Background: For a heart attack, an occlusive thrombus must resist a high arterial shear rate and blood pressure. White clots formed under high shear in arteries may have different permeability and ultimate strength compared to red clots formed in veins. We quantify the permeability and ultimate strength as critical properties for vWF versus fibrin clots.

Aims: To quantify the permeability and ultimate strength of white clots and compare these to red clots.

Methods: To create white clots, heparinized (3.5 IU/ml) porcine whole blood was perfused through two stenotic flow systems coated with type 1 fibrillar collagen having high shear >3,500 s^-1. Red clots were generated by re-calcifying a citrated porcine blood (3.2%) under stagnant conditions. The blood flow was driven by a constant pressure head or a constant flow rate by a syringe pump. The upstream pressure and mass flow rate were measured and applied to Darcy’s law to quantify the bulk permeability. The upstream blow-out pressure was used to calculate the ultimate strength of the clots.

Results: The platelet dominant white clots were significantly more permeable (Figure 2A, 0.1 to 17 µm²). The red blood cell and fibrin-rich clots had much smaller permeabilities of < 0.001 µm² (p< 0.05). The white clots demonstrated an ultimate strength of 4.6±1.3 kPa that was 7x stronger than; whereas, the red clots yielded a weaker 0.63±0.3 kPa (Figure 2B, p< 0.001).

Conclusions: White clots are 2-4 orders of magnitude more permeable than the red clots. White clots also have seven times greater ultimate strength. Both attributes allow the white clots to occlude a stenotic artery where a red clot would be too weak. The two types of clots are quite different in structure and mechanics to create thrombosis and hemostasis to stop arterial flow.

[Figure 1. A: A white clot B: Histology images. Platelets (upper right), Fibrin (bottom left), and void space (bottom right). ]

[Figure 2. A: Permeability with 2 stenotic chambers and 2 flow conditions (F: constant flow, P: constant pressure head). B: Clot ultimate strengths.]

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ISTH Congress Abstracts - https://abstracts.isth.org/abstract/white-clot-is-more-permeable-and-stronger-than-the-red-clot/