Laboratory assessments of therapeutic platelet inhibition in endovascular neurosurgery: comparing results of the VerifyNow P2Y12 assay to thromboelastography with platelet mapping

Population pharmacokinetic-pharmacodynamic modeling of clopidogrel for dose regimen optimization based on CYP2C19 phenotypes: A proof of concept study

Clopidogrel is an antiplatelet drug used to reduce the risk of acute coronary syndrome and stroke. It is converted by CYP2C19 to its active metabolite; therefore, poor metabolizers (PMs) of CYP2C19 exhibit diminished antiplatelet effects. Herein, we conducted a proof-of-concept study for using population pharmacokinetic-pharmacodynamic (PK-PD) modeling to recommend a personalized clopidogrel dosing regimen for individuals with varying CYP2C19 phenotypes and baseline P2Y12 reaction unit (PRU) levels. Data from a prospective phase I clinical trial involving 36 healthy male participants were used to develop the population PK-PD model predicting the concentrations of clopidogrel, clopidogrel H4, and clopidogrel carboxylic acid, and linking clopidogrel H4 concentrations to changes in PRU levels. A two-compartment model effectively described the PKs of both clopidogrel and clopidogrel carboxylic acid, and a one-compartment model of those of clopidogrel H4. The CYP2C19 phenotype was identified as a significant covariate influencing the metabolic conversion of the parent drug to its metabolites. A PD submodel of clopidogrel H4 that stimulated the fractional turnover rate of PRU levels showed the best performance. Monte Carlo simulations suggested that PMs require three to four times higher doses than extensive metabolizers to reach the target PRU level. Individuals within the top 20th percentile of baseline PRU levels were shown to require 2.5-3 times higher doses than those in the bottom 20th percentile. We successfully developed a population PK-PD model for clopidogrel considering the impact of CYP2C19 phenotypes and baseline PRU levels. Further studies are necessary to confirm actual dosing recommendations for clopidogrel.

The Effect of Antiplatelet Agents on Thromboelastography

BACKGROUND

Thomboelastography (TEG) is a point of care viscoelastic test that provides an assessment of clot formation and kinetics. Antiplatelet agents are commonly used but there is limited literature evaluating their possible effects on overall clot kinetics. We aimed to evaluate the relationship between antiplatelet agents and clot kinetics as defined by TEG.

METHODS

This is a retrospective study of adult patients who underwent TEG from February 2018 to July 2020. Patients who received anticoagulants or blood transfusions within 72 hours, had an incomplete TEG, were diagnosed with COVID-19, or had liver failure were excluded. Patients were stratified based on antiplatelet status.

RESULTS

Of 1060 patients, 119 were included (50 controls, 69 antiplatelet agents-37 aspirin monotherapy, 26 dual antiplatelet therapy). Between the control and antiplatelet therapy groups, there was no significant difference in clot time, maximal clot strength, or fibrinogen level. When compared to control patients, patients on dual antiplatelets had significantly higher fibrinogen levels (408.1 mg/dL vs 481.5 mg/dL, P = .013) but no significant differences in clot time or maximal clot strength. In our subgroup analysis, patients on dual antiplatelets had increased maximal clot strength (58.8° vs 63°, P = .005) and fibrinogen levels (384.1 mg/dL vs 481.5 mg/dL, P = .005) compared to those on aspirin alone.

DISCUSSION

Compared to control patients and those on aspirin alone, patients on dual antiplatelets have increased maximal clot strength and increased fibrinogen levels. These results can help physicians better target product resuscitation in patients who are on antiplatelet agents.

Thromboelastography in the Perioperative Period: A Literature Review

Assessing coagulation status is essential for prompt intervention to reduce morbidity and mortality related to bleeding and thrombotic complications during the perioperative period. Traditional coagulation tests such as platelet count, activated partial thromboplastin time (aPTT), prothrombin time (PT), international normalized ratio (INR), and activated clotting time (ACT) provide only static evaluation. These tests are not designed for assessment of dynamically changing coagulation conditions during the perioperative time. However, viscoelastic coagulation testing such as thromboelastography (TEG) produces a rapid numerical and graphical representation that helps to detect and direct targeted hemostatic therapy. Searching the literature through PubMed, Medline, Ovid, CINAHL, and ClinicalTrials.gov we retrieved 210 studies, which represent the use of TEG in the perioperative period. The included studies were categorized under various settings such as trauma, obstetrics, orthopedics, intensive care unit (ICU), cardiovascular, transplant, and miscellaneous scenarios. TEG showed promising results in trauma surgeries in predicting mortality, hypercoagulability, and bleeding even when it was compared to conventional methods. TEG was also useful in monitoring anticoagulant therapy in orthopedic and obstetric surgeries; however, its role in predicting thrombotic events, hypercoagulability, or complications was questionable. In ICU patients, it showed promising results, especially in the prediction or improvement of sepsis, coagulopathy, thrombotic events, ICU duration, hospital stay, and ventilator duration. TEG parameters effectively predicted hypercoagulation in transplant surgeries. Regarding cardiovascular surgeries, they were effective in the prediction of the need for blood products, coagulopathy, thrombotic events, and monitoring anticoagulation therapy. More randomized clinical trials comparing TEG parameters with standardized tools are needed to produce robust results to standardize its use in different perioperative settings.

Platelet reactivity after clopidogrel loading in patients with acute ischemic stroke

Objective

It remains unclear when sufficient antiplatelet effect is achieved after administration of a loading dose of clopidogrel in patients with acute ischemic stroke (AIS). This study aimed to evaluate the clopidogrel response in patients with AIS identified by the platelet function test (PFT).

Methods

P2Y12 reaction unit (PRU) values measured using VerifyNow at baseline and at 6, 24, and 72 h after administration of a loading dose (300 mg) of clopidogrel were compared between patients with AIS and those of other cerebrovascular diseases (CVD). The prevalence of clopidogrel abnormal response and its associated factors were examined.

Results

The PRU value was significantly reduced with time in the other CVD group (p < 0.0001), and also in the AIS group (p = 0.0073). The PRU values were significantly higher in the AIS group than in the other CVD group (p < 0.0001 between the groups, baseline: 314 ± 53 vs. 284 ± 62, p = 0.35; 6 h: 290 ± 66 vs. 214 ± 71, p = 0.016; 24 h: 270 ± 75 vs. 190 ± 70, p < 0.0001; and 72 h: 231 ± 76 vs. 163 ± 93, p = 0.105). The prevalence of clopidogrel hypo-responder (PRU > 240 at 24 h after administration) was higher in the AIS group (79 vs. 33%, p < 0.0001) and associated with the baseline PRU value but not with the cytochrome P450 2C19 genotype or clinical ischemic events.

Conclusions

Residual platelet reactivity at 24 h after clopidogrel loading was substantially higher in patients with AIS than in patients with other CVD. In addition, most patients with AIS were judged to be hypo-responders on PFT. This should be carefully interpreted in patients with AIS because of poor specificity for predicting clinical ischemic events.

Late complications of visual impairment and hydrocephalus after flow diverter-assisted coil embolisation for intracranial large aneurysm: a case report and literature review

Large or giant paraclinoid aneurysms typically have good indication for flow diverter (FD) treatment. Here, we report a very rare case of a patient with an unruptured supraclinoid large aneurysm who underwent FD deployment with coil embolisation that resulted in delayed visual field defect (VFD) and hydrocephalus. A 75-year-old woman with a large right supraclinoid aneurysm presented with severe hemianopia in the right eye. She underwent FD deployment with coil embolisation of the aneurysm. However, permanent left visual field loss occurred four months after surgery. Magnetic resonance imaging (MRI) showed severe oedema surrounding the aneurysm along the optic tract. Inflammation led to postoperative hydrocephalus, requiring ventriculoperitoneal shunt placement. To the best of our knowledge, this is the first report of both a delayed VFD and hydrocephalus following FD treatment. In cases of FD treatment with coil embolisation for large paraclinoid aneurysms, clinicians should keep in mind that postoperative visual impairment or/and hydrocephalus may occur.

Can we think of a TAT, that is a "tailored antiplatelet therapy"?

What can be seen from the case report by Verzelloni et al. has a double value, beyond the case itself. First of all, the use of platelet aggregation assessment tests, such as TEG-PM, allows clinicians to verify the exact timing between the suspension of thienopyridines and the possibility of surgery without further temporal delays and is also able to favor the evolution of ischemic problems or hemodynamic instability not easily treatable. It, therefore, allows clinicians to optimize the bleeding/thrombosis matching. Second, the use of point of care methodologies for the evaluation of platelet aggregation allows us to evaluate the adequacy of the antiaggregation, facilitating, where resistance or percentages of antiaggregation are lower than expected, modification of the therapeutic regimen.

Ticagrelor resistance: a case series and algorithm for management of non-responders

The placement of cervical and intracranial stents requires the administration of antiplatelet drugs to prevent thromboembolic complications. Ticagrelor has emerged as the most widely used alternative in clopidogrel non-responders owing to its potent antiplatelet effects. Because ticagrelor does not require hepatic activation, many neurointerventionalists choose to forgo laboratory testing of platelet inhibition. In rare instances, patients may not achieve adequate platelet inhibition following ticagrelor administration. In this paper we review the mechanism of action of ticagrelor and its use in cerebrovascular procedures. We present two cases of ticagrelor non-responsiveness from two high-volume cerebrovascular centers, discuss their management, and propose an algorithm for managing ticagrelor non-responsiveness.

Thromboelastography (TEG) results are predictive of ischemic and hemorrhagic complications in patients with unruptured intracranial aneurysms treated with flow diversion

INTRODUCTION

Flow diversion is an effective treatment modality for intracranial aneurysms but is associated with ischemic and hemorrhagic complications. Patients treated with flow diversion require dual antiplatelet therapy and subsequent platelet function tests. At our institution, Thromboelastography with Platelet Mapping (TEG-PM) is the test of choice. The primary objective of this study was to identify TEG parameters that are predictive of postoperative complications in patients treated with elective flow diversion.

METHODS

This was a retrospective study of 118 patients with unruptured intracranial aneurysms treated with flow diversion. Data was collected via chart review. Bivariate analyses were performed to identify significant variables in patients who suffered an ischemic stroke or a groin hematoma. ROC curves were constructed for the TEG parameters with statistical significance. Bivariate analyses were repeated using dichotomized TEG results.

RESULTS

Patients who experienced a symptomatic ischemic stroke had a history of stroke (p value = 0.007), larger aneurysm neck width (p value = 0.017), and a higher alpha angle (p value = 0.013). Cut off point for ischemic complication is 63° on ROC curve with a sensitivity of 100% and specificity of 65%. Patients who experienced a groin hematoma were no different from their healthy peers but had a lower alpha angle (p value = 0.033). Cut off point for hemorrhagic complication is 53.3° with a sensitivity of 82% and specificity of 67%.

CONCLUSION

The Alpha Angle parameter of TEG-PM has a sizeable predictive ability for both ischemic complications of the central nervous system and hemorrhagic complications of the access site after elective flow diversion.

Comparison of VerifyNow, thromboelastography, and PL-12 in patients with minor ischemic stroke or transient ischemic attack

High on-treatment platelet reactivity (HOPR) is associated with stroke recurrence. It is important to find a reliable method to assess HOPR. We aimed to compare the correlations between VerifyNow™ system, thromboelastography (TEG), and Aggrestar platelet function analyzer (PL-12) on platelet activity in patients with minor ischemic stroke or transient ischemic attack (TIA) after dual antiplatelet therapy for 7 days. About 276 patients were included. Spearman’s correlation coefficient and the kappa coefficient were adopted to evaluate associations among the three test methods. An obvious correlation between VerifyNow and TEG on HOPR-ADP (r=0.64, p<0.001) was found. The correlations of HOPR-ADP between PL-12 and the other two platelet function analyzers were moderate (PL-12 versus VerifyNow, r=0.47, p<0.001; PL-12 versus TEG, r=0.25, p<0.001). The correlations of HOPR-AA were limited among these three platelet function analyzers (VerifyNow versus TEG, r=0.09, p=0.14; VerifyNow versus PL-12, r=0.15, p=0.01; PL-12 versus TEG, r=0.10, p=0.09). Correlations among different platelet function analyzers were varied. VerifyNow and TEG were more correlative than PL-12 on HOPR-ADP. The consistence of HOPR-AA was limited among VerifyNow, TEG and PL-12. The proportion of stroke recurrence and composite events in patients with HOPR-ADP assessing by PL-12 was higher than VerifyNow and TEG.

Laboratory assessments of therapeutic platelet inhibition in endovascular neurosurgery: complication prediction using the VerifyNow P2Y12 assay and thromboelastography with platelet mapping

OBJECTIVE

Inhibition of platelet aggregation is universally used to prevent thromboembolic complications related to stent placement in endovascular neurosurgery, but excessive inhibition potentiates hemorrhagic complications. Previously, the authors demonstrated that two different commercially available measures of adenosine diphosphate (ADP)-dependent platelet inhibition-the VerifyNow P2Y12 clopidogrel assay (measured in platelet reactivity units [PRU]) and maximal amplitude (MA) attributable to ADP activity (MA-ADP) derived from thromboelastography (TEG) with platelet mapping (PM)-yielded wildly different results. This study sought to analyze observed complications to quantify the ideal therapeutic windows for both tests.

METHODS

Ninety-one patients with simultaneous or near-simultaneous PRU and TEG-PM results who underwent craniocervical endovascular stenting at the authors' institution between September 2015 and November 2017 were identified and retrospectively enrolled. From November 2017 until June 2019, 109 additional patients were prospectively enrolled. For this study, in-hospital thrombotic and hemorrhagic complications (both CNS and non-CNS) were tabulated, and receiver operating characteristic (ROC) curve analysis was used to identify threshold values of the PRU and MA-ADP for predicting each type of complication.

RESULTS

Of the 200 patients enrolled, 7 were excluded because of anemia or thrombocytopenia outside of the test manufacturer's specified ranges and 1 was excluded because they did not have a TEG-PM result. Including complications of all severities, there were a total of 15 CNS thrombotic complications, 1 access-site thrombotic complication, 3 CNS hemorrhages, 8 access-site hemorrhagic complications, and 3 hemorrhagic complications not affecting either the CNS or the access site. ROC curve analysis yielded therapeutic threshold values of 118-144 PRU. The results demonstrated PRU has a significant dose-dependent effect on the rates of thrombosis and hemorrhage. Logistic regression models did not demonstrate statistically significant relationships between the MA-ADP and either thrombosis or hemorrhage. ROC analysis based on these models is of little value and did not identify significant threshold values for MA-ADP.

CONCLUSIONS

There continues to be poor correlation between the results of TEG-PM and PRU. PRU accurately predicted complications, with a relatively narrow ideal value range of 118-144. The MA-ADP alone does not appear able to accurately predict either hemorrhagic or thrombotic complications in this group.

Antiplatelet effect of ticagrelor with aspirin in acute minor stroke and transient ischemic attack stratified by CYP2C19 metabolizer status: subgroup analysis of the PRINCE trial

Studies on antiplatelet effect of ticagrelor/aspirin and clopidogrel/aspirin in patients with acute minor stroke and transient ischemic attack (TIA) stratified by CYP2C19 metabolizer status is limited. We gained data from the Platelet Reactivity In Non-disabling Cerebrovascular Events study. Platelet reactivity was tested at baseline, 2 hours, 24 hours, 7 days and 90 days after initial dose, including high on-treatment platelet reactivity (HOPR), which was defined as P2Y12 reaction unit >208, and percentage inhibition of platelet aggregation (IPA). A total of 365 patients were included. There were 199 (54.5%) individuals classified as carriers of CYP2C19 loss-of-function alleles. For carriers and non-carriers, the proportions of HOPR were significantly lower in those with ticagrelor/aspirin compared with those with clopidogrel/aspirin at 2 hours, 24 hours, 7 days, respectively (all p<0.05). IPA was higher at all time points except at baseline in patients with ticagrelor/aspirin compared with those with clopidogrel/aspirin in both carriers and non-carriers of CYP2C19 lose-of-function alleles (all p<0.05). Our findings showed that ticagrelor/aspirin therapy possessed greater platelet inhibition and more rapid onset in platelet inhibition compared with clopidogrel/aspirin therapy both in carriers and non-carriers of CYP2C19 lose-of-function alleles with acute minor stroke or TIA.

Increased risk of Ventriculostomy-Associated hemorrhage in patients treated with antiplatelet agents for stent-assisted coiling of ruptured intracranial aneurysms

PURPOSE

The aim of this study is to evaluate the impact of antiplatelet agents for stent-assisted coiling, including intravenous (IV) tirofiban as an antiplatelet premedication, on rates of external ventricular drain (EVD)-related hemorrhage in acutely ruptured intracranial aneurysms. The impact of IV tirofiban in particular was also evaluated.

METHODS

Rates of radiographically identified hemorrhage associated with EVD placement were compared between patients who received an antiplatelet agent for stent-assisted coil embolization (SACE), and patients who did not receive an antiplatelet agent between June 2013 and June 2019.

RESULTS

78 patients treated for a ruptured aneurysm which required an EVD were included. A total of 46 patients who underwent stent-assisted coiling and received IV tirofiban and oral asipirin and clopidogrel (DAPT) were included in the antiplatelet group, while 32 who underwent single coiling and received no antiplatelet therapy were included in the control group. Overall, EVD-related hemorrhage occurred in 13 patients (16.67%): 11 (23.91%) in the antiplatelet group and 2 (6.25%) in the control group (p = 0.040). Of 37 patients who underwent computed tomography after SACE, but before the use of DAPT, 8 (21.62%) exhibited EVD-related hemorrhage after IV tirofiban therapy (p = 0.070 vs. control group). EVD-related hemorrhage was not significantly different between patients with EVD placement after coil embolization versus before coil embolization (p = 0.124). In the subgroup analysis for the antiplatelet group, we did not observed increased EVD-related hemorrhage in patients receiving EVD placement after administration of antiplatelet agents (8/27 [29.63%]) versus before administration of antiplatelet agents (3/19 [15.79%]).

CONCLUSION

Patients with ruptured aneurysm who receive an antiplatelet agent for stent-assisted coiling are at a higher risk for EVD-related hemorrhage. The order of EVD placement and EVT, as well as the order of EVD placement and antiplatelet initiation do not appear to be significantly different regarding the outcome of EVD-related hemorrhage.HighlightsPatients with ruptured aneurysm who receive an antiplatelet agent for stent-assisted coiling are at a higher risk for EVD-related hemorrhage.There was a trend towards higher EVD related haemorrhage when tirofiban was used but it did not reach statisitical significance.The order of EVD-whether before vs after endovascular treatment, or before vs after antiplatelet therapy did not influence the EVD-related hemorrhage rates.

A 70-Year-Old Female with Unexpected Platelet Function Testing Results

A 70-year-old female with a history of hypertension and left A2 segment aneurysm was scheduled for pipeline embolization device (PED) placement. Preinterventional antiplatelet prophylaxis included aspirin and ticagrelor. Unexpectedly, after 13 days of treatment, VerifyNow showed a P2Y12 reaction unit (PRU) value of 216, approximately >5 times the mean PRU of other patients on aspirin and ticagrelor. We confirmed platelet reactivity and ticagrelor resistance with light transmission aggregometry. Antiplatelet therapy was switched to prasugrel, and aspirin was continued. Eight days later, the P2Y12 reaction value (PRU) was 164. PED was placed without complications. Unlike clopidogrel, ticagrelor is a direct P2Y12 inhibitor that does not require metabolism to an active metabolite. Ticagrelor resistance is very rarely reported. To the best of our knowledge, there has been no case of ticagrelor resistance reported in the context of pre-PED placement prophylaxis.

The Effect of Ticagrelor on Platelet Reactivity in Patients with Clopidogrel Resistance Undergoing Neuroendovascular Procedures

BACKGROUND AND PURPOSE

Suboptimal platelet inhibition by clopidogrel (clopidogrel resistance) may be associated with high rates of stent thrombosis and ischemic events. Our objective was to determine if ticagrelor, a P2Y₁₂ receptor inhibitor, can result in platelet inhibition in patients with clopidogrel resistance.

METHODS

A thromboelastography-platelet mapping assay was used in all patients undergoing neuroendovascular procedures requiring oral clopidogrel. In patients with suboptimal platelet inhibition (<60%) on clopidogrel, ticagrelor was imitated after an oral bolus of 180 mg followed by 90 mg twice daily and the platelet mapping assay was repeated. The primary endpoint was hemorrhagic complications classified as major (hemoglobin decrease >5 g/dL or intracranial hemorrhage with deficits), minor (hemoglobin decrease 3-5 g/dL or intracranial hemorrhage without residual deficits), or insignificant.

RESULTS

Suboptimal platelet inhibition on clopidogrel was seen in 70 of 106 patients undergoing neuroendovascular procedures. There was a significantly higher magnitude of platelet inhibition with ticagrelor compared with clopidogrel in patients with clopidogrel resistance (mean ± SD: 85.90 ± 10.74% vs. 29.26 ± 17.71%; P < .001); 50 of 70 patients showed optimal inhibition. Two patients had major (fatal) hemorrhagic events (both received either intravenous thrombolytics and/or eptifibatide infusion). Three patients had minor hemorrhagic events, and two patients had insignificant hemorrhagic events. Four of seven hemorrhagic events occurred in patients with optimal response to clopidogrel, two occurred in patients with suboptimal response to ticagrelor, and one occurred in a patient with optimal response to ticagrelor.

CONCLUSIONS

Oral ticagrelor can augment platelet inhibition in patients who have clopidogrel resistance.

Sensitivity of Viscoelastic Tests to Platelet Function

Viscoelastic tests provide a dynamic assessment of coagulation, by exploring the time to clot formation and the clot strength. Using specific activators or inhibitors, additional factors can be explored, like the fibrinogen contribution to clot strength. Since the early days, various attempts have been done to measure platelet function with viscoelastic test. In general, the difference between the maximum clot strength and the fibrinogen contribution is considered an index of platelet contribution. However, this parameter does not clearly split platelet count from function; additionally, the extensive thrombin generation of standard activated viscoelastic tests activates platelet through the protease activated receptors, bypassing the other pathways. For this reason, standard viscoelastic tests cannot be used to assess platelet reactivity under the effects of aspirin or P2Y12 inhibitors. To overcome this limitation, a specific test was developed (thromboelastography platelet mapping). This test has been compared with the gold standard of light transmission aggregometry and with other point-of-care tests, with conflicting results. In general, the use of viscoelastic tests to assess the effects of antiplatelet agents is still limited. Conversely, platelet contribution to clot strength in the setting of coagulopathic bleeding is considered an important parameter to trigger platelet transfusion or desmopressin.

Antiplatelet Therapy in Flow Diversion

Dual antiplatelet therapy is typically employed as a means to mitigate thromboembolic complications after deployment of flow diverters, most commonly consisting of aspirin with either clopidogrel, prasugrel, or ticagrelor. Recent studies have demonstrated at least similar efficacy for ticagrelor as compared to clopidogrel in the form of periprocedural complications and angiographic results. Though controversial, systematic reviews of platelet function assay usage have demonstrated greater rates of thrombotic complications in antiplatelet hyporesponders and greater rates of hemorrhagic complications in hyperresponders. Though in its infancy, the management of antiplatelet therapy for acutely ruptured aneurysms treated with flow diversion is not yet standardized, with approaches including intravenous glycoprotein IIb-IIIa inhibitors and subsequent antiplatelet loading vs antiplatelet loading, response assessment, and subsequent treatment.