Clinical trials, the renin angiotensin system and atrial fibrillation

Renin Angiotenin Blocker Pre-treatment and Recurrence After Pulmonary Vein Isolation in Patients with Paroxysmal and Persistent Atrial Fibrillation

Introduction: Pulmonary venous isolation has emerged as an effective method for preventing atrial fibrillation (AF) recurrence. Yet, recurrence is common. Angiotensin-receptor-blockers (ARBs) and angiotensin-converting-enzyme-inhibitors (ACEI) are effective in reducing the extent of myocardial remodeling and fibrosis. Our aim was to study whether pretreatment with ARBs and ACEI was effective in decreasing recurrence after pulmonary vein isolation for patients with AF. Methods: Three hundred and twelve consecutive patients who underwent ablation from 12/2006 until 7/2010 were followed for at least one year. All patients underwent MRI before ablation to assess atrial fibrosis. Data include demographic characteristics, comorbidities, AF type and information regarding treatment with ACEI or ARBs. Results: Most patients were men (62%), mean age was 64. Hypertension (HTN) was present in 60%. Their mean ejection fraction was 60%. There were 104 patients (33.3%) treated with ACEI, and 13.5 % were treated with ARBs prior to ablation. Ninety seven patients (31.1%) had AF recurrence. AF type was a significant predictor for recurrence (recurrence with paroxysmal, persistent and long-standing persistent: 23.75, 37.3 and 60%, respectively, p=0.005). The most important factor predicting recurrence was increased pre-ablation atrial fibrosis (p<0.0001). Recurrence was more frequent in patients treated with ACEI (40.4% vs 26.4% untreated patients, p=0.012). In the ARB treated group, 38.1% vs 30.0% untreated experienced recurrence (p=0.3). After multivariable adjustment for demographics, risk factors and atrial fibrosis, treatment with ACEI was associated with increased rate of recurrence in patients with persistent AF (hazard ratio: 2.6, p=0.003). There was no significant relation between ACEI pretreatment and recurrence in patients with paroxysmal AF (HR- 0.83, p=0.7), or between ARB pre-treatment and recurrence in patients with paroxysmal as well as persistent AF (p=0.2 and 0.53, respectively). Conclusions: Pretreatment with ACEI or ARBs is not associated with reduced recurrence rate in patients with paroxysmal or persistent AF undergoing ablation.

Circulating and local renin-angiotensin-aldosterone system express differently in atrial fibrillation patients with different types of mitral valvular disease

Mitral valvular disease is strongly related to atrial fibrillation (AF), but the different types of mitral valvular disease have a different prevalence of AF. In this study we explored the expressions of the circulating and local renin-angiotensin-aldosterone system (RAAS) in order to determine the relationship between circulating and local RAAS expressions and its effects on AF in different types of mitral valvular disease patients. Our study group consisted of 24 mitral valvular disease patients scheduled for mitral valve replacement surgery. Peripheral blood samples and left atrial appendage tissue samples were obtained from all patients. Radioimmunoassay was performed to assess the expression levels of circulating and local renin, angiotensin II and aldosterone. In mitral valvular diseases, linear correlation analyses were done for local and circulating renin, angiotensin II and aldosterone; the p values were 0.979, 0.518 and 0.125, respectively. Expression levels of local angiotensin II, circulating angiotensin II and local aldosterone were significantly increased in the AF group compared with sinus rhythm; the p values were 0.023, 0.042 and 0.035, respectively. In mitral stenosis patients, AF was primarily associated with local angiotensin II (p=0.010), as well as being associated with circulating angiotensin II (p=0.038). In mitral regurgitation patients, AF was only significantly associated with local angiotensin II (p=0.038). Circulating and local RAAS expressions are associated with AF in mitral valvular disease patients. The levels of circulating and local RAAS expressions were different in AF patients with different types of mitral valvular diseases. The differentiation of circulating and local RAAS expression levels in AF patients between different types of mitral valvular disease can potentially improve the specific pharmacological interventions outcomes for these patients.

Characterization of the genomic structure and function of regions influencing renin and angiogenesis in the SS rat

Impaired regulation of renin in Dahl salt-sensitive rats (SS/JRHsdMcwi, SS) contributes to attenuated angiogenesis in this strain. This study examined angiogenic function and genomic structure of regions surrounding the renin gene using subcongenic strains of the SS and BN/NHsdMcwi (BN) rat to identify important genomic variations between SS and BN involved in angiogenesis. Three candidate regions on Chr 13 were studied: two congenic strains containing 0.89 and 2.62 Mb portions of BN Chr 13 that excluded the BN renin allele and a third strain that contained a 2.02 Mb overlapping region that included the BN renin allele. Angiogenesis induced by electrical stimulation of the tibialis anterior muscle was attenuated in the SS compared with the BN. Congenics carrying the SS renin allele had impaired angiogenesis, while strains carrying the BN renin allele had angiogenesis restored. The exception was a congenic including a region of BN genome 0.4 Mb distal to renin that restored both renin regulation and angiogenesis. This suggests that there is a distant regulatory element in the BN capable of restoring normal regulation of the SS renin allele. The importance of ANG II in the restored angiogenic response was demonstrated by blocking with losartan. Sequencing of the 4.05 Mb candidate region in SS and BN revealed a total of 8,850 SNPs and other sequence variants. An analysis of the genes and their variants in the region suggested a number of pathways that may explain the impaired regulation of renin and angiogenesis in the SS rat.

ACE I/D polymorphism associated with abnormal atrial and atrioventricular conduction in lone atrial fibrillation and structural heart disease: implications for electrical remodeling

BACKGROUND

The angiotensin-converting enzyme (ACE) gene contains a common polymorphism based on the insertion (I) or deletion (D) of a 287-bp intronic DNA fragment. The D allele is associated with higher ACE activity and thus higher angiotensin II levels. Angiotensin II stimulates cardiac fibrosis and conduction heterogeneity.

OBJECTIVE

The purpose of this study was to determine whether the ACE I/D polymorphism modulates cardiac electrophysiology.

METHODS

Three different cohorts of patients were studied: 69 patients with paroxysmal lone atrial fibrillation (AF), 151 patients with structural heart disease and no history of AF, and 161 healthy subjects without cardiovascular disease or AF. Patients taking drugs that affect cardiac conduction were excluded from the study. ECG parameters during sinus rhythm were compared among the ACE I/D genotypes.

RESULTS

The ACE I/D polymorphism was associated with the PR interval and heart block in the lone AF cohort. In multivariable linear regression models, the D allele was associated with longer PR interval in the lone AF and heart disease cohorts (12.0-ms and 7.1-ms increase per D allele, respectively). P-wave duration showed a similar trend, with increase in PR interval across ACE I/D genotypes in the lone AF and heart disease cohorts.

CONCLUSION

The ACE D allele is associated with electrical remodeling in patients with lone AF and in those with heart disease, but not in control subjects. ACE activity may play a role in cardiac remodeling after the development of AF and heart disease.

Does treatment of hypertension decrease the incidence of atrial fibrillation and cardioembolic stroke?

Hypertension is the most common disease affecting humans. Statistical surveys indicate that approximately one billion individuals worldwide suffer from this serious condition. The spotlight of the present review is on the cardiac involvement in patients with hypertension and especially on the possibility that treatment of increased blood pressure may abolish the incidence of cardiac arrhythmia and particularly atrial fibrillation. Modern therapeutic approach based on the electrical and structural remodeling process in the hypertensive heart with a consequent administration of ACE inhibitors and AT1 receptor blockers represent new and more efficient option compared to other antihypertensive drugs, such as calcium channel blockers, beta-blockers and thiazide-type diuretics and might be useful in the prevention of atrial fibrillation and incidence of stroke.

Congenic strains reveal the effect of the renin gene on skeletal muscle angiogenesis induced by electrical stimulation

Previous studies have indicated the importance of angiotensin II (ANG II) in skeletal muscle angiogenesis. The present study explored the effect of regulation of the renin gene on angiogenesis induced by electrical stimulation with the use of physiological, pharmacological, and genetic manipulations of the renin-angiotensin system (RAS). Transfer of the entire chromosome 13, containing the physiologically regulated renin gene, from the normotensive inbred Brown Norway (BN) rat into the background of an inbred substrain of the Dahl salt-sensitive (SS/Mcwi) rat restored renin levels and the angiogenic response after electrical stimulation. This restored response was significantly attenuated when SS-13BN/Mcwi consomic rats were treated with lisinopril or high-salt diet. The role of ANG II on this effect was confirmed by the complete restoration of skeletal muscle angiogenesis in SS/Mcwi rats infused with subpressor doses of ANG II. Congenic strains derived from the SS-13BN/Mcwi consomic were used to further verify the role of the renin gene in this response. Microvessel density was markedly increased after stimulation in congenic strains that contained the renin gene from the BN rat (congenic lines A and D). This angiogenic response was suppressed in control strains that carried regions of the BN genome just above (congenic line C) or just below (congenic line B) the renin gene. The present study emphasizes the importance of maintaining normal renin regulation as well as ANG II levels during the angiogenesis process with a combination of physiological, genetic, and pharmacological manipulation of the RAS.

Renin: at the heart of the mast cell

Cardiac mast cells proliferate in cardiovascular diseases. In myocardial ischemia, mast cell mediators contribute to coronary vasoconstriction, arrhythmias, leukocyte recruitment, and tissue injury and repair. Arrhythmic dysfunction, coronary vasoconstriction, and contractile failure are also characteristic of cardiac anaphylaxis. In coronary atherosclerosis, mast cell mediators facilitate cholesterol accumulation and plaque destabilization. In cardiac failure, mast cell chymase causes myocyte apoptosis and fibroblast proliferation, leading to ventricular dysfunction. Chymase and tryptase also contribute to fibrosis in cardiomyopathies and myocarditis. In addition, mast cell tumor necrosis factor-alpha promotes myocardial remodeling. Cardiac remodeling and hypertrophy in end-stage hypertension are also induced by mast cell mediators and proteases. We recently discovered that cardiac mast cells contain and release renin, which initiates local angiotensin formation. Angiotensin causes coronary vasoconstriction, arrhythmias, fibrosis, apoptosis, and endothelin release, all demonstrated mechanisms of mast-cell-associated cardiac disease. The effects of angiotensin are further amplified by the release of norepinephrine from cardiac sympathetic nerves. Our discovery of renin in cardiac mast cells and its release in pathophysiological conditions uncovers an important new pathway in the development of mast-cell-associated heart diseases. Several steps in this novel pathway may constitute future therapeutic targets.

Nonantiarrhythmic drug therapy for atrial fibrillation

Recent studies have begun to elucidate the molecular mechanisms that promote the generation and progressive nature of atrial fibrillation. Evidence from both experimental and clinical investigations has implicated an important role for the renin-angiotensin-aldosterone system, inflammation, and oxidative stress, with data that suggest a potential beneficial effect for angiotensin-converting enzyme inhibitors, angiotensin receptor blockers, aldosterone receptor antagonists, antiinflammatory agents, 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitors (statins), and omega-3 polyunsaturated fatty acids. In addition, compounds that increase gap junctional conductance or that block 5-hydroxytryptamine-4 receptors have also shown promise in the experimental setting. Large-scale, prospective clinical trials will clarify the utility of these new therapeutic approaches to prevent atrial fibrillation in specific clinical settings.