The feasibility of using focused ultrasound for transmyocardial revascularization.

Transmyocardial laser revascularization (TMR) is used for improving the 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, duty cycle, focal depth and exposure time) on the vaporized tissue size and to determine the feasibility of using ultrasound for creating cavities and/or channels in the left ventricular wall for transmyocardial revascularization. Based on in vitro experiments using bovine myocardium, the experiments indicate that a 1 mm diameter channel could be created by using, for example, a focused transducer with a diameter of 10 cm and a radius of curvature of 8 cm operating at a frequency of 2.52 MHz. The required spatial peak intensity during the 0.5-s sonications was found to be 2300 W/cm2 with a pulse repetition period of 40 ms and a 50% duty cycle. These parameters have been used to create cavities during in vivo tests using canine myocardium. The results demonstrated that ultrasound could be used to create small channels through myocardium. The most important potential for ultrasound is its ability to generate these channels completely noninvasively.