Mechanism and prevention of atrial remodeling and their related genes in cardiovascular disorders

Atrial fibrillation (AF) is associated with profound structural and functional changes in the atrium. Inflammation mediated atrial fibrosis is one of the key mechanisms in the pathogenesis of AF. The collagen deposition in extracellular matrix (ECM) is mainly mediated by transforming growth factor β1 (TGF-β1) which promotes AF via controlling smads mediated-collagen gene transcription and regulating the balance of metalloproteinases (MMPs)/ tissue inhibitor of metalloproteinases (TIMPs). Although many processes can alter atrial properties and promote AF, animal models and clinical studies have provided insights into two major forms of atrial remodeling: Atrial tachycardia remodeling (ATR), which occurs with rapid atrial tachyarrhythmia's such as AF and atrial flutter, and atrial structural remodeling (ASR), which is associated with CHF and other fibrosis-promoting conditions. The mechanism of atrial remodeling such as atrial enlargement, ultra structural changes of atrial muscle tissue and myocardial interstitial fibrosis in AF is still unclear. At present, many studies focus on calcium overload, renin angiotensin aldosterone system and transforming growth factor β1, that effect on atrial structural remodeling. Recent experimental studies and clinical investigations have provided structural remodeling is important contributor to the AF. This paper reviews the current understanding of the progresses about mechanism of atrial structural remodeling, and highlights the potential therapeutic approaches aimed at attenuating structural remodeling to prevent AF. Now some recent advancements of this area are reviewed in this paper.

Precise Drug Sequential Therapy Can Improve the Cardioversion Rate of Atrial Fibrillation with Valvular Disease after Radiofrequency Ablation

OBJECTIVE

Based on pathogenesis of atrial fibrillation (AF), investigate the effects of precision drugs continuous therapy on AF cardioversion rate after radiofrequency catheter ablation.

METHODS

We included 1334 patients who underwent mitral valve replacement with bipolar radiofrequency ablation due to mitral valve disease with AF during June 2011 to July 2017. The data of clinical and related laboratory examinations at discharge and follow-up were recorded. All patients were treated with or without angiotensin-converting enzyme inhibitor (ACEI) and angiotensin II-receptor blocker (ARB) drugs according to their conditions and doctor's willingness. The heart rhythm was evaluated after treatment and follow-up of 6 months.

RESULTS

All 1162 cases were followed up, including 825 cases in mitral stenosis (MS) group, 337 cases in mitral regurgitation (MR) group. In MS group, left atrial diameter(LAD) and left ventricular diameter(LVD) of the patients taking ACEI and ARB were significantly lower (P < 0.05), and they can increase AF cardioversion rate from 79.1% of the control group to 83.7% and 82.8%, respectively (P = 0.03 and 0.04). In MR group, the patients with ACEI compared with control group, there were no significant differences in LAD, LVD, right atrial diameter (RAD), right ventricular diameter (RVD), left ventricular ejection fraction(LVEF), and left ventricular fractional shortening(LVFS) (P > 0.05); but ARB group, LAD, LVD decreased significantly (P < 0.05). And ACEI can increase AF cardioversion rate from 76.1% in the control group to 77.2% (P = 0.62), ARB to 81.6% (P = 0.02).

CONCLUSION

It does improve AF cardioversion rate after radiofrequency catheter ablation that the precise anti-structural remodeling drugs continuous therapy was adopted based on the pathogenesis of AF.

The Use of Statins in the Treatment and Prevention of Atrial Fibrillation

The hydroxy-methyl-glutaryl-CoA reductase inhibitors (statins) are used extensively in the treatment of hyperlipidemia and in the primary and secondary prevention of cardiovascular and cerebrovascular diseases. Statins have also been demonstrated to confer secondary pleiotropic benefits in a variety of other disease processes, including a potential advantage in treating and preventing atrial fibrillation. These effects are primarily due to the up-regulation of endothelial nitric oxide synthase activity and a decrease in nicotinamide adenine dinucleotide phosphate oxidase production, which leads to downstream effects that improve the electromechanical function of atrial and myocardial tissue. The following serves as a focused and updated review of the published clinical data regarding the pleiotropic effects of statins in atrial fibrillation.

TPEN prevents rapid pacing-induced calcium overload and nitration stress in HL-1 myocytes

INTRODUCTION

Atrial fibrillation (AF) is the most common cardiac arrhythmia. However, the current drug interference of antiarrhythmia has limited efficacy and off-target effects. Accumulating evidence has implicated a potential role of nitration stress in the pathogenesis of AF. The aim of the study was to determine whether TPEN provided antinitration effects on atrial myocytes during AF, especially under circumstances of nitration stress.

METHODS

We utilized a rapid paced HL-1 cells model for AF. The changes of electrophysiological characteristics and structure of paced HL-1 cells were determined by a patch clamp and a TEM method. The effects of TPEN on pacing and ONOO(-) pretreated HL-1 cells were examined using MTT assay, TUNEL technique, confocal microscope experiment, and Western blot analysis.

RESULTS

The results revealed that ONOO(-) reduced the viability of HL-1 cells in a dose-dependent manner, and 1 μmol/L TPEN significantly ameliorated the damage caused by 50 μmol/L ONOO(-) (P < 0.05). Pacing and/or ONOO(-) -induced marked shortening of APD, myolysis, and nuclear condensation. TPEN inhibited the Ca(2+) overload induced by rapid pacing (P < 0.05) and ONOO(-) stimulation (P < 0.05). The application of TPEN significantly prevented the protein nitration caused by pacing or pacing plus ONOO(-) (P < 0.05). Additionally, pacing in combination with ONOO(-) treatment led to increase in apoptosis in HL-1 cells (P < 0.01), which could be reduced by pretreatment with TPEN (P < 0.05).

CONCLUSIONS

TPEN prevents Ca(2+) overload and nitration stress in HL-1 atrial myocytes during rapid pacing and circumstances of nitration stress.

Comparison of the effects of bepridil and aprindine for the prevention of atrial fibrillation after cardiac and aortic surgery: A prospective randomized study

BACKGROUND

Approximately one-third of the patients undergoing cardiovascular surgery reportedly experience paroxysmal atrial fibrillation (AF) during the postoperative period. However, the usefulness of antiarrhythmic drugs for preventing postoperative AF recurrence in the Japanese population has not been extensively studied.

METHODS

From a total of 118 patients who developed postoperative paroxysmal AF between April 2009 and March 2011, 72 patients (45 men, mean age 68±8 years) requiring treatment for postoperative AF due to symptoms lasting ≥30 min were enrolled to prospectively investigate the efficacy of oral bepridil (100 mg/day, n=37) or aprindine (40 mg/day, n=35).

RESULT

The AF recurrence-free survival rates at 1, 3, 7, and 14 days were 100%, 94%, 57%, and 49%, respectively, in the aprindine group, and 100%, 97%, 86%, and 76%, respectively, in the bepridil group (P=0.028, aprindine vs. bepridil).

CONCLUSION

Bepridil, at a fixed dose of 100 mg/day, was considered to be more effective than a routine dose of aprindine for the prevention of postoperative AF recurrence.

Effect of pravastatin on echocardiographic circulation parameters in dogs

The purpose of this study was to determine the effect of pravastatin (PS) on hemodynamic parameters in healthy dogs. Five beagle dogs were repeatedly used in each of the 4 groups. One group was not medicated (control). Dogs in other groups received 0.5, 1.0 or 2.0 mg/kg PS orally q24hr, for 4 weeks. Physical examination, blood biochemical tests, blood pressure measurements and Doppler echocardiography were performed before and 1, 2 and 4 weeks after PS administration in all dogs. PS significantly reduced the left atrial-to-aortic diameter ratio (LA/Ao), early diastolic transmitral flow (E) wave, E/early diastolic mitral annulus motion velocity (Em) ratio, left ventricular (LV) fractional shortening, LV ejection fraction, mid systolic myocardial velocity gradient, stroke volume (SV), cardiac output (CO), right and left ventricular Tei indices and elevated Em and early diastolic myocardial velocity gradient. Heart rate was not significantly altered during PS administration, but mean blood pressure decreased slightly. The hematological and blood biochemical values were within normal limits during PS administration. These results revealed that PS administration increases LV expansion capacity and decreases LV constriction and left atrial pressure. It has been suggested that PS may be effective in improving heart failures with LV diastolic dysfunction or elevated left atrial pressure in dogs.

The preventive effect of statin therapy on new-onset and recurrent atrial fibrillation in patients not undergoing invasive cardiac interventions: a systematic review and meta-analysis

BACKGROUND

Previous meta-analyses suggest that pre-procedural use of statin therapy may reduce atrial fibrillation (AF) following invasive cardiac interventions (coronary artery by-pass grafting and percutaneous coronary intervention). However, the current evidence on the benefit of statins unrelated to invasive cardiac interventions has not been clarified systematically.

METHODS

Through a systematic literature search, trials examining the effect of statin therapy on AF were selected. Trials using statins before any percutaneous or surgical cardiac interventions were excluded.

RESULTS

The search identified 11 randomized and 16 observational eligible studies, totaling 106,640 patients receiving statin therapy and 129,305 serving as controls. Fourteen studies investigated the effect of statins on new-onset AF, 13 studies investigated the effect of statins on recurrent AF and one in both new-onset and recurrent AF. In the statin versus control group the mean age was 60.7 ± 8.3 versus 68.6 ± 6.2 years and females comprised 8.4% versus 10.3%. Statin therapy was associated with significant reduction of AF (Risk ratio (RR): 0.81 [95% confidence interval (CI): 0.80-0.83], p<0.001) combining all studies. Assessing exclusively randomized trials, statin therapy showed no significant risk reduction (RR: 0.97 [95%CI: 0.90-1.05], p=0.509), heterogeneity p>0.05. Assessing exclusively observational studies the risk reduction of new-onset AF was 12% (RR: 0.88 [95%CI: 0.85-0.91], p<0.001) and recurrent AF 15% (RR: 0.85 [95%CI: 0.80-0.90], p<0.001), heterogeneity p<0.001.

CONCLUSION

The hitherto published randomized clinical trials do not support a beneficial effect of statins on AF in patients not undergoing invasive cardiac interventions. This is in contrast to the results of observational and interventional studies.

Nitric oxide synthases and atrial fibrillation

Oxidative stress has been implicated in the pathogenesis of atrial fibrillation. There are multiple systems in the myocardium which contribute to redox homeostasis, and loss of homeostasis can result in oxidative stress. Potential sources of oxidants include nitric oxide synthases (NOS), which normally produce nitric oxide in the heart. Two NOS isoforms (1 and 3) are normally expressed in the heart. During pathologies such as heart failure, there is induction of NOS 2 in multiple cell types in the myocardium. In certain conditions, the NOS enzymes may become uncoupled, shifting from production of nitric oxide to superoxide anion, a potent free radical and oxidant. Multiple lines of evidence suggest a role for NOS in the pathogenesis of atrial fibrillation. Therapeutic approaches to reduce atrial fibrillation by modulation of NOS activity may be beneficial, although further investigation of this strategy is needed.

Long-term efficacy of upstream therapy with lipophilic or hydrophilic statins on antiarrhythmic drugs in patients with paroxysmal atrial fibrillation: comparison between atorvastatin and pravastatin

There is little information available on the benefits of selection of statins as upstream therapy for the prevention of paroxysmal atrial fibrillation (AF). We compared the efficacy and safety of atorvastatin (A-group, n = 43) and pravastatin (P-group, n = 41) as upstream therapy in patients with paroxysmal AF and dyslipidemia. A total of 84 patients (45 men, mean age, 66 ± 9 years, mean follow-up, 49 ± 32 months) were retrospectively assigned to receive atorvastatin (n = 41;10 mg/day) or pravastatin (n = 43 ; 10 mg/day). Survival rates free from AF recurrence at 1, 6, 12, and 24 months were 93%, 74%, 60%, and 53% in A-group, and 88%, 49%, 37%, and 29%, respectively, in P-group (P = 0.029, A-group versus P-group). Survival rates free from conversion to permanent AF at 12, 36, 60, and 90 months were 100%, 100%, 98%, and 95% in A-group, and 100%, 95%, 88%, and 83%, respectively, in P-group (P = 0.063, A-group versus P-group). Using a logistic regression model, atorvastatin was found to be associated with a significantly reduced risk of AF recurrence in comparison to pravastatin (unadjusted odds ratio [OR] = 0.27, 95% confidence interval 0.11-0.68, P = 0.005). This association remained significant after adjustment for potentially confounding variables (OR = 0.26, 95% CI 0.08-0.86, P = 0.027). Using a logistic regression model, atorvastatin was not associated with a significantly reduced risk of converting to permanent AF in comparison to pravastatin (unadjusted OR = 0.29, 95% CI 0.05-1.50, P = 0.138), but this association did show a significant difference after adjustment for potentially confounding variables in a multivariate model (OR = 0.08, 95% CI 0.06-0.96, P = 0.046). Adverse effects requiring discontinuation of statins were observed in 1 case (2%, myalgia) in A-group, and 1 case (2%, elevation in CPK level ≥ 500 IU/L) in P-group, respectively (P = NS, A-group versus P-group). Atorvastatin, a lipophilic statin, was considered to be more effective in preventing recurrence of paroxysmal AF and conversion to permanent AF than pravastatin, a hydrophilic statin.

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.

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.