Erythrocyte deformability and white blood cell count are associated with aspirin resistance in high-risk vascular patients

Recently the phenomenon of aspirin resistance has been object of several studies, but no data are available on the possible role of the haemorheologic parameters in affecting platelet function and resistance to antiplatelet agents. Aim of our study was to evaluate platelet function and haemorheology in patients with acute coronary syndromes (ACS), receiving double antiplatelet therapy with aspirin and clopidogrel. The study population included 301 (231M/70F; age: 66 +/- 13 yrs) consecutive adult patients admitted to the Coronary Care Unit of the Azienda Ospedaliero-Universitaria Careggi, with diagnosis of acute myocardial infarction or unstable angina. We assessed: whole blood viscosity (WBV) at shear rates of 0.512 s(-1) and 94.5 s(-1), plasma viscosity (PLV) at 94.5 s(-1) shear rate, erythrocyte deformability index (DI) and PFA-100 closure times with ADP (PFA/ADP) and epinephrine (PFA/EPI). We considered any PFA-100-EPI result < 203 sec (95th percentile of control distribution) to be indicative of aspirin resistance. 104/301 patients (34.5%) had PFA/EPI CTs in the reference range (group 1) whereas the remaining had values higher than 203 sec (group 2). WBV at 94.5 sec (-1) s.r. was similar in group 1 and 2 (WBV: 4.43 +/- 0.25 vs 4.45 +/- 0.61 mPa center dot sec, respectively). PLV and WBV at 0.512 sec (-1) s.r. were slightly higher, but not significantly, in group 1 than in group 2 (PLV: 1.47 +/- 0.13 vs 1.44 +/- 0.15 mPa center dot sec; p=0.08 and WBV: 23.37 +/- 4.6 vs 22.54 +/- 3.90 mPa center dot sec; p=0.07). DI was significantly lower in group 1 with respect to group 2 (4.05 +/- 2.93 vs 5.71 +/- 3.30, p < 0.0001). White blood count (WBC) was significantly higher in group 1 than in group 2 (11464 +/- 3504 vs 7867 +/- 2162, p < 0.0001). In conclusion, these results demonstrate that in patients with acute coronary syndromes the antiaggregant effect of aspirin is modulated not only by the direct action on platelets, but also by erythrocyte deformability and white blood cell count.