Thromboembolism was studied as heparinized (3 U/ml) bovine blood was gravity fed through a conduit with a deployed coronary stent or a prototype flow cell. The initial flow rate was established with a pinch valve, and monitored with a clamp-on ultrasonic probe. Emboli production was continuously monitored using a light scattering microemboli detector. Accumulated thrombus at the end of the experiment was assessed gravimetrically in stents or by magnetic resonance imaging in flow cells. Hemodynamic parameters were varied to assess their effects on thromboembolism. With the flow cells, the hemodynamics were controlled by varying the geometry of the stagnation zones. With the stents, the flow characteristics were altered by placing 75% stenoses upstream and/or downstream of the stent. The average values of the shear stress and residence time around the stent were modeled using the commercial fluid dynamics software FLUENT. Combining the computed hemodynamic parameters with the experimental results showed that 1) thrombus accumulation decreased with increasing shear stress and increased with increasing residence time; 2) embolization was promoted by high shear, and did not correlate with the amount of thrombus accumulated at the end of the experiment; and 3) a reconfiguration of the magnetic resonance imaging system is necessary to monitor thrombus accumulation continuously.
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Sukavaneshvar et al. (1998) studied this question.