Is the hypercoagulable state in atrial fibrillation mediated by vascular endothelial growth factor?

Characterization of Biomarkers of Thrombo-Inflammation in Patients with First-Diagnosed Atrial Fibrillation

Patients with first-diagnosed atrial fibrillation (FDAF) exhibit major adverse cardiovascular events (MACEs) during follow-up. Preclinical models have demonstrated that thrombo-inflammation mediates adverse cardiac remodeling and atherothrombotic events. We have hypothesized that thrombin activity (FIIa) links coagulation with inflammation and cardiac fibrosis/dysfunction. Surrogate markers of the thrombo-inflammatory response in plasma have not been characterized in FDAF. In this prospective longitudinal study, patients presenting with FDAF (n = 80), and 20 matched controls, were included. FIIa generation and activity in plasma were increased in the patients with early AF compared to the patients with chronic cardiovascular disease without AF (controls; p < 0.0001). This increase was accompanied by elevated biomarkers (ELISA) of platelet and endothelial activation in plasma. Pro-inflammatory peripheral immune cells (TNF-α+ or IL-6+) that expressed FIIa-activated protease-activated receptor 1 (PAR1) (flow cytometry) circulated more frequently in patients with FDAF compared to the controls (p < 0.0001). FIIa activity correlated with cardiac fibrosis (collagen turnover) and cardiac dysfunction (NT-pro ANP/NT-pro BNP) surrogate markers. FIIa activity in plasma was higher in patients with FDAF who experienced MACE. Signaling via FIIa might be a presumed link between the coagulation system (tissue factor-FXa/FIIa-PAR1 axis), inflammation, and pro-fibrotic pathways (thrombo-inflammation) in FDAF.

Vascular Endothelial Barrier Protection Prevents Atrial Fibrillation by Preserving Cardiac Nanostructure

BACKGROUND

Atrial fibrillation (AF), the most common cardiac arrhythmia, is widely associated with inflammation, vascular dysfunction, and elevated levels of the vascular leak-inducing cytokine, vascular endothelial growth factor (VEGF). Mechanisms underlying AF are poorly understood and current treatments only manage this progressive disease, rather than arresting the underlying pathology. The authors previously identified edema-induced disruption of sodium channel (NaV1.5)-rich intercalated disk nanodomains as a novel mechanism for AF initiation secondary to acute inflammation. Therefore, we hypothesized that protecting the vascular barrier can prevent vascular leak-induced atrial arrhythmias.

OBJECTIVES

In this study the authors tested the hypothesis that protecting the vascular barrier can prevent vascular leak-induced atrial arrhythmias. They identified 2 molecular targets for vascular barrier protection, connexin43 (Cx43) hemichannels and pannexin-1 (Panx1) channels, which have been implicated in cytokine-induced vascular leak.

METHODS

The authors undertook in vivo electrocardiography, electron microscopy, and super-resolution light microscopy studies in mice acutely treated with a clinically relevant level of VEGF.

RESULTS

AF incidence was increased in untreated mice exposed to VEGF relative to vehicle control subjects. VEGF also increased the average number of AF episodes. VEGF shifted NaV1.5 signal to longer distances from Cx43 gap junctions, measured by a distance transformation-based spatial analysis of 3-dimensional confocal images of intercalated disks. Similar effects were observed with NaV1.5 localized near mechanical junctions composed of neural cadherin. Blocking connexin43 hemichannels (αCT11 peptide) or Panx1 channels (PxIL2P peptide) significantly reduced the duration of AF episodes compared with VEGF alone with no treatment. Concurrently, both peptide therapies preserved NaV1.5 distance from gap junctions to control levels and reduced mechanical junction-adjacent intermembrane distance in these hearts. Notably, similar antiarrhythmic efficacy was also achieved with clinically-relevant small-molecule inhibitors of Cx43 and Panx1.

CONCLUSIONS

These results highlight vascular barrier protection as an antiarrhythmic strategy following inflammation-induced vascular leak.

Identification of Hub mRNAs and lncRNAs in Atrial Fibrillation Using Weighted Co-expression Network Analysis With RNA-Seq Data

Atrial fibrillation (AF)/paroxysmal AF (PAF) is the main cause of cardiogenic embolism. In recent years, the progression from paroxysmal AF to persistent AF has attracted more and more attention. However, the molecular mechanism of the progression of AF is unclear. In this study, we performed RNA sequencing for normal samples, paroxysmal AF and persistent AF samples to identify differentially expressed gene (DEG) and explore the roles of these DEGs in AF. Totally, 272 differently expressed mRNAs (DEmRNAs) and 286 differentially expressed lncRNAs (DElncRNAs) were identified in paroxysmal AF compared to normal samples; 324 DEmRNAs and 258 DElncRNAs were found in persistent atrial fibrillation compared with normal samples; and 520 DEmRNAs and 414 DElncRNAs were identified in persistent AF compared to paroxysmal AF samples. Interestingly, among the DEGs, approximately 50% were coding genes and around 50% were non-coding RNAs, suggesting that lncRNAs may also have a crucial role in the progression of AF. Bioinformatics analysis demonstrated that these DEGs were significantly related to regulating multiple AF associated pathways, such as the regulation of vascular endothelial growth factor production and binding to the CXCR chemokine receptor. Furthermore, weighted gene co-expression network analysis (WGCNA) was conducted to identify key modules and hub RNAs and lncRNAs to determine their potential associations with AF. Five hub modules were identified in the progression of AF, including blue, brown, gray, turquoise and yellow modules. Interestingly, blue module and turquoise module were significantly negatively and positively correlated to the progression of AF respectively, indicating that they may have a more important role in the AF. Moreover, the hub protein-protein interaction (PPI) networks and lncRNA-mRNA regulatory network were constructed. Bioinformatics analysis on the hub PPI network in turquoise was involved in regulating immune response related signaling, such as leukocyte chemotaxis, macrophage activation, and positive regulation of α-β T cell activation. Our findings could clarify the underlying molecular changes associated fibrillation, and provide a useful resource for identifying AF marker.

Increased fibroblast accumulation in the equine heart following persistent atrial fibrillation

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Persistent atrial fibrillation is associated with increased fibroblast accumulation.

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Six weeks of persistent AF is not associated with structural remodeling.

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Fibroblasts are potentially contributing to alteration in atrial electrophysiology.

Background

Fibroblasts maintain the extracellular matrix homeostasis and may couple to cardiomyocytes through gap junctions and thereby increase the susceptibility to slow conduction and cardiac arrhythmias, such as atrial fibrillation (AF). In this study, we used an equine model of persistent AF to characterize structural changes and the role of fibroblasts in the development of an arrhythmogenic substrate for AF.

Material and methods

Eleven horses were subjected to atrial tachypacing until self-sustained AF developed and were kept in AF for six weeks. Horses in sinus rhythm (SR) served as control. In terminal open-chest experiments conduction velocity (CV) was measured. Tissue was harvested and stained from selected sites. Automated image analysis was performed to assess fibrosis, fibroblasts, capillaries and various cardiomyocyte characteristics.

Results

Horses in SR showed a rate-dependent slowing of CV, while in horses with persistent AF this rate-dependency was completely abolished (CV•basic cycle length relation p = 0.0295). Overall and interstitial amounts of fibrosis were unchanged, but an increased fibroblast count was found in left atrial appendage, Bachmann's bundle, intraatrial septum and pulmonary veins (p < 0.05 for all) in horses with persistent AF. The percentage of α-SMA expressing fibroblasts remained the same between the groups.

Conclusion

Persistent AF resulted in fibroblast accumulation in several regions, particularly in the left atrial appendage. The increased number of fibroblasts could be a mediator of altered electrophysiology during AF. Targeting the fibroblast proliferation and differentiation could potentially serve as a novel therapeutic target slowing down the structural remodeling associated with AF.

Exosomes in atrial fibrillation: therapeutic potential and role as clinical biomarkers

Atrial fibrillation (AF), the most common cardiac arrhythmia, is a global epidemic. AF can cause heart failure and myocardial infarction and increase the risk of stroke, disability, and thromboembolic events. AF is becoming increasingly ubiquitous and is associated with increased morbidity and mortality at higher ages, resulting in an increasing threat to human health as well as substantial medical and social costs. Currently, treatment strategies for AF focus on controlling heart rate and rhythm with medications to restore and maintain sinus rhythm, but this approach has limitations. Catheter ablation is not entirely satisfactory and does not address the issues underlying AF. Research exploring the mechanisms causing AF is urgently needed for improved prevention, diagnosis, and treatment of AF. Exosomes are small vesicles (30-150 nm) released by cells that transmit information between cells. MicroRNAs in exosomes play an important role in the pathogenesis of AF and are established as a biomarker for AF. In this review, a summary of the role of exosomes in AF is presented. The role of exosomes and microRNAs in AF occurrence, their therapeutic potential, and their potential role as clinical biomarkers is considered. A better understanding of exosomes has the potential to improve the prognosis of AF patients worldwide, reducing the global medical burden of this disease.

Atrial fibrillation: the role of hypoxia-inducible factor-1-regulated cytokines

Atrial fibrillation (AF) is a common arrhythmia that has major morbidity and mortality. Hypoxia plays an important role in AF initiation and maintenance. Hypoxia-inducible factor (HIF), the master regulator of oxygen homeostasis in cells, plays a fundamental role in the regulation of multiple chemokines and cytokines that are involved in different physiological and pathophysiological pathways. HIF is also involved in the pathophysiology of AF induction and propagation mostly through structural remodeling such as fibrosis; however, some of the cytokines discussed have even been implicated in electrical remodeling of the atria. In this article, we highlight the association between HIF and some of its related cytokines with AF. Additionally, we provide an overview of the potential diagnostic benefits of using the mentioned cytokines as AF biomarkers. Research discussed in this review suggests that the expression of these cytokines may correlate with patients who are at an increased risk of developing AF. Furthermore, cytokines that are elevated in patients with AF can assist clinicians in the diagnosis of suspect paroxysmal AF patients. Interestingly, some of the cytokines have been elevated specifically when AF is associated with a hypercoagulable state, suggesting that they could be helpful in the clinician's and patient's decision to begin anticoagulation. Finally, more recent research has demonstrated the promise of targeting these cytokines for the treatment of AF. While still in its early stages, tools such as neutralizing antibodies have proved to be efficacious in targeting the HIF pathway and treating or preventing AF.

Vascular endothelial growth factor promotes atrial arrhythmias by inducing acute intercalated disk remodeling

Atrial fibrillation (AF) is the most common arrhythmia and is associated with inflammation. AF patients have elevated levels of inflammatory cytokines known to promote vascular leak, such as vascular endothelial growth factor A (VEGF). However, the contribution of vascular leak and consequent cardiac edema to the genesis of atrial arrhythmias remains unknown. Previous work suggests that interstitial edema in the heart can acutely promote ventricular arrhythmias by disrupting ventricular myocyte intercalated disk (ID) nanodomains rich in cardiac sodium channels (Na_V1.5) and slowing cardiac conduction. Interestingly, similar disruption of ID nanodomains has been identified in atrial samples from AF patients. Therefore, we tested the hypothesis that VEGF-induced vascular leak can acutely increase atrial arrhythmia susceptibility by disrupting ID nanodomains and slowing atrial conduction. Treatment of murine hearts with VEGF (30–60 min, at clinically relevant levels) prolonged the electrocardiographic P wave and increased susceptibility to burst pacing-induced atrial arrhythmias. Optical voltage mapping revealed slower atrial conduction following VEGF treatment (10 ± 0.4 cm/s vs. 21 ± 1 cm/s at baseline, p < 0.05). Transmission electron microscopy revealed increased intermembrane spacing at ID sites adjacent to gap junctions (GJs; 64 ± 9 nm versus 17 ± 1 nm in controls, p < 0.05), as well as sites next to mechanical junctions (MJs; 63 ± 4 nm versus 27 ± 2 nm in controls, p < 0.05) in VEGF–treated hearts relative to controls. Importantly, super-resolution microscopy and quantitative image analysis revealed reorganization of Na_V1.5 away from dense clusters localized near GJs and MJs to a more diffuse distribution throughout the ID. Taken together, these data suggest that VEGF can acutely predispose otherwise normal hearts to atrial arrhythmias by dynamically disrupting Na_V1.5-rich ID nanodomains and slowing atrial conduction. These data highlight inflammation-induced vascular leak as a potential factor in the development and progression of AF.

Vascular endothelial growth factor enhances profibrotic activities through modulation of calcium homeostasis in human atrial fibroblasts

Vascular endothelial growth factor (VEGF), a pivotal activator of angiogenesis and calcium (Ca²⁺) signaling in endothelial cells, was shown to increase collagen production in atrial fibroblasts. In this study, we evaluated whether VEGF may regulate Ca²⁺ homeostasis in atrial fibroblasts and contribute to its profibrogenesis. Migration, and proliferation analyses, patch-clamp assay, Ca²⁺ fluorescence imaging, and western blotting were performed using VEGF-treated (300 pg/mL or 1000 pg/mL) human atrial fibroblasts with or without coadministration of Ethylene glycol tetra-acetic acid (EGTA, 1 mmol/L), or KN93 (a Ca²⁺/calmodulin-dependent protein kinase II [CaMKII] inhibitor, 10 μmol/L). VEGF (1000 pg/mL) increased migration, myofibroblast differentiation, pro-collagen type I, pro-collagen type III production, and phosphorylated VEGF receptor 1 expression of fibroblasts. VEGF (1000 pg/mL) increased the nonselective cation current (I_NSC) of transient receptor potential (TRP) channels and potassium current of intermediate-conductance Ca²⁺-activated K⁺ (K_Ca3.1) channels thereby upregulating Ca²⁺ entry. VEGF upregulated phosphorylated ERK expression. An ERK inhibitor (PD98059, 50 μmol/L) attenuated VEGF-activated I_NSC of TRP channels. The presence of EGTA attenuated the profibrotic effects of VEGF on pro-collagen type I, pro-collagen type III production, myofibroblast differentiation, and migratory capabilities of fibroblasts. VEGF upregulated the expression of phosphorylated CaMKII in fibroblasts, which was attenuated by EGTA. In addition, KN93 reduced VEGF-increased pro-collagen type I, pro-collagen type III production, myofibroblast differentiation, and the migratory capabilities of fibroblasts. In conclusion, we found that VEGF increases atrial fibroblast activity through CaMKII signaling by enhancing Ca²⁺ entry. Our findings provide benchside evidence leading to a potential novel strategy targeting atrial myopathy and arrhythmofibrosis.

Risk Assessment of Stroke in Patients with Atrial Fibrillation: Current Shortcomings and Future Directions

Atrial fibrillation is a well-known risk factor for cardioembolic stroke; a number of risk stratification scoring systems have been developed to help differentiate which patients would stand to benefit from anticoagulation. However, these scoring systems cannot be utilized in patients whose atrial fibrillation has not been diagnosed. As implantable cardiac monitors become more prevalent, it becomes possible to identify occult, subclinical atrial fibrillation. With this data, it is also possible to examine the relationship between episodes of paroxysmal atrial fibrillation and thromboembolism and the total burden of paroxysmal atrial fibrillation and thromboembolic risk. The data gleaned from these devices provides insight and raises questions regarding the underlying mechanism of thromboembolism in atrial fibrillation, and in doing so, exposes shortcomings in the present clinical use of current risk scoring systems, specifically, the inability to account for atrial fibrillation burden and to apply scores at all in subclinical atrial fibrillation.

The prothrombotic state in atrial fibrillation: pathophysiological and management implications

Atrial fibrillation (AF) is the commonest sustained cardiac arrhythmia and is associated with significant morbidity and mortality. There is plenty of evidence available to support the presence of a prothrombotic or hypercoagulable state in AF, but the contributory factors are multifactorial and cannot simply be explained by blood stasis. Abnormal changes in atrial wall (anatomical and structural, as ‘vessel wall abnormalities’), the presence of spontaneous echo contrast to signify abnormal changes in flow and stasis (‘flow abnormalities’), and abnormal changes in coagulation, platelet, and other pathophysiologic pathways (‘abnormalities of blood constituents’) are well documented in AF. The presence of these components therefore fulfils Virchow’s triad for thrombogenesis. In this review, we present an overview of the established and professed pathophysiological mechanisms for thrombogenesis in AF and its management implications.

Endocardial Changes in Nonvalvular Atrial Fibrillation Without Atrial Thrombus-Thrombomodulin and Tissue Factor Pathway Inhibitor

Atrial fibrillation (AF) is a well-known cause for thromboembolism. Although blood stasis in the left atrium and hypercoagulable state of the blood have been emphasized as important mechanisms, limited attention has been paid to the endocardial changes in maintaining the balance of local coagulation, which may also contribute to the thrombus formation in AF. In the present study, left atrial appendage samples were obtained at heart surgery from nonvalvular AF and non-AF patients without atrial thrombus. Immunohistochemistry for endocardial markers including thrombomodulin (TM) and tissue factor pathway inhibitor (TFPI) was performed and semiquantitatively graded. In immunohistochemistry analysis, decreased expression of TM was found in patients with nonvalvular AF compared with those without AF ( P < .001). There was no difference in TFPI expression between the 2 groups ( P = .213). Patients with TM score of 0 or 1 seemed to have larger left atrial diameter (LAD) than those with TM score of 2 or 3 (44.0 (7.9) vs 40.6 (3.9); P = .009), while no relationship between LAD and TFPI expression was found (43.4 (7.0) vs 42.9 (7.8); P = .485). In conclusion, TM expression in the atrial endocardium is decreased in nonvalvular AF without atrial thrombus, while TFPI expression is not. Downregulated TM expression might be associated with enlarged LAD.

Association of hemostatic markers with atrial fibrillation: a meta-analysis and meta-regression

BACKGROUND

There is growing evidence that indicates the presence of a prothrombotic state in atrial fibrillation (AF). However, the role of hemostatic markers in AF remains inconclusive.

METHODS

We conducted a meta-analysis of observational studies to evaluate the association between hemostatic markers and AF. A meta-regression was performed to explore potential sources of heterogeneity.

RESULTS

A total of 59 studies met our inclusion criteria for the meta-analysis. For platelet activation, increased circulating platelet factor-4, β-thromboglobulin (BTG) and P-selectin were significantly higher in AF cases compared with controls (standardized mean difference [SMD][95% confidence interval (CI)]: 1.72[0.96-2.49], 1.61[1.03-2.19] and 0.50[0.23-0.77], respectively). For coagulation activation, increased levels of plasma D-dimer, fibrinogen, thrombin-antithrombin, prothrombin fragment 1+2, and antithrombin-III were significantly associated with AF (SMD[95% CI]: 1.82[1.38-2.26], 0.72[0.55-0.89], 0.42[0.13-0.72], 1.00 [0.00-1.99] and 1.38[0.16-2.60], respectively). For fibrinolytic function, tissue-type plasminogen activator and plasminogen activator inhibitor-1 were significantly increased in AF cases compared with controls (SMD[95% CI]: 0.86[0.04-1.67] and 0.87[0.28-1.47], respectively) but the associations became nonsignificant after performing subgroup analysis by anticoagulants treatment status. For endothelial function, increased von Willebrand factor was significantly associated with AF (SMD, 0.79; 95% CI, 0.60-0.99); however, no association was observed for soluble thrombomodulin (SMD, 0.60; 95% CI, -0.13-1.33).

CONCLUSIONS

Increased circulating hemostatic factors (PF-4, BTG, P-selectin, D-dimer, fibrinogen, TAT, F1+2, AT- III, and vWf) are significantly associated with AF. Future research is necessary to elucidate the precise mechanism of the prothrombotic state and how hemostatic markers promote thromboembolism in AF.

Hypercoagulability, D-dimer and atrial fibrillation: an overview of biological and clinical evidence

Atrial fibrillation (AF) is the most common among the severe cardiac arrhythmias and carries a significant risk of mortality and morbidity in the general population. The most important complication is represented by development of one or more thrombi in the left atrium of the dyskinetic heart, and their successive cerebral and peripheral embolization. The pathophysiological basis of the thromboembolic complications in AF entails the presence of a hypercoagulable state, which is mirrored by increased concentrations of a variety of prothrombotic markers. D-dimer is universally considered the gold standard among the various biomarkers that reflect activation of coagulation, fibrinolysis, or both, and several studies have assessed its diagnostic and prognostic role in AF. With a few exceptions and despite a broad heterogeneity in the study designs, published data seem to demonstrate that D-dimer values may be associated with the presence of atrial thrombosis, may be predictive of primary adverse outcomes and death, may be correlated with cerebral infarction volume, and may also be a useful parameter for assessing the degree of hypercoagulability of AF patients after cardioversion. If larger prospective studies confirm these findings, D-dimer assessment may hence become an integral part of the clinical decision-making in patients with AF.

Embryology and Anatomy of the Left Atrial Appendage: Why Does Thrombus Form?

The left atrial appendage (LAA) is a long tubular structure that opens into the left atrium. In patients with atrial fibrillation, the LAA develops mechanical dysfunction and fibroelastotic changes on the endocardial surface. The complex anatomy of the LAA makes it a good site for relative blood stasis. In addition, systemic factors exacerbate the hypercoagulable state, eventually resulting in endothelial dysfunction, release of tissue factor, and production of inflammatory cytokines and oxidative free radicals, and eventually initiating the coagulation cascade. Thus, the LAA is susceptible to thrombus formation and is the most common source of systemic thromboembolism.

Atrial Fibrillation and Stroke: A Neurologic Perspective

Atrial fibrillation (AF) is the most common supraventricular arrhythmia in the United States. The incidence and prevalence of AF are increasing as the population ages and associated risk factors become more prevalent. Stroke is the most severe complication of AF. Various risk stratification schemes to guide therapy and the associated risk of bleeding are described. AF is also associated with cognitive decline, which may be secondary to recurrent microemboli; microbleeds secondary to anticoagulation therapy, or progression of vascular risk factors associated with AF. Prolonged monitoring can be performed to detect AF in patients with cryptogenic stroke.

A review of oral anticoagulants in patients with atrial fibrillation

There is a high prevalence of atrial fibrillation in the United States, particularly in the elderly population. Patients with atrial fibrillation are at an increased risk of stroke and anticoagulant therapy is recommended. However, many eligible patients are not receiving therapy due to limitations and concerns related to the use of the vitamin K antagonist warfarin, such as slow onset of action, variable drug metabolism, risk of bleeding, and requirement for monitoring. Novel oral anticoagulants (NOACs) have been developed and may be used as an alternative to warfarin. This review article summarizes the current clinical trial data for warfarin compared with the NOACs dabigatran (direct thrombin inhibitor), and rivaroxaban and apixaban (factor Xa inhibitors). Dabigatran (150 mg twice daily) demonstrated superiority in reducing the stroke or systemic embolism rate compared with warfarin (1.53% vs 1.69%; P < 0.001). The risk of major bleeding was similar for dabigatran and warfarin (3.32% per year vs 3.57% per year; P = 0.32). Rivaroxaban (20 mg once daily) demonstrated noninferiority in reducing the stroke or systemic embolism rate compared with warfarin (2.1% vs 2.4%; P < 0.001). There was no significant difference between rivaroxaban and warfarin for the risk of major bleeding and clinically relevant nonmajor bleeding (14.9% per year vs 14.5% per year; P = 0.44). Apixaban (5 mg twice daily) demonstrated superiority compared with warfarin in preventing stroke or systemic embolism (1.27% vs 1.60%; P = 0.01). Apixaban significantly reduced major bleeding compared with warfarin (2.13% per year vs 3.09% per year; P < 0.001). Compared with warfarin, all-cause mortality was numerically lower for dabigatran (P = 0.051) and similar for rivaroxaban (P = 0.15). Apixaban demonstrated significantly lower mortality rates compared with warfarin (3.52% vs 3.94%; P = 0.047). All 3 NOACS--dabigatran, rivaroxaban, and apixaban--significantly reduced intracranial hemorrhage compared with warfarin. Novel oral anticoagulants may be a suitable alternative to warfarin for different patient populations due to minimal drug interactions, lower bleeding risk, and no monitoring requirement.

Atrial fibrillation-associated remodeling does not promote atrial thrombus formation in canine models

BACKGROUND

The most important complication of atrial fibrillation (AF) is thromboembolic stroke. Although AF-related remodeling is considered important in atrial thrombogenesis, its role never has been directly tested. This study assessed effects of AF-related remodeling on the atrial thrombogenic milieu by using radiofrequency ablation (RFA) to create a quantifiable prothrombotic nidus.

METHODS AND RESULTS

We studied normal control dogs (control, n=16) and 3 canine AF-models: (1) atrial tachycardia remodeling (ATR; n=16) induced by atrial tachypacing (400 bpm for 1 week, with atrioventricular block and ventricular pacing at 80 bpm); (2) congestive heart failure (CHF; n=14) attributable to ventricular tachypacing (240 bpm for 2 weeks); and (3) chronic AF (CAF; n=8) induced by atrial tachypacing (35±3 days) without atrioventricular block. CAF dogs had AF for 13±1 days until euthanization. After remodeling was established, RFA lesions were created in both atria. Half the ATR and CHF dogs were subjected to atrial tachypacing during 7-day post-RFA follow-up. Electrophysiological and echocardiographic studies were performed before RFA and 7 days after RFA, and then hearts were removed and atrial thrombi were quantified by histomorphometry. Burst-pacing-induced AF duration was significantly greater in ATR, CHF, and CAF groups versus control group. The atrial effective refractory period shortened in ATR and CAF groups. Left atrial diameter was significantly larger with CHF, but not with ATR. Neither total thrombus volume nor thrombus volume per lesion differed significantly among groups. Table.Properties of Ablation Lesions and Atrial Thrombi Experimental GroupControl (n=16)ATR (n=16)CHF (n=14)CAF (n=8)N of ablation lesions per dog6.9±0.36.6±0.27.2±0.26.9±0.4Ablation lesion area, mm(2)53.1±3.558.3±4.857.7±4.944.3±3.7Ablation lesion depth, mm5.2±0.25.1±0.35.3±0.25.2±0.2Ablation lesion volume, mm(3)205.2±17.8211.6±17.6231.5±29.0176.8±22.2N of thrombi per dog5.4±0.44.7±0.35.6±0.46.5±0.4Presence of thrombus, %80±572±577±695±3Mean thrombus volume in both atria, mm(3)20.8±3.414.9±2.212.2±2.622.5±5.6Mean thrombus volume in left atria, mm(3)8.2±1.54.0±0.95.5±1.68.1±3.3Mean thrombus volume in right atria, mm(3)30.1±5.422.7±4.317.9±4.132.8±8.3Total thrombus volume in both atria, mm(3)140.5±21.399.7±16.886.1±17.5131.1±22.7Total thrombus volume in left atria, mm(3)22.8±5.311.8±3.317.0±3.723.3±6.4Total thrombus volume in right atria, mm(3)117.7±21.587.8±17.269.1±16.1107.8±23.3Thrombus volume normalized to ablation lesion area in both atria, mm(3)/mm(2)0.5±0.10.4±0.11.5±1.10.8±0.3Thrombus volume normalized to ablation lesion volume in both atria0.2±0.10.1±0.00.5±0.40.3±0.1 ATR indicates atrial tachycardia remodeling; CAF, chronic atrial fibrillation; and CHF, congestive heart failure. There were no statistically significant differences for any groups vs control group for any of these variables studied.

CONCLUSIONS

None of the AF substrates tested, including sustained atrial tachycardia/AF itself, enhanced post-RFA atrial thrombus formation. Indices of electrical and structural remodeling did not predict post-RFA thrombogenic potential. Contrary to widely held but previously untested notions, we were unable to demonstrate prothrombotic effects of AF-related remodeling.

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.

Update on the management of atrial fibrillation: anticoagulation and medical therapy

2010 saw the introduction of dabigatran (Pradaxa; Boehringer Ingelheim Pharmaceuticals, Ridgefield, CT), following US Food and Drug Administration approval, into daily clinical practice in the United States as an alternative to Coumadin (Bristol-Myers-Squibb, New York, NY) therapy. Dronedarone (Multaq; Sanofi-Aventis, Bridgewater, NJ), originally approved for use in the United States in 2009, has seen further widespread deployment in contemporary clinical practice. Intravenous vernakalant (Cardiome Pharm, Vancouver, B.C., Canada; Merck & Co., Whitehouse Station, NJ) is being considered for approval in the United States and may serve as an alternative to current agents for safe and efficacious acute conversion from atrial fibrillation. We focus primarily on new information concerning these and other antiarrhythmic drug and anticoagulation therapies. We provide brief updates of recently published articles along with our perspective on how they will likely alter clinical practice now and in the future.

Association of soluble fms-like tyrosine kinase-1 with pulmonary hypertension and haemolysis in sickle cell disease

The pathophysiology of pulmonary hypertension (PHT) in sickle cell disease (SCD) is probably multifactorial. Soluble fms-like tyrosine kinase-1 (sFLT-1) is a member of the vascular endothelial growth factor receptor (VEGFR) family. By adhering to and inhibiting VEGF and placenta growth factor, it induces endothelial dysfunction. We sought to evaluate the association of sFLT-1 with clinical complications of SCD. We confirmed that sFLT-1 was significantly elevated in SCD patients compared to healthy, race-matched control subjects. The level of sFLT-1 was significantly higher in patients with PHT, but no association was observed between sFLT-1 and the frequency of acute pain episodes or history of acute chest syndrome. sFLT-1 was correlated with various measures of haemolysis, erythropoietin and soluble vascular cell adhesion molecule-1. By inducing endothelial dysfunction, sFLT-1 may contribute to the pathogenesis of SCD-associated PHT, although this effect does not appear to be independent of haemolysis.

[Is atrial fibrillation an independent marker of cardiovascular risk?]

Atrial fibrillation (AF) is the most frequent cardiac arrhythmia and its prevalence rises with age. AF may cause stroke and heart failure but the relationship between AF and mortality is less clear. It is difficult to determine if cardiovascular events in patients with AF are attributable to the arrhythmia itself or if they are merely related to the comorbidities frequently associated with AF. Review of the literature suggests that lone AF (without structural heart disease), a rare clinical entity except in young patients, is not an independent risk factor for mortality. On the other hand, if illnesses usually associated with AF are present (hypertension, heart failure...), AF has a negative impact on outcome in terms of survival and morbidity. Current antiarrhythmic medications have not shown reduction in mortality of AF patients, but new agents and catheter ablation are promising paths to explore in order to decrease AF burden.

Genetic polymorphisms and atrial fibrillation: Insights into the prothrombotic state and thromboembolic risk

The pathophysiology of thromboembolism in atrial fibrillation (AF) is a multifactorial and complex process. Abnormalities of haemostasis, fibrinolysis, endothelium, and platelets have all been described in AF. This prothrombotic state observed in AF appears to be additive to the presence of clinical and echocardiography risk factors for thromboembolism. Nonetheless, the precise mechanistic pathway(s) leading to the prothrombotic state in AF remain to be elucidated. Of note, there are limited data on the influence of genetic polymorphisms in thromboembolic risk associated with AF. On the other hand, the response to coumarin derivatives depends on several factors, such as sex, age, diet, or interacting drugs. Optimal anticoagulation control is usually hampered by significant interindividual variability in dose requirements for a given target level of anticoagulation. There is increasing evidence that interindividual sensitivity and side-effects to coumarinics may be largely determined genetically. Thus, genetic polymorphisms could explain the individual risk of developing an adverse drug reaction (bleeding) or drug inefficacy (thrombosis) with oral anticoagulation. In this article, we provide an overview of the limited data about the possible influence of genetic polymorphisms on thromboembolic risk in AF, as well as the genetic influences on anticoagulant drug responsiveness.

Stroke prevention treatment of patients with atrial fibrillation: old and new

Atrial fibrillation is the most common cause of cardioembolic ischemic stroke and has a rising prevalence worldwide. Stroke prevention in this condition is poised to take a substantial leap forward with the evolution of new anticoagulant medications, with superior properties compared to vitamin K antagonists. New, safer and more effective chronic therapy is on the horizon. However, many issues surrounding the management of stroke prevention after an acute stroke and during the course of chronic anticoagulant therapy remain to be resolved.

Inflammatory cytokines and atrial fibrillation: current and prospective views

Atrial fibrillation (AF) is the most common sustained arrhythmia and a challenging clinical problem encountered in daily clinical practice. There is an increasing body of evidence linking inflammation to a broad spectrum of cardiovascular conditions including AF. Historical evidence supports an association between AF and inflammation and is consistent with the association of AF with inflammatory conditions of the heart, such as myocarditis and pericarditis. AF has been associated with myocardial oxidative stress, and antioxidant agents have demonstrated antiarrhythmic benefit in humans. Increased plasma interleukin (IL)-6, C-reactive protein (CRP), and plasma viscosity support the existence of an inflammatory state among "typical" populations with chronic AF. These indexes of inflammation are related to the prothrombotic state and may be linked to the clinical characteristics of the patients (underlying vascular disease and comorbidities), rather than simply to the presence of AF itself. It has been suggested that inflammation may have a role in the development of atrial arrhythmias after cardiac surgery, and that a genetic predisposition to develop postoperative complications exists. Cytokines can have a prognostic significance; IL-6 levels, CRP, and other cytokines may have prognostic value in AF. Cytokine lowering therapies, statins, angiotensin converting enzyme inhibitors and other anti-inflammatory agents may have a role in the treatment of AF. The present article provides an overview of the evidence linking inflammatory cytokines to AF and their therapeutic and prognostic implications.

Are atrial fibrillation patients receiving warfarin in accordance with stroke risk?

BACKGROUND

Clinical guidelines for the management of atrial fibrillation and atrial flutter provide recommendations for anticoagulation based on patients' overall risk of stroke. To determine the real-world compliance of physicians with these recommendations, we conducted a retrospective cohort study examining the utilization of warfarin in atrial fibrillation/flutter patients by stroke risk level.

METHODS

Patients with a qualifying atrial fibrillation/flutter diagnosis during > or =18 months' continuous enrollment between January 2003 and September 2007, and with > or =6 months' eligibility after the first atrial fibrillation/flutter diagnosis, were identified from the US MarketScan database (Thomson Reuters, New York, NY). Warfarin use within 30 days of the first diagnosis was assessed according to stroke risk, estimated using the Congestive heart failure, Hypertension, Age >75 years, Diabetes, Stroke (CHADS(2)) score.

RESULTS

Of 171,393 patients included in the analysis, 20.0% had a CHADS(2) score of 0 (low risk), 61.6% a score of 1-2 (moderate risk), and 18.4% a score of 3-6 (high risk). Warfarin, recommended for high stroke-risk patients, was given to only 42.1% of those with a CHADS(2) score of 3-6. A similar percentage of patients with moderate (43.5%) or low stroke risk (40.1%) received warfarin. Only 29.6% of high-risk, 33.3% of moderate-risk, and 34.1% of low-risk patients who were started on warfarin received uninterrupted therapy for 6 months following their initial prescription.

CONCLUSIONS

These data suggest that guideline recommendations that anticoagulation should be provided in accordance with stroke risk in atrial fibrillation patients are not routinely followed in clinical practice. The causes and clinical implications of under-utilization of anticoagulation in atrial fibrillation patients with high stroke risk warrant further study.

Impact of proteinuria and glomerular filtration rate on risk of thromboembolism in atrial fibrillation: the anticoagulation and risk factors in atrial fibrillation (ATRIA) study

BACKGROUND

Atrial fibrillation (AF) substantially increases the risk of ischemic stroke, but this risk varies among individual patients with AF. Existing risk stratification schemes have limited predictive ability. Chronic kidney disease is a major cardiovascular risk factor, but whether it independently increases the risk for ischemic stroke in persons with AF is unknown.

METHODS AND RESULTS

We examined how chronic kidney disease (reduced glomerular filtration rate or proteinuria) affects the risk of thromboembolism off anticoagulation in patients with AF. We estimated glomerular filtration rate using the Modification of Diet in Renal Disease equation and proteinuria from urine dipstick results found in laboratory databases. Patient characteristics, warfarin use, and thromboembolic events were ascertained from clinical databases, with validation of thromboembolism by chart review. During 33,165 person-years off anticoagulation among 10,908 patients with AF, we observed 676 incident thromboembolic events. After adjustment for known risk factors for stroke and other confounders, proteinuria increased the risk of thromboembolism by 54% (relative risk, 1.54; 95% CI, 1.29 to 1.85), and there was a graded, increased risk of stroke associated with a progressively lower level of estimated glomerular filtration rate compared with a rate > or =60 mL x min(-1) x 1.73 m(-2): relative risk of 1.16 (95% CI, 0.95 to 1.40) for estimated glomerular filtration rate of 45 to 59 mL x min(-1) x 1.73 m(-2) and 1.39 (95% CI, 1.13 to 1.71) for estimated glomerular filtration rate <45 mL x min(-1) x 1.73 m(-2) (P=0.0082 for trend).

CONCLUSIONS

Chronic kidney disease increases the risk of thromboembolism in AF independently of other risk factors. Knowing the level of kidney function and the presence of proteinuria may improve risk stratification for decision making about the use of antithrombotic therapy for stroke prevention in AF.

Atrial fibrillation is associated with cardiac hypoxia

BACKGROUND

Atrial fibrillation (AF), the most common human arrhythmia, is responsible for substantial morbidity and mortality and may be promoted by selective atrial ischemia and atrial fibrosis. Consequently, we investigated markers for hypoxia and angiogenesis in AF.

METHODS

Right atrial appendages (n=158) were grouped according to heart rhythm [sinus rhythm (SR) or AF]. The degree of fibrosis and microvessel density of all patients were determined morphometrically using Sirius-Red- and CD34/CD105-stained sections, respectively. Next, sections (n=77) underwent immunostaining to detect hypoxia- and angiogenesis-related proteins [hypoxia-inducible factor (HIF)1 alpha, HIF2 alpha, vascular endothelial growth factor (VEGF), VEGF receptor 2 (KDR), phosphorylated KDR (pKDR), carboanhydrase IX, platelet-derived growth factor] and the apoptosis-related B-cell lymphoma 2 protein.

RESULTS

Fibrosis progressed significantly from 14.7+/-0.8% (SR) to 22.3+/-1.4% (AF). While the positive cytoplasmic staining of HIF1 alpha, HIF2 alpha, VEGF, KDR, and pKDR rose significantly from SR to AF, their nuclear fractions fell (only pKDR significantly). The median CD34/CD105-positive microvessel size increased significantly from SR to AF.

CONCLUSIONS

AF is closely associated with an atrial up-regulation of hypoxic and angiogenic markers. Whether this is cause, effect, or co-phenomenon of fibrosis remains to be investigated. It is conceivable that fibrosis might lead to an increased O(2) diffusion distance and thus induce ischemic signaling, which, in turn, leads to angiogenesis.

Mechanisms of thrombogenesis in atrial fibrillation: Virchow's triad revisited

Atrial fibrillation is the most common sustained cardiac arrhythmia, which is associated with a high risk of stroke and thromboembolism. Increasing evidence suggests that the thrombogenic tendency in atrial fibrillation is related to several underlying pathophysiological mechanisms. Abnormal changes in flow are evident by stasis in the left atrium, and seen as spontaneous echocontrast. Abnormal changes in vessel walls-essentially, anatomical and structural defects-include progressive atrial dilatation, endocardial denudation, and oedematous or fibroelastic infiltration of the extracellular matrix. Additionally, abnormal changes in blood constituents are well described, and include haemostatic and platelet activation, as well as inflammation and growth factor changes. These changes result in the fulfilment of Virchow's triad for thrombogenesis, and accord with a prothrombotic or hypercoagulable state in this arrhythmia. In this Review, we present an overview of the established and purported mechanisms for thrombogenesis in atrial fibrillation.

Brain natriuretic peptide correlates with the extent of atrial fibrillation-associated silent brain lesions

OBJECTIVE

Identification of plasma markers indicative for atrial fibrillation-associated silent brain lesions.

DESIGN AND METHODS

1. Comparative determination of the plasma concentrations of secretagogin, S100B, neuropeptide Y, brain fatty acid binding protein, matrix metalloprotease 9, brain natriuretic peptide, and of D-Dimer in 222 patients with atrial fibrillation and 28 controls by immunoassays. 2. Correlation of the biochemical marker plasma concentration with the extent of silent white matter brain lesions, as determined by the Fazekas score and N-acetylaspartate-spectroscopy.

RESULTS

1. Plasma concentrations of brain natriuretic peptide, of neuropeptide Y, and of matrix metalloprotease 9 were significantly higher (all with a p<0.05) in patients suffering from atrial fibrillation than in control subjects. 2. Brain natriuretic peptide correlated significantly with the Fazekas score (R=0.41; p<0.005). 3. Brain natriuretic peptide plasma concentrations were significantly higher in patients with a pathological N-acetylaspartate magnetic resonance-spectrometry (p<0.05).

CONCLUSION

Brain natriuretic peptide plasma concentrations correlate with the extent of atrial fibrillation-associated silent brain lesions.

The feasibility of tissue Doppler acceleration as a new predictor of thrombogenesis in the left atrial appendage associated with nonvalvular atrial fibrillation

BACKGROUND

Tissue acceleration utilizing the tissue Doppler imaging (TDI) technique is a new marker of ventricular contraction. We evaluated whether the left atrial appendage (LAA) wall acceleration was associated with thrombosis in patients with nonvalvular atrial fibrillation (NVAF).

METHODS

Seven NVAF patients with thromboembolism (TE), eight without TE, and eight with normal sinus rhythm (NSR) were studied using transesophageal echocardiography. TDI was used to evaluate the LAA wall acceleration.

RESULTS

There was a decrease in the peak flow velocity in the TE group compared with the other two groups. There was greater LAA expansion in NVAF with TE groups (with TE [8.9 +/- 2.1 cm(2)] compared with the group without TE [7.3 +/- 2.8 cm(2)]), but the difference was not statistically significant; the difference was statistically significant compared with the NSR group (5.3 +/- 1.2 cm(2); P = 0.0035). The average of the continuous 40-frames area where tissue Doppler acceleration (TDA) was >0.024 cm/sec(2) was significantly lower in the TE group (0.12 +/- 0.05 cm(2)) compared to the group without TE (0.33 +/- 0.17 cm(2); P = 0.0017) and NSR group (0.30 +/- 0.13 cm(2); P = 0.0042), although wall velocity was not significantly different comparing the two NVAF groups. Furthermore, peak flow velocity of LAA was well correlated with LAA wall acceleration (r = 0.864, P < 0.0001).

CONCLUSIONS

LAA wall acceleration obtained utilizing the TDI technique may be a new predictor of thrombogenesis in patients with NVAF.

Elevated Platelet Microparticle Levels in Nonvalvular Atrial Fibrillation

BACKGROUND

Platelet microparticles (PMPs), are procoagulant membrane vesicles that are derived from activated platelets, the levels of which are elevated in patients with hypertension, coronary artery disease (CAD), diabetes, and stroke, all of which are conditions that lead to (and are associated with) atrial fibrillation (AF). We hypothesized the following: (1) PMP levels are elevated in patients with AF compared to levels in both healthy control subjects (ie, patients without cardiovascular diseases who are in sinus rhythm) and disease control subjects (ie, patients with hypertension, CAD, diabetes or stroke, but who are in sinus rhythm); (2) PMP levels correlate with levels of soluble P-selectin (sP-selectin) [a marker of platelet activation]; and (3) PMP levels are related to the underlying factors in patients with AF that contribute to the overall risk of stroke secondary to AF.

METHODS

We performed a case-control study of 70 AF patients, 46 disease control subjects and 33 healthy control subjects. Peripheral venous levels of PMP and sP-selectin were analyzed by flow cytometry and enzyme-linked immunosorbent assay, respectively.

RESULTS

Both AF patients and disease control subjects had significantly higher levels of PMPs (p < 0.001) and sP-selectin (p = 0.001) compared to healthy control subjects, but there was no difference between AF patients and disease control subjects. There was no difference in PMP levels between patients with paroxysmal and permanent AF (p = 0.581), and between those receiving therapy with aspirin and warfarin (p = 0.779). No significant correlation was observed between PMP and sP-selectin levels (p = 0.463), and the clinical characteristics that contribute to increased stroke risk in patients with AF. On stepwise multiple regression analysis in the combined cohort of AF patients plus disease control subjects, the presence/absence of AF was not an independent determinant of PMP and sP-selectin levels.

CONCLUSION

There is evidence of platelet activation (ie, high PMP and sP-selectin levels) in AF patients, but this is likely to be due to underlying cardiovascular diseases rather than the arrhythmia per se.

A longitudinal population-based study of prothrombotic factors in elderly subjects with atrial fibrillation: the Rotterdam Study 1990-1999

BACKGROUND

A prothrombotic or hypercoagulable state in atrial fibrillation may contribute to stroke and thromboembolism. Results of longitudinal population-based studies in elderly people with atrial fibrillation are not yet available.

METHODS

In the Rotterdam Study, a population-based prospective cohort study, 162 participants with atrial fibrillation at baseline, aged 55 years and over, were matched for age and gender with 324 people in sinus rhythm. Associations were examined between three coagulation factors and the risk of total and cardiac mortality and stroke. Hazard rate ratios were calculated with 95% confidence intervals using Cox's proportional hazards model, adjusted for potential confounders.

RESULTS

Plasma von Willebrand factor was, age- and gender-adjusted, associated with cardiac mortality in the total population (relative risk 1.16; 1.06-1.27, per 10 IU dL(-1) increase), but statistical significance was lost after additional adjustments. A strong association (1.27; 1.08-1.50, per 5-unit increase) was found between soluble P-selectin (sP-sel) and cardiac mortality in atrial fibrillation patients but not in participants in sinus rhythm. Furthermore, the expected association between fibrinogen and cardiac mortality was observed only in those in sinus rhythm (2.60; 1.69-4.01, per unit increase), and not in atrial fibrillation. No associations were found between coagulation factors and stroke.

CONCLUSIONS

In this population-based study, plasma levels of sP-sel predicted clinical adverse outcomes in atrial fibrillation, suggesting a role of platelets in the prothrombotic state associated with atrial fibrillation. Fibrinogen was a risk factor of cardiac and all-cause mortality in sinus rhythm, but not in atrial fibrillation.

Acute anticoagulation adjustment in patients with atrial fibrillation at risk for stroke: approaches, strategies, risks and benefits

The acute management of anticoagulation in patients with atrial fibrillation to prevent stroke and other thromboembolic complications includes the use of individualized strategies tailored to the patient and based on the situation (cardioversion, surgeries, dental procedures, cardiac interventions, other invasive procedures and initiation of, or adjustment to, warfarin dosing). The vast range of choices can cause confusion and few randomized controlled clinical trials in this area provide adequate guidance. Chronic anticoagulation management is more straightforward since clinical evidence is ample, randomized clinical trial data provides cogent informaiton and guidelines have been established. Acute management of anticoagulation in patients with atrial fibrillation to prevent thromboembolic complications is often unrecognized but is emerging as a crucial, but challenging, and increasingly complex aspect of the care of patients with atrial fibrillation. This review addresses issues regarding such patients who may be at risk for stroke and require acute adjustments of anticoagulation (in light of, or in lieu of, chronic anticoagulation). Several promising new strategies are considered in light of established medical care. This analysis provides practical recommendations based on available data and presents results from recent investigations that may provide insight into future strategies.

Is hypertension a prothrombotic state?

Hypertension is complicated by thrombosis-related events (such as myocardial infarction and stroke), and despite the high vascular pressures, these thrombotic occlusive events paradoxically occur more often than hemorrhagic episodes. The predisposition for thrombogenesis is increased in hypertension, which leads to changes in the platelets, endothelium, and matrix metalloproteinases and their inhibitors, as well as the coagulation and fibrinolytic pathways, which help promote the induction and the maintenance of this prothrombotic or hypercoagulable state. Other cardiovascular diseases, such as atrial fibrillation, congestive heart failure, and left ventricular hypertrophy, which may occur as a result of untreated hypertension, can also activate the prothrombotic state. These changes can, to a certain degree, be reversed by the treatment of hypertension, although the effects may be inconsistent. The evidence for antithrombotic therapy is less consistent, but in "high risk" hypertensive patients, antiplatelet therapy is useful.

Protein-, gene-, and cell-based therapeutic angiogenesis for the treatment of myocardial ischemia

Therapeutic angiogenesis aims at restoring perfusion to chronically ischemic myocardial territories by using growth factors or cells, without intervening on the epicardial coronary arteries. Despite angiogenesis having received considerable scientific attention over the last decade, it has not yet been shown to provide clinical benefit and is still reserved for patients who have failed conventional therapies. Nevertheless, angiogenesis is a very potent physiologic process involved in the growth and development of every animal and human, and it is likely that its use for therapeutic purposes, once its underlying mechanistic basis is better understood, will one day become an important modality for patients with CAD and other types of organ ischemia. This review summarizes current knowledge in therapeutic angiogenesis research.

Angiogenic factors in atrial fibrillation: a possible role in thrombogenesis?

BACKGROUND

The precise pathophysiological processes underlying the prothrombotic or hypercoagulable state in atrial fibrillation (AF) remain uncertain. We hypothesized a relationship between abnormal endothelial damage/dysfunction, coagulation, and angiogenic factors, thereby contributing to increased thrombogenicity.

METHODS

Plasma levels of von Willebrand factor (vWF, an index of endothelial damage/dysfunction) and tissue factor (TF, an index of coagulation), as well as the angiogenic factors, vascular endothelial growth factor (VEGF), angiopoietin-1 (Ang-1) and angiopoietin-2 (Ang-2), were measured by enzyme-linked immunosorbant assay (ELISA) in 59 chronic AF patients. Data were compared to 40 age- and sex-matched healthy controls in sinus rhythm.

RESULTS

Plasma vWF, VEGF and Ang-2 were significantly higher in AF patients compared to healthy controls (P=0.005, P=0.0055 and P<0.0001 respectively) but there were no significant differences in plasma Ang-1 or TF levels between the two groups (P=0.925 and P=0.121 respectively). Significant correlations were found between VEGF and vWF levels (Spearman, r=0.262, P=0.011) and between VEGF and Ang-2 (r=0.333, P=0.001).

CONCLUSIONS

Raised VEGF in association with Ang-2 and vWF may reflect a link between abnormal endothelial damage/dysfunction and angiogenic factors. These may act together to alter TF expression and endothelial integrity, thereby contributing to the prothrombotic state in AF.

Factor XIII Val34Leu polymorphism modulates the prothrombotic and inflammatory state associated with atrial fibrillation

Atrial fibrillation (AF) has been shown to confer a prothrombotic or hypercoagulable state, which could be related to inflammation. Factor XIII (FXIII) catalyses the cross-linking of fibrin monomers, increasing clot resistance; specifically, a common polymorphism, Val34Leu, in the FXIII-A subunit gene has been associated with more rapid FXIII activation. We hypothesised a role for this polymorphism in the prothrombotic state and inflammation in AF, and tested this hypothesis by measurement of indices of coagulation (tissue factor (TF) and fibrinogen), inflammation (interleukin-6 (IL6)) and platelet activation (soluble P selectin (sPsel)).

METHODS

We studied 90 stable outpatients (73 +/- 8 years) with persistent AF. The FXIII Val34Leu polymorphism was determined by polymerase chain reaction-allelic specific restriction assay (PCR-ASRA). Prevalence of Val34Leu polymorphism of patients was compared to 585 unrelated subjects from the same geographical area. Plasma fibrinogen (Clauss), TF, IL6 and sPsel (all ELISA) were quantified in patient group. Research indices were compared to 74 controls in sinus rhythm with similar clinical characteristics.

RESULTS

There were no statistical differences in FXIII polymorphism prevalence between AF patients and controls. Patients carrying the Leu34 allele had higher plasma levels of TF, IL6 and sPsel (all P < 0.05) compared to controls. Plasma IL6 and TF levels were significantly correlated (Spearman coefficient, r = 0.33, P < 0.01). On multivariate analysis, the Leu34 allele was independently associated with IL6 levels (P < 0.01), whereas TF levels were only associated with IL6 concentrations. However, sPsel and fibrinogen levels were not related to Leu34 allele.

CONCLUSION

FXIII Val34Leu polymorphism was independently associated with IL6 levels in AF. The Leu34 allele may potentially influence the prothrombotic state in these patients by modulating the inflammatory state.

Tissue factor expression in atrial endothelia associated with nonvalvular atrial fibrillation: possible involvement in intracardiac thrombogenesis

INTRODUCTION

Tissue factor plays a key role in the extrinsic coagulation pathway and is induced by inflammatory cytokines. Atrial myocarditis has been detected recently in some patients with lone atrial fibrillation. Virchow's triad of low blood flow, hypercoagulability, and endothelial dysfunction, enhances thrombus formation. The present study was designed to elucidate the role of endothelial dysfunction in thrombogenesis associated with nonvalvular atrial fibrillation.

MATERIAL AND METHODS

We investigated tissue factor expression in the endothelia of left atrial appendages obtained from seven patients with nonvalvular atrial fibrillation and cardiogenic thromboembolism. Tissues were divided into 7-13 sections and compared with control specimens from four patients who died of noncardiac events. Expression of tissue factor, von Willebrand factor and tissue factor pathway inhibitor was evaluated by immunohistochemistry.

RESULTS

Histopathologically, inflammatory cells infiltrated the endocardium and all seven patients showed features of persistent myocarditis. Activated T cells [15.3+/-9.4 cells/high power field (HPF, mean+/-S.D.) vs. control 2.2+/-4.4/HPF (P=0.0294)] and a few macrophages [5.1+/-8.4 cells/HPF vs. control 2.4+/-3.5 cells/HPF (P=NS)] infiltrated the endocardium. Tissue factor was overexpressed in the endothelia particularly in tissues containing inflammatory cells and denuded matrix of the endocardium, compared with the control group. Von Willebrand factor, but not tissue factor pathway inhibitor, was also overexpressed in these tissues.

CONCLUSION

Tissue factor expression induced by local inflammation is involved in the pathogenesis of thrombosis in patients with nonvalvular atrial fibrillation.

Relationship of interleukin-6 and C-Reactive protein to the prothrombotic state in chronic atrial fibrillation

OBJECTIVES

We sought to test the hypothesis that there is a relationship between inflammation and the prothrombotic state in atrial fibrillation (AF).

BACKGROUND

Atrial fibrillation is associated with a prothrombotic or hypercoagulable state, which may contribute to an increased risk of stroke and thromboembolism. Inflammation may be involved in the pathogenesis of AF, but the role of inflammation in the pathophysiology of the prothrombotic state of AF has not been studied in detail, despite evidence of a link between inflammation and arterial atherothrombotic disorders.

METHODS

We measured plasma indexes of inflammation (C-reactive protein [CRP] and interleukin-6 [IL-6]) and the prothrombotic state, including markers of platelet activation (soluble P-selectin), endothelial damage/dysfunction (von Willebrand factor), the coagulation cascade (tissue factor [TF], fibrinogen), and indexes of blood rheology (plasma viscosity, plasma fibrinogen, and hematocrit) in 106 patients with chronic AF and 41 healthy control subjects included in a cross-sectional analysis.

RESULTS

Compared with controls, AF patients had higher levels of IL-6 (p = 0.034), CRP (p = 0.003), TF (p = 0.019), and plasma viscosity (p = 0.045). Plasma IL-6 levels were higher among AF patients at "high" risk of stroke (p = 0.003). After adjusting for potential confounding clinical variables (e.g., vascular disease), AF remained significantly associated with a raised logarithmic transformation (log) of TF (p = 0.04), but the relationships between AF and log IL-6, log CRP, and plasma viscosity became nonsignificant. Among AF patients, log TF (p < 0.001) and high stroke risk (p = 0.003) were independent associates of log IL-6 (adjusted r(2) = 0.443), whereas log fibrinogen (p < 0.001) and plasma viscosity (p = 0.04) were independent associates of log CRP (adjusted r(2) = 0.259).

CONCLUSIONS

Increased plasma IL-6, CRP, and plasma viscosity support the case for the existence of an inflammatory state among "typical" populations with chronic AF. These indexes of inflammation are related to indexes of the prothrombotic state and may be related to the clinical variables of the patients (underlying vascular disease and co-morbidities), rather than simply to the presence of AF itself.