Stent Development

A Self-Expandable, Nitinol Stent for the Stabilization of Non-Obstructive, Soft Coronary Lesions: The vProtect™ Luminal Shield

Cath Lab Digest talks with Juan F. Granada, MD, Medical Director, The Skirball Center for Cardiovascular Research, Cardiovascular Research Foundation, New York, New York
Cath Lab Digest talks with Juan F. Granada, MD, Medical Director, The Skirball Center for Cardiovascular Research, Cardiovascular Research Foundation, New York, New York
What is unique about the vProtect™ Luminal Shield? This stent is part of a new generation of self-expandable nitinol stents. In this particular stent design, the radial force has been calculated to achieve less chronic outward force — an issue with previous designs — while maintaining a similar crush-resistant force to that of balloon-expandable stents. Even though the stent tends to expand gradually over time, the resulting radial force level is half or less than that of earlier self-expandable coronary stents. At the same time, the stent is able to maintain a stable crush-resistant force, avoiding collapse following implantation. This generation is a major advance in the development of self-expandable nitinol stents, offering better bio-mechanics compared with first-generation self-expandable coronary stents. Balloon-expandable and self-expandable stent platforms were actually developed almost simultaneously, but because balloon-expandable coronary stents were easier to use and deploy, self-expandable stent platforms didn’t ‘stick’ and the technology stalled. Yet nitinol has mechanical properties that seem to be superior in terms of the potential to treat atherosclerosis. Nitinol self-expandable stents always expand to achieve and maintain full contact with the vessel wall, securing device-vessel apposition. Also, if properly designed, these stents tend to cause less overall injury by virtue of their relatively gentle deployment mechanism. Self-expandable stents have two different forces. One that forces the device to expand outwards and one that prevents the stent from collapse against the forces imposed by the vessel on the outer area of the stent. If you want a device that can adapt to the mechanical forces imposed by the vessel wall, self-expandable technologies provide a good compliance match to the vessel wall compared with balloon-expandable scaffoldings. Balloon-expandable stents rely on the plastic deformation of the metal caused by the balloon during the process of stent deployment. The device tends to grow with the balloon as much as the tissue resistance permits. I am a big believer in self-expandable technology for coronary applications. It provides better biomechanics as compared to balloon-expandable stents. There is the possibility of less vascular injury and a good opportunity to provide permanent contact with the vessel wall, a positive attribute for all coronary prostheses, especially drug-eluting devices, which are known to display late malapossition. Current device sizing for the vProtect Luminal Shield allows the treatment of vessels up to 3.5 mm in diameter. The technology also has a lot of applicability for small and long vessels. What is the primary intent of the vProtect Luminal Shield? One of the primary intentions is treatment of acute coronary syndromes, but I should note that this device is experimental and is still in a validation phase. It’s true that the manufacturer’s intention has always been to treat patients with complex atheromas or thin-cap fibroatheromas, the so-called vulnerable plaques. However, in order to enter into a clinical application for this condition, the first step is to use this device in patients with acute coronary syndromes and understand its behavior. We believe that acute coronary syndromes, including myocardial infarction, are derived from non-obstructive lesions, mostly containing complex atheromatous lesions located in positively remodeled vessels. This type of technology could potentially serve to passivate these types of lesions better than a balloon-expandable stent or a drug-eluting stent by causing remodeling of the necrotic core, avoiding rupture of the fibrous cap and facilitating proper vascular healing. The hypothesis still needs to be proven, but this therapy could have a niche application in highly remodeled vessels with a big necrotic core. Why are non-obstructive lesions important to treat? It is believed that a big proportion of sudden cardiac death and acute myocardial infarction events are related to the presence of complex, non-obstructive atherosclerotic lesions that appear to be focally located within the coronary tree. If properly identified and characterized, there is a potential to change the natural history of the disease by acting focally. This approach will not replace the need for systemic therapy by any means, and the hypothesis remains to be tested and most importantly, proven. How might the vProtect Luminal Shield help stabilize vulnerable plaque? For vulnerable plaque, or a thin-capped fiberatheroma, essentially what you are trying to do is remodel the necrotic core. The production of a healthy neointima on top of the device could potentially passivate the plaque. With a ruptured plaque, minus the presence of the thrombus, you can achieve a similar result. For purely thrombotic lesions, this device is not going to provide the same conceptual protection of a fully-covered stent, but that is not really the primary intent of the device. However, if thrombotic lesions like those seen in acute myocardial infarction are related to the presence of ruptured non-obstructive atheromas, then the use of this type of device makes more sense than the use of balloon-expandable stents. You reported results from a study on the vProtect Luminal Shield at TCT. Yes, we did a safety and feasibility study in Latin America (Corbic Research Institute, Colombia, South America), including patients with evidence of myocardial ischemia and simple atherosclerotic lesions undergoing percutaneous coronary intervention. We reported interim analysis of the first 29 patients enrolled, in which we had excellent technical success. Our reported binary restenosis rate to date with the patients receiving a single stent who have been followed by angiography thus far (85%) is around 10%. Are there any other ongoing trials? The SECRITT I trial is underway in Rotterdam. It is a primary prevention pilot study in which the patients undergo multimodality imaging with optical coherence tomography (OCT) and intravascular ultrasound (IVUS), and then undergo vProtect Luminal Shield implantation. Can you tell us more about the vProtect Luminal Shield and its potential for use in vulnerable plaque? This device is designed to treat vulnerable plaque. Let’s say a patient comes to the cath lab with a lesion that is angiographically non-obstructive, perhaps 40-50%, and has no indication for intervention. One could use a detection modality such as infra-red technology or IVUS/OCT. Perhaps we find the patient has a thin-cap fibroatheroma in the proximal left anterior descending artery (LAD). If one could prove there is some prediction value in any of the imaging techniques currently under development, we could potentially design a primary prevention study using a device like the vProtect, and “shield” or exclude this lesion, potentially changing the natural history of the disease. But we are not there yet. The first logical step is trying to use this device in situations where a vulnerable plaque has become very symptomatic, such as acute coronary syndromes. However, that focus does not preclude the use of this technology in day-to-day lesions, because at the end of the day, it is a stent, and on top of that, has some biomechanical properties that make this device a good candidate for a drug-eluting stent platform as well. Prescient Medical is also developing a product to image vulnerable plaque, the vPredict™ Optical Catheter. We don’t have any clinical experience with that device yet; everything we’ve seen has been at the preclinical level. The only thing we’ve done so far is testing the safety of the catheter. We don’t have any efficacy data in vivo but we do have safety data to demonstrate the catheter is safe and can be positioned in the artery without causing significant damage. I can tell you that Raman spectroscopy, the technology concept behind the catheter, is highly precise and has excellent resolution. The potential for this technology to detect the specific components of a plaque is quite interesting. The technology is still at a developmental stage and it will be quite interesting to see its continuing development in the future. We are learning how to find vulnerable plaque, but I don’t think we have defined its natural history as yet. We have learned that some plaques do well despite the fact that they look complex by imaging. Once we understand the true natural history of these plaques, we are going to be able to advocate appropriate therapies. Dr. Granada can be contacted at jgranada@crf.org Additional Reading 1. Granada JF, Pomeranz M, Heringes J, Odess I. vProtect™ luminal shield system. EuroInterv 2007;3:416-419. Available online at www.europcronline.com/eurointervention/download_pdf.php? Accessed November 5, 2009.
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