Lack of release of platelet factor 4 during exercise-induced myocardial ischemia

PLATELETS have long been implicated as a cause of acute myocardial ischemia,1 2 3 but absolute proof is lacking. Attempts to quantitate in vivo platelet activation during myocardial ischemia have led to the development of a number of indexes of platelet involvement, including the measurement of platelet aggregates4 and of platelet-specific proteins such as β-thromboglobulin and platelet factor 4. However, results have been inconsistent5 , 6 and controversial, and platelets may not be involved in acute myocardial ischemia. Recently, Green and his coworkers presented evidence that patients with coronary-artery disease who are undergoing exercise-stress testing have elevations in platelet factor 4,7 a heparin-neutralizing protein . . .