One type of implantable device is a synthetic vascular graft such as is commonly used to replace damaged or dysfunctional arterial or venous pathways, for example at the site of an aneurysm or occlusion. Bypass grafts are often used to divert blood flow around damaged regions to restore blood flow. Another use of vascular prostheses is for creating a bypass shunt between an artery and vein, specifically for multiple needle access, such as is required for hemodialysis treatments. Following multiple percutaneous invasions into a vein, the vein may either collapse along the puncture track or become aneurysmal, leaky or fill with clot, causing significant risk of pulmonary embolization. Vascular prostheses have been used for many years as an alternative to patients' own veins for vascular access during hemodialysis.
Materials research has led to the development of some synthetic materials for use in artificial vascular prostheses. For example, polytetrafluoroethylene (PTFE), a polymeric material which may be stretched to a specific length and expanded to a specific thickness, is often used to fabricate single lumen artificial veins and arteries. Typically, however, PTFE vascular grafts cannot safely be used to withdraw blood until they have been in place in the body for a minimum of 14 days after surgery and have become surrounded by fibrotic tissue. This is because bleeding occurs at the site of a needle puncture in PTFE grafts if fibrotic tissue is absent. Complications which can result from early puncturing of PTFE arteriovenous fistulas include a hematoma surrounding the graft, false aneurysm, and graft occlusion.
Various other synthetic materials, in addition to PTFE, have been used for vascular grafts, including Dacron.RTM. brand and other synthetic polyester fibers, mandrel spun polyurethane, and silicon elastomer fibers. Additionally, vascular grafts have been formed using autologous saphenous vein, modified bovine carotid xenograft, and modified human umbilical vein. None, however, has overcome the problems associated with early failure of the graft following implantation.
A problem associated with known vascular grafts stems from their delicate structure making them difficult to handle and position properly during surgery. Due to their circumferentially uniform appearance, the grafts may be twisted during implantation, which can reduce the openness, or patency, of the implanted graft.
Another problem associated with known vascular grafts is that they are transparent to known non-surgical techniques for viewing that are generally used to detect structures in the body. These techniques include x-rays, MRI scanning, fluoroscopy, ultrasound, and nuclear magnetic resonance. As a result, post-implantation examination of known vascular grafts is difficult. If a surgeon suspects that a blockage of an implanted vascular graft has occurred, for example, she must inject radiopaque dye into the patient through the graft. The dye allows the graft to be visible during fluoroscopic examination to determine whether it has collapsed or is satisfactorily transporting blood flow. This process is invasive to the patient and places further burdens on the patient's circulatory system.
Various marking devices have been developed to avoid the need for injecting dye into a patient who has undergone vascular graft implantation. U.S. Pat. No. 4,202,349 (Jones, May 13, 1980), for example, discloses a radiopaque blood vessel marker for attachment to the side wall of a blood vessel or vascular graft. The marker is a substantially flattened disk which is sutured into place by the surgeon. The Jones vessel markers are not well suited for use with PTFE vascular prostheses because it is difficult to elicit natural occlusion of suture holes in PTFE due to the relative elasticity of the porous PTFE tubing materials.
U.S. Pat. No. 4,787,391 (Elefteriades Nov. 29, 1988) discloses a device for the marking the anastomosis, or joining site, of a coronary graft so that the anastomosis can be localized fluoroscopically after surgery. The device includes gold indicators which are arranged on a hemostatic material which is absorbed or dissolved completely in the body during the healing period, leaving the gold markers at the site. This device is useful for marking the area of the anastomosis, but does not allow the vascular graft itself to be viewed during fluoroscopic examination.
It is, therefore, an object of the present invention to provide a vascular graft having integral diagnostic indicia for determining the patency (openness) of the graft vessel by non-invasive techniques. It is also an object of the present invention to provide a vascular graft having integral radiopaque or MRI markers that do not need to be sutured to the graft. It is still another object of the present invention to provide a method for treating a patient having a damaged or dysfunctional arterial or venous pathway using the detectible vascular grafts of the present invention.