11,12 The severity of the tissue response and destruction is directly related to the intensity of the freezing temperature.5 For example, a minor freezing temperature (tissue temperature higher than −25°C to −30°C) causes only inflammation leaving the potential for the tissue to recover, while severe freezing will actually kill the cardiac muscle cells and results in non-reversible tissue destruction. The mechanism Inhibitors,research,lifescience,medical of action of the use of freezing temperatures is that there is direct cell necrosis and vascular stasis which occurs only

during the thawing period.11,12 The use of cryothermy as a method of treating different pathologies has been around for a long time. In 1961, Cooper and Lee developed a device that was capable of cooling liquid nitrogen that could be applied Inhibitors,research,lifescience,medical on tissue.13 In recent years, a number of devices have been developed based on the Joule–Thomson effect, which is a principle in thermodynamics that describes the change in temperature of a thermally insulated gas as it is forced through a small hole or a porous material. For each gas there is a temperature of inversion above Inhibitors,research,lifescience,medical which the change is positive and below which it is negative.14 A number of devices developed to use cryothermy are able to achieve the boiling points of the gases which is −189°C for argon

and −75°C for nitrous Inhibitors,research,lifescience,medical oxide. Heat is transferred from the tissue to the probe forming an ice ball which expands over time, and the myocytes are killed when the tissue reaches a temperature below −25°C. It takes about 2 minutes to achieve these lethal temperatures in order to create a full thickness atrial wall lesion minus a heat sink effect which can occur (in atrial tissue up to about 6–8 mm in thickness).15–17 The full Cox maze III and IV procedure using cryothermy only was performed early on using an older generation nitrous oxide base platform at Georgetown University and Hadassah University medical center.4 The use of cryothermy has evolved, and the creation of complete transmural

Inhibitors,research,lifescience,medical lesions has been confirmed CYTH4 histologically with argon cryoprobes applied endocardially and epicardially in an experimental sheep model, as compared with the nitrous oxide platform.7,12 The major advantages of cryothermy are: 1) visual confirmation of transmurality by “ice ball” formation; 2) rapid creation of focal lesion; and 3) low risk of injury to adjacent tissues. The advantage of argon-based cryothermy over nitric oxide is that it can reach temperatures of −140° to −160°C compared with −60°C for nitric oxide, allowing for a much faster and more reliable lesion and the ability to treat thicker tissue.7,11,12 Radiofrequency Energy Radiofrequency (RF) energy uses alternating current to heat tissue, creating XAV-939 purchase thermal injury that results in a line of conduction block.