Thrombolysis accelerated by ultrasound and microbubbles

Therapeutic applications of ultrasound are currently limited to dental plaque removal, physiotherapy and lithotripsy. However, several in vitro and experimental studies have shown the ability of ultrasound to accelerate clot dissolution. This effect is mainly influenced by the intensity and frequency of the beam. High ultrasound energies, although effective, can induce early reocclusion, while moderate intensities and low ultrasound frequencies are better tolerated and equally effective. So far, few patients with acute myocardial infarction have been treated by ultrasound catheters. In patients with ischemic stroke, transcranial Doppler was monitored during the venous administration of recombinant tissue-type plasminogen activator (rt-PA) and the occluded vessel was recanalyzed earlier than in other studies by rt-PA alone (without Doppler monitoring). Ultrasound-accelerated thrombolysis is caused by a strengthening of the enzymatic action, favored by acoustic cavitation. As the microbubbles of echocontrast agents lower the cavitation threshold, they can further enhance the thrombolytic process. New generation microbubbles, able to bind to the thrombus surface, could facilitate thrombus-microbubbles interaction. The combination of ultrasound, microbubbles and fibrinolytic agents could benefit the treatment of a variety of cardiovascular diseases.