Surgery – Instruments – Electrical application
Reexamination Certificate
2000-11-30
2004-01-20
Dvorak, Linda C. M. (Department: 3739)
Surgery
Instruments
Electrical application
C607S104000, C607S105000
Reexamination Certificate
active
06679879
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to medical devices and techniques, and more particularly to catheter systems and medical interventions for treating elongate occluded regions in vascular coronary artery grafts. The inventive catheter system is adapted for capturing and extracting embolic fragments that typically develop in any endovascular intervention. The catheter system utilizes sequences of micro-electrical discharges in catheter channels to (i) remove occlusive materials from the vessel walls around a treatment site; (ii) generate fluid extraction forces; and (iii) to emulsify or ablate large fragments of dislodged occlusive materials, thus allowing the emboli extraction system to be fabricated in a very small diameter catheter.
2. Description of Related Art
Vascular grafts in coronary artery bypass procedures (CABG) often become occluded over time by plaque, thrombus, or other deposits that can significantly reduce blood flow through the graft. In such bypass grafts, the occlusions are frequently diffuse and elongate making medical interventions problematic. It has been found that conventional treatments of such saphenous vein bypass grafts (e.g., balloon angioplasty, atherectomy, etc.) can cause significant risk of embolisms by dislodging occlusive material that can then migrate downstream. If an embolism occurs at a critical location in the patient's circulatory system, a permanent injury or even death may occur.
The risk of embolism also is prevalent in medical interventions to treat occlusions in native vessels. For example, it is known that stent deployment often leads to the dislodgement of embolic fragments. In some occlusions in native vessels, such as the carotid arteries, the risks of emboli reaching the brain are so significant that catheter-based treatments of such occlusions are rarely practiced.
Various endovascular catheter systems have been developed for treating occluded vascular grafts and for capturing embolic material during the intervention. As an example, it is believed that the leading candidate for commercialization is an assembly of concentric catheter sleeves that allows for irrigation and aspiration of fluids from a vessel that is temporarily blocked upstream and downstream by inflatable balloons, using an assembly of catheter sleeves as depicted in FIG.
1
A. The irrigation and aspiration systems provide a looped flow of fluid (e.g., saline) through inflow and outflow pathways between the various catheter sleeves wherein the pathways communicate with external positive and negative pressure sources. The arrangement of concentric catheters of
FIG. 1A
was disclosed by Zadno-Azizi et al. in U.S. Pat. No. 6,022,336. In using the type of catheter assembly just described, the physician is supposed to use the intermediate catheter to carry an additional functional component for performing a medical intervention, such as an angioplasty or any other form of treatment. Such treatments may dislodge emboli between the upstream and downstream balloons. The contemporaneous in-and-out irrigation and aspiration of fluids is then intended to flush any embolic particles from the treatment region between the balloons. In order understand the shortcomings of this type of catheter assembly that relies on external irrigation ration systems, it first is necessary to describe the operating parameters of a typical intervention—in terms of (i) the dimensions of the operating space within the vessel and (ii) the dimensions of potential emboli that must be captured and removed
The principal difficulty in designing an interventional catheter system for controlling emboli in vascular grafts relates to the small size of a typical bypass graft. A saphenous vein graft in a CABG procedre has a lumen diameter ranging between about 3 mm. and 4 mm., although some grafts can range to about 5 mm. to 6 mm. Thus, the outside diameter of a catheter system must be small enough to navigate 3 mm. or 4 mm. lumens, and preferably much smaller to treat vessels with smaller lumens, and to pass through the partially occluded lumen of a graft.
The other important consideration in such an intervention treatment relates to the crosssectional dimensions of potential embolic fragments. It is postulated that the most dangerous emboli have cross-sections ranging from greater that a few hundred micrometers &mgr;m), for example, from about 200 &mgr;m or 300 &mgr;m to about 600 &mgr;m Certainly, smaller emboli are common and also are targeted for capture and removal—but particles in the range of 50 &mgr;m or less may not prove as dangerous as larger emboli since they may pass through the blood stream. Therefore, the catheter system of the type shown in
FIG. 1A
ideally would have an emboli extraction pathway with a cross-section capable of extracting 500 &mgr;m to 600 &mgr;m particles without clogging.
As one can easily understand, it is problematic to construct a catheter assembly that has an outer diameter of significantly less than about 3 mm. and still provide an inner lumen diameter of 600 &mgr;m or more for extracting emboli—particularly when the catheter will require as many as four other inflow/outflow channels or lumens. A second channel will be required for irrigation; third and fourth channels will be required for inflating the proximal and distal balloons; and in most cases, a fifth channel will be required to accommodate a guidewire. Another sixth channel within the working end will be required if the intervention is time-consuming so that blood perfusion around the balloon assembly is needed. Even if the desired functionality associated with the above described five or more lumens could be packaged in a 3.0 mm. cross-section catheter, the overall system still would be much larger than optimal. As can be seen in
FIG. 1A
, the external dimension of the outer catheter is too large to for easy navigation through a typical blood vessel targeted for treatment. The system of
FIG. 1A
also has several other serious drawbacks, as will be described next.
In order to better understand the functionality of the prior art catheter assembly of
FIG. 1A
, it is necessary to explain the parameters for providing “optimized paths for irrigation and aspiration” as proposed in U.S. Pat. No. 6,022,336. Further, it is necessary to analyze real-world dimensions of a typical treatment space. For this reason, TABLE A is provided below, which along with
FIGS. 1A & 1B
, describe the practical dimensions of an exemplary catheter assembly of the type proposed in U.S. Pat. No. 6,022,336.
The figures in TABLE A are listed in or &mgr;m (i.e., micrometers with an approximation in inches) to allow reference to emboli dimensions which are typically given in micrometers. For the catheter assembly of
FIGS. 1A-1B
to function optimally in capturing and removing emboli, there are essentially three dimensional factors that must be considered: (i) the radial dimension of the free space between the catheter's exterior and the vessel wall to allow fluid flows therein to remove, capture and entrain emboli; (ii) the cross-sectional dimension of the fluid irrigation pathway within the catheter assembly to allow sufficient fluid inflows; and (iii) most importantly, the cross-sectional dimension of the extraction pathway within the catheter assembly to allow embolic fragment to flow therethrough to the remote handle of the catheter.
As discussed above, consider that the typical vessel lumen targeted for treatment is either 3 mm. or 4 mm. (i.e., 3000 &mgr;m to 4000 &mgr;m) as indicated in TABLE A The dimensions of the exemplary catheter assembly are best aggregated from the inner catheter outwardly. The inner catheter sleeve indicated at 4 in
FIGS. 1A-1B
has a lumen diameter of 500 &mgr;m to place over a typical 0.014″ guidewire. As can be seen in
FIG. 1A
, this catheter sleeve
4
requires a balloon inflation lumen in a thickened wall portion that results in an outer catheter sleeve diameter of about 960 &mgr;m.
FIG. 1A
shows the irrigation pathway comprising
Dvorak Linda C. M.
Schopfer Kenneth G
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