OF NORTH AMERICA Coagulation 2006 : A Modern View of Hemostasis (original) (raw)

HOW WELL DO WE REALLY UNDERSTAND COAGULATION? In the 1960s two groups proposed a waterfall or cascade model of coagulation composed of a sequential series of steps in which activation of one clotting factor led to the activation of another, finally leading to a burst of thrombin generation [1,2]. Each clotting factor was believed to exist as a proenzyme that could be converted to an active enzyme. The original cascade models were subsequently modified to include the observation that some procoagulants were cofactors and did not possess enzymatic activity. The coagulation process is now often outlined in a Y-shaped scheme, with distinct intrinsic and extrinsic pathways initiated by factor XII (FXII) and FVIIa/tissue factor (TF), respectively, as outlined in Fig. 1. The pathways converge on a common pathway at the level of the FXa/Fva (prothrombinase) complex. The coagulation complexes are generally noted to require phospholipid and calcium for their activity. This scheme was not actu...