[Ultrastructural differences of fibrin coagulation before and after cardiovascular arrest]

The reconstruction of killing offences often requires the differentiation between vital and postmortal blood traces at the sites of action and finding. Earlier investigations seemed to imply the possibility of such a differentiation depending on the different clot structure. We therefore examined clots prior and after 10 minutes of complete occlusion of the upper extremity morphologically and morphometrically with the REM. The morphologic comparison of these clots revealed narrow, round shaped fibrin fiber networks for clots of native blood, whereas clots after occlusion showed linear, rarely connected long fibrin fibers. The morphometry of the fibrin free spaces revealed a significant enlargement of the single fibrin free spaces as well as of the total fibrin free space after occlusion. For capillary blood a significant decrease in fiber diameter was observed after occlusion. The examination of clinical clotting parameters revealed alterations of thrombocyte aggregation for the collagen induction, a slightly reduced thrombocyte retention and slightly steeper flanks in the thromboelastogram after occlusion. The reason for these changes was interpreted as lack of high energetic phosphates in the retraction process as the clotting cascade itself requires a very high amount of these phosphates. Use of these results in the forensic practice will have to take factors as temperature, drying out, surface-structure and many others into account.