Bernard S P Chin

Prognostic Value of Plasma von Willebrand Factor and Soluble P-Selectin as Indices of Endothelial Damage and Platelet Activation in 994 Patients With Nonvalvular Atrial Fibrillation

Background—Abnormal plasma markers of a prothrombotic state have been described in atrial fibrillation (AF), but no such marker has yet been shown to reliably predict future stroke or cardiovascular outcome in AF. We hypothesized that raised plasma levels of von Willebrand factor (vWf, an index of endothelial damage/dysfunction) and/or soluble P-selectin (sP-sel, an index of platelet activation) might predict vascular events in AF. Methods and Results—We measured vWf and sP-sel levels by ELISA in 994 participants receiving aspirin in the Stroke Prevention in Atrial Fibrillation III trial, at study entry or after 3 months, and related these indices to the subsequent incidence of stroke and vascular events. Plasma vWf levels were a significant predictor of both stroke (P =0.03) and vascular events (P <0.001), with the greatest risk for those with the highest levels of vWf. After adjustment for other clinical predictors, the relationship between vWf and stroke became nonsignificant, but vWf remained an independent predictor of vascular events (relative risk, 1.2 [95% CI, 1.0–1.4] per 20 IU/dL increase in vWf; P =0.02). No significant relationships were found between sP-sel levels and outcome. Conclusion—Among patients with AF who received aspirin, raised levels of vWf (endothelial damage/dysfunction) were predictive of stroke and vascular events, but raised sP-sel levels (platelet activation) were not associated with increased cardiovascular risk. Endothelial damage/dysfunction (or vWf itself) may play an important role in the mechanisms behind stroke and cardiovascular outcome among aspirin-treated AF patients and might represent a target for novel therapies or an adjunctive aid to risk stratification in AF.

Cancer and the prothrombotic state

Thrombosis is a frequent complication of cancer, so it follows that the presence of a tumour confers a prothrombotic state. Indeed, in patients with cancer, each of the three components of Virchows triad that predispose for thrombus formation have abnormalities, thus fulfilling the requirement for a prothrombotic or hypercoagulable state. The many signs and symptoms of the prothrombotic state in cancer range from asymptomatic basic abnormal coagulation tests to massive clinical thromboembolism, when the patient may be gravely ill. Many procoagulant factors, such as tissue factor and cancer procoagulant, are secreted by or are expressed at the cell surface of many tumours. Platelet turnover and activity are also increased. Damaged endothelium and abnormalities of blood flow in cancer also seem to play a part, as does abnormal tumour angiogenesis. Some studies have even suggested that these abnormalities may be related to long-term prognosis and treatment. We briefly describe the various clinical manifestations of thrombosis in cancer and discuss the evidence for the existence of a prothrombotic or hypercoagulable state associated with this disease. Further work is needed to examine the mechanisms leading to the prothrombotic state in cancer, the potential prognostic and treatment implications, and the possible value of quantifying indices of hypercoagulability in clinical practice.

Plasma von Willebrand Factor and Soluble P-Selectin as Indices of Endothelial Damage and Platelet Activation in 1321 Patients With Nonvalvular Atrial Fibrillation Relationship to Stroke Risk Factors

Background—Epidemiological studies have identified clinical and echocardiographic factors associated with increased stroke risk in atrial fibrillation (AF), but mechanisms linking these factors to stroke in AF are incompletely understood. We hypothesized that stroke risk factors may be associated with increased endothelial damage/dysfunction and platelet activation among patients with AF. Methods and Results—We measured plasma levels of von Willebrand factor (vWF, a marker of endothelial damage/dysfunction) and soluble P-selectin (sP-sel, a marker of platelet activation) by ELISA in 1321 participants in the Stroke Prevention in Atrial Fibrillation (SPAF) III study and related these indices to the presence of stroke risk factors and cardiovascular disease. Age (P <0.001), prior cerebral ischemia (P <0.01), recent heart failure (P <0.001), diabetes (P <0.001), and body mass index (P <0.001) were independently associated with increased vWF (r2 adjusted=9%). Independent associates of increased sP-sel were diabetes (P =0.01), peripheral vascular disease (P <0.001), and current smoking (P =0.01), whereas prior cerebral ischemia (P =0.002) and female sex (P <0.001) were associated with reduced sP-sel (r2 adjusted=4%). Using prospectively validated stroke risk stratification criteria, we observed a significant stepwise increase in vWF from low- to moderate- to high-risk groups (r2 adjusted=3%, P <0.001), whereas sP-sel remained constant (P = 0.24). Conclusions—Four recognized risk factors for stroke in AF (advancing age, prior cerebral ischemia, recent heart failure, and diabetes) were independently associated with raised plasma vWF (or endothelial damage/dysfunction), whereas only 1 (diabetes) was associated with increased sP-sel (platelet activation). Further longitudinal studies are now needed to confirm relationships between endothelial damage/dysfunction, platelet activation, and stroke in AF.

ABC of antithrombotic therapy: Venous thromboembolism: pathophysiology, clinical features, and prevention

Venous thromboembolism is a common complication among hospital inpatients and contributes to longer hospital stays, morbidity, and mortality. Some venous thromboembolisms may be subclinical, whereas others present as sudden pulmonary embolus or symptomatic deep vein thrombosis. Ultrasonic Doppler and venographic techniques have shown deep vein thrombosis of the lower limb to occur in half of all major lower limb orthopaedic operations performed without antithrombotic prophylaxis. Deep vein thrombosis of the lower limb is also seen in a quarter of patients with acute myocardial infarction, and more than half of patients with acute ischaemic stroke. Deep vein thrombosis of the lower limb normally starts in the calf veins. About 10-20% of thromboses extend proximally, and a further 1-5% go on to develop fatal pulmonary embolism. Appropriate antithrombotic measures can reduce this complication. Until recently, some clinicians were reluctant to provide such prophylaxis routinely. As unfounded fears of major bleeding complications from anticoagulant regimens wane, preventive treatments are used more often with medical and surgical patients. However, the risk of bleeding can be serious and this has particular bearing in postoperative patients. Venous thromboembolism can also arise spontaneously in ambulant individuals particularly if they have associated risk factors such as thrombophilia, previous thrombosis, or cancer. However, in over half of these patients, no specific predisposing factors can be identified at presentation. Venous thromboembolism often manifests clinically as deep vein thrombosis or pulmonary embolism, and is possibly one of the preventable complications that occur in hospitalised patients Thrombus formation and propagation depend on the presence of abnormalities of blood flow, blood vessel wall, and blood clotting components, known collectively as Virchows triad. Abnormalities of blood flow or venous stasis normally occur after prolonged immobility or confinement to bed. Venous obstruction can arise from …

A prospective randomized trial of aspirin-clopidogrel combination therapy and dose-adjusted warfarin on indices of thrombogenesis and platelet activation in atrial fibrillation

OBJECTIVES This study was designed to investigate whether or not combination aspirin-clopidogrel therapy would reduce markers of thrombogenesis and platelet activation in atrial fibrillation (AF), in a manner similar to warfarin. BACKGROUND Dose-adjusted warfarin is beneficial as thromboprophylaxis in AF, but potentially serious side effects and regular monitoring leave room for alternative therapies. METHODS; We randomized 70 patients with nonvalvular AF who were not on any antithrombotic therapy to either dose-adjusted warfarin (international normalized ratio 2 to 3) (Group I) or combination therapy with aspirin 75 mg and clopidogrel 75 mg (Group II). Plasma indices of thrombogenesis (fibrin D-dimer, prothrombin fragment 1+2) and platelet activation (beta-thromboglobulin [TG] and soluble P-selectin) were quantified, along with platelet aggregation responses to standard agonists, at baseline (pretreatment) and at six weeks posttreatment. RESULTS; Pretreatment levels of fibrin D-dimer (p = 0.001), beta-TG (p = 0.01) and soluble P-selectin (p = 0.03) were raised in patients with AF, whereas plasma prothrombin fragment 1+2 levels and platelet aggregation were not significantly different compared with controls. Dose-adjusted warfarin reduced plasma levels of fibrin D-dimer, prothrombin fragment 1+2 and beta-thromboglobulin levels at six weeks (all p < 0.001), enhanced plasma levels of soluble P-selectin (p < 0.001) and had no significant effect on platelet aggregation. Aspirin-clopidogrel combination therapy made no difference to the plasma markers of thrombogenesis or platelet activation (all p = NS), but the platelet aggregation responses to adenosine diphosphate (p < 0.001) and epinephrine (p = 0.02) were decreased. CONCLUSIONS Aspirin-clopidogrel combination therapy failed to reduce plasma indices of thrombogenesis and platelet activation in AF, although some aspects of ex vivo platelet aggregation were altered. Anticoagulation with warfarin may be superior to combination aspirin-clopidogrel therapy as thromboprophylaxis in AF.

Vascular endothelial growth factor and soluble P-selectin in acute and chronic congestive heart failure

Because congestive heart failure (CHF) is characterized clinically by tissue hypoxia, we hypothesized that there would be evidence of neovascularization, possibly resulting from this process. To test this, we measured levels of vascular endothelial growth factor (VEGF), associated with angiogenesis, in the plasma of patients with varying degrees of CHF (presenting acutely and in the chronic phase) and compared levels with those in healthy controls. To test the hypothesis of a link between VEGF and platelet activation and a tendency to hypercoagulability in CHF, 1,2 we also measured plasma levels of fibrinogen and soluble P-selectin, because these markers of coagulation and platelet activation have previously been shown to increase in patients with chronic CHF. 2 Our methods to testing these hypotheses were cross sectional (comparing patients with acute and chronic CHF with healthy controls), interventional (examining markers before and after successful treatment of acute CHF), and using a follow-up approach (at which time we questioned whether or not plasma markers could predict those at risk of mortality). ••• We recruited consecutive patients admitted with acute CHF secondary to impaired left ventricular systolic function, which was documented as an ejection fraction 40%, either by echocardiography, radionuclide imaging, or left ventriculography on admission, or within the previous 6 months. Patients were excluded from the study for the following criteria: concomitant acute coronary syndromes; infection or pyrexial illness; recent (3 months) myocardial infarction or stroke; unstable angina or ventricular arrhythmias; chronic and systemic illnesses including renal failure, hepatic impairment, cancer, and inflammatory connective tissue disease; and use of oral steroids or hormone replacement therapy. Baseline results from patients with acute CHF (i.e., subjects presenting acutely with severe symptomatic disease) were compared with 2 age- and gender-matched control groups; these were outpatients with chronic stable CHF in sinus rhythm (chronic CHF) and healthy control subjects recruited from among healthy hospital staff and from subjects attending the hospital for hernia repairs, varicose vein procedures, or other relatively minor operations. Subjects with CHF were classified according to the New York Heart Association (NYHA) criteria, with class I to II being no or mild symptoms and class III to IV being moderate to severe symptoms. Left ventricular ejection fraction was estimated using transthoracic M-mode echocardiography. All healthy controls had no clinical evidence of vascular, metabolic, neoplastic, diabetic, or in flammatory disease on careful history, examination, and routine laboratory tests. Blood tests were performed in patients with acute decompensated CHF between days 1 and 7 after hospital admission, and again at 3 months after standard treatment for heart failure according to local guidelines. 3 Patients were followed up for clinical end points that consisted of all-cause mortality and hospitalizations for stroke, myocardial infarction, thromboembolism, unstable angina, and revascularization for up to 6 months. Citrated plasma and serum were obtained from

Platelet P-Selectin Levels in Relation to Plasma Soluble P-Selectin and β-Thromboglobulin Levels in Atrial Fibrillation

Background and Purpose— The increased risk of stroke and thromboembolism in atrial fibrillation (AF) may be related to a prothrombotic or hypercoagulable state, with abnormalities of hemostasis and platelet activation. To investigate the role of platelets in AF and the influence of antithrombotic therapy, we developed and then applied a new assay to detect the absolute amount of P-selectin per platelet (pP-selectin) based on cell lysis. Thus, pP-selectin in AF patients was compared with that of healthy controls and also with plasma soluble P-selectin (sP-selectin) and &bgr;-thromboglobulin as established indices of platelet activation. Methodsmdash; We studied 122 patients (mean [SD] age, 71 [9] years; 65 men) with chronic AF of >6 weeks’ duration: 34 were not on antithrombotic therapy, 30 were taking aspirin (75 to 300 mg/d), and 58 were fully anticoagulated with warfarin. pP-selectin was compared with sP-selectin and plasma &bgr;-thromboglobulin levels (enzyme-linked immunosorbent assay). Results were compared with those of 23 healthy controls (mean [SD] age, 74 [9] years; 7 men) in sinus rhythm. Results— pP-selectin was significantly lower in AF patients on no antithrombotic therapy (P ∓0.03) than in healthy controls, but sP-selectin and &bgr;-thromboglobulin levels were not significantly different and did not differ in patients taking aspirin or warfarin. However, pP-selectin was lower in patients with AF on aspirin than in those on warfarin (P <0.05). pP-selectin/sP-selectin correlated significantly in healthy controls (r ∓0.47, P ∓0.03) but inversely (r ∓−0.43, P ∓0.03) in AF patients on no antithrombotic therapy. Conclusions— Lower levels of pP-selectin may represent a depletion of pP-selectin after platelet activation in AF. Aspirin further decreases pP-selectin levels compared with warfarin. On the basis of the principle of platelet lysis, we demonstrate that it is possible to determine the amount of P-selectin per platelet, which may be regulated in the megakaryocyte through a cyclooxygenase-dependent pathway.

A study of platelet activation in paroxysmal, persistent and permanent atrial fibrillation.

We hypothesized that the ‘residual’ thromboembolic risk in therapeutically anticoagulated patients undergoing cardioversion could potentially be related to abnormal haemorheology and platelet activation. To test this hypothesis, we firstly investigated the role of haemorheology and platelet activation in patients with paroxysmal and persistent atrial fibrillation (AF), who were compared with healthy controls and patients with permanent AF. Second, we compared these indices in patients with persistent AF, before and after successful cardioversion. We measured indices of haemorheology (haematocrit, plasma viscosity, and fibrinogen), fibrin D-dimer (an index of thrombogenesis and fibrin turnover) and platelet activation (as assessed by platelet aggregation and plasma levels of β-thromboglobulin, and soluble P-selectin) in 29 patients with paroxysmal AF, 87 patients with permanent AF and 29 healthy controls in sinus rhythm. The effects of cardioversion were studied in 20 patients with persistent AF, who maintained sinus rhythm at 2 months follow-up. Plasma levels of β-thromboglobulin (P = 0.03) and fibrin D-dimer (P = 0.001) were higher in patients with AF, when compared with controls; the highest levels were seen in those with permanent AF (Tukeys test, P < 0.05). Plasma viscosity was significantly higher in the patients with paroxysmal AF compared with healthy controls (P = 0.02). Plasma soluble P-selectin levels and platelet aggregation responses to all four platelet agonists (adenosine diphosphate, collagen, epinephrine and thrombin) in patients with paroxysmal AF and permanent AF were similar to controls. Plasma fibrinogen, viscosity and other markers of platelet activation (including platelet aggregation) were not significantly different in patients with paroxysmal AF, during episodes of AF and sinus rhythm (P = not significant), although mean haematocrit was significantly higher during the episodes of AF compared with episodes of sinus rhythm (P = 0.03). Among the patients with persistent AF who remained in sinus rhythm at 2 months following successful cardioversion, there was a significant decrease in the plasma levels of soluble P-selectin at 2 weeks and 2 months, when compared with baseline (pre-cardioversion) levels (P < 0.001). Haemorheology and platelet aggregation response to agonists did not change significantly, except for a transient increase in platelet aggregation response to collagen at 2 weeks (P = 0.045). In conclusion. abnormal haemostatic and platelet activation in patients with permanent AF are not consistently observed in patients with paroxysmal and persistent AF. Abnormal haemorheology appears to play an important role in patients with paroxysmal AF, especially during the paroxysms of AF. Cardioversion of persistent AF to sinus rhythm appears to decrease the platelet activation, but whether this translates into a beneficial reduction in thromboembolic risk requires further study.

Antithrombotic therapy in acute coronary syndromes

The use of antithrombotic therapy in acute coronary syndromes has reduced the incidence of death and Q wave myocardial infarction dramatically in recent years. Antithrombotic drugs in routine use include antiplatelet drugs (aspirin, clopidogrel, and glycoprotein IIb/IIIa receptor antagonists) and anticoagulants (unfractionated and low molecular weight heparin, warfarin, and direct thrombin inhibitors). Thrombosis in relation to acute coronary syndromes Thrombosis is the basic pathophysiological process underlying the acute coronary syndromes. Thus, antithrombotic therapy is the cornerstone of management, and the appropriate choice of antithrombotic drugs to reduce platelet aggregation or interfere with the clotting process can be critical. Rupture of the fibrous cap of an atheromatous plaque exposes the lipid core, which is highly thrombogenic and contains an abundance of procoagulant tissue factor. Plaque rupture (exposing surface binding glycoproteins) allows platelets to adhere to the plaque, become activated, and release thromboxane A2, which causes further platelet aggregation and vasoconstriction. As the platelets aggregate around the ruptured plaque, membrane glycoprotein IIb/IIIa receptors undergo a configuration change to bind fibrinogen and form a complex platelet linkage. Further incorporation of fibrin and red blood cells within this platelet-rich thrombus results in a partial or total occlusion of the coronary artery. Alternatively, thrombus may break off from a ruptured plaque and occlude a downstream vessel. Occlusion may also follow from trapping of circulating thrombi formed elsewhere in the circulation. Thrombus within right coronary artery (arrow) in a patient with unstable angina Reduction of adverse events in patients treated with aspirin, heparin, or both compared with neither drug ### Antiplatelet drugs #### Aspirin Aspirin has been in use for more than 150 years and is cheap and effective. It has been shown to reduce the risk of fatal and non-fatal myocardial infarction by at least 50% in patients with unstable angina. Aspirin blocks cyclo-oxygenase and formation of thromboxane A2, thus …

Neither carvedilol nor bisoprolol in maximally tolerated doses has any specific advantage in lowering chronic heart failure oxidant stress: implications for β-blocker selection

We hypothesized that abnormal oxidative stress in chronic heart failure (CHF) could be related to endothelial damage and platelet activation, and that the vasodilating beta-blocker carvedilol would have beneficial effects on these processes compared with a selective non-vasodilating cardioselective beta-blocker, bisoprolol. We therefore assessed the effects of introducing carvedilol and bisoprolol in a prospective manner on indices of oxidative stress [lipid hydroperoxides (LHP)], endothelial damage [von Willebrand factor (vWf)], platelet activation (soluble P-selectin) and coagulation (fibrinogen) and their inter-relationships in stable outpatients with CHF in sinus rhythm. We recruited 46 patients [23 male; age 64 +/- 13 years (mean +/- S.D.); range 38-85 years] with CHF. Baseline levels of serum LHP (P<0.002), plasma vWf (P<0.001) and soluble P-selectin (P=0.02), but not fibrinogen (P=0.16), were higher in CHF patients compared with 22 age- and sex-matched healthy controls. After treatment for 2 months, systolic blood pressure fell in both arms of the study (both P<0.01), but there were no statistically significant (defined as P<0.01) decreases in LHP, vWf, fibrinogen or soluble P-selectin levels with either carvedilol or bisoprolol. In conclusion, patients with CHF have increased levels of plasma LHP and vWf, indicating increased oxidative stress and endothelial damage respectively. Contrary to the proposed antioxidative effects of carvedilol, initiating and titrating such therapy did not result in a reduction in levels of LHP in CHF.