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Methods and devices for delivering refrigerant to cryo catheter

IP.com Disclosure Number: IPCOM000157719D
Publication Date: 2007-Aug-31
Document File: 11 page(s) / 2M

Publishing Venue

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Abstract

Present methods of delivering refrigerant to a cryoablation catheter have two strategies available to them: deliver the liquid refrigerant at high pressure at ambient temperature, or refrigerate it first and deliver it at a lower pressure. The latter is difficult to achieve because of the need for effective counter current heat transfer within the extension hose assembly and catheter. Present methods of pressurizing the refrigerant include heating the tank to elevate its temperature and thus increase its vapor pressure. The method is efficient of energy and of refrigerant, if all the refrigerant is to be used. However, if the tank has enough refrigerant for many uses, this requires extra energy to heat the unused refrigerant as well, and then leaves the tank at an elevated temperature and pressure. The large amount of refrigerant at elevated temperature increases the level of hazard should there be a leak in the system. The present invention aims to remedy these problems. This invention isolates the proper quantity of refrigerant and then pressurizes it to a controlled pressure for delivery into the catheter system. Three methods are described: (1) use of a separate tank of gas such as air or N2, (2) use of a refrigerant gas powered hydraulic pressure amplifier, and (3) use of an electric motor for hydraulic application of pressure. Each has its advantages, but the latter is preferred.

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Present methods of delivering refrigerant to a cryoablation catheter have two strategies available to them: deliver the liquid refrigerant at high pressure at ambient temperature, or refrigerate it first and deliver it at a lower pressure. The latter is difficult to achieve because of the need for effective counter current heat transfer within the extension hose assembly and catheter.

Present methods of pressurizing the refrigerant include heating the tank to elevate its temperature and thus increase its vapor pressure. The method is efficient of energy and of refrigerant, if all the refrigerant is to be used. However, if the tank has enough refrigerant for many uses, this requires extra energy to heat the unused refrigerant as well, and then leaves the tank at an elevated temperature and pressure. The large amount of refrigerant at elevated temperature increases the level of hazard should there be a leak in the system.

The present invention aims to remedy these problems.

This invention isolates the proper quantity of refrigerant and then pressurizes it to a controlled pressure for delivery into the catheter system. Three methods are described:

(1)     use of a separate tank of gas such as air or N2, (2) use of a refrigerant gas powered hydraulic pressure amplifier, and (3) use of an electric motor for hydraulic application of pressure. Each has its advantages, but the latter is preferred.

Atrial fibrillation may be treated with RF ablation, but with some risk of stroke when done in the left side of the heart. It is also reported to be very painful if done without anesthesia. Further, over treatment may result in a fistula with the esophagus, which is very dangerous or fatal. Cryoablation is reported to be free of these problems, and thus has the potential to supplant the use of RF in the future.

Refrigeration is most effective if a phase change in the refrigerant material is exploited to extract heat. Efficiency is important if catheter shaft size is to be minimized, which eases delivery and reduces damage due to the diameter of the catheter.

Several refrigerants have been tried for cryoablation. Among these is liquid N20, C02, ether, and RI4 flurocarbon, and N2. An ideal refrigerant can attain the low temperature needed, and is minimal1y toxic to patient, operator, and to the environment. is also desirable that the temperature of the triple point be below the desired operating temperature, to avoid formation of solid refrigerant which could clog the exhaust tube. is also desirable that the pressure of the liquid refrigerant and the gaseous exhaust be at as

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pressure as possible, to avoid hazard to the patient and operator. It should also be non-flammable to avoid unnecessary hazard. Refrigerants in use for cryo include C02, N20, and N2.

For use with cryo catheters, several manufacturers have settled on N2,...