山崎 昌子

INTRODUCTION: A single assay to assess the effect of the direct FXa inhibitor is needed clinically because prothrombin (PT) assay is not yet sensitive enough for accurate evaluation. We developed modified diluted prothrombin time (mdPT) assay showing a high reactivity to direct FXa inhibitors based on prothrombin time (PT) reagent. The purpose of this study was to evaluate the reactivity of mdPT to direct FXa inhibitors comparing to that of commercial PT reagents and diluted prothrombin time (dPT). METHODS: The correlation and slopes of mdPT against the drug concentrations by anti-Xa assay were compared to those of the four commercial reagents of PT or dPT in 275, 257, and 243 clinical samples collected from non-valvular atrial fibrillation (NVAF) patients who are prescribed apixaban, edoxaban or rivaroxaban for stroke prevention, respectively. RESULTS: The correlation coefficient (95% confidence interval) of mdPT against apixaban, edoxaban, and rivaroxaban was 0.818 (0.775-0.854), 0.914 (0.892-0.932), and 0.814 (0.766-0.852), respectively. The slope (95% confidence interval) of mdPT for apixaban, edoxaban, and rivaroxaban was 0.0068 (0.0063-0.0075), 0.0076 (0.0072-0.0080), and 0.0072 (0.0065-0.0078), respectively, which were higher than that of four commercial PT and dPT reagents, ranging within 0.0006-0.0023, 0.0017-0.0038, and 0.0016-0.0057 (all, p < 0.001), respectively. CONCLUSION: Compared with other PT and dPT reagents, mdPT reagent showed sharper slope to all direct FXa inhibitors, and higher correlation to apixaban and comparable correlation to edoxaban and rivaroxaban. This new reagent is expected to be a coagulation screening assay having a consistently high response to any types of direct FXa inhibitors.

Moyamoya disease is an uncommon vascular disease, which causes obstruction and stenosis of arteries of the circle of Willis, and preferentially affects children and young adults. This disease is seen across the world, but is more common in East Asia. It may cause hemorrhagic or ischemic stroke, or transient ischemic attack. If symptoms or cerebral blood flow become worse, revascularization surgery is recommended. We present 2 cases of moyamoya disease who underwent bypass surgery. We also discuss the epidemiology, pathology, genomics, and symptomatology as well as diagnosis, and management of moyamoya disease.

Essentials A consensus methodology for assessing the effects of antiplatelet agents has not been established. Measuring platelet thrombus formation (PTF) for evaluating antiplatelet effects was assessed. PTF differentially reflected antiplatelet effects compared to other tests. PTF may be associated with the severity of carotid or intracranial arterial stenosis. Click to hear a presentation on platelet function testing in the clinic by Gresele and colleagues. Summary: Background A consensus methodology for assessing the effects of antiplatelet agents has not been established. Objective We investigated the usefulness of directly measuring platelet thrombus formation (PTF) using a microchip-based flow chamber system for evaluating antiplatelet therapy. Patients/Methods Platelet thrombus formation in the whole blood of 94 patients with ischemic cerebrovascular disease treated with clopidogrel and/or aspirin was measured in a flow chamber system at a shear rate of 1500 s−1 and was compared with the results of assays for agonist-induced platelet aggregability, phosphorylation of vasodilator-stimulated phosphoprotein, platelet p-selectin expression (PS), and platelet-monocyte complexes. Results In all patients tested, area under the flow pressure curve (AUC10), which represents platelet thrombogenicity, showed weak correlation with platelet aggregation induced by either adenosine diphosphate or collagen. In addition, AUC10 was lower in patients treated with dual antiplatelet therapy (median 79.4) compared with patients treated with aspirin or clopidogrel alone (217.7 and 301.0, respectively), whereas the parameters evaluated by the other assays did not reflect the combined treatment efficacy. In clopidogrel monotherapy patients, AUC10 was associated with the severity of arterial stenosis (R2 = 0.127, β = 1.25), and AUC10 and PS were higher in patients with severe carotid or intracranial arterial stenosis than in those with mild stenosis. Conclusions Platelet thrombus formation measurement using a flow-chamber system was useful for evaluating the efficacy of treatment with aspirin and clopidogrel, both alone and in combination. The present findings indicate that high residual platelet thrombogenicity in patients treated with clopidogrel may be associated with the severity of carotid or intracranial arterial stenosis.

BACKGROUND: Advanced glycation end products (AGEs) promote atherosclerosis through binding to their receptor, RAGE. Since soluble RAGE (sRAGE) and endogenous secretory RAGE (esRAGE) may suppress AGEs-RAGE signaling, we examined the usefulness of sRAGE and esRAGE as biomarkers of early-stage atherosclerosis. METHODS: Serum sRAGE and esRAGE levels were measured in 284 subjects with no history of atherothrombotic diseases. The subjects were divided into high-sRAGE and low-sRAGE groups and high-esRAGE and low-esRAGE groups based on respective median values. We investigated the relationships between these parameters and the following factors: number of metabolic components, maximum intima-media thickness of the common carotid artery (IMT Cmax), carotid plaque calcification, and asymptomatic cerebral white matter lesions. RESULTS: The low-sRAGE and low-esRAGE groups exhibited significantly more components of metabolic syndrome than the high-sRAGE and high-esRAGE groups, respectively. IMT Cmax was significantly higher in the low-sRAGE and low-esRAGE groups. Low-sRAGE levels were significantly associated with carotid plaque calcification. Multiple linear regression analysis identified body mass index (BMI), age, and high-sensitivity C-reactive protein as determinants of sRAGE, whereas only BMI was identified as a determinant of esRAGE. CONCLUSIONS: We demonstrated that sRAGE and esRAGE are associated with atherosclerotic risk factors in early-stage atherosclerosis, suggesting that their levels evolve in correlation with those of metabolic components and inflammation. Interestingly, low-sRAGE and esRAGE levels are associated with high IMT Cmax, but only low-sRAGE levels were associated with carotid plaque calcification. Thus, sRAGE and esRAGE may reflect different aspects of atherosclerosis in its early stage.

Carotid stenosis is an important cause of atherothrombotic cerebral infarction. Moreover, it reflects the severity of systemic atherosclerosis and is a useful predictor of cardiovascular events. Atherosclerotic changes often develop at the site of carotid bifurcation, where shear stress can easily induce endothelial cell damage. The extent of this damage depends on various risk factors such as hypertension, dyslipidemia, and diabetes mellitus. Endothelial cell dysfunction induces the accumulation of inflammatory cells, migration and proliferation of smooth muscle cells, and release of various cytokines and chemokines, which cause carotid plaques and stenosis. Carotid plaques consist of a lipid core with infiltration inflammatory cells covered with a fibrous cap. Cerebral infarction occurs as a result of rupture and thrombus formation on the surface of the carotid plaque by thromboembolic and hemodynamic mechanisms. Rupture-prone carotid plaques are called vulnerable or unstable plaques. The characteristics of vulnerable plaques are active inflammation, with extensive macrophage accumulation, a thin cap with a large lipid core, endothelial denudation with superficial platelet aggregation, fissures, and severe stenosis. To assess the risk of cardiovascular events, it is important to identify vulnerable plaques by imaging techniques and novel assays such as the high-sensitivity C-reactive protein assay. In patients at a high risk of developing cerebral infarction, carotid endoarterectomy or stenting with the best medical treatment is useful in reducing cerebrovascular events.

INTRODUCTION: The Cilostazol Stroke Prevention Study found that cilostazol, a phosphodiesterase 3 inhibitor, can reduce the risk of subsequent stroke in Japanese patients with cerebral infarction. Here, we measured the effects of cilostazol in vitro on shear-induced platelet aggregation, an important mechanism of thrombosis at arterial bifurcations or stenotic lesions. We also evaluated the influences of intrinsic adenosine on the ability of cilostazol to inhibit shear-induced platelet aggregation by investigating the effect of dipyridamole, an inhibitor of cellular adenosine reuptake, in combination with cilostazol in vitro. MATERIALS AND METHODS: We measured platelet aggregation induced by a shear rate of 10,800 s(-1) in whole blood and in platelet-rich plasma from healthy volunteers using a cone-plate streaming chamber. RESULTS: Both cilostazol and adenosine dose-dependently inhibited shear-induced platelet aggregation in platelet-rich plasma samples. Adding a low concentration of adenosine (0.3 microM) did not inhibit shear-induced platelet aggregation, but significantly enhanced the inhibitory effect of cilostazol in platelet-rich plasma. Dipyridamole dose-dependently inhibited shear-induced platelet aggregation in whole blood and significantly enhanced the inhibitory effect of cilostazol on shear-induced platelet aggregation, but did not affect shear-induced platelet aggregation in platelet-rich plasma. The inhibitory effects of cilostazol combined with dipyridamole in whole blood were almost completely reversed by adenosine deaminase. CONCLUSIONS: Dipyridamole appears to synergistically enhance the inhibitory effect of cilostazol on shear-induced platelet aggregation by maintaining high plasma levels of adenosine.

Antiplatelet therapy is indicated for secondary prevention of ischaemic stroke. The first-line antiplatelet agent is aspirin. The effect of aspirin is, however, very limited, and this limited effect of aspirin is argued with termed 'aspirin resistance'. Strategies against aspirin resistance may include alternative use of other antiplatelet agents, combination of aspirin with other antiplatelet agents and investigation into molecular targets to develop novel antiplatelet agents. Progress in antiplatelet therapy should be directed at further reducing the risk of ischaemic events including ischaemic stroke without increasing the risk of haemorrhagic events including haemorrhagic stroke.

Remnant-like particles (RLPs) have been reported to promote atherosclerosis and to have effects on platelet function. We studied the effects of RLP on shear-induced platelet activation and their inhibition by antiplatelet agents in vitro. RLP were separated using two monoclonal antibodies, anti apo B-100 and anti apo A-I. These RLP fractions were added to whole blood (WB) or platelet-rich plasma (PRP) in serial dilution of 1, 10 or 100 microg RLP triglyceride (TG) per ml of total sample volume. These samples were incubated, and then stimulated with a high shear stress of 108 dyn/cm(2). Shear-induced platelet aggregation (SIPA) was calculated from the percentage of single platelet loss. P-selectin expression on platelet surface and platelet-derived microparticle (PMP) generation were measured before and after stimulation with shear stress using flow cytometer. SIPA was significantly enhanced by RLP in WB but not in PRP. This enhancing effect was not dose-dependent and was greatest at 10 microg TG/ml. P-selectin expression induced by shear stress was only enhanced by RLP at a concentration of 100 microg TG/ml in both WB and PRP, while generation of PMP induced by shear stress was only enhanced by RLP at a concentration of 100 microg TG/ml in WB. Aspirin inhibited only the enhancement of SIPA by RLPs, while cilostazol inhibited the enhancement of not only SIPA but also p-selectin expression and PMP generation by RLPs.

BACKGROUND: Antiphospholipid syndrome is important as a cause of ischemic stroke, although clinical characteristics of the syndrome are not well documented. METHODS: We analyzed differences in clinical characteristics between 40 antiphospholipid-antibody (aPL)-positive and 40 aPL-negative stroke patients. RESULTS: Stroke patients with aPL were significantly younger and were more likely to be women in comparison with stroke patients without aPL. Valvular heart disease, neurological complications and hematological disorders were more frequent in the aPL-positive group. The mean value of thrombin-antithrombin III complex was significantly lower in the aPL-positive group. Cerebral infarctions in the carotid system were less and large-artery lesions more frequent in the aPL-positive patients. CONCLUSIONS: Stroke patients with aPL have clinical characteristics distinct from stroke patients without aPL.

In case a pre-senile patient presented subacutely progressive dementia, secondary dementia, such as paraneoplastic neurological syndrome (PNS), hypothyroidism, confusion, early phase of primary degenerative dementia and prion diseases are to be considered. It is a case of pathologically confirmed, and clinico-pathologically assessed limbic encephalitis with cerebellar degeneration. The patient was a 63-year old male, with a well followed up medical history of gastric cancer 8 years earlier. Four weeks after he presented himself at our hospital his memory and disorientation progressively declined. A neurological examination revealed gaze nystagmus, with potential secondary dementia. However, no abnormal findings were detected from systemic radiological examination, or from chemical analyses. Two months later, after the onset of the disease, he presented additional symptoms, including seizure, gait disturbance, and insomnia. On admission, neurological examinations revealed gaze nystagmus and progression of dementia; however, his thought process was relatively preserved. No paroxysmal synchronized discharge was seen on electroencephalogram. Chest X-rays showed an inflammatory infiltration. In spite of anti-biotic medication, he died due to respiratory failure. The autopsy was limited to the brain. Histologically, limited lymphocytic infiltration into the hippocampus through the entorhinal cortex, with marked neuronal loss and gliosis was observed. Neuronophagia, microglial nodules, and perivascular lymphocytic infiltration were also seen. Additionally, most of the Purkinje cells in the cerebellum were lost, with Bergmann's gliosis and sparse lymphocytic infiltration. No tumor was observed in the brain. Pathological findings of the brain were compatible with paraneoplastic limbic encephalitis and cerebellar degeneration, though no neoplasm, clinically or pathologically, was detected in this patient. Consequently, it is suggested that when a senile patient presents sub-acute onset of progressive dementia, with a variety of neurological symptoms, paraneoplastic syndrome is to be taken into consideration, even if a tumor or an auto-antibody is not detected since the resection of the tumor is still the best therapeutic means. Otherwise immuno-suppressive and steroid therapies should be used.

Remnant lipoprotein (RLP) and lipoprotein (Lp) (a) are known to promote atherosclerosis and thrombosis. We studied whether these lipoproteins can be risk factors for stroke and carotid disease in 170 consecutive subjects (87 males and 83 females, mean age of 70 years). RLP was significantly higher in patients with (N=45) than without (N=125) ischemic stroke (Mann–Whitney's U-test, p=0.01), while there was no difference in Lp (a) between patients with and without it (p=0.83). In contrast, there was a significant difference in Lp (a) (p=0.003) but not in RLP (p=0.26) between patients with (N=76) and without (N=94) maximum intima-media thickness (IMT) of 2.0 mm or more at carotid bifurcations. Logistic regression analysis showed that RLP is an independent risk factor for ischemic stroke [7.5 mg/dl or more, relative risk (RR) 2.84, 95% confidence interval (CI) 1.26–6.40]. Multivariate regression analysis showed that Lp (a) (p=0.032) but not RLP (p=0.518) is significantly correlated with IMT. The results indicate that RLP but not Lp (a) is an independent risk factor for ischemic stroke, while Lp (a) but not RLP is an independent risk factor for carotid disease in our Japanese subjects. © 2004, Elsevier B.V. All rights reserved.

In patients with ischemic stroke, findings of platelet activation are frequent in platelet function tests. They include increases in plasma levels of beta-thromboglobulin and platelet factor 4, shortening of platelet survival and increasing of platelet lysis, enhancing of shear-induced platelet aggregation (SIPA), and increasing of reticulated platelets as well as platelet fibrinogen binding (PFB) and P-selectin expression (PSE). Aspirin can reduce vascular events including stroke, myocardial infarction and vascular death in high-risk patients with occlusive vascular disease. Aspirin's effect on vascular events is J-shaped, which appeared to be related to the effects on platelet aggregation and release reaction as well as prostaglandin synthesis. Thienopyridines can reduce vascular events even more than aspirin. SIPA was inhibited by thienopyridines but not by aspirin. Combination of aspirin and dipyridamole has an additive effect on preventing subsequent stroke. Aspirin enhanced an inhibitory effect of dipyridamole on SIPA in whole blood. PFB and PSE were not inhibited by aspirin but were partially inhibited by ticlopidine, and markedly inhibited by aspirin plus ticlopidine. Glycoprotein (GP) IIb/IIIa inhibitors can block the final common pathway of platelet aggregation. However, PSE and platelet-derived microparticle formation induced by shear stress were never inhibited at lower concentrations and were rather enhanced at higher concentrations of GP IIb/IIIa inhibitors. These results might be related to the fact that many oral GP IIb/IIIa inhibitors fail to show efficacy in patients with acute coronary syndrome. © 2003, Elsevier B.V.

Reticulated platelets are newly formed platelets containing a residual amount of RNA, and percentage of reticulated platelets (%RP) has been shown to reflect platelet turnover. Recently, a new flow cytometric approach for analyzing %RP in patients with thrombocytopenic disorders has been reported. We measured %RP by flow cytometry using the fluorescent dye thiazole orange (TO) to evaluate platelet kinetics in patients with different clinical categories of ischemic stroke. Patients with ischemic stroke were categorized into lacunar (n=25), atherothrombotic (n=26) and cardioembolic stroke (n=17). %RP was significantly higher in patients with cardioembolic stroke than in controls (n=140). Stepwise multiple regression analysis also showed cardioembolic stroke (R(2)=0.14) to be significant independent predictors of %RP among stroke patients even after adjustment for other factors. We concluded that %RP is increased in patients with cardioembolic stroke, which may reflect increased platelet turnover as a consequence of platelet consumption during thrombogenesis.

Background: Shear-induced platelet aggregation (SIPA) is an important mechanism of thrombosis at arterial bifurcations or stenotic lesions. Methods: We investigated the in vitro effects of dipyridamole (DP) and acetylsalicyclic acid (ASA) on SIPA in whole blood and platelet-rich plasma (PRP).Results:In whole blood, DP 20 μM significantly inhibited SIPA, while DP 5 μM or ASA 5 or 20 μM did not. SIPA in whole blood was, however, significantly inhibited by the combination of 5 or 20 μM of DP and ASA. SIPA in PRP was not inhibited by any concentration of DP or ASA, alone or in combination. Conclusions: These results suggest that DP has an effect on red blood cells and that ASA enhances the inhibitory effect of DP on SIPA in whole blood. These effects may be related to the additive effect of combination therapy with DP and ASA on stroke prevention. Copyright® 2002 S. Karger AG, Basel.

A meta-analysis by the Cochrane Stroke Group (CSG) showed that thrombolytic therapy increased deaths as well as symptomatic and fatal intracranial hemorrhage within the first seven to 10 days and at final follow-up, although these risks are offset by a reduction in disability in survivors, so that there is overall a significant net reduction in the proportion of patients dead or dependent. Trials testing intravenous (IV) tPA suggest that it may be associated with less hazard and more benefit. A recent trial demonstrated that intra-arterial pro-urokinase improved long-term outcome in patients with M 1 or M 2 occlusion within 6 hours of onset. Trials of the third generation of thromobolytic agents are ongoing in patients with acute ischemic stroke. The latest CSG's meta-analysis showed that immediate anticoagulant therapy in patients with acute ischemic stroke was not associated with net short or long-term benefit because there was no evidence that anticoagulant therapy reduced deaths or non-fatal stroke during treatment or patients dead or dependent at the end of follow-up. However, an IV low-molecular-weight heparinoid showed a trend toward improving long-term outcome in subgroup of patients with atherothrombotic stroke. The thrombin inhibitor argatroban was proven to be comparable to the thromboxane A2 synthetase inhibitor ozagrel in the effect on the outcome at one month in patients with atherothrombotic stroke within 48 hours of onset in Japan, and a trial of the agent is ongoing in patients with ischemic stroke within 12 hours of onset in the United States. Two large trials of aspirin in patients with ischemic stroke within 48 hours of onset indicated that aspirin had a modest effect on reducing patients dead or dependent at the end of follow-up. An international trial of abciximab, a monoclonal antibody directed against platelet glycoprotein IIb/IIIa, is ongoing in patients with ischemic stroke within 6 hours of onset.

We determined the percentages of fibrinogen-bound and P-selectin-expressed platelets in whole blood using flow cytometry in 254 patients with various cerebral infarction subtypes, as well as in 30 age-matched controls. Patients with atherothrombotic stroke showed significant increases in both fibrinogen-bound and P-selectin-expressed platelets. Patients with lacunar stroke also showed significant increases in both of them, but the percentage of P-selectin expression was significantly lower than that in atherothrombotic stroke. Patients with cardioembolic stroke showed a significant increase in P-selectin-expressed platelets without any increase in fibrinogen-bound platelets. Platelet fibrinogen binding and P-selectin expression were significantly lower in patients treated with ticlopidine but not with aspirin than in those not treated with any antiplatelet agent, and were lowest in those treated with both ticlopidine and aspirin. Our findings suggest that expression of adhesion molecules on platelet membrane surface differs among the patients with subtypes of ischemic stroke and differs among the types of antiplatelet regimens. © 2001 Elsevier Science Ltd. All rights reserved.

Aggregation of leukocytes induced by shear stress may play a pivotal role in microcirculatory derangement associated with cerebral ischemia. We studied leukocyte aggregation induced by shear stress and its in vitro inhibition by various pharmacological agents. Leukocytes were separated from heparinized venous blood of healthy volunteers, and were suspended in HEPES- Tyrode's buffer containing 2% autologous platelet-poor plasma at a final concentration of 5,000/μl. A cone-plate streaming chamber was applied to determine leukocyte aggregation by inducing low shear stress (18 dynes/cm2) and high shear stress (108 dynes/cm2). Maximal light transmittance rates and percent reduction in leukocyte counts were measured as parameters of leukocyte aggregation. Leukocyte aggregation was found to be induced by shear stresses, which was more pronounced at low than high shear stress. Granulocytes were involved more closely in leukocyte aggregation than lymphocytes. Prostaglandins E1 and I2/- did not affect shear-induced leukocyte aggregation (SILA). In contrast, SILA was inhibited by EGTA, as well as by anti-CD 18 and anti-CD 50 antibodies. These results indicate that SILA plays an important role in low shear circumstances such as the venous system and arterial blood stasis, and also indicate that SILA requires extracellular calcium and LFA-1/ICAM-3 cell adhesion mechanism but does not require adenylate cyclase-cyclic AMP pathway for intracellular signal transduction.

Alterations of platelet, coagulation, and fibrinolysis markers were investigated to determine the indications for antithrombotic therapy in patients with different clinical categories of acute cerebral infarction. Marked platelet activation was observed in platelet function tests, including measurements of platelet-specific proteins and platelet survival, platelet scintigraphy in the brain, and platelet fibrinogen binding assay, in patients with atherothrombotic stroke. Among patients with atherothrombotic stroke, increases of thrombin-antithrombin III complex (TAT) and D-dimer were frequent in addition to the findings of platelet activation in patients showing progressing stroke. Patients with cardioembolic stroke demonstrated marked elevation of coagulation markers, TAT and fibrinopeptide A, and fibrinolysis markers, D-dimer and plasmin-α2-plasmin inhibitor complex, as well as platelet activation. In contrast, neither activation was seen in patients with lacunar stroke. On the basis of these findings, antiplatelet therapy is indicated for stable or improving stroke, whereas anticoagulant therapy is indicated for progressing stroke among patients with atherothrombotic stroke. In patients with cardioembolic stroke, anticoagulant therapy should be started as soon as possible, or should be followed by thrombolytic therapy in the hyperacute phase. However, further investigation appears necessary for recommendations for patients with lacunar stroke.

Recent epidemiological studies have suggested that 15 to 30% of all ischemic stroke is comprised of cardioembolic stroke. The presence of intracardiac thrombi might prove to be the most reliable tool when making a diagnosis of cardioembolic stroke, although not always easy to determine even with recent advanced technique. In this study, sensitivities to detect intracardiac thrombi of transthoracic echocardiography (TTE), transesophageal echocardiography (TEE), cardiac-enhanced CT (CCT) and scintigraphy with indium-111-tropolone-labelled platelets (PSG) were compared, in order to provide a relevant guideline for the diagnosis of intracardiac thrombi in 83 patients suspected of cardioembolic stroke. Also studied was the correlation of intracardiac thrombi with activation of platelets and coagulation- fibrinolysis through performing various hemostatic tests in order to investigate their utility for the evaluation of in situ thrombosis or prothrombotic state in the heart chamber. Detection rates of intracardiac thrombi were 35% in TEE, 26% in CCT, 19% in PSG, and 11% in TTE. There was a significant difference in the sensitivity between TEE and TTE (p<0.05). Left atrial thrombi were frequently detected in TEE (4 out of 5 patients) and CCT (7 out of 10), while they were found less in PSG (2 out of 4) an TTE (4 out of 10). Thrombi in the left appendage were visualized in 3 out of 3 by TEE, while only in 1 out of 3 by PSG, 1 out of 4 by TTE and 1 out of 4 by CCT. Left ventricular thrombi; CCT (3 out of 3), TTE (2 out of 3), PSG (1 out 1); TEE was not performed since this technique could not be expected to provide high-quality images of left ventricular thrombi. Thus, left atrial thrombi were considered to be more sensitively detected by TEE and CCT, left appendage thrombi by TEE, and left ventricular thrombi by TTE and CCT. There was no patient in whom an intracardiac thrombus was visualized by PSG alone. On the basis of the results above, we propose the following guideline for the detection of intracardiac thrombi in patients presented with cardioembolic stroke. First, TTE and CCT appear to be relevant for screening tests because of simple and non-invasive techniques. These two tools might be sensitive enough to find left ventricular thrombi. Second, TEE should be recommended when a thrombus is suspected in the left atrium or appendage. Finally, PSG may be used to determine the activity of the thrombus, according to its necessity. Among the patients having intracardiac thrombi, frequently observed was the increase of β-thromboglobulin, platelet factor 4, platelet lysis, thrombin-antithrombin III complex, D-dimer in 67%, 75%, 71%, 80% and 80%, respectively, as well as the shortening of platelet survival in 100%, while antithrombin III was reduced in only 38%. In addition, when hemostatic abnormalities were compared between positive and negative groups of intracardiac thrombi, the shortening of platelet survival (p<0.0001), the increase of platelet lysis, and the increase of D-dimer (p<0.04) were more frequent in the positive group than in the negative group. These results indicate that the findings of activation of platelets and coagulation- fibrinolysis, except for the reduction of antithrombin III, especially the findings of platelet consumption and lysis as well as fibrinolysis activation are useful as sensitive parameters of in situ thrombosis or prothrombotic state, which may lead to the formation of intracardiac thrombi.

Atherothrombotic stroke and transient ischemic attack (TIA) are platelet-dependent disease states since they are attributable to platelet-rich thrombi formed on the atheromatous plaques or ulcers of extracranial or intracranial major arteries. Actually, they were found to be frequently associated with the findings of platelet activation in various platelet function tests including agonists- and shear-induced platelet aggregation, platelet specific proteins, platelet survival, lysis and imaging, and platelet cytoplasmic ionized calcium. According to a current meta-analysis by the Antiplatelet Trialists' Collaboration, stroke, myocardial infarction and vascular death were significantly reduced by antiplatelet agents including aspirin and ticlopidine, although the rate of reduction was only 27%, which was still unsatisfactory. We showed that the recurrence of stroke or TIA was significantly less frequent in patients in whom multipathway leading to platelet aggregation was inhibited by aspirin and/or ticlopidine than in those in whom only single or no any pathway was inhibited. Among novel antiplatelet agents, fibrinogen receptor antagonists including RGD peptides and anti-GP IIb/IIIa monoclonal antibody might be most promising agents since they can block the final common pathway of platelet aggregation.

Background and Purpose Recent evidence has suggested that shear-induced platelet aggregation is an important mechanism of thrombosis at arterial bifurcations or stenoses. We measured shear-induced platelet aggregation with a new apparatus in patients with cerebral ischemia and also studied correlations with other hemostatic parameters as well as the effect of antiplatelet agents. Methods The subjects were 75 patients with cerebral ischemia and 26 control subjects. Platelet aggregation was induced in titrated platelet-rich plasma by a high shear stress (108 dynes/cm2) that was applied by means of a cone-plate streaming chamber based on turbidimetry. We studied the correlation of test results with hemostatic parameters and also the effects of antiplatelet agents. Results Compared with the control subjects, an increase of shear-induced platelet aggregation was observed in 21 patients with atherothrombotic stroke and 12 with transient ischemic attacks, but not in 11 with cardioembolic stroke or 31 with lacunar stroke. There was no significant correlation of shearinduced platelet aggregation with platelet count, agonistinduced platelet aggregation, fibrinogen level, or 0-thrombo-globulin level. The extent of shear-induced aggregation was not correlated with von Willebrand factor antigen levels but was significantly correlated with the amounts of larger von Willebrand factor multimers. Oral aspirin (81 mg/d) did not inhibit shear-induced platelet aggregation, whereas oral ticlopidine (200 mg/d) significantly inhibited it. Conclusions These results indicate that shear-induced platelet aggregation is increased in patients with atherothrombotic stroke and transient ischemic attacks, is correlated with the incre. © 1994 American Heart Association, Inc.

Recent evidence suggests that shear-induced platelet aggregation (SIPA)is an important mechanism of thrombosis at arterial bifurcations or stenotic lesions. We measured SIPA using newly-developed equipment in patients with cerebralischemia, and also studied the effects of various pharmacological agents on SIPAin vitro and ex vivo. Platelet aggregation was induced by high shear stress (lORdyne/cm2), which is dependent on von Willebrand factor and on glycoproteins lIb/lIla and lb. In vitro studies, SIPA was inhibited by agents that increase the activity of adenylate cyclase as well as inhibitors of platelet ionizedcalcium, ADP receptor and Gj protein. but it was not affected by inhibitors of cyclooxygenase, lipoxygenase, thromboxane A2 synthetase, or platelet-activating factor. An increase of SIPA was observed in patients with atherothrombotic strokeand transient ischemic attacks, but not in those with lacunar stroke. SIPA was more oftenincreased in patients who showed an increase of larger von Willebrand factor multimers on SDS agarose gel electrophoresis. Oral aspirin did not inhibitSIPA, but oral ticlopidine significantly inhibited it. The above results indicate that SIPA is mediated or regulated by cyclic AMP, cytoplasmic calcium, and AD, and also indicate that SIPA is increased in some SUbtypes of cerebral ischemia, and can be corrected by ticlopidine but not by aspirin. © 1993 Pergamon Press Ltd.

The purpose of this study was to clarify differences in coagulation and fibrinolytic activation between the various subtypes and phases of ischaemic stroke. Haemostatic activation markers were measured in 52 patients with cardioembolic stroke, 32 with atherothrombotic stroke and 54 with lacunar stroke and compared with 23 age-matched controls. Data were obtained in the acute (≤ 7 days after onset), subacute (8-28 days) and chronic (≥ 29 days) phases of stroke. In patients with cardioembolic stroke, D-dimer and α2-antiplasmin-plasmin complex levels were higher during the acute and subacute phases, while thrombin-antithrombin III complex levels were higher during the acute phase than in patients with lacunar stroke and controls. In cardioembolic stroke, fibrinopeptide A was increased during the acute and subacute phases, thrombin-antithrombin III complexes were higher during the subacute phase and D-dimer levels were higher during the chronic phase. Protein C activity was lower during the acute phase than in atherothrombotic stroke, lacunar stroke and controls. Protein C antigen was lower during the acute phase than in lacunar stroke and controls and during the chronic phase than in lacunar stroke. In contrast, only D-dimer levels were higher in atherothrombotic stroke patients than controls during the acute and chronic phases and no significant alterations in these markers were observed in the patients with lacunar stroke. These findings suggest that measurement of molecular markers of coagulation and fibrinolysis may be useful for detecting intracardiac thrombin and plasmin generation in patients with cardioembolic stroke.

Clopidogrel is a new thieno-pyridine derivative and has a more potent inhibitory effect on platelet aggregation, dependent on ADP rather than ticlopidine. In a phase I study performed in Japan, significant inhibition of ADP-induced platelet aggregation and prolongation of bleeding time was observed in the dose range of 25, 50 and 75 mg. These effects were comparable to 200 or 300 mg of ticlopidine. Antithrombotic effects have also been shown in experimental animal models. Clopidogrel is expected to reduce the incidence of neutropenia since smaller doses are sufficient to suppress platelet aggregation compared to ticlopidine. Clopidogrel has been proven to be a potent and well-tolerated antiplatelet agent for atherosclerosis patients at risk of thrombosis, in Europe.

Leukocyte and platelet aggregation stimulated with formyl-methionyl-leucyl-phenylalanine (FMLP) was measured in 32 patients with cerebral ischemia and in 15 controls, using a whole blood aggregometer. The increases in impedance and the reductions in leukocyte and platelet counts were significantly greater in stroke patients than in controls. Aggregation was inhibited by oral ticlopidine, but not by oral aspirin. The effects were clearly counteracted by platelet-activating factor (PAF) antagonists, and counteracted in part by a 5-lipoxygenase inhibitor. The results suggest that platelets tend to be activated by PAF and leukotrienes liberated from hyperaggregable leukocytes in patients with ischemic stroke. © 1991 American Oil Chemists' Society.