Abstract: A 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.

Abstract: A cryostat (10') with a heat exchanger (13'); a valve (25') for controlling the flow of fluid through said heat exchanger (13'); and a snap disk (30') for actuating the valve (25'). In a specific embodiment, the snap disk (30') is constructed of at least two different materials (32', 34'), each having a different coefficient of thermal expansion. The snap disk (30') is mounted upon an orifice block (38') and coupled to a needle valve (25') by a connecting rod (40'). The needle valve (25') engages an orifice (16') in the orifice block (38'). The orifice (16') is in communication with the tubing (14') of a heat exchanger (13') via a channel (44') in the orifice block (38'). The geometry of the snap disk (30') is such that when the disk changes state, it snaps due to the thermal properties thereof. This ensures fast response with abrupt closure characteristics and considerable travel. In addition, the snap disk (30') allows for a simplified cryostat design with minimal weight and cost.