Patent Application
20120101515
The invention relates to the field of intravascular medical devices, and more particularly to devices for detecting and preventing over-pressurization of a balloon catheter.
In percutaneous transluminal coronary angioplasty (PTCA) procedures, a guiding catheter is advanced until the distal tip of the guiding catheter is seated in the ostium of a desired coronary artery. A guidewire, positioned within an inner lumen of a dilatation catheter, is first advanced out of the distal end of the guiding catheter into the patient's coronary artery until the distal end of the guidewire crosses a lesion or obstruction to be dilated. The dilatation catheter having an inflatable balloon on the distal portion thereof is then advanced into the patient's coronary anatomy, over the previously introduced guidewire, until the balloon of the dilatation catheter is properly positioned across the lesion or obstruction. Once properly positioned, the dilatation balloon is inflated with liquid one or more times to a predetermined size at relatively high pressures (e.g., greater than 8 atmospheres) so that the stenosis is compressed against the arterial wall and the wall expanded to open up the passageway. Generally, the inflated diameter of the balloon is approximately the same diameter as the native diameter of the body lumen being dilated so as to effect the dilatation without over-expanding the arterial wall. Substantial, uncontrolled expansion of the balloon against the vessel wall can cause trauma to the vessel wall. After the balloon is finally deflated, blood flow may resume through the dilated artery and the dilatation catheter can be withdrawn from the patient.
In such angioplasty procedures, there may be restenosis of the artery, i.e. reformation of the arterial blockage, or obstructions that cannot be resolved by inflation of the balloon alone. These conditions often necessitate either another angioplasty procedure, or some other method of repairing, strengthening, or unblocking the dilated area. To reduce the restenosis rate and to strengthen or unblock the dilated area, physicians frequently implant an intravascular prosthesis, generally called a stent, inside the artery at the site of the lesion. Stents may also be used to repair vessels having an intimal flap or dissection or to generally strengthen a weakened section of a vessel. Stents are usually delivered to a desired location within a coronary artery in a contracted condition on a balloon of a catheter which is similar in many respects to a balloon angioplasty catheter and expanded to a larger diameter by expansion of the balloon. The balloon is deflated to remove the catheter and the stent left in place within the artery at the site of the dilated lesion.
In the design of catheter balloons, balloon characteristics such as strength, flexibility and compliance must be tailored to provide optimal performance for a particular application. Angioplasty and stent delivery balloons preferably have high strength for inflation at relatively high pressure, and high flexibility and softness for improved ability to track the tortuous anatomy and cross lesions. The balloon compliance is chosen so that the balloon will have the required amount of expansion during inflation. Compliant balloons, for example balloons made from materials such as polyethylene, exhibit substantial stretching upon the application of a tensile force. Noncompliant balloons, for example balloons made from materials such as PET, exhibit relatively little stretching during inflation, and therefore provide controlled radial growth in response to an increase in inflation pressure within the working pressure range. However, noncompliant balloons generally have relatively low flexibility and softness, making it challenging to provide a low compliant balloon with high flexibility and softness for enhanced catheter trackability. A compromise is typically struck between the competing considerations of softness/flexibility and noncompliance, which, as a result, has limited the degree to which the compliance of catheter balloons can be further lowered.
The latest generation of balloon and stent delivery systems provides the most deliverable, lowest profile devices yet for cardiologists to treat patients. Cardiologists are able to access and deliver balloons to the most distal, challenging legion types than ever before. This has led to an increasing demand for higher and higher balloon and stent delivery systems balloon rated burst pressures. Often the desired pressures exceed twenty (20) atmospheres.
In this procedure, cardiologists very often inflate the balloon and stent catheters beyond their rated burst pressure. This is usually done to achieve a better PTCA result for the patient and the physicians rely on the rated burst pressure to have a known factor of safety incorporated therein. It is widely held that the risk is low for small increases over the rated burst pressure. Because of this prevalence to overinflate the balloons, when a balloon does burst it is difficult for the manufacturer to evaluate whether there was a flaw in the design or whether the balloon was simply over-inflated by the physician.
Further, balloon and stent delivery systems are designed from a safety stand point to fail, under hydraulic pressure, at the balloon and not the chassis. There is a considerably higher patient risk associated with catheter chassis failures for rupture compared to balloon burst failures. This requires the chassis to be designed to statistically withstand a significantly higher burst pressure compared with balloons. This design requirement can limit the material choices and dimensions needed for best catheter deliverability and low profile performance. The latest multiple layer balloon technologies allow for even higher rated burst pressures, which challenges the current technology to create chasses able to withstand even higher burst pressures and maintain safety needed for the balloon to fail before the chassis.
The present invention is directed to devices and methods for detecting over-pressurization of a catheter, either in situ or post-procedure. In situ devices can alert a physician to the possible risk of rupture of the catheter, which post-procedure devices allow a forensics evaluation of why a catheter may have failed during an operation. For example, in one preferred embodiment, a catheter incorporates a force-sensitive polymer that can change color when mechanically stressed to form a catheter chassis. In some stress-induced color changing materials, force-sensitive polymers contain mechanically active molecules called mechanophores. When stretched with a certain force, specific chemical reactions are triggered in the mechanophores. Mechanophores contain molecules called spiropyrans capable of vivid color changes when they undergo mechanically induced stress. Normally colorless, the spiropyran turns, for example, red or purple when exposed to certain levels of mechanical stress. Other types of mechanophores can also be used. This material can be used within or in conjunction with a catheter's luer assembly or catheter chassis, and the mechanophores are selected so as to indicate (i.e., color change) above a predetermined internal pressure on the catheter. If the mechanophore was selected to indicate above the rated burst pressure of the catheter and the catheter failed, a forensic review of the catheter would quickly determine whether the failure was due to the cardiologist over-pressurizing the catheter beyond the rated burst pressure or whether the catheter failed for some other reason. This would provide invaluable feedback to both the practitioner as well as the catheter's manufacturer or complaint investigation team regarding the cause of the failure as well as ways to correct the problem.
Alternatively, existing polymers may be used to form structure that will mechanically deform at a certain internal pressure of the catheter. For example, a portion of the catheter luer that is exposed to the chassis internal pressure and located within view of the cardiologist during catheter balloon inflation can be designed to physically deform under a specified pressure. The structure could have a wall thickness or wall section designed to deform above a selected pressure. The deformation could be a permanent deformation caused by exceeding the yield point of the material and this could also cause discoloration. The inflation/deflation and operation of the catheter would not ordinarily be compromised by this deformation in a preferred embodiment. There could also be a tactile deformation that could be felt as well as observed.
A third embodiment involves the use of a pressure relief valve that is designed to open and relieve applied pressure above a certain material stress. The valve would close and maintain inflation/deflation integrity below the designated maximum material stress. The valve would also preferably include a visual indication that the relief valve was actuated, alerting the physician and/or the manufacturer in the case where there was a failure of the catheter or for collecting data about the procedure.
In the illustrated embodiment, the shaft 11 comprises an outer tubular member 19 which cooperates with an inner tubular member 20 to define the inflation lumen 21, and where the inner tubular member 20 further defines the guidewire lumen 22 as seen in
Although not illustrated, the balloon 14 of the invention typically has a deflated configuration with wings wrapped around the balloon to form a low profile configuration for introduction and advancement within a patient's body lumen. As a result, the balloon 14 inflates to a nominal working diameter by unfolding and filling the molded volume of the balloon.
Balloon 14 has a first layer 30, and a second layer 31 which is an inner layer relative to the first layer 30. In the illustrated embodiment, the second layer 31 is on an inner surface of the balloon 14 with the first layer 30 defining an outer surface of the balloon 14 and the second layer 31 defining an inner surface of the balloon 14. However, the balloon 14 of the invention can alternatively have more or fewer layers. Additional layer(s) increase the dimensions of the tube/balloon formed therefrom to a desired value, and/or can be used to provide an inner or outer surface of the balloon with a desired characteristic. Therefore, it should be understood that the balloon 14 of the invention discussed below has at least two layers, and optionally includes one or more additional layers, unless otherwise noted as having a specified set number of layers.
A variety of suitable materials can be used to form the balloon layers 30, 31. In one embodiment, the first and second polymeric materials are elastomers providing a relatively low flexural modulus for balloon flexibility, although nonelastomers can alternatively be used. Presently preferred materials are from the same polymeric family/class such as polyamides including nylons and polyether block amides (PEBAX). Forming the layers of compatible polymeric materials allows for heat fusion bonding the layers together. The layers can alternatively be formed of different polymer classes which are not sufficiently compatible to fusion bond together, in which case a tie layer is typically provided between the outer and inner layers 30, 31 to bond the balloon layers together. For example, a PET inner layer and a PEBAX outer layer typically have a tie layer of an adhesive polymer such as Primacor (a functionalized polyolefin) therebetween. With all balloon catheters, however, it is a primary objective that the balloon, regardless of the materials used to form the balloon, should fail before the catheter chassis fails. If the balloon fails, the catheter can still be withdrawn from the patient and the procedure repeated with a new catheter. However, if the catheter chassis fails and part of the catheter becomes lodged in the patient's vascular, a potentially life threatening condition could result.
The dimensions of catheter 10 are determined largely by the size of the balloon and guidewire to be employed, the catheter type, and the size of the artery or other body lumen through which the catheter must pass or the size of the stent being delivered. Typically, the outer tubular member 14 has an outer diameter of about 0.025 to about 0.04 inch (0.064 to 0.10 cm), usually about 0.037 inch (0.094 cm), and the wall thickness of the outer tubular member 14 can vary from about 0.002 to about 0.008 inch (0.0051 to 0.02 cm), typically about 0.003 to 0.005 inch (0.0076 to 0.013 cm). The inner tubular member 16 typically has an inner diameter of about 0.01 to about 0.018 inch (0.025 to 0.046 cm), usually about 0.016 inch (0.04 cm), and a wall thickness of about 0.004 to about 0.008 inch (0.01 to 0.02 cm). The overall length of the catheter 10 may range from about 100 to about 150 cm, and is typically about 143 cm. Preferably, balloon 24 has a length about 0.8 cm to about 6 cm, and an inflated working diameter of about 2 to about 5 mm.
The various components may be joined using conventional bonding methods such as by fusion bonding or use of adhesives. Although the shaft is illustrated as having an inner and outer tubular member, a variety of suitable shaft configurations may be used including a dual lumen extruded shaft having a side-by-side lumens extruded therein. Similarly, although the embodiment illustrated in
To accomplish the objects of the present invention, a first embodiment is shown in
Alternatively, the adapter 100 or the nose piece 105 can deform mechanically as a result of the pressure without actually changing color, such as forming a bulge or bubble if the pressure becomes too high. This deformation can alert the doctor that the inflation pressure has exceeded the recommended pressure, but does not jeopardize the integrity of the catheter. In
a-c illustrate an alternative embodiment employing a check valve 140 as a safety measure to ensure that the maximum allowable internal pressure in the inflation lumen and balloon 14 is not exceeded. The check valve 140 is designed to allow air or gas to escape when a predetermined pressure is achieved to prevent over-pressurization. The check valve 140 includes a chamber 145 with vent holes that allow a gas to escape when it enters the chamber. A plug 150 is biased against the mouth 160 of the chamber 145 by a biasing element 155 to bias the check valve 140 in the closed position (
In another alternative embodiment in
a,b show a visual pressure indicator that is reversible and therefore not especially suitable for post-procedure forensics, but rather for in-procedure monitoring of over-pressurization. A cylindrical drum 200 is attached to the catheter at the luer 24 or elsewhere where the inflation pressure is present. The drum 200 includes a flexible membrane 205 stretched over the top surface, where the membrane 205 may have a concave orientation under nominal pressure conditions. However, as shown in
a illustrates another embodiment in which a pressure sensitive tube 300 is located over the proximal shaft section 12 and being in communication with the inflation lumen 21 of the balloon catheter through small vents as shown in
a illustrates yet another embodiment of the present invention wherein a portion of the inner surface 320 of the inflation lumen 21 contains a strip 325 of force sensitive material such as a mechanophore that extends along the longitudinal length of the inflation lumen, as shown in the cut-away view of
Alternatively, as shown in
In each of the embodiments using a force sensitive material such as one including mechanophores, the various indicators can be used with multiple pressure sensing devices that measure different levels, so that a more accurate assessment can be made of the pressure experienced by the lumen. For example, by using one mechanophore that changes color at one stress level and a second mechanophore that and others are not the level of pressurization can be more accurately determined.
The structure includes material that reacts to a specific stress by changing color. Descriptions of such materials can be found in articles such as “Mechanical Stress Leads To Self-Sensing In Solid Polymers,” Biochemistry, May 6, 2009, found at http://www.phvsorg.com/news160834918.html, and “Development Of Polymer Films That Change Color In Response To Tension,” AIST press release of Oct. 7, 2008, found at http://www.aist.go.ip/aist_e/lastest research/2008/20081117/20081117.html. From the latter, such material can be formed by polymerization of acetylene substituted with a substituted phenyl group using [Rh(norbornadiene)Cl]2 as a catalyst to produce a polymer in which the main chain is in the cis conformation and has a helical structure. A film of this polymer may be prepared by spin-coating from a chloroform solution of the polymer on a colorless elastic sheet. The color of the obtained film of the substituted polyacetylene is, for example, yellow at the time of formation. By stretching this film together with the sheet by using a stretching machine, the substituted polyacetylene molecules were oriented along the direction of stretching. Further stretching led to a color change in the film from yellow to red. Measurement of the ultraviolet-visible absorption spectrum indicated an increase in absorption from approximately 500 to 600 nm. Removal of the tension and contracting the film led to the return of the color of the film from red to yellow, and the absorption spectrum agreed with the spectrum before stretching. Thus, the change in color due to stretching and contracting was reversible.
The color of the film changes instantaneously in response to quick manual stretching and contraction. The change in color is repeatable, that is, the change in color between yellow and red can be repeated by stretching and contraction repeatedly. In addition, the change in color is not dependent on the stretching ratio but on the tension applied. This color change is believed to be the result of a change in the conjugated system of the main chain due to the change in length of the polymer molecules associated with the stretching and contraction of the film.
Films prepared from other substituted polyacetylenes also showed instantaneous reversible changes in color between colorless and yellow or between purple and blue. These changes in color were also repeatable. However, when polymer was stressed to failure, the color change remained in the specimen, indicated that the designated pressure threshold had been reached. Thus, it can be used as a forensic tool to evaluate the pressure or stress of the material at failure and provide feedback on the conditions of the balloon catheter at the time of failure.
While the present invention is described herein in terms of certain preferred embodiments, those skilled in the art will recognize that various modifications and improvements may be made to the invention without departing from the scope thereof. Moreover, although individual features of one embodiment of the invention may be discussed herein or shown in the drawings of the one embodiment and not in other embodiments, it should be apparent that individual features of one embodiment may be combined with one or more features of another embodiment or features from a plurality of embodiments.
