a system that breaks calcium in a liquid includes a catheter including first and second electrodes arranged to receive there - across a high electrical voltage at an initial low current . the high electrical voltage causes an electrical arc to form across the electrodes creating a gas bubble within the liquid , a high current to flow through the electrodes , and a mechanical shock wave . a power source provides the electrodes with the high electrical voltage at the initial current and terminates the high electrical voltage in response to the high current flow through the electrodes .