Prosthesis (i.e. – artificial body members) – parts thereof – or ai – Arterial prosthesis
Reexamination Certificate
1998-09-30
2002-08-13
Mancene, Gene (Department: 3731)
Prosthesis (i.e., artificial body members), parts thereof, or ai
Arterial prosthesis
Reexamination Certificate
active
06432126
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to methods and devices for inducing angiogenesis in ischemic tissue.
BACKGROUND OF THE INVENTION
Tissue becomes ischemic when it is deprived of adequate blood flow. Ischemia causes pain in the area of the affected tissue and, in the case of muscle tissue, can interrupt muscular function. Left untreated, ischemic tissue can become infarcted and permanently non-functioning. Ischemia can be caused by a blockage in the vascular system that prohibits oxygenated blood from reaching the affected tissue area. However, ischemic tissue can be revived to function normally despite the deprivation of oxygenated blood because ischemic tissue can remain in a hibernating state, preserving its viability for some time. Restoring blood flow to the ischemic region serves to revive the ischemic tissue.
Although ischemia can occur in various regions of the body, often tissue of the heart, the myocardium, is affected by ischemia due to coronary artery disease, occlusion of the coronary artery, which otherwise provides blood to the myocardium. Muscle tissue affected by ischemia can cause pain to the individual affected. Ischemia can be treated, if a tissue has remained viable despite the deprivation of oxygenated blood, by restoring blood flow to the affected tissue.
Treatment of myocardial ischemia has been addressed by several techniques designed to restore blood supply to the affected region. Coronary artery bypass grafting CABG involves grafting a venous segment between the aorta and the coronary artery to bypass the occluded portion of the artery. Once blood flow is redirected to the portion of the coronary artery beyond the occlusion, the supply of oxygenated blood is restored to the area of ischemic tissue.
Early researchers, more than thirty years ago, reported promising results for revascularizing the myocardium by piercing the muscle to create multiple channels for blood flow. Sen, P. K. et al., “Transmyocardial Acupuncture—A New Approach to Myocardial Revascularization”,
Journal of Thoracic and Cardiovascular Surgery
, Vol. 50, No. 2, August 1965, pp. 181-189. Although others have reported varying degrees of success with various methods of piercing the myocardium to restore blood flow to the muscle, many have faced common problems such as closure of the created channels. Various techniques of perforating the muscle tissue to avoid closure have been reported by researchers. These techniques include piercing with a solid sharp tip wire, hypodermic tube and physically stretching the channel after its formation. Reportedly, many of these methods still produced trauma and tearing of the tissue that ultimately led to closure of the channel.
An alternative method of creating channels that potentially avoids the problem of closure involves the use of laser technology. Researchers have reported success in maintaining patent channels in the myocardium by forming the channels with the heat energy of a laser. Mirhoseini, M. et al., “Revascularization of the Heart by Laser”,
Journal of Microsurgery
, Vol. 2, No. 4, June 1981, pp. 253-260. The laser was said to form channels in the tissue were clean and made without tearing and trauma, suggesting that scarring does not occur and the channels are less likely to experience the closure that results from healing. U.S. Pat. No. 5,769,843 (Abela et al.) dicloses creating laser-made TMR channels utilizing a catheter based system. Abela also discloses a magnetic navigation system to guide the catheter to the desired position within the heart. Aita U.S. Pat. Nos. 5,380,316 and 5,389,096 disclose another approach to a catheter based system for TMR.
Although there has been some published recognition of the desirability of performing transmyocardial revascularization (TMR) in a non-laser catheterization procedure, there does not appear to be evidence that such procedures have been put into practice. For example, U.S. Pat. No. 5,429,144 Wilk discloses inserting an expandable implant within a preformed channel created within the myocardium for the purposes of creating blood flow into the tissue from the left ventricle.
Performing TMR by placing stents in the myocardium is also disclosed in U.S. Pat. No. 5,810,836 (Hussein et al.). The Hussein patent discloses several stent embodiments that are delivered through the epicardium of the heart, into the myocardium and positioned to be open to the left ventricle. The stents are intended to maintain an open channel in the myocardium through which blood enters from the ventricle and perfuses into the myocardium.
Angiogenesis, the growth of new blood vessels in tissue, has been the subject of increased study in recent years. Such blood vessel growth to provide new supplies of oxygenated blood to a region of tissue has the potential to remedy a variety of tissue and muscular ailments, particularly ischemia. Primarily, study has focused on perfecting angiogenic factors such as human growth factors produced from genetic engineering techniques. It has been reported that injection of such a growth factor into myocardial tissue initiates angiogenesis at that site, which is exhibited by a new dense capillary network within the tissue. Schumacher et al., “Induction of Neo-Angiogenesis in Ischemic Myocardium by Human Growth Factors”,
Circulation
, 1998; 97:645-650. The authors noted that such treatment could be an approach to management of diffused coronary heart disease after alternative methods of administration have been developed.
SUMMARY OF THE INVENTION
The vascular inducing implants of the present invention provide a mechanism for initiating angiogenesis within ischemic tissue. The implants interact with the surrounding tissue in which they are implanted and the blood that is present in the tissue to initiate angiogenesis by various mechanisms.
Primarily, it is expected that the implants will trigger angiogenesis in the ischemic tissue by interacting in one or more ways with the tissue to initiate an injury response. The body's response to tissue injury involves thrombosis formation at the site of the injury or irritation. Thrombosis leads to arterioles and fibrin growth which is believed to ultimately lead to new blood vessel growth to feed the new tissue with blood. The new blood vessels that develop in this region also serve to supply blood to the surrounding area of ischemic tissue that was previously deprived of oxygenated blood.
The presence of the implants in the tissue, alone, may trigger a foreign body response leading to endothelialization and fibrin growth around the implant. However, the implants of the present invention are specially configured to interact with the surrounding tissue to induce angiogenesis by a variety of mechanisms.
Implant embodiments of the invention serve to initiate angiogenesis by providing a chamber or interior into which blood may enter and collect leading to thrombosis. The implants are configured to have a wall defining an interior, with at least one opening in the wall to permit passage of blood into and from the interior. The material and structure of the implants permits them to be flexible such that the implant compresses when the surrounding tissue contracts and the implant returns to an uncompressed configuration when the surrounding tissue relaxes. Cyclical compression and expansion of the implant in concert with the motion of the surrounding tissue creates a pumping action, drawing blood into the implant interior when expanded, then expelling the blood when the implant is compressed. One of the openings of the implant may include a check valve to control the flow of blood from the implant interior. Blood that enters the interior of the implant and remains, evenly temporarily, tends to coagulate and thrombose. Over time, continued pooling of the blood in the interior will cause thrombosis and fibrin growth throughout the interior of the implant and into the surrounding tissue. New blood vessels will grow to serve the new growth with oxygenated blood, the process of angiogenesis.
Some embodiments are configured to have a high de
Choh Richard T.
Forcucci Stephen J.
Forde Sean
Gambale Richard A.
Weiser Michael F.
C.R. Bard Inc.
Kirkpatrick & Lockhart LLP
Mancene Gene
Robert Eduardo C.
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