THROMBOLYSIS OF MURAL THROMBUS BY ULTRASOUND - AN EXPERIMENTAL IN-VITRO STUDY

RATIONALE AND OBJECTIVES. The authors perform an in vitro evaluation o f the thrombus fragmentation to determine the efficacy and degree of d ownstream clot fragment embolization that occurs during transcatheter ultrasound treatment of fibrin-rich mural thrombus in a peripheral ven ous flow model with variable diameter tubing. METHODS. The authors use d a 22.5-kHz prototype intravascular ultrasound device with a flexible 0.8-mm (.032-inch) titanium wire probe encased in a 7-French teflon g uide catheter, at the tip of which is a 2-mm ball. In 50 silicone tube segments (inner diameter 3, 5, 7, 9, and 11 mm; n = 10 each), firmly adherent mural thrombus was produced using bovine blood in a modificat ion of the Chandler's loop technique, Ultrasound energy (30-36 watts/c m), maximal longitudinal catheter tip amplitude 70 m) was applied to t he thrombus while a continuous flow of water was maintained in the clo sed loop system. Clot fragment emboli were trapped in ''downstream'' p olyethylene filters. RESULTS. The mean rate of thrombus removal ranged from 99% +/- 0.3% in the 3-mm segments to 76% +/- 6% in the 11-mm seg ments. The average weight of the fragments that embolized ''downstream '' and were trapped in the filters, expressed as a percentage of the i nitial clot weight, was 11% in the 3-mm segment, 14% in the 5-mm segme nt, 30% in the 7-mm segment, 29% in the 9-mm segment, and 28% in the 1 1-mm segments. The majority of the embolized fragments appear to be la rger than 1 mm. CONCLUSIONS. In this in vitro venous how model a lack of catheter steerability was the major obstacle to complete thrombus f ragmentation in vessel calibers larger than two times the tip diameter . The rate of embolism and the amount of remaining thrombus that could not be removed from the vessel were higher in the larger vessels.