Surgery: light – thermal – and electrical application – Light – thermal – and electrical application – Thermal applicators
Reexamination Certificate
2000-02-09
2002-12-17
Nasser, Robert L. (Department: 3736)
Surgery: light, thermal, and electrical application
Light, thermal, and electrical application
Thermal applicators
C128S898000, C606S033000, C606S042000, C607S122000, C607S156000
Reexamination Certificate
active
06496736
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to methods and apparatus for using arterial blood pressure to dilate the lumen rather than expanding/cutting mechanical means so as to preserve the sensitive endothelial lining of the artery. More specifically, the present intention relates to production of a temperature profile within the arterial wall that corresponds to the atherosclerotic lesion size, shape, and position so as to necrose (ablate) connective tissue and soften plaque to thereby impart increased flexibility to the arterial
2. Description of Prior Art
Atheroscleroses, also known as hardening of the arteries, is one of the most common types of heart disease. Each year several hundred thousand people die of this disease or of complications relating thereto. By the age of forty, many people have already developed atherosclerotic lesions although no symptoms may appear. Atherosclerosis is a progressive disease wherein fatty, fibrous, calcific, or thrombotic deposits produce atheromatous plaques within the arterial walls as indicated generally in FIG.
11
. Moreover, atherosclerosis tends to involve large and medium sized arteries such as the aorta, iliac, femoral, cerebral, as well as the coronary artery.
The atherosclerotic lesions are substantially comprised of plaque and scar tissue. The plaque is typically encapsulated within living connective tissue. Plaque is a heterogenous material, sometimes non-living, that may include calcified, wax-like. fibrotic, fatty, and brittle components. As the lesions within the arterial, walls grow in size, the lumen or passageway through the coronary artery may be correspondingly reduced in effective cross-sectional diameter (stenosis). The constricted (stenotic) lumen may then restrict the nutrient blood flow to muscles of the heart. Therefore, atheroscleroses is often a major contributing factor in both acute and chronic heart problems. Also, when the lumen is sufficiently narrowed, the rate of blood flow may be so diminished that an affixed blood clot (thrombus) or circulating blood clot (embolus) may spontaneously occur. Thus, the presence of atherosclerotic plaque not only reduces blood flow to the heart muscle but also is a major predisposing factor in coronary thrombosis.
While pharmacological treatment is often used to treat atherosclerosis, such treatment is sometimes considered to be insufficiently effective for increasing blood flow. Therefore, techniques such as balloon angioplasty (percutaneous transluminal coronary angioplasty) have been developed to mechanically increase the luminal opening.
However, mechanical techniques tend to traumatize the artery and often result in restenosis (reclosing of the lumen). Standard balloon angioplasty produces a gross trauma that severely injures the endothelium or lining of the artery. The endothelium is a very fragile layer of cells that performs the very important function of limiting thrombotic processes (See FIG.
12
). Unlike other surfaces and materials, when blood cells come in contact with the endothelium there is no tendency to form a clot. The layer of endothelial cells normally covers the internal surface of all vessels, rendering the vessel surface compatible, i.e., non-thrombogenic and non-reactive with blood. If the endothelium is damaged, platelet deposition becomes a problem. Once this layer is injured, it does not normally row back uniformly and so damage thereof tends to permanently induce thrombotic processes. Injury to the endothelium has been associated with accelerating of atherosclerotic processes and/or restenosis.
At least one patent discussed hereinafter teaches to alleviate, at least to some extent, damage caused to the endothelium by providing a bioprotective layer around the angioplasty balloon to cushion, coat, and insert anti-inflammatory agents prior to opening the balloon. Another patent discussed hereinafter teaches reducing trauma damage to the endothelium by reducing angioplasty balloon pressure using heat and feedback control. However, due to the mechanical forces in balloon angioplasty, damage to the fragile endothelium may still occur. The bioprotective coatings may, according to the patent teachings, also reduce problems created by angioplasty-induced tissue tears or cleavages that can result in blood accumulation along the cleavage planes of arterial wall layers. The thickening caused during such problems may acutely block or occlude the arterial lumen and require emergency interventions such as stents or open heart surgery.
The trauma to the endothelium and to arterial walls from balloon angioplasty often evoke a potent inflammatory response, or restenosis (reclosing of the artery), whereby scar tissue growth and other processes occur to once again reduce the arterial lumen opening. As discussed in some detail below with respect to numerous different techniques, restenosis is probably one of the most significant problems that occurs with existing techniques for dilating or opening the arteries. Restenosis may occur due to numerous processes including the following: clots that crow gradually or contain growth hormones released by plateletes within the clot, clots formed due to exposure to collagen (connective tissue) which is highly thrombogenic, growth hormones released by other cells that cause smooth muscle cells and fibroblasts in the region to multiply, tears in the artery wall that expose blood to foreign material and proteins thereby producing clots, white cells that migrate to the area and lay down scar tissue, growth of new tissue due to any, kind of inflammatory response, and/or other factors that may cause the artery lumen to reclose. Several different processes may operate simultaneously to cause restenosis.
After balloon angioplasty procedures, narrowing of the artery by 50% may occur in more than one-half of the patients and about one quarter of the patients may require a repeat procedure by the end of one year. As mentioned above, restenosis (reclosing of the artery) remains a major problem in treatment of atherosclerosis by balloon angioplasty. While significant efforts have been made to dampen the reactive proliferation with a variety of pharmacological and genetic interventions, these interventions have thus far found limited or no successful clinical application.
Another problem with balloon angioplasty relates to the fact that the lesions, or atheromas, within arterial cross-sections are typically asymmetrically distributed. That is to say the lesions often occur on one side, portion, or sector of the artery while an opposite or adjacent sector of the artery is relatively free of the disease. It was initially postulated that the increase in endovascular pressure created with a balloon would somehow selectively crush lesions. However, given that the thick-walled sectors containing atheromas are typically abundant with dense collagen or connective tissue, the lesions may actually be less likely to undergo deformation than the opposite relatively thin-walled, lesion-free sectors. Thus, the maximum trauma produced by balloon angioplasty may well occur in the healthy sector of the artery. Some of the patents discussed hereinafter attempt to reduce, at least to some extent, this problem and related problems by first heating the artery to soften the plaque. However, unless the heating is applied selectively to the atheromas heat damage may occur to the artery and endothelium. As well, mechanical trauma may still occur to the endothelium and or other arterial components.
Acute closure of the lumen after balloon angioplasty remains the most common cause of failed angioplasty and occurs in approximately 5% of the patients. This complication may be associated with varying degrees of mortality that may exceed 50% when emergency coronary bypass surgery has to be performed.
For the above reasons, balloon angioplasty is often problematic due to restenosis or, less frequently, abrupt closure. Therefore, other catheter techniques for the mechanical widening of the lumen of diseased coronary arteries
Arndt G. Dickey
Beer N. Reginald
Carl James R.
Fink Patrick W.
Henry Phillip D.
Barr Hardie R.
Nasser Robert L.
The United States of America as represented by the United States
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