Original contribution
Pro- and antifibrinolytic effects of ultrasound on streptokinase-induced thrombolysis

https://doi.org/10.1016/0301-5629(95)00014-IGet rights and content

Abstract

We have earlier documented that ultrasound can enhance the fibrinolytic effect of streptokinase and shorten the reperfusion time under experimental conditions. The present study concerns the magnitude of the effect in relation to ultrasound frequency, intensity and exposure time. The effect of ultrasound on the structural properties of the fibrin network was evaluated by scanning electron microscopy. Whole blood clots were created and exposed to streptokinase (5000 U/mL). In paired experiments, one clot was also exposed to pulsed ultrasound. Lysis is expressed as the percentage decrease in clot weight. Clot lysis was equally affected by ultrasound in the range of 0.5 to 2.3 MHz. Below 0.5 W/cm2 no enhancing effect was observed, while intensities between 0.5 and 1.5 W/cm2 resulted in a singnificant enhancement of clot lysis. Intensities above 4 W/cm2 inhibited the fibrinolytic effect of streptokinase but not of rt-PA. From scanning electron microscopy there was no evidence that ultrasound disrupted the clot surface or damaged the fibrin structure.

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    In all instances the platelet aggregation rate did not reach the initial values during the period of observation. Numerous articles report that high-frequency US enhances the action of thrombolytic agent in vitro (Lauer et al. 1992; Francis et al. 1992; Blinc et al. 1993; Olsson et al. 1994; Francis et al. 1995; Nilsson et al 1995; Härdig 2005; Härdig et al. 2006a, 2006b) and in vivo (Kudo 1989; Tachibana 1992; Luo et al. 1993; Härdig 2005). On the other hand, the frequencies in the mid-kilohertz range may offer advantages over higher frequencies, especially for pulse-modulated US, leading to acceleration of enzymatic fibrinolysis, reducing over-heating effects and improving tissue penetration (Suchkova et al. 1998, 2002b).

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