Ultrastructure of platelets before and during atrial stimulation. Differences in the coronary sinus and aortic blood in patients with angina pectoris.

We studied 15 patients with strain-induced angina pectoris performing an ultrastructural analysis of platelets withdrawn simultaneously from the aorta and coronary sinus. In coronary sinus blood, all platelets exhibited shape changes with pseudopod formation but without degranulation. In the aortic blood we observed on average fewer shape changes of the platelets. During tachycardia stress, shape change formation did not increase in most patients. In three patients however, micro-aggregation of the platelets was observed only in the aortic blood. These patients had a paucity of risk factors. They also had fewer critical coronary artery stenoses compared with the other patients. We conclude that there may be minority among the patients with angina pectoris exhibiting hyper-aggregation of the platelets.