Refrigeration source for a cryoablation catheter

Abstract

An apparatus and method for automatic operation of a refrigeration system to provide refrigeration power to a catheter for tissue ablation or mapping. The primary refrigeration system can be open loop or closed loop, and a precool loop will typically be closed loop. Equipment and procedures are disclosed for bringing the system to the desired operational state, for controlling the operation by controlling refrigerant flow rate, for performing safety checks, and for achieving safe shutdown. The catheter-based system for performing a cryoablation procedure uses a precooler to lower the temperature of a fluid refrigerant to a sub-cool temperature (−40° C.) at a working pressure (400 psi). The sub-cooled fluid is then introduced into a supply line of the catheter. Upon outflow of the primary fluid from the supply line, and into a tip section of the catheter, the fluid refrigerant boils at an outflow pressure of approximately one atmosphere, at a temperature of about −88° C. In operation, the working pressure is computer controlled to obtain an appropriate outflow pressure for the coldest possible temperature in the tip section.

Description

[0001] This application is continuation of application Ser. No. 10 / 243,997, which is currently pending and which is a continuation-in-part of application Ser. No. 09 / 635,108 filed Aug. 9, 2000, now U.S. Pat. No. 6,471,694. The contents of application Ser. Nos. 10 / 243,997 and 09 / 635,108 are incorporated herein by reference.FIELD OF THE INVENTION [0002] The present invention pertains generally to systems and methods for implementing cryoablation procedures. More particularly, the present invention pertains to systems and methods that precool a primary fluid to a sub-cooled, fully saturated liquid state, for use in a cryoablation procedure. The present invention is particularly, but not exclusively, useful as a system and method for cooling the distal tip of a cryoablation catheter during cardiac cryoablation therapy to cure heart arrhythmias. The present invention also relates to the field of methods and apparatus used to generate and control the delivery of cryosurgical refrigeration...

AI Technical Summary

Benefits of technology

[0010] In a cryosurgical system, contaminants such as oil, moisture, and other impurities are often deposited in the impedance tubing or other restriction through which the refrigerant is pumped. In the impedance tubing, the temperature is very low, and the flow diameter is very small. Deposit of these impurities can significantly restrict the flow of the cooling medium, thereby significantly reducing the cooling power.

[0011] A cryosurgical catheter used in a cardiac tissue ablation process should be able to achieve and maintain a low, stable, temperature. Stability is even more preferable in a catheter used in a cardiac signal mapping process. When the working pressure in a cryosurgery system is fixed, the flow rate can vary significantly when contaminants are present, thereby varying the temperature to which the probe and its surrounding tissue can be cooled. For a given cryosurgery system, there is an optimum flow rate at which the lowest temperature can be achieved, with the highest possible cooling power. Therefore, maintaining the refrigerant flow rate at substantially this optimum level is beneficial.

[0012] In either the ablation process or the mapping process, it may be beneficial to monitor the flow rates, pressures, and temperatures, to achieve and maintain the optimum flow rate. Further, these parameters can be used to more safely control the operation of the system.

[0016] The present invention provides methods and apparatus for controlling the operation of a cryosurical catheter refrigeration system by monitoring pressures, temperature, and / or flow rate, in order to automatically maintain a stable refrigerant flow rate at or near an optimum level for the performance of crysurgical tissue ablation or mapping. Different refrigerant flow rates can be selected as desired for ablation or mapping. Flow rate, pressures, and temperature can be used for automatic shut down control. Refrigerant sources which provide separate high side and low side pressure controls add to the performance of the system. Continuous displays of temperature, high side refrigerant pressure, low side refrigerant pressure, and refrigerant flow rate are provided to the operator on a single display, to enhance system efficiency and safety.

Problems solved by technology

Radiofrequency energy, however, is not amenable to safely producing circumferential lesions without the potential for serious complications.

Specifically, while ablating the myocardial cells, heating energy also alters the extracellular matrix proteins, causing the matrix to collapse.

Moreover, radiofrequency energy is known to damage the lining of the heart, which may account for thromboembolic complications, including stroke.

Temperature alone, however, is not the goal.

This notion, however, has it limits.

This increased flow rate, however, creates additional increases in the return pressure that will result in a detrimental increase in temperature.

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