Exploring the clinical utility of a novel multichannel platelet function test in patients with stable coronary disease

Inhibition of platelet reactivity is crucial in preventing ischemic events in
patients undergoing procedures like percutaneous coronary intervention (PCI) or
trans-catheter aortic valve implantation (TAVI). An optimal level of PR should
be maintained, as too low a platelet reactivity predisposes patients to
bleeding. Peri-procedural assessment of platelet reactivity can be done with
various tests. Many studies have shown that treatment adjusted for platelet
reactivity is beneficial for patients1. Several clinical, genetic, and cellular
factors are responsible for the variability in platelet reactivity, for
instance; alternative pathways of platelet activation, patients* noncompliance,
or drug*drug interactions with different gene polymorphisms which account for
15% to 20% of the variation in pharmaco-dynamic response1.

For over two decades, parallel-plate flow chambers have been used to measure
platelet adhesion and activation under arterial or venous flow conditions, in
particular using surfaces such as extracellular matrix or collagen. Currently,
this process of platelet adhesion and aggregation in flow devices is described
as flow-dependent thrombus formation, regardless of the presence or absence of
anticoagulants2. Many commercial and home-made flow devices, in particular for
the assessment of human platelet activity in preclinical settings, have been
developed to study platelet reactivity, in spite of the fact that international
recommendations stress the need for further standardization of devices,
protocols and measurement parameters. In recent years, various types of
microfluidic devices have been developed requiring only small volumes of human
blood, including devices containing endothelium, for instance to study blood
from patients with sickle cell disease3. Unfortunately, however, the great
variation in design and use of the microfluidic chips hinders the process of
standardization.

Clinically, the PFA-100 is the only device currently validated that assesses
platelet function under high-shear flow conditions. The PFA-100 is frequently
utilized to evaluate deficiencies in platelet function or von Willebrand factor
(vWF) activity, but it only provides a single end-stage parameter4. Taken
together, there are promising possibilities for clinical employment of flow
assays to test platelet adhesion and aggregation, but current methods often are
incompletely developed and insufficiently standardized.

So far, only single adhesive molecules and a single flow state could be tested.
Recently, a novel multi-microspot test has been developed to test for all major
adhesive receptors, alone and in combination, to support whole-blood thrombus
formation at specified wall shear rates5. Such an approach is able to study the
role of an entire spectrum of platelet-adhesive molecules and its combinations.
Using a systems biology approach, a model has been created to predict the role
of platelet receptors in shear dependent thrombus formation. However, such a
model has only been tested in a relatively small subset of patients with rare
bleeding disorders5. Establishing a model in stable coronary artery disease
patients would help future clinical application of this promising technique.

We therefore aim to study a set of patients with SIHD on single antiplatelet
drug, and compare platelet reactivity and surface receptor expression to a
group of healthy control subjects. As analysis is done on whole blood
immediately after blood draw, a single visit will be scheduled for included
subjects.

The main objective of the current study is to investigate platelet reactivity
and underlying mechanisms using the novel multi-microspot analysis in a group
of patients with SIHD and a healthy control group.

After careful consideration of in- and exclusion criteria, and after informed
consent has been obtained, subjects will be scheduled for a single visit for a
blood draw of 15 mL of whole blood via venipuncture. The blood will be divided
over 3 tubes, as described previously5. For analytic variation, all platelet
reactivity testing will be carried out in duplicate on the same sample of
blood. At times, pharmacological activators and inhibitors will be added to
explore underlying mechanisms contributing to reactivity. Two tubes of 5 mL
blood with be used for multiparameter assessment of thrombus formation. One
tube of 5 mL blood will be used to investigate receptor expression of key
platelet receptors by flow cytometry to further build exploratory hypotheses
for mechanistic links to platelet reactivity. After having given the single
blood sample, patients will have completed the study.

Limited burden, test subjects will have a single visit in which 15 ml of blood
is drawn