The present invention relates generally to medical devices and more particularly to delivery systems for self-expandable medical devices.
Self-expanding medical devices are used by physicians to treat numerous conditions using minimally invasive procedures. Examples of self-expanding medical devices include stents, stent-grafts, filters, valves, etc. Typically, self-expanding medical devices are made from an elastic structure that may be compressed into a low profile state that can be passed through vessels in a patient with minimal trauma. Once at the desired treatment site, the self-expanding medical device is released and self-expands like a spring until it contacts a tissue wall which prevents further expansion. Common materials that are used in self-expanding medical devices include nitinol and stainless steel, although other materials are also possible.
One type of self-expanding medical device that has become especially common is intraluminal stents. Stents are used to treat various organs, such as the vascular system, colon, biliary tract, urinary tract, esophagus, trachea and the like. For example, stents are commonly used to treat blockages, occlusions, narrowing ailments and other similar problems that restrict flow through a passageway. One area where stents are commonly used for treatment involves implanting an endovascular stent into the vascular system in order to improve or maintain blood flow through narrowed arteries. However, stents are also used in other treatments as well, such as the treatment of aneurysms. Stents have been shown to be useful in treating various vessels throughout the vascular system, including both coronary vessels and peripheral vessels (e.g., carotid, brachial, renal, iliac and femoral). In addition, stents have been used in other body vessels as well, such as the digestive tract.
The use of stents in coronary and peripheral vessels has drawn particular attention from the medical community because of the growing number of people each year that suffer from vasculature problems associated with stenosis (i.e., narrowing of a vessel). This has led to an increased demand for medical procedures to treat such problems. The widespread frequency of heart problems and other vasculature problems may be due to a number of societal changes, including the tendency of people to exercise less and the prevalence of unhealthy diets, in conjunction with the fact that people generally have longer life spans now than previous generations. Stents have become a popular alternative for treating vascular stenosis because stenting procedures are considerably less invasive than conventional procedures. For example, stenosis of the coronary arteries was traditionally treated with bypass surgery. In general, bypass surgery involves splitting the chest bone to open the chest cavity and grafting a replacement vessel onto the heart to bypass the blocked, or stenosed, artery. However, coronary bypass surgery is a very invasive procedure that is risky and requires a long recovery time for the patient. Vascular stents are also being more widely used to treat many different peripheral arteries due to the minimally invasive nature of stenting procedures. To address the growing demand for minimally invasive medical procedures for the treatment of coronary arteries, peripheral arteries and other passageway problems, the medical community has begun to turn away from conventional invasive procedures like bypass surgery and increasingly the treatment of choice now involves a variety of stenting procedures.
Many different types of stents and stenting procedures are possible. In general, however, stents are typically designed as tubular support structures that may be inserted percutaneously and transluminally through a body passageway. Traditionally, stents are made from a metal or other synthetic material with a series of radial openings extending through the support structure of the stent to facilitate compression and expansion of the stent. Although stents may be made from many types of materials, including non-metallic materials, common examples of metallic materials that may be used to make stents include stainless steel, nitinol, cobalt-chrome alloys, amorphous metals, tantalum, platinum, gold and titanium. Typically, stents are implanted within a passageway by positioning the stent within the area to be treated and then expanding the stent from a compressed diameter to an expanded diameter. The ability of the stent to expand from a compressed diameter makes it possible to thread the stent to the area to be treated through various narrow body passageways while the stent is in the compressed diameter. Once the stent has been positioned and expanded at the area to be treated, the tubular support structure of the stent contacts and radially supports the inner wall of the passageway. As a result, the implanted stent mechanically prevents the passageway from narrowing and keeps the passageway open to facilitate fluid flow through the passageway.
Stents can generally be characterized as either balloon-expandable or self-expanding. Traditionally, balloon-expandable stents have been used most often in coronary vessels than in peripheral vessels because of the deformable nature of these stents. One reason for this is that peripheral vessels tend to experience frequent traumas from external sources (e.g., impacts to a person's arms, legs, etc.) which are transmitted through the body's tissues to the vessel. In the case of peripheral vessels, there is an increased risk that an external trauma could cause a balloon-expandable stent to plastically deform in unexpected ways with potentially severe and/or catastrophic results. However, in the case of coronary vessels, this risk is minimal since coronary vessels rarely experience traumas transmitted from external sources.
Self-expanding stents are increasingly used and accepted by physicians for treating a variety of ailments. Self-expanding stents are usually made of shape memory materials or other elastic materials that act like a spring. Typical metals used in this type of stent include nitinol and 304 stainless steel. A common procedure for implanting a self-expanding stent involves a two-step process. First, the narrowed vessel portion to be treated is dilated with a balloon but without a stent mounted on the balloon. Second, a stent is implanted into the dilated vessel portion. To facilitate stent implantation, the stent is installed on the end of an inner catheter in a compressed, small diameter state and is usually retained in the small diameter by inserting the stent into an outer sheath at the end of the catheter. The stent is then guided to the balloon-dilated portion and is released from the inner catheter by pulling the outer sheath away from the stent. Once released from the outer sheath, the stent radially springs outward to an expanded diameter until the stent contacts and presses against the vessel wall. Traditionally, self-expanding stents have been more commonly used in peripheral vessels than in coronary vessels due to the shape memory characteristic of the metals that are used in these stents. One advantage of self-expanding stents for peripheral vessels is that traumas from external sources do not permanently deform the stent. Instead, the stent may temporarily deform during an unusually harsh trauma but will spring back to its expanded state once the trauma is relieved. Self-expanding stents, however, are often considered to be less preferred for coronary vessels as compared to balloon-expandable stents. One reason for this is that balloon-expandable stents can be precisely sized to a particular vessel diameter and shape since the ductile metal that is used can be plastically deformed to a desired size and shape. In contrast, self-expanding stents are designed with a particular expansible range. Thus, after being implanted, self-expanding stents continue to exert pressure against the vessel wall.
Commonly, delivery systems for self-expanding medical devices have a handle arrangement that remains outside of the patient's body during the deployment procedure. One portion of the handle is typically connected to an inner catheter upon which the self-expanding medical device is mounted, and another portion of the handle is typically connected to an outer sheath which restrains the self-expanding medical device in the compressed state. When the distal end of the delivery system is positioned within the patient's body at the intended treatment site, the physician actuates the handle by moving the two portions relative to each other so that the outer sheath is withdrawn from the self-expanding medical device and inner catheter. As a result, the self-expanding medical device expands outward away from the inner catheter. The handle may then be pulled by the physician to withdraw the inner catheter and outer sheath from the patient's body, while leaving the self-expanding medical device implanted in the body.
Precise placement of self-expanding medical devices is a concern in most medical procedures. However, precise placement can be more difficult with certain delivery systems due to their design, shape and other factors. Precise placement of self-expanding medical devices is generally a function of the relative movement and placement between the delivery system handle and the patient's body, and the relative movement between the portions of the handle connected to the inner catheter and outer sheath during deployment. A lack of control over any part of this system can result in inaccurate placement of a self-expanding medical device, and thus, less than desirable treatment of the medical condition being treated.
Accordingly, the inventor believes it would be desirable to provide a new delivery system for self-expanding medical devices.