Platelet Deposition In Coronary Vasculature During And After Global Myocardial Ischemia
Recent evidence indicates that myocardial ischemia activates circulating platelets. Open heart surgery imposes global ischemia and platelet activation could lead to intravascular platelet deposition in ischemically injured myocardium. Platelets were labeled with111In and 51cr. The radioactive cells were injected into dogs prior to cardiopulmonary bypass. Following bypass the aorta was clamped to induce 60 min of global normothermic ischemia. The clamp was then removed to reperfuse the myocardium. Tissue biopsy 111In and 51cr activity indexed platelet content and the extent of perfusion respectively. The tissue platelet content in excess of that predicted from the tissue blood content was determined. A substantial increase in platelet content (X = 400%) was found during the reperfusion period following ischemic insult. Although platelets were sequestered in other organs the increases were moderate and unrelated to ischemia. Thus, the significant excess of platelets found in myocardium during coronary reperfusion indicates the presence of platelet thrombi. Low output failure, a complication of open heart surgery, may be the result of platelet microthrombi lodged in the small vasculature.