WO2019023185A1

WO2019023185A1 - Method for manufacturing cryogenic balloon for intravascular catheter system

Info

Publication number: WO2019023185A1
Application number: PCT/US2018/043410
Authority: WO
Inventors: Eugene J. Jung, Jr.
Original assignee: Cryterion Medical, Inc.
Priority date: 2017-07-26
Filing date: 2018-07-24
Publication date: 2019-01-31

Abstract

A method for manufacturing a cryogenic balloon (236) for an intravascular catheter system (210) includes the steps of forming the cryogenic balloon (236); and pressurizing the cryogenic balloon (236) before insertion of the cryogenic balloon (236) into a body of a patient (212). The step of pressurizing can occur before or after the cryogenic balloon (236) is bonded (e.g., heat-bonded or adhesive-bonded) to a catheter shaft (234). Additionally, the step of pressurizing can occur at any suitable inflation pressure, i.e. at, below or above a normal operating pressure range of between approximately 2.5 psig and 7.5 psig), and at any suitable temperature, i.e. at, above or below 23 degrees Celsius. The method can further include the step of sterilizing the cryogenic balloon (236), with the step of pressurizing occurring before or after the step of sterilizing.

Description

METHOD FOR MANUFACTURING CRYOGENIC BALLOON

FOR INTRAVASCULAR CATHETER SYSTEM

RELATED APPLICATION

This application claims priority on U.S. Provisional Application Serial No. 62/537,151 , filed on July 26, 2017, and entitled "METHOD FOR MANUFACTURING CRYOGENIC BALLOON FOR A CRYOGENIC BALLOON CATHETER ASSEMBLY". As far as permitted, the contents of U.S. Provisional Application Serial No. 62/537,151 are incorporated in their entirety herein by reference.

BACKGROUND

Cardiac arrhythmias involve an abnormality in the electrical conduction of the heart and are a leading cause of stroke, heart disease, and sudden cardiac death. Treatment options for patients with arrhythmias include medications and/or the use of medical devices, which can include implantable devices and/or catheter ablation of cardiac tissue, to name a few. In particular, catheter ablation involves delivering ablative energy to tissue inside the heart to block aberrant electrical activity from depolarizing heart muscle cells out of synchrony with the heart's normal conduction pattern. The procedure is performed by positioning the tip of an energy delivery catheter adjacent to diseased or targeted tissue in the heart. The energy delivery component of the system is typically at or near the most distal (i.e. farthest from the user or operator) portion of the catheter, and often at the tip of the catheter.

Various forms of energy can be used to ablate diseased heart tissue. These can include cryoablation procedures which use cryogenic fluid within cryoballoons (also sometimes referred to herein as "cryogenic balloons" or "balloon catheters"), radio frequency (RF), ultrasound and laser energy, to name a few. During a cryoablation procedure, with the aid of a guide wire, the distal tip of the catheter is positioned adjacent to targeted cardiac tissue, at which time energy is delivered to create tissue necrosis, rendering the ablated tissue incapable of conducting electrical signals. The dose of energy delivered is a critical factor in increasing the likelihood that the treated tissue is permanently incapable of conduction. At the same time, delicate collateral tissue, such as the esophagus, the bronchus, and the phrenic nerve surrounding the ablation zone can be damaged and can lead to undesired complications. Thus, the operator must finely balance delivering therapeutic levels of energy to achieve intended tissue necrosis while avoiding excessive energy leading to collateral tissue injury.

Atrial fibrillation (AF) is one of the most common arrhythmias treated using catheter ablation. AF is typically treated by pulmonary vein isolation, a procedure that removes unusual electrical conductivity in the pulmonary vein. In the earliest stages of the disease, paroxysmal AF, the treatment strategy involves isolating the pulmonary veins from the left atrial chamber. Cryoballoon ablation procedures to treat atrial fibrillation have increased in use in the last several years. In part, this stems from the ease of use, shorter procedure times and improved patient outcomes that are possible through the use of cryoballoon ablation procedures. Despite these advantages, there remains needed improvement to further improve patient outcomes and to better facilitate real-time physiological monitoring of tissue to optimally titrate energy to perform both reversible "ice mapping" and permanent tissue ablation.

The objective of any device for the treatment of AF is to achieve isolation in all, not just some, of the pulmonary veins. Also, it is understood that complete occlusion of each pulmonary vein with the cryogenic balloon is required for adequate antral ablation and electrical isolation. Without pulmonary vein occlusion, blood flow over the balloon during ablation decreases the likelihood of sufficient lesion formation. In order to achieve pulmonary vein occlusion with a balloon, the balloon outer diameter (also sometimes referred to herein as the "balloon diameter" or the "outer diameter") should ideally be a little larger than the opening, or ostium, of the pulmonary vein. If the balloon is too small, there can be gaps between the balloon and the pulmonary vein, enabling blood to flow through the gaps. Conversely, if the balloon is too large, a distal surface of the balloon may be improperly positioned due to the presence of other anatomical features so that the balloon is not sealed tightly against the ostium of the pulmonary vein.

In intravascular catheter systems such as cryogenic balloon catheter systems, it is common that two balloons are used (although a single balloon may also be used) to create a cryo-chamber near the distal tip of the catheter. The balloons are configured such that there is an inner balloon that receives the cryogenic cooling fluid and an outer balloon that surrounds the inner balloon. The outer balloon acts as part of a safety system to capture the cryogenic cooling fluid in the event of a leak from the inner balloon. In a typical cryogenic balloon catheter system, the cryogenic balloons are relatively non-compliant and are of a single diameter when in the ablation mode. Thus, current cryogenic balloons are limited in utility because the diameter of the inflated cryogenic balloon cannot be changed during ablation. However, human pulmonary vein diameter and shape can vary significantly within and between patients. Consequently, current cryogenic balloons offer an all or nothing capability in treating pulmonary veins in pulmonary vein isolation procedures.

Thus, a cryogenic balloon that is adjustable in size and shape so as to be more adaptable to common variations in human pulmonary vein diameter and shape is desired in order to better achieve pulmonary vein occlusion and isolation in a greater percentage of patients treated. Furthermore, a cryogenic balloon is needed that has a relatively wide-ranging diameter which can be determined by an operator based primarily or solely upon pressure within the cryoballoon.

In a cryogenic balloon catheter system, the balloon operating pressure (also sometimes referred to herein as the "balloon pressure" or the "inflation pressure"), the balloon diameter, and the energy flow rate through the balloon catheter are interrelated. A cryogenic balloon catheter system is unique in that the inflation pressure is a consequence of the refrigerant flow rate through the balloon catheter. The flow rate of the refrigerant determines the amount of energy delivered to the treatment site, such as the targeted cardiac tissue of the heart. The amount of energy delivered to the treatment site must be accurate and precise to increase the likelihood of an adequate therapeutic effect, such as obtaining pulmonary vein isolation, but also freedom from collateral tissue injury, which can result from excessive energy delivery. Thus, a relatively narrow therapeutic dose window is desired to attain better procedure outcomes. Ideally, a small increase in inflation pressure should correspond to a specific, yet clinically meaningful increase in balloon diameter while remaining within an optimal dose window.

Additionally, in some applications, it is desirable that the change from one balloon outer diameter to another using the same balloon should be achievable multiple times in a predictable fashion. An ideal variable-diameter balloon would offer a useful range of diameters achievable during ablation within a relatively narrow range of inflation pressures constrained by the need for providing a prescribed amount of cryo-energy delivered into the body of the patient by a cryoablation balloon catheter. This feature would enable the operator to move the balloon catheter from one pulmonary vein to the next, change the outer diameter of the balloon to occlude the pulmonary vein, apply therapy to achieve a successful outcome, and then move to the next pulmonary vein to repeat the process.

SUMMARY

The present invention is directed toward a method for manufacturing a cryogenic balloon for an intravascular catheter system. In various embodiments, the method includes the steps of forming the cryogenic balloon; and pressurizing the cryogenic balloon before insertion of the cryogenic balloon into a body of a patient.

In some embodiments, the method further includes the step of heat-bonding the cryogenic balloon to a catheter shaft. In certain such embodiments, the step of pressurizing occurs after the step of heat-bonding. Alternatively, in other such embodiments, the step of pressurizing occurs before the step of heat-bonding.

Additionally, in certain embodiments, the method further includes the step of adhesive-bonding the cryogenic balloon to a catheter shaft. In some such embodiments, the step of pressurizing occurs after the step of adhesive-bonding. Alternatively, in other such embodiments, the step of pressurizing occurs before the step of adhesive-bonding.

In some embodiments, the step of pressurizing includes inflating the cryogenic balloon to within a normal operating pressure range (e.g., between approximately 2.5 psig and 7.5 psig) that occurs while the cryogenic balloon is within the body of the patient and is receiving a cryogenic fluid. Alternatively, in other embodiments, the step of pressurizing includes inflating the cryogenic balloon to below a normal operating pressure range (e.g., below approximately 2.5 psig) that occurs while the cryogenic balloon is within the body of the patient and is receiving a cryogenic fluid. Still alternatively, in still other embodiments, the step of pressurizing includes inflating the cryogenic balloon to above a normal operating pressure range (e.g., above approximately 7.5 psig) that occurs while the cryogenic balloon is within the body of the patient and is receiving a cryogenic fluid.

Additionally, the method can further include the step of deflating the cryogenic balloon, wherein the step of deflating occurs after the step of pressurizing and before insertion of the cryogenic balloon into the body of the patient.

In certain embodiments, the step of pressurizing occurs at approximately 23 degrees Celsius. Alternatively, the step of pressurizing can also occur at above 23 degrees Celsius or at below 23 degrees Celsius.

Further, in some embodiments, the step of pressurizing occurs before the intravascular catheter assembly has been fully assembled. Alternatively, the step of pressurizing can occur after the intravascular catheter assembly has been fully assembled.

Additionally, in various embodiments, the method further includes the step of sterilizing the cryogenic balloon. In some such embodiments, the step of pressurizing occurs after the step of sterilizing. Alternatively, in other such embodiments, the step of pressurizing occurs before the step of sterilizing.

In some embodiments, the step of pressurizing is controlled by an operator of the intravascular catheter system. In other embodiments, the step of pressurizing is controlled by a control system of the intravascular catheter system.

Additionally, in certain applications, the present invention is further directed toward a method for manufacturing a cryogenic balloon for an intravascular catheter system, the method including the steps of forming the cryogenic balloon; heat- bonding the cryogenic balloon to a catheter shaft; sterilizing the cryogenic balloon; pressurizing the cryogenic balloon before insertion of the cryogenic balloon into a body of a patient; and deflating the cryogenic balloon after pressurizing the cryogenic balloon, but before insertion of the cryogenic balloon into the body of the patient.

BRIEF DESCRIPTION OF THE DRAWINGS

The novel features of this invention, as well as the invention itself, both as to its structure and its operation, will be best understood from the accompanying drawings, taken in conjunction with the accompanying description, in which similar reference characters refer to similar parts, and in which:

Figure 1 is a simplified schematic side view illustration of a patient and one embodiment of an intravascular catheter system having features of the present invention;

Figure 2 is a simplified schematic side view illustration of a portion of the patient and a portion of an embodiment of the intravascular catheter system including a balloon catheter;

Figure 3 is a graph showing one representative embodiment of a balloon usable within the balloon catheter of the intravascular catheter system including outer diameter of the balloon as a function of inflation pressure for four consecutive inflation/deflation cycles;

Figure 4 is a graph showing another representative embodiment of the balloon including outer diameter of the balloon as a function of inflation pressure for five consecutive inflation/deflation cycles; and

Figure 5 is a flow chart showing one embodiment of a method for manufacturing a balloon for the balloon catheter.

DESCRIPTION

Embodiments of the present invention are described herein in the context of a method for manufacturing a cryogenic balloon for an intravascular catheter system. More specifically, in various embodiments, embodiments of the present invention are directed toward a method of balloon manufacture, which can be controlled to provide improved balloon diameter adjustability at different, e.g., lower, inflation pressures.

Those of ordinary skill in the art will realize that the following detailed description of the present invention is illustrative only and is not intended to be in any way limiting. Other embodiments of the present invention will readily suggest themselves to such skilled persons having the benefit of this disclosure. Reference will now be made in detail to implementations of the present invention as illustrated in the accompanying drawings.

In the interest of clarity, not all of the routine features of the implementations described herein are shown and described. It will, of course, be appreciated that in the development of any such actual implementation, numerous implementation- specific decisions must be made in order to achieve the developer's specific goals, such as compliance with application-related and business-related constraints, and that these specific goals will vary from one implementation to another and from one developer to another. Moreover, it will be appreciated that such a development effort might be complex and time-consuming, but would nevertheless be a routine undertaking of engineering for those of ordinary skill in the art having the benefit of this disclosure.

Although the disclosure provided herein focuses mainly on cryogenics, it is understood that various other forms of energy can be used to ablate diseased heart tissue. These can include radio frequency (RF), ultrasound, pulsed DC electric fields and laser energy, as non-exclusive examples. The present invention is intended to be effective with any or all of these and other forms of energy.

As an overview, with the cryogenic balloon manufacturing methodology as provided in detail herein, cryoenergy and cryoablation can be improved by substantially repeatable balloon diameter changes of several millimeters at relatively low operating pressures.

Figure 1 is a simplified schematic side view illustration of an embodiment of a medical device 10 for use with a patient 12, which can be a human being or an animal. Although the specific medical device 10 illustrated and described herein pertains to and refers to an intravascular catheter system 10 such as a cryogenic balloon catheter system, it is understood and appreciated that other types of medical devices 10 or systems can equally benefit by the teachings provided herein. For example, in certain non-exclusive alternative embodiments, the present invention can be equally applicable for use with any suitable types of ablation systems and/or any suitable types of catheter systems. Thus, the specific reference herein to use as part of an intravascular catheter system is not intended to be limiting in any manner.

The design of the intravascular catheter system 10 can be varied. In certain embodiments, such as the embodiment illustrated in Figure 1 , the intravascular catheter system 10 can include one or more of a control system 14 (illustrated in phantom), a fluid source 16 (illustrated in phantom), a balloon catheter 18, a handle assembly 20, a control console 22, and a graphical display 24.

It is understood that although Figure 1 illustrates the structures of the intravascular catheter system 10 in a particular position, sequence and/or order, these structures can be located in any suitably different position, sequence and/or order than that illustrated in Figure 1 . It is also understood that the intravascular catheter system 10 can include fewer or additional components than those specifically illustrated and described herein.

In various embodiments, the control system 14 is configured to monitor and control various processes of the ablation procedure. More specifically, the control system 14 can monitor and control release and/or retrieval of a cooling fluid 26 (e.g., a cryogenic fluid) to and/or from the balloon catheter 18. The control system 14 can also control various structures that are responsible for maintaining and/or adjusting a flow rate and/or pressure of the cryogenic fluid 26 that is released to the balloon catheter 18 during the cryoablation procedure. In such embodiments, the intravascular catheter system 10 delivers ablative energy in the form of cryogenic fluid 26 to cardiac tissue of the patient 12 to create tissue necrosis, rendering the ablated tissue incapable of conducting electrical signals. Additionally, in various embodiments, the control system 14 can control activation and/or deactivation of one or more other processes of the balloon catheter 18. Further, or in the alternative, the control system 14 can receive data and/or other information (hereinafter sometimes referred to as "sensor output") from various structures within the intravascular catheter system 10. In some embodiments, the control system 14 can receive, monitor, assimilate and/or integrate the sensor output and/or any other data or information received from any structure within the intravascular catheter system 10 in order to control the operation of the balloon catheter 18. As provided herein, in various embodiments, the control system 14 can initiate and/or terminate the flow of cryogenic fluid 26 to the balloon catheter 18 based on the sensor output. Still further, or in the alternative, the control system 14 can control positioning of portions of the balloon catheter 18 within the body of the patient 12, and/or can control any other suitable functions of the balloon catheter 18.

Additionally, in some embodiments, the control system 14 can include, incorporate or utilize a pressure sensor 28 that can be configured to sense a contact pressure between the balloon and the targeted vein to be occluded. As provided herein, the pressure sensor 28 can be utilized to better ensure that a desired, predetermined contact force or contact pressure is generated between the balloon and the targeted vein to achieve the desired vein occlusion. It is appreciated that the pressure sensor 28 can be positioned in any suitable manner within the intravascular catheter system 10.

The fluid source 16 contains the cryogenic fluid 26, which is delivered to the balloon catheter 18 with or without input from the control system 14 during a cryoablation procedure. Once the ablation procedure has initiated, the cryogenic fluid 26 can be delivered to the balloon catheter 18 and the resulting gas, after a phase change, can be retrieved from the balloon catheter 18, and can either be vented or otherwise discarded as exhaust. Additionally, the type of cryogenic fluid 26 that is used during the cryoablation procedure can vary. In one non-exclusive embodiment, the cryogenic fluid 26 can include liquid nitrous oxide. However, any other suitable cryogenic fluid 26 can be used. For example, in one non-exclusive alternative embodiment, the cryogenic fluid 26 can include liquid nitrogen.

The design of the balloon catheter 18 can be varied to suit the specific design requirements of the intravascular catheter system 10. As shown, the balloon catheter 18 is configured to be inserted into the body of the patient 12 during the cryoablation procedure, i.e. during use of the intravascular catheter system 10. In one embodiment, the balloon catheter 18 can be positioned within the body of the patient 12 using the control system 14. Stated in another manner, the control system 14 can control positioning of the balloon catheter 18 within the body of the patient 12. Alternatively, the balloon catheter 18 can be manually positioned within the body of the patient 12 by a healthcare professional (also referred to herein as an "operator"). As used herein, a healthcare professional and/or an operator can include a physician, a physician's assistant, a nurse and/or any other suitable person and/or individual. In certain embodiments, the balloon catheter 18 is positioned within the body of the patient 12 utilizing at least a portion of the sensor output that is received by the control system 14. For example, in various embodiments, the sensor output is received by the control system 14, which can then provide the operator with information regarding the positioning of the balloon catheter 18. Based at least partially on the sensor output feedback received by the control system 14, the operator can adjust the positioning of the balloon catheter 18 within the body of the patient 12 to ensure that the balloon catheter 18 is properly positioned relative to targeted cardiac tissue (not shown). While specific reference is made herein to the balloon catheter 18, as noted above, it is understood that any suitable type of medical device and/or catheter may be used.

The handle assembly 20 is handled and used by the operator to operate, position and control the balloon catheter 18. The design and specific features of the handle assembly 20 can vary to suit the design requirements of the intravascular catheter system 10. In the embodiment illustrated in Figure 1 , the handle assembly 20 is separate from, but in electrical and/or fluid communication with the control system 14, the fluid source 16, and the graphical display 24. In some embodiments, the handle assembly 20 can integrate and/or include at least a portion of the control system 14, e.g., the pressure sensor 28, within an interior of the handle assembly 20. It is understood that the handle assembly 20 can include fewer or additional components than those specifically illustrated and described herein.

In various embodiments, the handle assembly 20 can be used by the operator to initiate and/or terminate the cryoablation process, e.g., to start the flow of the cryogenic fluid 26 to the balloon catheter 18 in order to ablate certain targeted heart tissue of the patient 12. In certain embodiments, the control system 14 can override use of the handle assembly 20 by the operator. Stated in another manner, in some embodiments, based at least in part on the sensor output, the control system 14 can terminate the cryoablation process without the operator using the handle assembly 20 to do so.

The control console 22 is coupled to the balloon catheter 18 and the handle assembly 20. Additionally, in the embodiment illustrated in Figure 1 , the control console 22 includes at least a portion of the control system 14, the fluid source 16, and the graphical display 24. However, in alternative embodiments, the control console 22 can contain additional structures not shown or described herein. Still alternatively, the control console 22 may not include various structures that are illustrated within the control console 22 in Figure 1 . For example, in certain nonexclusive alternative embodiments, the control console 22 does not include the graphical display 24.

In various embodiments, the graphical display 24 is electrically connected to the control system 14. Additionally, the graphical display 24 provides the operator of the intravascular catheter system 10 with information and data that can be used before, during and after the cryoablation procedure. For example, the graphical display 24 can provide the operator with information based on the sensor output and any other relevant information that can be used before, during and after the cryoablation procedure. The specifics of the graphical display 24 can vary depending upon the design requirements of the intravascular catheter system 10, or the specific needs, specifications and/or desires of the operator.

In one embodiment, the graphical display 24 can provide static visual data and/or information to the operator. In addition, or in the alternative, the graphical display 24 can provide dynamic visual data and/or information to the operator, such as video data or any other data that changes over time, e.g., during an ablation procedure. Further, in various embodiments, the graphical display 24 can include one or more colors, different sizes, varying brightness, etc., that may act as alerts to the operator. Additionally, or in the alternative, the graphical display 24 can provide audio data or information to the operator.

Figure 2 is a simplified schematic side view illustration of a portion of the patient 212 and a portion of one embodiment of the intravascular catheter system 210. As shown in Figure 2, in this embodiment, the intravascular catheter system 210 includes a balloon catheter 218. In certain embodiments, the balloon catheter 218 can be a low-profile, anatomy-conforming balloon catheter for cryogenically or thermally ablating tissue surrounding one or more pulmonary veins 242 for the treatment of atrial fibrillation in order to improve outcomes and procedural safety. Certain embodiments of the intravascular catheter system 210 can also or alternatively provide a structure able to be delivered through a small profile delivery device.

The design of the balloon catheter 218 can be varied to suit the design requirements of the intravascular catheter system 210. In the embodiment illustrated in Figure 2, the balloon catheter 218 includes one or more of a guidewire 230, a guidewire lumen 232, a catheter shaft 234, and a balloon assembly 235 including an inner inflatable balloon 236 (sometimes referred to herein as a "first inflatable balloon", an "inner balloon" or a "first balloon") and an outer inflatable balloon 238 (sometimes referred to herein as a "second inflatable balloon", an "outer balloon" or a "second balloon"). As used herein, it is recognized that either balloon 236, 238 can be described as the first balloon or the second balloon. Further, the inner balloon 236 and/or the outer balloon 238 can also be referred to generally as a "cryogenic balloon". For example, in certain applications, the inner balloon 236 can be the cryogenic balloon that is manufactured utilizing the methodology as described in detail herein. Alternatively, the balloon catheter 218 can be configured to include only a single balloon.

Additionally, it is understood that the balloon catheter 218 can include other structures as well. However, for the sake of clarity, these other structures have been omitted from the Figures. Further, as shown in Figure 2, the balloon assembly 235, i.e. the inner balloon 236 and/or the outer balloon 238, has an outer diameter 239.

As shown in the embodiment illustrated in Figure 2, the balloon catheter 218 is configured to be positioned within the circulatory system 240 of the patient 212. The guidewire 230 and guidewire lumen 232 are inserted into a pulmonary vein 242 of the patient 212, and the catheter shaft 234 and the balloons 236, 238 are moved along the guidewire 230 and/or the guidewire lumen 232 to near an ostium 244 of the pulmonary vein 242.

Additionally, as shown, the guidewire lumen 232 encircles at least a portion of the guidewire 230. During use, the guidewire 230 is inserted into the guidewire lumen 232 and can course through the guidewire lumen 232 and extend out of a distal end 232A of the guidewire lumen 232. In various embodiments, the guidewire 230 can also include a mapping catheter (not shown) that maps electrocardiograms in the heart, and/or can provide information needed to position at least portions of the balloon catheter 218 within the patient 212.

As illustrated in this embodiment, the inner balloon 236 is positioned substantially, if not completely, within the outer balloon 238. Additionally, in some embodiments, one end of the inner balloon 236 is bonded to a distal end 234A of the catheter shaft 234, and the other end of the inner balloon 236 is bonded near the distal end 232A of the guidewire lumen 232. Further, one end of the outer balloon 238 may be bonded to a neck of the inner balloon 236 or to the distal end 234A of the catheter shaft 234, and the other end of the outer balloon 238 may be bonded to the guidewire lumen 232. Additionally, it is further appreciated that in embodiments that include only a single balloon, the balloon can be secured to the catheter shaft 234 and the guidewire lumen 232 in a similar manner. Alternatively, the balloons 236, 238 can be secured to other suitable structures.

It is appreciated that a variety of bonding techniques can be used and include heat-bonding and adhesive-bonding. For example, in at least some embodiments, the bonding can be accomplished using thermal fusing techniques. These techniques are possible because of the use of materials in both the inner balloon 236 and the outer balloon 238 to enhance compatibility for fusing while preserving the respective functional requirements of each balloon 236, 238, which can be rather different from one another. In such embodiments, each of the balloons 236, 238 can be heat-bonded, e.g., to the catheter shaft 234 and/or the guidewire lumen 232, to achieve a small diameter, using a laser or clam shell heated die set, for example. To facilitate a heat-bond, the catheter shaft 234, the guidewire lumen 232 and the balloons 236, 238 can be chosen so they are compatible for heat-bonding. Alternatively, as noted, the balloons 236, 238 can be adhesive-bonded to the catheter shaft 234 and/or the guidewire lumen 232.

During use, the inner balloon 236 can be partially or fully inflated so that at least a portion of the inner balloon 236 expands against at least a portion of the outer balloon 238. Stated in another manner, during use of the balloon catheter 218, at least a portion of an outer surface 236A of the inner balloon 236 expands and is positioned substantially directly against a portion of an inner surface 238A of the outer balloon 238. As such, when the inner balloon 236 has been fully inflated, the inner balloon 236 and the outer balloon 238 have a somewhat similar physical footprint. Thus, since the inner balloon 236 and the outer balloon 238 have a similar physical footprint, any of the inner balloon 236, the outer balloon 238 and/or the balloon assembly 235 can be said to include the outer diameter 239.

At certain times during usage of the intravascular catheter system 210, the inner balloon 236 and the outer balloon 238 define an inter-balloon space 246, or gap, between the balloons 236, 238. The inter-balloon space 246 is illustrated between the inner balloon 236 and the outer balloon 238 in Figure 2 for clarity, although it is understood that at certain times during usage of the intravascular catheter system 210, the inter-balloon space 246 has very little or no volume. As provided herein, once the inner balloon 236 is sufficiently inflated, an outer surface 238B of the outer balloon 238 can then be positioned within the circulatory system 240 of the patient 212 to abut and/or substantially form a seal with the ostium 244 of the pulmonary vein 242 to be treated. In particular, during use, it is generally desired that the outer diameter 239 of the balloon assembly 235 be slightly larger than the diameter of the pulmonary vein 242 to best enable occlusion of the pulmonary vein 242. As noted above, having a balloon assembly 235 with an outer diameter 239 that is either too small or too large can create problems that inhibit the ability to achieve the desired occlusion of the pulmonary vein 242.

As provided herein, one way to treat a wider range of human anatomy is to better size the balloons 236, 238 of the balloon catheter 218 to match the diameter of the pulmonary vein 242. In general, it is the object of the balloon catheter 218 to seal the pulmonary vein 242 so that blood flow is occluded. Only when occlusion is achieved does the cryothermic energy, e.g., of the cryogenic fluid 26 (illustrated in Figure 1 ), cause tissue necrosis which, in turn, provides for electrically blocking aberrant electrical signals that trigger atrial fibrillation. Unfortunately, as noted above, human anatomy varies, and the diameter of pulmonary veins varies within a given patient as well as between patients.

In various embodiments, the variety of pulmonary vein diameters can be treated by providing a balloon catheter 218 that includes balloons 236, 238 that are selectively adjustable to provide a range of available outer diameters 239. An intravascular catheter system 210 that varies the outer diameter 239 of the balloon assembly 235 can preclude the need to utilize multiple balloon catheters to successfully complete a procedure. The use of multiple balloon catheters increases procedure time, risk of injury to the patient 212, and procedural cost. Thus, the balloon catheter 218 disclosed herein includes a balloon assembly 235, i.e. an inner balloon 236 and/or an outer balloon 238, that can vary the outer diameter 239 predictably and reliably over the course of numerous inflation, deflation, and ablation cycles. This attribute enables the operator to move the balloon catheter 218 from one pulmonary vein 242 to the next, change the outer diameter 239 of the balloon assembly 235 to occlude the pulmonary vein 242, apply therapy to achieve successful outcomes, then move to the next pulmonary vein 242 and repeat the process. Ideally, this process of advancing the balloon catheter 218 to a pulmonary vein 242, adjusting the outer diameter 239 to occlude the pulmonary vein 242, and applying therapy, can be repeated any number of times as the operator desires to complete the procedure. In effect, the balloon assembly 235, along with the remainder of the intravascular catheter system 210, offers the operator the capability to adjust the outer diameter 239 of the balloon assembly 235 to better seal the pulmonary vein 242 while effectively keeping the energy dose (balloon pressure or inflation pressure) within a narrow, safe, and effective therapeutic window.

As noted above, the operating balloon pressure or inflation pressure of the balloon assembly 235, the outer diameter 239 of the balloon assembly 235, and the energy flow rate through the balloon catheter 218 are inter- related. During use of the intravascular catheter system 210, the inflation pressure is a consequence of the flow rate of the cryogenic fluid 26 (illustrated in Figure 1 ) through the balloon catheter 218. The flow rate of the cryogenic fluid 26 determines the amount of energy delivered to the treatment site, such as the targeted cardiac tissue of the heart. The amount of energy delivered to the treatment site should be accurate and precise to increase the likelihood of adequate therapeutic effect, including obtaining isolation of the pulmonary vein 242, and freedom from collateral tissue injury, which can result from excessive energy delivery. Importantly, a relatively narrow therapeutic dose window is required to increase the likelihood of improved patient outcomes. Thus, it follows that a small increase in inflation pressure corresponds to a specific, yet clinically meaningful increase in the outer diameter 239 of the balloon assembly 235, while remaining within a narrow dose window. It may be advantageous to increase the energy delivered as the balloon assembly 235 is inflated to a larger outer diameter 239 to offset heat loss resulting from larger surface area of the larger outer diameter 239.

Additionally, as provided herein, the balloons 236, 238 can be designed to include certain performance parameters. For example, in various embodiments, performance parameters of the balloons 236, 238 and/or the balloon assembly 235 can include one or more of (i) a relatively predictable outer diameter-pressure curve, (ii) balloons 236, 238 having a relatively thin wall, (iii) an ability to expand to a desired operating range of outer diameters 239 at relatively low inflation pressures and/or with small pressure changes, (iv) a relatively high burst pressure for the balloons 236, 238 having a given wall thickness, (v) dimensional stability including resistance to shrinkage during sterilization, and/or (vi) other manufacturing processes and resistance against pinholes and other defects in the balloons 236, 238. Additionally, in certain embodiments, the balloons 236, 238 that are ultimately inserted into the body of the patient 212 will have little or no hysteresis so that the operator can inflate the balloons 236, 238 to variable and predictable sizes based on known inflation pressures.

The specific design of and materials used for each of the inner inflatable balloon 236 and the outer inflatable balloon 238 can be varied. For example, in order to meet some or all of the above-noted performance parameters, a polymer capable of being extruded and formed into a thin, homogeneous film can be used. In various embodiments, specialty polymers with engineered properties can be used.

In addition to single polymers, blends of polymers can result in a suitable material for use in the inner inflatable balloon 236. For example, some representative materials suitable for the inner inflatable balloon 236 include various grades of polyether block amides (PEBA), which include a copolymer family comprised of rigid polyamide blocks and flexible polyether blocks, such as the commercially available PEBAX^® (marketed by Arkema, Colombes, France), or a thermoplastic polyurethane such as Pellathane™ (marketed by Lubrizol). Additionally, or in the alternative, the materials can include PET (polyethylene terephthalate), nylon, polyurethane, and other co-polymers of these materials, as non-exclusive examples. In another embodiment, a polyester block copolymer known in the trade as Hytrel^® (DuPont™) is also a suitable material for the inner inflatable balloon 236. Further, the materials may be mixed in varying amounts to fine tune properties of the inner inflatable balloon 236. Other suitable materials can additionally or alternatively be used for the inner inflatable balloon 236, and the foregoing examples of materials used for the inner inflatable balloon 236 are not intended to be limiting in any manner.

As illustrated, the outer inflatable balloon 238 substantially encircles the inner inflatable balloon 236. In certain embodiments, the outer inflatable balloon 238 can be formed from similar materials and can be formed in a similar manner as the inner inflatable balloon 236. For example, some representative materials suitable for the outer inflatable balloon 238 for this variable-diameter compliant two-balloon system include various grades of polyether block amides (PEBA) such as the commercially available PEBAX^®, or a polyurethane such as Pellathane™. Additionally, or in the alternative, the materials can include aliphatic polyether polyurethanes in which carbon atoms are linked in open chains, including paraffins, olefins, and acetylenes. Another suitable material goes by the trade name Tecoflex^® (marketed by Lubrizol). Other available polymers from the polyurethane class of thermoplastic polymers with exceptional elongation characteristics are also suitable for use as the outer inflatable balloon 238. Further, the materials may be mixed in varying amounts to fine tune properties of the outer inflatable balloon 238.

Figure 3 is a graph showing one representative embodiment of a relatively compliant balloon, e.g., a cryogenic balloon or "cryoballoon", usable within the balloon catheter 218 (illustrated in Figure 2) of the intravascular catheter system 210 (illustrated in Figure 2) including outer diameter 239 (illustrated in Figure 2) of the balloon as a function of inflation pressure for four consecutive inflation/deflation cycles. It is appreciated that the cryogenic balloon being depicted in the graph shown in Figure 3 can be an embodiment of the inner balloon 236 (illustrated in Figure 2). Alternatively, the cryogenic balloon being depicted in the graph shown in Figure 3 can be an embodiment of the outer balloon 238 (illustrated in Figure 2).

As illustrated, a separate curve is used to depict the outer diameter-pressure curve for each of the four inflation/deflation cycles. In particular, as shown in Figure 3, the inflation cycles include a first cycle 350, a second cycle 352, a third cycle 354 and a fourth cycle 356. Between each of the cycles 350, 352, 354, 356, the cryogenic balloon 236 is deflated to an initial inflation pressure. Each cycle 350, 352, 354, 356, includes inflating the cryogenic balloon 236 from the initial inflation pressure of approximately 1 .5 psig, up to approximately 10.0 psig. In certain embodiments, the normal operating pressure range of the cryogenic balloon 236 can be approximately 2.5 - 7.5 psig. However, other operating pressure ranges can alternatively be utilized. During the first cycle 350, increasing the inflation pressure yields a somewhat inconsistent increase in the outer diameter 239 of the cryogenic balloon 236. This inconsistency is illustrated in Figure 3 by the changes in slope of the curve of the first cycle 350. In contrast, changes in slope of the curves for the second cycle 352, the third cycle 354 and the fourth cycle 356 are less pronounced. Stated another way, the curves for the second cycle 352, the third cycle 354 and the fourth cycle 356 are more linear, thereby indicating a more consistent and more predictable correlation between the inflation pressure and the outer diameter 239 of the cryogenic balloon 236 than with the first cycle 350.

For example, at 2.5 psig during the first cycle 350, the outer diameter 239 of the cryogenic balloon 236 is approximately 29.25 mm, while the outer diameter 239 of the cryogenic balloon 236 at 2.5 psig for the second cycle 352 is approximately 29.42 mm; for the third cycle 354 is approximately 29.50 mm; and for the fourth cycle 356 is approximately 29.42 mm. In other words, the outer diameters 239 of the cryogenic balloon 236 for the second cycle 352, the third cycle 354 and the fourth cycle 356 are more consistently within a narrower range, while the outer diameter 239 of the cryogenic balloon 236 for the first cycle 350 is significantly lower and falls outside this narrow range.

As another example, at 5.0 psig during the first cycle 350, the outer diameter 239 of the cryogenic balloon 236 is approximately 29.47 mm, while the outer diameter 239 of the cryogenic balloon 236 at 5.0 psig for the second cycle 352 is approximately 29.70 mm; for the third cycle 354 is approximately 29.67 mm; and for the fourth cycle 356 is approximately 29.65 mm. Again, the outer diameters 239 of the cryogenic balloon 236 for the second cycle 352, the third cycle 354 and the fourth cycle 356 are more consistently within a narrower range, while the outer diameter 239 of the cryogenic balloon 236 for the first cycle 350 is significantly lower and falls outside of this range.

In another example, at 7.5 psig during the first cycle 350, the outer diameter 239 of the cryogenic balloon 236 is approximately 30.32 mm, while the outer diameter 239 of the cryogenic balloon 236 at 7.5 psig for the second cycle 352 is approximately 30.08 mm; for the third cycle 354 is approximately 30.08 mm; and for the fourth cycle 356 is approximately 30.20. Again, the outer diameters 239 of the cryogenic balloon 236 for the second cycle 352, the third cycle 354 and the fourth cycle 356 are more consistently within a narrower range, while the outer diameter 239 of the cryogenic balloon 236 for the first cycle 350 is now higher and falls outside of this range.

Therefore, an operator of the balloon catheter 218 (illustrated in Figure 2) who relies on the outer diameter 239 of the cryogenic balloon 236 based upon inflation pressure would have difficulty in doing so consistently with a cryogenic balloon 236 such as that used in the embodiment illustrated in Figure 3.

Figure 4 is a graph showing another representative embodiment of the balloon, e.g., a cryogenic balloon or "cryoballoon", including the outer diameter 239 (illustrated in Figure 2) of the balloon as a function of inflation pressure for five consecutive inflation/deflation cycles. It is appreciated that the cryogenic balloon being depicted in the graph shown in Figure 4 can be an embodiment of the inner balloon 236 (illustrated in Figure 2). Alternatively, the cryogenic balloon being depicted in the graph shown in Figure 4 can be an embodiment of the outer balloon

238 (illustrated in Figure 2).

As illustrated, a separate curve is used to depict the outer diameter-pressure curve for each of the five inflation/deflation cycles. In particular, as shown in Figure 4, the inflation cycles include a first cycle 458, a second cycle 460, a third cycle 462, a fourth cycle 464 and a fifth cycle 466. Between each of the cycles 458, 460, 462, 464, 466, the cryogenic balloon 236 is deflated to an initial inflation pressure. Each cycle 458, 460, 462, 464, 466, includes inflating the cryogenic balloon 236 from the initial inflation pressure of approximately 2.5 psig, up to approximately 7.5 psig. In certain embodiments, the normal operating pressure range of the cryogenic balloon 236 can be approximately 2.5 - 7.5 psig. However, other operating pressure ranges can alternatively be utilized.

In the embodiment illustrated in Figure 4, the first cycle 458 of the cryogenic balloon 236 yields an outer diameter 239 having a range of approximately 1 .07 - 1 .31 inches. In contrast, for the second cycle 460, the third cycle 462, the fourth cycle 464 and the fifth cycle 466, the cryogenic balloon 236 yields an outer diameter 239 having a range of approximately 1 .12 - 1 .36 inches. Thus in this embodiment, the outer diameter 239 of the cryogenic balloon 236 is consistently higher (and consistent with one another) for the second cycle 460, the third cycle 462, the fourth cycle 464 and the fifth cycle 466 than for the first cycle 458. Therefore, an operator of the balloon catheter 218 (illustrated in Figure 2) who relies on the outer diameter

239 of the cryogenic balloon 236 based upon inflation pressure would have difficulty in doing so consistently with a cryogenic balloon 236 such as that used in the embodiment illustrated in Figure 4.

It is understood that the cryogenic balloons 236 used to generate the graphs illustrated in Figures 3 and 4 are merely representative of the numerous cryogenic balloons 236 that are relatively compliant in nature, and inherently have a relatively high hysteresis, particularly between the first cycle 350, 458, and the corresponding second cycle 352, 460. No limitation of the type of cryogenic balloon 236 that is subject to the methods disclosed herein is intended.

Figure 5 is a flow chart showing one embodiment of a method for manufacturing a balloon that is usable within the balloon catheter of the intravascular catheter system, e.g., a cryogenic balloon or "cryoballoon" that can be used as the inner balloon. It is understood that the method pursuant to the disclosure herein can include greater or fewer steps than those shown and described relative to Figure 5. Stated another way, the method according to the present invention can omit one or more steps illustrated in Figure 5, or can add additional steps not shown and described in Figure 5, and still fall within the purview of the present invention. Further, the sequence of the steps can be varied from those shown and described relative to Figure 5. The sequence of steps illustrated in Figure 5 is not intended to limit the sequencing of steps in any manner.

At step 501 , pellets of balloon material are dried. In one embodiment, a candidate material (e.g., Nylon-12, for example) in small pellets is dried in a sealed chamber with a desiccant bed. Circulated air at an elevated temperature is passed through the pellets to achieve a relatively low dew point (e.g., well below zero degrees Fahrenheit). This relatively low dew point increases the likelihood that the raw material used to make the cryogenic (inner) balloon is dry and that moisture is not present during the tubing extrusion process.

At step 503, the dried pellets are extruded into a substantially homogeneous melt in the shape of a balloon tubing. In one embodiment, the dried pellets are loaded through a hopper into an extrusion system. Those skilled in the art recognize that such extrusion systems can vary and yet still produce balloon tubing capable of making specification conforming cryogenic balloons. The extrusion system can utilize a screw or a metal rod with spiral elements, which turns inside a barrel. In certain embodiments, a three-quarter inch or one-inch diameter screw can result in clean extrusion tubing suitable for making a cryogenic balloon.

The dried pellets are fed into the extrusion screw, which rotates the pellets into a melt. There may be numerous heater bands placed along the path of the pellets. In one embodiment, the pellets are heated to temperatures approaching their melting point. The action of the heaters and the screw in turn mixes the pellets to homogenize the melt, thus resulting in a clean film melt that is relatively free from imperfections. Importantly, because the cryogenic balloon is designed to have extremely thin walls, excellent homogeneity of the melt can avoid flaws in the film that lead to premature balloon burst pressures or other undesirable defects.

At step 505, the melted tubing is solidified. In one embodiment, the melted polymer mix exits the extrusion die set, i.e. the tooling that shapes the balloon tubing, which is pulled across a small air gap, and then is passed into a water filled trough. The water filled trough quickly solidifies the tubing, helping to provide for tubing dimensions and properties that facilitate the balloon forming process. A variety of extrusion systems and extrusion parameters can be used to arrive at a balloon tubing of ideal properties. The diameter of the extrusion die set is chosen to properly size the inner and outer diameter of the tubing, providing for a draw-down ratio that results in a tubing elongation suitable for balloon forming. The extrusion system may have a cross-head design to provide for uniform back pressure of the melt and extruded tubing. Air pressure provided through the hypotube serves to support the extruded tubing inner diameter. Likewise, screen packs, a stack of open metal screens of multiple micron sized openings, capture contamination and provide added back pressure. Lastly, a pulley system incorporating a laser microscope that works in concert with a puller can achieve and control outer tubing dimensions to ensure the designed balloon wall thickness is met. Variations to this process can still result in tubing suitable for an improved cryogenic balloon.

At step 507, the balloon tubing undergoes a stretching process known as necking. In one non-exclusive embodiment, an eighteen-inch segment (for example) of balloon tubing is stretched. The two end sections of the balloon tubing are heated to a temperature that softens the tubing and enables stretching of the heated section while not stretching the unheated middle segment. Thus, a small segment in the center of the tubing is left unstretched. This unstretched middle segment, called the parison, will be blow molded into a balloon. At step 509, the balloon tubing is blow-formed into a cryogenic balloon using a balloon forming machine. In one embodiment, the balloon forming machine can include one or more of a balloon mold, movable clamps, a pressurized line and a control system that adjusts and regulates gas pressure inside the balloon tubing and the temperature of the mold. The stretched section of the tubing is reduced in diameter so it can be passed through the end of a mold within the balloon forming machine. The forming process will cycle through various temperatures and pressures to heat and soften the balloon tubing, and stretch and pressurize the tubing to expand the parison into a balloon. The formed balloon may subsequently be heat-processed in a final step to stabilize the balloon size.

At step 51 1 , the cryogenic balloon is cooled while still in the mold. In various embodiments, the cryogenic balloon may be cooled to less than one hundred (100) degrees Fahrenheit while still under pressure to prevent unwanted shrinking. When the balloon is cooled to less than one hundred (100) degrees Fahrenheit, the mold is opened and the pressure inside the balloon is released.

At step 513, the cryogenic balloon is extracted from the mold.

At step 515, and after extraction from the mold (step 513), the cryogenic balloon is pressurized prior to insertion of the cryogenic balloon inside of the patient. In order to manufacture a low hysteresis, substantially predictable compliance cryogenic balloon, inherent hysteresis in the cryogenic balloon is removed after the balloon forming process is complete. This is accomplished by conditioning the cryogenic balloon. In one embodiment, the method to condition the cryogenic balloon includes the step of pressurizing (inflating) the cryogenic balloon to a pressure within a normal operating range during flow of the cryogenic fluid to the cryogenic balloon. Alternatively, the cryogenic balloon can be pressurized to somewhat below or somewhat above the normal operating range so that the cryogenic balloon can expand freely without the constraint of the forming mold.

It is appreciated that with the step of pressurization occurring prior to insertion of the cryogenic balloon inside of the patient, the cryogenic balloon will subsequently be deflated prior to insertion to better enable the cryogenic balloon to be effectively moved and positioned within the body of the patient. In one embodiment, the pressurization step can be performed at room temperature (approximately twenty-three (23) degrees Celsius). Alternatively, the pressurization step can be performed at a temperature that is somewhat above room temperature, or at a temperature that is somewhat below room temperature.

In certain alternative embodiments, the pressurization step can be performed on the cryogenic balloon after the cryogenic balloon has been formed, prior to full assembly of the intravascular catheter assembly, or on a fully assembled intravascular catheter assembly.

In some embodiments, the pressurization step can be performed after the cryogenic balloon has been sterilized (typically by the operator or other staff), but prior to insertion of the balloon catheter into the body of the patient. Alternatively, the step of pressurizing the cryogenic balloon can be performed prior to the cryogenic balloon being sterilized.

In one embodiment, the control system or the control console can be programmed to initiate and/or control pressurization of the cryogenic balloon at any time prior to positioning the balloon catheter within the body of the patient, thereby reducing or removing cryogenic balloon hysteresis so that the cryogenic balloon has a predictable and substantially repeatable diameter at various prescribed inflation pressures. Alternatively, the operator (or other staff) can initiate and/or control pressurization of the cryogenic balloon at any time prior to positioning the balloon catheter within the body of the patient.

It is understood that although a number of different embodiments of the intravascular catheter system 210 and/or the balloon catheter 218 have been illustrated and described herein, one or more features of any one embodiment can be combined with one or more features of one or more of the other embodiments, provided that such combination satisfies the intent of the present invention.

While a number of exemplary aspects and embodiments of the intravascular catheter system 210 and/or the balloon catheter 218 have been discussed above, those of skill in the art will recognize certain modifications, permutations, additions and sub-combinations thereof. It is therefore intended that the following appended claims and claims hereafter introduced are interpreted to include all such modifications, permutations, additions and sub-combinations as are within their true spirit and scope.

Claims

What is claimed is:

1 . A method for manufacturing a cryogenic balloon for an intravascular catheter system, the method comprising the steps of:

forming the cryogenic balloon; and

pressurizing the cryogenic balloon before insertion of the cryogenic balloon into a body of a patient.

2. The method of claim 1 further comprising the step of heat-bonding the cryogenic balloon to a catheter shaft, and wherein the step of pressurizing occurs after the step of heat-bonding.

3. The method of claim 1 further comprising the step of adhesive-bonding the cryogenic balloon to a catheter shaft, and wherein the step of pressurizing occurs after the step of adhesive-bonding.

4. The method of claim 1 further comprising the step of heat-bonding the cryogenic balloon to a catheter shaft, and wherein the step of pressurizing occurs before the step of heat-bonding.

5. The method of claim 1 further comprising the step of adhesive-bonding the cryogenic balloon to a catheter shaft, and wherein the step of pressurizing occurs before the step of adhesive-bonding.

6. The method of claim 1 wherein the step of pressurizing includes inflating the cryogenic balloon to within a normal operating pressure range that occurs while the cryogenic balloon is within the body of the patient and is receiving a cryogenic fluid.

7. The method of claim 1 further comprising the step of deflating the cryogenic balloon, the step of deflating occurring after the step of pressurizing and before insertion of the cryogenic balloon into the body of the patient.

8. The method of claim 1 wherein the step of pressurizing includes inflating the cryogenic balloon to below a normal operating pressure range that occurs while the cryogenic balloon is within the body of the patient and is receiving a cryogenic fluid.

9. The method of claim 1 wherein the step of pressurizing includes inflating the cryogenic balloon to above a normal operating pressure range that occurs while the cryogenic balloon is within the body of the patient and is receiving a cryogenic fluid.

10. The method of claim 1 wherein the step of pressurizing occurs at approximately 23 degrees Celsius.

1 1 . The method of claim 1 wherein the step of pressurizing occurs at above 23 degrees Celsius.

12. The method of claim 1 wherein the step of pressurizing occurs at below 23 degrees Celsius.

13. The method of claim 1 wherein the step of pressurizing occurs before the intravascular catheter assembly has been fully assembled.

14. The method of claim 1 wherein the step of pressurizing occurs after the intravascular catheter assembly has been fully assembled.

15. The method of claim 1 further comprising the step of sterilizing the cryogenic balloon, and wherein the step of pressurizing occurs after the step of sterilizing.

16. The method of claim 1 further comprising the step of sterilizing the cryogenic balloon, and wherein the step of pressurizing occurs before the step of sterilizing.

17. The method of claim 1 wherein the step of pressurizing is controlled by an operator of the intravascular catheter system.

18. The method of claim 1 wherein the step of pressurizing is controlled by a control system of the intravascular catheter system.

19. A method for manufacturing a cryogenic balloon for an intravascular catheter system, the method comprising the steps of:

forming the cryogenic balloon;

heat-bonding the cryogenic balloon to a catheter shaft;

sterilizing the cryogenic balloon;

pressurizing the cryogenic balloon before insertion of the cryogenic balloon into a body of a patient; and

deflating the cryogenic balloon after pressurizing the cryogenic balloon, but before insertion of the cryogenic balloon into the body of the patient.

20. The method of claim 19 wherein the step of pressurizing includes inflating the cryogenic balloon to within a normal operating pressure range that occurs while the cryogenic balloon is within the body of the patient and is receiving a cryogenic fluid.