Platelet function testing as a biomarker for efficacy of antiplatelet drugs

Relationship between in-stent restenosis following carotid artery stenting and platelet reactivity to clopidogrel

OBJECTIVE

To analyze the relationship between in-stent restenosis (ISR) following carotid artery stenting (CAS) and platelet clopidogrel reactivity confirmed by the P2Y12 reaction unit (PRU) and inhibition rate (IR).

METHODS

We retrospectively analyzed 171 patients who underwent CAS with extracranial carotid stenosis from January 2016 to December 2019. Dual antiplatelet therapy with 100 mg aspirin and 75 mg clopidogrel was started ≥5 days before CAS. Clopidogrel resistance was measured with the PRU and IR the day before CAS. The ISR degree was classified into R1, R2, and R3 (moderate to severe luminal stenosis of ≥50% or occlusion) by carotid CT angiography after 24-30 months. The degree of quantitative association between platelet reactivity and ISR R3 was determined by the receiver operating characteristic curve method. The optimal cut-off values of PRU and IR were derived using the maximum Youden index.

RESULTS

There were 33 R3 degrees of ISR (19.3%) and nine ipsilateral ischemic strokes (5.3%). The PRU and IR were different between R1+R2 degrees (176.4±50.1, 27.5±18.7%) and R3 degree (247.5±55.0, 10.3±13.4%) (P<0.001). The areas under the curves of PRU and IR were 0.841 and 0.781, and the optimal cut-off values were 220.0 and 14.5%, respectively. Multivariate logistic regression analysis showed that PRU ≥220 and IR ≤14.5% were significant predictive factors for ISR R3 (P<0.001 and P=0.017, respectively). ISR R3 was independently associated with ipsilateral ischemic stroke after CAS (P=0.012).

CONCLUSIONS

High PRU (≥220) and low IR (≤14.5%) are related to ISR R3 following CAS, which may cause ipsilateral ischemic stroke.

Factors that modulate platelet reactivity as measured by 5 assay platforms in 3429 individuals

Background

Assessment of platelet function is key in diagnosing bleeding disorders and evaluating antiplatelet drug efficacy. However, there is a prevailing "one-size-fits-all" approach in the interpretation of measures of platelet reactivity, with arbitrary cutoffs often derived from healthy volunteer responses.

Objectives

Our aim was to compare well-used platelet reactivity assays.

Methods

Blood and platelet-rich plasma obtained from the Framingham Heart Study (N = 3429) were assayed using a range of agonists in 5 platelet assays: light transmission aggregometry, Optimul aggregometry, Multiplate impedance aggregometry (Roche Diagnostics), Total Thrombus-Formation Analysis System, and flow cytometry. Using linear mixed-effect models, we determined the contribution of preanalytical and technical factors that modulated platelet reactivity traits.

Results

A strong intra-assay correlation of platelet traits was seen in all assays, particularly Multiplate velocity (r = 0.740; ristocetin vs arachidonic acid). In contrast, only moderate interassay correlations were observed (r = 0.375; adenosine diphosphate Optimul Emax vs light transmission aggregometry large area under the curve). As expected, antiplatelet drugs strongly reduced platelet responses, with aspirin use primarily targeting arachidonic acid-induced aggregation, and explained substantial variance (β = -1.735; P = 4.59 × 10-780; variance proportion = 46.2%) and P2Y12 antagonists blocking adenosine diphosphate responses (β = -1.612; P = 6.75 × 10-27; variance proportion = 2.1%). Notably, female sex and older age were associated with enhanced platelet reactivity. Fasting status and deviations from standard venipuncture practices did not alter platelet reactivity significantly. Finally, the agonist batch, phlebotomist, and assay technician (more so for assays that require additional sample manipulation) had a moderate to large effect on measured platelet reactivity.

Conclusion

Caution must be exercised when extrapolating findings between assays, and the use of standard ranges must be medication-specific and sex-specific at a minimum. Researchers should also consider preanalytical and technical variables when designing experiments and interpreting platelet reactivity measures.

Monitoring of Antiplatelet Therapy

In the late 1990s, the antithrombotic antiplatelet agent, clopidogrel, a P2Y12 inhibitor, was introduced. Around the same time, there was an increase in a number of new methods to measure platelet function (e.g., PFA-100 in 1995), and this has continued. It became evident that not all patients responded to clopidogrel in the same way and that some patients had a relative "resistance" to therapy, termed "high on-treatment platelet reactivity." This then led to some publications to advocate platelet function testing being used for patients on antiplatelet therapy. Platelet function testing was also suggested for use in patients awaiting cardiac surgery after stopping their antiplatelet therapy as a way of balancing thrombotic risk pre-surgery and bleeding risk perioperatively. This chapter will discuss some of the commonly used platelet function tests used in these settings, particularly those that are sometimes referred to as point-of-care tests or that require minimal laboratory sample manipulation. The latest guidance and recommendations for platelet function testing will be discussed following several clinical trials looking at the usefulness of platelet function testing in these clinical settings.

Incorporation of Laboratory Test Biomarkers Into Dual Antiplatelet Therapy Score Improves Prediction of Ischemic and Bleeding Events in Post-percutaneous Coronary Intervention Patients

This study aimed to examine the performance of the dual antiplatelet therapy (DAPT) score in two retrospective cohorts of post-percutaneous coronary intervention (PCI) patients and to explore whether incorporating additional biomarkers could further improve the predictive power of the DAPT score. In a retrospective derivation cohort of 4,798 PCI patients, the validity of DAPT score for stratifying ischemic/bleeding risks was explored. Then, the association between the baseline status of 54 laboratory test biomarkers and ischemic/bleeding events was revealed while adjusting for the DAPT score. Combinations of individual laboratory test biomarkers that were significantly associated with ischemic/bleeding events were explored to identify the ones that improved discrimination of ischemic and bleeding events when incorporated into DAPT score. Finally, the impact of the combination of biomarkers with DAPT score was validated in an independent retrospective validation cohort of 1,916 PCI patients. Patients with a high DAPT score (DAPT score ≥ 2) had significantly higher risk of ischemic events and significantly lower risk of bleeding than patients with a low DAPT score (DAPT score < 2). Moreover, the addition of aspartate aminotransferase (AST) and red cell distribution width CV (RDW-CV) into the DAPT score further improved discrimination of ischemia and bleeding. Furthermore, the incremental predictive value of AST + RDW-CV maintained with measurements was updated at post-baseline time points. DAPT score successfully stratified the risks of ischemia/bleeding post PCI in the current cohorts. Incorporation of AST + RDW-CV into the DAPT score further improved prediction for both ischemic and bleeding events.

A systematic review and meta-analysis of traumatic intracranial hemorrhage in patients taking prehospital antiplatelet therapy: Is there a role for platelet transfusions?

BACKGROUND

Platelet transfusion has been utilized to reverse platelet dysfunction in patients on preinjury antiplatelets who have sustained a traumatic intracranial hemorrhage (tICH); however, there is little evidence to substantiate this practice. The objective of this study was to perform a systematic review on the impact of platelet transfusion on survival, hemorrhage progression and need for neurosurgical intervention in patients with tICH on prehospital antiplatelet medication.

METHODS

Controlled, observational and randomized, prospective and retrospective studies describing tICH, preinjury antiplatelet use, and platelet transfusion reported in PubMed, Embase, Cochrane Reviews, Cochrane Trials and Cochrane DARE databases between January 1987 and March 2019 were included. Investigations of concomitant anticoagulant use were excluded. Risk of bias was assessed using the Newcastle-Ottawa scale. We calculated pooled estimates of relative effect of platelet transfusion on the risk of death, hemorrhage progression and need for neurosurgical intervention using the methods of Dersimonian-Laird random-effects meta-analysis. Sensitivity analysis established whether study size contributed to heterogeneity. Subgroup analyses determined whether antiplatelet type, additional blood products/reversal agents, or platelet function assays impacted effect size using meta-regression.

RESULTS

Twelve of 18,609 screened references were applicable to our questions and were qualitatively and quantitatively analyzed. We found no association between platelet transfusion and the risk of death in patients with tICH taking prehospital antiplatelets (odds ratio [OR], 1.29; 95% confidence interval [CI], 0.76-2.18; p = 0.346; I = 32.5%). There was no significant reduction in hemorrhage progression (OR, 0.88; 95% CI, 0.34-2.28; p = 0.788; I = 78.1%). There was no significant reduction in the need for neurosurgical intervention (OR, 1.00; 95% CI, 0.53-1.90, p = 0.996; I = 59.1%; p = 0.032).

CONCLUSION

Current evidence does not support the use of platelet transfusion in patients with tICH on prehospital antiplatelets, highlighting the need for a prospective evaluation of this practice.

LEVEL OF EVIDENCE

Systematic Reviews and Meta-Analyses, Level III.

Novel Risk Markers and Risk Assessments for Cardiovascular Disease

The use of risk markers has transformed cardiovascular medicine, exemplified by the routine assessment of troponin, for both diagnosis and assessment of prognosis in patients with chest pain. Clinical risk factors form the basis for risk assessment of cardiovascular disease and the addition of biochemical, cellular, and imaging parameters offers further refinement. Identifying novel risk factors may allow greater risk stratification and a steady, but gradual progression toward precision medicine. Indeed, the generation of data in this area of research is explosive and when combined with new technologies and techniques provides the potential for more refined, targeted approaches to cardiovascular medicine. Although discussing the most recent developments in this field, this review article aims to strike a balance between novelty and validity by focusing on recent large sample-size studies that have been validated in a separate cohort in most cases. Risk markers related to atherosclerosis, thrombosis, inflammation, cardiac injury, and fibrosis are introduced in the context of their pathophysiology. Rapidly developing new areas, such as assessment of micro-RNA, are also explored. Subsequently the prognostic ability of these risk markers in coronary artery disease, heart failure, and atrial fibrillation is discussed in detail.