Par4 is required for platelet thrombus propagation but not fibrin generation in a mouse model of thrombosis

Thrombin, a central mediator of hemostasis and thrombosis, converts fibrinogen to fibrin and is a potent platelet activator. Activated platelets provide a surface for assembly of the tenase and prothrombinase complexes required for thrombin generation. The role of thrombin-induced platelet activation in platelet accumulation and its interplay with fibrin deposition during thrombus assembly has not been fully defined. We studied these processes during laser-induced thrombus formation by using real-time digital fluorescence microscopy in mice lacking protease-activated receptor-4 (Par4), which is necessary for thrombin responsiveness in mouse platelets. Juxtamural platelet accumulation immediately after laser injury was not different in wild-type and Par4(-/-) mice. However, subsequent growth of platelet thrombi was markedly diminished in Par4(-/-) mice. At the time of maximal thrombus size in wild type, platelet accumulation was more than 10-fold higher in wild type than in Par4(-/-) mice. P-selectin expression, a marker of platelet activation, was reduced and delayed in Par4(-/-) thrombi. In contrast to platelet activation and accumulation, the rate and amount of fibrin deposition, predominantly intramural and juxtamural in this model, were indistinguishable in Par4(-/-) and wild-type mice. These results suggest that platelet activation by thrombin is necessary for normal propagation of a platelet thrombus at a distance from the injured vessel wall and hence for normal thrombus growth. However, platelet activation by thrombin is unnecessary for initial and limited accumulation of platelets at or near the vessel wall, and this limited accumulation of platelets and/or platelet-independent mechanism(s) of thrombin generation are sufficient for normal fibrin deposition in this model.     

"Attitudes" toward the elderly: a comparison of measures.

College students were presented five questionnaires traditionally used to assess attitudes toward old people. The intercorrelations among the measures were low, accounting for no more than 24% of the variance between any two measures. The results suggest that the measures are not equivalent; it was argued that the practice of utilizing a single instrument to measure attitudes toward the elderly may contribute to inconsistencies reported in the literature.     

Streptokinase-induced, antibody-mediated platelet aggregation: a potential cause of clot propagation in vivo

The administration of intracoronary streptokinase to a patient with a prior history of rheumatic fever was associated with the retrograde propagation of thrombus from the left anterior descending coronary artery into the left main coronary artery with near catastrophic consequences. The addition of streptokinase to platelet-rich plasma from the patient initiated platelet aggregation and secretion in vitro. Platelet aggregation was also seen in 1 of 15 control subjects after the addition of streptokinase, and the addition of plasma or immunoglobulin G (IgG) from the index patient supported platelet aggregation in the presence of streptokinase in all of the previously nonreactive control subjects. This in vitro platelet aggregation was specific for streptokinase and not initiated by either urokinase or tissue plasminogen activator. Streptokinase-induced platelet aggregation was not inhibited by aprotinin, but was completely attenuated by the addition of an excess of antihuman IgG Fab. These findings suggest that streptokinase can initiate specific antibody-mediated platelet aggregation in vitro and may be more than coincidentally related to clot propagation or thromboembolism in vivo.     

The rate of fibrinopeptide B release modulates the rate of clot formation: a study with an acquired inhibitor to fibrinopeptide B release

An asymptomatic 50-year-old male with a gamma globulin paraprotein was found to have prolonged prothrombin time, activated partial thromboplastin time, and thrombin time but a normal reptilase time. The prolonged clotting times were not the result of a factor deficiency because they were not corrected by the addition of normal plasma. Instead, this patient had an antibody that delayed thrombin-mediated fibrinopeptide B release thereby producing an apparent dysfibrinogenaemia. His isolated IgG prolonged the thrombin clotting time of both normal plasma and fibrinogen. Precincubation of his IgG with fibrinopeptide B, but not with fibrinopeptide A or thrombin, decreased its ability to prolong the thrombin clotting time. The patient's purified IgG but not control IgG delayed thrombin-mediated fibrinopeptide B release from fibrinogen without affecting the release of fibrinopeptide A. These studies define a novel, clinically silent dysfibrinogenaemia due to an antibody that delays thrombin-mediated fibrinopeptide B release from fibrinogen thereby markedly prolonging the clotting times.     

Deep venous thrombosis: rate of spontaneous lysis and thrombus extension.

AIM: Although recanalization occurs after an episode of venous thrombosis, the exact timing for this process, the rate of clearing at the different venous segments and the nature of the mechanisms involved and their progression are not well known. Recognition of these competing events is important in understanding the natural history and the mechanisms responsible for lysis of the thrombus and for the development of the post-thrombotic syndrome METHODS: During the course of 5 consecutive years, 110 patients (126 legs) with deep vein thrombosis (DVT) were prospectively followed using ultrasonic duplex. Follow-up studies were performed at intervals of 1 and 7 days, 1 month, every 3 months for the 1(st) year, and yearly thereafter. Mean duration of follow-up was 329 days. RESULTS: When only legs with initial complete occlusion are considered, the prevalence of occlusion progressively decreases to 33% after 6 months, 17% after the 1(st) year, and 0% after 3 years. Recanalization of individual segments occurred even more rapidly. After 3 months, recanalization of completely occluded segments was present in 93% of common femoral veins, 79% of superficial femoral veins (proximal segment), 84% of popliteal veins, and 72% of posterior tibial veins. The rate of recanalization was highest for multisegmental disease. Propagation of thrombi to adjacent venous segments occurred in 15% of the limbs. Propagation was usually limited to 1 or 2 adjacent segments. CONCLUSION: Lysis occurred early and was progressive. After 1 year most legs have recanalized. After 3 years recanalization occurred in all legs although residual thrombosis (partial obstruction) was still present in 50% of the limbs. Propagation of the thrombus was a limited process.     

Photon propagation function: a comparison of asymptotic functions

An earlier paper asserts the logarithmic asymptotic identity of various asymptotic functions associated with the photon propagation function, including the spectral weight function and the Gell-Mann-Low function. This note exhibits explicit expressions for the deviations between pairs of functions. It is emphasized that the differences are quantitatively small, and that the various functions have common qualitative characteristics. The discussion refers to a particular method for comparing the functions, which has no special physical status. When that restriction is removed, it becomes possible to prove the general existence of a transformation of variable that will produce the Gell-Mann-Low function from the spectral weight function. This supplies a physical interpretation that has otherwise been missing in the Gell-Mann-Low approach.     

Effects of laser irradiation on human thrombus: Demonstration of a linear dissolution-dose relation between clot length and energy density

Because vascular thrombosis often accompanies arteriosclerotic disease in occluding blood vessels, the dissolution properties of laser irradiation were investigated and the energies needed to penetrate different lengths of thrombus were quantitated. Spectrophotometric studies show that the blood clot due to the presence of hemoglobin is well absorbed by argon laser energies, which emit blue-green wavelengths between 454 and 514 nm. Thus, laser energies transmitted directly from an argon-ion source produced vaporization and penetration of human thrombus in a linear dose-response fashion; the longer the thrombus, the greater the power intensity or time exposure necessary to penetrate the clot.     

Abnormal heart rate recovery after exercise: a comparison with known indicators of increased mortality.

BACKGROUND: Abnormal heart rate (HR) recovery at 1 min after exercise (< or =12 beats) was recently suggested to be a predictor of all cause and cardiac mortality. AIM: This study aimed to (1) correlate HR recovery at 1 min after exercise with known exercise and myocardial perfusion markers of increased cardiac mortality, and (2) compare the known exercise and myocardial perfusion markers of increased cardiac mortality between patients with a normal and abnormal HR recovery at 1 min after exercise. METHODS: One hundred patients with known or suspected coronary artery disease referred for exercise stress testing (ETT) were prospectively enrolled. Percent, ETT time peak HR, HR reserve, summed stress score (SSS), extent of stress (SE%) and reversible perfusion abnormalities (RE%) were recorded in every patient. RESULTS: There was poor correlation with markers of myocardial ischemia or infarction [SSS (r = 0.15), SE% (r = 0.05), RE% (r = 0.12), all p = n.s.] but highly significant correlation between HR recovery at 1 min after exercise and chronotropic variables [ETT time (r = 0.56), peak HR (r = 0.65), HR reserve % (r = 0.64), all p < 0.001]. Patients on beta-blockers had significantly more incidence of an abnormal HR recovery at 1 min after exercise, compared to patients not on beta-blockers (88 vs. 56%, p < 0.01). CONCLUSION: Abnormal HR recovery at 1 min after exercise has no correlation with known myocardial perfusion markers of increased cardiac mortality. Patients with an abnormal HR recovery do not appear to have an increased incidence or more severe myocardial infarction or ischemia. However, there is a strong correlation between HR recovery at 1 min after exercise and the chronotropic variables during exercise.     

Ventricular rate smoothing for atrial fibrillation: a quantitative comparison study.

AIMS: To quantitatively compare the ventricular rate-smoothing (VRS) effects of different ventricular pacing (VP) protocols for atrial fibrillation (AF). METHODS AND RESULTS: Using a recently developed open-source model that can simulate the ventricular response in AF and VP, the performance of fixed-rate pacing and four previously published VRS algorithms were assessed by the mean RR (mRR), the root mean square of successive RR differences (RMSSD), the percentage of ventricular senses (VS%), and the percentage of short RR intervals (sRR%). All pacing protocols cause rate-dependent reduction of RMSSD, VS%, and sRR% with or without shortening of mRR compared to spontaneous AF. Fixed-rate pacing was more sensitive to the intrinsic rate than the VRS algorithms. The performance was generally comparable between different VRS algorithms, although higher mRR and VS% can be achieved at the expense of larger RMSSD and sRR%. CONCLUSION: The effect of VP on ventricular rhythm in AF depends on both intrinsic rate and the aggressiveness of the pacing protocol. Adequate rate control is necessary for effective operation of the VRS algorithm. Choosing VRS algorithm should balance between the beneficial effects of rate regularization and the negative effects of increasing heart rate and percentage of VP.     

Dusart syndrome: a new concept of the relationship between fibrin clot architecture and fibrin clot degradability: hypofibrinolysis related to an abnormal clot structure

Fibrinogen Dusart is a congenital dysfibrinogenemia (A-alpha 554 Arginine-->Cysteine) associated with severe thrombotic disorder, high incidence of thrombotic embolism, and abnormal fibrin polymerization. This thrombotic disorder was attributed to an abnormal clot thrombolysis with reduced plasminogen binding to fibrin and defective plasminogen activation by tissue plasminogen activator. The purpose of this work was to assess whether clot architecture could be involved in the thromboresistance of the fibrin Dusart and the high incidence of embolism. An important change in Dusart fibrin clot structure was identified with dramatic decrease of gel porosity (Ks), fiber diameters (d), and fiber mass-length ratios (mu) derived from permeation analysis. In addition, rigidity of the Dusart clot was found to be greatly increased compared with normal fibrin. We provide evidence that both thrombolysis resistance and abnormal rigidity of the fibrin Dusart are related to this abnormal architecture, which impairs the access of fibrinolytic enzymes to the fibrin and which is responsible for a brittle clot that breaks easily, resulting in a high incidence of embolism. Indeed, when restoring a normal clot structure by adding dextran 40 (30 mg/mL) before coagulation, clot thrombolysis and clot rigidity recovered normal values. This effect was found to be dose- dependent. We conclude that clot architecture is crucial for the propensity of blood clot to be degraded and that abnormal clot structure can be highly thrombogenic in vivo. The alpha-C domains of fibrinogen are determinant in fibrin clot structure.     

Evaluating asthma control: a comparison of measures using an item response theory approach.

Self-reported symptoms, FEV(1), and clinician judgment are all used to evaluate asthma control. The relative utility of each measure of control cannot be easily assessed. Item response theory (IRT) approaches allow for the direct comparison of the utility of different types of measures used to assess control. The objective of this study was to evaluate the validity and reliability of evaluating asthma control using symptom, clinical, and physiologic measures by applying an IRT approach. Subjects receiving care at an asthma clinic were evaluated on measures of asthma control. Based on 114 evaluations, IRT parameters were estimated to evaluate whether measures assessed a single underlying construct, the hierarchical relationship between the measures and the level of control each measure assessed, whether measures targeted all levels of asthma control, and whether the scoring categories distinguished between different levels of control. Infit statistics (0.74-1.5) for individual items showed that all items fit the underlying concept of asthma control. The reproducibility of the hierarchal scale was high (0.9). The results also demonstrated that items differentiated two strata (high, low) of control. The gaps in the hierarchal scale showed that for many subjects (37%) there were no items at their level of asthma control. The IRT approach identified gaps in current measurement that need to be addressed to provide more precise evaluations of control required to accurately monitor changes in patient status.     

Factor XIIa regulates the structure of the fibrin clot independently of thrombin generation through direct interaction with fibrin

Recent data indicate an important contribution of coagulation factor (F)XII to in vivo thrombus formation. Because fibrin structure plays a key role in clot stability and thrombosis, we hypothesized that FXII(a) interacts with fibrin(ogen) and thereby regulates clot structure and function. In plasma and purified system, we observed a dose-dependent increase in fibrin fiber density and decrease in turbidity, reflecting a denser structure, and a nonlinear increase in clot stiffness with FXIIa. In plasma, this increase was partly independent of thrombin generation, as shown in clots made in prothrombin-deficient plasma initiated with snake venom enzyme and in clots made from plasma deficient in FXII and prothrombin. Purified FXII and α-FXIIa, but not β-FXIIa, bound to purified fibrinogen and fibrin with nanomolar affinity. Immunostaining of human carotid artery thrombi showed that FXII colocalized with areas of dense fibrin deposition, providing evidence for the in vivo modulation of fibrin structure by FXIIa. These data demonstrate that FXIIa modulates fibrin clot structure independently of thrombin generation through direct binding of the N-terminus of FXIIa to fibrin(ogen). Modification of fibrin structure by FXIIa represents a novel physiologic role for the contact pathway that may contribute to the pathophysiology of thrombosis.     

Catheter-based local thrombolysis with urokinase: Comparative efficacy of intraluminal clot lysis with conventional urokinase infusion techniques in an in vivo porcine thrombus model

Local delivery of urokinase directly to the site of intraluminal clot using catheter-based technology has recently been introduced as a new technique to treat intracoronary thrombus and thrombus-containing stenoses. The purpose of this study was to compare the efficacy of urokinase therapy administered by local drug-delivery catheters with conventional urokinase-infusion techniques in dissolving intraluminal clot and intramurally depositing drug at the site of arterial injury in an in vivo porcine model. Five techniques of urokinase administration were studied in 65 pigs, including intravenous systemic bolus (1,000,000 units), guiding catheter infusion (500,000 units), local intraluminal infusion with a Roubin catheter (150,000 units), local infusion by the Dispatch catheter (150,000 units), and local delivery by the hydrogel-coated balloon (700 units). All five techniques were initially compared with respect to the quantity of intraluminal lysis of ¹²³I-fibrinogen-labeled thrombus in an in vivo thrombus model. Conventional balloon angioplasty was also assessed in this model as a nonpharmacologic, mechanical control. In addition, all five techniques were compared with respect to the quantity and efficiency of intramural urokinase deposition at coronary angioplasty sites. In the in vivo thrombolysis experiments, the quantity of artificial clot lysis measured 8.8% for systemic therapy, 20.8% for guiding catheter infusion, 25.2% for Roubin catheter infusion, 62.8% for Dispatch catheter infusion, 98.8% for hydrogel balloon delivery, and 53.6% for conventional balloon angioplasty. Both the Dispatch catheter and the hydrogel balloon resulted in more clot lysis than the systemic, guiding catheter, or Roubin catheter approaches (P < 0.05). In comparison with conventional balloon angioplasty, only the hydrogel balloon resulted in higher levels of thrombus dissolution (P < 0.05). In the intramural deposition studies, the efficiency of urokinase delivery was 0.0004% for systemic therapy, 0.004% for guiding catheter infusion, 0.004% for Roubin catheter infusion, 0.08% for Dispatch catheter infusion, and 1.8% for hydrogel balloon delivery. The Dispatch catheter resulted in higher intramural drug levels than did all other techniques (P < 0.05), whereas the efficiency of urokinase deposition was higher with the hydrogel balloon than with all other approaches (P < 0.05). In the porcine model, it is subsequently concluded that local delivery of urokinase by catheter-based techniques can result in more complete lysis of intraluminal thrombus by using similar or lower doses of drug than by using conventional urokinase infusion techniques. Mechanical deformation of thrombus, possibly to increase the surface area available for thrombolysis and to physically disrupt clot, may be an important component of the mechanism of site-specific thrombolysis, particularly with the hydrogel balloon. Local delivery techniques also deposit significant quantities of urokinase at balloon angioplasty sites, creating an intramural reservoir of drug that may result in prolonged local thrombolysis. Cathet. Cardiovasc. Diagn. 41:293–302, 1997. © 1997 Wiley-Liss, Inc.