At the recent Society of Interventional Radiology meeting in Toronto, Canada, Dr Thomas McNamara from the University of California at Los Angeles presented the results from two studies assessing the effectiveness of CryoPlasty Therapy (PolarCath Peripheral Dilation System, Boston Scientific) in the treatment of peripheral arterial disease. He commented that the outcomes of the Below-The-Knee (BTK) CHILL Study and PolarCath IDE Study support the use of CryoPlasty Therapy as a valuable interventional treatment option for femoropopliteal and infrapopliteal lesions.
In the CryoPlasty procedure the balloon is filled with liquid nitrous oxide which expands into gas when it enters the balloon, simultaneously cooling the vessel wall to a temperature of -10 degrees Celsius and expanding the balloon.
Simultaneous cooling and dilation of the artery is believed to change the properties of the artery in such a way as to reduce the likelihood of tearing that can lead to the need for a stent. The procedure also reduces the subacute elastic recoil typically seen in vessels after conventional balloon angioplasty. In addition, the freezing of the tissue also kills a substantial fraction of the smooth muscle cells in the vessel wall, which helps to prevent later neointimal hyperplasia. Cell death is by apoptosis, and thus the therapy avoids the inflammatory response correlated to cellular necrosis.
Interim results released from the Below-The-Knee (BTK) CHILL Study, a prospective, multi-center study evaluating the PolarCath System for treatment of stenoses or occlusions in infrapopliteal vessels, have concluded that the system provides a safe and effective method of treating infrapopliteal stenoses and occlusions in patients with critical limb ischemia (CLI).
The study enrolled 111 patients with CLI (Rutherford PAD Categories 4-6) at 16 sites in the US. The majority of patients had lower limb ulcerations and 24% had gangrene. The primary study endpoints are: absence of major amputation of the target limb six months post index procedure, and primary technical success. Secondary endpoints include frequency of serious adverse events and absence of major amputation of the target limb at one, three, and twelve months post index procedure. Patients had a mean age of 72.8 years, 72% were male, 67% had diabetes, and 84% had hypertension. Mean reported follow-up is 136 days, ranging from 120 to 520 days.
The results revealed that the primary technical success rate was 96.3%. There were no deaths or major complications associated with the index procedures. Currently, 69 patients have been enrolled for more than six months. Only four major amputations have been reported yielding a six-month absence of major amputation rate of 94.2%. Adverse events included 16 revascularizations and 11 minor amputations of toes.
Discussing the results, McNamara commented, "Something is happening that makes the vessel look better immediately, compared with after a regular balloon angioplasty, and there's a reduced incidence of re-stenosis."
"CryoPlasty has every possibility of emerging as the front-runner in treating patients with critical limb ischemia," commented Dr John Rundback, Columbia University, NY and Holy Name Hospital, Teaneck, NJ. Dr. Rundback also commented that he believes that the plaque modification due to cooling results in a more controlled and reliable disruption of the stenosis, yielding greater initial and long term success.
McNamara also announced the results from the non-randomised, multi-center, PolarCath IDE Study, which examined the use of CryoPlasty Therapy in 102 patients with stenotic or occluded lesions in the superficial femoral and popliteal arteries.
The results were assessed for acute outcomes, serious adverse events, nine-month clinical outcomes and the incidence of target lesion revascularization (TLR) within the study period. Enrollment began in November 2001 and was completed in December 2002. In March 2005, investigational sites were invited to participate in continued surveillance of the study subjects to determine target lesion patency using clinical assessments. Extended follow-up information was available for 70 patients, with a mean follow-up of 31.3 months (a range of 10.7 to 41.2 months).
The results showed that the mean lesion length for these patients was 47.7 ± 26.9 mm (mean lesion length for the entire study population was 46.7 ± 25.7 mm). The clinical patency rate was 83.2% at 300 days, and 73.5% at 1,253 days, utilizing Kaplan-Meier methods.
McNamara concluded that continued surveillance of IDE subjects has demonstrated persistent excellent patency rates in longer term follow-up, and that these results demonstrate favorable long term patency with CryoPlasty Therapy compared to conventional angioplasty or stent outcomes in the femoropopliteal segment.
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