Shockwave catheter system with energy control
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.
1. A method of delivering shock waves to treat calcified lesions in the body of a patient using a delivery device including a catheter carrying a pair of electrodes near the distal end thereof, the distal end of the catheter including a balloon surrounding the electrode pair, the electrode pair being connected to a power source including a capacitor and a switch, said method comprising the steps of:
advancing the catheter through a body lumen so that the balloon is adjacent to the calcified lesion;
filling the balloon with a conductive liquid;
delivering a series of voltage pulses from the power source to the electrode pair, each voltage pulse having a voltage between 1000 volts and 10,000 volts, each voltage pulse being generated by closing the switch that causes a charge stored on the capacitor to be delivered to the electrode pair, each voltage pulse having sufficient energy to generate an arc in the liquid within the balloon and allowing current to flow across the pair of electrodes to produce a shock wave associated with the expansion of a steam bubble;
sensing the current flowing through the pair of electrodes during each voltage pulse; and
for each given voltage pulse, terminating the delivery of the electrical voltage pulse across the first and second electrodes after the sensed current reaches a predetermined value, the predetermined value being high enough to ensure the creation of the arc for each pulse, wherein the termination includes opening the switch in order to prevent the remaining charge on the capacitor from being delivered to the electrode pair thereby conserving electrode material.
2. The method of claim 1 wherein the switch is a solid state switch.
3. The method of claim 1 wherein the switch is an insulated gate bipolar transistor (IGBT).
4. The method of claim 3 wherein the IGBT is driven by a FET driver.
5. The method of claim 4 wherein the gate of the IGBT is negatively biased by the FET driver to facilitate the opening of the IGBT.
6. The method of claim 1 , wherein the step of terminating the delivery of the electrical voltage pulse across the first and second electrodes includes activating a delay timer in response to the sensing of the current reaching the predetermined value prior to the switch being opened.
7. The method of claim 1 , wherein sensing the current comprises sensing the current using a current sensor including a resistor and wherein the voltage drop across the resistor is monitored to determine the current flowing between the pair of electrodes.
8. The method of claim 1 , wherein the predetermined value is selected to ensure the creation of the shock wave associated with the expansion of a steam bubble and minimize energy available for a trailing shock wave associated with the subsequent collapse of the steam bubble.
9. The method of claim 1 wherein a dwell time between initial delivery of a given voltage pulse and creation of the arc is variable from pulse to pulse and the predetermined value is high enough to ensure the creation of the arc while compensating for the variable dwell time.