PERICARDIAL BLOOD ACTIVATES THE EXTRINSIC COAGULATION PATHWAY DURING CLINICAL CARDIOPULMONARY BYPASS

Background Coagulation during cardiopulmonary bypass (CPB) traditional ly has been attributed to activation of the contact system of plasma p roteins and the intrinsic coagulation pathway by blood contact with ne gatively charged surfaces not lined by endothelium. Recent studies hav e focused on the possible role of the extrinsic coagulation pathway du ring cardiac surgery. We postulated that the wound activates the extri nsic coagulation pathway during CPB by producing procoagulant cells an d enzymes that enter the general circulation. Methods and Results Bloo d samples taken from 20 consenting patients who had elective cardiac s urgery were assayed for peripheral blood mononuclear cell tissue facto r (TF) expression, plasma F1.2, and factor VII and VIIa concentrations . Peripheral blood mononuclear cell TF expression increased in the per fusate after the surgical incision and after CPB was started and in mo nocytes that adhered to the perfusion circuit. TF on circulating monoc ytes, however, did not continue to rise during CPB. Peripheral blood m ononuclear cell TF was elevated in cells isolated directly from blood in the pericardial cavity and was twice that detected in simultaneous samples from the perfusate (P<.05). F1.2 levels were highest in perica rdial blood and increased progressively during CPB. Plasma factor VIIa concentrations, corrected for hemodilution, and ratios of factor VIIa to factor VII were highest in pericardial samples (P<.05) and increas ed progressively during and immediately after CPB. Pericardial biopsie s obtained before and after CPB in 7 patients did not show TF expressi on by mesothelial cells. Conclusions These data provide direct evidenc e of TF expression, activation of the extrinsic coagulation pathway, a nd thrombin formation in the surgical wound. Addition of pericardial b lood to the perfusate and expression of TF by both circulating and adh erent monocytes strongly promote thrombus formation during open heart surgery.