Platelet counts and aggregates in coronary artery disèase

Platelet counts and aggregates have been measured in arterial, coronary sinus and peripheral venous blood in groups of patients with and without coronary artery disease, and under various conditions associated with myocardial ischaemia. No changes in platelet counts were observed. An increase in platelet aggregates across the coronary vascular bed was observed during spontaneous or ergometrine-induced ischaemia, but not with pacing-induced angina nor at the onset of coronary occlusion causing infarction. Platelet aggregates were high in systemic blood samples from patients with frequent episodes of spontaneous angina but not in samples from patients with stable effort angina, nor were they increased with exercise-induced angina or after myocardial infarction. The findings suggest that platelet aggregates are found in coronary sinus blood when there is very severe proximal narrowing (but not complete occlusion) of a coronary artery sufficient to cause cardiac pain at rest, but not when proximal constriction is less severe and the ischaemia is pacing-induced. Increased platelet aggregates in systemic blood samples may be a marker of recent episodes of rest pain.