THE FEASIBILITY OF USING FOCUSED ULTRASOUND FOR TRANSMYOCARDIAL REVASCULARIZATION

Transmyocardial laser revascularization (TMR) is used for improving th e blood supply to damaged myocardium due to advanced heart disease, We hypothesize that focused ultrasound can be used to generate channels through the cardiac muscle by vaporizing the tissue at the focal spot. The purpose of this study was to evaluate the effects of varying the ultrasound exposure parameters (frequency, amplitude, pulse period, du ty cycle, focal depth and exposure time) on the vaporized tissue size and to determine the feasibility of using ultrasound for creating cavi ties and/or channels in the left ventricular wall for transmyocardial revascularization, Based on ill vitro experiments using bovine myocard ium, the experiments indicate that a 1 mm diameter channel could be cr eated by using, for example, a focused transducer with a diameter of 1 0 cm and a radius of curvature of 8 cm operating at a frequency of 2.5 2 MHz. The required spatial peak intensity during the 0.5-s sonication s was found to be 2300 W/cm(2) with a pulse repetition period of 40 ms and a 50% duty cycle. These parameters have been used to create cavit ies during in vivo tests using canine myocardium. The results demonstr ated that ultrasound could be used to create small channels through my ocardium. The most important potential for ultrasound is its ability t o generate these channels completely noninvasively, (C) 1998 World Fed eration for Ultrasound in Medicine & Biology.