Prosthesis (i.e. – artificial body members) – parts thereof – or ai – Arterial prosthesis
Reexamination Certificate
1999-06-30
2002-03-26
Willse, David H. (Department: 3738)
Prosthesis (i.e., artificial body members), parts thereof, or ai
Arterial prosthesis
C128S899000
Reexamination Certificate
active
06361554
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to medical devices and methods. More particularly, the present invention relates to methods and apparatus for enhancing and localizing the delivery of vibrational energy to internal body target sites, such as sites within the vasculature at risk of hyperplasia.
A number of percutaneous intravascular procedures have been developed for treating atherosclerotic disease in a patient's vasculature. The most successful percutaneous treatment is percutaneous transluminal angioplasty (PTA) which employs a catheter having an expansible distal end, usually in the form of an inflatable balloon, to dilate a stenotic region in the vasculature to restore adequate blood flow beyond the stenosis. Other procedures for opening stenotic regions include directional atherectomy, rotational atherectomy, laser angioplasty, and the like. While these procedures, particularly PTA, have gained wide acceptance, they continue to suffer from the subsequent occurrence of restenosis.
Restenosis refers to the re-narrowing of an artery within weeks or months following an initially successful angioplasty or other primary treatment. Restenosis afflicts up to 50% of all angioplasty patients and results at least in part from smooth muscle cell proliferation in response to the injury caused by the primary treatment, generally referred to as “hyperplasia.” Blood vessels in which significant restenosis occurs will require further treatment.
A number of strategies have been proposed to treat hyperplasia and reduce restenosis. Such strategies include prolonged balloon inflation, treatment of the blood vessel with a heated balloon, treatment of the blood vessel with radiation, the administration of anti-thrombotic drugs following the primary treatment, stenting of the region following the primary treatment, and the like. While enjoying different levels of success, no one of these procedures has proven to be entirely successful in treating all occurrences of restenosis and hyperplasia.
Of particular interest to the present invention, the use of stents has shown great promise for the reduction of restenosis, particularly in the time period immediately after angioplasty or other primary interventional treatment. Even the use of stents, however, is subject to hyperplasia where the lumen defined by the stent becomes occluded, typically within months following the stent placement.
For that reason, the inhibition of hyperplasia following stent placement has become an area of significant research and commercial effort. For example, it has been proposed to expose a stented region within the vasculature to radiation from radioisotopes in order to inhibit hyperplasia. While initial data appear promising, the need to employ radioisotopes is problematic for the patient, the treating staff, and the hospital which must maintain and dispose of the radioisotopes. As an improvement over the use of radioisotopes, the use of catheters for delivering ultrasonic energy to an angioplasty and/or stent placement site has also been proposed. See, U.S. Pat. No. 5,836,896, and copending application Ser. No. 09/223,230. The latter is commonly assigned with the present application, and its full disclosure is incorporated herein by reference.
While the delivery of radiation, ultrasonic energy, and possibly other forms of energy, by catheter immediately following angioplasty, stent implantation or other interventional procedures appears to be at least partially effective, it has been noted that hyperplastic activity reaches a peak several days following the initial intervention. Thus, ameliorative treatment immediately following the initial intervention may be ill-timed. It is possible that treatment delayed by one or more days after the initial intervention would be more effective. Moreover, it may be desirable to treat the interventional site multiple times following the interventional procedure, possibly over a period of days, weeks, or even months. The need to reintroduce a treatment catheter, however, makes such delayed and repetitive treatment much less feasible.
For these reasons, it would be desirable to provide alternative and improved methods and apparatus for the treatment and inhibition of hyperplasia in blood vessels following placement of a stent or other vascular prosthesis. It would be particularly desirable to provide methods and apparatus for the delivery of acoustic or vibrational energy to a target site within the vasculature or elsewhere where a stent, graft, or other device has been previously implanted. Such methods and apparatus should permit non-invasive delivery of the acoustic energy to the target site and preferably facilitate localization of the energy at the target site. Such methods and apparatus should be suitable for treatment of the vasculature, particularly following placement of a stent or other vascular prosthesis, and should also find use in virtually any situation where an artificial structure has been implanted at a target site within the patient's body.
2. Description of the Background Art
U.S. Pat. No. 5,836,896, and copending application Ser. No. 09/223,230, have been described above. Intravascular inhibition of hyperplasia by exposure to radioisotopes is described in a number of patents and publications, including U.S. Pat. Nos. 5,616,114; 5,302,168; 5,199,939; and 5,059,166. The therapeutic application of ultrasonic energy is described in a number of patents and publications including U.S. Pat. Nos. 5,362,309; 5,318,014; 5,315,998; and others. A high frequency ultrasonic catheter employing an air-backed transducer is described in He et al. (1995) Eur. Heart J. 16:961-966.
SUMMARY OF THE INVENTION
The present invention provides methods and apparatus for non-invasive delivery of vibrational energy to target sites within a patient's body. The target sites will be defined by the prior implantation of a structure having pre-selected mechanical characteristics which allow at least a portion of the structure to resonate when excited by externally applied acoustic energy. In the exemplary embodiment, the implanted structure is a stent (as defined below), but it could also be a vascular graft, filter, valve, or other type of structure which is known to be implanted within the vasculature for therapeutic or diagnostic purposes. In all cases, the structure will be modified to resonate at a pre-selected frequency when the structure is exposed to externally applied acoustic energy at a suitable excitation frequency. In addition to vascular structures, the methods of the present invention are suitable for use with a variety of non-vascular implanted structures where it is desired to deliver and localize vibrational energy to a subcutaneous target site. For example, resonant structures may be implanted at or near tumor sites in order to localize and facilitate the delivery of vibrational energy to such sites, typically to induce heating and hyperthermic treatment of the site.
In the case of stents and other vascular structures, the purpose of the treatment will usually be to inhibit hyperplasia, most usually inhibiting hyperplasia within a stent or vascular graft. In the case of stents, the materials, geometries, and other design features will be selected to allow at least a portion of the stent, typically the entire stent, to resonate at a relatively low frequency, typically from 5 kHz to 500 kHz, preferably from 50 kHz to 100 kHz. The frequency, power, duty cycle, and other characteristics of the acoustic energy being delivered from an external source to the stent will be selected to be compatible with the stent characteristics. Typically, the excitation frequency will be within the range from 5 kHz to 500 kHz, preferably from 50 kHz to 100 kHz, while the intensity level (spatial peak temporal average; SPTA) measured at the tissue surface through which the energy is being delivered will be in the range from 0.01 W/cm
2
to 1000 W/cm
2
, preferably from 0.5 W/cm
2
to 50 W/cm
2
. The acoustic energy may be applie
Pharmasonics, Inc.
Stewart Alvin
Willse David H.
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