Measuring the Efficacy of CryoPlasty


Submitted on Fri, 09/05/2008 - 16:36

Tony S. Das, MD, FACP, FACC

Q. What is CryoPlasty® Therapy? A. In CryoPlasty® Therapy, nitrous oxide is used to fill an angioplasty balloon within a blocked artery, cooling the balloon’s surface to -10° C. As the balloon is inflated, its cold surface cools the lesion, which exerts both mechanical and biological effects that may help prevent re-blockage of the artery (Figure 2). Q. Can you describe the Below-The-Knee (BTK) CHILL study? A. BTK CHILL was a prospective, multi-center study designed to evaluate the technical effectiveness and limb salvage potential of CryoPlasty Therapy using Boston Scientific’s PolarCath™ Peripheral Dilatation System for the treatment of critical limb ischemia (CLI). The 108 patients included in BTK CHILL were in relatively high Rutherford classes, which is defined as having either resting pain (category 4) or minor or major tissue loss (categories 5 and 6) due to CLI. The complex patient population had multiple medical problems, including hypertension, hyperlipidemia, coronary artery disease and diabetes. BTK CHILL evaluated whether the dilatation of stenotic or occlusive lesions in below-the-knee arteries with the PolarCath Peripheral Dilatation System could reduce the need for amputation and improve limb salvage in patients with CLI. There were two major primary endpoints. The first was acute technical success, which was defined as Q. What were the most significant results from the study? A. The outcomes of BTK CHILL were very interesting. First of all, the real highlight of the study was that 93% of patients were free from amputation at six months. This is a very significant result, considering the anticipated amputation rate was 25%. Secondly, acute technical success, measured at the time of the procedure, was very high at 97%. We did not compare outcomes of CryoPlasty patients with those of patients undergoing open-surgical procedures in BTK CHILL. Nevertheless, I am encouraged that improving circulation to the lower extremity via CryoPlasty Therapy in this group of patients — even with multiple medical problems and extensive disease — would clearly reduce their risk for amputation over open surgery, which is associated with many comorbid complications. I think this was clearly borne out in the study. Q. There was a great deal of complexity among the patients in BTK CHILL. Can you describe the complexities investigators faced? A. BTK CHILL evaluated a relatively sick population that was ripe for vascular disease and ultimately ripe for peripheral vascular disease. The anticipated amputation rate was 25%, so nearly one-quarter of these patients had either minor or major tissue loss with some anticipated amputation. Patients were 70+ years old (mean age = 73 ± 11), 84% had high blood pressure, and 67.6% were diabetic. Seventy percent had coronary artery disease. The majority of them, over 70%, were also previous smokers. Furthermore, we were dealing with vessels that are traditionally difficult to treat, including small diameters (mean = 3.2 mm) and occluded vessels (mean diameter stenosis = 86.9%). In fact, approximately one-third of the lesions were 100% blocked. Despite these complexities, we still achieved excellent outcomes with CryoPlasty. Q. Why is the BTK CHILL study so significant? What implications does this study have for patients and physicians? A. BTK CHILL is significant for a few reasons. First, CLI and its subsequent complication of amputation are frequently encountered in vascular medicine, and treatment options are very limited when it comes to tissue loss, whether minor or major. Although angioplasty and stenting are attractive treatment options because they are minimally invasive, arteries frequently become blocked again, requiring repeat procedures. The results of BTK CHILL allow patients with CLI to pursue a safe, viable alternative to reduce their likelihood of amputation, so this is a huge win not only for them but also their physicians. Patients who undergo amputations, especially below-the-knee amputations, usually do not live for more than two years after amputation because of comorbid illnesses, so avoiding amputation is key to survival. Second, there have been only a few studies that have specifically evaluated any one particular intervention as to its benefit in CLI, so this is a great new source of information in an understudied population. For example, although we have anecdotal evidence on stenting below the knee in these patients, there are no specific data that analyze this procedure. Pairing anecdotal evidence and clinical data, like the BTK CHILL results, allows you to select an appropriate treatment option much more easily. BTK CHILL certainly puts CryoPlasty Therapy high in the list of options, since it shows us two things: 1) it has high technical success, and 2) there is a high likelihood of achieving the reduction of amputation. Based on the results of this study, CryoPlasty Therapy is a tool that I would reach for sooner rather than later. Q. Are there certain features of the PolarCath Peripheral Dilatation System that contributed to the successful results of BTK CHILL? A. With the particular lesion subset evaluated in BTK CHILL, there are concerns about significant calcification, which leads to some dissection. CryoPlasty has been found to reduce the dissection rate, and this is clearly shown in the study. Furthermore, by decreasing the temperature at the site of the inflation, the PolarCath system promotes smooth muscle cell apoptosis. This has been shown to reduce the overgrowth of smooth muscle cells, which contributes to restenosis. Cooling may also help to prevent the vessel and lesion from “recoiling,” or snapping back to its original form. By addressing these factors, especially in very small vessels in which it is more difficult to maintain large lumens, you may significantly improve long-term outcome. I think BTK CHILL helps to illustrate this. Dr. Tony Das is currently compensated pursuant in his consulting and clinical arrangements with Boston Scientific Corporation. He is also the recipient of grant support from Boston Scientific Corporation. Sponsored and produced in collaboration with Boston Scientific Corporation.