Prethrombotic State in Young Very Low-Risk Patients With Atrial Fibrillation

A novel factor IXa-specific enzyme-linked immunosorbent assay detects factor IXa in human plasma

Background

Factor (F)IXa activity has been detected in human plasma and may impact thrombotic risk. Current FIXa activity assays are complex and cumbersome.

Objectives

To develop a reproducible enzyme-linked immunosorbent assay (ELISA) using a novel monoclonal antibody that detects total FIXa in human plasma.

Methods

A monoclonal antibody was raised against the new N-terminus exposed upon activation of FIX to FIXa by cleavage after R226. This antibody is specific for FIXa protease and does not recognize FIX zymogen or FIXα. The antibody was used to develop a FIXa-specific ELISA capable of quantifying total FIXa (free FIXa and FIXa-antithrombin complex) in human plasma. Total FIXa quantified using the ELISA was compared to that of FIXa-antithrombin quantified using modifications of a previously described ELISA.

Results

The FIXa-specific ELISA was reproducible and quantified total FIXa in human plasma. Total FIXa levels correlated with FIXa-antithrombin levels.

Conclusion

A monoclonal antibody was developed that specifically detects human FIXa protease. A FIXa-specific ELISA using the new antibody is capable of reproducibly measuring total FIXa in human plasma (both free FIXa and FIXa-antithrombin). This assay should facilitate the evaluation of total FIXa levels in a variety of clinical circumstances.

Cytotoxic CD8+ T Cells Are Involved in the Thrombo-Inflammatory Response during First-Diagnosed Atrial Fibrillation

BACKGROUND

Atrial myopathy and atrial fibrillation (AF) accompany thrombo-inflammation. This facilitates disease progression and promotes major adverse cardiovascular events (MACEs). Thrombin receptor (protease-activated receptor 1, PAR1) signalling is central in mediating thrombo-inflammation. We hypothesised that PAR1 signalling links coagulation and inflammation through cytotoxic CD8⁺ T lymphocytes in patients presenting with first-diagnosed AF (FDAF).

METHODS

A total of 210 patients were studied. We included data and blood samples from patients presenting with FDAF (n = 160), cardiac tissue from patients with paroxysmal AF (n = 32) and 20 controls.

RESULTS

During early AF, a pro-inflammatory and cytotoxic subset of T lymphocytes (CD8⁺) circulated more frequently when compared to patients with chronic cardiovascular disease but without AF, accompanied by elevated plasma levels of CD8⁺ effector molecules, which corresponded to biomarkers of adverse cardiac remodelling and atrial dysfunction. Activation of tissue factor (TF) and PAR1 was associated with pro-inflammatory and cytotoxic effector functions. PAR1-related CD8⁺ cell activation was more frequent in FDAF patients that experienced a MACE.

CONCLUSIONS

In patients with FDAF, the TF-factor Xa-factor IIa-axis contributes to thrombo-inflammation via PAR1 in CD8⁺ T cells. Intervening in this cascade might be a promising synergistic approach to reducing disease progression and the vascular complications of AF.

The Complex Relation between Atrial Cardiomyopathy and Thrombogenesis

Heart disease, as well as systemic metabolic alterations, can leave a ‘fingerprint’ of structural and functional changes in the atrial myocardium, leading to the onset of atrial cardiomyopathy. As demonstrated in various animal models, some of these changes, such as fibrosis, cardiomyocyte hypertrophy and fatty infiltration, can increase vulnerability to atrial fibrillation (AF), the most relevant manifestation of atrial cardiomyopathy in clinical practice. Atrial cardiomyopathy accompanying AF is associated with thromboembolic events, such as stroke. The interaction between AF and stroke appears to be far more complicated than initially believed. AF and stroke share many risk factors whose underlying pathological processes can reinforce the development and progression of both cardiovascular conditions. In this review, we summarize the main mechanisms by which atrial cardiomyopathy, preceding AF, supports thrombogenic events within the atrial cavity and myocardial interstitial space. Moreover, we report the pleiotropic effects of activated coagulation factors on atrial remodeling, which may aggravate atrial cardiomyopathy. Finally, we address the complex association between AF and stroke, which can be explained by a multidirectional causal relation between atrial cardiomyopathy and hypercoagulability.

Concealed Coronary Atherosclerosis In Idiopathic Paroxysmal Atrial Fibrillation is Associated with Imminent Cardiovascular Diseases

Background

Previous research showed a significant difference in the presence of subclinical coronary artery disease (CAD) on cardiac CT angiography (CTA) between patients with idiopathic paroxysmal atrial fibrillation (iAF) versus a matched sinus rhythm population (iSR). Here we present 5-year follow-up data and the consequences of subclinical CAD on baseline CTA on the development of cardiovascular disease in iAF.

Methods

In 99 iAF patients (who underwent CTA as part of work-up for pulmonary vein isolation) and 221 matched iSR controls (who underwent CTA for CAD assessment), the incidence of hypertension, diabetes and major cardiovascular events (MACCE) during follow-up was obtained. Multivariable Cox regression analysis was used to reveal predictors of incident cardiovascular disease in the iAF group.

Results

During a follow-up of 68±11 months, over one third of patients developed cardiovascular disease, with no difference between iAF and iSR (log-rank p=0.56), and comparable low rates of MACCE (4.0% vs 5.0%,p=0.71). Within the iAF group, age (HR1.12(1.03-1.20);p=0.006), left atrial diameter (HR1.16(1.03-1.31);p=0.01), Segment Involvement Score (total number of coronary segments with atherosclerotic plaque; HR1.43(1.09-1.89);p=0.01) and the number of calcified plaques on CTA (HR0.53(0.30-0.92);p=0.01) were independent predictors of incident cardiovascular disease.

Conclusions

Subclinical coronary disease on CTA may be useful to identify the subset of patients with iAF that harbour concealed cardiovascular risk factors and need intensive clinical follow-up to ensure timely initiation of appropriate therapy once CV disease develops, including anticoagulation and vascular prophylactic therapy.

Thrombin generation by calibrated automated thrombography in goat plasma: Optimization of an assay

The goat model of atrial fibrillation (AF) allows investigation of the effect of AF on coagulation. However, assays for goat plasma are not available from commercial sources. Calibrated automated thrombography (CAT) provides a global view of the coagulation profile by assessing in vitro thrombin generation (TG). We describe the customization of the CAT assay in goat platelet-poor plasma (PPP) and in factor Xa (FXa)-inhibitor-anticoagulated PPP. TG was initiated in the presence of phospholipids and either (a) PPP reagent, reagent low, or reagent high; (b) goat brain protein extraction (GBP); or (c) Russell's viper venom-factor X activator (RVV-X). Contact activation was assessed by adding corn trypsin inhibitor. Different concentrations of prothrombin complex concentrate (PCC) were used to determine the sensitivity of both the GBP and RVV-X method. To obtain FXa-inhibitor anticoagulated plasma, rivaroxaban was added to plasma. TG settings with human reagents were not suitable for goat plasma. TG triggered with GBP increased peak height and ETP values. Similarly, the RVV-X method produced comparable TG curves and was more sensitive to PCC titration. Finally, both methods were able to detect the decrease in clotting potential induced by FXa inhibition. This is the first study that reports the customization of the CAT assay for goats. The GBP and RVV-X methods were comparable in triggering TG in goat plasma. The RVV-X method seemed to better discriminate changes in TG curves due to increases in clotting potential as well as to FXa inhibition by rivaroxaban in goat plasma.

Vitamin K antagonist use induces calcification and atherosclerotic plaque progression resulting in increased hypercoagulability

Aims

Vascular calcification is a hallmark of atherosclerotic burden and can predict the cardiovascular outcome. Vitamin K antagonists (VKA) are widely used anticoagulant drugs to treat patients at risk of arterial and venous thrombosis but are also associated with increase vascular calcification progression. We aim to unravel the paradox that VKA suppresses plasma coagulation but promotes vascular calcification and subsequent atherosclerosis-dependent coagulability of the vessel wall.

Methods and results

Apoe^−/− mice were placed on western-type diet enriched with the VKA warfarin for 18 weeks to measure atherosclerotic plaque burden, calcification, and coagulation. Patients (n = 54) displaying paroxysmal atrial fibrillation with a low cardiovascular risk, who were treated with VKA were included to measure pre-thrombotic state. Finally, primary vascular smooth muscle cells (VSMC) derived from human tissue explants were used for in vitro experiments. In Apoe^−/− mice, VKA increases both atherosclerotic plaque size and calcification. Higher plaque calcification was associated with increased plasma levels of thrombin-antithrombin and factor IXa-antithrombin complexes in mice and patients treated with VKA. Mechanistically, phenotypic switching of VSMC into synthetic VSMC promotes thrombin generation, which is enhanced in a tissue-factor (TF)-dependent manner by VSMC calcification. Moreover, calcified VSMC exposed to whole blood under flow significantly enhanced platelet deposition and TF-dependent fibrin formation.

Conclusions

Oral anticoagulation with VKA aggravates vascular calcification and atherosclerosis. VSMC phenotype differentiation impacts coagulation potential in a TF-dependent manner. VKA-induced vascular calcification increases hypercoagulability and could thereby potentially positively affect atherothrombosis.

Activated factor XI-antithrombin complex presenting as an independent predictor of 30-days mortality in out-of-hospital cardiac arrest patients

BACKGROUND

Cardiac arrest and cardiopulmonary resuscitation (CPR) are associated with activated coagulation and microvascular fibrin deposition with subsequent multiorgan failure and adverse outcome.

OBJECTIVES

Activated Factor XI-antithrombin (FXIa-AT) complex, activated Factor IX-antithrombin (FIXa-AT) complex and thrombin-antithrombin (TAT) complex were measured as markers of coagulation activation, and evaluated as independent prognostic indicators in out-of-hospital cardiac arrest (OHCA) patients.

METHODS

From February 2007 until December 2010 blood samples were collected in close approximation to CPR from patients with OHCA of assumed cardiac origin. Follow-up samples in survivors were drawn 8-12 h and 24-48 h after hospital admission. All measurements were determined by ELISA.

RESULTS

Thirty-seven patients presented with asystole and 77 with ventricular fibrillation as first recorded heart rhythm. At 30-days follow-up, 70 patients (61.4%) had died. All patients had elevated levels of FXIa-AT complex, FIXa-AT complex and TAT. Initial levels were significantly higher in non-survivors compared to 30-days survivors. A significant increase in risk of 30-days all-cause mortality was observed through increasing quartiles of all three biomarkers in univariate Cox regression analysis. Compared to the lowest quartile (Q1), only FXIa-AT complex levels in Q3 (HR 3.17, p = 0.011) and Q2 (HR 3.02, p = 0.016) were independently associated with all-cause mortality in the multivariable analysis. FIXa-AT complex and TAT-complex did not behave as independent predictors.

CONCLUSIONS

Complexes of FXIa-AT were independently associated with 30-days survival in OHCA-patients.

CLINICAL TRIAL REGISTRATION

ClinicalTrials. gov, NCT02886273.

Atrial fibrillation: villain or bystander in vascular brain injury

Atrial fibrillation (AF) and stroke are inextricably connected, with classical Virchow pathophysiology explaining thromboembolism through blood stasis in the fibrillating left atrium. This conceptualization has been reinforced by the remarkable efficacy of oral anticoagulant (OAC) for stroke prevention in AF. A number of observations showing that the presence of AF is neither necessary nor sufficient for stroke, cast doubt on the causal role of AF as a villain in vascular brain injury (VBI). The requirement for additional risk factors before AF increases stroke risk; temporal disconnect of AF from a stroke in patients with no AF for months before stroke during continuous ECG monitoring but manifesting AF only after stroke; and increasing recognition of the role of atrial cardiomyopathy and atrial substrate in AF-related stroke, and also stroke without AF, have led to rethinking the pathogenetic model of cardioembolic stroke. This is quite separate from recognition that in AF, shared cardiovascular risk factors can lead both to non-embolic stroke, or emboli from the aorta and carotid arteries. Meanwhile, VBI is now expanded to include dementia and cognitive decline: research is required to see if reduced by OAC. A changed conceptual model with less focus on the arrhythmia, and more on atrial substrate/cardiomyopathy causing VBI both in the presence or absence of AF, is required to allow us to better prevent AF-related VBI. It could direct focus towards prevention of the atrial cardiomyopathy though much work is required to better define this entity before the balance between AF as villain or bystander can be determined.

Plasma Kallikrein Contributes to Coagulation in the Absence of Factor XI by Activating Factor IX

Objectives:

FXIa (factor XIa) induces clot formation, and human congenital FXI deficiency protects against venous thromboembolism and stroke. In contrast, the role of FXI in hemostasis is rather small, especially compared with FIX deficiency. Little is known about the cause of the difference in phenotypes associated with FIX deficiency and FXI deficiency. We speculated that activation of FIX via the intrinsic coagulation is not solely dependent on FXI(a; activated FXI) and aimed at identifying an FXI-independent FIX activation pathway.

Approach and Results:

We observed that ellagic acid and long-chain polyphosphates activated the coagulation system in FXI-deficient plasma, as could be demonstrated by measurement of thrombin generation, FIXa-AT (antithrombin), and FXa-AT complex levels, suggesting an FXI bypass route of FIX activation. Addition of a specific PKa (plasma kallikrein) inhibitor to FXI-deficient plasma decreased thrombin generation, prolonged activated partial thromboplastin time, and diminished FIXa-AT and FXa-AT complex formation, indicating that PKa plays a role in the FXI bypass route of FIX activation. In addition, FIXa-AT complex formation was significantly increased in F11 −/− mice treated with ellagic acid or long-chain polyphosphates compared with controls and this increase was significantly reduced by inhibition of PKa.

Conclusions:

We demonstrated that activation of FXII leads to thrombin generation via FIX activation by PKa in the absence of FXI. These findings may, in part, explain the different phenotypes associated with FIX and FXI deficiencies.

Clot Lysis Time Predicts Stroke During Anticoagulant Therapy in Patients with Atrial Fibrillation

BACKGROUND

Formation of dense fibrin clots has been reported in both atrial fibrillation (AF) and ischemic stroke. We have previously demonstrated that such clot properties can predict thromboembolism and major bleeding in AF patients treated with vitamin K antagonists (VKAs). In this longitudinal cohort study, we evaluated whether impaired fibrinolysis is associated with clinical outcomes in AF.

METHODS

In 236 patients with AF receiving VKAs, we measured ex vivo plasma clot lysis time (CLT), a measure of global fibrinolysis along, with von Willebrand factor antigen (vWF), plasminogen activator inhibitor 1 antigen (PAI-1), and other fibrinolysis modulators. The primary outcome were ischemic cerebrovascular events. Secondary end points were death and major bleeding.

RESULTS

During a median follow-up time of 4.3 (interquartile range 3.7-4.8) years, annual rates of death, ischemic cerebrovascular events, and major bleeding were 1.48%, 2.96%, and 3.45%, respectively. Patients with CLT in the fourth quartile (> 115 min) had 8-fold higher stroke or transient ischemic attack (TIA) rates compared with the other patients (8.67% vs 1.1%; P < 0.0001). CLT correlated with PAI-1 and vWF (r = 0.59; P < 0.0001 for both). In the multivariate Cox regression analysis adjusted for potential confounders, the independent predictors of stroke or TIA were CLT > 115 minutes (hazard ratio [HR] 7.67, 95% confidence interval [CI] 2.78-21.17; P < 0.0001), PAI-1 (HR 1.16, 95% 1.05-1.28; P = 0.003), and CHA₂DS₂-VASc score ≥3 (HR 5.18, 95% 1.76-15.29; P = 0.003). CLT was not associated with death or major and minor bleeding events.

CONCLUSIONS

Impaired fibrinolysis may predict thromboembolic events in AF patients receiving VKA.

Prothrombotic State in Atrial Fibrillation Patients With One Additional Risk Factor of the CHA2DS2-VASc Score (Beyond Sex)

BACKGROUND

It is unclear whether a prothrombotic state occurs in atrial fibrillation (AF) with low stroke risk.

METHODS

We studied 118 patients with AF with the Congestive Heart Failure, Hypertension, Age (≥ 75 years), Diabetes, Stroke/Transient Ischemic Attack/Systemic Embolism, Vascular Disease, Age (65-74 years), Sex (Female) (CHA₂DS₂-VASc) score of 1 in men or 2 in women vs 52 patients with AF with the CHA₂DS₂-VASc score of 0 in men or 1 in women. Plasma clot permeability (K_s), a measure of fibrin clot density, and clot lysis time (CLT), endogenous thrombin potential (ETP), von Willebrand factor antigen, and plasminogen activator inhibitor-1 were evaluated in nonanticoagulated subjects.

RESULTS

Patients with the CHA₂DS₂-VASc score of 1 (beyond sex), compared with those with 0, had lower K_s, prolonged CLT, increased ETP, von Willebrand factor antigen, and plasminogen activator inhibitor-1 (all P < 0.001), without any sex-dependent differences. Heart failure (odds ratio [OR]: 10.28; 95% confidence interval [CI]: 2.32-45.41), age 65-74 years (OR: 4.37; 95% CI: 1.76-10.83), and hypertension (OR: 5.03; 95% CI: 1.81-13.94) were independently associated with low K_s (the lowest quartile, ≤ 6.4 × 10^-9 cm²), whereas only age 65-74 years (OR: 3.33; 95% CI: 1.59-6.96) significantly predicted prolonged CLT (the top quartile, ≥ 108 minutes). Age 65-74 years (OR: 5.21; 95% CI: 2.12-12.80), heart failure (OR: 6.58; 95% CI: 1.49-29.06), and hypertension (OR: 4.33; 95% CI: 1.54-12.15) were independently associated with high ETP (the top quartile, ≥ 1681.3 nM × minutes).

CONCLUSIONS

A prothrombotic state (increased thrombin generation, denser fibrin clots, impaired fibrinolysis, and endothelial injury) characterizes patients with AF with 1 additional clinical stroke risk factor (beyond sex), with age 65-74 years being particularly associated with prothrombotic indices.

The Biomarkers NT-proBNP and CA-125 are Elevated in Patients with Idiopathic Atrial Fibrillation

BACKGROUND

Blood biomarkers related to AF could be useful to detect silent AF and to develop stratified strategies for AF prevention. Previous studies identified markers that predict incident AF. However, it is difficult to differentiate whether biomarkers relate to underlying cardiovascular diseases, are generated by the atria in response to an AF episode, or both. We therefore measured a panel of blood biomarkers in patients without overt CVD with and without AF to investigate the association between biomarkers and atrial fibrillation (AF) in patients without overt cardiovascular disease (CVD).

METHODS

Blood samples - drawn remote from an AF episode - of 60 patients with AF but without overt forms of CVD (idiopathic AF; iAF) were compared to 120 matched patients with sinus rhythm only. A novel antibody-based method for quantification of blood biomarkers (OlinkProseek Multiplex Cardiovascular) was used to compare 92 biomarkers between the two groups.

RESULTS

N-terminal pro-B-type natriuretic peptide (NT-proBNP), Cathepsin L1, Endothelial cell-specific molecule 1, Cancer Antigen-125 (CA-125), Heat shock 27kDa protein, Galanin peptides, Proteinase-activated receptor 1, Stem cell factor, and CD40-ligand were all higher in iAF patients than in SR controls. Both NT-proBNP (OR1.55(1.07-2.25);p=0.022) and CA-125 (OR1.68(1.07-2.64);p=0.026) were independently associated with iAF.

CONCLUSIONS

This exploratory study, investigating over 90 cardiovascular blood biomarkers in patients without known CVD, identified one established biomarker for paroxysmal AF, NT-proBNP, and a novel marker, CA-125. CA-125 - previously unrelated to paroxysmal AF in an otherwise healthy population - may thus be a potential indicator of remote paroxysms of AF.

Atherothrombosis and Thromboembolism: Position Paper from the Second Maastricht Consensus Conference on Thrombosis

Atherothrombosis is a leading cause of cardiovascular mortality and long-term morbidity. Platelets and coagulation proteases, interacting with circulating cells and in different vascular beds, modify several complex pathologies including atherosclerosis. In the second Maastricht Consensus Conference on Thrombosis, this theme was addressed by diverse scientists from bench to bedside. All presentations were discussed with audience members and the results of these discussions were incorporated in the final document that presents a state-of-the-art reflection of expert opinions and consensus recommendations regarding the following five topics: 1. Risk factors, biomarkers and plaque instability: In atherothrombosis research, more focus on the contribution of specific risk factors like ectopic fat needs to be considered; definitions of atherothrombosis are important distinguishing different phases of disease, including plaque (in)stability; proteomic and metabolomics data are to be added to genetic information. 2. Circulating cells including platelets and atherothrombosis: Mechanisms of leukocyte and macrophage plasticity, migration, and transformation in murine atherosclerosis need to be considered; disease mechanism-based biomarkers need to be identified; experimental systems are needed that incorporate whole-blood flow to understand how red blood cells influence thrombus formation and stability; knowledge on platelet heterogeneity and priming conditions needs to be translated toward the in vivo situation. 3. Coagulation proteases, fibrin(ogen) and thrombus formation: The role of factor (F) XI in thrombosis including the lower margins of this factor related to safe and effective antithrombotic therapy needs to be established; FXI is a key regulator in linking platelets, thrombin generation, and inflammatory mechanisms in a renin-angiotensin dependent manner; however, the impact on thrombin-dependent PAR signaling needs further study; the fundamental mechanisms in FXIII biology and biochemistry and its impact on thrombus biophysical characteristics need to be explored; the interactions of red cells and fibrin formation and its consequences for thrombus formation and lysis need to be addressed. Platelet-fibrin interactions are pivotal determinants of clot formation and stability with potential therapeutic consequences. 4. Preventive and acute treatment of atherothrombosis and arterial embolism; novel ways and tailoring? The role of protease-activated receptor (PAR)-4 vis à vis PAR-1 as target for antithrombotic therapy merits study; ongoing trials on platelet function test-based antiplatelet therapy adjustment support development of practically feasible tests; risk scores for patients with atrial fibrillation need refinement, taking new biomarkers including coagulation into account; risk scores that consider organ system differences in bleeding may have added value; all forms of oral anticoagulant treatment require better organization, including education and emergency access; laboratory testing still needs rapidly available sensitive tests with short turnaround time. 5. Pleiotropy of coagulation proteases, thrombus resolution and ischaemia-reperfusion: Biobanks specifically for thrombus storage and analysis are needed; further studies on novel modified activated protein C-based agents are required including its cytoprotective properties; new avenues for optimizing treatment of patients with ischaemic stroke are needed, also including novel agents that modify fibrinolytic activity (aimed at plasminogen activator inhibitor-1 and thrombin activatable fibrinolysis inhibitor.