Patients with Coronary Artery Disease Have an Increased Incidence of Aspirin Resistance: Association of PFA-100 Closure Time with Clinical Findings.

Background: The occurrence of thrombotic events despite aspirin (ASA) therapy in patients with vascular disease has been termed ASA resistance. However, limited data are available correlating laboratory evidence of platelet function with clinical ASA resistance. The PFA-100 collagen/epinephrine (COL/EPI) cartridge can detect the ASA-induced inhibition of platelet cyclooxygenase 1 in a high shear flow environment that mimics in vivo arterial conditions.

Aim: To investigate whether there is an association of PFA-100 test results with clinical ASA resistance.

Methods: Peripheral blood was collected prior to angiography from 560 sequential ASA-treated patients (81 or 325 mg > 3 d). Patients receiving thienopyridines were not excluded but those receiving GPIIb-IIIa antagonists were. Patients with normal angiographic arteries ("No CAD", low probability of ASA resistance) were compared to those with angiographic CAD or a single prior CAD event and to those with multiple CAD events ("CAD" and "Repeat CAD" respectively, higher probability of ASA resistance). Citrate 3.8% anticoagulated blood was tested in the PFA-100 in duplicate using the COL/EPI test cartridge. Patients in the No CAD group were younger, more often female, and less often diabetic, hypertensive, and lipidemic than CAD or Repeat CAD patients.

Results: A short (< 142 s) closure time (CT) in at least one of the duplicate PFA-100 COL/EPI cartridges occurred more frequently in CAD and Repeat CAD patients compared to No CAD patients (p < 0.05, Table).

Conclusions: Failure of ASA to inhibit platelet function, as measured by the PFA-100, is associated with CAD, even in patients without prior history of CAD. The PFA-100, a shear-dependent system, may therefore be a useful test to assess the presence of ASA resistance. This test, unlike some tests for aspirin resistance, does not include ADP and therefore can be used in patients receiving thienopyridines (a frequent co-medication with aspirin).