Recent insights into the pathophysiology of atrial fibrillation

Randomized controlled trial of remote ischemic preconditioning and atrial fibrillation in patients undergoing cardiac surgery

AIM

To study whether remote ischemic preconditioning (RIPC) has an impact on clinical outcomes, such as post-operative atrial fibrillation (POAF).

METHODS

This was a prospective, single-center, single-blinded, randomized controlled study. One hundred and two patients were randomized to receive RIPC (3 cycles of 5 min ischemia and 5 min reperfusion in the upper arm after induction of anesthesia) or no RIPC (control). Primary outcome was POAF lasting for five minutes or longer during the first seven days after surgery. Secondary outcomes included length of hospital stay, incidence of inpatient mortality, myocardial infarction, and stroke.

RESULTS

POAF occurred at a rate of 54% in the RIPC group and 41.2% in the control group (P = 0.23). No statistically significant differences were noted in secondary outcomes between the two groups.

CONCLUSION

This is the first study in the United States to suggest that RIPC does not reduce POAF in patients with elective or urgent cardiac surgery. There were no differences in adverse effects in either group. Further studies are required to assess the relationship between RIPC and POAF.

Reactive oxygen species-targeted therapeutic interventions for atrial fibrillation

Atrial fibrillation (AF) is the most common arrhythmia that requires medical attention, and its incidence is increasing. Current ion channel blockade therapies and catheter ablation have significant limitations in treatment of AF, mainly because they do not address the underlying pathophysiology of the disease. Oxidative stress has been implicated as a major underlying pathology that promotes AF; however, conventional antioxidants have not shown impressive therapeutic effects. A more careful design of antioxidant therapies and better selection of patients likely are required to treat effectively AF with antioxidant agents. Current evidence suggest inhibition of prominent cardiac sources of reactive oxygen species (ROS) such as nicotinamide adenine dinucleotide phosphate (NADPH) oxidase and targeting subcellular compartments with the highest levels of ROS may prove to be effective therapies for AF. Increased serum markers of oxidative stress may be an important guide in selecting the AF patients who will most likely respond to antioxidant therapy.

A Randomized, Placebo-Controlled Trial of Omega-3 Fatty Acids for Inhibition of Supraventricular Arrhythmias After Cardiac Surgery: The FISH Trial

BACKGROUND

Omega-3 polyunsaturated fatty acids (n3-PUFAs) might have antiarrhythmic properties, but data conflict on whether n3-PUFAs reduce rates of atrial fibrillation (AF) after coronary artery bypass graft surgery (CABG). We hypothesized that n3-PUFAs would reduce post-CABG AF, and we tested this hypothesis in a well-powered, randomized, double-blind, placebo-controlled, multicenter clinical trial.

METHODS AND RESULTS

Patients undergoing CABG were randomized to pharmaceutical-grade n3-PUFAs 2 g orally twice daily (minimum of 6 g) or a matched placebo ≥24 hours before surgery. Gas chromatography was used to assess plasma fatty acid composition of samples collected on the day of screening, day of surgery, and postoperative day 4. Treatment continued either until the primary end point, clinically significant AF requiring treatment, occurred or for a maximum of 2 weeks after surgery. Two hundred sixty patients were enrolled and randomized. Before surgery, n3-PUFA dosing increased plasma n3-PUFA levels from 2.9% to 4% and reduced the n6:n3-PUFA ratio from 9.1 to 6.4 (both P<0.001). Similar changes were noted on postoperative day 4. There were no lipid changes in the placebo group. The rate of post-CABG AF was similar in both groups (30% n3-PUFAs versus 33% placebo, P=0.67). The post-CABG AF odds ratio for n3-PUFAs relative to placebo was 0.89 (95% confidence interval 0.52-1.53). There were no differences in any secondary end points.

CONCLUSIONS

Oral n3-PUFA supplementation begun 2 days before CABG did not reduce AF or other complications after surgery.

CLINICAL TRIAL REGISTRATION

URL: http://www.clinicaltrials.gov Unique identifier: NCT00446966. (J Am Heart Assoc. 2012;1:e000547 doi: 10.1161/JAHA.111.000547.).

Prevention of postoperative atrial fibrillation: novel and safe strategy based on the modulation of the antioxidant system

Postoperative atrial fibrillation (AF) is the most common arrhythmia following cardiac surgery with extracorporeal circulation. The pathogenesis of postoperative AF is multifactorial. Oxidative stress, caused by the unavoidable ischemia-reperfusion event occurring in this setting, is a major contributory factor. Reactive oxygen species (ROS)-derived effects could result in lipid peroxidation, protein carbonylation, or DNA oxidation of cardiac tissue, thus leading to functional and structural myocardial remodeling. The vulnerability of myocardial tissue to the oxidative challenge is also dependent on the activity of the antioxidant system. High ROS levels, overwhelming this system, should result in deleterious cellular effects, such as the induction of necrosis, apoptosis, or autophagy. Nevertheless, tissue exposure to low to moderate ROS levels could trigger a survival response with a trend to reinforce the antioxidant defense system. Administration of n-3 polyunsaturated fatty acids (PUFA), known to involve a moderate ROS production, is consistent with a diminished vulnerability to the development of postoperative AF. Accordingly, supplementation of n-3 PUFA successfully reduced the incidence of postoperative AF after coronary bypass grafting. This response is due to an up-regulation of antioxidant enzymes, as shown in experimental models. In turn, non-enzymatic antioxidant reinforcement through vitamin C administration prior to cardiac surgery has also reduced the postoperative AF incidence. Therefore, it should be expected that a mixed therapy result in an improvement of the cardioprotective effect by modulating both components of the antioxidant system. We present novel available evidence supporting the hypothesis of an effective prevention of postoperative AF including a two-step therapeutic strategy: n-3 PUFA followed by vitamin C supplementation to patients scheduled for cardiac surgery with extracorporeal circulation. The present study should encourage the design of clinical trials aimed to test the efficacy of this strategy to offer new therapeutic opportunities to patients challenged by ischemia-reperfusion events not solely in heart, but also in other organs such as kidney or liver in transplantation surgeries.

Ablation of sarcolipin results in atrial remodeling

Sarcolipin (SLN) is a key regulator of sarco(endo)plasmic reticulum (SR) Ca(2+)-ATPase (SERCA), and its expression is altered in diseased atrial myocardium. To determine the precise role of SLN in atrial Ca(2+) homeostasis, we developed a SLN knockout (sln-/-) mouse model and demonstrated that ablation of SLN enhances atrial SERCA pump activity. The present study is designed to determine the long-term effects of enhanced SERCA activity on atrial remodeling in the sln-/- mice. Calcium transient measurements show an increase in atrial SR Ca(2+) load and twitch Ca(2+) transients. Patch-clamping experiments demonstrate activation of the forward mode of sodium/calcium exchanger, increased L-type Ca(2+) channel activity, and prolongation of action potential duration at 90% repolarization in the atrial myocytes of sln-/- mice. Spontaneous Ca(2+) waves, delayed afterdepolarization, and triggered activities are frequent in the atrial myocytes of sln-/- mice. Furthermore, loss of SLN in atria is associated with increased interstitial fibrosis and altered expression of genes encoding collagen and other extracellular matrix proteins. Our results also show that the sln-/- mice are susceptible to atrial arrhythmias upon aging. Together, these findings indicate that ablation of SLN results in increased SERCA activity and SR Ca(2+) load, which, in turn, could cause abnormal intracellular Ca(2+) handling and atrial remodeling.

Use of vitamins C and E as a prophylactic therapy to prevent postoperative atrial fibrillation

Oxidative stress has been strongly involved in the underlying mechanism of atrial fibrillation, particularly in the arrhythmia occurring in patients undergoing cardiac surgery with extracorporeal circulation (postoperative atrial fibrillation). The ischemia/reperfusion injury thus occurring in the myocardial tissue contributes to the development of tissue remodeling, thought to be responsible for the functional heart impairment. Consequently, structural changes due to the cardiac tissue biomolecules attack by reactive oxygen and/or nitrogen species could account for functional changes in ion channels, transporters, membrane conductance, cytosolic transduction signals, and other events, all associated with the occurrence of arrhythmic consequences. The lack of success and significant side effects of anti-arrhythmic drugs have given rise to attempts aimed to develop alternative novel pharmacologic treatments. On this line, the biological properties of the antioxidant vitamins C and E suggest that they could decrease the vulnerability of the heart to the oxidative damage. Nevertheless, very few studies to assess their anti-arrhythmic effects have been reported in humans. The clinical and experimental evidence supporting the view that the pharmacological use of antioxidant vitamins could contribute to prevent postoperative atrial fibrillation is presented.

Oxidative stress and inflammation in atrial fibrillation: role in pathogenesis and potential as a therapeutic target

Atrial fibrillation (AF) is one of the most prevalent and vexing cardiovascular conditions. Available treatments for AF based on ion channel blockade are only poorly effective. The fundamental mechanisms that underlie AF are still not clearly understood, and likely vary depending on the etiology of AF. In older individuals with senile AF, likely mechanisms include abnormal calcium cycling, oxidant stress, and deleterious inflammatory responses. Clinical and experimental evidence is provided to support the role of oxidant and inflammatory mechanisms in AF. On the basis of these studies, the prospects of manipulating oxidant and inflammatory pathways as targets for therapeutic intervention are discussed.

Astaxanthin: a novel potential treatment for oxidative stress and inflammation in cardiovascular disease

Oxidative stress and inflammation are implicated in several different manifestations of cardiovascular disease (CVD). They are generated, in part, from the overproduction of reactive oxygen species (ROS) and reactive nitrogen species (RNS) that activate transcriptional messengers, such as nuclear factor-kappaB, tangibly contributing to endothelial dysfunction, the initiation and progression of atherosclerosis, irreversible damage after ischemic reperfusion, and even arrhythmia, such as atrial fibrillation. Despite this connection between oxidative stress and CVD, there are currently no recognized therapeutic interventions to address this important unmet need. Antioxidants that provide a broad, "upstream" approach via ROS/RNS quenching or free radical chain breaking seem an appropriate therapeutic option based on epidemiologic, dietary, and in vivo animal model data. However, human clinical trials with several different well-known agents, such as vitamin E and beta-carotene, have been disappointing. Does this mean antioxidants as a class are ineffective, or rather that the "right" compound(s) have yet to be found, their mechanisms of action understood, and their appropriate targeting and dosages determined? A large class of potent naturally-occurring antioxidants exploited by nature-the oxygenated carotenoids (xanthophylls)-have demonstrated utility in their natural form but have eluded development as successful targeted therapeutic agents up to the present time. This article characterizes the mechanism by which this novel group of antioxidants function and reviews their preclinical development. Results from multiple species support the antioxidant/anti-inflammatory properties of the prototype compound, astaxanthin, establishing it as an appropriate candidate for development as a therapeutic agent for cardiovascular oxidative stress and inflammation.

Routine ganglionic plexi ablation during Maze procedure improves hospital and early follow-up results of mitral surgery

OBJECTIVE

Ganglionic plexi are claimed to be potentially responsible for atrial fibrillation. We evaluated whether ganglionic plexi isolation improves the results of the Maze procedure during mitral valve surgery.

METHODS

A total of 75 patients with atrial fibrillation underwent radiofrequency ablation during mitral valve surgery without (group A) or with (group B) ganglionic plexi ablation with bipolar radiofrequency plus fat pad resection along the Waterston groove, left pulmonary veins, and Marshall's ligament. Ganglionic plexi were intraoperatively mapped, and fat pad specimens were sectioned and analyzed. Hospital and follow-up results were recorded. Amiodarone was discontinued at the sixth month.

RESULTS

Active ganglionic plexi were mainly located in the upper parts of fat pads. Active specimens demonstrated more ganglionic plexi than inactive specimens (P <or= .015 at different levels) but did not correlate with atrial fibrillation recurrence (P = not significant). Atrial fibrillation was higher in group A at aortic declamping (P = .03) and discharge (P = .03). Early events were comparable (P = .565). At 16.7 +/- 0.95 (standard error) months, the cumulative freedom from atrial fibrillation, atrial flutter, and atrial tachycardia with antiarrhythmic therapy was 63.2% +/- 7.3% and proved higher in group B (83.9% +/- 7.9% vs group A 52.8% +/- 8.7%; P = .035). However, after the sixth month, at 12.8 +/- 0.80 months, freedom from atrial fibrillation, atrial flutter, and atrial tachycardia without antiarrhythmic therapy was 72.5% +/- 7.7% and proved higher in group B (92.9% +/- 6.9% vs 62.5% +/- 9.4%; P = .023). A higher proportion of patients in group B showed normalized E/A ratio (61.3% vs group A 36.4%; P = .029). No differences were detected in follow-up freedom from congestive heart failure (group A: 83.4% +/- 7.0% vs group B: 93.5% +/- 4.4%; P = .978) and hospital readmission (group A: 84.2% +/- 5.9% vs group B: 92.6% +/- 5.1%; P = .376).

CONCLUSION

Ganglionic plexi isolation can improve hospital and follow-up results during mitral valve surgery and possibly ameliorate echocardiographic recovery of atrial function during follow-up.

Prevention of atrial fibrillation following cardiac surgery: basis for a novel therapeutic strategy based on non-hypoxic myocardial preconditioning

Atrial fibrillation is the most common complication of cardiac surgical procedures performed with cardiopulmonary bypass. It contributes to increased hospital length of stay and treatment costs. At present, preventive strategies offer only suboptimal benefits, despite improvements in anesthesia, surgical technique, and medical therapy. The pathogenesis of postoperative atrial fibrillation is considered to be multifactorial. However oxidative stress is a major contributory factor representing the unavoidable consequences of ischemia/reperfusion cycle occurring in this setting. Considerable evidence suggests the involvement of reactive oxygen species (ROS) in the pathogenic mechanism of this arrhythmia. Interestingly, the deleterious consequences of high ROS exposure, such as inflammation, cell death (apoptosis/necrosis) or fibrosis, may be abrogated by a myocardial preconditioning process caused by previous exposure to moderate ROS concentration known to trigger survival response mechanisms. The latter condition may be created by n-3 PUFA supplementation that could give rise to an adaptive response characterized by increased expression of myocardial antioxidant enzymes and/or anti-apoptotic pathways. In addition, a further reinforcement of myocardial antioxidant defenses could be obtained through vitamins C and E supplementation, an intervention also known to diminish enzymatic ROS production. Based on this paradigm, this review presents clinical and experimental evidence supporting the pathophysiological and molecular basis for a novel therapeutic approach aimed to diminish the incidence of postoperative atrial fibrillation through a non-hypoxic preconditioning plus a reinforcement of the antioxidant defense system in the myocardial tissue.