Ultrasound Has Synergistic Effects in Vitro with Tirofiban and Heparin for Thrombus Dissolution

Abstract

Previous studies have shown synergism between ultrasound and thrombolytic agents or microbubbles on blood clot dissolution. It has not been investigated whether heparin or glycoprotein IIb/IIIa blockers enhance clot lysis by ultrasound. We compared the blood clot dissolution effect of saline, heparin, tissue plasminogen activator (tPA), tirofiban, and an echocardiographic contrast media (Optison) without and with ultrasound application. Human blood clots from four donors, 2 to 4 hours old, were cut into 200- to 400-mg sections, weighed, and immersed for 2 minutes in 1 L of normal saline 0.9% solution containing either heparin 1000 U, tirofiban 150 μg, tPA 20 mg, Optison 0.5 mL, or normal saline alone. Clots were randomized to 2 minutes ultrasound application or immersion alone without ultrasound. Ultrasound was applied with a 19.5 KHz catheter. After treatment, the clots were weighed, and the absolute and percent difference in weight was calculated. Immersion in heparin, tirofiban, and tPA without ultrasound did not augment clot disruption relative to normal saline alone. Immersion in Optison ( p=0.07) tended to result in less lysis than saline alone. Ultrasound enhanced clot dissolution compared to immersion alone with: saline (48.1±15.3% vs. 26.0±13.8%, p<0.0000002); heparin (60.8±17.5% vs. 30.8±15.1%, p=0.000001); tirofiban (61.8±13.6% vs. 30.1±12.2%, p<0.0000001); tPA (53.1±15.3% vs. 30.2±11.5%, p<0.000002); and Optison (47.8±16.0% vs. 18.4±11.5%, p<0.0000001). The combination of tirofiban with ultrasound, as well as heparin with ultrasound, was associated with a significant augmentation of clot dissolution compared with the saline plus ultrasound group ( p=0.002, 0.013, respectively). Ultrasound with tPA or with Optison had no significant augmentation of clot dissolution over the ultrasound+saline effect. This in vitro study of catheter-delivered high-intensity low-frequency ultrasound demonstrates that: (1) tirofiban and heparin, as well as perfluorocarbon microbubbles, augment clot dissolution by ultrasound; (2) augmentation of clot dissolution is evident even after only brief exposure of ultrasound and the drug studied.