Thrombolysis of mural thrombus by ultrasound: an experimental in vitro study

The authors perform an in vitro evaluation of the thrombus fragmentation to determine the efficacy and degree of downstream clot fragment embolization that occurs during transcatheter ultrasound treatment of fibrin-rich mural thrombus in a peripheral venous flow model with variable diameter tubing.

The authors used 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 guide 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 modification of the Chandler's loop technique. Ultrasound energy (30-36 watts/cm), maximal longitudinal catheter tip amplitude 70 m) was applied to the thrombus while a continuous flow of water was maintained in the closed loop system. Clot fragment emboli were trapped in "downstream" polyethylene filters.

The mean rate of thrombus removal ranged from 99% +/- 0.3% in the 3-mm segments to 76% +/- 6% in the 11-mm segments. The average weight of the fragments that embolized "downstream" and were trapped in the filters, expressed as a percentage of the initial clot weight, was 11% in the 3-mm segment, 14% in the 5-mm segment, 30% in the 7-mm segment, 29% in the 9-mm segment, and 28% in the 11-mm segments. The majority of the embolized fragments appear to be larger than 1 mm.

In this in vitro venous flow model a lack of catheter steerability was the major obstacle to complete thrombus fragmentation 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.