Ultrasonically enforced thrombolysis: Effect of combining pharmacologic therapy and ultrasound on in vitro thrombolysis

Aim of the Study: The project is dedicated to the investigation of thrombolysis enhancement by externally applied ultrasound. Based on a set of in vitro experiments, in the first step the optimal acoustic parameters (frequency, energy density, treatment mode and duration of sonication) shall be determined. Secondly, the influence of ultrasound thrombolysis on the synergetic effect of thrombolytic, anti-thrombotic, and anti-platelet aggregation substances will be studied. Thirdly, the obtained results may serve as basis for future in vivo experiments employing thrombolysis by external ultrasound. Background: Myocardial infarction: Prognosis of patients suffering acute myocardial infarction has been improved significantly in the past 20 to 30 years. Thrombolytic therapy applied within 6 hours from the onset of pain results in a significant reduction of 30 day mortality. Early restoration of blood flow and consequently perfusion of infarct area have shown to play a key role in long term outcome after acute myocardial infarction. Optional role of ultrasound thrombolysis: Early reperfusion of the infarct-area has the major benefits of i) reducing the infarct area, ii) preserving left ventricular function, iii) reducing post-infarct complications, and iv) improving long-term survival. By increasing thrombolytic activity, ultrasound thrombolysis promises to significantly reduce the time until onset of reperfusion. Furthermore, ultrasound thrombolysis shows the potential to achieve fast reperfusion of the infarcted myocardial tissue with low procedural risk and low additional hospital costs. Therefore, application of ultrasound might significantly change the management of acute myocardial infarction. The thrombolytic effect of low frequency ultrasound is primarily based on mechanical disruption and disintegration of blood clots. In contrast, exposure to higher ultrasound frequencies is not associated with mechanical alterations but enhances enzymatic activity of thrombolytic agents. This effect is accomplished by several mechanisms of ultrasound, like cavitation, microstreaming into the thrombus, acoustic stress, and thertnal effects. Method: Blood clots will be sonicated in vitro at well-defined experimental conditions by means of an external ultrasound source. Clots will be exposed to a high frequency acoustic field while being placed into a saline solution containing a thrombolytic agent (rt-Pa). The enhancing effect of ultrasound on clot lysis will be determined by comparison to a control clot receiving the same drug dose but no ultrasound. Clot lysis will be evaluated as the percentage decrease in clot weight during the experiment. Maximum acoustic treatment time for each experimental run will be one hour. Ultrasonically enhanced thrombolysis will be investigated in vitro in a total of 354 clots in 34 groups, comparing standing and traveling sound waves of different frequencies, energy densities, field. geometries, and application modes (continuous/intermittent sonication). Furthermore, different adjunctive therapies to pharmacologie thrombolysis (Heparin, Hirudin, Abciximab) will be tested in this set-up. Experiments will be performed at defined levels of acoustic energy density, allowing for quantitative comparison of results obtained at various experimental conditions.