Markers of thrombin and platelet activity in patients with atrial fibrillation: correlation with stroke among 1531 participants in the stroke prevention in atrial fibrillation III study

Atrial fibrillation and stroke

INTRODUCTION

Stroke is one of the leading causes of mortality and morbidity globally. Atrial fibrillation (AF) is the most common sustained cardiac arrhythmia. It is set to reach epidemic proportions. AF is associated with a five-fold increase in risk of stroke. Strokes caused by AF more often are fatal or result in severe disability. Even though the incidence of stroke has been significantly reduced by oral anticoagulation, AF is thought to account for a significant proportion of cryptogenic strokes where no etiology is identified.

AREAS COVERED

This article reviews the literature related to AF and stroke, pathophysiological insights, diagnosis of AF in stroke patients, and its management (Graphical Abstract).

EXPERT OPINION

The pathophysiology of thrombogenesis that links AF and stroke is not well understood and is an area of active research to identify new therapeutic targets to prevent AF and stroke. As the nature of AF and stroke is multifaceted, an integrated care approach to managing AF and stroke is increasingly essential.

The Role of Major Inflammatory Biomarkers in the Pathogenesis of Atrial Fibrillation

Many studies have reported a relationship between inflammation and atrial fibrillation (AF). According to the literature, inflammation is the key component in pathophysiological processes during the development of AF; the amplification of inflammatory pathways triggers AF, and, at the same time, AF increases the inflammatory state. The plasma levels of several inflammatory biomarkers are elevated in patients with AF; therefore, inflammation might contribute to both the maintenance and occurrence of AF and its thromboembolic complications. Numerous inflammatory markers have been linked to AF, including CD40 ligand, fibrinogen, matrix metalloproteinase (MMP)-9, monocyte chemoattractant protein-1, myeloperoxidase, plasminogen activator inhibitor-1, and serum amyloid A. There are many pathophysiological aspects of AF that are linked to these inflammatory biomarkers, including atrial structural remodeling and atrial dilatation, increased atrial myocyte expression, fluctuations in calcium cycling, cardiac remodeling promotion, increased cardiac myocyte proliferation and terminal differentiation, production of several MMPs, the pathogenesis of atherosclerosis and cardiomyocyte apoptosis, an increased degree of fibrosis in atrial myocardium, and the progression and development of atherogenesis and atherothrombosis. The present review article aims to provide an updated overview and focus on the basic role of different biomarkers of inflammation in the pathophysiological aspects of the pathogenesis of AF.

Thrombin: A Pivotal Player in Hemostasis and Beyond

The serine protease thrombin, a naturally derived enzyme, plays a key role in hemostasis by converting fibrinogen to fibrin and activating coagulation factor XIII whereby the fibrin clot is stabilized. Furthermore, thrombin activates platelets through protease-activated receptors on the platelet surface. Conversely, thrombin also exerts anticoagulant effects, enhancing the protein C activity while complexed with thrombomodulin. During recent years, it has become evident that thrombin has significant effects beyond hemostasis, as it contributes also to modulation of the endothelium, promotes inflammation and angiogenesis, and plays a role in tumor progression. Yet, due to the very short half-life and almost immediate inhibition in fluid phase by antithrombin, thrombin itself remains elusive, and only indirect measurement of thrombin generation is possible. This review provides a description of structure and mechanisms of action of thrombin both in physiological and pathological processes. Furthermore, it summarizes laboratory tests that measure in vivo or ex vivo thrombin generation, and presents knowledge on the value of these biomarkers in bleeding disorders, cardiopulmonary bypass surgery, and thromboembolic risk assessment in different patient populations. Finally, this review outlines further perspectives on using thrombin generation biomarkers for research purposes and in clinical practice.

Von Willebrand Factor and ADAMTS13 as Predictors of Adverse Outcomes in Patients With Nonvalvular Atrial Fibrillation

Background

Von Willebrand factor (VWF) elevation correlates with the left atrial blood stasis in nonvalvular atrial fibrillation (NVAF). However, the long-term impact of elevated VWF in patients with NVAF is not well established.

Methods

To assess the impact of VWF and a disintegrin and metalloproteinase with a thrombospondin type 1 motif, member 13 (ADAMTS13) in conjunction with echocardiographic measures of left atrium blood stasis on clinical outcomes, 414 NVAF prospectively recruited (October 4, 2007, to April 27, 2009) patients were followed for 3 years. VWF antigen, VWF activity, ADAMTS13 activity, and echocardiographic findings were assessed at baseline. Thromboembolism (TE) (stroke/transient ischemic attack (TIA)), myocardial infarction, or TE of other locations), major bleeding, clinically relevant nonmajor bleeding, and all-cause mortality were assessed by clinical follow-up, questionnaire, or telephone communication.

Results

Among 374 patients (mean age, 63.4 ± 12.7 years; 25% females) who had complete follow-up data, there were 33 TE in 32 patients (8.6%), 18 deaths (5.1%), and 33 bleeding events (21 major bleeding and 12 clinically relevant nonmajor bleeding) in 25 patients (6.7%). VWF antigen was predictive of TE in the univariate examination (hazard ratio [HR]: 1.007, 95% confidence interval [CI]: 1.002, 1.013, P = 0.011) but not in multivariate analysis. VWF was an independent predictor of all-cause mortality (HR: 1.011, 95% CI: 1.003, 1.020, P = 0.011) and a composite of TE and all-cause mortality (HR: 1.006, 95% CI: 1.001, 1.012, P = 0.039) in multivariate analysis. ADAMTS13 was not predictive of clinical outcomes in multivariate analysis.

Conclusions

Among patients with NVAF, VWF is an independent predictor of poor outcomes including death and a composite of death and TE. As such, VWF measure may help identify high-risk patients and provide further stratification beyond CHA₂DS₂-VASc assessment.

Atrial fibrillation and the prothrombotic state: revisiting Virchow’s triad in 2020

Atrial fibrillation (AF) is characterised by an increased risk of pathological thrombus formation due to a disruption of physiological haemostatic mechanisms that are better understood by reference to Virchow’s triad of ‘abnormal blood constituents’, ‘vessel wall abnormalities’ and ‘abnormal blood flow’. First, there is increased activation of the coagulation cascade, platelet reactivity and impaired fibrinolysis as a result of AF per se, and these processes are amplified with pre-existing comorbidities. Several prothrombotic biomarkers including platelet factor 4, von Willebrand factor, fibrinogen, β-thromboglobulin and D-dimer have been implicated in this process. Second, structural changes such as atrial fibrosis and endothelial dysfunction are linked to the development of AF which promote further atrial remodelling, thereby providing a suitable platform for clot formation and subsequent embolisation. Third, these factors are compounded by the presence of reduced blood flow secondary to dilatation of cardiac chambers and loss of atrial systole which have been confirmed using various imaging techniques. Overall, an improved understanding of the various factors involved in thrombus formation will allow better clinical risk stratification and targeted therapies in AF.

Stroke and Bleeding Risk Assessments in Patients With Atrial Fibrillation: Concepts and Controversies

Risk assessments are an important element in the management of patients with atrial fibrillation (AF). In this review, we aim to discuss the concepts and controversies surrounding the various risk factors for stroke and bleeding in AF. Indeed, there are a variety of clinical, electrical, biological, and genetic markers to guide stroke and bleeding risk assessments in AF. The more common factors have been used to formulate risk stratification scores. Some risk factors have shown promise, but others remain less well-defined. Our aim is to discuss concepts and controversies surrounding current evidence of risk factors for stroke and bleeding assessments in AF.

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.

Predictive Role of Coagulation, Fibrinolytic, and Endothelial Markers in Patients with Atrial Fibrillation, Stroke, and Thromboembolism: A Meta-Analysis, Meta-Regression, and Systematic Review

Background

The pathophysiological mechanism associated with the higher prothrombotic tendency in atrial fibrillation (AF) is complex and multifactorial. However, the role of prothrombotic markers in AF remains inconclusive.

Material/Methods

We conducted a meta-analysis of observational studies evaluating the association of coagulation activation, fibrinolytic, and endothelial function with occurrence of AF and clinical adverse events. A comprehensive subgroup analysis and meta-regression was performed to explore potential sources of heterogeneity.

Results

A literature search of major databases retrieved 1703 studies. After screening, a total of 71 studies were identified. Pooled analysis showed the association of coagulation markers (D-dimer (weighted mean difference (WMD)=197.67 and p<0.001), fibrinogen (WMD=0.43 and p<0.001), prothrombin fragment 1–2 (WMD=0.53 and p<0.001), antithrombin III (WMD=23.90 and p=0.004), thrombin-antithrombin (WMD=5.47 and p=0.004)); fibrinolytic markers (tissue-type plasminogen activator (t-PA) (WMD=2.13 and p<0.001), plasminogen activator inhibitor (WMD=11.44 and p<0.001), fibrinopeptide-A (WMD=4.13 and p=0.01)); and endothelial markers (von Willebrand factor (WMD=27.01 and p<0.001) and soluble thrombomodulin (WMD=3.92 and p<0.001)) with AF.

Conclusions

The levels of coagulation, fibrinolytic, and endothelial markers have been reported to be significantly higher in AF patients than in SR patients.

Activated factor IX, factor XI and tissue factor identify patients with permanent atrial fibrillation treated with warfarin who are at risk of ischemic stroke

INTRODUCTION

Previously, we have demonstrated that significant proportions of patients with various cardiovascular diseases have active tissue factor and active factor XIa in their plasma. In the current study, we evaluated active tissue factor and active factors (F)XI and FIX in plasma from patients with atrial fibrillation.

MATERIAL AND METHODS

In 110 consecutive patients with permanent atrial fibrillation receiving warfarin, we determined active tissue factor, together with plasma FIXa and FXIa, using clotting assays by measuring the response to inhibitory monoclonal antibodies.

RESULTS

Sixteen (14.5%) patients had detectable active tissue factor and active FXIa, including 11 subjects with both factors, while FIXa was observed in 28 (25.7%) patients. The three positive groups did not differ from the patients without these factors with regard to demographic and clinical characteristics. Von Willebrand factor was higher in the active tissue factor-positive group (p < 0.0001) and FXIa-positive group (p = 0.0037). Individuals positive for active tissue factor and FXIa had higher plasma interleukin-6 levels (p = 0.0014 and 0.0322, respectively). The presence of active tissue factor, FXIa and FIXa in anticoagulated patients with permanent atrial fibrillation correlated with elevated von Willebrand factor and interleukin-6. During a 3-year follow-up, ischemic stroke (n = 12, 10.9%) occurred more commonly among atrial fibrillation patients who had circulating TF (p = 0.002) or FXIa (p = 0.013).

CONCLUSIONS

These data suggest that circulating active coagulation factors, in particular TF and FXIa, can be detected despite oral anticoagulation in a significant proportion of patients with atrial fibrillation, and could represent novel markers of persistent prothrombotic alterations predisposing to ischemic stroke.

Do Different Atrial Flutter Types Carry the Same Thromboembolic Risk?

Thromboembolic risk of atrial flutter (AFl) types has not been elucidated sufficiently in previous reports. The authors classified the patients according to surface electrocardiogram and electrophysiologic characteristics as those with typical AFl (37 patients, 78.4% male, mean age 59.8 ±9.5 years) and atypical AFl (13 patients, 69.2% male, mean age 60.9 ±6.9 years) and compared them regarding some clinical, echocardiographic, and hematologic parameters. An age- and gender-matched control group composed of 20 individuals without any organic heart disease in sinus rhythm was chosen (80% male, mean age 60.3 ±7.9 years). Clinical features such as age, gender, organic heart disease, hypertension, diabetes mellitus, AFl duration, and the prevalence of paroxysmal atrial fibrillation were similar in both AFl groups. Echocardiographic parameters such as left ventricular ejection fraction, left atrial (LA) diameter, LA spontaneous echo contrast, and LA appendage emptying velocities were similar in both AFl groups. Fibrinogen, fibrin D-dimer, and thrombin-antithrombin III levels reflecting coagulation system activity were found to be increased in the patients with atypical AFl when compared with those with typical AFl and the control group (p<0.001). In Pearson’s correlation analysis, significant correlation between these hematologic markers and clinical and echocardiographic parameters were not found (p>0.05). The coagulation system activity was found to be increased in patients with atypical AFl. Thus, anticoagulation due to the increased thromboembolic risk should be considered in patients with atypical AFl.

Hypercoagulopathy in Stroke Patients with Nonvalvular Atrial Fibrillation: Hematologic and Cardiologic Investigations

The coagulation system is activated and coagulation activation markers are elevated in acute ischemic stroke with nonvalvular atrial fibrillation (NVAF). The etiology, severity, and prognosis of the ischemic stroke might be estimated with the level of the activation of the coagulation system. In this study, prothrombin F1+2 (F1+2), D-dimer, and fibrinogen levels were measured in patients with acute ischemic stroke with and without NVAF, and stroke severity was compared with these hemostatic parameters. Of 55 patients, 29 had sinus rhythm (group I), 26 had NVAF (group II); 20 healthy subjects (group III) were included in the study. Subtypes of cerebral infarction were classified. The patients underwent stroke severity, electrocardiography, echocardiography, cranial computed tomography, cervical duplex ultrasonography, and hemostatic parameter studies. In group II, F1+2 level (2.83±0.89) was significantly higher than in group I (2.33±0.80) and III (1.94±0.64) (p values: group I-II, 0.036; groups II-III, 0.001; groups I-III, 0.104). In group III, fibrinogen level (251.64±60.96) was significantly lower than that in groups I (347.97±111.49) and II (364.04±86.20) (p=0.001). D-dimer was not significantly different between groups. In group I, lacunar syndrome (LACS), and in group II, partial and total anterior circulation syndrome (PACS+TACS) were more common (p=0.013, p=0.001, respectively). In group II, Scandinavian Stroke Scale scores were lower than those in group I (group I=45.2±14, group II=35.4±18.9, p=0.02). In conclusion, activation of coagulation, demonstrated by increment F1+2, is more abundant in the stroke patients with NVAF than in the stroke patients with sinus rhythm. Our results also showed that activation of the hemostatic system might be related to stroke subtype and stroke severity. It is suggested that the oral anticoagulation treatment as prophylaxis is important in the prevention of stroke in patients with NVAF.

Association of inflammatory and hemostatic markers with stroke and thromboembolic events in atrial fibrillation: a systematic review and meta-analysis

BACKGROUND

Atrial fibrillation (AF) increases the risk of stroke and thromboembolic events. Recently, biomarkers have been proposed as a practical tool to predict adverse outcomes in patients with AF. The prognostic value of inflammatory and hemostatic markers in AF has been widely studied; however, the results of previous studies have been inconclusive.

METHODS

We conducted a systematic review and meta-analysis to evaluate the association of inflammatory and hemostatic markers with stroke and thromboembolic events in patients with AF.

RESULTS

A total of 27 studies including 22,176 participants met our inclusion criteria for the systematic review. Our meta-analysis determined that elevated circulating plasminogen activator inhibitor-1 (PAI-1) and thrombin-antithrombin (TAT) were significantly associated with increased risk of stroke in patients with AF (standardized mean difference [SMD], 0.89; 95% confidence interval [CI], 0.20-1.59 and 1.43; 95% CI, 0.40-2.47, respectively). Higher levels of D-dimer were associated with increased subsequent thromboembolic event risk with a pooled hazard ratio of 2.90 (95% CI, 1.22-6.90) for cohort studies and an SMD of 0.93 (95% CI, 0.36-1.50) for case-control studies. There was also very limited evidence indicating that other biomarkers-such as interleukin-6, von Willebrand factor, P-selectin, and mean platelet volume-could predict adverse outcomes in AF.

CONCLUSIONS

In conclusion, increased circulating PAI-1 and TAT levels were significantly associated with subsequent stroke in patients with AF, and high levels of D-dimer were associated with thromboembolic events in AF. Further epidemiologic studies are needed to accumulate more evidence on the prognostic role of inflammatory and hemostatic markers in AF.

Hemostasis and alterations of the central nervous system

Modulation of coagulation has been successfully applied to ischemic disorders of the central nervous system (CNS). Some components of the coagulation system have been identified in the CNS, yet with limited exception their functions have not been clearly defined. Little is known about how events within the cerebral tissues affect hemostasis. Nonetheless, the interaction between cerebral cells and vascular hemostasis and the possibility that endogenous coagulation factors can participate in functions within the neurovascular unit provide intriguing possibilities for deeper insight into CNS functions and the potential for treatment of CNS injuries. Here, we consider the expression of coagulation factors in the CNS, the coagulopathy associated with focal cerebral ischemia (and its relationship to hemorrhagic transformation), the use of recombinant tissue plasminogen activator (rt-PA) in ischemic stroke and its study in animal models, the impact of rt-PA on neuron and CNS structure and function, and matrix protease generation and matrix degradation and hemostasis. Interwoven among these topics is evidence for interactions of coagulation factors with and within the CNS. How activation of hemostasis occurs in the cerebral tissues and how the brain responds are difficult questions that offer many research possibilities.

Endogenous t-PA-antigen is an independent predictor of adverse cardiovascular events and all-cause death in patients with atrial fibrillation

BACKGROUND

Atrial fibrillation (AF) is associated with raised levels of P-selectin and an apparent prothrombotic state. However, levels of tissue plasminogen activator (t-PA)-antigen are increased also. We investigated whether high levels of endogenous t-PA-antigen or soluble P-Selectin (sP-Selectin), independently of CHADS(2-) or CHA(2) DS(2) VASc-scores, predict major adverse cardiovascular events (MACE) in patients with AF when treated according to current guidelines.

METHODS

This prospective, longitudinal single-center study included 269 patients with AF. Blood samples were analyzed for sP-Selectin and t-PA-antigen concentration by means of commercially available enzyme-linked immunoassays.

RESULTS

Patients were followed for a median duration of 1933 (1517-2277) days, during which 78 MACE and 82 deaths occurred. In multivariable analyses t-PA-antigen above the median of 4.22 ng mL(-1) was associated with MACE and all-cause death (HR 2.55 [1.43-4.57]; P = 0.002) and (HR 2.54 [1.38-4.68]; P = 0.003), respectively. There was no association of sP-Selectin with MACE or all-cause death. Furthermore, t-PA-antigen above the median independently of the CHADS(2-) or CHA(2) DS(2) VASc-scores predicted MACE and all-cause death. In patients with low and intermediate-risk for cardiovascular events according to the CHADS(2)-score the addition of high t-PA-antigen levels (> 4.22 ng mL(-1) ) had a significant impact on the patients' outcome (low-risk group, HR 3.25 [1.13-9.38]; P = 0.029 and intermediate-risk group, HR 2.33 [1.27-4.26]; P = 0.006, respectively).

CONCLUSION

High endogenous t-PA-antigen independently predicts MACE and all-cause death in patients with AF. Accordingly, t-PA-antigen as an indicator of a prothrombotic state represents a novel biomarker, which might add to risk stratification in patients with AF.

Plasminogen activators and ischemic stroke: conditions for acute delivery

Appropriate acute treatment with plasminogen activators (PAs) can significantly increase the probability of minimal or no disability in selected ischemic stroke patients. There is a great deal of evidence showing that intravenous recombinant tissue PAs (rt-PA) infusion accomplishes this goal, recanalization with other PAs has also been demonstrated in the development of this treatment. Recanalization of symptomatic, documented carotid or vertebrobasilar arterial territory occlusions have also been achieved by local intra-arterial PA delivery, although only a single prospective double-blinded randomized placebo-controlled study has been reported. The increase in intracerebral hemorrhage with these agents by either delivery approach underscores the need for careful patient selection, dose-appropriate safety and efficacy, proper clinical trial design, and an understanding of the evolution of cerebral tissue injury due to focal ischemia. Principles underlying the evolution of focal ischemia have been expanded by experience with acute PA intervention. Several questions remain open that concern the manner in which PAs can be applied acutely in ischemic stroke and how injury development can be limited.

Evidence-based percutaneous closure of the left atrial appendage in patients with atrial fibrillation

Atrial fibrillation is the most common cardiac arrhythmia, and its prevalence is increasing. Cardioembolic stroke, most of the times secondary to thrombus formation in the left atrial appendage, is its most feared and life threatening consequence. Oral anticoagulation with vitamin-K-antagonists is currently the most used prophylaxis for stroke in patients with atrial fibrillation; unfortunately, its benefits are limited by a narrow therapeutic window and an increased risk for bleeding, making it often undesired. Percutaneous occlusion of the left atrial appendage is a novel alternative strategy for cardioembolic stroke prophylaxis in patients with atrial fibrillation at a high risk of stroke but with contraindication for long-term oral anticoagulation therapy. At present, several devices have been developed specifically for percutaneous occlusion of the left atrial appendage. Current results show good feasibility and efficacy for these devices, with a high rate of successful implantation, although also associated with the inherent potential periprocedural complications. This work reviews the current state of the art of percutaneous left atrial appendage closure for stroke prophylaxis in patients with atrial fibrillation.

Atherosclerosis and thromboembolic risk in atrial fibrillation: focus on peripheral vascular disease

Atrial fibrillation (AF) is the most common cardiac arrhythmia in clinical practice. It results in a 5-fold increased risk for stroke and thromboembolism and is associated with a high morbidity and mortality. AF shares several risk factors and pathophysiological features with atherosclerosis. Hence AF is often complicated by a variety of other cardiovascular conditions. Indeed, peripheral vascular disease (PVD) is highly prevalent among AF patients and associates with increased mortality. Inclusion of PVD within stroke risk scoring systems such as the CHA2DS2-VASc score improves risk stratification of AF patients. Of note, PVD has not been previously well documented nor looked for in observational studies or clinical trials. The aim of this present review article is to provide an overview of the association between atherosclerosis (with particular focus on PVD) and AF as well as its complications.

Genetic dissection of platelet function in health and disease using systems biology

Technological advances in protein and genetic analysis have altered the means by which platelet disorders can be characterized and studied in health and disease. When integrated into a single analytical framework, these collective technologies are referred to as systems biology, a unified approach that links platelet function with genomic/proteomic studies to provide insight into the role of platelets in broad human disorders such as cardiovascular and cerebrovascular disease. This article reviews the historical progression of these applied technologies to analyze platelet function, and demonstrates how these approaches can be systematically developed to provide new insights into platelet biomarker discovery.

Platelet systems biology using integrated genetic and proteomic platforms

Platelets retain megakaryocyte-derived mRNA, an abundant and diverse array of miRNAs, and have evolved unique adaptive signals for maintenance of genetic and protein diversity. Quiescent platelets generally display minimal translational activity, although maximally-activated platelets retain the capacity for protein synthesis. Progressive data using multiple platelet activation models clearly demonstrate that platelet responses to the majority (if not all) agonists are highly variable within the population, demonstrating considerable heritability in siblings, twins, and families with premature coronary artery disease. Research from our laboratory has adapted global profiling strategies to close the knowledge gap currently existing between genetic variability and platelet phenotypic responsiveness. We have applied iterative algorithms for genetic biomarker discovery and class prediction models of platelet phenotypes, with the goal of systematically analyzing integrated mRNA/miRNA/proteomic datasets for identification of regulatory networks that define phenotypic variability in platelet responses. This approach has the potential to define platelet genetic biomarkers predictive of thrombohemorrhagic outcomes in both normal and widely disparate clinical conditions.

Gender differences in anticoagulation and antithrombotic therapy

Cardiovascular disease is the main cause of mortality and morbidity worldwide. The rate of thromboembolic events has increased in women but not in men. Large clinical studies support the use of a variety of antithrombotic drugs for the treatment of patients with different cardiovascular diseases. The heterogeneous patient population included in these trials affects the attempt to generalize the study results to subgroups, which are not sufficiently represented in the study population, such as women and other minorities. Gender-related differences in the clinical presentation and outcome seem to relate to differences in platelet biology and coagulation reactions, resulting in different rates of thromboembolic and bleeding events. The effectiveness of antithrombotic therapies and the occurrence of adverse events define the clinical benefit of the treatment for each patient. This chapter gives an overview of the currently available data on gender-differences in anticoagulation and antithrombotic therapy.

Pharmacologic strategies for the prevention of stroke in patients with atrial fibrillation

OPINION STATEMENT

Stroke is a dreaded complication of atrial fibrillation. In the past, preventive therapy included aspirin and oral anticoagulation. Selected patients who are not suitable for oral anticoagulation may benefit from the addition of clopidogrel with aspirin. This combination, when compared with aspirin, offers a reduced risk of stroke at a cost of more major bleeding. We use this therapy in patients with atrial fibrillation who have unstable coronary syndromes or in patients who receive coronary artery stents who are not good candidates for "triple therapy" with aspirin, clopidogrel, and warfarin. The duration of therapy is tempered by many variables. In the case of coronary stents, we ask the interventionalist to consider a bare metal stent to shorten the duration of need for clopidogrel plus aspirin. After several months of combination therapy, we stop this therapy and begin warfarin therapy. Dabigatran is commercially available in the United States. In patients who have difficult to control International Normalized Ratio (INR) values or who do not wish to have regular coagulation monitoring, dabigatran offers a huge advantage. The benefit seems less if the INR is consistently within range. We are impressed with the superior reduction in stroke and systemic embolism with 150 mg of dabigatran twice daily compared to warfarin and also its low risk of intracranial hemorrhage. The results of clinical trials involving factor Xa agents are now being presented. How these agents fit into the marketplace remains to be seen but they will offer clinicians additional therapy for stroke prevention in atrial fibrillation.

Antithrombotic therapy in cardiac embolism

Anticoagulation is indicated in most cardioembolic ischemic strokes for secondary prevention. In many cardiac conditions, anticoagulation is also indication for primary stroke prevention, mainly when associated to vascular risk factors. Anticoagulation should be started as soon as possible, as it is safe even in moderate acute strokes. The efficacy of early anticoagulation after cardioembolic stroke in relation to outcome has not been assessed adequately, but there is evidence from animal models and clinical studies that anticoagulation with unfractionated heparin is associated with a better outcome mediated in part by its anti-inflammatory properties.

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.

Prothrombin fragments in cardiovascular disease

Prothrombin fragment 1+2 (F1+2), which comes from in vivo cleavage of prothrombin by factor Xa, is considered to be useful for diagnosis of thrombosis. Recognition of the central role of thrombosis in the pathogenesis ofcardiovascular disease has prompted growing interest in the association o F1+2 with cardiovascular clinical syndromes. Increased F1+2 levels have reported in venous thromboembolism, inflammation, cancer, sepsis, acute coronary syndromes, stroke, peripheral arterial disease, atrial fibrillation and during the postoperative period. However, a clear relationship with the appearance of thrombosis has not always been consistently demonstrated. Besides its potential prognostic and diagnostic value, it could also be usefu in assessing the impact of various therapies. However, it should be kept in mind that measurement of hemostasis activation markers has several important biological and methodological disadvantages. Activation markers reflect the presence of thrombosis in any vascular bed, so they are not specific. Furthermore, elevations occur not only in the presence of overt thrombosis but also during the hypercoagulable state. The cutoff level to be used for the definition of elevations is still largely unknown due to the use of different analytical methods, none of which have been standardized until know. Finally, the prognostic value of F1+2 and other markers of coagulation activation remains to be fully defined in future studies.

A study of blood soluble P-selectin, fibrinogen, and von Willebrand factor levels in idiopathic and lone atrial fibrillation

AIMS

A prothrombotic state with elevated levels of soluble P-selectin (sP-sel), fibrinogen, von Willebrand factor (vWf), and other haemostatic indices has been reported in some patients with atrial fibrillation (AF). Whether these changes are due to AF itself or coexistent cardiovascular diseases remains a matter of debate. Therefore, in the present study, the differences in plasma levels of sP-sel, fibrinogen, and vWf between patients with idiopathic/lone AF and sex-, age-, and risk factor-matched controls were investigated to determine whether AF itself might be associated with a hypercoagulable state.

METHODS AND RESULTS

Ninety consecutive patients (63 males, 54.1 ± 10.1 years) with idiopathic AF were studied, 60 (43 males, 48.8 ± 7.5 years) of whom were diagnosed as lone AF. Plasma sP-sel and vWf were measured by enzyme-linked immunosorbent assay. Plasma fibrinogen was measured by chromometry. These indices in AF patients were compared with those in sex-, age- and risk factor-matched controls. Compared with the controls, patients with idiopathic AF had higher levels of sP-sel (AF vs. control: 33.4 ± 7.4 vs. 29.2 ± 6.5 ng/mL, P < 0.001) and fibrinogen (AF vs. control: 3.3 ± 0.9 vs. 3.0 ± 0.6 g/L, P = 0.02), but not vWf, whether with the adjustment of covariates or not. As for those < 60 years, between lone AF and age-matched controls, significant difference existed in the levels of sP-sel (AF vs. control: 34.5 ± 7.3 vs. 30.2 ± 7.3 ng/mL, P = 0.002), but not in those of fibrinogen and vWf, whether with the adjustment of covariates or not.

CONCLUSIONS

Both platelet activation and abnormal changes in coagulation were suggested in idiopathic AF and a platelet activation state in lone AF. This supports the notion that AF per se contributes to a state of hypercoagulation.

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.

Sex-related differences in the risk factor profile and medications of patients with atrial fibrillation recruited in J-TRACE

BACKGROUND

Clinical characteristics, including risk factors for thromboembolism, and medications differ between men and women with atrial fibrillation (AF) in Western countries. Whether such a difference exists for Japanese patients with AF is unclear, so data from J-TRACE were used to investigate this issue.

METHODS AND RESULTS

A total of 2,892 patients (2,028 men, 864 women; 70.3 years old) with AF were analyzed for the respective prevalences of risk factors and medications. CHADS2 score was calculated to determine thromboembolic risk level. Women were older (P<0.001), and more frequently had heart failure (P<0.001), and hypertension (P=0.051) than men. The proportion of subjects aged 75 years or older was higher among women than among men (P<0.001). CHADS2 score was therefore significantly higher in women than in men (2.05+/-1.29 vs 1.88+/-1.33, P<0.001). Sex-related differences were not observed for the prevalence of diabetes mellitus, myocardial infarction or ischemic stroke, nor did warfarin usage differ between men and women.

CONCLUSIONS

Sex-related differences were observed in the risk factor profile and medications of Japanese patients with AF. CHADS2 score was higher in women than in men.

Cardioembolic stroke in atrial fibrillation-rationale for preventive closure of the left atrial appendage

Atrial fibrillation is the most common cardiac arrhythmias, and a major cause of morbidity and mortality due to cardioembolic stroke. The left atrial appendage is the major site of thrombus formation in non-valvular atrial fibrillation. Loss of atrial systole in atrial fibrillation and increased relative risk of associated stroke point strongly toward a role for stasis of blood in left atrial thrombosis, although thrombus formation is multifactorial, and much more than blood flow irregularities are implicated. Oral anticoagulation with vitamin-K-antagonists is currently the most effective prophylaxis for stroke in atrial fibrillation. Unfortunately, this treatment is often contraindicated, particularly in the elderly, in whom risk of stroke is high. Moreover, given the risk of major bleeding, there is reason to be skeptical of the net benefit when warfarin is used in those patients. This work reviews the pathophysiology of cardioembolic stroke and critically spotlights the current status of preventive anticoagulation therapy. Various techniques to exclude the left atrial appendage from circulation were discussed as a considerable alternative for stroke prophylaxis.

Coagulation activity is increased in the left atria of patients with paroxysmal atrial fibrillation during the non-paroxysmal period. Comparison with chronic atrial fibrillation

BACKGROUND

Evaluation of plasma markers of thrombin activity (thrombin-antithrombin III complex: TAT), active fibrinolysis (plasmin-alpha 2-plasmin inhibitor complex: PIC), and platelet activity (platelet factor 4: PF4) is useful for identifying patients with various cardiovascular disorders who are at high risk of thromboembolism. In this study, these markers were investigated in the left atria (LA) of patients with paroxysmal atrial fibrillation (pAF) in the non-paroxysmal period.

METHODS AND RESULTS

Patients with pAF (n=10) and chronic AF (cAF) (n=10) were enrolled. TAT, PIC, and PF4 levels were determined in blood samples obtained from the LA of AF patients before radiofrequency catheter ablation. TAT levels were high in both pAF and cAF patients. PF4 levels were slightly elevated in both groups, but there was no significant difference between the groups. On the other hand, PIC levels in both groups were almost within normal limits, again with no significant difference between groups.

CONCLUSIONS

Coagulation activity is elevated in the LA of patients with pAF, even in the non-paroxysmal period, so these patients are at high risk of thromboembolism and anticoagulant therapy is indicated.

Prospective, observational study of antiplatelet and coagulation biomarkers as predictors of thromboembolic events after implantation of ventricular assist devices

BACKGROUND

Long-term success in ventricular assist device (VAD) recipients is limited by thromboembolic events, the prediction of which remains elusive. We evaluated the predictive value of aspirin hyporesponsiveness and markers of coagulation and fibrinolysis.

METHODS

We prospectively enrolled patients scheduled to undergo VAD implantation between June 2004 and March 2006. Once before surgery, daily during hospitalization, and weekly after discharge we assessed platelet function, measured prothrombin activation fragment 1.2 (F1.2) and plasminogen activator inhibitor-1 (PAI-1) concentrations, and evaluated aspirin hyporesponsiveness by whole-blood aggregometry and thromboelastography. All patients received 325 mg oral aspirin daily from at least 7 days before VAD implantation. Follow-up continued until heart transplantation, death or closure of the database.

RESULTS

We included 26 patients (median follow-up 315 days, range 9-833 days). In eight (31%) patients, 14 thromboembolic events occurred at a median of 42 (interquartile range 26-131) days. Only six (43%) events based on whole-blood aggregometry and one (7%) based on thromboelastography coincided with aspirin hyporesponsiveness. Within-patient variability was high for both tests (59% and 567%, respectively). Compared with levels before surgery, PAI-1 concentrations were raised for up to 45 days (P <0.0001) and those of F1.2 for up to 3 days (P = 0.0001) after VAD implantation. PAI-1 and F1.2 levels did not rise significantly further before thromboembolic events.

CONCLUSIONS

Aspirin hyporesponsiveness was not associated with raised risk of future clinical thromboembolic events after VAD implantation. Impaired fibrinolysis, demonstrated by raised PAI-1 concentrations, might, however, indicate a predisposition to such events early after surgery.

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.

Accumulation of risk factors enhances the prothrombotic state in atrial fibrillation

BACKGROUND

The present study was conducted to investigate the relation between the accumulation of the risk factors of thromboembolism and the levels of hemostatic markers in patients with nonvalvular atrial fibrillation (NVAF).

METHODS

Five hundred ninety-one NVAF patients and 129 control subjects were categorized into low, moderate or high risk of thromboembolism, according to CHADS(2) index. One point each was given to patients with advanced age (> or =75 years), hypertension, congestive heart failure, and diabetes mellitus, and 2 points, to those with prior ischemic stroke or transient ischemic attack. Patients with CHADS(2) score of 0, 1 or 2, and > or =3 were classified as low, moderate and high risk, respectively. Levels of hemostatic markers (platelet factor 4, beta-thromboglobulin, prothrombin fragment F1+2 and D-dimer) were determined.

RESULTS

Of 591 patients with NVAF, 302 were treated with warfarin (mean international normalized ratio 1.88). D-dimer levels increased as the risk level increased irrespective of warfarin use. Particularly, NVAF patients without receiving warfarin (n=289) had significantly higher D-dimer levels than control patients (e.g., for high risk patients, 175+/-144 vs 75+/-87 ng/ml, p<0.001), while NVAF patients receiving warfarin had intermediate levels (136+/-156 ng/ml). F1+2 levels increased as the risk level increased, and were significantly suppressed by warfarin. Levels of markers of platelet activation (platelet factor 4 and beta-thromboglobulin) were increased in NVAF patients but not affected by the risk level.

CONCLUSION

Coagulation and fibrinolytic activity is increased along with the accumulation of the risk factors of thromboembolism in NVAF patients.

Factor VII -323 decanucleotide D/I polymorphism in atrial fibrillation: implications for the prothrombotic state and stroke risk

There are limited data on the influence of genetic polymorphisms in atrial fibrillation (AF) stroke risk. We hypothesized that a functional haemostatic polymorphism, that is, the factor VII -323 Del/Ins polymorphism, would influence the prothrombotic state associated with AF, as well as stroke risk. Other functional polymorphisms were also tested.

METHODS

We performed a cross-sectional study of 119 AF patients, who were compared to 96 patients with stroke secondary to AF. In the first patient group, we analysed plasma prothrombin fragment 1+2 levels (F1+2, an index of thrombin generation) to reflect the prothrombotic state of AF.

RESULTS

AF patients carrying the -323 Ins allele had lower plasma F1+2 levels (P=0.015). After multivariate analysis adjusted by age, sex and clinical risk factors, advanced age and 807C/T polymorphism of glycoprotein Ia (GPIa) gene were associated with higher risk of ischaemic stroke (OR: 1.06; P=0.003 and OR: 1.91; P=0.025), whilst FVII Ins -323 allele was associated with lower stroke risk (OR: 0.41; P=0.017).

CONCLUSION

FVII -323 Ins allele may modulate the prothrombotic state associated with AF. Despite the small sample size, we found that FVII Ins -323 allele could be associated with a lower stroke risk in AF, whereas the 807C/T polymorphism may increase the risk.