“Tibial vessels have typically a limited patency after endovascular therapy and this has to be improved, because they are key to successful critical limb ischaemia (CLI) management,” said Dr Minar, Medical University Vienna, Austria, who gave an honest appraisal of limitations of infrapopliteal interventions in one session. “The crucial point about this really is how we can increase the applicability of angioplasty for chronic occlusions in the tibial segment,” said Dr Fusaro, San Pellegrino Hospital, Italy, who implied that coronary technology should be transferred more. According to Minar, however, coronary stents are too short and not flexible enough for infrapopliteal lesions.
Transluminar crossing, even of long tibial lesions, seems to be the preferred approach. Although the subintimal technique has been established in experts’ hands, “you should always try to avoid the subintimal plane,” said Dr Peeters, Imelda Hospital, Bonheiden, Belgium. “There are a lot of toys for boys available nowadays to cross and debulk such lesions or to help improve outcome of angioplasty. The Excimer laser seems to work quite well in infrapopliteal arteries, even though the experience is still limited.” The LACI registry (laser assisted PTA for CLI) had prospectively observed 145 patients and reported 86% procedural success rate and a six-month limb salvage rate of 92%.
New approaches that are being explored to improve the longer-term success of primary angioplasty included focused force angioplasty and cryoplasty. Boston Scientific’s PolarCath Peripheral Dilatation System delivers cryotherapy and is designed to initiate both mechanical and biological responses in order to produce long-lasting beneficial vascular effects. The below-the-knee CHILL study followed 111 treated limbs with critical ischaemia prospectively and found a procedural success rate of 97% and a one-year limb salvage rate of 85%.
Scoring balloons such as the new AngioSculpt catheter (AngioScore) use external struts with nitinol scoring elements mounted on a semi-compliant balloon to concentrate the dilation force locally thus providing targeted scoring of lesions while minimizing barotrauma, elastic recoil and uncontrolled dissection. This is believed to improve the outcome of the intervention and reduce the number of stents required, particularly in small calibre vessels.
With the AngioSculpt catheter the struts are configured in three spirals. Its safety and efficacy is currently being investigated in the multi-centre FeMoropopliteal AngioSculpt SCoring BallOon CaTheter Study (MASCOT). Peeters, who is a principle investigator of this study, is convinced of this approach: “The angioplasty results looks histologically much more physiologic, and longer-term results are very promising. However, the study is still enrolling and we expect first results in 2009.”
An alternative focused-force angioplasty device is being promoted by YMed: the Vascutrak 2 catheter. In this catheter the balloon inflation force is being focused by external wires aligned in a longitudinal rather than spiral configuration creating a different controlled stress pattern along the lesion to optimise angioplasty results in diffuse and calcified below the knee lesions. However, the device can be used equally after stent deployment. “It has become clear that such dedicated devices for focal pressure balloon angioplasty hold great promise as new first line technology in our CLI tool box for this upcoming global epidemic of infrapopliteal disease,” said Peeters.
A totally different approach was presented by Dr David Allie from the Cardiovascular Institute of the South. He claimed that precise vessel sizing to determine exact luminal diameters for optimal stent expansion were considered a prerequisite for coronary intervention for improved outcome; however, they were almost never considered in peripheral interventions. He introduced the Metricath Libra (Angiometrx) which is a low pressure balloon catheter that measures vessel diameter and cross-sectional area to a hundredth mm. In a recent study, 69 infrapopliteal vessels were assessed using this system and no device related complications were reported. “This might be a promising alley to pursue also in the periphery, since we can deploy only the right appliances if we know what dimensions they ideally should have,” Allie said, closing the session.