Thrombin kinetics determines robust plasma clot architecture.

Background: Altered fibrin clot architecture is a distinct signature in cardiovascular diseases. To determine the origin and importance of these alterations, a fundamental understanding of normal plasma clotting mechanisms is essential. While biochemical and structural aspects of fibrin formation are individually well documented, their mechanistic link lacks a quantitative description. Objectives: This study addresses two questions: How does fibrin architecture vary with tissue factor concentration ([TF]) in normal plasma, and can a simple mechanistic relationship between fibrin structure and thrombin generation be extracted? Methods: The structuring of clots formed in TF-triggered normal pooled plasma and IIa-triggered fibrinogen was compared by varying the trigger concentrations. Architecture was quantified using confocal microscopy (pore size) and fibrinography (nanostructure). Thrombin kinetics were monitored using thrombinography. Results: Although purified and plasma clots appeared morphologically identical, their ultrastructural parameters showed fundamentally different sensitivities to trigger concentrations. In purified systems, a 100-fold [IIa] increase induced a 30-fold decrease in protofibril number ( Conclusions: Our findings show that the unique functional shape of the thrombin burst, rather than the trigger concentration, governs plasma fibrin architecture. This inherent robustness supports the existence of a "normal" clot structure and the potential of fibrinography as a robust structural biomarker candidate.