Platelet Survival in Patients with Angiographically Diseased and Normal Coronary Arteries

Platelets as Predictors of Vascular Risk: Is There a Practical Index of Platelet Activity?

Activated platelets play a role in the pathogenesis of coronary heart disease (CHD). Following activation, platelets change shape, aggregate, and release several bioactive substances. The aim of this review is to identify if there is a simple and cost-effective method that indicates platelet activation and predicts the risk of CHD and vascular events. The rationale for identifying high-risk patients is to reduce their risk of vascular events by administering appropriate and effective antiplatelet treatment, like aspirin, clopidogrel, or combination regimens. Many laboratory tests estimating platelet activity have been described. Some are relatively simple, such as spontaneous or agonist-induced platelet aggregation. Other tests include measuring the mean platelet volume (MPV) or plasma soluble P-selectin levels. Some more complex tests include flow cytometry to determine platelet GP Ilb/Illa receptors, platelet surface P-selectin, plateletmonocyte aggregates, and microparticles. Only few prospective studies assessed the predictive value of platelet activation in healthy individuals. Although the MPV seems an 'easy method, there are insufficient data supporting its ability to predict the risk of a vascular event in healthy adults. Platelet aggregation, in whole blood or in platelet-rich plasma was not consistently predictive of vascular risk. Soluble P-selectin measurement is a promising method but it needs further evaluation. Flow cytometry methods are costly, time-consuming, and need specialized equipment. Thus, they are unlikely to be useful in estimating the risk in large numbers of patients. There is as yet no ideal test for the detection of platelet activation. Each currently available test has merits and disadvantages. Simple methods such as the MPV and the determination of platelet release products need further evaluation.

Increased plasma beta-thromboglobulin in patients with coronary artery vein graft occlusion: response to low dose aspirin

The therapeutic effect of aspirin on vein graft patency was studied in patients undergoing coronary artery bypass graft surgery. The study design enabled the prospective evaluation of the relation of platelet activation, as measured by plasma beta-thromboglobulin concentration, to subsequent coronary vein graft occlusion. Serial beta-thromboglobulin levels were measured in 105 patients randomized to receive aspirin (324 mg/day) or placebo beginning within 1 h after surgery. Graft patency was assessed angiographically at 1 week and 1 year after surgery. Of 49 patients receiving placebo, 17 (34.7%) had one or more graft occlusions, 6 early, 10 late and 1 with both early and late occlusion. Of 56 patients receiving aspirin, 7 (12.5%) had one or more occlusions, 3 early and 4 late (p less than 0.01). Preoperatively, the beta-thromboglobulin level in surgical patients (29 +/- 13.5 ng/ml) was significantly higher than that of 51 control subjects (22.6 +/- 11.1 ng/ml) (p less than 0.004). Plasma beta-thromboglobulin levels remained comparatively constant at 3 and 12 months after surgery in the 43 patients who had both samples available (p less than 0.001, r = 0.65). The reduction in beta-thromboglobulin concentration from the preoperative level to 12 months postoperatively was greater in the aspirin-treated group (p less than 0.001). Multivariate logistic regression analysis demonstrated a significant association between preoperative beta-thromboglobulin concentration and graft occlusion (p less than 0.02), and aspirin treatment was effective in preventing occlusion when adjusted for the preoperative beta-thromboglobulin level (p less than 0.005). Plasma beta-thromboglobulin concentrations are elevated in patients with coronary artery disease, suggesting ongoing platelet activation.(ABSTRACT TRUNCATED AT 250 WORDS)

In vitro and in vivo behavior of 111In-labelled platelets: an experimental study of healthy male volunteers

The aim of this study was to obtain a critical evaluation of a simple method for labelling platelets with 111In-oxine. All experiments were carried out on healthy volunteers. 65 +/- 7 (SD) % of the platelets in collected blood were labelled and reinjected. As compared to control experiments, only in response to a low final ADP concentration (1.0 mumol/l) did 111In-labelled platelets show reduced in vitro aggregability. The mean platelet volume for 111In-labelled platelets was slightly lower than the mean platelet volume in whole blood. The results for initial platelet recovery and platelet mean lifespan closely agreed with those of other studies in which considerably higher platelet extraction from whole blood was obtained. After injection, the splenic uptake and blood disappearance of 111In-labelled platelets followed a monoexponential function with almost identical rate constants. By compartmental analysis of the equilibration of platelets between blood and spleen, the splenic blood flow was estimated to be 4.8 +/- 1.9 (SD) % of the total blood volume/min; the intrasplenic platelet transit time was 9.7 +/- 1.6 (SD) min, and the exchangeable splenic platelet pool 31 +/- 8 (SD) %. Highly significant relationships were present between the splenic blood flow and the splenic platelet pool size, as well as between the splenic blood flow and the initial platelet recovery. It is concluded that the requirements for adequate interpretation of platelet kinetics are well met with the present method for harvesting and labelling of platelets.

Influence of acetylsalicylic acid (1.0 g/day) on platelet survival time, beta-thromboglobulin and platelet factor 4 in patients with peripheral arterial occlusive disease

In this study we investigated the influence of acetylsalicylic acid (ASA) 1.0 g/day on 111-In-platelet survival time (PST) and on plasma levels of beta-thromboglobulin (beta-TG) and platelet factor 4 (PF 4) in 37 patients (median age: 63.4 years) with arteriographically proven peripheral arterial occlusive disease (PAOD) in a chronic stable phase. We found a slight but significant increase of PST during therapy with ASA (weighted mean (WM): 184.3----193.2 [median] hours, p less than 0.05; multiple hit (MH): 182.4----192.8 hours, p less than 0.005) for the total group of patients. Concerning the influence of risk factors of PAOD on PST during ASA-therapy, there was a significant increase of PST only in the nondiabetics (WM: 180.3----204.6 hours, p less than 0.01; MH: 176.8----195.3 hours, p less than 0.01). There was a negative correlation between the baseline values of PST and their increase following ASA therapy (WM: r = -0.63; p less than 0.0001; MH: r = -0.61, p less than 0.0001). The pretreatment levels of beta-TG--but not PF 4--were significantly (p less than 0.001) elevated compared to healthy controls. Therapy with ASA caused a significant decrease in the plasma levels of beta-TG (median: 30.4----26.6 ng/ml, p less than 0.001) and PF 4 (2.95----2.2 ng/ml, p less than 0.01).