Targeting the renin–angiotensin–aldosterone system in atrial fibrillation: from pathophysiology to clinical trials

Antiarrhythmic Drug Therapy for Atrial Fibrillation

Atrial fibrillation (AF) is the most frequently encountered arrhythmia. Prevalence increases with advancing age and so as its associated comorbidities, like heart failure. Choice of pharmacologic therapy depends on whether the goal of treatment is maintaining sinus rhythm or tolerating AF with adequate control of ventricular rates. Antiarrhythmic therapy and conversion of AF into sinus rhythm comes with the side effect profile, and we should select best antiarrhythmic therapy, individualized to the patient. New antiarrhythmic drugs are being tested in clinical trials. Drugs that target remodeling and inflammation are being tested for their use as prevention of AF or as upstream therapy.

Understanding and Managing Atrial Fibrillation in Patients with Kidney Disease

Chronic kidney disease (CKD) is on the rise due to the increased rate of related comorbidities such as diabetes and hypertension. Patients with CKD are at higher risk of cardiovascular events and atrial fibrillation is more common in this patient population. It is estimated that the prevalence of chronic atrial fibrillation in patients with CKD is two to three times higher than general population. Furthermore, patients with CKD are less likely to stay in sinus rhythm. Atrial fibrillation presents a major burden in this population due to difficult treatment decisions in the setting of a lack of evidence from randomized clinical trials. Patients with CKD have higher risk of stroke with more than half having a CHADS2 score ≥ 2. Anticoagulation have been shown to significantly decrease embolic stroke risk, however bleeding complications such as hemorrhagic stroke is twofold higher with warfarin. Although newer novel anticoagulation drugs have shown promise with lower intracranial hemorrhage risk in comparison to warfarin, lack clinical trial data in CKD and the unavailability of an antidote remains an issue. In this review, we discuss the treatment options available including anticoagulation and the evidence behind them in patients with chronic kidney disease suffering from atrial fibrillation.

Renal Denervation And Pulmonary Vein Isolation In Patients With Drug Resistant Hypertension And Symptomatic Atrial Fibrillation

Systemic hypertension is the most consistent modifiable risk factor for atrial fibrillation (AF) in adults with consistent data from both animal models and human studies suggesting a consistent pattern of autonomic imbalance underlying both conditions. Relative sympathetic nervous system activation is a demonstrably common attendant to the local mechanisms in pulmonary veins that sustain persistent or recurrent AF and may represent a new objective for adjunctive treatment. Established management of AF aims to achieve durable control through either pharmacologic or catheter-based interventions. The introduction of catheter-based renal denervation as a safe, alternate approach to target the sympathetic nervous system therapeutically represents a potential opportunity to treat the shared pathophysiological mechanisms with minimal additional treatment burden when added in this context. Preliminary investigations have demonstrated both proof-of-concept and the technical feasibility of combined renal denervation and AF ablation procedures with the suggestion of benefit in terms of freedom from AF recurrence. The available data is promising but absolute confirmation of efficacy remains unconfirmed in the absence of more definitive evidence. This paper reviews the role of autonomic imbalance in the initiation and maintenance of AF by summarizing the observations from both experimental models and clinical studies from the perspective of potential therapeutic overlap between catheter-based treatments.

During ablation for atrial fibrillation, is simultaneous renal artery ablation appropriate?

Over the past few decades, the mainstay of hypertension management has been pharmacological therapy; however, there is now a growing body of evidence that drug-resistant hypertension can be managed effectively by renal artery ablation. Several studies have documented the feasibility and safety of this treatment, although data regarding long-term outcomes are still emerging. Atrial fibrillation (AF) and hypertension commonly coexist, and recent work has demonstrated improved outcomes from catheter ablation of AF with concomitant renal artery denervation at little extra cost in terms of time and resource. The aim of this review is to explore the link between hypertension and AF, the synergistic effect of renal artery ablation on AF ablation, explain how this may work and address unanswered questions.

The role of inflammatory markers in atrial fibrillation: a review

This review is focused on the role of latent inflammation in atrial fibrillation (AF) pathogenesis. The modern views and available evidence on the association between the levels of inflammatory markers and AF development and recurrence are presented. The justification for the use of pleiotropic effects of pharmacological therapy in AF prevention and treatment is discussed.

Abnormal vascular function in PR-interval prolongation

BACKGROUND

Underlying mechanisms of PR-interval prolongation leading to increased risk of adverse cardiovascular outcomes, including atrial fibrillation, are unclear. This study aims to investigate the relation between PR interval and changes in vascular function.

HYPOTHESIS

We hypothesize that there exists an intermediate pathological stage between electrocardiographic PR prolongation and adverse cardiovascular outcomes, which could be reflected by changes in surrogate measurements of vascular function.

METHODS

We recruited 88 healthy subjects (mean age 57.5 ± 9.8 y, 46% male) from a community-based health screening program who had no history of cardiovascular disease or diabetes mellitus. PR interval was determined from a resting 12-lead electrocardiogram. Vascular function was noninvasively assessed by flow-mediated dilation (FMD) using high-resolution ultrasound and brachial-ankle pulse wave velocity (PWV) using a vascular profiling system.

RESULTS

Only 3 subjects had a PR-interval length longer than the conventional cutoff of 200 ms. The PR-interval length was associated inversely with FMD (Pearson r = -0.30, P = 0.004) and positively with PWV (r = 0.40, P < 0.001). Adjusting for potential confounders, increased PR-interval length by each 25 ms was independently associated with reduced FMD by -1 unit (absolute %, B = -0.04 [95% confidence interval: -0.080 to -0.002, P = 0.040)] and increased PWV by +103 cm/second (B = +4.1 [95% confidence interval: 0.6-7.6, P = 0.023]).

CONCLUSIONS

This study shows that PR-interval length, even in the conventionally normal range, is independently associated with endothelial dysfunction and increased arterial stiffness in healthy subjects free of atherosclerotic disease. This suggests the presence of a systemic, intermediate pathologic stage of the vasculature in PR prolongation before clinically manifest cardiovascular events, and could represent a mediating mechanism.

Predictors of atrial fibrillation occurrence after coronary artery bypass graft surgery

PURPOSE

Postoperative atrial fibrillation (AF) is the most common complication after coronary artery bypass graft (CABG) surgery, with an incidence of 20%-50%. The objective of this study was to investigate perioperative risk factors of postoperative sustained AF by the way of logistic regression analysis.

METHODS

Data for the last 98 patients who had undergone CABG surgery before January 2010 were retrospectively collected and analyzed.

RESULTS

Postoperative sustained AF was detected in 34 (34.7%) patients. Mean arterial blood pressure, previous hypertension (HT), previous AF, previous chronic obstructive pulmonary disease, aortic cross-clamp time, cardiopulmonary bypass time, postoperative urea, postoperative creatinine, postoperative potassium, extubation time, chest tube drainage, units of transfused packed red blood cells (pRBC), and postoperative pneumonia were associated with higher occurrence of postoperative sustained AF according to the univariate analysis. Upon logistic regression analysis, pRBC transfusion, previous AF, and preoperative HT remained independent predictors for the development of postoperative sustained AF.

CONCLUSION

On-pump versus off-pump CABG is not significantly associated with AF development so long as the operating time does not extend over a certain time period. pRBC transfusion was the single risk factor that is amenable to intervention at the time of operation. Unneeded transfusion of pRBCs must be prohibited. Also, serious precautions must be taken against postoperative pneumonia to avoid postoperative AF occurrence.

Non-antiarrhythmic drugs to prevent atrial fibrillation

Atrial fibrillation (AF) is the most frequent arrhythmia found in clinical practice. The majority of patients with AF are still candidates for antiarrhythmic drug treatment, not only for acute reversion to sinus rhythm but also for long-term treatment to prevent recurrences of AF. Currently available antiarrhythmic drugs, however, are unable to provide complete efficacy in all patients, and present problematic risks of proarrhythmia. The progressively increasing prevalence of AF supports the need to develop improved therapeutic approaches for the clinical management of arrhythmia. Accordingly, new treatment techniques aimed at suppressing the origin of the arrhythmogenic foci have been developed in the last decade. However, ablative treatments are only available for selected patients. Because of these factors, and also because primary prevention of AF should be our goal, the introduction of non-antiarrhythmic agents that could prevent both new-onset AF and recurrences of AF may eventually improve patient outcomes and reduce the incidence of this epidemic disease. The potential clinical value of these non-antiarrhythmic options is currently under active investigation. There is now clinical and experimental evidence that many drugs may have beneficial effects in preventing AF through several possible mechanisms. Non-antiarrhythmic drugs, such as ACE inhibitors and angiotensin receptor blockers, HMG-CoA reductase inhibitors (statins), corticosteroids, and N-3 polyunsaturated fatty acids may have a positive effect in patients with AF or in preventing AF in patients at risk.

Demographic determinants and effect of pre-operative angiotensin converting enzyme inhibitors and angiotensin receptor blockers on the occurrence of atrial fibrillation after CABG surgery

BACKGROUND

Atrial fibrillation (AF) occurs in about 27% to 40% of post cardiac surgery patients. AF following coronary artery bypass graft surgery (CABG) is associated with a two-fold increase in morbidity and mortality. Various demographic risk factors and medications have been studied to predict the occurrence of this arrhythmia. The role of angiotensin related medications on the occurrence of AF in CABG patients is not determined.

METHODS

Retrospective clinical and statistical analysis was made of all the patients who had undergone CABG surgery at Lehigh Valley Hospital during the years 2005 and 2006. Patients with chronic AF and those undergoing valvular surgery with CABG were excluded. Statistic analysis included chi-square test for categorical and student t-test for continuous variables.

RESULTS

757 patients (560 males and 197 females) were studied. AF occurred in 19% of the patients. Age (70.5 vs. 65.1, p < 0.005. OR per year of age: 1.02, 95%CI: 1.018-1.023) and presence of hypertension (OR: 1.92, 95%CI: 1.086-3.140, p = 0.025) were significantly associated with occurrence of AF. Neither ARBs (OR: 0.78, 95%CI: 0.431-1.410, p = 0.41) nor ACE inhibitors (OR: 1.01, 95%CI: 0.753-1.608, p = 0.63) reduced the occurrence of post operative AF. Patients with post operative AF had a significantly longer hospital stay (9.5 +/- 5.4 days vs. 6.9 +/- 4.3 days, p = 0.001).

CONCLUSIONS

Advanced age and presence of hypertension were independent predictors of post-CABG AF. Patients with post operative AF had significantly longer hospital stay. Neither ARBs nor ACE inhibitors were associated with reduction of post-surgical AF. Further studies are needed to better delineate the role of angiotensin related medications on reduction of post-surgical AF.

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.

Drug therapy for atrial fibrillation

Atrial fibrillation (AF) is the most frequently diagnosed arrhythmia. Prevalence increases with age, and the overall incidence is expected to increase as the population continues to age. Choice of pharmacologic therapy for atrial fibrillation depends on whether or not the goal of treatment is maintaining sinus rhythm or tolerating atrial fibrillation with adequate control of ventricular rates. New antiarrhythmic drugs are being tested in clinical trials. Drugs that target remodeling and inflammation are being tested for their use as prevention of AF or as adjunctive therapy.

Management of atrial fibrillation

Atrial fibrillation is the most common sustained cardiac rhythm disorder, and confers a substantial mortality and morbidity from stroke, thromboembolism, heart failure, and impaired quality of life. With the increasingly elderly population in the developed world, as well as improvements in the management of myocardial infarction and heart failure, the prevalence of atrial fibrillation is increasing, resulting in a major public-health problem. This Review aims to provide an overview on the modern management of atrial fibrillation, with particular emphasis on pharmacological and non-pharmacological approaches. Irrespective of a rate-control or rhythm-control strategy, stroke prevention with appropriate thromboprophylaxis still remains central to the management of this common arrhythmia. Electrophysiological approaches could hold some promise for a curative approach in atrial fibrillation.

Inhibition of the renin-angiotensin system and the prevention of stroke

BP is the most important determinant of the risk of stroke. A small reduction in BP results in a substantial reduction of both ischemic and hemorrhagic stroke. Any of the commonly used antihypertensive drugs lower the incidence of stroke, with larger reductions in BP resulting in larger reductions in risk. Experimental evidence has linked the renin-angiotensin system (RAS) to the development and progression of cerebrovascular disease. Inhibition of the RAS has beneficial cerebrovascular effects and may reduce the risk of stroke in a manner possibly independent from the alterations of BP. Some clinical trials even suggest that ACE inhibitors and angiotensin II type 1 receptor antagonists (angiotensin receptor blockers [ARBs]) exert cerebroprotective effects beyond BP lowering, but the evidence is controversial. Studies on specific protective actions of antihypertensive drugs are generally hampered by the fact that any treatment-related difference in BP may play a dominant role in the prevention of stroke. There are also indications that the protective potency of ARBs might be superior to that of ACE inhibitors, due to their differential activation of angiotensin II type 2 receptors, but the clinical relevance of this mechanism is unclear. Some studies in primary prevention of stroke, acute stroke, and secondary prevention show advantages for ARBs beyond controlling BP alone. In primary prevention, the LIFE randomized trial showed a significant difference in stroke rate in favor of losartan compared with atenolol despite similar reductions in BP. In acute stroke, the role of hypertension and its treatment remains controversial. ACCESS, however, suggested that an ARB is safe in hypertensive acute stroke patients and may offer advantages independent from BP control. In secondary stroke prevention, there are very few antihypertensive trials. These trials show that BP lowering is at least as successful as in primary prevention, but the absolute stroke risk is much higher. An ACE inhibitor was effective compared with placebo in the PROGRESS trial. The MOSES study showed that eprosartan prevented vascular events more effectively than nitrendipine, despite similar BP-lowering effects. Hypertension is not only the most important risk factor for stroke, but is also closely correlated with cognitive decline and dementia. Therefore, prevention of cognitive decline or even improvement of slightly diminished brain function should be an important goal for antihypertensive treatment in the future. Some clinical data suggest advantages for ACE inhibitors, ARBs, and calcium channel antagonists. Currently, however, the existing data are not sufficient for clinical recommendations. Therefore, ongoing trials will further define the exact role of inhibitors of the RAS and are urgently needed in secondary prevention, in acute stroke, and in the prevention of cognitive decline.

Angiotensin converting enzyme inhibitor and angiotensin receptor blockade use in relation to outcomes in anticoagulated patients with atrial fibrillation

BACKGROUND

The renin-angiotensin-aldosterone-system (RAAS) plays an important role in atrial fibrillation (AF). Evidence shows that blocking the RAAS with angiotensin converting enzyme inhibitors (ACEIs) and angiotensin receptor blockers (ARBs) has a definite role in preventing new onset AF and in maintaining sinus rhythm in recurrent AF. Our aim was to determine if ACEI/ARB treatment was associated with clinical outcomes [stroke/systemic embolic events (SEE), mortality] in a controlled, anticoagulated AF population.

METHODS

An ancillary retrospective cross-sectional and longitudinal analysis of participants in the Stroke Prevention using an ORal Thrombin Inhibitor in AF (SPORTIF) III and V trials, in relation to use (or nonuse) of ACEI/ARBs.

RESULTS

Rates of stroke/SEEs, mortality or major bleeding were no different between users and nonusers in the whole cohort, or in relation to the presence/absence of hypertension, coronary artery disease and previous stroke/transient ischaemic attack, nor amongst those aged <75 years. Patients aged > or = 75 years taking ACEIs or ARBs had lower mortality (HR 0.71, 95% CI 0.52-0.95), but no significant influence on other end-points was noted. Diabetics and those with left ventricular dysfunction on ximelagatran had a higher odds ratio of abnormal liver enzyme levels. There was no apparent benefit of ACEIs or ARBs on other event rates.

CONCLUSIONS

This analysis from two large randomized trials of anticoagulation has not demonstrated a significant benefit of ACEI or ARB use amongst AF patients, except amongst elderly subjects.

Renin-angiotensin system and cardiovascular risk

The renin-angiotensin system is a major regulatory system of cardiovascular and renal function. Basic research has revealed exciting new aspects, which could lead to novel or modified therapeutic approaches. Renin-angiotensin system blockade exerts potent antiatherosclerotic effects, which are mediated by their antihypertensive, anti-inflammatory, antiproliferative, and oxidative stress lowering properties. Inhibitors of the system-ie, angiotensin converting enzyme inhibitors and angiotensin receptor blockers, are now first-line treatments for hypertensive target organ damage and progressive renal disease. Their effects are greater than expected by their ability to lower blood pressure alone. Angiotensin receptor blockers reduce the frequency of atrial fibrillation and stroke. Renin-angiotensin system blockade delays or avoids the onset of type 2 diabetes and prevents cardiovascular and renal events in diabetic patients. Thus, blockade of this system will remain a cornerstone of our strategies to reduce cardiovascular risk.

The role of oxidative stress in the pathogenesis and perpetuation of atrial fibrillation

Atrial fibrillation (AF) is the most common arrhythmia encountered in clinical practice representing a major health hazard. Owing to relative inefficacy and side effects of classic antiarrhythmic drugs, current interest has shifted to treatments that target AF substrate. Accumulating evidence suggests that there is a link between oxidative processes and AF. In atrial myocardium during AF, there is substantial oxidative damage that may contribute to atrial remodeling. Several pathophysiological changes that possibly associated with increased oxidative stress in AF have been proposed. These include changes in gene transcriptional profiles and mitochondrial DNA, increased activity of enzymes such as NAD(P)H oxidase and xanthine oxidase, inflammatory processes, activation of the renin-angiotensin system and others. Moreover, oxidative stress is involved in the pathophysiology of several predisposing factors and cardiovascular disorders that correspondingly associated with AF. Preliminary studies using dietary antioxidants such as vitamin C have shown promising results. More evidence has been obtained from studies examining agents with pleiotropic effects, including antioxidant, such as inhibitors of the renin-angiotensin system, statins, corticosteroids and carvedilol. Further investigations are needed in order to elucidate the impact of oxidative stress on atrial remodeling. The clarification of these processes in the setting of AF may lead to the development of novel therapeutic strategies.

Clinical trials, the renin angiotensin system and atrial fibrillation

PURPOSE OF REVIEW

Atrial fibrillation is the most common clinical arrhythmia. Current treatment strategies are far from optimal. One new research direction is to target the atrial fibrillation substrate and to examine whether drugs can produce atrial structural and/or electrophysiological remodeling and whether this results in a reduction in atrial fibrillation burden.

RECENT FINDINGS

Two prospective randomized studies have shown that the addition of an angiotensin converting enzyme inhibitor or an angiotensin receptor blocker to amiodarone reduces the recurrence rate of atrial fibrillation after electrical cardioversion. There are ten completed prospective clinical trials with atrial fibrillation as a secondary endpoint or assessed in post-hoc analysis. Five of these studies have reported a positive impact of angiotensin converting enzyme inhibitors or angiotensin receptor blockers on atrial fibrillation burden. A meta-analysis showed that active drugs reduced the overall risk of development of atrial fibrillation by 28%. Patients in the heart failure trials obtained most benefit from these drugs (relative risk reduction 44%, P = 0.07).

SUMMARY

The initial basic science and clinical trial data suggest that modulation of the renin angiotensin system may be an effective treatment for atrial fibrillation. The following, however, remain to be clarified: do these drugs have a clinically meaningful impact on atrial fibrillation burden; if there is an impact, is it similar in all atrial fibrillation patients or just in certain subsets; do angiotensin converting enzyme inhibitors and angiotensin receptor blockers have similar benefits; and is there a role for aldosterone antagonists?