Platelet counts and aggregates in coronary artery disease

Platelet counts and aggregates have been measured in arterial,coronary sinus and peripheral venous blood in groups of patientswith and without coronary artery disease, and under variousconditions associated with myocardial ischaemia. No changesin platelet counts were observed. An increase in platelet aggregatesacross the coronary vascular bed was observed during spontaneousor ergometrine-induced ischaemia, but not with pacing-inducedangina nor at the onset of coronary occlusion causing infarction.Platelet aggregates were high in systemic blood samples frompatients with frequent episodes of spontaneous angina but notin samples from patients with stable effort angina, nor werethey increased with exercise-induced angina or after myocardialinfarction. The findings suggest that platelet aggregates arefound in coronary sinus blood when there is very severe proximalnarrowing (but not complete occlusion) of a coronary arterysufficient to cause cardiac pain at rest, but not when proximalconstriction is less severe and the ischaemia is pacing-induced.Increased platelet aggregates in systemic blood samples maybe a marker of recent episodes of rest pain.