Cardiovascular disease is commonly accepted as being one of the most serious health risks facing our society today. Diseased and obstructed coronary arteries can restrict the flow of blood and cause tissue ischemia and necrosis. While the exact etiology of sclerotic cardiovascular disease is still in question, the treatment of narrowed coronary arteries is more defined. Surgical construction of coronary artery bypass grafts (CABG) is often the method of choice when there are several diseased segments in one or multiple arteries. Open heart surgery is, of course, very traumatic for patients. In many cases, less traumatic, alternative methods are available for treating cardiovascular disease percutaneously. These alternate treatment methods generally employ various types of percutaneous transluminal angioplasty (PTCA) balloons or excising devices (atherectomy) to remodel or debulk diseased vessel segments. A further alternative treatment method involves percutaneous, intraluminal installation of expandable, tubular stents or prostheses in sclerotic lesions.
A recurrent problem with the previous devices and PTCA procedures is their failure to maintain patency due to the growth of injured vascular tissue. This is known as "restenosis" and may be a result of the original injury to the vessel wall occurring during the angioplasty procedure. Pathologically restenosis represents a neointimal proliferative response characterized by smooth muscle cell hyperplasia that results in reblockage of the vessel lumen necessitating repeat PTCA procedures up to 35-50% of all cases. It has been generally accepted that a radioisotope source may be capable of selectively inhibiting the growth of these hyperproliferating smooth muscle cells and thereby reduce the rate of restenosis after the primary interventional procedure.
Heretofore, various devices have been disclosed which may be used to expose a blood vessel undergoing angioplasty to intravascular radiation therapy. Balloon angioplasty catheters have been used to place and deploy a radioactive stent or prosthesis within human vessels. For example, in U.S. Pat. Nos. 5,059,166 and 5,176,617 a stent containing a radioactive source for irradiating an arterial segment to prevent restenosis is disclosed. In U.S. Pat. No. 5,199,939 an intravascular catheter and method for providing a radioactive means to the treated vessel segment is disclosed. In U.S. Pat. No. 5,616,114, an angioplasty balloon capable of inflation with a radioactive liquid for treatment of the affected vessel is described. U.S. Pat. No. 5,618,266 discloses a catheter for treating restenosis which contains a radioactive treatment source wire therein.
There are several disadvantages using either a stent or balloon catheter to uniformly expose a vascular segment to radiation. Regarding the radioactive stent, once the stent is deployed, there is no means outside of invasive surgical excision, to remove the radioactive source from the vascular segment. Therefore, stents or implanted prostheses with radioactive properties must employ a radioisotope whose half-life and penetration properties must be precisely calibrated to deliver an exact quantity of radiation to the vascular segment upon stent deployment. Balloon catheters employed to irradiate a vascular segment have limitations including potential balloon rupture and ischemia due to the fact that balloons cannot be inflated within the vessel for long periods of time because it interrupts the flow of blood to distal vessels. This leads to tissue ischemia and potential necrosis. Even "perfusion" type angioplasty balloons used to deliver a radiation source to the affected artery provide far less than physiological blood flow during balloon inflation and dwell times are limited by ischemia and tissue necrosis. Simple intravascular catheters used to deliver alpha, beta or gamma radioactive source wire to the affected vessel do not permit centering of the radioactive source uniformly within the vessel lumen and therefore deliver radiation which is undesirably unequal to different walls of the vessel. Lack of centering the radiation source may provide up to four (4) times the radioactive dose to the vessel wall nearer the source than the wall farther from the source.
Thus, it can be seen that there is a need for a new and improved device to selectively irradiate an arterial segment and which overcomes these disadvantages.
In general, it is an object of this present invention to provide a mechanical dilatation device and method which is capable of dilating an obstruction within a vascular segment while providing radiation to the vessel segment.
Another object of the invention is to provide a percutaneous device and method of the above character which can be used for prolonged periods in exposing a vascular segment to an intravascular radiation source while allowing continuous perfusion of blood into the distal to the treatment area.
Another object of the invention is to provide a device that is not susceptible to structural damage (balloon rupture) and subsequent release of radioactive materials into the vasculature.
A further object of the invention is to provide a device and method capable of providing a uniform dose of radiation to the vascular segment while dilating an obstruction within the vessel segment.