Unusual properties of platelet shape in coronary and cerebral artery disease.

Platelet shape was examined in freshly fixed whole blood, using phase contrast microscopy, from 7 patients post-myocardial infarction, 9 patients undergoing elective angiography for the investigation of angina, and 17 patients with stroke. Platelet shape was abnormal in 29/33 patients and in 20 of them the distribution of platelet shape did not resemble that produced by known platelet activators, by venipuncture techniques known to produce platelet activation, nor by shearing platelet-rich plasma. In particular, the proportion of spherical platelets is too high relative to the proportion of smooth discoid shaped platelets. Addition of platelet-poor plasma from a patient post-myocardial infarction to normal platelet-rich plasma did not reproduce the abnormality in platelet shape. In contrast, for patients post-myocardial infarction platelet shape was normal in platelet-rich plasma, but the platelets were hypersensitive to ADP-induced aggregation. Incubation of citrated whole blood at 37 degrees C resulted in an incomplete disappearance of the spherical platelets suggesting that the abnormal distribution of platelet shape consists of both a reversible and a more persistent abnormality. The reversible portion of the platelet shape abnormality seen in patients with stroke and coronary artery disease may be related to venipuncture-induced platelet activation; however, the nature of the persistent abnormality in platelet shape is presently unknown.