Surgery – Miscellaneous
Reexamination Certificate
2002-03-28
2004-05-04
Lacyk, John P. (Department: 3736)
Surgery
Miscellaneous
C128S899000
Reexamination Certificate
active
06729336
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a medical device that can be used to evaluate in-stent restenosis. The present invention also relates to a combination electromagnetic wave excitation and ultrasound detection device that can be used to monitor occlusions inside implanted stents.
2. Description of Related Art
An estimated seven million Americans suffer from coronary artery disease, which causes 1.5 million myocardial infarctions (heart attacks) and over half a million deaths annually at a cost of over $100 billion. Coronary artery disease results from atherosclerosis, a complex process in which fatty and other deposits (e.g., cellular intimal and mineral additives, and engrained proteinaceous or clotting/platelet debris) build up in the walls of arteries, resulting in blockages and reduced blood flow. This process leads to the formation of a plaque of atherosclerotic material that can be comprised of various cells, lipids (fats or cholesterol), and collagen (fibrous tissue). This process progresses over a number of years and may eventually result in the formation of a blockage (stenosis) in the coronary artery. If the artery is sufficiently narrowed, blood flow is reduced (ischemia), and chest pain (angina pectoris), heart attack, or sudden death may follow. In addition to the narrowing produced by atherosclerosis, plaques may also rupture, resulting in the formation of a thrombus (clot) on the plaque surface, leading to an abrupt cessation of blood flow to the heart. Plaque rupture plays a key role in most cases of heart attack and stroke.
In 1977, Dr. Andreas Gruentzig from Switzerland introduced a novel method for treating coronary artery stenosis, which he termed “Percutaneous Transluminal Coronary Angioplasty” (PTCA), also commonly known as balloon angioplasty. Over 500,000 coronary angioplasties (the term angioplasty is derived from angio, which refers to a blood vessel, and plasty, which means to reshape) were performed in the U.S., surpassing the number of coronary bypass operations. The advantage of this technique is that it can be performed using minimally invasive catheter procedures. Using special x-ray equipment and contrast dye to visualize the arteries, the cardiologist advances a guide catheter (hollow tube) through a vascular access sheath and up the aorta to the origin of the coronary arteries. Using this catheter as a track to the coronary artery, a long, fine guidewire (generally 0.014 inches in diameter) is negotiated across the stenosis. A catheter with a deflated balloon on the far end is then advanced over the guidewire to the narrowed arterial segment. At this point the balloon is inflated and the occluding plaque compressed to the arterial wall.
In conventional PTCA the occluding plaque is simply compressed and no material is removed. In about one-third of cases, re-narrowing of the treated segment may occur over a period of several months, necessitating a repeat procedure or coronary artery bypass surgery. This re-narrowing is termed “restenosis” and appears to be distinct from the process of atherosclerosis. Despite intense research efforts and numerous drug trials, a solution to this problem remains elusive.
In order to reduce the restenosis rate and improve blood flow, stents are now routinely inserted into arteries after PTCA. Stents are wire mesh tubes usually made of metal that are expanded within the artery to form a scaffold that keeps the artery open. The stent stays in the artery permanently, holds it open, improves blood flow to the heart muscle and relieves symptoms (usually chest pain).
After placement, the stent will normally be covered with epithelium over the course of several weeks. In the case of in-stent restenosis, this tissue growth process continues. The hyperproliferation of normal cells results in the obstruction of the flow of blood through the stented vessel. Even with stents, the restenosis rate can be as high as 25%.
Restenosis within the stent can be detected in several ways. If a patient is symptomatic with angina, several diagnostic procedures may be performed. Stress Echo Cardiography may be performed whereby the heart is imaged using ultrasound, and differences between the motion of the resting heart and the exercised heart are used to determine abnormalities that indicate restricted blood flow. Unfortunately this test typically cannot detect a blockage less than 50%. A Thallium Stress Test may also be performed to indicate the degree of blood supply to the heart under differing load conditions (at rest or exercised). Unfortunately, this procedure requires injecting radioactive markers into the patient and the use of expensive gamma imaging cameras and requires above 70% blockage of blood flow to give a positive result Stress Echo Cardiography and Thallium Stress Tests are expensive, and can subject a patient with a dysfunctional heart to exercise loads, which can be dangerous.
If preliminary test results are positive then a physician generally performs coronary angiography. In this procedure a catheter is inserted into the patient and x-ray contrast agent injected so that the blood flow can be imaged with x-rays. This is an invasive procedure requiring the use of an operating room and exposes the patient to x-ray radiation. The procedure is also very costly. In addition there is a finite risk that the patient will experience a stroke or other adverse event that is associated with the procedure, and this risk can extend long period after the angiography is performed.
Another emerging technique, referred to as “intravascular ultrasound” where a miniature ultrasound transducer is inserted by a catheter and the acoustic impedance of the blood vessel is monitored by external acoustic receivers is also being evaluated for efficacy. Unfortunately this is an invasive procedure.
Recently Spillman et al. (WO 00/56210) and Cimochowski et al. (WO 99/26530) described a novel stent design that incorporates a miniature sensor that can be used to measure flow or pressure and diagnose restenosis. Unfortunately, these devices require incorporating a sensor into the stent that could adversely affect the mechanical properties of the stent.
Given the limitations of current techniques to diagnose restenosis, there is a need for a novel device that can safely, quickly and effectively detect restenosis after stenting. The present invention fulfills this need, and further provides related advantages.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a device and method to evaluate in-stent restenosis.
Another object of the present invention is to provide an endoluminal implant (or stent) that can be inserted into the body and excited by electromagnetic radiation to oscillate.
Another object is to provide an ultrasound transducer that detects the excited ultrasound oscillations for analysis to detect a change in the aperture (i.e., lumen) for blood flow within the stent.
These and other objects will be apparent to those skilled in the art based on the disclosure herein.
There are several possible approaches to detecting in-stent restenosis according to the present invention. Stent structures have characteristic resonant behavior in their interaction with electromagnetic and or acoustic energy. These resonance features are influenced by the dimensions, structure, materials of the stent, as well as other features of the stent itself, and the surrounding materials and structures. Thus electromagnetic and or acoustic energy may be utilized to determine the physical properties of the stent itself, and the materials surrounding and enclosed by the stent.
The approaches to determining the in-stent restenosis may include, but are not limited to, the following:
1. RF excitation, Probing RF resonant modes, Detecting RF radiation. Using Radio Frequency EM energy to interrogate the stent, the frequency of the RF energy is scanned, and the response of the stent is detected, in reflection, absorption, scatter, or other characteristic EM phenomena, by detecting the modified RF ene
Collins Gilbert W.
Da Silva Luiz B.
Esch Victor C.
Hares Jonathan
Kilkenny Joseph D.
Lacyk John P.
Pearl Technology Holdings, LLC
Wooldridge John P.
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