Unstable angina pectoris. Platelet behavior and prognosis in progressive angina and intermediate coronary syndrome.

Platelet behavior was compared in two groups of patients with unstable angina: 13 patients with rest pain and ST depression on the electrocardiogram (the intermediate coronary syndrome), 14 patients with progressive angina without rest pain, and 20 healthy controls. Both patient groups had hyperaggregating platelets when compared with the controls (p less than 0.01). Platelet aggregation was measured ex vivo in the presence of arachidonic acid. Serum thromboxane B2, plasma beta-thromboglobulin, and platelet factor 4 were all temporarily increased in the group with intermediate coronary syndrome (p less than 0.01), whereas measurements in patients with progressive angina were not significantly different from the controls. Thus, patients with the intermediate coronary syndrome, who have a high frequency of suboccluding coronary artery thrombus and a very serious prognosis, had severely altered platelet behavior in contrast to patients with progressive angina.