Platelet aggregability under shear is enhanced in patients with unstable angina pectoris who developed acute myocardial infarction

The study investigated whether patients hospitalized for unstable angina pe ctoris (UAP), who subsequently develop complete coronary thrombosis (acute transmural myocardial infarction (AMT)) despite medical treatment, exhibit platelet hyperaggregability in an assay system that does not employ agonist stimulation. The study comprised 89 patients with UAP (Braunwald type B). Unfractionated heparin and nitrate were administered to all patients via co ntinuous intravenous drip together with aspirin taken orally. Citrated plat elet-rich plasma (230-250 x 10(3)/mul) was obtained on admission and again, in some patients, following the AMI. Platelet aggregability was measured i n an optically modified cone-plate viscometer that enables the detection of platelet aggregation without agonist stimulation. A continuous shear late of 1,200/s was employed. Of the 89 patients, 85 were finally stabilized, wh ile 4 developed an AMI accompanied by persistent ST-segment elevation with increased levels of plasma creatine kinase within 3 h after starting the tr eatment. The extent of platelet aggregation on admission was significantly greater in these 4 patients compared with the 85 who were stabilized (87.8 +/-6.8%, n=4 vs 26.8 +/-. 9.1%, n=85; mean +/- SD). These data suggest that platelet hyperaggregability mediated mainly by fibrinogen binding to the a ctivated glycoprotein IIb/IIIa complex occurs before a complete thrombotic occlusion and this evaluation may provide important information before the onset of myocardial infarction.