Catheter cryoablation: biology and clinical uses.

C ryotherapy, or the use of freezing temperatures to elicit a specific tissue response, has a long history of safe and effective use in medicine. Cryothermal ablation results in discrete homogenous lesions that are sharply demarcated, with preserved ultrastructural tissue integrity and low propensity for thrombosis. Its unique safety profile is well established. Although cryoenergy has been used in modern surgical procedures for more than 50 years, the development of steer-able percutaneous cryocatheters represents a more recent landmark in the history of clinical cardiac electrophysiology. This review examines the current state of knowledge regarding cryothermal catheter ablation. Pertinent features related to biophysics and biomechanics of cryothermal tissue injury are summarized, potential advantages compared with standard radiofrequency (RF) catheter ablation (RFCA) are discussed, and the contemporary clinical experience with transcatheter cryoablation is reviewed. Practical aspects relevant to clinical electrophysiologists are emphasized throughout. The concept of cooling to treat medical disorders dates back to the ancient Egyptians, where the use of hypothermic therapy was described in ≈1600 to 3000 BCE. 1 More recently, iced saline was used in the mid-1800s for the treatment of carcino-mas of the breast and uterine cervix, followed by the topical use of liquid oxygen, nitrogen, and hydrogen for superficial carcinomas in the early 1900s. Preceded by a near half-decade of experimentation, the modern era of cryosurgery was initiated by Cooper and Lee 4 in 1961 when vacuum-insulated cryosurgical probes cooled by liquid nitrogen (−196 o C) were introduced. Novel cryoprobes were subsequently developed using thermoelectric cooling (Peltier effect) or cooling by the Joule–Thomson effect (ie, from the expansion of a highly compressed nonideal gas into a region of low pressure). Whereas the thermoelectric method (cooling by the passage of a direct current through dissimilar metal junctions) offered limited thermal efficiency, the Joule–Thomson effect was relatively efficacious. Thus, the inclusion of pressurized gases as refrig-erants (nitrous oxide, carbon dioxide, and argon) spurred the development of diverse instruments (thin needle-like probes, clamp devices, catheter probes, and balloon structures), which in turn expanded the indications of cryoenergy for the treatment of a wide spectrum of diseases including dermatologic, In the 1970s, rigid hand-held cryothermal ablation probes were adapted for cardiac surgical applications. 5–8 Although insights gained from the extensive cryosurgical experience invaluably contributed to the conceptualization of the modern transvenous catheter cryoablation system, significant engineering advances were required to achieve the safe and effective delivery of pressurized cryorefrigerant to the …