Shock-Wave Thrombus Ablation, a New Method for Noninvasive Mechanical Thrombolysis Uri Rosenschein, MD, Steven J. Yakubov, MD, Dejan Guberinich, BSB, David S. Bach, MD, Paul L. Sonda, MD, Gerald D. Abrams, MD, and Eric J. Topol, MD Successful experimental and clinical experience with thrombus ablation has been attained with high-power acoustic energy delivered in a cathe- ter. The goal of this study was to investigate the feasibility of noninvasive thrombus ablation by fo- cused high-power acoustic energy. The source for high-power acoustic energy was a shock-wave generator in a water tank equipped with an acouss- tic lens with a fixed focal point at 22.5 cm. Throm- bus was prepared in vitro, weighed (0.24 f 0.08 g), and inserted in excised human femoral artery segments. The arterial segments were ligated, po- sitioned at the focal point and then randomized into either test (n = 8) or control (n = 7). An x-ray system verified the $-dimensional positioning of the arterial segment at the focal point. A 5 MHz ultrasound imaging system continuously visual- ized the arterial segment at the focal point before, during and after each experiment. The test seg- ments were exposed to shock waves (1,000 shocks/24 kv). The arterial segment content was then flushed and the residual thrombus weighed. The arterial segment and thrombus were fixed and submitted to histologic examination. The test group achieved a significant ablation of throm- bus mass (0.25 f 0.15 vs 0.07 f 0.003 g; p = 0.0001) after application of shock waves. Arterial segments showed no gross or microscopic dam- age. Ultrasound imaging revealed a localized (1.9 f 0.5 cm*), transient (744 f 733 ms), cavitation field at the focal point at the time of application of focused shock waves. Thus, focused high-power acoustic energy can effect noninvasive thrombus ablation without apparent damage to the arterial wall. The mechanism underlying shock-wave thrombus ablation may be associated with the car itation effect. (Am J Cardiol1992;70:1356-1361) From the Departments of Urology and Pathology, Division of Cardiolo- gy, University of Michigan, Ann Arbor, Michigan, and the Department of Cardiology, The Cleveland Clinic Foundation, Cleveland, Ohio. Dr. Rosenschein’s current address is: Department of Cardiology, Tel Aviv Medical Center, Tel Aviv 64239, Israel. Manuscript received February 24,1992; revised manuscript received May 26,1992, and accepted May 21. Address for reprints: Eric J. Topol, MD, The Cleveland Clinic Foundation, Desk F25, One Clinic Center, 9500 Euclid Avenue, Cleve- land, Ohio 44195. A cute thrombosis of the coronary and peripheral arteries is the major cause of morbidity and mortality. Despite major advances in thrombo- lytic therapy for acute myocardial infarction, it still has considerable shortcomings. Approximately 30% of pa- tients with acute myocardial infarction are eligible for thrombolytic therapy, and early reperfusion rates are approximately 7O%.l Because of these limitations, more efficient and applicable therapies are being vigorously investigated. Rosenschein et aP3 have reported the de- velopment of high-power, low-frequency, ultrasound catheter for arterial recanalization. This method was in- vestigated both in experimental and clinical settings. These studies suggest that high-power, acoustic energy selectively ablates thrombi with a wide margin of safety. We hypothesized that high-power acoustic energy from an external acoustic generator can be focused and con- verged into the body to induce selective ablation of a target thrombus. The goal of this study was to test the feasibility of noninvasive acoustic thrombus ablation in a thrombotic artery model in vitro. METHODS lhrombotic artery model preparation: Human fem- oral and iliac arteries were obtained during postmortem examinations. The arterial segments were fmed in 10% neutral formalin for 24 hours, and then transferred to a saline solution and kept at 4°C for <7 days. Every 48 hours, the saline solution was changed. Fresh thrombus was prepared by filling a 3 mm diameter plastic tube with fresh, human blood mixed with thrombin (1 ml blood/20 NIH unit bovine thrombin, T4648, Sigma, St. Louis, Missouri). After 30 minutes, the thrombus was removed from the plastic tube and dissected to a length approximately one third that of each arterial segment. The thrombus was weighed (Model AB-4, Christian Becker, Germany) and inserted in the artery. The ar- tery was filled with saline solution to preclude an artifi- cial acoustic interface between air and fluid (i.e., air bubbles), and ligated at both ends. Shock-wave ablation pro&ok A shock-wave litho- tripter (HM3, Dormer Medical Systems, Marietta, Georgia) was used as a source for focused, high-power, acoustic energy. Underwater, high-current, electrical spark-gap discharges (pulse duration approximately 1 ms) generated underwater explosive vaporization of wa- ter between the spark-gap electrodes. This generated shock waves in the surrounding fluid, which propagated spherically from the site of origin. Positioning the spark- gap electrode in a symmetric, hemi-ellipsoid, metal re- flector focused the shock waves. The reflector reflects and converges the shock waves at a focal point where 90% of the energy is concentrated on a spherical area 1358 THE AMERICAN JOURNAL OF CARDIOLOGY VOLUME 70 NOVEMBER 15, 1992