Surgery – Diagnostic testing – Cardiovascular
Reexamination Certificate
1998-02-23
2001-05-15
O'Connor, Cary (Department: 3736)
Surgery
Diagnostic testing
Cardiovascular
C600S481000
Reexamination Certificate
active
06231516
ABSTRACT:
TECHNICAL FIELD
This invention relates generally to implantable devices, and, more particularly, to implantable medical devices having therapeutic or diagnostic functions within a lumen of an endoluminal implant such as a stent or other type of endovascular conduit, and methods related to such implantable medical devices.
BACKGROUND OF THE INVENTION
In the 1970s, the technique of percutaneous transluminal coronary angioplasty (PTCA) was developed for the treatment of atherosclerosis. Atherosclerosis is the build-up of fatty deposits or plaque on the inner walls of a patient's arteries; these lesions decrease the effective size of the artery lumen and limit blood flow through the artery, prospectively causing a myocardial infarction or heart attack if the lesions occur in coronary arteries that supply oxygenated blood to the heart muscles. In the angioplasty procedure, a guide wire is inserted into the femoral artery and is passed through the aorta into the diseased coronary artery. A catheter having a balloon attached to its distal end is advanced along the guide wire to a point where the sclerotic lesions limit blood flow through the coronary artery. The balloon is then inflated, compressing the lesions radially outward against the wall of the artery and substantially increasing the size of its internal lumen, to improve blood circulation through the artery.
Increasingly, stents are being used in place of or in addition to PTCA for treatment of atherosclerosis, with the intent of minimizing the need to repeatedly open an atherosclerotic artery. Although a number of different designs for stents exist in the prior art, all are generally configured as elongate cylindrical structures that are provided in a first state and can assume a second, different state, with the second state having a substantially greater diameter than the first state. A stent is implanted in a patient using an appropriate delivery system for the type of stent being implaced within the patient's arterial system. There are two basic types of stents—those that are expanded radially outward due to the force from an inflated angioplasty type balloon, such as the Palmaz-Schatz stent, the Gianturco-Roubin stent and the Strecker stent, and those that are self expanding, such as the Maass double helix spiral stent, the Nitinol stent (made of nickel titanium memory alloy), the Gianturco stent and the Wallstent. Problems with the Maass double helix spiral stent and the Nitinol stent have limited their use.
Stents are sometimes used following a PTCA procedure if the artery is totally occluded or if the lesions have occluded a previously placed surgical graft. Typically, a stent constrained within an introducer sheath is advanced to a site within the patient's artery through a guide catheter. For the balloon expanded type, after the introducer sheath is retracted, a balloon disposed inside the stent is inflated to a pressure ranging from about six to ten atmospheres. The force produced by the inflated balloon expands the stent radially outward beyond its elastic limit, stretching the vessel and compressing the lesion to the inner wall of the vessel. A self expanding stent expands due to spring force following its implacement in the artery, after a restraining sheath is retracted from the compressed stent, or in the case of the Nitinol version, the stent assumes its expanded memory state after being warmed above the transition temperature of the Nitinol alloy (e.g., above 30° C.). Following the expansion process, when the balloon catheter is used, the balloon is removed from inside the stent and the catheter and other delivery apparatus is withdrawn. The lumen through the vessel is then substantially increased, improving blood flow.
After a stent or other endoluminal device is implanted, a clinical examination and either an angiography or an ultrasonic morphological procedure is performed to evaluate the success of the stent emplacement procedure in opening the diseased artery or vessel. These tests are typically repeated periodically, e.g., at six-month intervals, since restenosis of the artery may occur. Due to the nature of the tests, the results of the procedure can only be determined qualitatively, but not quantitatively, with any degree of accuracy or precision. It would clearly be preferable to monitor the flow of blood through the stent after its implacement in a vessel, both immediately following the treatment for the stenosis and thereafter, either periodically or on a continuous basis. Measurements of volumetric rate and/or flow velocity of the blood through the stent would enable a medical practitioner to much more accurately assess the condition of the stent and of the artery in which the stent is implanted. Currently, no prior art mechanism is available that is implantable inside a blood vessel for monitoring blood flow conditions through a stent.
Following stent implantation, it is difficult to monitor the condition of the affected area. Stents often fail after a period of time and for a variety of reasons. Several of the causal mechanisms are amenable to drug treatment. It is highly desirable in at least some of these cases to localize the drug treatment to the site of the graft or surgery. For example, when thrombus forms in a given area, thrombolytic drugs are capable of providing significant assistance in resolving the thrombosis, but may present problems such as hemorrhaging, if they also act in other portions of the patient's body.
SUMMARY OF THE INVENTION
The present invention provides a capability for including a therapeutic transducer together with an endoluminal implant such as a stent or stent graft. Therapeutic transducers may include ultrasonic, magnetic, iontophoretic, heating or optical devices, which may permit localized drug delivery or localized drug activation. Provision is made for delivering energy to the implanted transducers and for coupling signals to or from the implanted transducers. The present invention also permits inclusion of diagnostic transducers together with the endoluminal implant and allows signals to be transmitted from the diagnostic transducers to an area outside of the patient's body.
The present invention can allow steps that may be taken to restore full fluid flow through, e.g., a stent that is becoming restricted. In these cases, it is desirable to initiate treatment before the problem proceeds too far to be corrected without stent replacement or further PTCA treatment. Clearly, it would be preferable to be able to monitor the condition of a stent without resorting to invasive surgical procedures and without prescribing medication that may not be necessary, so that the useful life of the stent may be extended, problems associated stent failure avoided and so that medications are only prescribed when required by the known condition of the stent and associated vasculature.
Other advantages that may be realized via embodiments of the present invention including monitoring of other parameters measurable within a stent or other type of endoluminal implant using one or more appropriate sensors or transducers according to embodiments of the present invention. For example, monitoring pressure at the distal and proximal ends of the lumen in the implant and determining the differential pressure can provide an indication of fluid velocity through the lumen. Temperature can also be used to monitor fluid flow by applying heat to the fluid within the lumen and monitoring the rate at which the temperature of the fluid decreases as the fluid flows through the lumen of the implant. Integrated circuit (IC) transducers are currently known and available for sensing the levels of many different types of biochemical substances, such as glucose, potassium, sodium, chloride ions and insulin. Any of these IC sensors could be provided in an endoluminal implant to monitor these parameters.
Since it is impractical to pass a conductor through the wall of an artery or vessel for long periods of time, use of a conventional sensor that produces signals indicative of f
Cimochowski George E.
Keilman George W.
Astorino Michael
O'Connor Cary
Seed IP Law Group PLLC
VacuSense, Inc.
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