Variation in compressive mechanical properties between subacute and chronic venous thrombosis in a novel unilateral iliac thrombosis model.

Background: Interventional therapies to relieve chronic deep vein thrombosis (DVT) fail through inability to penetrate, cross, and remove the occlusion. Development of suitable tools requires fundamental understanding of chronic DVT mechanical properties and a reliable model for testing. Methods: Female farm swine underwent a novel, endovenous generation of long-segment unilateral iliac vein thrombosis. Thrombus was confirmed via venogram, intravascular ultrasound, and transabdominal duplex for 14 days. Thrombus components were quantified via histology. Thrombus mechanical properties were assessed via uniaxial compression. Results: Among seven swine, technical success was 100%. Compared to subacute thrombi (7-day), chronic thrombi (14-day) showed organizing thrombus with diffuse myointimal thickening and collagen matrix formation on histology. The thrombi collagen content was 41% versus 55% (p = 0.17) and the thrombus erythrocyte percentage was 4.3% versus 2.2%, p = 0.21 in 7- versus 14-day thrombi, respectively. The onset point (compression required to load the thrombus fiber network) was 66.6% versus 35.3% (p = 0.004), the secant modulus (resistance to deformation) measured at the onset point was 153.8 versus 275.99 kPa (p = 0.18), and the average shear constant (resistance to shearing), as defined by the Yeoh hyperelastic model, was 1.85 kPa versus 2.85 kPa in 7- versus 14-day thrombi. Conclusions: This study demonstrates the feasibility of an endovenous model generating chronic unilateral venous thrombi in 2 weeks with similar anatomy to humans and provides critical mechanical properties of thrombi for future research.