Device and method for improved safety and efficacy for cryoablation

A method of ablating tissue, the method comprising:

• positioning a treatment element coupled to the distal end of a medical device proximate an area of target tissue;
• and
• operating a control unit in accordance with a duty cycle, the control unit being in communication with the treatment element, the duty cycle including at least one freeze-warm cycle, each freeze-warm cycle including:
• supplying coolant to the treatment element at a first flow rate, the first flow rate causing the treatment element to reach a first temperature, the first temperature causing ablation of the target tissue and causing cryoadhesion between the treatment element and target tissue;
• and
• supplying coolant to the treatment element at a second flow rate, the second flow rate causing the treatment element to reach a second temperature, the second temperature being higher than the first temperature and the second flow rate being lower than the first flow rate, the second temperature being above a temperature at which ablation occurs and below a temperature at which cryoadhesion is broken.

A system for ablating tissue, the system comprising:

• a medical device including a distal portion defining a treatment element;
• a fluid supply in communication with the treatment element, the fluid supply continuously delivering fluid to the treatment element when the treatment element is activated;
• and
• a control unit having a processor, the processor operating to control the flow of fluid according to a duty cycle, the duty cycle including:
• a freezing cycle over a first time interval during which the fluid flow rate is increased to lower the temperature of the treatment element to a first ablation temperature;
• a warming cycle over a second time interval during which the fluid flow rate is decreased to raise the temperature of the treatment element to a first maintenance temperature, the first maintenance temperature being higher than the first ablation temperature;
• a freezing cycle over a third time interval during which the fluid flow rate is increased to lower the temperature of the treatment element to a second ablation temperature, the second ablation temperature being higher than the first ablation temperature but lower than the first maintenance temperature;
• and
• a freezing cycle over a fourth time interval during which the fluid flow rate is decreased to raise the temperature of the treatment element to a second maintenance temperature, the second maintenance temperature being higher than the first ablation temperature but lower than the first maintenance temperature.