Patent Description:
Catheters are widely used today in connection with a variety of intravascular medical procedures or treatments. One such widely adopted use or application of an intravascular catheter is in a thrombectomy medical procedure following an acute ischemic stroke (AIS) in which a sheath guide catheter (non-balloon guide catheter) or balloon guide catheter is introduced into the internal carotid artery to serve as a conduit for ancillary devices such as guidewire(s), microcatheter(s), stentriever(s) and intermediate catheter(s). The sheath guide catheter (non-balloon guide catheter) maintains access to the intended treatment location within a blood vessel and shortens procedural times by facilitating multiple passes with ancillary devices to the treatment location. Use of a balloon guide catheter provides the additional benefit, once inflated to an expanded state, of arresting blood flow and achieving complete apposition of the vessel. The blood flow arrest offers extra security in limiting the blood pressure exerted on the clot as well as maximizing the suction performance during the aspiration stage, as the stentriever and/or direct aspiration catheter retracts back into the balloon guide catheter with the captured clot. While such benefits are readily apparent and clinically proven, use of a balloon guide catheter requires somewhat arduous prepping steps be followed in ridding the inflating lumen and balloon of residual air to be replaced with a pressurized liquid inflating media. These prepping steps, performed prior to the introduction of the balloon guide catheter into the body, deter some physicians or interventionalists from using a balloon guide catheter altogether despite such advantages, instead choosing to employ a sheath guide catheter (non-balloon guide catheter) that doesn't require such prepping steps.

Prior to being introduced into the target vessel of the body, a conventional balloon guide catheter is prepped by the physician or interventionalist following a multi-step process to properly purge residual air trapped therein. This preparatory procedure typically calls for applying a vacuum or negative pressure at an inflation port to remove the residual air, followed immediately thereafter by dispensing of pressurized liquid inflation media back into the catheter. This step is repeated multiple times until no air is visible in the inflated balloon. If the purging steps are not followed correctly or skipped over entirely, the residual air in the balloon guide catheter may be exhausted into the blood vessel, in the event of a possible balloon failure, having a dangerous and harmful effect on the patient. <CIT> describes an apparatus and system for a heated ablation balloon. <CIT> described medical devices using electro sensitive gels.

It is therefore desirable to eliminate the need for a pressurized liquid inflation media to purge the balloon guide catheter of residual air thereby increasing the desirability and ease of use of the device while optimizing time efficiency as well reducing safety risks.

An aspect of the present invention is directed to an improved balloon catheter that eliminates the need for pressurized liquid inflation media to be dispensed/expelled in order to inflate/deflate, respectively, the balloon.

Another aspect of the present invention relates to an improved balloon catheter that substitutes thermally expandable material for the pressurized liquid inflation media to expand and contract the balloon.

Still another aspect of the present invention relates to an improved balloon catheter that eliminates the need for inflation/deflation lumen thereby maximizing the inner diameter of the catheter.

While still another aspect of the present invention is directed to a balloon catheter including a heating element disposed about a portion of an outer surface of a catheter shaft. A balloon is mounted about the outer surface of the catheter shaft to coincide with the heating element. Thermally expandable material is disposed inside the mounted balloon.

Yet another aspect of the present invention relates to a method for using in a medical procedure in a vessel the balloon catheter described in the preceding paragraph. The method including the steps of, while the thermally expandable material is in a thermally compressed state with the balloon having a reduced outer diameter, advancing the balloon catheter through the vessel to a target site. Thereafter, applying an electrical signal to the heating element generating heat causing the thermally expandable material to automatically expand and enlarge the outer diameter of the balloon occluding blood flow in a distal direction beyond the enlarged balloon.

While still another aspect of the present invention is directed to a method of manufacture of an assembled balloon catheter. A catheter shaft is provided having a proximal end, an opposite distal end and an outer surface. About a portion of the outer surface of the catheter a heating element is wrapped. Then, a balloon is positioned about the catheter shaft to coincide with the heating element. A volume defined between an inner surface of the balloon and the outer surface of the catheter shaft is then filled with thermally expandable material. Lastly, the balloon is mounted to the outer surface of the catheter shaft encapsulating therein the thermally expandable material while in the compressed state.

The foregoing and other features of the present invention will be more readily apparent from the following detailed description and drawings illustrative of the invention wherein like reference numbers refer to similar elements throughout the several views and in which:.

The terms "distal" or "proximal" are used in the following description with respect to a position or direction relative to the treating physician or medical interventionalist. "Distal" or "distally" are a position distant from or in a direction away from the physician or interventionalist. "Proximal" or "proximally" or "proximate" are a position near or in a direction toward the physician or medical interventionalist. The terms "occlusion", "clot" or "blockage" are used interchangeably.

The present inventive balloon catheter as defined in claim <NUM> eliminates altogether the need for a pressurized liquid inflation media (typically, a <NUM>% contrast saline solution) to be dispensed/expelled in order to inflate/deflate, respectively, the balloon. Instead, at the time of manufacture the balloon is filed with a thermally expandable material (e.g., thermally expandable liquid(s), thermally expandable solid(s) or any combination thereof) while in a thermally compressed (non-expanded) state that need not be exhausted/removed/expelled from the catheter thereafter. Referring to Figure 1A, the balloon catheter in accordance with the present invention includes a catheter shaft or body <NUM> having a proximal end <NUM> and an opposite distal end <NUM>. A heating element <NUM> is disposed about a portion of the outer surface of the catheter shaft or body <NUM> that coincides with a balloon <NUM> mounted proximate the distal end <NUM> of the catheter shaft <NUM>. The heating element <NUM> in Figure 1A is a wire, coil, strip or ribbon of electrically conductive material such as tungsten, platinum, nickel, titanium, nitinol or stainless steel. Electrical wires or leads electrically connect the heating element <NUM> to a power supply <NUM> providing electrical energy exciting the heating wire thereby producing or generating heat. In the exemplary embodiment depicted in Figure 1A the heating coil <NUM> is crisscrossed, but other configurations of the wrapping of the heating coil about the outer surface of the catheter shaft are contemplated and within the intended scope of the present invention. Where the heating coil is crisscrossed, the coil is insulated to prevent an electrical short from occurring.

Rather than being inflated or filled with a pressurized liquid inflation media that must later be expelled or purged via an inflation/deflation lumen during prepping of the catheter prior to introduction into the body, the balloon <NUM> of the present inventive catheter during manufacture is filled with a thermally expandable material such as thermally expandable liquids, thermally expandable solids or any combination thereof. Once the thermally expandable material, while in a compressed (non-expanded) state, has been introduced into the balloon, thereafter in order to transition the balloon back to its compressed/reduced/non-expanded state the thermally expandable material need not be removed, dispensed or purged from the catheter. Rather, the thermally expandable material automatically returns to its original compressed state (non-expanded state) upon removal or withdrawal of the heat. Typically, the thermally expandable material is a thermally expandable particle or microsphere. Furthermore, the thermally expandable solid may serve a dual purpose of heating coil and expandable material, wherein a stent (e.g., stent shaped like a sinusoidal wave pattern) is employed to facilitate greater expansion, as described in greater detail below.

<FIG> is a cross-sectional view of a single exemplary thermally expandable microsphere <NUM> that comprises an outer polymer shell such as thermoplastic resin <NUM> having a relatively low glass transition temperature (Tg) and a gas blowing agent (pressurized gas inner core) <NUM> encapsulated therein. The relatively low glass transition temperature may be in the range of approximately <NUM> to approximately <NUM>, preferably in the range of approximately <NUM> to approximately <NUM>, more preferably in the range of approximately <NUM> to approximately <NUM>. The gas blowing agent <NUM> may include hydrocarbons, pentane <NUM> or other gases. When the outer polymer shell <NUM> is heated above its glass transition temperature (Tg), the pressurized gas inner core <NUM> forces the outer polymer shell <NUM> to expand. The outer polymer shell <NUM> itself may also be encapsulated with an outer elastomeric shell <NUM> (e.g., thermoplastic polyurethane (TPU)) such that the outer elastomeric shell <NUM> compresses the thermoplastic shell <NUM> to recompress the contained pressurized gas <NUM> upon removal of heat from the heating element or source, the thermoplastic shell <NUM> having a memory to revert to its original smaller/reduced size when its temperature is lowered to a point below its softening point. An alternative configuration is depicted in <FIG> wherein the outer polymer shell is formed of a single elastomeric shell <NUM>' (e.g., thermoplastic polyurethane (TPU), styrene-ethylene-butylene-styrene (SEBS) or other elastomers) such that when heated above a softening point, the compressed gas inner core <NUM> expands the elastomeric shell <NUM>' to inflate the balloon. It is advantageous to supply the thermally expanding pressurized gas contained in numerous microspheres to limit exposure to gas leakage in the event of a failure if the gas was supplied in a single larger sphere or balloon. Each of the microspheres may range from approximately <NUM> to approximately <NUM>, preferably from approximately <NUM> to approximately <NUM>, more preferably from approximately <NUM> to approximately <NUM>.

During manufacture, the heating coil <NUM> is wrapped about a portion of the outer surface of the catheter shaft <NUM> that coincides with the positioning of the balloon <NUM> to be mounted thereafter to the outer surface of the catheter shaft. In the exemplary embodiment shown in Figure 1A, the heating coil <NUM> is wrapped in a crisscross configuration but other arrangements or designs are contemplated and within the intended scope of the present invention. As the balloon is being mounted to the outer surface of the catheter shaft during manufacture, the volume between the balloon <NUM> and catheter shaft <NUM> is filled with thermally expandable material <NUM>, while the thermally expandable material is in a compressed (non-expanded) state. After being filed with the thermally expandable material <NUM>, the balloon <NUM> is then mounted, bonded, welded or otherwise secured to the outer surface of the catheter shaft <NUM> using conventional techniques. Once assembled, the balloon catheter comprises the heating coil <NUM> disposed between the outer surface of the catheter shaft <NUM> and the inner surface of the balloon <NUM>. The mounted balloon may be tightly wrapped about the outer surface of the catheter shaft for minimizing profile delivery or alternatively, a pliable and/or loose balloon may be utilized such that when the thermally expandable material is in its compressed (non-expanded) state, the balloon is free to contort in an atraumatic manner as it is being advanced through tortuous vasculature and when the thermally expandable material is in its expanded state, the balloon becomes taught to fully oppose the vessel and arrest blood flow. Furthermore, the thermally expandable material disposed inside the balloon during manufacture or assembly is contained therein, never being removed from nor more added to the balloon thereafter. That is, at no time during prepping or thereafter introduction of the catheter in the body is anything introduced into or purged from inside the balloon. The assembled balloon catheter is introduced into the vessel while the thermally expandable material is in a compressed (non-expanded) state so that the balloon has a minimum outer diameter advanceable through the vessel to the target site in the body.

Upon reaching the target site in the vessel, an electrical signal generated by the power source <NUM> is applied to the heating coil <NUM> generating heat which radiates outward. The heat produced by the heating element <NUM> causes the thermally expandable material such as a thermoplastic outer shell <NUM> of the thermally expandable microspheres <NUM> to soften and expand under pressure of the inner core <NUM> thereby expanding the outer diameter of the thermally expandable microspheres which, in turn, expands or increases the outer diameter of the balloon <NUM>. Alternatively, heat produced by the heating coil <NUM> causes a thermally expandable liquid or gel <NUM> to expand in volume which, in turn, expands or increases the outer diameter of the balloon <NUM>, as shown in <FIG>. In another embodiment illustrated in <FIG>, the heat produced by the heating coil <NUM> causes a metallic stent like frame <NUM> disposed within the balloon to expand which, in turn, expands or increases the outer diameter of the balloon <NUM>. In yet another embodiment, the heating coil <NUM> itself is formed from a shape memory metal with high impedance, such as Nitinol, and the heat generated from the heating coil causes the heating coil to revert to a shape previously set through conventional shape setting techniques, the pre-set shape having a larger diameter than the compressed balloon which expands or increases the outer diameter of the balloon <NUM>. Where a taught elastic balloon is incorporated into the catheter, the force exerted by the expandable material is greater than the force required to stretch the biased closed balloon to an expanded state. In its expanded state, the outer walls of the balloon physically contact the inner walls of the vessel occluding blood flow distally beyond the inflated balloon. Prior to withdrawal of the balloon catheter from the body, the electrical signal provided by the power source to the heating element is cut off allowing the thermally expandable material to cool/reduce/lower in temperature and automatically compress (reduce in outer diameter) allowing the balloon, in turn, to reduce in outer diameter as well. Upon the balloon returning to its compressed (non-expanded) state, the balloon may be easily removed in a proximal direction from the body.

Numerous advantages are provided with the current configuration of the balloon catheter, some of which are discussed in detail below. The thermally expandable material(s) are dispensed into the balloon at the time of manufacture/assembly of the catheter and thereafter remain in the balloon at all times thereafter.

Accordingly, the need for both an inflation lumen and/or exhaust lumen defined in the catheter shaft of conventional balloon catheters for inflating the balloon using a pressurized liquid inflation media and thereafter exhausting the pressurized liquid inflation media in order to deflate the balloon prior to removal from the body has been eliminated. Since the need for an inflation/deflation lumen has been eliminated, the inner diameter may be maximizable to accommodate ancillary devices having a larger diameter. Still another benefit is that residual air need not be purged from the balloon itself thereby reducing prepping time making the device simpler and more desirable to use. Yet another advantage is that the conductive heating wire may serve the dual function of reinforcing the catheter shaft. Arranging the conductive heating wire in or as part of a braid, coil, or longitudinal brace pattern enhances the kink resistance, pushability and torqueability of the catheter shaft providing optimized and varied stiffness anywhere axially along the catheter from its proximal end to its distal end.

Claim 1:
A balloon catheter comprising:
a catheter shaft (<NUM>) having a proximal end, an opposite distal end and an outer surface;
a heating element (<NUM>, <NUM>, <NUM>, <NUM>) disposed about a portion of the outer surface of the catheter shaft (<NUM>);
a balloon (<NUM>, <NUM>, <NUM>, <NUM>) mounted about the outer surface of the catheter shaft (<NUM>) to coincide with the heating element (<NUM>, <NUM>, <NUM>, <NUM>); and
thermally expandable material disposed inside the mounted balloon (<NUM>, <NUM>, <NUM>, <NUM>), wherein the thermally expandable material is a thermally expandable solid, a thermally expandable liquid or a combination thereof and wherein heat produced by the heating element causes the thermally expandable material to expand, thereby increasing the outer diameter of the balloon.