Residual perfusion defects in patients with pulmonary embolism are related to impaired fibrinolytic capacity

Reduced fibrin clot permeability on admission and elevated E-selectin at 3 months as novel risk factors of residual pulmonary vascular obstruction in patients with acute pulmonary embolism

BACKGROUND

Residual pulmonary vascular obstruction (RPVO) is common following pulmonary embolism (PE) but its association with fibrin clot properties is poorly understood. We investigated whether prothrombotic state and hypofibrinolysis markers can identify patients with RPVO.

METHODS

In 79 normotensive noncancer patients (aged 56 ± 13.3 years) with acute PE, we determined fibrin clot permeability (Ks), clot lysis time (CLT), endogenous thrombin potential (ETP), fibrinolysis proteins, oxidative stress markers, and E-selectin on admission before initiation of anticoagulant therapy, after 5-7 days, and 3 months of anticoagulation. RPVO was diagnosed using computed tomography angiography 3-6 months since PE.

RESULTS

Patients with RPVO (n = 23, 29.1%) had at baseline higher simplified Pulmonary Embolism Severity Index (sPESI) (P = 0.004), higher N-terminal brain natriuretic propeptide (P = 0.006) and higher D-dimer (P = 0.044). Patients with versus without RPVO had lower Ks (P < 0.001) and longer CLT (P < 0.05), both at baseline and 5-7 days since admission, but not at 3 months. Patients with RPVO showed 40.6% higher E-selectin (P < 0.001) solely at 3 months. By multivariable logistic regression, baseline Ks (odds ratio [OR] 0.010, 95% confidence interval [CI] 0.001-0.837, P = 0.042, per 10- 9 cm2), baseline D-dimer (OR 1.105, 95% CI 1.000-1.221, P = 0.049, per 100 ng/ml), and E-selectin levels after 3 months (OR 3.874, 95% CI 1.239-12.116, P = 0.020, per 1 ng/ml) were associated with RPVO.

CONCLUSIONS

RPVO patients despite anticoagulation characterize with the formation of denser fibrin clots on admission and higher E-selectin at 3 months. Those parameters could be the potential novel RPVO risk factors that warrant further evaluation in an independent cohort.

SIRT1 and thrombosis

Thrombosis is a major cause of morbidity and mortality worldwide, with a complex and multifactorial pathogenesis. Recent studies have shown that SIRT1, a member of the sirtuin family of NAD + -dependent deacetylases, plays a crucial role in regulating thrombosis, modulating key pathways including endothelial activation, platelet aggregation, and coagulation. Furthermore, SIRT1 displays anti-inflammatory activity both in vitro, in vivo and in clinical studies, particularly via the reduction of oxidative stress. On these bases, several studies have investigated the therapeutic potential of targeting SIRT1 for the prevention of thrombosis. This review provides a comprehensive and critical overview of the main preclinical and clinical studies and of the current understanding of the role of SIRT1 in thrombosis.

Demographic, clinical, and echocardiographic factors associated with residual perfusion defects beyond six months after pulmonary embolism

BACKGROUND

Residual perfusion defects (RPD) after pulmonary embolism (PE) are common.

PRIMARY AIM

This study aimed to determine the prevalence of RPD in a cohort diagnosed with PE 6-72 months earlier, and to determine demographic, clinical, and echocardiographic variables associated with RPD.

METHODS

Patients aged 18-75 years with prior PE, confirmed by computed tomography pulmonary angiography 6-72 months earlier, were included. Participants (N = 286) completed a diagnostic work-up consisting of transthoracic echocardiography and ventilation/perfusion scintigraphy. Demographic, clinical, and echocardiographic characteristics between participants with RPD and those without RPD were explored in univariate analyses using t-test or Mann-Whitney U test. Multiple logistic regression analysis was used to assess the association between selected variables and RPD.

RESULTS

RPD were detected in 72/286 patients (25.2 %, 95 % CI:20.5 %-30.5 %). Greater tricuspid annular plane systolic excursion (TAPSE) (adjusted odds ratio (aOR) 1.10, 95 % CI:1.00-1.21, p = 0.048) at echocardiographic follow-up, greater thrombotic burden at diagnosis, as assessed by mean bilateral proximal extension of the clot (MBPEC) score 3-4 (aOR 2.08, 95 % CI:1.06-4.06, p = 0.032), and unprovoked PE (aOR 2.25, 95 % CI:1.13-4.48, p = 0.021) were independently associated with increased risk of RPD, whereas increased pulmonary artery acceleration time was associated with a lower risk of RPD (aOR 0.72, 95 % CI:0.62-0.83, p < 0.001, per 10 ms). Dyspnoea was not associated with RPD.

CONCLUSION

RPD were common after PE. Reduced pulmonary artery acceleration time and greater TAPSE on echocardiography at follow-up, greater thrombotic burden at diagnosis, and unprovoked PE were associated with RPD.

Erythrocyte oxidative stress and thrombosis

Thrombosis is a common disorder with a relevant burden of morbidity and mortality worldwide, particularly among elderly patients. Growing evidence demonstrated a direct role of oxidative stress in thrombosis, with various cell types contributing to this process. Among them, erythrocytes produce high quantities of intracellular reactive oxygen species (ROS) by NADPH oxidase activation and haemoglobin autoxidation. Concomitantly, extracellular ROS released by other cells in the blood flow can be uptaken and accumulate within erythrocytes. This oxidative milieu can alter erythrocyte membrane structure, leading to an impaired erythrocyte function, and promoting erythrocytes lysis, binding to endothelial cells, activation of platelet and of coagulation factors, phosphatidylserine exposure and release of microvesicles. Moreover, these abnormal erythrocytes are able to adhere to the vessel wall, contributing to thrombin generation within the thrombus. This process results in accelerated haemolysis and in a hypercoagulable state, in which structurally impaired erythrocytes contribute to increase thrombus size, to reduce its permeability and susceptibility to lysis. However, the wide plethora of mechanisms by which oxidised erythrocytes contribute to thrombosis is not completely elucidated. This review discusses the main biochemical aspects linking erythrocytes, oxidative stress and thrombosis, addressing their potential implication for clinical and therapeutic management.

Altered clot formation and lysis are associated with increased fibrinolytic activity in ascites in patients with advanced cirrhosis

Analysis of coagulation disorders and assessment of rebalanced hemostasis with the use of traditional coagulation assays is challenging in cirrhotic patients. Therefore, alternative tests are under investigation for the evaluation of coagulopathy in this specific setting. Aim of this study was to analyze the modifications of clot structure and function in cirrhotic patients with different degrees of severity. Cirrhotic patients referred to our Unit were consecutively enrolled. Global test measurements, including clot and lysis assays, clot lysis time, and determination of other fibrinolytic parameters, were performed. Analyses of clot formation, morphology, and lysis were performed with a turbidimetric clotting and lysis assay (EuroCLOT). Lysis of a tissue factor-induced clot by exogenous tissue plasminogen activator was analyzed by studying the modifications of turbidity during clot formation and the following lysis. We evaluated coagulative and fibrinolytic parameters in both plasma and ascites. Urokinase plasminogen activator (uPA) and gelatinase activity in ascites were also measured. We analyzed data from 33 cirrhotic patients (11 in Child-Pugh class A; 22 in class B or C and with ascites) and 21 healthy subjects (HS). In class B/C patients prolonged latency time, a decline in clotting absorbance, and decreased fibrin formation were observed in comparison with class A and HS. Generated curves and Thrombin-Activatable Fibrinolysis Inhibitor (TAFI) progressively declined from HS to class C patients, whereas levels of plasminogen activator inhibitor-1 and tissue plasminogen activator increased. D-dimer levels were markedly increased in ascites, together with significantly smaller levels of TAFI, αlfa2-antiplasmin, and plasminogen. Caseinolytic activity was also present. Class C patients showed smaller amount of uPA and significantly lower levels of matrix metallopeptidases (MMP)2 in ascites in comparison with Class B subjects. Clot formation and lysis are altered in cirrhosis and fibrinolysis is activated in ascites. Ascitic levels of uPA and MMP2 are reduced and inversely related to the severity of liver disease.

Super-Resolution Microscopy Reveals an Altered Fibrin Network in Cirrhosis: The Key Role of Oxidative Stress in Fibrinogen Structural Modifications

Cirrhotic patients show a reduced synthesis of both pro- and anti-coagulant factors. Recent reports indicate that they are characterized by a higher risk of thrombotic rather than hemorrhagic complications, but the mechanisms conferring this risk are not fully elucidated. Oxidative-mediated fibrinogen modifications may explain, at least in part, a prothrombotic profile. The aim of the present pilot study was to investigate the alterations in fibrinogen structure and function in patients with cirrhosis of various severity and to correlate these findings with the mechanisms of thrombus formation. We assessed in plasma specific oxidative stress markers and measured oxidative modifications, functional and structural parameters in purified fibrinogen fractions obtained from cirrhotic patients and control subjects. We enrolled 15 cirrhotic patients (5 patients belonging to each of the three Child-Turcotte-Pugh classes) and 20 age- and sex-matched healthy controls. Plasma redox status, fibrinogen oxidative modifications, thrombin-catalyzed fibrin polymerization and fibrin resistance to plasmin-induced lysis were significantly altered in cirrhotic patients and were associated to disease severity. Importantly, clot structure obtained by stimulated emission depletion (STED) super-resolution microscopy indicated modifications in fiber diameter and in clot porosity in cirrhotic patients. Fibrin fiber diameter significantly decreased in cirrhotic patients when compared to controls, and this difference became more marked with disease progression. In parallel, fibrin pore size progressively decreased along with disease severity. In cirrhotic patients, fibrinogen clot analysis and oxidative-dependent changes reveal novel structural and functional fibrinogen modifications which may favor thrombotic complications in cirrhosis.

A multifaceted investigation into molecular associations of chronic thromboembolic pulmonary hypertension pathogenesis

Purpose

Chronic thromboembolic pulmonary hypertension is characterized by incomplete thrombus resolution following acute pulmonary embolism, leading to pulmonary hypertension and right ventricular dysfunction. Conditions such as thrombophilias, dysfibrinogenemias, and inflammatory states have been associated with chronic thromboembolic pulmonary hypertension, but molecular mechanisms underlying this disease are poorly understood. We sought to characterize the molecular and functional features associated with chronic thromboembolic pulmonary hypertension using a multifaceted approach.

Methods

We utilized functional assays to compare clot lysis times between chronic thromboembolic pulmonary hypertension patients and multiple controls. We then performed immunohistochemical characterization of tissue from chronic thromboembolic pulmonary hypertension, pulmonary arterial hypertension, and healthy controls, and examined RNA expression patterns of cultured lymphocytes and pulmonary arterial specimens. We then confirmed RNA expression changes using immunohistochemistry, immunofluorescence, and Western blotting in pulmonary arterial tissue.

Results

Clot lysis times in chronic thromboembolic pulmonary hypertension patients are similar to multiple controls. Chronic thromboembolic pulmonary hypertension endarterectomized tissue has reduced expression of both smooth muscle and endothelial cell markers. RNA expression profiles in pulmonary arteries and peripheral blood lymphocytes identified differences in RNA transcript levels related to inflammation and growth factor signaling, which we confirmed using immunohistochemistry. Gene expression data also suggested significant alterations in metabolic pathways, and immunofluorescence and Western blot experiments confirmed that unglycosylated CD36 and adiponectin expression were increased in chronic thromboembolic pulmonary hypertension versus controls.

Conclusions

Our data do not support impaired clot lysis underlying chronic thromboembolic pulmonary hypertension, but did demonstrate distinct molecular patterns present both in peripheral blood and in pathologic specimens of chronic thromboembolic pulmonary hypertension patients suggesting that altered metabolism may play a role in chronic thromboembolic pulmonary hypertension pathogenesis.

Faster fibrin clot degradation characterizes patients with central pulmonary embolism at a low risk of recurrent peripheral embolism

It is unclear whether thrombus location in pulmonary arteries is associated with particular clot characteristics. We assessed 156 patients following either central or peripheral pulmonary embolism (PE). Plasma clot lysis time, the rate of D-dimer release from plasma clots (D-D_rate) with the maximum D-dimer concentration achieved (D-D_max), as well as fibrin formation on turbidimetry, plasma clot permeation, thrombin generation, and fibrinolytic parameters were measured 3–6 months after PE. Patients following central PE (n = 108, 69.3%) were more likely smokers (38.9% vs 18.8%; p = 0.01), less likely carriers of factor XIII Val34Leu allele (40.7% vs 62.5%, p = 0.01), exhibited 16.7% higher D-D_rate and 12.7% higher tissue plasminogen activator antigen (tPA:Ag) compared with peripheral PE (p = 0.02 and p < 0.0001, respectively). Saddle PE patients (n = 31, 19.9%) had 11.1% higher D-D_rate and 7.3% higher D-D_max compared with central PE (both p < 0.05). Twenty-three recurrent PE episodes, including 15 central episodes, during a median follow-up of 52.5 months were recorded. Plasma D-dimer and tPA:Ag were independent predictors for central recurrent PE, whereas D-D_rate and peak thrombin predicted peripheral recurrent PE. Plasma clots degradation is faster in patients following central PE compared with peripheral PE and fibrinolysis markers might help to predict a type of recurrent PE.

Fibrinogen and the prediction of residual obstruction manifested after pulmonary embolism treatment

Residual pulmonary vascular obstruction (RPVO) and chronic thromboembolic pulmonary hypertension (CTEPH) are both long-term complications of acute pulmonary embolism, but it is unknown whether RPVO can be predicted by variants of fibrinogen associated with CTEPH.We used the Akaike information criterion to select the best predictive models for RPVO in two prospectively followed cohorts of acute pulmonary embolism patients, using as candidate variables the extent of the initial obstruction, clinical characteristics and fibrinogen-related data. We measured the selected models' goodness of fit by analysis of deviance and compared models using the Chi-squared test.RPVO occurred in 29 (28.4%) out of 102 subjects in the first cohort and 46 (25.3%) out of 182 subjects in the second. The best-fit predictive model derived in the first cohort (p=0.0002) and validated in the second cohort (p=0.0005) implicated fibrinogen Bβ-chain monosialylation in the development of RPVO. When the derivation procedure excluded clinical characteristics, fibrinogen Bβ-chain monosialylation remained a predictor of RPVO in the best-fit predictive model (p=0.00003). Excluding fibrinogen characteristics worsened the predictive model (p=0.03).Fibrinogen Bβ-chain monosialylation, a common structural attribute of fibrin, helped predict RPVO after acute pulmonary embolism. Fibrin structure may contribute to the risk of developing RPVO.

From Acute to Chronic Thromboembolic Disease

After achievement of adequate anticoagulation, the natural history of acute pulmonary emboli ranges from near total resolution of vascular perfusion to long-term persistence of hemodynamically consequential residual perfusion defects. The persistence of perfusion defects is necessary, but not sufficient, for the development of chronic thromboembolic pulmonary hypertension (CTEPH). Approximately 30% of patients have persistent defects after 6 months of anticoagulation, but only 10% of those with persistent defects subsequently develop CTEPH. A number of clinical risk factors including increasing age, delay in anticoagulation from symptom onset, and the size of the initial thrombus have been associated with the persistence of perfusion defects. Likewise, a number of cellular and molecular pathways have been implicated in the failure of thrombus resolution, including impaired fibrinolysis, altered fibrinogen structure and function, increased local or systemic inflammation, and remodeling of the embolic material by neovascularization. Treatment with fibrinolytic agents at the time of initial presentation has not clearly improved the frequency or degree of recovery of pulmonary vascular perfusion. A better understanding of the interplay between clinical risk factors and pathogenic mechanisms may enhance the ability to prevent and treat CTEPH in the future.

Prothrombotic Fibrin Clot Phenotype in Patients with Deep Vein Thrombosis and Pulmonary Embolism: A New Risk Factor for Recurrence

Prothrombotic fibrin clot phenotype, involving faster formation of dense meshwork composed of thinner and highly branched fibers that are relatively resistant to plasmin-induced lysis, has been reported in patients with not only myocardial infarction or stroke, but also venous thromboembolism (VTE), encompassing deep vein thrombosis (DVT), and/or pulmonary embolism (PE). Prothrombotic fibrin clot phenotype, in particular prolonged clot lysis time, is considered a novel risk factor for VTE as well as venous thrombosis at unusual location, for example, cerebral sinus venous thrombosis, retinal vein obstruction, and Budd-Chiari syndrome. Growing evidence from observational studies indicates that abnormal fibrin clot properties can predict recurrent DVT and PE and they are involved in serious complications of VTE, for example, thromboembolic pulmonary hypertension and postthrombotic syndrome. The purpose of this article is to review our current understanding of the role of fibrin clot structure and function in venous thrombosis with emphasis on clinical issues ranging from prognosis to therapy.

Identifying the heterogeneity of COPD by V/P SPECT: a new tool for improving the diagnosis of parenchymal defects and grading the severity of small airways disease

Introduction

Airway obstruction and possible concomitant pulmonary diseases in COPD cannot be identified conventionally with any single diagnostic tool. We aimed to diagnose and grade COPD severity and identify pulmonary comorbidities associated with COPD with ventilation/perfusion single-photon emission computed tomography (V/P SPECT) using Technegas as the functional ventilation imaging agent.

Methods

94 COPD patients (aged 43–86 years, Global Initiative for Chronic Obstructive Lung Disease (GOLD) stages I–IV) were examined with V/P SPECT and spirometry. Ventilation and perfusion defects were analyzed blindly according to the European guidelines. Penetration grade of Technegas in V SPECT measured the degree of obstructive small airways disease. Total preserved lung function and penetration grade of Technegas in V SPECT were assessed by V/P SPECT and compared to GOLD stages and spirometry.

Results

Signs of small airway obstruction in the ventilation SPECT images were found in 92 patients. Emphysema was identified in 81 patients. Two patients had no signs of COPD, but both of them had a pulmonary embolism, and in one of them we also suspected a lung tumor. The penetration grade of Technegas in V SPECT and total preserved lung function correlated significantly to GOLD stages (r=0.63 and −0.60, respectively, P<0.0001). V/P SPECT identified pulmonary embolism in 30 patients (32%). A pattern typical for heart failure was present in 26 patients (28%). Parenchymal changes typical for pneumonia or lung tumor were present in several cases.

Conclusion

V/P SPECT, using Technegas as the functional ventilation imaging agent, is a new tool to diagnose COPD and to grade its severity. Additionally, it revealed heterogeneity of COPD caused by pulmonary comorbidities. The characteristics of these comorbidities suggest their significant impact in clarifying symptoms, and also their influence on the prognosis.

Prothrombotic Fibrin Clot Phenotype Is Associated With Recurrent Pulmonary Embolism After Discontinuation of Anticoagulant Therapy

OBJECTIVE

Pulmonary embolism (PE) is a life-threatening manifestation of venous thromboembolism with a high recurrence rate after anticoagulation cessation. Recently, we have reported that prothrombotic clot phenotype in venous thromboembolism patients is associated with an increased risk of recurrent deep-vein thrombosis.

APPROACH AND RESULTS

We tested whether abnormal clot properties are predictive of recurrent PE. We investigated 156 consecutive white patients aged 18 to 65 years after the first-ever provoked or unprovoked PE (n=89), with or without deep-vein thrombosis. Plasma fibrin clot permeability (K_s), turbidity measurements, calibrated automated thrombography, and efficiency of fibrinolysis using clot lysis time, maximum D-dimer levels, and rate of increase in D-dimer levels were evaluated at ≥3 months of anticoagulant therapy, at least 4 weeks since the anticoagulation withdrawal. The primary end point was recurrent PE during a median follow-up of 50 months. Recurrent PE was diagnosed in 23 (14.7%; 5%/yr) patients. Recurrent PE was associated with formation of denser fibrin networks reflected by lower K_s (P=0.007) and impaired fibrinolysis, as evidenced by prolonged clot lysis time (P=0.012) and reduced maximum rate of increase in D-dimer levels in the lysis assay (P=0.004). Patients with recurrent PE had higher plasma D-dimer (P<0.001) and thrombin peak (P=0.007) compared with the remainder, whereas turbidity measurements and maximum D-dimer levels did not differ in the recurrence. Multivariate model showed that independent predictors of recurrent PE were female sex, unprovoked venous thromboembolism, higher plasma D-dimer, reduced K_s, and reduced maximum rate of increase in D-dimer levels in the lysis assay (all P<0.05).

CONCLUSIONS

Altered fibrin clot properties including formation of more compact clots displaying impaired susceptibility to lysis may predispose to recurrent PE.