiological mechanisms of action of different and related drug types in different disease settings, and the likely clinical significance and potential future exploitation of such mechanisms.

Angiotensin-converting enzyme inhibitors and angiotensin receptor blockers decrease the incidence of atrial fibrillation: a meta-analysis

BACKGROUND

There is not a general agreement regarding antiarrhythmic effects on atrial fibrillation (AF) of angiotensin-converting enzyme inhibitors (ACEIs) and angiotensin receptor blockers (ARBs). This study was to assess whether ACEIs and ARBs could decrease the incidence of AF.

MATERIALS AND METHODS

Medline, Embase and Cochrane Library databases were searched for trials reported from 1950 to May 2009. Search terms included 'randomized controlled trial (RCT), controlled clinical trials, random allocation' and medical subject headings that included all spellings of ACEIs and ARBs agents, 'atrial fibrillation' and 'atrial flutter'. Randomized, controlled human trials of ACEIs or ARBs reporting AF were included. Data were extracted independently by two reviewers using a predefined data extraction sheet, including study quality indicators. Meta-analysis and subgroup analyses were carried out with a random effects model.

RESULTS

Twenty-one trials including 91,381 patients and 5730 AF events were identified. Overall, ACEIs/ARBs reduced the relative risk (c) of AF by 25%. In primary and secondary prevention, ACEIs/ARBs decreased the incidence of AF by 24% and 27%, respectively. Patients with hypertension (RR: 0·71, 95%CI: 0·54-0·92), patients with chronic heart failure (RR: 0·58, 95%CI: 0·39-0·87) and those with AF (RR: 0·71, 95%CI: 0·52-0·96) benefited from ACEIs/ARBs treatment.

CONCLUSIONS

ACEIs/ARBs are effective for primary prevention and secondary prevention of AF. They decrease the incidence of AF especially in patients with hypertension, patients with chronic heart failure and those with AF.

Chronic kidney disease is associated with the incidence of atrial fibrillation: the Atherosclerosis Risk in Communities (ARIC) study

BACKGROUND

Chronic kidney disease is associated with the incidence of cardiovascular disease. Chronic kidney disease may also increase the risk of atrial fibrillation (AF), but existing studies have reported inconsistent results.

METHODS AND RESULTS

We estimated cystatin C-based glomerular filtration rate (eGFR(cys)) and measured urinary albumin-to-creatinine ratio (ACR) in 10 328 men and women free of AF from the Atherosclerosis Risk in Communities (ARIC) Study in 1996 to 1998. Incidence of AF was ascertained through the end of 2007. During a median follow-up of 10.1 years, we identified 788 incident AF cases. Compared with individuals with eGFR(cys) ≥90 mL · min(-1) · 1.73 m(-2), multivariable hazard ratios and 95% confidence intervals (CIs) of AF were 1.3 (95% CI, 1.1 to 1.6), 1.6 (95% CI, 1.3 to 2.1), and 3.2 (95% CI, 2.0 to 5.0; P for trend <0.0001) in those with eGFR(cys) of 60 to 89, 30 to 59, and 15 to 29 mL · min(-1) · 1.73 m(-2), respectively. Similarly, the presence of macroalbuminuria (ACR ≥300 mg/g; hazard ratio, 3.2; 95% CI, 2.3 to 4.5) and microalbuminuria (ACR, 30 to 299 mg/g; hazard ratio, 2.0; 95% CI, 1.6 to 2.4) was associated with higher AF risk compared with those with ACR <30 mg/g. Risk of AF was particularly elevated in those with both low eGFR(cys) and macroalbuminuria (hazard ratio, 13.1; 95% CI, 6.0 to 28.6, comparing individuals with ACR ≥300 mg/g and eGFR(cys) of 15 to 29 mL · min(-1) · 1.73 m(-2) and those with ACR <30 mg/g and eGFR(cys) ≥90 mL · min(-1) · 1.73 m(-2)).

CONCLUSION

In this large population-based study, reduced kidney function and presence of albuminuria were strongly associated with the incidence of AF independently of other risk factors.

Upstream therapies for management of atrial fibrillation: review of clinical evidence and implications for European Society of Cardiology guidelines. Part I: primary prevention

Atrial fibrillation (AF) is associated with significant morbidity and mortality. It is also a progressive disease secondary to continuous structural remodelling of the atria due to AF itself, to changes associated with ageing, and to deterioration of underlying heart disease. Current management aims at preventing the recurrence of AF and its consequences (secondary prevention) and includes risk assessment and prevention of stroke, ventricular rate control, and rhythm control therapies including antiarrhythmic drugs and catheter or surgical ablation. The concept of primary prevention of AF with interventions targeting the development of substrate and modifying risk factors for AF has emerged as a result of recent experiments that suggested novel targets for mechanism-based therapies. Upstream therapy refers to the use of non-antiarrhythmic drugs that modify the atrial substrate- or target-specific mechanisms of AF to prevent the occurrence or recurrence of the arrhythmia. Such agents include angiotensin-converting enzyme inhibitors (ACEIs), angiotensin receptor blockers (ARBs), statins, n-3 (ω-3) polyunsaturated fatty acids, and possibly corticosteroids. Animal experiments have compellingly demonstrated the protective effect of these agents against electrical and structural atrial remodelling in association with AF. The key targets of upstream therapy are structural changes in the atria, such as fibrosis, hypertrophy, inflammation, and oxidative stress, but direct and indirect effects on atrial ion channels, gap junctions, and calcium handling are also applied. Although there have been no formal randomized controlled studies (RCTs) in the primary prevention setting, retrospective analyses and reports from the studies in which AF was a pre-specified secondary endpoint have shown a sustained reduction in new-onset AF with ACEIs and ARBs in patients with significant underlying heart disease (e.g. left ventricular dysfunction and hypertrophy), and in the incidence of AF after cardiac surgery in patients treated with statins. In the secondary prevention setting, the results with upstream therapies are significantly less encouraging. Although the results of hypothesis-generating small clinical studies or retrospective analyses in selected patient categories have been positive, larger prospective RCTs have yielded controversial, mostly negative, results. Notably, the controversy exists on whether upstream therapy may impact mortality and major non-fatal cardiovascular events in patients with AF. This has been addressed in retrospective analyses and large prospective RCTs, but the results remain inconclusive pending further reports. This review provides a contemporary evidence-based insight into the role of upstream therapies in primary (Part I) and secondary (Part II) prevention of AF.

Atrial remodeling in an ovine model of anthracycline-induced nonischemic cardiomyopathy: remodeling of the same sort

INTRODUCTION

All preclinical studies of atrial remodeling in heart failure (HF) have been confined to a single model of rapid ventricular pacing. To evaluate whether the atrial changes were specific to the model or represented an end result of HF, this study aimed to characterize atrial remodeling in an ovine model of doxorubicin-induced cardiomyopathy.

METHODS AND RESULTS

Fourteen sheep, 7 with cardiomyopathy induced by repeated intracoronary doxorubicin infusions and 7 controls, were studied. The development of HF was monitored by cardiac imaging and hemodynamic parameters. Open chest electrophysiological study was performed using custom-made 128-electrode epicardial plaque assessing effective refractory period (ERP) and conduction velocity. Atrial tissues were harvested for structural analysis. The HF group had demonstrable moderate global HF (left ventricular ejection fraction [LVEF]: 37.1 vs 46.4%; P = 0.003) and showed the following compared to controls: left atrial dilatation (P = 0.02) and dysfunction (P = 0.005); longer P-wave duration (P < 0.05); higher ERP at all cycle lengths (P ≤ 0.002) and locations (P < 0.001); slower conduction velocity (P < 0.001); increased conduction heterogeneity index (P < 0.001); increased atrial fibrosis (right atrial [RA]: 5.9 ± 2.6 vs 2.8 ± 0.9%; P < 0.0001, left atrial [LA]: 3.7 ± 2.2 vs 2.4 ± 1.1%; P = 0.002), and longer induced atrial fibrillation (AF) episodes (16 ± 22 vs 2 ± 3 seconds; P = 0.04).

CONCLUSION

In this model of HF, there was significant atrial remodeling characterized by atrial enlargement/dysfunction, increased fibrosis, slowed/heterogeneous conduction, and increased refractoriness associated with more sustained AF. These findings appear the "same sort" to previous models of HF implicating a final common substrate leading to the development of AF in HF.

Reviewing the future of renin-angiotensin system blockade: the role of angiotensin-converting enzyme inhibitors and angiotensin receptor blockers in the prevention of atrial fibrillation

Atrial fibrillation (AF) is the most common sustained arrhythmia encountered in clinical practice, affecting approximately 250,000 Canadians and accounting for more than 120,000 hospitalizations each year. Atrial remodelling, which is at least partially induced by activation of the renin-angiotensin system (RAS), can be reversed by RAS blockade using angiotensin-converting enzyme inhibitors or angiotensin receptor blockers. While RAS antagonists are not considered to be conventional anti-arrhythmic agents, several studies have shown that they may reduce the incidence of AF in patients with heart failure, after myocardial infarction with reduced ejection fraction, and in hypertensive patients. Angiotensin-converting enzyme inhibitors and angiotensin receptor blockers have also been used in association with amiodarone to facilitate sinus rhythm maintenance after electrical cardioversion. Whether RAS blockade prevents recurrent AF in patients at high cardiovascular risk remains unknown.

Statin treatment for patients with paroxysmal atrial fibrillation

Recent clinical evidence and animal experiments support the belief that statins have beneficial effects on cardiovascular outcomes and prevention of atrial fibrillation (AF). We investigated whether the use of statins reduces the mortality, morbidity, and recurrence rate of AF in patients with paroxysmal AF. A post hoc analysis of the Japanese Rhythm Management Trial for Atrial Fibrillation (J-RHYTHM) study was conducted.Of the 823 patients with paroxysmal AF in the J-RHYTHM study, 101 (12.3%) were receiving a statin at baseline. Patients taking statins were older and more likely to have hypertension, dyslipidemia, coronary artery disease, and ischemic stroke compared to patients not taking statins. During a mean follow-up period of 19.3 months, 40 patients (5.5%) reached the primary endpoint (a composite of all-cause death, stroke, systemic embolism, major bleeding, and hospitalization for heart failure) and 140 patients (19.4%) experienced a recurrence of AF. Multivariate Cox proportional-hazard regression analysis revealed statin use was not associated with improved mortality and morbidity (hazard ratio [HR] 0.409, 95% confidence interval [CI] 0.113-1.482), or a decreased risk of AF recurrence (HR 0.662, 95% CI 0.299-1.466).This analysis provides evidence that statin use did not affect clinical outcomes in patients with paroxysmal AF and emphasizes the need for randomized clinical trials defining more clearly the role of statins in treating AF.

Eicosapentaenoic acid prevents atrial fibrillation associated with heart failure in a rabbit model

Atrial fibrillation (AF) is associated with morbidity and mortality of heart failure. Eicosapentaenoic acid (EPA), which is contained in fish oil, was shown to reduce the risk of cardiovascular diseases. We investigated the effects of EPA on AF associated with heart failure in a rabbit model. Rabbits were subjected to ventricular tachypacing (VTP) for 4 wk with or without EPA treatment. Continuous VTP induced heart failure status in these rabbits. The duration of AF (DAF) induced by burst pacing was analyzed by electrophysiological studies. VTP resulted in increased DAF following burst pacing. EPA treatment attenuated increased DAF. Atrial fibrosis increased in response to VTP, accompanied by extracellular signal-regulated kinase (ERK) phosphorylation and transforming growth factor-β1 (TGF-β1) expression in the atrium. Treatment with EPA attenuated atrial fibrosis, ERK phosphorylation, and TGF-β1 expression in response to VTP. EPA treatment increased adiponectin as an anti-inflammatory adipokine and decreased tumor necrosis factor-α as a proinflammatory adipokine in the atrium and epicardial adipose tissues. EPA attenuated VTP-induced AF promotion and atrial remodeling, which was accompanied by modulating the profiles of adipokine production from epicardial adipose tissue. EPA may be useful for prevention and treatment of AF associated with heart failure.

Advances in cardiology: clinical trial update

Multiple key cardiology trials have been presented or published over recent months, several with the potential to change clinical practice. In this article, we summarize and place in clinical context new trial findings regarding anticoagulation in the cardiac catheterization laboratory (enoxaparin, fondaparinux and unfractionated heparin), the implications of genetic polymorphisms and functional testing for antiplatelet therapy (clopidogrel and ticagrelor), new oral anticoagulants for use in atrial fibrillation (apixiban and rivaroxaban), optimal pacing strategies and pharmacological agents in heart failure (ivabradine, eplerenone, cardiac resynchronization therapy, telemonitoring and intracoronary bone marrow stem cell infusion). Clinical trials in percutaneous structural intervention (transcatheter aortic valve implantation, MONARC™ mitral annular implant, STARFlex® patent foramen ovale device) and advanced percutaneous coronary intervention (everolimus-eluting stents, biodegradable polymer/polymer-free technologies and contemporary use of intravascular ultrasound) are also discussed.

From guidelines to bench: implications of unresolved clinical issues for basic investigations of atrial fibrillation mechanisms

The 2011 Canadian Cardiovascular Society Atrial Fibrillation (AF) Guidelines provide detailed recommendations for AF management, as well as extensive background information. The Guidelines documents highlight many important unresolved questions and areas of clinical need that could benefit from basic research investigations. This article discusses basic research priorities emanating from the Guidelines reflections. Topics addressed include forms of AF and their interrelations, limitations of the presently available experimental models of AF, genetic factors, determinants of drug efficacy for pharmacologic cardioversion, mechanisms of AF-related thromboembolism, ventricular rate control, drugs for rhythm control, upstream therapy, mechanisms by which catheter ablation controls AF, mechanisms of postoperative AF, and the possibility of novel patient-based surgical procedures. A guidelines-to-bench approach to research may allow for the development of important, clinically relevant new knowledge with impacts on patient management and future AF guidelines.

Polymorphisms of the angiotensin-converting enzyme and angiotensinogen gene in patients with atrial fibrillation

Activation of the renin-angiotensin system (RAS) is associated with atrial fibrillation (AF). The aim of this study was to investigate the relation between AF and polymorphisms in RAS. One hundred and fifty patients with AF, 100 patients with no documented episode of AF and 100 healthy subjects were consecutively recruited into the study. The angiotensin-converting enzyme (ACE) insertion/deletion (I/D) polymorphism, and the M235T, A-20C, and G-6A polymorphisms of the angiotensinogen gene were genotyped. Patients with AF had significantly lower frequency of II genotype of ACE I/D and higher frequency of angiotensinogen M235T polymorphism T allele and TT genotype and G-6A polymorphism G allele and GG genotype compared with the controls. AF patients had significantly larger left atrium, higher left ventricular mass index (LVMI) and higher frequency of significant valvular pathology. ACE I/D polymorphism II genotype, angiotensinogen M235T polymorphism TT genotype and G allele and GG genotype of angiotensinogen G-6A polymorphism were still independently associated with AF when adjusted for left atrium, LVMI and presence of significant valvular pathology. Genetic predisposition might be underlying the prevalence of acquired AF. Patients with a specific genetic variation in the RAS genes may be more liable to develop AF.

Association between angiotensin-converting enzyme insertion/deletion gene polymorphism and atrial fibrillation: a meta-analysis

AIMS

Recent observations have raised concerns regarding the activation of the renin-angiotensin system and the development of atrial fibrillation (AF). Some initial studies indicated an association between an angiotensin-converting enzyme insertion/deletion (ACE I/D) polymorphism and AF, however, the results have been inconsistent. Our aim was to perform a meta-analysis of relevant studies to assess the validity of this association.

METHODS AND RESULTS

PubMed, Cochrane clinical trials database, and EMBASE were searched through July 2009, and a manual search was also performed. Of the 68 initially identified studies, 18 case-control studies with 7577 patients were finally analysed. No statistically significant associations were found between the ACE I/D polymorphism and AF risk in the genetic additive model and dominant model, whereas a significant association was observed in the recessive model. A significant heterogeneity between individual studies was evident in all three models. Subgroup analyses showed a strong association between the ACE I/D polymorphism and hypertensive AF without significant heterogeneity.

CONCLUSION

Our meta-analysis suggests that there is insufficient evidence to demonstrate an association between ACE I/D polymorphism and AF risk. However, there seems to be a significant association between ACE I/D gene polymorphic variation and AF in patients with hypertension. Additional studies are warranted to further explore this association in ethnically diverse populations and varied cardiovascular substrates.

Pathophysiological mechanisms of atrial fibrillation: a translational appraisal

Atrial fibrillation (AF) is an arrhythmia that can occur as the result of numerous different pathophysiological processes in the atria. Some aspects of the morphological and electrophysiological alterations promoting AF have been studied extensively in animal models. Atrial tachycardia or AF itself shortens atrial refractoriness and causes loss of atrial contractility. Aging, neurohumoral activation, and chronic atrial stretch due to structural heart disease activate a variety of signaling pathways leading to histological changes in the atria including myocyte hypertrophy, fibroblast proliferation, and complex alterations of the extracellular matrix including tissue fibrosis. These changes in electrical, contractile, and structural properties of the atria have been called "atrial remodeling." The resulting electrophysiological substrate is characterized by shortening of atrial refractoriness and reentrant wavelength or by local conduction heterogeneities caused by disruption of electrical interconnections between muscle bundles. Under these conditions, ectopic activity originating from the pulmonary veins or other sites is more likely to occur and to trigger longer episodes of AF. Many of these alterations also occur in patients with or at risk for AF, although the direct demonstration of these mechanisms is sometimes challenging. The diversity of etiological factors and electrophysiological mechanisms promoting AF in humans hampers the development of more effective therapy of AF. This review aims to give a translational overview on the biological basis of atrial remodeling and the proarrhythmic mechanisms involved in the fibrillation process. We pay attention to translation of pathophysiological insights gained from in vitro experiments and animal models to patients. Also, suggestions for future research objectives and therapeutical implications are discussed.

Update on the association of inflammation and atrial fibrillation

Atrial fibrillation (AF) is a common arrhythmia and is associated with significant morbidity and mortality. The pathogenesis of AF remains incompletely understood and management remains a difficult task. Over the past decade there has been accumulating evidence implicating inflammation in the pathogenesis of AF. Inflammation appears to play a significant role in the initiation and perpetuation of AF as well as the prothrombotic state associated with AF. Inflammatory biomarkers (C-reactive protein and interleukin-6) have been shown to be associated with the future development, recurrence and burden of AF, and the likelihood of successful cardioversion. Therapies directed at attenuating the inflammatory burden appear promising. Animal and clinical studies have evaluated statins, angiotensin-converting enzyme inhibitors/angiotensin-II receptor blockers, and corticosteroids for the treatment or prevention of AF. The purpose of this review is to provide current evidence on the relationship between inflammation and AF and potential therapies available to modulate the inflammatory state in AF.

Association of left atrial fibrosis detected by delayed-enhancement magnetic resonance imaging and the risk of stroke in patients with atrial fibrillation

OBJECTIVES

This study tried to determine the association between left atrial (LA) fibrosis, detected using delayed-enhanced magnetic resonance imaging (DE-MRI), and the CHADS(2) score (point system based on individual clinical risk factors including congestive heart failure, hypertension, age, diabetes, and prior stroke) variables, specifically stroke.

BACKGROUND

In patients with atrial fibrillation (AF), conventional markers for the risk of stroke base their higher predictive effect on clinical features, particularly previous stroke history, and not individual LA pathophysiological properties. We aimed to determine the association between LA fibrosis, detected using DE-MRI, and the CHADS(2) score variables, specifically stroke.

METHODS

Patients with AF who presented to the AF clinic and received a DE-MRI of the LA were evaluated. Their risk factor profiles, including a CHADS(2) score, were catalogued. The degree of LA fibrosis was determined as a percentage of the LA area. Any history of previous strokes, warfarin use, or cerebrovascular disease was recorded.

RESULTS

A total of 387 patients, having a mean age of 65 ± 12 years, 36.8% female, were included in this study. A history of previous stroke was present in 36 (9.3%) patients. Those patients with previous strokes had a significantly higher percentage of LA fibrosis (24.4 ± 12.4% vs. 16.2 ± 9.9%, p < 0.01). A larger amount of LA fibrosis was also seen in those patients with a higher CHADS(2) score (≥ 2: 18.7 ± 11.4 vs. <2: 14.7 ± 9.2, p < 0.01). A logistic regression analysis of all variables except strokes (CHAD score) demonstrated that LA fibrosis independently predicted cerebrovascular events (p = 0.002) and significantly increased the predictive performance of the score (area under the curve = 0.77).

CONCLUSIONS

Our preliminary, multicenter results suggest DE-MRI-based detection of LA fibrosis is independently associated with prior history of strokes. We propose that the amount of DE-MRI-determined LA fibrosis could represent a marker for stroke and a possible therapeutic target with potential applicability for clinical treatment for patients with AF.

Focus on renin-angiotensin system modulation and atrial fibrillation control after GISSI AF results

Atrial fibrillation is the most frequently encountered arrhythmia in clinical practice. Given that atrial fibrillation is steadily increasing and that the medium to long-term efficacy of antiarrhythmic drugs has proved poor, it is essential to seek new therapies to prevent its onset and to effectively control recurrences. The study of nonantiarrhythmic drugs that act on the atrial remodeling that constitutes the substrate of the arrhythmia is a new and very interesting field of research. In this regard, several molecules that interact with the renin-angiotensin system at the level of the enzymatic or receptor cascade have been investigated in the past 10 years; some results have been very promising, whereas others have been extremely disappointing. In particular, the publication in 2008 of the results of GISSI AF, a rigorously designed Italian prospective study conducted on a large number of patients, revealed no statistically significant differences between the active drug and a placebo in preventing arrhythmia recurrences. In this study, we reassess the rationale behind the use of this class of drugs for 'antiarrhythmic' purposes, re-examine the most significant results reported in the clinical literature since 1999 and discuss the results of the GISSI AF study in this light.

Inhibition of the renin-angiotensin system for prevention of atrial fibrillation

Atrial fibrillation (AF) is a source of considerable morbidity and mortality. There has been compelling evidence supporting the role of renin-angiotensin system (RAS) in the genesis and perpetuation of AF through atrial remodeling, and experimental studies have validated the utilization of RAS inhibition for AF prevention. This article reviews clinical trials on the use of angiotensin-converting enzyme inhibitors (ACEIs) and angiotensin receptor blockers (ARBs) for the prevention of AF. Results have been variable, depending on the clinical background of treated patients. ACEIs and ARBs appear beneficial for primary prevention of AF in patients with heart failure, whereas they are not equally effective in hypertensive patients with normal left ventricular function. Furthermore, the use of ACEIs or ARBs for secondary prevention of AF has been found beneficial only after electrical cardioversion. Additional data are needed to establish the potential clinical role of renin-angiotensin inhibition for prevention of AF.

Prevention of recurrent atrial fibrillation with angiotensin-converting enzyme inhibitors or angiotensin receptor blockers: a systematic review and meta-analysis of randomized trials

BACKGROUND

Controversy persists regarding the efficacy of angiotensin-converting enzyme inhibitors (ACEIs) and angiotensin receptor blockers (ARBs) in the prevention of recurrent atrial fibrillation (AF). We performed a meta-analysis of randomized controlled trials (RCTs), not designed a priori to test this hypothesis, to explore whether ACEs and ARBs reduce recurrent AF.

METHODS

We performed a systematic literature search for RCTs using ACEIs or ARBs and providing data on the outcome of recurrent AF. Statistical heterogeneity across the trials was tested using the Cochran Q statistic and I(2) was computed to quantify heterogeneity. A 2-sided α error of less than .05 was considered statistically significant (P < .05).

RESULTS

The analysis was based on 8 RCTs including 2323 patients. The Mantel-Haenszel random-effect model was used to calculate relative risk (RR) for studies using ACEIs or ARBs, and for studies using ARBs. The fixed-effect model was used to calculate RR for studies using ACEIs. Meta-analysis of the studies revealed that ACEIs or ARBs significantly reduced the incidence of recurrent AF (RR, 0.611; 95% CI, 0.441-0.847; P = .003). The RR for recurrent AF was 0.643 (95% CI, 0.439-0.941; P = .023) for studies using ARBs and 0.54 (95% CI, 0.377-0.80; P = .002) for studies using ACEIs.

CONCLUSION

In this meta-analysis of RCTs not designed a priori to test the hypothesis, ACEs and ARBs were associated with a significant reduction in recurrent AF. Large-scale randomized trials designed a priori to test the hypothesis are necessary to complete the totality of evidence.

Advanced left-atrial fibrosis is associated with unsuccessful maze operation for valvular atrial fibrillation

OBJECTIVE

Atrial dilatation and fibrosis are considered to be important factors in the occurrence and maintenance of atrial fibrillation (AF). However, the relationship between those structural remodeling and postoperative sinus conversions after a maze operation has been rarely studied. The purpose of this study was to determine whether pathological evaluation of atrial tissues was useful for predicting an unsuccessful maze operation in patients with valvular AF.

METHODS

Between March 2006 and June 2007, left-atrial tissues in the posterior wall and right-atrial appendage were obtained from 47 consecutive patients (24 patients with chronic AF, and 23 with sinus rhythm) undergoing mitral valve surgery (MVS). A concomitant maze operation was performed for all patients with chronic AF. Atrial cell diameters were measured using hematoxylin and eosin staining, and quantitative assessment of atrial fibrosis was performed with Masson trichrome staining using an image analyzer (Image Processor for Analytical Pathology, Sumika Technoservice Co., Hyogo, Japan).

RESULTS

Successful MVS was performed for all patients and there were no complications associated with tissue sampling. Patients with chronic AF had more advanced histological features in both atria as compared with those with sinus rhythm. Sixteen of 24 patients, who underwent a maze operation, had successfully restored sinus rhythm (successful maze group), while that in the remaining eight was not restored (unsuccessful maze group). Patients in the unsuccessful maze group had a larger left-atrial dimension and cardiothoracic ratio as compared with those in the successful group, whereas the duration of AF was not significantly different. Patients in the unsuccessful maze group also had greater hypertrophy of cardiomyocytes and more extensive intercellular fibrosis in the left atrium, while there were no differences for right-atrial pathological features between the groups. Multivariate logistic analysis confirmed that a larger amount of left-atrial fibrosis (>15%) was significantly associated with an unsuccessful maze operation.

CONCLUSIONS

The present results suggested that advanced fibrosis in the left atrium, but not in the right atrium, might be significantly associated with an unsuccessful maze operation in patients with valvular AF.

Natriuretic peptide levels predict recurrence of atrial fibrillation after radiofrequency catheter ablation

BACKGROUND

the presence of atrial fibrillation (AF) is related to increased levels of natriuretic peptides. In addition, increased natriuretic peptide levels are predictive of the development of AF. However, the role of natriuretic peptides to predict recurrence of AF after radiofrequency catheter ablation (RFCA) is controversial.

OBJECTIVE

the study aimed to investigate the role of natriuretic peptides in the prediction of AF recurrence after RFCA for AF.

METHODS

pre-procedural amino-terminal pro-atrial natriuretic peptide (NT-proANP) and amino-terminal-pro-B-type natriuretic peptide (NT-proBNP) plasma levels were determined in 87 patients undergoing RFCA for symptomatic drug-refractory AF. In addition, a comprehensive clinical and echocardiographic evaluation was performed at baseline. Left atrial volumes, left ventricular volumes, and function (systolic and diastolic) were assessed. During a 6-month follow-up period, AF recurrence was monitored and defined as any registration of AF on electrocardiogram or an episode of AF longer than 30 seconds on 24-hour Holter monitoring. The role of natriuretic peptide plasma levels to predict AF recurrence after RFCA was studied.

RESULTS

During follow-up, 66 patients (76%) maintained sinus rhythm, whereas 21 patients (24%) had AF recurrence. Patients with AF recurrence had higher baseline natriuretic peptide levels than patients who maintained sinus rhythm (NT-proANP 3.19 nmol/L [2.55-4.28] vs 2.52 nmol/L [1.69-3.55], P = .030; NT-proBNP 156.4 pg/mL [64.1-345.3] vs 84.6 pg/mL [43.3-142.7], P = .036). However, NT-proBNP was an independent predictor of AF recurrence, whereas NT-proANP was not. Moreover, NT-proBNP had an incremental value over echocardiographic characteristics to predict AF recurrence after RFCA.

CONCLUSION

baseline NT-proBNP plasma level is an independent predictor of AF recurrence after RFCA.

Angiotensin II induces complex fractionated electrogram in a cultured atrial myocyte monolayer mediated by calcium and sodium-calcium exchanger

Angiotensin II (AngII) has been implicated in the mechanism of atrial fibrillation (AF). There may be calcium-dependent pro-fibrillatory effect of AngII on atrial myocytes. We used cultured confluent HL-1 atrial myocyte monolayer with spontaneously propagated depolarization to study direct pro-fibrillatory effect of AngII and its molecular mechanism. AngII stimulation induced fibrillatory-like complex electrogram and calcium wave propagation. AngII shortened action potential duration and augmented calcium transient, thus increasing electrochemical gradient of forward-mode sodium-calcium exchanger (NCX) current and induced frequent irregular afterdepolarizations. AngII increased expression of sodium-calcium exchanger (NCX), further increasing calcium-membrane voltage coupling gain. The fibrillatory effect of AngII was attenuated by NCX blocker SEA0400 and NCX siRNA knockdown. AngII increased expression of L-type calcium channel and augmented calcium transient through PKC and CREB. The fibrillatory effect of AngII was also attenuated by PKC inhibitor chelerythrine and dominant negative form of CREB. In conclusions, AngII itself may electrically contribute to the mechanism of AF through increasing NCX expression and augmenting calcium transient, which is PKC and CREB dependent. Specific genetic knockdown of NCX attenuated calcium mediated afterdepolarization and complex electrogram.

Tachycardia of atrial myocytes induces collagen expression in atrial fibroblasts through transforming growth factor β1

AIMS

We investigated the molecular mechanism of rapid-depolarization-induced atrial fibrosis.

METHODS AND RESULTS

We used a direct atrial myocyte-fibroblast contact co-culture and a fibroblast-specific transforming growth factor β1 (TGF-β1), connective tissue growth factor (CTGF) and procollagen type I α-1 (COL1A1) luciferase reporter system to investigate the possible molecular mechanism of rapid-depolarization-induced atrial fibrosis. Mouse atrial fibroblasts were first transfected with promoter-luciferase reporters, and then co-cultured with HL-1 atrial myocytes. Rapid depolarization of atrial myocytes by rapid electrical field stimulation induced increased TGF-β1, CTGF and COL1A1 promoter activities in the co-cultured atrial fibroblasts (2.4 ± 0.3-fold increase, P= 0.008 for TGF-β1; 2.9 ± 0.4-fold increase, P< 0.001 for CTGF; and 2.1 ± 0.2-fold increase, P= 0.008 for COL1A1). Rapid depolarization of atrial myocytes increased paracrine secretion of angiotensin II (Ang II) and reactive oxygen species in the co-culture medium. Rapid electrical field stimulation-induced ROS generation in atrial myocytes was attenuated by the membrane NADPH oxidase inhibitor, apocynin. Atrial myocyte-induced expression of TGF-β1, CTGF and COL1A1 in atrial fibroblasts was attenuated by co-treatment with the Ang II receptor blocker, losartan, and apocynin. Atrial myocyte-induced COL1A1 expression in atrial fibroblasts was attenuated by anti-TGF-β1 antibody and RNA interference knockdown of the TGF-β1 receptor.

CONCLUSION

We first demonstrated that tachycardia of atrial myocytes induced paracrine secretion of Ang II and reactive oxygen species, which in turn induced expression of CTGF and procollagen in co-cultured atrial fibroblasts through increasing TGF-β1 expression. The results may imply that use of an Ang II receptor blocker, in combination with an anti-oxidant, blocks rapid-depolarization-induced atrial fibrosis.

Upstream effect for atrial fibrillation: still a dilemma?

Atrial fibrillation is the most common arrhythmia in clinical practice. Ion channel blocking agents are often characterized by limited long-term efficacy and several side effects. In addition, ablative invasive procedures are neither easily accessible nor always efficacious. The "upstream therapy," which includes angiotensin-converting enzyme inhibitors, aldosterone receptor antagonists, statins, glucocorticoids, and ω-3 poly-unsaturated fatty acids, targets arrhythmia substrate, influencing atrial structural and electrical remodeling that play an essential role in atrial fibrillation induction and maintenance. The mechanisms involved and the most important clinical evidence regarding the upstream therapy influence on atrial fibrillation are presented in this review. Some open questions are also proposed.

Molecular determinants of cardiac fibroblast electrical function and therapeutic implications for atrial fibrillation

Cardiac fibroblasts account for about 75% of all cardiac cells, but because of their small size contribute only ∼10-15% of total cardiac cell volume. They play a crucial role in cardiac pathophysiology. For a long time, it has been recognized that fibroblasts and related cell types are the principal sources of extracellular matrix (ECM) proteins, which organize cardiac cellular architecture. In disease states, fibroblast production of increased quantities of ECM proteins leads to tissue fibrosis, which can impair both mechanical and electrical function of the heart, contributing to heart failure and arrhythmogenesis. Atrial fibrosis is known to play a particularly important role in atrial fibrillation (AF). This review article focuses on recent advances in understanding the molecular electrophysiology of cardiac fibroblasts. Cardiac fibroblasts express a variety of ion channels, in particular voltage-gated K(+) channels and non-selective cation channels of the transient receptor potential (TRP) family. Both K(+) and TRP channels are important determinants of fibroblast function, with TRP channels acting as Ca(2+)-entry pathways that stimulate fibroblast differentiation into secretory myofibroblast phenotypes producing ECM proteins. Fibroblasts can couple to cardiomyocytes and substantially affect their cellular electrical properties, including conduction, resting potential, repolarization, and excitability. Co-cultured preparations of cardiomyocytes and fibroblasts generate arrhythmias by a variety of mechanisms, including spontaneous impulse formation and rotor-driven reentry. In addition, the excess ECM proteins produced by fibroblasts can interrupt cardiomyocyte-bundle continuity, leading to local conduction disturbances and reentrant arrhythmias. A better understanding of the electrical properties of fibroblasts should lead to an improved comprehension of AF pathophysiology and a variety of novel targets for antiarrhythmic intervention.

Prevention of atrial fibrillation by Renin-Angiotensin system inhibition a meta-analysis

OBJECTIVES

The authors reviewed published clinical trial data on the effects of renin-angiotensin system (RAS) inhibition for the prevention of atrial fibrillation (AF), aiming to define when RAS inhibition is most effective.

BACKGROUND

Individual studies examining the effects of RAS inhibition on AF prevention have reported controversial results.

METHODS

All published randomized controlled trials reporting the effects of treatment with angiotensin-converting enzyme inhibitors or angiotensin receptor blockers in the primary or secondary prevention of AF were included.

RESULTS

A total of 23 randomized controlled trials with 87,048 patients were analyzed. In primary prevention, 6 trials in hypertension, 2 trials in myocardial infarction, and 3 trials in heart failure were included (some being post-hoc analyses of randomized controlled trials). In secondary prevention, 8 trials after cardioversion and 4 trials assessing the medical prevention of recurrence were included. Overall, RAS inhibition reduced the odds ratio for AF by 33% (p < 0.00001), but there was substantial heterogeneity among trials. In primary prevention, RAS inhibition was effective in patients with heart failure and those with hypertension and left ventricular hypertrophy but not in post-myocardial infarction patients overall. In secondary prevention, RAS inhibition was often administered in addition to antiarrhythmic drugs, including amiodarone, further reducing the odds for AF recurrence after cardioversion by 45% (p = 0.01) and in patients on medical therapy by 63% (p < 0.00001).

CONCLUSIONS

This analysis supports the concept of RAS inhibition as an emerging treatment for the primary and secondary prevention of AF but acknowledges the fact that some of the primary prevention trials were post-hoc analyses. Further areas of uncertainty include potential differences among specific RAS inhibitors and possible interactions or synergistic effects with antiarrhythmic drugs.

Recent advances in pharmacotherapy of atrial fibrillation

Atrial fibrillation (AF) is the most common sustained arrhythmia associated with increased morbidity and mortality. Efficacy and safety of currently employed antiarrhythmic drugs (AADs) continue to be less optimal in AF. Development of newer AADs has recently been made possible through a greater understanding of electro-pathophysiology of AF. Highly specific drugs acting on atria are currently being explored, although there is little data available on effectiveness of atrial specific agents in maintaining sinus rhythm. Combining AADs and non-AADs such as angiotensin converting enzyme inhibitors (ACEIs) and angiotensin receptor blockers (ARBs) may increase effectiveness of AADs in patients with AF. Controlled clinical trials are required to precisely define the efficacy of single agents versus various combinations in maintaining sinus rhythm in patients with AF. This review describes some of the most promising therapeutic approaches that may overcome some of the limitations of drugs used at present for the management of AF.

Reverse remodeling of the atria after treatment of chronic stretch in humans: implications for the atrial fibrillation substrate

OBJECTIVES

The aim of this report was to study the effect of chronic stretch reversal on the electrophysiological characteristics of the atria in humans.

BACKGROUND

Atrial stretch is an important determinant for atrial fibrillation. Whether relief of stretch reverses the substrate predisposed to atrial fibrillation is unknown.

METHODS

Twenty-one patients with mitral stenosis undergoing mitral commissurotomy (MC) were studied before and after intervention. Catheters were placed at multiple sites in the right atrium (RA) and sequentially within the left atrium (LA) to determine: effective refractory period (ERP) at 10 sites (600 and 450 ms) and P-wave duration (PWD). Bi-atrial electroanatomic maps determined conduction velocity (CV) and voltage. In 14 patients, RA studies were repeated >or=6 months after MC.

RESULTS

Immediately after MC, there was significant increase in mitral valve area (2.1 +/- 0.2 cm(2), p < 0.0001) with decrease in LA (23 +/- 7 mm Hg to 10 +/- 4 mm Hg, p < 0.0001) and pulmonary arterial pressures (38 +/- 16 mm Hg to 27 +/- 12 mm Hg, p < 0.0001) and LA volume (75 +/- 20 ml to 52 +/- 18 ml, p < 0.0001). This was associated with reduction in PWD (139 +/- 19 ms to 135 +/- 20 ms, p = 0.047), increase in CV (LA: 1.3 +/- 0.3 mm/ms to 1.7 +/- 0.2 mm/ms, p = 0.006; and RA: 1.0 +/- 0.1 mm/ms to 1.3 +/- 0.3 mm/ms, p = 0.002) and voltage (LA: 1.7 +/- 0.6 mV to 2.5 +/- 1.0 mV, p = 0.005; and RA: 1.8 +/- 0.6 mV to 2.2 +/- 0.7 mV, p = 0.09), and no change in ERP. Late after MC, mitral valve area remained at 2.1 +/- 0.3 cm(2) (p = 0.7) but with further decrease in PWD (113 +/- 19 ms, p = 0.04) and RA ERP (at 600 ms, p < 0.0001), with increase in CV (1.0 +/- 0.1 mm/ms to 1.3 +/- 0.2 mm/ms, p = 0.006) and voltage (1.8 +/- 0.7 mV to 2.8 +/- 0.6 mV, p = 0.002).

CONCLUSIONS

The atrial electrophysiologic and electroanatomic abnormalities that result from chronic stretch due to MS reverses after MC. These observations suggest that the substrate predisposing to atrial arrhythmias might be reversed.

Early management of atrial fibrillation: from imaging to drugs to ablation

Atrial fibrillation (AF) is the most common cardiac arrhythmia, and is responsible for the highest number of rhythm-related disorders and cardioembolic strokes worldwide. Early management of this condition will lower the risk of AF-associated morbidity and mortality. Targeted drug therapy has an important role in preventing the progression of AF through modification of the substrate. Discovery of the role of pulmonary veins as a trigger has been an important breakthrough, leading to the development of pulmonary vein ablation-an established curative therapy for drug-resistant AF. Identifying the underlying reasons for the abnormal firing of venous cardiomyocytes and the widespread progressive alterations of atrial tissue found in persistent AF are challenges for the future. Novel imaging techniques may help to determine the right time for intervention, provide specific targets for ablation, and judge the efficacy of treatment. If new developments can successfully address these issues, the knowledge acquired as a result will have a vital role in preclinical and early management of AF.

New antiarrhythmic drugs for treatment of atrial fibrillation

Inadequacies in current therapies for atrial fibrillation have made new drug development crucial. Conventional antiarrhythmic drugs increase the risk of ventricular proarrhythmia. In drug development, the focus has been on favourable multichannel-blocking profiles, atrial-specific ion-channels, and novel non-channel targets (upstream therapy). Molecular modification of the highly effective multichannel blocker, amiodarone, to improve safety and tolerability has produced promising analogues such as dronedarone, although this drug seems less effective than does amiodarone. Vernakalant, an atrial-selective drug with reduced proarrhythmic risk, might be useful for cardioversion in atrial fibrillation. Ranolazine, another atrial-selective agent initially developed as an antianginal, has efficacy for atrial fibrillation and is being tested in prospective clinical trials. So-called upstream therapy with angiotensin-converting enzyme and angiotensin-receptor inhibitors, statins, or omega-3 fatty acids and fish oil that target atrial remodelling could be effective, but need further clinical validation. We focus on the basic and clinical pharmacology of newly emerging antiarrhythmic drugs and non-traditional approaches such as upstream therapy for atrial fibrillation.

Increased expression of mineralocorticoid receptor in human atrial fibrillation and a cellular model of atrial fibrillation

OBJECTIVES

This study was designed to evaluate the status of steroidogenesis proteins and de novo synthesis of aldosterone in the atrium, and relationships of these factors to atrial fibrillation (AF).

BACKGROUND

The role of mineralocorticoid in the pathogenesis of AF is unknown.

METHODS

We studied atrial expression of steroidogenesis proteins and aldosterone level in patients with and without AF, and in HL-1 atrial myocytes. We also investigated the electrophysiologic effects and signal transduction of aldosterone on atrial myocytes.

RESULTS

We found basal expressions of mineralocorticoid receptors (MRs), glucocorticoid receptors, and 11-beta-hydroxysteroid dehydrogenase type 2 (11bHSD2) but not 11-beta-hydroxylase (CYP11B1) or aldosterone synthase (CYP11B2) in human atria and HL-1 myocytes. There was no significant difference of mean atrial aldosterone level between patients with AF and those with normal sinus rhythm. However, patients with AF had a significantly higher atrial MR expression compared with those with normal sinus rhythm (1.73 +/- 0.24-fold, p < 0.001). Using mouse HL-1 atrial myocytes as a cellular AF model, we found that rapid depolarization increased MR expression (1.97 +/- 0.72-fold, p = 0.008) through a calcium-dependent mechanism, thus augmenting the genomic effect of aldosterone signaling as evaluated by MR reporter. Aldosterone increased intracellular oxidative stress through a nongenomic pathway, which was attenuated by nicotinamide adenine dinucleotide phosphate oxidase inhibitor diphenyleneiodonium, but not by MR-blockade spironolactone. Aldosterone increased expression of the alpha-1G and -1H subunits of the T-type calcium channel and thus increased the T-type calcium current (-13.6 +/- 2.9 pA/pF vs. -4.5 +/- 1.6 pA/pF, p < 0.01) and the intracellular calcium load through a genomic pathway, which were attenuated by spironolactone, but not by diphenyleneiodonium.

CONCLUSIONS

Expression of MR increased in AF, thus augmenting the genomic effects of aldosterone. Aldosterone induced atrial ionic remodeling and calcium overload through a genomic pathway, which was attenuated by spironolactone. These results suggest that aldosterone may play a role in AF electrical remodeling and provide insight into the treatment of AF with MR blockade.

Rac1-induced connective tissue growth factor regulates connexin 43 and N-cadherin expression in atrial fibrillation

OBJECTIVES

We studied the signal transduction of atrial structural remodeling that contributes to the pathogenesis of atrial fibrillation (AF).

BACKGROUND

Fibrosis is a hallmark of arrhythmogenic structural remodeling, but the underlying molecular mechanisms are incompletely understood.

METHODS

We performed transcriptional profiling of left atrial myocardium from patients with AF and sinus rhythm and applied cultured primary cardiac cells and transgenic mice with overexpression of constitutively active V12Rac1 (RacET) in which AF develops at old age to characterize mediators of the signal transduction of atrial remodeling.

RESULTS

Left atrial myocardium from patients with AF showed a marked up-regulation of connective tissue growth factor (CTGF) expression compared with sinus rhythm patients. This was associated with increased fibrosis, nicotinamide adenine dinucleotide phosphate oxidase, Rac1 and RhoA activity, up-regulation of N-cadherin and connexin 43 (Cx43) expression, and increased angiotensin II tissue concentration. In neonatal rat cardiomyocytes and fibroblasts, a specific small molecule inhibitor of Rac1 or simvastatin completely prevented the angiotensin II-induced up-regulation of CTGF, Cx43, and N-cadherin expression. Transfection with small-inhibiting CTGF ribonucleic acid blocked Cx43 and N-cadherin expression. RacET mice showed up-regulation of CTGF, Cx43, and N-cadherin protein expression. Inhibition of Rac1 by oral statin treatment prevented these effects, identifying Rac1 as a key regulator of CTGF in vivo.

CONCLUSIONS

The data identify CTGF as an important mediator of atrial structural remodeling during AF. Angiotensin II activates CTGF via activation of Rac1 and nicotinamide adenine dinucleotide phosphate oxidase, leading to up-regulation of Cx43, N-cadherin, and interstitial fibrosis and therefore contributing to the signal transduction of atrial structural remodeling.

Atrial fibrillation in heart failure: a comprehensive review

Chronic heart failure and atrial fibrillation are 2 major disorders that are closely linked. Their coexistence is associated with adverse prognosis. Both share several common predisposing conditions, but their interaction involves complex ultrastructural, electrophysiologic, and neurohormonal processes that go beyond mere sharing of mutual risk factors. Rate control approach remains the standard therapy for atrial fibrillation in heart failure because current strategies at rhythm control have so far failed to positively impact mortality and morbidity. This is largely because of the shortcomings of current pharmacologic anti-arrhythmic agents. Surgical and catheter-based therapies are promising, but long-term data are lacking. The role of non-anti-arrhythmic therapeutic agents also is being explored. Further progress toward improved understanding the complex relationship between atrial fibrillation and heart failure should improve management strategies.

[Pathophysiopathology of atrial fibrillation: applications to treatment]

The origin and persistence of AF result from a complex interaction between triggers, autonomic nervous system, substrate, and factors involved in atrial remodelling. The pathophysiology of AF differs from one patient to another, but recent advances have helped us to understand more about involved mechanisms and to translate this knowledge into improvements in AF therapy. An illustration is the elimination of triggers within pulmonary veins by means of catheter ablation. Dealing with structural atrial remodelling and atrial fibrosis remains still a great challenge. Solving these problems could help us to develop new approaches to AF prevention and treatment.

Angiotensin II receptor type 1 is upregulated in atrial tissue of patients with rheumatic valvular disease with atrial fibrillation

OBJECTIVE

The purpose of this study was to examine the changes in expression of angiotensin II receptor type 1/2 in left or right atrial tissue from patients with rheumatic valvular disease with or without atrial fibrillation.

METHODS

Atrial tissue samples were obtained from 39 patients with rheumatic mitral valve disease during cardiac surgery. Among these patients, there were 25 with atrial fibrillation and 14 with sinus rhythm. The level of angiotensin II receptor type 1 or type 2 mRNA transcription was measured by means of a semiquantitative reverse transcription-polymerase chain reaction technique. Expression of angiotensin II receptor type 1 or type 2 protein was detected by means of immunohistochemistry assay and Western blot analysis.

RESULTS

The inner diameter of the left atrium was clearly enlarged in the atrial fibrillation group in comparison with that seen in the sinus rhythm group. The expression levels of both angiotensin II receptor type 1 mRNA and protein in the left atrial tissue were significantly increased in the patients with atrial fibrillation compared with those seen in patients with sinus rhythm (P < .05). Interestingly, the comparison of angiotensin II receptor type 2 expression levels in the left atrial tissue between these 2 groups is not statistically significant. In addition, the results of angiotensin II receptor type 1 or 2 expression in the right atrial tissue did not show any obvious change in the patients with atrial fibrillation versus those with sinus rhythm.

CONCLUSIONS

Expression of angiotensin II receptor type 1 but not type 2 is highly upregulated only in the left atrial tissue of patients with rheumatic valvular disease with atrial fibrillation. This suggests that there is a possible pathophysiologic role of the renin-angiotensin system in patients with atrial fibrillation and that a series of effects mediated by the activation of angiotensin II receptor type 1 in the left atrial tissue might be one of the molecular mechanisms involved in the process of atrial remodeling in atrial fibrillation.

Angiotensin-(1-7) prevents atrial fibrosis and atrial fibrillation in long-term atrial tachycardia dogs

Renin-angiotensin system (RAS) is activated in the fibrillating atria. Angiotensin-(1-7) [Ang-(1-7)] counterbalances the actions of angiotensin II (Ang II). To investigate the effects of Ang-(1-7) on the long-term atrial tachycardia-induced atrial fibrosis and atrial fibrillation (AF) vulnerability, eighteen dogs were assigned to sham group, paced group, or paced+Ang-(1-7) group, 6 dogs in each group. Rapid atrial pacing at 500 bpm was maintained for 14 days, but dogs in the sham group were instrumented without pacing. During the pacing, Ang-(1-7) (6 microg x kg(-1) x h(-1)) was given intravenously. After pacing, atrial mRNA expression of ERK1/ERK2 and atrial fibrosis were assessed, the inducibility and duration of AF were measured. Compared with sham, ERK1/ERK2 mRNA expression was increased in the paced group (P<0.05). Atrial tissue from the paced dogs showed a large amount of interstitial fibrosis, and the inducible rate of AF was increased at various BCLs in paced dogs (P<0.01). Compared with the paced group, Ang-(1-7) prevented the increase of ERK1/ERK2 mRNA expression (P<0.01 and P<0.05, respectively), and attenuated the interstitial fibrosis (P<0.01). Inducibility and duration of AF were reduced by Ang-(1-7) at various BCLs. In conclusion, Ang-(1-7) reduced AF vulnerability in chronic paced atria, and antifibrotic actions contributed to its preventive effects on AF.