Thromboembolization associated with sudden increases in flow in a coronarystent ex vivo shunt model

To observe the dynamics of thromboembolism (TE) in an animal model, a carot id-carotid arterial ex vivo shunt was developed. A coronary stent deployed in a 3.5 mm polyvinylchloride (PVC) tubing segment was used as a model devi ce in the shunt. A light-scattering microemboli detector monitored the embo lic content of the blood flowing through the shunt at 50-150 ml/min as dete rmined by a clamp-on ultrasound flow probe. The stent was found to actively develop thrombi and release emboli for 1-3 hours when the activated clotti ng time (ACT) was maintained between 125 and 150 seconds. The shunt flow ra te fluctuated considerably (from 50 to 150 ml/min) depending on the animal' s activity. When the time profile of this fluctuating flow rate was super i mposed on the time profile of embolization, it was noted that sudden increa ses in flow rate were associated with incidents of embolization. Statistica lly, sudden flow rate increases of 100% or more were accompanied by embolic events 95% of the time (p < 0.01). Based on the results of this study, it was postulated that the increased embolization may be due to the fluid forc es associated with accelerating flow. To explore this postulate, in vitro s tudies were conducted to compare the effects of pulsatile flow with steady flow on stent induced TE. Results of this study suggested a significant inc rease (100%) in both stent thrombosis and embolism during pulsatile flow co mpared with steady flow.