Monitoring anticoagulation of primary haemostasis

This article provides an overview on current commercially available methods to determine primary haemostasis as a target of drug-mediated anticoagulation. It focuses on whole blood methods only, and references the currently major achievements that have been reported with each method in respect to its clinical use. Advantages and disadvantages of the various methods are presented, based on considerations of platelet physiology, and on feasibility of the procedures.

Vollblutaggregometrie zur Kontrolle der Wirksamkeit von Azetylsalizylsäure bei Patienten mit koronarer Herzkrankheit

In dieser Studie wurden zwei Methoden evaluiert und verglichen, welche die Wirkung von Azetylsalizylsäure (ASS) auf die Thrombozytenaggregation im Vollblut erfassen. Die In-vitro-Blutungszeit wurde im PFA-100 (Dade Behring, Marburg) mit der Kollagen/Adrenalin-Messzelle im Zitratblut bestimmt. Die Vollblutaggregation wurde am Multiplate- System (Dynabyte medical, München) mit Hirudinblut (25 μg/ml) bestimmt. Zur Aggregation wurden die Induktoren Arachidonsäure (ASPItest), Kollagen (COLtest) sowie TRAP-6 (thrombin receptor activating peptide, TRAPtest) eingesetzt. Nach Aufklärung und Einwilligung wurden zur Analyse der In-vitro-Blutungszeit sowie der Vollblutaggregometrie Zitratblut und Hirudinblut von 76 Patienten mit koronarer Herzkrankheit, die unter langfristiger Azetylsalizylsäure- Behandlung standen (ASS-Patienten), entnommen. Zusätzlich wurde von 57 gesunden Blutspendern Hirudinblut für die Vollblutaggregometrie entnommen.

Im PFA-100 betrugen die Verschlusszeiten der ASS-Patienten 273 ± 49 s. Basierend auf dem Grenzwert (cut-off) von 170 s wurde bei 5 von 76 Patienten kein Ansprechen des Tests auf die ASS-Therapie nachgewiesen (Aspirin-Non-Response). Die Vollblutaggregometrie war bei den ASS-Patienten im Vergleich (vs. AUC-Werte) zu den Blutspendern in TRAPtest vergleichbar, hingegen im COLtest und ASPItest signifikant vermindert (p <0,05). Von den fünf Patienten, die im PFA-100 normwertige Verschlusszeiten zeigten, hatte nur einer eine normwertige Aggregation im ASPItest, und ebenfalls nur eine normwertige Aggregation im COLtest.

Die in der Studie gefundenen hohen Ansprechraten des PFA-100 sowie ASPItest auf die Azetylsalizylsäuretherapie kann durch die erwartete gute Compliance im untersuchten Kollektiv erklärt werden. In den verschiedenen Tests wurden unterschiedliche Patienten als Non-Responder zugeordnet. Dies verdeutlicht die Bedeutung der Testbedingungen für die Diagnose einer Azetylsalizylsäure-Resistenz oder Aspirin- non-Response.

Influence of High Polyphenol Beverage on Stress-Induced Platelet Activation

OBJECTIVES

Platelets are playing a crucial role in acute cardiovascular events. We investigated if physical stress activates platelets and whether this activation can be inhibited by a polyphenol-enriched diet.

METHODS

Blood samples were taken from a total of 103 athletes three weeks before, one day before, immediately as well as 24 hours and 72 hours after a marathon run. Participants were randomized, double-blinded and divided into two groups. One group received a polyphenol-rich beverage the other the same beverage without polyphenols. Besides analysis of platelet counts and impedance-aggregometric-measurement of platelet activity, soluble P-selectin and Endothelin-A measurements were performed.

RESULTS

In the control group, runners showed a 2.2-fold increased platelet aggregation directly after completing a marathon and within the following three days when compared with baseline values (p<0.01). In accordance, significant increases in sP-selectin (57.52ng/ml vs. 94.86ng/ml;p<0.01) were detectable. In contrast, for the group consuming a beverage with increased polyphenol content (upper quartile of study beverage intake) we did not find any increase of platelet aggregation.

DISCUSSION

Physical stress causes a significant increase in platelet activity. Our results demonstrate that a diet enriched in polyphenols is capable of preventing platelet activation. These findings might indicate a diminished cardiovascular stress-reaction following pre-exposition to polyphenol-enriched diet.

Monitoring anticoagulation of primary haemostasis--estimation of platelet function in whole blood assays

This article provides an overview on current commercially available methods to determine primary haemostasis as a target of drug-mediated anticoagulation. It focuses on whole blood methods only, and references the currently major achievements that have been reported with each method in respect to its clinical use. Advantages and disadvantages of the various methods are presented, based on considerations of platelet physiology, and on feasibility of the procedures.

Platelet concentrates transfusion in cardiac surgery and platelet function assessment by multiple electrode aggregometry

BACKGROUND

Platelet dysfunction contributes to the pathophysiology of bleeding complications during and after cardiac surgery. In most surgical institutions, no peri-operative point-of-care monitoring of platelet function is used. We evaluated the usefulness of the Multiplate platelet function analyser based on impedance aggregometry for identifying groups of patients at a high risk of transfusion of platelet concentrates (PC).

METHODS

Platelet function parameters were determined in 60 patients before and after routine cardiac surgery. Impedance aggregometry measurements were performed on Multiplate using ADP (ADPtest), collagen (COLtest) and thrombin receptor activating peptide (TRAPtest) as platelet activators. The correlations between the aggregometry results and the transfusion of PC were calculated. The results of the aggregation tests were also divided into tertiles and the differences in PC transfusion between the low and the high tertile were assessed.

RESULTS

Low aggregometry delimited groups of patients with significantly higher PC transfusion. In the receiver operating characteristic curve, low pre-operative aggregation in the ADPtest identified patients with high total transfusion of PC (area under the curve 0.74, P=0.001), while the ADPtest performed at the end of the operation identified patients with high PC transfusion on the intensive care unit (ICU) (area under the curve 0.76, P=0.002).

CONCLUSIONS

Near-patient platelet aggregation may allow the identification of patients with enhanced risk of PC transfusion, both pre-operatively and upon arrival on the ICU.

[Control of aspirin effect in chronic cardiovascular patients using two whole blood platelet function assays. PFA-100 and Multiplate]

In this study two aspirin sensitive platelet function tests which are based on the analysis of whole blood were evaluated and correlated with each other. In vitro bleeding time was determined using the PFA-100 analyzer (Dade Behring, Marburg, Germany) using the collagen/epinephrine cartridge and citrated blood. Whole blood aggregometry was performed using the Multiplate analyzer (Dynabyte medical, Munich, Germany) using hirudin blood (25 mug/ml). Aggregatin was triggered using arachidonic acid (ASPItest), collagen (COLtest) or TRAP-6 (thrombin receptor activating peptide, TRAPtest). Following informed consent citrated blood and hirudin blood was drawn from 76 cardiovascular patients which were on long-term aspirin therapy (aspirin patients). In addition hirudin blood was drawn from 57 healthy blood donors for assessment of whole blood aggregometry. PFA-100 closure times of the aspirin patients were 273 +/- 49 s. Based on the cut-off of 170 s a non response to the aspirin therapy was detected in 5 of 76 patients. Whole blood aggregation was comparable in the aspirin patients vs the blood donors AUC values in the TRAP test, whereas in COLtest and ASPItest significantly reduced aggregations were detected (p < 0.05). Of the five patients that had a normal PFA-100 closure time only one had normal aggregation in ASPItest, and also only one had a normal aggregation in COLtest. The high rate of response to the aspirin therapy which was found in PFA-100 and ASPItest can be explained by the assumed high level of compliance of the cohort. In the applied tests different patients were stratified as aspirin-non-responders. This highlights the importance of the assay conditions for the diagnosis of an aspirin-non-response.

[Point-of-care testing of hemostatic alterations in anaesthesia and intensive care]

In recent years point-of-care testing (POCT) has seen wider applications in the clinical management of surgical and critically ill patients. The available methods for haemostasis analysis include simple-to-handle tests for the assessment of plasmatic coagulation, platelet function tests and the more complex visco-elastic assays. The main advantage of POCT is the fast availability of the results allowing a targeted management of haemostasis disorders. The benefits and risks of POCT depend on the urgency of the analysis, the turn-around time of the laboratory tests, the availability of motivated staff at the point-of-care and the expected haemostatic alterations. An underestimated aspect of POCT is the importance of established quality management procedures. For this purpose control materials based on plasma or artificial fluids are being applied. In spite of often higher costs we appraise the use of POC analysis in many settings as justified because of the gain of time and the overall better process quality, i.e. targeted haemostasis therapy instead of consecutive application of different therapeutic options.

Management and monitoring of recombinant activated factor VII

Recombinant factor VIIa (rFVIIa) has recently been introduced as a new 'bypassing' agent to improve haemostasis in haemophilia patients with inhibitors to factor (F) VIII or FIX. In noninhibitor patients, levels of circulating FVIII or FIX can be used to assess the quality of substitution therapy. In contrast, laboratory monitoring of haemostatic efficacy in patients treated with rFVIIa has proved more complex. Evaluation of patient samples saved during rFVIIa treatment have revealed some correlation between FVII:C levels and improved haemostasis, while whole blood elasticity, as determined by thromboelastography, has been shown to improve following rFVIIa treatment. The investigation aimed to study the efficacy of rFVIIa in activating FX:C and in shortening the whole blood clotting time (WBCT) using the newly-developed roTEG coagulation instrument. Results indicated a substantial and apparently dose-dependent activation of FX:C by rFVIIa. In addition, the presence of FIX appeared to influence FX:C activation. In-vitro and ex-vivo roTEG thromboelastograph measurements showed that FVIIa shortened WBCT, although normalization did not occur. The results presented here are based on a small number of observations in a few patients and further studies should be planned to test the efficacy of these monitoring principles in clinical treatment practice with rFVIIa.