Effects induced on blood platelets in ischemic and nonischemic myocardium

The function of blood platelets sampled from the coronary sinus and the superior vena cava was studied in 50 men with coronary artery disease at rest and during pacing-induced angina. At rest, a lower platelet aggregation and retention response was found in coronary sinus compared with vena caval blood. This may be due to refractoriness after previous platelet stimulation or to release of platelet inhibitors in the coronary circulation. During pacing-induced angina, lactate levels indicated that blood was sampled from ischemic myocardium in only 27 of the patients. Pacing-induced angina influenced platelet function differently in blood from ischemic and nonischemic regions. Adenosine diphosphate- and collagen-induced aggregation, platelet retention and plasma beta-thromboglobulin levels remained unchanged in blood from ischemic myocardium during pacing, but increased in blood from nonischemic regions. Thus, factors other than ischemia activated platelets in the coronary circulation during tachycardia-induced stress.