Platelet reactivity in acute coronary syndromes: Evidence for differences in platelet behaviour between unstable angina and myocardial infarction

Previous work has shown that P-selectin and mean platelet volume, two marke rs associated with platelet reactivity, are elevated in acute coronary synd romes. This study investigated the possibility that these markers may defin e unstable angina (UA) and acute myocardial infarction (MI) as two separate conditions based on platelet behaviour. Mean platelet volume (MPV) was hig her in UA patients (n = 15) than in those diagnosed with MI (n = 15) (10.7 +/- 0.25 fL, vs. 9.8 +/- 0.27 n, P = 0.005). Platelet count was lower in UA than in MI (215 +/- 13 X 10(9)/L, vs. 271 +/- 20 x 10(9)/L, P = 0.03). The percentage of platelets ex pressing P-selectin was higher in MI than in UA (9.1 +/- 1.9% vs. 4.2 +/- 0.85%, P = 0.03). This parameter was positively correlated with MPV in UA (r = 0.5, P = 0,04) but negatively correlated in MI (r = -0.6. P = 0.01), with no correlation for ACS as a whole (r = -0.32. P = 0.1). Our results suggest that in MI there is an acute process of gene ralised platelet activation that is unrelated to changes in MPV, whereas in UA there is an ongoing process of platelet consumption that leads to an in crease in platelet size to compensate for a persistent decrease in platelet count. This study suggests that there is a fundamental difference in plate let biology between these two diseases.