Pathophysiology and prevention of atrial fibrillation

Levosimendan Use Decreases Atrial Fibrillation in Patients after Coronary Artery Bypass Grafting: A Pilot Study

Background: Atrial fibrillation (AF) often occurs after coronary artery bypass grafting (CABG) and can result in increased morbidity and mortality due to complications. In the present study, our goal was to investigate whether the use of levosimendan can reduce the frequency of AF after coronary artery bypass grafting in patients with poor left ventricle function. Material and Methods: To investigate the effectiveness of levosimendan in the prophylaxis of AF, we conducted a prospective, randomized, placebo-controlled clinical study on 200 consecutive patients in whom we performed elective CABG operations. Baseline characteristics were similar in both groups. A control group of 100 patients were treated with placebo (500 mL saline solution), whereas the levosimendan group (n = 100 patients) was treated with levosimendan. High-sensitivity C-reactive protein, cardiac troponin, and creatine kinase–MB levels were measured before surgery and 5 days postoperatively. Results: AF occurred in 12% of the levosimendan group and 36% of the control group. The occurrence of AF was significantly lower in the levosimendan group (P < 0.05). The duration of AF in the levosimendan group was significantly shorter than that in the control group (4.83 ± 1.12 and 6.50 ± 1.55 hours, respectively; P = 0.028). Our research showed that C-reactive protein was higher postoperatively in the control group than in the levosimendan group (P < 0.05). Conclusions: The incidence of postoperative AF in the levosimendan group was reduced significantly in patients with poor left ventricle function after CABG operations.

Performance of an external transtelephonic loop recorder for automated detection of paroxysmal atrial fibrillation

BACKGROUND

Although atrial fibrillation (AF) is the most commonly encountered arrhythmia, some of the properties make its detection challenging. In daily practice, underdiagnosis can lead to less effective treatment in prevention of stroke. Based on data from studies on treatment of AF, more intensive follow-up strategies, including 7-day Holter recording, 30-day event recording, and even implantable cardiac monitoring devices, are suggested. The study purpose is to evaluate the performance of a continuous single-channel loop recorder with automatic AF detection and transtelephonic electrocardiogram (ECG) transmission capabilities.

METHODS AND RESULTS

A consecutive cohort of 153 patients admitted to the stroke unit with a presumptive diagnosis of ischemic cerebrovascular accident was screened for AF. Twenty-four-hour rhythm observation was performed using a single-channel external loop recorder (ELR) configured for automated AF detection. A total of 45 patients with a known history of AF, AF on the admission ECG, or incomplete registrations were excluded. Extensive additional frequency-based settings were used to establish a reference registration. In total, 2923 recordings were transmitted. We evaluated all events, of which 1190 were designated by the device as AF. The sensitivity, specificity, PPV, and NPV for identifying AF using the ELR were, respectively, 93%, 51%, 5%, and 99%.

CONCLUSIONS

In this ELR validation study, the dedicated AF detection algorithm showed to be highly sensitive but not specific for AF. Applicability of an ELR might be limited for efficacious detection of AF, as manual verification is mandatory for a vast amount of recordings.

Connexin Remodeling Contributes to Atrial Fibrillation

Atrial fibrillation significantly contributes to mortality and morbidity through increased risk of stroke, heart failure and myocardial infarction. Investigations of mechanisms responsible for the development and maintenance of atrial fibrillation have highlighted the importance of gap junctional remodeling. Connexins 40 and 43, the major atrial gap junctional proteins, undergo considerable alterations in expression and localization in atrial fibrillation, creating an environment conducive to sustained reentry. Atrial fibrillation is initiated and/or maintained in this reentrant substrate. This review will focus on connexin remodeling in the context of underlying mechanism and possible therapeutic target for atrial fibrillation.

HEART AND AGE (PART II): CLINICAL MANIFESTATIONS OF AGEING

Ageing is an inevitable process which affects quality of life and reduces life expectancy. Age-related cardiac changes reduce compensatory reserves of the heart and accelerate the disease development. Such changes in cardiac structure and function, observed in the absence of cardiovascular disease (CVD), are considered age-related. However, taking into account the high prevalence of CVD in the elderly, it is problematic to define the genuine cardiac ageing. This review discusses a range of subclinical cardiac conditions which are common in older people. 

Aging-associated changes in L-type calcium channels in the left atria of dogs

Action potential (AP) contours vary considerably between the fibers of normal adult and aged left atria. The underlying ionic and molecular mechanisms that mediate these differences remain unknown. The aim of the present study was to investigate whether the L-type calcium current (I_Ca.L) and the L-type Ca²⁺ channel of the left atria may be altered with age to contribute to atrial fibrillation (AF). Two groups of mongrel dogs (normal adults, 2-2.5 years old and older dogs, >8 years old) were used in this study. The inducibility of AF was quantitated using the cumulative window of vulnerability (WOV). A whole-cell patch-clamp was used to record APs and I_Ca.L in left atrial (LA) cells obtained from the two groups of dogs. Protein and mRNA expression levels of the a1C (Cav1.2) subunit of the L-type calcium channel were assessed using western blotting and quantitative PCR (qPCR), respectively. Although the resting potential, AP amplitude and did not differ with age, the plateau potential was more negative and the APD₉₀ was longer in the aged cells compared with that in normal adult cells. Aged LA cells exhibited lower peak I_Ca.L current densities than normal adult LA cells (P<0.05). In addition, the Cav1.2 mRNA and protein expression levels in LA cells were decreased in the aged group compared with those in the normal adult group. The lower AP plateau potential and the decreased I_Ca.L of LA cells in aged dogs may contribute to the slow and discontinuous conduction of the left atria. Furthermore, the reduction of the expression levels of Cav1.2 with age may be the molecular mechanism that mediates the decline in I_Ca.L with increasing age.

Very long-term results of surgical and transcatheter ablation of long-standing persistent atrial fibrillation

BACKGROUND

New hybrid approaches for atrial fibrillation (AF) ablation, combining surgical and percutaneous procedures, are emerging to enhance the long-term success rate of these 2 procedures severally considered. Recent guidelines underline the need for long-term follow-up to really assess the efficacy of AF ablation.

METHODS

From 2000 to 2002, 33 patients with long-standing persistent AF and valvular heart disease underwent valve surgery and cryoablation (pulmonary veins isolation and mitral isthmus and roof line lesions). The surgically created ablation scheme was validated with electroanatomic mapping and percutaneous radiofrequency ablation was performed in case of lesion incompleteness.

RESULTS

In 19 of 33 patients (58%) the electroanatomic mapping showed a complete lesion scheme, which increased to 79% (26 of 33) with the addition of radiofrequency ablation. At the mean follow-up of 10.7 ± 3.1 years, 73% (24 of 33) of patients were in sinus rhythm (SR), whereas 27% had permanent AF. At the end of follow-up 81% of patients with a complete lesion scheme were in SR, while 43% with an incomplete one maintained SR (p = 0.048).

CONCLUSIONS

In patients with long-standing persistent AF and valvular heart disease, the hybrid approach with surgical cryoablation consisting of pulmonary veins isolation and left atrial linear lesions combined with transcatheter radiofrequency ablation was highly effective in maintaining SR for a very long-term follow-up. Electrophysiological evaluation, to validate the transmurality of the surgical lesions and to complete the lesion scheme applying radiofrequency energy, improved the long-term efficacy.

Age-related changes in cellular electrophysiology and calcium handling for atrial fibrillation

This study was to investigate whether or not the dysfunction of atrial repolarization and abnormality of the intracellular Ca²⁺ handling protein was augmented with ageing. Four groups of dogs were studied, adult and aged dogs in sinus rhythm (SR) and atrial fibrillation (AF) induced by rapid atrial pacing. We used whole cell patch clamp recording techniques to measure L-type Ca²⁺ current in cardiomyocytes dispersed from the left atria. Expressions of the Ca²⁺ handling protein were measured by real-time quantitative reverse transcription-polymerase chain reaction and Western blot methods. Cardiomyocytes from old atria showed longer action potential (AP) duration to 90% repolarization, lower AP plateau potential and peak L-type Ca²⁺ current densities at both age groups in SR. AF led to a higher maximum diastolic potential, an increase of amplitude of phase 0, decreases of AP duration to 90% repolarization, plateau potential and peak L-type Ca²⁺ current densities. Compared to the adult group, mRNA and protein expressions of the L-type calcium channel a1c were decreased, whereas expressions of calcium adenosine triphosphatase were increased in the aged group. Compared to SR group, expressions of Ca²⁺ handling protein except for phospholamban were significantly decreased in both age groups with AF. We conclude that these ageing-induced electrophysiological and molecular changes showed that general pathophysiological adaptations might provide a substrate conducive to AF.

Does Off-pump Coronary Artery Bypass Reduce the Prevalence ofAtrial Fibrillation?

INTRODUCTION

To examine whether or not off-pump CABG (Coronary Artery Bypass Reduce) reduces the incidence of AF after cardiac surgery.

METHODS

The study was carried out in 939 consecutive coronary artery disease patients with sinus rhythm from which 383 patients underwent off-pump CABG, and 556 patients were operated through on-pump CABG. All patients were monitored postoperatively during intensive care unit (ICU) stay. Then, the incidence and predictive risk factors of post operative AF (POAF) in two groups were determined and compared with each other.

RESULTS

Overall, the mean age of the patients was 56.0±12.8 years with 234 patients (24.9%) being older than 65 years. POAF developed in 38 patients (9.9%) of the off-pump and in 93 patients (16.7%) of the on-pump CABG. There was significant difference between two groups when considering the incidence of POAF (P=0.002). Among preoperative risk factors, age>65 years had a significant association with the incidence of AF in both groups. This study also showed that most of the POAF cases converted to sinus rhythm after treatment. Moreover, these finding demonstrated that conversion to sinus rhythm is significantly more probable in off-pump group (P=0.006).

CONCLUSION

A reduced prevalence of POAF could be observed in patients with off-pump as compared with on-pump techniques. Furthermore, conversion to sinus rhythm in off-pump group was significantly more probable than on-pump group.

Intrinsic left atrial histoanatomy as the basis for reentrant excitation causing atrial fibrillation/flutter in rats

BACKGROUND

Although the pulmonary veins are accepted as preferential trigger sites for paroxysmal atrial fibrillation/flutter (AF/AFL), the intrinsic basis for reentrant excitation is undetermined in persistent AF/AFL.

OBJECTIVE

To identify histoanatomic substrates for reentrant AF/AFL in rats.

METHODS

Spatiotemporal patterns of impulse propagation were visualized optically on the posterior surface of the atria in di-4-ANEPPS-stained Langendorff-perfused rat heart/lung preparations. The relevant histology was also analyzed.

RESULTS

Burst (S1-S2) pacing at the right atrium provoked AF/AFL in 15 of 19 hearts, and most cases developed by organized reentrant excitation through the coronary sinus (CS) and left atrial (LA) roof, with nonorganized irregular propagation in 3 cases. The reentrant circuit developed along 2 pathways of propagation: a slower pathway at the LA roof (conduction velocity, 42.4 ± 16.6 cm/s) and a faster pathway along the CS (conduction velocity, 53.3 ± 9.2 cm/s). Upon extra stimulus (S2) after consecutive S1 pacing, the impulse at the roof propagated retrogradely from the CS, resulting in reentrant propagation anchored by the atrial septum and posterior LA. Histologic quantification revealed significantly lower myocardial density in the posterior LA and the septum than elsewhere in the atria. Moreover, myocytes in the LA roof, than in the CS, were of lower density, more randomly arranged in the direction of conduction, and characterized by more disorganized distribution of connexin 43 over the entire cell membrane, which is consistent with the slower impulse propagation there.

CONCLUSION

The intrinsic histoanatomic heterogeneity in the LA would constitute a pro-reentrant substrate responsible for perpetuating AF/AFL.

The role of action potential alternans in the initiation of atrial fibrillation in humans: a review and future directions

This review highlights the role of atrial monophasic action potential duration (APD) in understanding atrial electrical properties in paroxysmal, persistent, and permanent atrial fibrillation (AF) states. Alternans of APD and rate maladaptation in a spatially divergent way appear mechanistically involved in AF initiation, development, and persistence. The underlying pathophysiology warrants further investigation.

Role of Stress in Cardiac Arrhythmias

Stress is a major trigger of cardiac arrhythmias; it exerts profound effects on electrophysiology of the cardiomyocytes and the cardiac rhythm. Psychological and physiological stressors impact the cardiovascular system through the autonomic nervous system (ANS). While stressors vary, properties of the stress response at the level of cardiovascular system (collectively referred to as the autonomic cardiovascular responses) are similar and can be studied independently from the properties of specific stressors. Here, we will review the clinical and experimental evidence linking common stressors and atrial arrhythmias. Specifically, we will describe the impact of psychological and circadian stressors on ANS activity and arrhythmogenesis. We will also review studies examining relationships between autonomic cardiovascular responses and cardiac arrhythmias in ambulatory and laboratory settings.

Post-operative Atrial Fibrillation - Pathophysiology, Treatment and Prevention

Atrial fibrillation occurring after cardiac surgery has been the subject of intensive research over the past decades. However, the incidence remains high, despite numerous preventive and treatment strategies. In addition, several reports show that the impact of post-operative atrial fibrillation (POAF) is high. It is an independent risk factor for mortality after several years. These findings make clear that the pathophysiology of POAF is not fully understood and POAF-associated risks to some extent might be underestimated. On the one hand, excessive triggers during the acute post operative phase after cardiac surgery might initiate AF even in atria with low vulnerability. On the other hand, many patients undergoing surgery have an atrial substrate at the time of operation promoting AF not only in the post-operative phase but also in the days and weeks thereafter. Progress in our understanding of the AF mechanisms in general has provided valuable insights into processes involved in atrial structural remodeling due to advanced age, hypertension, obesity, and congestive heart failure. These patient characteristics strongly contribute to cardiac disease, predict POAF and likely have an impact on the risk of thrombus formation in the weeks and months after cardiac surgery. For a better understanding of the mechanisms involved, it is important to not only recognize the occurrence of POAF by continuous monitoring after surgery, but also to identity the extent of atrial vulnerability to AF in these patients.

Atrial Remodelling : Role in Atrial Fibrillation Ablation

There have been considerable advances in understanding the relationship of atrial fibrillation (AF) and atrial remodelling suggesting that remodelling states have a significant impact on treatment results. Therefore, we reviewed the literature about the role of atrial remodelling in AF treatment, focussing on AF ablation. Atrial fibrillatory activity, dominant frequencies (DF), complex fractionated atrial electrograms (CFAE) as well as function, volume, and fibrosis of the - especially left - atrium are most important characteristics for electrical, contractile, and structural remodelling predicting success of AF treatment. In particular, the results of AF ablation, either using catheter-based or surgical techniques, predominantly depend on the degree of structural remodelling, namely dilatation and fibrosis of the left atrium. The available data suggest that recognizing parameters of remodelling as predictors for AF treatment facilitates differentiation between patients who may or may not benefit from the procedure and individualization of AF treatment by adapting lesion sets, by ablating additional targets, by reducing left atrial size, or by applying extended pharmacological treatment.

Rationale for minimally invasive pulmonary vein isolation and partial autonomic denervation for surgical treatment of atrial fibrillation

We seek to demonstrate the rationale of a minimally invasive surgical approach to the treatment of atrial fibrillation which combines pulmonary vein antral isolation with targeted partial autonomic denervation. The literature supporting the rationale of this approach is reviewed. There is evidence-based literature that supports both pulmonary vein electrical isolation and targeted partial autonomic denervation in the treatment of atrial fibrillation. These techniques can be combined in a minimally invasive surgical approach.

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.

Risk Stratification in Atrial Fibrillation Patients - A Review Focused on Mortality

Atrial fibrillation (AF) is associated with increased mortality that is largely due to the severe co-morbidities of patients with this rhythm disturbance rather than to its electrocardiographic features. Available evidence indicated that ageing, heart failure and stroke are the most important predictors of all-cause mortality. Additional clinical parameters such as smoking, renal impairment, chronic obstructive pulmonary disease may also identify patients at risk. The prevention of thromboembolic events is based on oral anticoagulant therapy, which reduces the severity and mortality of ischaemic strokes but slightly increase the rate of haemorrhagic events. Most of the traditional risk stratifiers commonly used in patients in sinus rhythm such as New York Heart Association (NYHA) functional class, left ventricular ejection fraction (LVEF) and resting heart rate seem to be less effective in AF patients thus leaving to the physician judgment the main responsibility of identifying patients with an increased mortality risk.

Role of Cholinergic Innervation and RGS2 in Atrial Arrhythmia

The heart receives sympathetic and parasympathetic efferent innervation as well as the ability to process information internally via an intrinsic cardiac autonomic nervous system (ICANS). For over a century, the role of the parasympathetics via vagal acetylcholine release was related to controlling primarily heart rate. Although in the late 1800s shown to play a role in atrial arrhythmia, the myocardium took precedence from the mid-1950s until in the last decade a resurgence of interest in the autonomics along with signaling cascades, regulators, and ion channels. Originally ignored as being benign and thus untreated, recent emphasis has focused on atrial arrhythmia as atrial fibrillation (AF) is the most common arrhythmia seen by the general practitioner. It is now recognized to have significant mortality and morbidity due to resultant stroke and heart failure. With the aging population, there will be an unprecedented increased burden on health care resources. Although it has been known for more than half a century that cholinergic stimulation can initiate AF, the classical concept focused on the M2 receptor and its signaling cascade including RGS4, as these had been shown to have predominant effects on nodal function (heart rate and conduction block) as well as contractility. However, recent evidence suggests that the M3 receptor may also playa role in initiation and perpetuation of AF and thus RGS2, a putative regulator of the M3 receptor, may be a target for therapeutic intervention. Mice lacking RGS2 (RGS2^−/−), were found to have significantly altered electrophysiological atrial responses and were more susceptible to electrically induced AF. Vagally induced or programmed stimulation-induced AF could be blocked by the selective M3R antagonist, darifenacin. These results suggest a potential surgical target (ICANS) and pharmacological targets (M3R, RGS2) for the management of AF.

Effect of skeletal muscle Na(+) channel delivered via a cell platform on cardiac conduction and arrhythmia induction

BACKGROUND

In depolarized myocardial infarct epicardial border zones, the cardiac sodium channel is largely inactivated, contributing to slow conduction and reentry. We have demonstrated that adenoviral delivery of the skeletal muscle Na(+) channel (SkM1) to epicardial border zones normalizes conduction and reduces induction of ventricular tachycardia/ventricular fibrillation. We now studied the impact of canine mesenchymal stem cells (cMSCs) in delivering SkM1.

METHODS AND RESULTS

cMSCs were isolated and transfected with SkM1. Coculture experiments showed cMSC/SkM1 but not cMSC alone and maintained fast conduction at depolarized potentials. We studied 3 groups in the canine 7d infarct: sham, cMSC, and cMSC/SkM1. In vivo epicardial border zones electrograms were broad and fragmented in sham, narrower in cMSCs, and narrow and unfragmented in cMSC/SkM1 (P<0.05). During programmed electrical stimulation of epicardial border zones, QRS duration in cMSC/SkM1 was shorter than in cMSC and sham (P<0.05). Programmed electrical stimulation-induced ventricular tachycardia/ventricular fibrillation was equivalent in all groups (P>0.05).

CONCLUSION

cMSCs provide efficient delivery of SkM1 current. The interventions performed (cMSCs or cMSC/SkM1) were neither antiarrhythmic nor proarrhythmic. Comparing outcomes with cMSC/SkM1 and viral gene delivery highlights the criticality of the delivery platform to SkM1 antiarrhythmic efficacy.

Atrial Fibrillation Associated with Heart Failure, Stroke and Mortality

Atrial Fibrillation (AF) is the most common arrhythmia in the western world. Because AF prevalence rises with age and western populations are increasingly aging, AF has been called a "growing epidemic", especially among older persons, with social and economic consequences. AF may concur to disability and may cluster with other co-existing clinical conditions. AF is an independent risk factor for stroke by increasing the thromboembolic risk profile and is associated with heart failure severity. Among persons with AF, prevalence of stroke, coronary heart disease, peripheral artery disease, cognitive impairment and physical disability is significantly higher. AF is associated with higher risk of mortality through the association with stroke and heart failure: ischemic strokes are more severe if AF is present and AF may represent a marker of more severe heart failure. Independently of other known predictors of mortality, death rates are almost doubled by AF. AF, therefore, is a considerable source of morbidity and mortality, is associated with disability, and is a major determinant of quality of life.

SkM1 and Cx32 improve conduction in canine myocardial infarcts yet only SkM1 is antiarrhythmic

AIMS

Reentry accounts for most life-threatening arrhythmias, complicating myocardial infarction, and therapies that consistently prevent reentry from occurring are lacking. In this study, we compare antiarrhythmic effects of gene transfer of green fluorescent protein (GFP; sham), the skeletal muscle sodium channel (SkM1), the liver-specific connexin (Cx32), and SkM1/Cx32 in the subacute canine infarct.

METHODS AND RESULTS

Immediately after ligation of the left anterior descending artery, viral constructs were implanted in the epicardial border zone (EBZ). Five to 7 days later, efficient restoration of impulse propagation (narrow QRS and local electrogram duration) occurred in SkM1, Cx32, and SkM1/Cx32 groups (P< 0.05 vs. GFP). Programmed electrical stimulation from the EBZ induced sustained ventricular tachycardia (VT)/ventricular fibrillation (VF) in 15/22 GFP dogs vs. 2/12 SkM1, 6/14 Cx32, and 8/10 SkM1/Cx32 (P< 0.05 SkM1 vs. GFP). GFP, SkM1, and SkM1/Cx32 had predominantly polymorphic VT/VF, whereas in Cx32 dogs, monomorphic VT predominated (P< 0.05 for Cx32 vs. GFP). Tetrazolium red staining showed significantly larger infarcts in Cx32- vs. GFP-treated animals (P< 0.05).

CONCLUSION

Whereas SkM1 gene transfer reduces the incidence of inducible VT/VF, Cx32 therapy to improve gap junctional conductance results in larger infarct size, a different VT morphology, and no antiarrhythmic efficacy.

Unprovoked atrial tachyarrhythmias in aging spontaneously hypertensive rats: the role of the autonomic nervous system

Experimental models of unprovoked atrial tachyarrhythmias (AT) in conscious, ambulatory animals are lacking. We hypothesized that the aging, spontaneously hypertensive rat (SHR) may provide such a model. Baseline ECG recordings were acquired with radiotelemetry in eight young (14-wk-old) and eight aging (55-wk-old) SHRs and in two groups of four age-matched Wistar-Kyoto (WKY) rats. Quantification of AT and heart rate variability (HRV) analysis were performed based on 24-h ECG recordings in unrestrained rats. All animals were submitted to an emotional stress protocol (air-jet). In SHRs, carbamylcholine injections were also performed. Spontaneous AT episodes were observed in all eight aging SHRs (median, 91.5; range, 4-444 episodes/24 h), but not in young SHRs or WKY rats. HRV analysis demonstrated significantly decreased low frequency components in aging SHRs compared with age-matched WKY rats (P < 0.01) and decreased low/high frequency ratios in both young (P < 0.01) and aging (P = 0.01) SHRs compared with normotensive controls. In aging SHRs, emotional stress significantly reduced the number of arrhythmic events, whereas carbamylcholine triggered AT and significantly increased atrial electrical instability. This study reports the occurrence of unprovoked episodes of atrial arrhythmia in hypertensive rats, and their increased incidence with aging. Our results suggest that autonomic imbalance with relative vagal hyperactivity may be responsible for the increased atrial arrhythmogenicity observed in this model. We also provide evidence that, in this model, the sympatho-vagal imbalance preceded the occurrence of arrhythmia. These results indicate that aging SHRs may provide valuable insight into the understanding of atrial arrhythmias.

Regulation of adipose tissue energy availability through blood flow control in the metabolic syndrome

Maintenance of blood flow rate is a critical factor for tissue oxygen and substrate supply. The potentially large mass of adipose tissue deeply influences the body distribution of blood flow. This is due to increased peripheral resistance in obesity and the role of this tissue as the ultimate destination of unused excess of dietary energy. However, adipose tissue cannot grow indefinitely, and the tissue must defend itself against the avalanche of nutrients provoking inordinate growth and inflammation. In the obese, large adipose tissue masses show lower blood flow, limiting the access of excess circulating substrates. Blood flow restriction is achieved by vasoconstriction, despite increased production of nitric oxide, the vasodilatation effects of which are overridden by catecholamines (and probably also by angiotensin II and endothelin). Decreased blood flow reduces the availability of oxygen, provoking massive glycolysis (hyperglycemic conditions), which results in the production of lactate, exported to the liver for processing. However, this produces local acidosis, which elicits the rapid dissociation of oxyhemoglobin, freeing bursts of oxygen in localized zones of the tissue. The excess of oxygen (and of nitric oxide) induces the production of reactive oxygen species, which deeply affect the endothelial, blood, and adipose cells, inducing oxidative and nitrosative damage and eliciting an increased immune response, which translates into inflammation. The result of the defense mechanism for adipose tissue, localized vasoconstriction, may thus help develop a more generalized pathologic response within the metabolic syndrome parameters, extending its effects to the whole body.

Serum amyloid a and C-reactive protein independently predict the recurrences of atrial fibrillation after cardioversion in patients with preserved left ventricular function

BACKGROUND

Subclinical inflammation and atrial stretch have been recognized as important contributors to atrial fibrillation (AF) onset and perpetuation. The aim of the study was to compare the predictive role of serum inflammatory markers (serum amyloid A [SAA], and C-reactive protein [CRP]) and N-terminal pro brain natriuretic peptide (NT-proBNP) an indice of atrial strain in relation to subacute arrhythmic recurrence rate in patients with persistent AF and normal left ventricular ejection fraction (LVEF).

METHODS

We studied 57 patients with a mean LVEF of 58.7 ± 6%. NT-proBNP, SAA and CRP levels were determined few hours before electrical cardioversion and 3 weeks after cardioversion.

RESULTS

Subacute AF recurrences were documented in 19 (33 %) patients. Whereas NT-proBNP levels did not predict arrhythmic outcome, higher SAA (> 6.16-6.19 mg/L) and CRP levels (> 2.99-3.10 mg/L) were significantly associated with AF recurrences (odds ratio [OR], 5.39; 95% confidence interval [CI], 1.59-18.26; P = 0.007 and OR, 14.93; 95% CI, 3.90-57.19; P < 0.001). Both SAA (OR, 18.29; 95% CI, 2.07-161.46; P = 0.009) and high sensitivity CRP (OR, 42.03; 95% CI, 4.83-365.45; P = 0.001) through the multivariate logistic regression analysis show an independent role in predicting the AF recurrence with a sensitivity of 100% (38/38) and a specificity of 52.6% (10/19).

CONCLUSIONS

The present study demonstrates that in patients with persistent AF and preserved LVEF, SAA and CRP levels are independent predictors of AF subacute recurrence rate, whereas NT-proBNP, not associated with arrhythmic outcome, reflects the hemodynamic alterations secondary to arrhythmia presence. The simultaneous determination of SAA and high sensitivity CRP has a very high sensitivity (100%) in predicting the AF recurrence.

Acupuncture for paroxysmal and persistent atrial fibrillation: An effective non-pharmacological tool?

In Traditional Chinese Medicine, stimulation of the Neiguan spot has been utilized to treat palpitations and symptoms related to different cardiovascular diseases. We evaluated whether acupuncture might exert an antiarrhythmic effect on patients with paroxysmal or persistent atrial fibrillation (AF). Two sets of data are reviewed. The first included patients with persistent AF who underwent electrical cardioversion to restore sinus rhythm. The second included patients with symptomatic paroxysmal AF. All subjects had normal ventricular function. Acupuncture treatment consisted of 10 acupuncture sessions on a once a week basis with puncturing of the Neiguan, Shenmen and Xinshu spots. In patients with persistent AF, the recurrence rate after acupuncture treatment was similar to that observed in patients on amiodarone, but significantly smaller than that measured after sham acupuncture treatment or in the absence of any antiarrhythmic drugs. In a small group of patients with paroxysmal AF, acupuncture resulted in a significant reduction in the number and duration of symptomatic AF episodes. In conclusion, we observed that acupuncture of the Neiguan spot was associated with an antiarrhythmic effect, which was evident in patients with both persistent and paroxysmal AF. These preliminary data, observed in 2 small groups of AF patients, need to be validated in a larger population but strongly suggest that acupuncture may be an effective non-invasive and safe antiarrhythmic tool in the management of these patients.

Atrial fibrillation and acid reflux disease

To date, the precise mechanism of atrial fibrillation (AF) as a possible cause of reflux disease remains uncertain, although some possibilities can be postulated. Inflammation and vagal stimulation may have a key role linking these 2 common diseases. There is some evidence in the form of case reports and limited observational studies reporting that reflux disease, and more specifically esophagitis, can cause paroxysmal AF, and various mechanisms have been proposed. Some studies have demonstrated that acid suppressive therapy by proton pump inhibitors (PPIs) may help ameliorate symptoms associated with AF and also facilitate conversion to normal sinus rhythm in a subset of patients. Further prospective studies are needed to determine if a true causal mechanism exists between the two and assess whether the mechanism is dependent on a specific subtype of AF. In addition, the response of AF-related symptoms to PPI therapy and the potential for PPI therapy to reduce the development of AF merits further investigation.

Lone atrial fibrillation: where are we now?

There is a growing pandemic of atrial fibrillation (AF), affecting nearly 2% of the general adult population. Atrial fibrillation is commonly associated with structural heart disease, and AF itself causes a sequence of complex processes of electrical, contractile, and structural remodeling of the atrial myocardium, which facilitate further AF progression. Nonetheless, AF may also affect individuals aged ≤ 65 years who have no evidence of associated cardiopulmonary or other disease, including hypertension; this is otherwise referred to as "lone" AF and is considered to have a generally favorable prognosis. The true prevalence of lone AF is unknown. Growing insights into the diversity of numerous mechanisms involved in the pathogenesis of AF, including acute atrial stretch, structural and electrophysiological alterations, systemic inflammation, oxidative stress, autonomic imbalance, genetic predisposition, and many others, and increasing recognition of novel risk factors for AF, including obesity, metabolic syndrome, subclinical atherosclerosis, sleep apnea, alcohol consumption, and endurance sports, suggest that apparently lone AF might not be so "lone" in many patients, which could have important prognostic and therapeutic implications. In this article, we summarize the current knowledge of epidemiology, etiopathogenesis, and pathophysiology of so-called lone AF and discuss the issues of long-term prognosis and management of patients who have an apparently lone AF.

Extracellular matrix alterations in the atria: insights into the mechanisms and perpetuation of atrial fibrillation

Atrial fibrillation is the most common arrhythmia in clinical practice and is associated with increased cardiovascular morbidity and mortality. Atrial fibrosis, a detrimental process that causes imbalance in extracellular matrix deposition and degradation, has been implicated as a substrate for atrial fibrillation, but the precise mechanisms of structural remodelling and the relationship between atrial fibrosis and atrial fibrillation are not completely understood. A large number of experimental and clinical studies have shed light on the mechanisms of atrial fibrosis at the molecular and cellular level, including interactions between matrix metalloproteinases and their endogenous tissue inhibitors, and profibrotic signals through specific molecules and mediators such as angiotensin II, transforming growth factor-β1, connective tissue growth factor, and platelet-derived growth factor. This review focuses on the mechanisms of atrial fibrosis and highlights the relationship between atrial fibrosis and atrial fibrillation.

Impact of decreased estimated glomerular filtration rate on Japanese acute stroke and its subtype

OBJECTIVE

Patients with chronic kidney disease (CKD) are at a high risk for cardiovascular diseases including stroke. However, the characteristics of the stroke subtypes in patients with CKD remain to be determined.

METHODS

We investigated the associations between stroke subtypes and estimated glomerular filtration rate (eGFR), and traditional risk factors in 451 (males, 239; mean age, 71.1 y) acute stroke patients at our hospital between 2006 and 2010.

RESULTS

The stroke subtype was cardiogenic cerebral embolism in 129 (29%), cerebral hemorrhage in 104 (23%), unclassified cerebral infarction in 65 (14%), lacunar infarction in 65 (14%), subarachnoid hemorrhage in 41 (9%), atherothrombosis in 30 (7%), and transient ischemic attacks in 17 (4%). Among the 451 patients, 134 (30%) had CKD with eGFR <60 mL/min/1.73 m². Compared with a group without CKD, mean age (75.9 vs. 69.0 years, p<0.05), the prevalence of atrial fibrillation (AF) (44% vs. 21%, p<0.01) and a history of cardiovascular disease (37% vs. 19%, p<0.01) were significantly higher in that with CKD. A comparison of stroke subtypes revealed a significantly higher incidence of cardiogenic cerebral embolism (36% vs. 26%, p<0.05) in the group with, than without CKD.

CONCLUSION

We showed the prevalence of CKD in about 30% of acute stroke patients, and those patients were older, had a significantly higher prevalence of AF and a higher rate of cardiogenic cerebral embolism compared with patients without CKD. Thus, strict control of blood pressure and management of AF should be important to prevent stroke among patients with CKD.

Idiopathic atrial fibrillation revisited in a large longitudinal clinical cohort

AIMS

An age of 60 years is often used as cut-off for the diagnosis of idiopathic atrial fibrillation (AF). We investigated the importance of age and atrial size in patients with idiopathic AF and AF patients with isolated hypertension.

METHODS AND RESULTS

Out of 3978 AF patients in the Euro Heart Survey on AF with known follow-up, 119 (3%) patients had idiopathic AF. We disregarded age and atrial size when selecting idiopathic AF patients since the atria may enlarge by AF itself. For comparison, we selected 152 patients with isolated hypertension from the database. A total of 57 (48%) of the patients were older than 60 years. Persistent or permanent AF was more prevalent in the older idiopathic AF patients (34% in the age <60 vs. 66% in the age >60 years group, P= 0.002) but mean duration of known AF did not differ between these groups [310 days (inter-quartile range, IQR) 60-1827) vs. 430 days (IQR 88-1669), P= 0.824]. Left atrial size did not differ significantly in relation to age (1.50 ± 0.29 mm/kg/m² in the age <60 vs. 1.56 ± 0.31 mm/kg/m² in the age >60 years group, P= 0.742). Only two paroxysmal AF patients progressed to permanent AF. No cardiovascular events occurred during the 1-year follow-up. In contrast, strokes occurred in five patients (6%) with isolated hypertension despite similar clinical profile and comparable atrial size as idiopathic AF patients.

CONCLUSION

Idiopathic AF may present at advanced age and is even then not associated with significant atrial enlargement, AF progression, or an adverse short-term prognosis. In contrast, elevated blood pressure even when found in the absence of significant atrial remodelling, seems of prognostic importance.

Prognostic factors of atrial fibrillation following elective coronary artery bypass grafting: the impact of quantified intraoperative myocardial ischemia

Background

Atrial fibrillation (AF) occurs in 28-33% of the patients undergoing coronary artery revascularization (CABG). This study focuses on both pre- and peri-operative factors that may affect the occurrence of AF. The aim is to identify those patients at higher risk to develop AF after CABG.

Patients and methods

Two patient cohorts undergoing CABG were retrospectively studied. The first group (group A) consisted of 157 patients presenting AF after elective CABG. The second group (group B) consisted of 191 patients without AF postoperatively.

Results

Preoperative factors presenting significant correlation with the incidence of post-operative AF included: 1) age > 65 years (p = 0.029), 2) history of AF (p = 0.022), 3) chronic obstructive pulmonary disease (p = 0.008), 4) left ventricular dysfunction with ejection fraction < 40% (p = 0.015) and 5) proximal lesion of the right coronary artery (p = 0.023). The intraoperative factors that appeared to have significant correlation with the occurrence of postoperative AF were: 1) CPB-time > 120 minutes (p = 0.011), 2) myocardial ischemia index < 0.27 ml.m²/Kg.min (p = 0.011), 3) total positive fluid-balance during ICU-stay (p < 0.001), 4) FiO₂/PO₂ > 0, 4 after extubation and during the ICU-stay (p = 0.021), 5) inotropic support with doses 15-30 μg/Kg/min (p = 0.016), 6) long ICU-stay recovery for any reason (p < 0.001) and perioperative myocardial infarction (p < 0.001).

Conclusions

Our results suggest that the incidence of post-CABG atrial fibrillation can be predicted by specific preoperative and intraoperative measures. The intraoperative myocardial ischemia can be sufficiently quantified by the myocardial ischemia index. For those patients at risk we would suggest an early postoperative precautionary anti-arrhythmic treatment.

Electroanatomic remodeling of the left atrium in paroxysmal and persistent atrial fibrillation patients without structural heart disease

INTRODUCTION

The nature of the atrial substrate thought to contribute toward maintaining atrial fibrillation (AF) outside the pulmonary veins remains poorly defined. Therefore, our objective was to determine whether patients with paroxysmal and persistent AF have an abnormal electroanatomic substrate within the left atrium (LA).

METHODS AND RESULTS

Thirty-one patients with AF (17 paroxysmal AF and 14 persistent AF) were compared with 15 age-matched controls with left-sided supraventricular tachycardia (SVT). High-density 3-dimensional electroanatomic maps were created and the LA was divided into 8 segments for regional analysis. Bipolar voltage, conduction, and effective refractory periods (ERPs) of the posterior LA, left atrial appendage (LAA), and distal coronary sinus (CSd) and percentage complex signals were assessed. In the majority of LA regions, compared with controls, AF patients had: (1) lower mean voltage and a higher percentage low voltage; (2) slower conduction; and (3) more prevalent complex signals. Many of these changes were more marked in the persistent than the paroxysmal AF group.

CONCLUSIONS

Patients with AF have lower regional voltage, increased proportion of low voltage, slowed conduction, and increased proportion of complex signals compared to controls. Many of these changes are more pronounced in persistent AF patients, suggesting there may be a progressive nature to the changes. Differences occurred in the absence of structural heart disease. These substrate abnormalities provide further insight into the progressive nature of atrial remodeling and the mechanisms involved in maintenance of AF.

Atrial fibrillation and heart failure parallels: lessons for atrial fibrillation prevention

Heart failure (HF) and atrial fibrillation (AF) are 2 of the most common cardiovascular diseases encountered in clinical practice, and the prevalence of these diseases continues to grow worldwide with the aging of the global population. While recognizing that AF is a heterogeneous disorder, we submit that the parallels between AF and HF may arise because many cases of AF and HF result from the cumulative exposure of the atria and ventricles to a common set of systemic cardiovascular risk factors. Over time, exposure to risk factors promotes development of atrial and ventricular structural and functional abnormalities through activation of several biologic pathways in concert: upregulation of neurohormonal signaling cascades, release of inflammatory mediators, programmed cell death, and fibrosis. Cardiac structural remodeling occurs in concert with electrophysiologic remodeling, both of which contribute to atrial and ventricular rhythm disturbances, including AF. AF and HF, instead of representing distinct disease processes, often represent different endpoints along a disease continuum. By reviewing some of the mechanistic parallels between AF and HF, we hope to emphasize the connection between established cardiovascular risk factors, cardiac remodeling and AF, with a view to promote strategies for AF prevention.

Usefulness of left ventricular diastolic dysfunction assessed by pulsed tissue Doppler imaging as a predictor of atrial fibrillation recurrence after successful electrical cardioversion

The impact of left ventricular (LV) diastolic dysfunction on risk of atrial fibrillation (AF) recurrence is still unknown. The aim of this study was to assess the role of LV diastolic dysfunction in predicting AF recurrence after successful electrical cardioversion in patients with nonvalvular AF. In 51 patients with a first episode of nonvalvular AF undergoing successful electrical cardioversion, tissue Doppler echocardiography was performed to measure peak early diastolic mitral annulus velocity (E(m)) and the ratio of mitral inflow to mitral annulus velocity at end-diastole (E/E(m)). Clinical end points were recurrent persistent AF at 2-week follow-up (early AF recurrence [ERAF]) and at 1-year follow-up (including ERAF and late AF recurrence). Seventeen patients showed evidence of ERAF, whereas late AF recurrence occurred in another 5 patients. In time-independent analysis E/E(m) (odds ratio [OR] 1.746, p = 0.0084) and indexed LV end-systolic volume (OR 1.083, p = 0.040) were independent predictors of ERAF. Based on a logistic model risk of ERAF was 25% for an E/E(m) of 5.6 but increased to 50% for an E/E(m) of 8.1 and to 75% for an E/E(m) of 10.5. In time-dependent analysis E/E(m) emerged as the only predictor of ERAF (OR 1.757, p = 0.0078). E/E(m) also independently predicted risk of recurrence at 1 year in time-independent (OR 1.757, p = 0.0078) and time-dependent (OR 1.319, p = 0.0003) analyses. In conclusion LV diastolic dysfunction independently predicts AF recurrence in patients with nonvalvular AF undergoing successful electrical cardioversion.

Influence of race on atrial fibrillation after cardiac surgery

BACKGROUND

Despite having fewer risk factors for atrial fibrillation (AF), white patients have a greater prevalence of AF in the community than black patients, and a genetic basis has been postulated. However, it is unknown whether occurrence of new-onset AF after cardiac surgery is different in white versus black patients, and secondarily, other non-Caucasian patients.

METHODS AND RESULTS

From 1995 through 2005, 20 282 white, 1323 black, and 1919 other non-Caucasian patients in sinus rhythm underwent coronary artery bypass grafting with or without valve surgery. To adjust for clinical and socioeconomic confounders, we performed propensity-adjusted analyses; 7093 white patients (35%) had postoperative AF, compared with 255 (22%) black patients and 550 (29%) other non-Caucasians (P<0.0001). Whites were older than black patients, had higher socioeconomic position, and greater left atrial size but were less likely to have hypertension or congestive heart failure. In 847 propensity-matched patient pairs, postoperative AF occurred more frequently in white than in black patients (odds ratio, 1.74; 95% confidence interval, 1.7-1.78). Other than higher occurrence of bradycardia requiring pacing and reintubation in white patients, occurrence of other postoperative complications, hospital mortality, and length of postoperative stay were similar. Age and valvular surgery were the strongest predictors of AF irrespective of race.

CONCLUSIONS

White patients had a markedly higher risk of postoperative AF than black and other non-Caucasian patients. The cause for racial differences of arrhythmic risk is unknown, but a genetic predisposition is plausible. Our results have implications for risk stratification and mechanistic understanding of postoperative 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.

Recent advances in the molecular pathophysiology of atrial fibrillation

Atrial fibrillation (AF) is an extremely common cardiac rhythm disorder that causes substantial morbidity and contributes to mortality. The mechanisms underlying AF are complex, involving both increased spontaneous ectopic firing of atrial cells and impulse reentry through atrial tissue. Over the past ten years, there has been enormous progress in understanding the underlying molecular pathobiology. This article reviews the basic mechanisms and molecular processes causing AF. We discuss the ways in which cardiac disease states, extracardiac factors, and abnormal genetic control lead to the arrhythmia. We conclude with a discussion of the potential therapeutic implications that might arise from an improved mechanistic understanding.