The role of platelets in acute vascular events.

Platelets are postulated to have an important role in acute and chronic cardiovascular events. Clinical events may result during the sequence of platelet activation reactions of adhesion, aggregate formation, release of granular constituents, thromboxane A2 formation, microembolization and platelet vascular occlusion. For example, sudden death may occur in patients with increased platelet sensitivity to catecholamine stimulation, platelet aggregate formation and thromboxane A2 generation resulting in ischemic ventricular arrhythmia induced by small-vessel platelet microembolization and local thromboxane A2 vasoconstriction. Whereas angina might be manifest if the microemboli disaggregated and vasospasm were transient, myocardial infarction would follow extensive permanent occlusion of small vessels or localized narrowing by vasospasm and extension of platelet thrombus formation at the site of intimal thickening. Platelets may also have an important role in atherogenesis through the mediation of the platelet-derived growth factor in the proliferative smooth muscle cell intimal lesion. Direct experimental and indirect clinical studies support the concept that platelets are important in cardiovascular events, but the relationship to spasm and to other possibly even more important mechanisms is not clear. Acute myocardial infarction and mural thrombogenesis appear to have the greatest evidence of being platelet-related.