Aspirin failure in patients presenting with acute cerebrovascular ischaemia.

Aspirin is the most commonly used antiplatelet drug for prevention of ischaemic stroke. In order to determine the prevalence and nature of aspirin failure, we studied 51 adults admitted with suspected ischaemic stroke and already prescribed daily aspirin. Within 48 hours (h) of onset, blood and urine samples were collected to assess platelet aggregation, activation and aspirin response by a range of methods. All tests were then repeated on a second sample taken 24 h after witnessed administration of 75 mg or 150 mg aspirin. At entry to the study, incomplete response to aspirin, measured by arachidonic acid (AA)-stimulated platelet aggregation, was found in 43% of patients. Following in-hospital aspirin administration, there was a significant decrease in AA-aggregation (p=0.001) suggesting poor adherence to therapy prior to admission. However, residual aggregation (10-15%) persisted in 11 subjects - suggesting alternative causes. In incomplete responders on admission, platelet aggregation with adenosine diphosphate (ADP) was significantly higher compared with responders (p<0.05) but there were no significant differences in collagen aggregation, platelet fibrinogen binding or P-selectin expression, plasma von Willebrand factor, fibrinogen, high-sensitivity C-reactive protein, or the urinary metabolite, 11-dehydro-TxB2. Incomplete platelet inhibition is common around the time of acute cerebrovascular ischaemic events in patients prescribed aspirin. Up to 50% of these observations appear due to incomplete adherence to aspirin therapy. Intervention studies are required to determine the clinical relevance of measured platelet response to aspirin in terms of outcome, and the effectiveness of improved pharmacotherapy for stroke prevention.

Platelet activation increases with the severity of peripheral arterial disease: implications for clinical management.

INTRODUCTION: Patients with peripheral arterial disease (PAD) have increased mortality from cardiovascular events compared with age and sex matched controls Platelets play a major role in atherosclerosis and thrombotic vascular events. Platelet reactivity is increased in patients with PAD compared with healthy controls. We aimed to determine the relationship, if any, between platelet activation and severity of disease. METHODS AND RESULTS: One hundred eighty-two patients with intermittent claudication (IC) or subcritical limb ischemia (SLI), defined as the presence of rest pain or ulceration, had the following investigations performed: platelet P-selectin expression and bound fibrinogen by flow cytometric analysis and platelet aggregation using the rapid platelet function assay with arachidonic acid (AA) and thrombin receptor activation peptide (TRAP) as agonists. Patients with SLI compared with IC had significantly enhanced ADP stimulated P-selectin expression (median 42.45% [inter-quartile range 33.32% to 58.5%] vs 35.2% [26.07% to 46.32%], P = .002) and bound fibrinogen (73.7% [54.3% to 83.2%] vs 63.7% [43.8% to 76.5%], P = .001). TRAP stimulated aggregation was higher (207 [153 to 238] PAU vs 183[155 to 199] PAU, P = .04) but AA mediated aggregation was not significantly different. An ankle-brachial pressure index (ABPI) of less than 0.6 was associated with increased ADP stimulated P-selectin and bound fibrinogen (P < .05). ABPI correlated inversely with ADP stimulated P-selectin expression (r = -0.228, P = .003), ADP stimulated fibrinogen binding (r = -0.156, P = .043) and TRAP stimulated aggregation (r = -0.179, P = .04). CONCLUSION: We have demonstrated for the first time that progression of severity of PAD is not only reflected by symptoms, signs, and ABPI but also by increased platelet activity as assessed by both flow cytometry and aggregation. As patients with more severe PAD have increased cardiovascular mortality, our findings suggest that new strategies for platelet inhibitory therapy are indicated in these patients.

Haemostasis, inflammation and renal function following exercise in patients with intermittent claudication on statin and aspirin therapy.

BACKGROUND: Previous studies have suggested that exercise in patients with intermittent claudication (IC) may induce a systemic thrombo-inflammatory response. The effect of secondary prevention therapy on this response is unknown. This study aimed to investigate the effects of treadmill exercise on markers of coagulation activation, inflammation and renal function in patients with IC, receiving aspirin and statin therapy compared to healthy controls. METHODS: Samples were taken before, immediately and 1 hour after exercising on a treadmill in 20 patients with IC and 20 healthy volunteers. Interleukin-6 (IL-6), thrombin-anti-thrombin complex (TAT) and fibrin D-dimer were measured by ELISA. High sensitivity CRP (HsCRP) and urinary albumin were measured via a nephelometric technique, urinary protein via a turbidometric assay and N-acetyl-beta-D-glucosaminidase (NAG) via a colorimetric assay. RESULTS: Elevated baseline levels of Hs-CRP, IL-6, white cell counts, D-dimer and urinary NAG occurred in patients with IC compared to volunteers (p > 0.05). Following exercise there was no increase in Hs CRP or IL-6. D-dimer levels significantly increased following exercise in the patients and volunteers. TAT levels increased immediately after exercise in the patient group only and were significantly increased at 1 hour in both patients and volunteers. A transient rise in the protein creatinine ratio occurred in both groups (p < 0.007), and in albumin creatinine ratio in the patient group. There was no change in urinary NAG. CONCLUSION: Elevated markers of inflammation occurred in patients with IC on statin and aspirin therapy but these did not increase following exercise. However, acute exercise resulted in a prothrombotic state evident in both groups, although this was more prolonged in patient with IC. The clinical significance of these findings in patients who are known to be at an increased risk of cardiac and other thrombotic event are unclear.

Effect of hypobaric hypoxia, simulating conditions during long-haul air travel, on coagulation, fibrinolysis, platelet function, and endothelial activation.

CONTEXT: The link between long-haul air travel and venous thromboembolism is the subject of continuing debate. It remains unclear whether the reduced cabin pressure and oxygen tension in the airplane cabin create an increased risk compared with seated immobility at ground level. OBJECTIVE: To determine whether hypobaric hypoxia, which may be encountered during air travel, activates hemostasis. DESIGN, SETTING, AND PARTICIPANTS: A single-blind, crossover study, performed in a hypobaric chamber, to assess the effect of an 8-hour seated exposure to hypobaric hypoxia on hemostasis in 73 healthy volunteers, which was conducted in the United Kingdom from September 2003 to November 2005. Participants were screened for factor V Leiden G1691A and prothrombin G20210A mutation and were excluded if they tested positive. Blood was drawn before and after exposure to assess activation of hemostasis. INTERVENTIONS: Individuals were exposed alternately (> or =1 week apart) to hypobaric hypoxia, similar to the conditions of reduced cabin pressure during commercial air travel (equivalent to atmospheric pressure at an altitude of 2438 m), and normobaric normoxia (control condition; equivalent to atmospheric conditions at ground level, circa 70 m above sea level). MAIN OUTCOME MEASURES: Comparative changes in markers of coagulation activation, fibrinolysis, platelet activation, and endothelial cell activation. RESULTS: Changes were observed in some hemostatic markers during the normobaric exposure, attributed to prolonged sitting and circadian variation. However, there were no significant differences between the changes in the hypobaric and the normobaric exposures. For example, the median difference in change between the hypobaric and normobaric exposure was 0 ng/mL for thrombin-antithrombin complex (95% CI, -0.30 to 0.30 ng/mL); -0.02 [corrected] nmol/L for prothrombin fragment 1 + 2 (95% CI, -0.03 to 0.01 nmol/L); 1.38 ng/mL for D-dimer (95% CI, -3.63 to 9.72 ng/mL); and -2.00% for endogenous thrombin potential (95% CI, -4.00% to 1.00%). CONCLUSION: Our findings do not support the hypothesis that hypobaric hypoxia, of the degree that might be encountered during long-haul air travel, is associated with prothrombotic alterations in the hemostatic system in healthy individuals at low risk of venous thromboembolism.

Pulmonary and systemic effects of short-term inhalation exposure to ultrafine carbon black particles.

While environmental particles are associated with mortality and morbidity related to pulmonary and cardiovascular (CV) disease, the mechanisms involved in CV health effects are not known. Changes in systemic clotting factors have been associated with pulmonary inflammation. We hypothesized that inhaled ultrafine particles result in an inflammatory response which may stimulate systemic clotting factor release. Adult male Wistar rats were exposed to either fine or ultrafine carbon black (CB) for 7 h. The attained total suspended particle concentrations were 1.66 mg/m(3) for ultrafine CB and 1.40 mg/m(3) for fine CB. Particle concentration of ultrafine particles was more than 10 times greater than that of fine particles and the count median aerodynamic diameter averaged 114 nm for the ultrafine and 268 nm for the fine carbon particles. Data were collected immediately, 16 and 48 h following exposure. Only ultrafine CB caused an increase in total bronchoalveolar lavage (BAL) leukocytes, whereas both fine (2-fold) and ultrafine (4-fold) carbon particles caused an increase in BAL neutrophils at 16 h postexposure. Exposure to the ultrafine, but not fine, carbon was also associated with significant increases in the total numbers of blood leukocytes. Plasma fibrinogen, factor VII and von Willebrand factor (vWF) were unaffected by particle treatments as was plasma Trolox equivalent antioxidant status (TEAC). Macrophage inflammatory protein-2 mRNA was significantly increased in BAL cells 48 h following exposure to ultrafine CB. The data show that there is a small but consistent significant proinflammatory effect of this exposure to ultrafine particles that is greater than the effect of the same exposure to fine CB.

Markers of endothelial activation and atherothrombosis in women with history of preeclampsia or gestational hypertension.

Women who have had preeclampsia (PE) or gestational hypertension (GH) exhibit relatively high rates of circulatory diseases. PE is a disease associated with inflammation and vascular endothelial dysfunction. We therefore hypothesised that women with a history of PE or GH might have abnormal levels of markers of endothelial activation or inflammation, reflecting either an innate predisposition to preeclampsia or changes induced by the eclamptic process. Levels of von Willebrand factor, fibrinogen and C-reactive protein were compared in 392 women with a history of PE between 1951 and 1970, 297 women with a history of GH and 163 matched controls. Although no significant differences between those with either PE or GH and controls were noted, subjects with a history of PE had significantly higher CRP values than those with GH. No significant differences were found when the three groups were compared for von Willebrand factor or fibrinogen. Overall, the data do not support our hypothesis. In addition, our data document increasing von Willebrand factor levels increase with age, which may help explain the age dependent increase in venous or arterial thrombosis. Moderate alcohol consumption was also associated with lower levels of inflammatory markers.

Role of coagulation testing in predicting bleeding risk.

Coagulation testing is employed widely prior to open surgery and invasive procedures. This is based on the assumption that such testing is of clinical value in the prediction of bleeding. In order to improve the clinical understanding of the potential limitations of first-line coagulation tests used in this way, we have systematically reviewed the literature that addresses the value of routine coagulation testing in helping to predict bleeding risk. We conclude unreservedly that indiscriminate coagulation testing is not useful in a surgical or a medical setting. This is due to the limited sensitivity and specificity of the tests, coupled with the low prevalence of bleeding disorders resulting in a high number of false positives, poor positive predictive value for bleeding and numerous false negatives resulting in false reassurance. Since most abnormal results can be predicted and most cases of significant bleeding disorder identified from a complete clinical assessment, the employment of selective laboratory testing is more cost-effective and represents evidence-based clinical practice.

Laboratory testing for prothrombotic states: clinical utility.

It is possible to detect a genetic contribution to venous thrombosis in a significant proportion of patients. This has led to a huge expenditure in clinical time and health resource. However, the gains to be made from the uncritical investigation of the causes of venous thromboembolism are limited and the approach raises significant issues in relation to the appropriateness of this form of genetic testing. In contrast, there are some acquired prothrombotic states that should be identified because the risk of further thrombosis may be sufficient to influence therapy. These states include antiphospholipid syndrome, myeloproliferative disorders, and cancer.

Pamidronate causes apoptosis of plasma cells in vivo in patients with multiple myeloma.

Anti-resorptive bisphosphonates, such as pamidronate, are an effective treatment for osteolytic disease and hypercalcaemia in patients with multiple myeloma, but have also been shown to cause apoptosis of myeloma cell lines in vitro. In this study, we found that a single infusion of pamidronate, in 16 newly diagnosed patients with multiple myeloma, caused a marked increase in apoptosis of plasma cells in vivo in 10 patients and a minimal increase in four patients (P < 0.05). The nitrogen-containing bisphosphonates pamidronate and zoledronic acid also induced apoptosis of authentic, human bone marrow-derived plasma cells in vitro. Apoptosis of plasma cells in vitro was probably caused by inhibition of the mevalonate pathway and loss of prenylated small GTPases, as even low concentrations (>or= 1 micro mol/l) of zoledronic acid caused accumulation of unprenylated Rap1A in cultures of bone marrow mononuclear cells in vitro. GGTI-298, a specific inhibitor of geranylgeranyl transferase I, also induced apoptosis in human plasma cells in vitro, suggesting that geranylgeranylated proteins play a role in signalling pathways that prevent plasma cell death. Our results suggest that pamidronate may have direct and/or indirect anti-tumour effects in patients with multiple myeloma, which has important implications for the further development of the more potent nitrogen-containing bisphosphonates, such as zoledronic acid, in the treatment of myeloma.

Antiphospholipid syndrome in pregnancy: a randomized, controlled trial of treatment.

OBJECTIVE: To compare the efficacy of low-dose aspirin alone versus low-dose aspirin plus low molecular weight heparin in pregnant women with antiphospholipid syndrome and recurrent miscarriage as prophylaxis against pregnancy loss. METHODS: From a regional miscarriage clinic, 119 consecutive women with persistently positive tests for lupus anticoagulant and/or anticardiolipin immunoglobulin G and M antibody were invited to participate in a randomized, controlled trial between 1997 and 2000. After ethical approval and adherence to a written protocol, 12 women were unwilling to participate, five failed exclusion/inclusion criteria, and four were nonpregnant. Laboratory analysis was performed by Sheffield University Coagulation Department, electronically generated randomization by Manchester University Centre for Cancer Epidemiology, and data collection and analysis by a research officer at Leeds University. Viability ultrasound every 2 weeks was provided until 12 weeks' gestation before transfer to the pregnancy support antenatal clinic. RESULTS: Ninety-eight women were randomized before 12 weeks' gestation. Forty-seven received low-dose aspirin 75 mg daily (group A), and 51 received low-dose aspirin plus low molecular weight heparin 5000 U subcutaneously daily (group B) throughout pregnancy. There were 13 pregnancy losses and 34 live births in group A and 11 losses and 40 live births in group B. The live-birth rate was 72% in group A and 78% in group B (odds ratio 1.39, 95% confidence interval 0.55, 3.47). There were no cases of maternal thrombosis in either group. CONCLUSION: A high success rate is achieved when low-dose aspirin is used for antiphospholipid syndrome in pregnancy. The addition of low molecular weight heparin does not significantly improve pregnancy outcome.