Utility of the PFA-100 instrument and the novel multiplate analyzer for the assessment of aspirin and clopidogrel effects on platelet function in patients with cardiovascular disease

The use of impedance aggregometry to evaluate platelet function after the administration of DDAVP in healthy dogs treated with aspirin or clopidogrel

OBJECTIVE

To evaluate the effect of 1-Desamino-8-d-arginine vasopressin (DDAVP; desmopressin acetate) on platelet aggregation in healthy dogs receiving aspirin or clopidogrel.

ANIMALS

7 healthy staff-owned dogs.

PROCEDURES

In this randomized double-blinded crossover study, impedance aggregometry was performed on samples of lithium-heparinized whole blood samples from dogs before (T0) treatment with aspirin (1 mg/kg, PO, q 24 h for 4 days; ASP group) or clopidogrel (1 mg/kg, PO, q 24 h for 4 days; CLP group) and then before (T1) and after (T2) treatment with DDAVP (0.3 μg/kg, IV, once). There was a 14-day washout period before the crossover component. Aggregometry was performed with 4 different assays, each of which involved a different agonist reagent to stimulate platelet function: ADP, thrombin receptor activating peptide-6, arachidonic acid, or collagen type 1.

RESULTS

Median results for platelet aggregometry with agonist reagents ADP, arachidonic acid, or thrombin receptor activating peptide-6 significantly decreased between T0 and T1 for the CLP group; however, no meaningful difference in platelet aggregation was detected in the ASP group. Results for platelet aggregometry did not differ substantially between T1 and T2 regardless of treatment group or assay.

CONCLUSIONS AND CLINICAL RELEVANCE

Findings suggested that administration of DDAVP may have no effect on platelet aggregation (measured with platelet aggregometry) in healthy dogs treated with clopidogrel. Because no inhibition of platelet aggregation was detected for dogs in the ASP group, no conclusion could be made regarding the effects of DDAVP administered to dogs treated with aspirin.

Pharmacokinetic, pharmacodynamic, and pharmacogenetic assays to monitor clopidogrel therapy

Clopidogrel is the most common and widely used antiplatelet agent for patients with coronary artery disease following confirmation by electrocardiographic studies. The nonresponsiveness of patients to clopidogrel and the possibility of testing for clopidogrel resistance by platelet function assays (PFA) are contentious issues. Light transmission aggregometry (LTA) is considered as the gold standard test among all PFA. In this review, the most commonly used PFA used for monitoring the effect of clopidogrel, LTA, vasodilator-stimulated phosphoprotein assay phosphorylation, rotational thromboelastometry (ROTEM) delta and ROTEM platelet, thromboelastography, PFA-100, VerifyNow P2Y12 assay, Multiplate analyzer, Plateletworks assay and pharmacogenetic studies, are comparatively discussed including their principles of action, advantages, and disadvantages. VerifyNow P2Y12 assay can be accepted as the ideal point of care test out of the discussed assays. However, modified assays are required which could overcome the limitations associated with currently available assays.

Clopidogrel Resistance in Lower Extremity Arterial Endovascular Interventions

Antiplatelet pharmacotherapy for endovascular interventions has been widely adopted, with clopidogrel being one of the most common agents prescribed. A fraction of patients is resistant to clopidogrel resulting in decreased platelet inhibition despite adequate use. This finding is often termed high on-treatment platelet reactivity (HPR) and may lead to decreased patency in lower extremity arterial endovascular interventions. Current literature on HPR with lower extremity arterial endovascular interventions is limited to only a few studies. Resistance to clopidogrel is largely a result of CYP2C19 enzyme loss of function alleles. Several tests are available to measure clopidogrel resistance but light transmittance aggregometry remains the gold standard, yet direct genetic testing may be more reliable. One-year patency rates following lower extremity arterial endovascular interventions in patients with clopidogrel resistance (HPR) range between 35%-83% whereas those with the proper response to clopidogrel range between 73%-100%. Patients with decreased CYP2C19 activity show a significant decrease in one-year patency of endovascular femoropopliteal interventions (35% vs. 73%; p=0.006). Among patients tested for platelet function after in-stent thrombosis, up to 53% are resistant to clopidogrel. Lack of robust data limits our ability to predict patency in lower extremity arterial interventions for patients with HPR, but there is little doubt that longer patency seems to favor non-HPR patients. Large population, prospective trials are needed to guide our practice.

Do antiplatelet drugs increase the risk of bleeding after tooth extraction? A case-crossover study

The aim of this study was to assess the risk of bleeding after tooth extraction in patients taking aspirin or clopidogrel. This case-crossover study evaluated patients taking aspirin (80mg/day) or clopidogrel (75mg/day) and undergoing tooth extraction. In the first session, extraction was performed without discontinuing aspirin (group 1) or clopidogrel (group 2). In the second session, patients ceased using antiplatelet drugs 5days prior to tooth extraction. Bleeding was evaluated using a visual analogue scale (VAS) for 72h after tooth extraction. The platelet function assay (PFA) was performed for group 1 and flow cytometry assessment of vasodilator-stimulated phosphoprotein (VASP) was performed for group 2, in both sessions. Thirty-eight patients were studied: 20 in group 1 and 18 in group 2. Analysis of the data did not demonstrate any difference in bleeding severity between sessions 1 and 2 in either group (P>0.05). There was a significant difference between sessions 1 and 2 in group 1 for the mean collagen/epinephrine membrane closure time (PFA) (P=0.001). A significant difference in platelet reactivity index (flow cytometry for VASP) was noted between sessions 1 and 2 in group 2 (P=0.001). According to this case-crossover study, dental extraction can be performed safely without withdrawal of aspirin or clopidogrel.

Novel strategies for assessing platelet reactivity

There are many approaches to assessing platelet reactivity and many uses for such measurements. Initially, measurements were based on the ability of platelets separated from other blood cells to aggregate together following activation with an appropriate 'aggregating agent'. Later, measurements of platelet aggregation in blood itself were performed, and this led to a point-of-care approach to platelet function testing. Measurement of secretory activity through the appearance of the activation marker P-selectin on platelets now provides an alternative approach, which enables remote testing. Measurement of vasodilator-stimulated phosphoprotein phosphorylation is also moving toward application in situations remote from the testing laboratory. Here we provide an overview of the various approaches that are now available, assess their advantages and disadvantages, and describe some of the clinical situations in which they are being used.

Influence of a low dosage of clopidogrel on platelet function in cats as measured by the platelet function analyser PFA-100 and the multiplate analyser

The antiplatelet drug clopidogrel is widely used for prophylaxis of arterial thromboses in cats in a standard dosage of 18.75mg per cat once daily. The aim of the study was to verify if a reduced daily dose of 10mg clopidogrel per cat has a similar antiplatelet effect as the standard dosage. Platelet function was measured with the platelet function analyser PFA-100^® and a novel impedance aggregometer. Suitability of the platelet function analyser was tested in citrated blood samples of 59 healthy cats and reference ranges were established. In addition, agonist concentrations for impedance aggregometry were optimised. In the main experiment two groups of 6 healthy cats received clopidogrel either in a dosage of 10 or 18.75mg per cat over a period of seven days. Analyses were performed on days 1, 2, 3, 5, and 7. In comparison to baseline both clopidogrel dosages showed an inhibitory effect on results of the platelet function analyser and velocity of ADP-induced platelet aggregation. Values at all times were different from baseline, with the exception of day 1 in cats receiving 10mg clopidogrel where the closure time of the platelet function analysis and part of ADP-induced aggregation did not show a significant difference. Significant differences were not found between the two doses. In conclusion, our study indicates that 10mg clopidogrel per day may be as effective as 18.75mg although the latter may be advantageous as an initial loading dosage to achieve effective levels more rapidly.

Monitoring ASA and P2Y12-specific platelet inhibition--comparison of conventional (single) and multiple electrode aggregometry

OBJECTIVE

Several platelet function test systems exist for the evaluation of the platelet inhibitory effect in patients on P2Y12 inhibitors and/or acetylsalicylic acid (ASA, aspirin) therapy. Studies comparing different available assays found only a poor correlation. The objective of the present study was to evaluate the correlation and agreement between single electrode (SEA) and multiple electrode (MEA) aggregometry.

METHODS AND RESULTS

In whole blood arachidonic acid (AA) and adenosine diphosphate (ADP)-induced platelet aggregation was measured simultaneously using SEA (Chrono-Log) and MEA (Multiplate). We analyzed a total of 226 measurements taken from 58 patients on single ASA therapy or dual antiplatelet therapy with ASA and a thienopyridine. A cut-off value for clopidogrel/prasugrel high on-treatment platelet reactivity (HPR) of > 47 units (U) was chosen for MEA testing using hirudin and > 5 Ohm for SEA with citrate anticoagulated blood samples. The respective cut-off values for ASA HPR were > 30 U for the MEA assay and > 1 Ohm for SEA testing. There was a good correlation of the prevalence of thienopyridine-HPR in both whole blood assays (Spearman rank correlation coefficient r = 0.698) and a good inter-rate accordance (Cohen's Kappa statistic κ = 0.648). For AA-induced aggregation, the correlation of the results obtained was significant (r = 0.536; p < 0.001) and detecting ASA-HPR revealed a moderate (κ = 0.482) correlation between both impedance aggregometry assays.

CONCLUSION

Platelet function testing using SEA and MEA provided both good accordance and correlation and therefore study results obtained by these two assays similarly enabled the detection of HPR of thienopyridine (and ASA) therapy.

Contemporary antiplatelet therapy in patients undergoing percutaneous coronary intervention

The proper use of antiplatelet agents in the cardiac catheterization laboratory is important for ensuring optimal results in patients undergoing percutaneous revascularization. Understanding the mechanisms by which these drugs exerts their effects is important for both interventional and non-interventional cardiologists. The effects of these agents on platelet function can be assessed and monitored using a variety of commercially available laboratory assays but so far these tests have not been adopted in routine clinical practice. Currently, aspirin, thienopyridines and glycoprotein IIb/IIIa inhibitors are the primary types of antiplatelet drugs being utilized. The use of these drugs and of several newer antiplatelet drugs in the treatment of patients undergoing percutaneous revascularization in the cardiac catheterization laboratory will be discussed, especially in the light of the recently published guidelines.

[Acetylsalicylic acid non-responders after ischemic insult in geriatric patients]

BACKGROUND

The cardiovascular and cerebral ischemic risk is defined as the risk of suffering a thromboembolic event. The common secondary prophylaxis is still the use of acetylsalicylic acid (ASA). The usual daily dose is 100 mg. Efficacy concerning platelet aggregation is not routinely checked.

MATERIAL AND METHODS

In this study, patients taking 100 mg aspirin daily (orally) were examined after admittance to the stroke unit due to a stroke or stroke recurrence. Platelet aggregation was performed using a Platelet Function Analyser (PFA 100).

RESULTS

A total of 71 patients were examined, 53(73%) had experienced a primary ischemic insult, and 18(25.4%) stroke recurrence. Patients with prolonged closure time in the collagen/epinephrine cell (normal range 85-165 s) were classified as responders to ASA, while 14 (19.7%) were classified as non-responders.

CONCLUSION

It remains open whether the secondary prophylaxis or a more effective inhibition of platelet aggregation results in the improved protection against a future event.

[Randomised comparative study of early versus delayed surgery in hip-fracture patients on concomitant treatment with antiplatelet drugs. Determination of platelet aggregation, perioperative bleeding and a review of annual mortality]

OBJECTIVE

A review of the perioperative management of patients with hip fractures and concomitant therapy with antiplatelet agents, and to analyse the differences in mortality and perioperative bleeding in early surgery (<48 h) versus delayed surgery (>5 days). Platelet aggregation was measured on admission and immediately before surgery in all patients included in the study

PATIENTS AND METHODS

A total of 175 patients over 65 years old, with low energy hip fracture were randomised into 3 groups: Patients on antiplatelet therapy undergoing early surgery, patients on antiplatelet therapy undergoing delayed surgery, and patients not on antiplatelet therapy undergoing early surgery. The same clinical and laboratory data were collected prospectively up to 12 months for all the patients. The platelet aggregation was determined by a semi-quantitative computerised system based on impedance aggregometry in whole blood.

RESULTS

Bleeding, transfusion requirements and analytical results showed no significant differences between groups. More than half (59.8%) of the patients not taking antiplatelet therapy had normal platelet aggregation on admission, while 13.5% of those taking antiplatelet agents did not. Multivariate analysis showed increased mortality at 12 months for the variables, low Barthel index before hip fracture (OR: 0.9-0.9) and number of transfusions (OR: 1.1-1.5). The average lenth of stay was 4.1 days greater in the delayed surgery group.

CONCLUSION

Early surgery for patients receiving antiplatelet therapy has similar clinical outcomes to the delayed, but improves hospital efficiency by reducing the average length of stay. The antiplatelet drug reported by the patient showed low concordance with the determination of the platelet aggregation.

Platelet function tests in clinical cardiology: unfulfilled expectations

This review is a critical evaluation of publications in the past decade on the usefulness of platelet function tests (PFTs) in clinical cardiology, in aiding diagnosis, predicting risk, and monitoring therapy. The ideal PFT should: 1) detect baseline platelet hyperreactivity; 2) allow individualization of antiplatelet medication; 3) predict thrombotic risk; and 4) predict bleeding risk. The practicalities of clinical cardiology demand rapid, accurate, and reliable tests that are simple to operate at the bedside and available 24 h a day, 7 days a week. Point-of-care PFTs most widely evaluated clinically include PFA-100 and VerifyNow. None of these tests can reliably detect platelet hyperreactivity and thus identify a prothrombotic state. Identification of antiplatelet nonresponsiveness or hyporesponsiveness is highly test specific, and does not allow individualization of therapy. The power of PFTs in predicting thrombotic events for a given individual is variable and often modest, and alteration of antithrombotic treatment on the basis of the results of PFTs has not been shown to alter clinical outcome. PFTs in current mainstream use cannot reliably assess bleeding risk. These tests have been in use for over a decade, but the hopes raised by PFTs in clinical practice remain unfulfilled. Although physiologically relevant measurement of platelet function now is more important than ever, a critical reappraisal of available techniques in light of clinical requirements is needed. The use of native blood, global stimulus instead of individual agonists, contribution of thrombin generation by activated platelets to the test results, and establishment of a PFT therapeutic range for each antiplatelet drug should be considered and is discussed.

Sample transport by pneumatic tube system alters results of multiple electrode aggregometry but not rotational thromboelastometry

Pneumatic tube systems (PTS) present a convenient way for blood sample transport in medical facilities. Associated preanalytical interference in various tests is largely unknown. Implementing point-of-care coagulation management at our institution, we investigated multiple electrode aggregometry (MEA) and rotational thromboelastometry (ROTEM) after PTS transportation. Whole blood samples from patients undergoing general or trauma surgery were analysed by MEA after collection (baseline, '0 × PTS') and sent on a predefined PTS track (n = 12). MEA was repeated after samples travelled the track 4 ('4 × PTS'), 8 ('8 × PTS') and 12 times ('12 × PTS') and compared with stationary controls analysed at the same time. Samples for ROTEM (n = 6) were analysed after collection and travelling the track 12 times. An acceleration detector recorded g-forces on the PTS track. At '0 × PTS' no significant differences in MEA results were detected. Values were significantly lower for transported samples compared with controls ('4 × PTS' to '12 × PTS', p < 0.001). Furthermore, MEA results of PTS samples were significantly decreased for '4 × PTS' to '12 × PTS' compared to baseline (p < 0.001). Except for the clotting time in EXTEM PTS transport did not significantly alter results for investigated ROTEM parameters, compared with baseline and stationary controls. Acceleration detector readout revealed alternating g-forces between -6.3 and +5.9 during transport. PTS transport caused invalid results in MEA while only one ROTEM parameter was found to be affected in this study. Variable acceleration during transport provides a potential reason for platelet activation. The authors recommend sample transport by hand or the device to be placed patient-side when MEA is performed.

Multiple electrode whole blood aggregometry, PFA-100, and in vivo bleeding time for the point-of-care assessment of aspirin-induced platelet dysfunction in the preoperative setting

BACKGROUND

Acquired platelet dysfunction due to aspirin ingestion may increase bleeding tendency during surgery. Thus, we examined the diagnostic accuracy of in vivo bleeding time (BT) and 2 platelet function assays for the preoperative assessment of a residual antiplatelet effect in patients treated with aspirin.

METHODS

Consecutive patients scheduled for surgery were prospectively enrolled in this study. The patients' last aspirin ingestion had occurred within the previous 48 hours before blood sampling in the "full aspirin effect" group, between 48 and 96 hours before in the "variable aspirin effect" group, and >96 hours before in the "recovered aspirin effect" group. The control group had not taken any aspirin. Multiple electrode aggregometry, platelet function analyzer (PFA)-100, and in vivo BT were performed to assess the effects of aspirin. One-way analysis of variance on ranks with a post hoc multiple-comparison procedure (Dunn) was used to detect differences among the groups. Categorical data were compared using the z test. Receiver operating characteristic (ROC) curves were created to determine the diagnostic accuracy of the platelet function assays investigated. The area under the ROC curve (AUC), sensitivity, and specificity of the assays were calculated. The level of statistical significance was set at P < 0.05.

RESULTS

Three hundred ninety-four patients were included in the analysis (133 control and 261 aspirin-treated patients). All 3 methods were able to detect the antiplatelet effect of aspirin in the full aspirin effect group. Furthermore, no difference in the measurement values between the recovered aspirin effect and control group was found, irrespective of the assay performed. Measurement values in the variable aspirin effect group were different from those of the control group in the ASPItest using multiple electrode aggregometry and COL-EPI using PFA-100 but not in BT. ROC analysis showed the highest diagnostic accuracy in excluding the residual aspirin effect in the ASPItest (AUC 0.81, P < 0.001), followed by COL-EPI (AUC 0.78, P < 0.001) and BT (AUC 0.56, P = 0.05). The cutoff value of 53 U in the ASPItest excluded the effect of aspirin with a sensitivity of 88% and specificity of 71%.

CONCLUSIONS

The full therapeutic antiplatelet effects of aspirin can be expected within 48 hours of the patient's last aspirin ingestion. Platelet function recovered in our study if aspirin cessation occurred >96 hours (4 days) before; thus, in these patients, preoperative platelet function testing is not useful. To quantify any residual aspirin effect in patients who ceased their intake of aspirin between 48 and 96 hours before surgery, the ASPItest might have the highest diagnostic accuracy.

Perioperative assessment of platelet function in patients under antiplatelet therapy

Platelets play a central role in primary hemostasis. Analysis of platelet function is therefore a cornerstone in the global assessment of the coagulation status in the perioperative setting, primarily in patients receiving antiplatelet medication, such as cyclooxygenase-1 inhibitors, adenosine diphosphate antagonists and glycoprotein IIb/IIIa inhibitors. In these patients, knowledge of residual platelet function is highly warranted in order to maintain an optimal and individual balance perioperatively between platelet function and inhibition - that is, bleeding and thrombosis. Traditional laboratory-based assays, such as light-transmission aggregometry and flow cytometry, are the clinical standards of platelet function testing today. Light-transmission aggregometry is one of the most widely used tests to identify and diagnose defects in platelet function. The majority of the conventional laboratory-based techniques are labor intensive, costly and time consuming, and require a high degree of experience and expertise to perform and interpret. Therefore, new automated technologies have been developed to measure platelet function more rapidly and easily, and several techniques can be used at the bedside, including whole blood aggregometry, high shear-induced platelet function assessment or viscoelastic measurement techniques. All methods assessing platelet function are summarized and their limitations are discussed in this article, emphasizing their perioperative use.

Platelet function testing in clinical diagnostics

Although the utility of platelet function testing is still under debate, the necessity to inhibit platelets in patients suffering from cardiovascular and cerebrovascular disease is undoubted and well proven. The wide variety of available platelet function tests often using different methodologies, the apparent lack of standardization, and finally the emerging evidence on the clinical value of platelet function testing are resulting in a considerable uncertainty in the clinical practice, how to deal with the issue of platelet function testing. Platelet function testing might not only yield clinical benefits for the patients but also economical advantages by identifying the right drug at the right dose for the right patient. This article intends to provide an overview of the current platelet function tests such as light transmittance aggregometry, whole blood impedance aggregometry, the PFA-1001 system, the VerifyNow2 system, flow cytometry, as well as other promising technologies like Plateletworks3, IMPACT-R4, PADA, thromboelastography, and the mean platelet component (MPC), briefly addressing strengths, weaknesses and clinical utility of these tests.

Evaluation of platelet function and pharmacological platelet inhibition in patients with myeloproliferative disorders using multiple electrode aggregometry

BACKGROUND

The aim of this study was to describe platelet aggregation characteristics by multiple electrode aggregometry (MEA) and to evaluate MEA for its potential to detect platelet dysfunction and response to anti-aggregatory drugs in patients with myeloproliferative disorders (MPD).

METHODS

We compared the platelet response to arachidonic acid (ASPI test), adenosine diphosphate (ADP test) and thrombin receptor activating peptide (TRAP test) in hirudin-anticoagulated blood of 55 patients with polycythaemia vera and essential thrombocythaemia and 75 controls.

RESULTS

Comparing MPD patients and controls no statistically significant difference indicative of platelet dysfunction was found in MPD patients. Analysis of covariance revealed platelet- and leukocyte count as a significant influencing factor on MEA function. Furthermore we could demonstrate that ASA and clopidogrel treatment results in a statistically significant lower ASPI (Controls: p<0.0001, MPD: p<0.0001) and ADPtest value (MPD: p=0.00125) compared to untreated patients thereby validating the method for monitoring of anti-aggregatory therapy.

CONCLUSION

In this study MEA was confirmed as a valid method for monitoring of ASA and clopidogrel treatment in patients with MPD and normal control subjects. The platelet and leukocyte count were identified as major influencing factors on MEA aggregation tests both in MPD patients and controls. No functional platelet abnormalities were detected in MPD patients.

Platelet function in brown bear (Ursus arctos) compared to man

Background

Information on hemostasis and platelet function in brown bear (Ursus arctos) is of importance for understanding the physiological, protective changes during hibernation.

Objective

The study objective was to document platelet activity values in brown bears shortly after leaving the den and compare them to platelet function in healthy humans.

Methods

Blood was drawn from immobilized wild brown bears 7-10 days after leaving the den in mid April. Blood samples from healthy human adults before and after clopidogrel and acetylsalicylic acid administration served as control. We analyzed blood samples by standard blood testing and platelet aggregation was quantified after stimulation with various agonists using multiple electrode aggregometry within 3 hours of sampling.

Results

Blood samples were collected from 6 bears (3 females) between 1 and 16 years old and from 10 healthy humans. Results of adenosine diphosphate, aspirin, and thrombin receptor activating peptide tests in bears were all half or less of those in humans. Platelet and white blood cell counts did not differ between species but brown bears had more and smaller red blood cells compared with humans.

Conclusion

Using three different tests, we conclude that platelet function is lower in brown bears compared to humans. Our findings represent the first descriptive study on platelet function in brown bears and may contribute to explain how bears can endure denning without obvious thrombus building. However, the possibility that our findings reflect test-dependent and not true biological variations in platelet reactivity needs further studies.

Selective and rapid monitoring of dual platelet inhibition by aspirin and P2Y12 antagonists by using multiple electrode aggregometry

Background

Poor platelet inhibition by aspirin or clopidogrel has been associated with adverse outcomes in patients with cardiovascular diseases. A reliable and facile assay to measure platelet inhibition after treatment with aspirin and a P2Y₁₂ antagonist is lacking. Multiple electrode aggregometry (MEA), which is being increasingly used in clinical studies, is sensitive to platelet inhibition by aspirin and clopidogrel, but a critical evaluation of MEA monitoring of dual anti-platelet therapy with aspirin and P2Y₁₂ antagonists is missing.

Design and Methods

By performing in vitro and ex vivo experiments, we evaluated in healthy subjects the feasibility of using MEA to monitor platelet inhibition of P2Y₁₂ antagonists (clopidogrel in vivo, cangrelor in vitro) and aspirin (100 mg per day in vivo, and 1 mM or 5.4 mM in vitro) alone, and in combination. Statistical analyses were performed by the Mann-Whitney rank sum test, student' t-test, analysis of variance followed by the Holm-Sidak test, where appropriate.

Results

ADP-induced platelet aggregation in hirudin-anticoagulated blood was inhibited by 99.3 ± 1.4% by in vitro addition of cangrelor (100 nM; p < 0.001) and by 64 ± 35% by oral clopidogrel (600 mg) intake (p < 0.05; values are means ± SD). Pre-incubation of blood with aspirin (1 mM) or oral aspirin intake (100 mg/day for 1 week) inhibited arachidonic acid (AA)-stimulated aggregation >95% and 100 ± 3.2%, respectively (p < 0.01). Aspirin did not influence ADP-induced platelet aggregation, either in vitro or ex vivo. Oral intake of clopidogrel did not significantly reduce AA-induced aggregation, but P2Y₁₂ blockade by cangrelor (100 nM) in vitro diminished AA-stimulated aggregation by 53 ± 26% (p < 0.01). A feasibility study in healthy volunteers showed that dual anti-platelet drug intake (aspirin and clopidogrel) could be selectively monitored by MEA.

Conclusions

Selective platelet inhibition by aspirin and P2Y₁₂ antagonists alone and in combination can be rapidly measured by MEA. We suggest that dual anti-platelet therapy with these two types of anti-platelet drugs can be optimized individually by measuring platelet responsiveness to ADP and AA with MEA before and after drug intake.

[Perioperative management of patients with coronary stents in non-cardiac surgery]

In patients with coronary stents scheduled for surgery the question arises whether and how antiplatelet therapy should be continued. Risks of perioperative bleeding and of acute stent thrombosis have to be considered simultaneously. The bleeding risk depends primarily on the kind of surgery and on patient comorbidity. The risk of stent thrombosis is increased in these patients due to the thrombogenic surface of the stents. The main determinants are hereby the time duration after stent implantation, the kind of the stent [uncoated (bare-metal stent, BMS) or coated (drug-eluting stent, DES)], as well as angiographic and clinical patient factors. Therefore, perioperative antiplatelet therapy has to be individually adapted for each patient. Bridging with heparin is ineffective. Bridging with intravenous antiplatelet drugs during the perioperative interruption of oral antiplatelet therapy might be a potential procedure in high-risk patients. Whether bedside monitoring of antiplatelet therapy improves the perioperative management of these patients and reduces adverse outcome is object of current studies.