Catheter-Based Cryoplasty for Coronary and Peripheral Vascular Disease

Revascularization methods exploring brachytherapy, debulking, intimal cutting techniques and pharmacological clotting therapies have been used to treat arterial disease, but stenting is the most frequently utilized choice among these various therapies. New drug-eluting stents have produced intriguing results, capturing the attention of the medical community. Drug-eluting stents are coated with an immunosuppressant or cytotoxic drug that may reduce neointimal proliferation in response to injury, but the complexity of brachytherapy and drug-eluting stent technologies have generated new concerns, such as the potential for late thrombosis, stent malapposition, and aneurysms. These early adverse event reports are still undergoing scientific analysis to determine their relationship to the use of drug-eluting stents as well as their effect on long-term outcomes. One alternative to drug-eluting stents is a new technology called cryoplasty. Cryoplasty is a novel vascular intervention that is designed to simultaneously dilate and treat a diseased vessel by cooling it to a precise temperature range and then allowing it to return to normal body temperature. A balloon is placed at a vascular lesion. Liquid nitrous oxide is delivered, expands into gas and dilates a balloon. The balloon surface temperature rapidly decreases from 37?C > -2?C. The state change (evaporation) draws energy, cooling the site. Frozen physiologic saline expands, generating high radial, longitudinal, and circumferential forces that result in micro-fractures. These micro-fractures weaken plaque, resulting in a temporary loss of the elasticity of the intima, in a more uniform manner than the focused injury of balloon angioplasty. This allows for homogenous dilation, less dissection, less depth of medial tearing, and lower magnitude of injury, inflammation and cell proliferation. As the warming cycle ensues, taking about ten seconds, smooth muscle cells eject the fluid. Results of cell culture tests demonstrate that this process of dehydration and rehydration may induce apoptosis in the injured region of the vessel wall. Apoptosis is programmed cell death that is non-inflammatory and results in a benign healing process, primarily void of neointimal proliferation. A very smooth intima (i.e., tissue solidification as an effect of the warming phase) minimizes the variation in compliance between the vessel wall and plaque, resulting in more uniform dilation. Theoretically, this may reduce dissection and have an annealing effect that may further decrease the extent of a potential dissection plane. After conventional angioplasty, arteries are prone to recoil due to a high relative composition of elastin fibers. Cryoplasty appears to alter the morphology of collagen and elastin fibers in a way that limits recoil but does not impair the conduit function of the artery. The combined effect is improved laminar flow, which promotes normal re-endothelialization of the vessel lumen. If proven successful, cryoplasty would address the shortfalls of angioplasty (dissection, elastic recoil, injury response) without leaving behind an implantable device such as a stent. Avoiding the implant eliminates the issue of foreign body response and removes the complexity and side effects associated with local drug delivery in the case of a drug-eluting stent. The Cryoplasty Procedure The device used to perform cryoplasty is a simple-to-operate, disposable instrument made up of three components: 1. A cryoinflation unit; 2. Catheter 3. Nitrous oxide cartridge (N20). The cryoinflation unit is a small, hand-held device that is pre-programmed to deliver the therapy while monitoring temperature and several parameters that are designed to ensure patient safety during the procedure. The interventionalist uses familiar, percutaneous, over-the-wire angioplasty techniques to place the catheter via femoral artery access. Once this is accomplished, the catheter is connected to the cryoinflator and a cartridge of pressurized liquid nitrous oxide is then inserted into a receptacle in the cryoinflator, secured in place, and the start button is pressed. The balloon has radiopaque markers indicating the treatment length/zone. The crossing profile is .062. Balloon inflation is pre-set at 6 atm, 25 seconds, with a 10 second warming phase. The total treatment time is less than one minute. While the pressure or duration cannot be increased, multiple treatments are possible. Physicians performed three live cases using the PolarCath Peripheral CryoPlasty system during the Paris Course on Revascularization (PCR) in May 2002. Procedures were broadcast via satellite as they were being performed at two major cardiovascular treatment centers in Germany: Herzzentrum Leipzig and Herzzen-trum Siegburg. Studies involving the use of cryoplasty on patients in Europe, the United States and South America are ongoing, with additional studies planned. Immediate results in a limited number are patients are very positive, according to Giancarlo Biamino, Prof. Director of Clinical Interventional Angiology at Herzzentrum Leipzig, Clinic for Heart Surgery and Cardiology Germany. We are also beginning to study its use to treat clogged arteries in the lower legs, a condition for which there are currently limited options. A patient I treated in January had such extensive atherosclerosis in his legs, I fully expected to see him back within a week for retreatment. To this day, he is symptom-free post-cryoplasty, and hasn’t needed further treatment. In a study of 15 patients treated in Greece and Chile, 80% of patients treated achieved optimal results with cryoplasty. Angiograms performed at 6- and 9-month intervals post-cryoplasty revealed no binary restenosis at the site of the treatment. The results were presented at the 14th Annual International Symposium on Endovascular Therapy (ISET) in January, (Miami Beach, Florida) by James Joye, DO, Director of the Cardiac Catheterization Laboratory, El Camino Hospital, Mountain View, CA. The presentation included recent follow-up angiography performed on the first patient to receive cryoplasty for a femoral popliteal lesion. Fourteen months post procedure, the patient was symptom-free and the treated vessel angiographically patent. Finally, the company indicates that a version of the cryoplasty device is currently being developed for use in the coronaries. Early results suggest cryoplasty may offer something that approaches the success of the drug-coated stent, without a permanent implant and without the high cost, said Antonio Colombo, Director of the Cardiac Catheterization Lab at Columbus Hospital in Milan, Italy. Prior to the Transcatheter Cardiovascular Therapeutics (TCT) meeting in September 2002, CryoVascular Systems received U.S. Food and Drug Administration clearance to market its PolarCath peripheral transluminal angioplasty system.

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