Abstract:
A system and method for occluding a pulmonary vein. The device includes a treatment device comprising an inner balloon, an outer balloon, and a space therebetween. Delivery of fluid to the inner balloon inflates the treatment element to a first diameter. If a greater treatment element diameter is required to completely occlude a pulmonary vein, fluid is delivered to the space between the first and second balloons, which expands the second balloon and causes the treatment element to have a second diameter that is greater than the first diameter. The fluid delivered to the inner balloon and fluid delivered to the space between the balloons may be from different sources and may be delivered and exhausted independently. Once the treatment element is caused to have a diameter sufficient to completely occlude the pulmonary vein, the treatment element is activated to cool or heat ostial tissue.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     n/a 
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     n/a 
     FIELD OF THE INVENTION 
     The present invention relates to a method and system for treating cardiac conditions such as cardiac arrhythmia. In particular, the present invention relates to a medical device and use thereof, the medical device having an adjustable treatment element. 
     BACKGROUND OF THE INVENTION 
     A cardiac arrhythmia is a condition in which the heart&#39;s normal rhythm is disrupted. There are many types of cardiac arrhythmias, including supraventricular arrhythmias that begin above the ventricles (such as premature atrial contractions, atrial flutter, accessory pathway tachycardias, atrial fibrillation, and AV nodal reentrant tachycardia), ventricular arrhythmias that begin in the lower chambers of the heart (such as premature ventricular contractions, ventricular tachycardia, ventricular fibrillation, and long QT syndrome), and bradyarrhythmias that involve slow heart rhythms and may arise from disease in the heart&#39;s conduction system. 
     Certain types of cardiac arrhythmias, including ventricular tachycardia and atrial fibrillation, may be treated by ablation (for example, radiofrequency (RF) ablation, cryoablation, hot balloon ablation, ultrasound ablation, laser ablation, microwave ablation, and the like), either endocardially or epicardially. For example, atrial fibrillation (AF) is frequently treated with pulmonary vein ablation (also called pulmonary vein antrum isolation, or PVAI), a procedure that involves positioning a treatment element, such as a cryoballoon or hot balloon (for example, the Toray-Satake balloon), at the mouth or ostium of a pulmonary vein such that the treatment element is in contact with an circumferential area of cardiac tissue at the ostium. After ablation of the ostial tissue, cardiac tissue, such as within or surrounding the pulmonary vein, may be mapped to confirm pulmonary vein isolation. That is, mapping may be used to determine whether aberrant electrical conductivity is still present. For example, a system such as the ARCTIC FRONT® over-the-wire cryoablation catheter system with the ACHIEVE® mapping catheter (both from Medtronic Inc., Minneapolis, Minn.) includes pulmonary vein ablation and mapping functionality. 
     When a cryoballoon or hot balloon is used as the treatment element in a PVAI procedure, it is desirable that the balloon is in complete contact with the pulmonary vein ostial tissue so as to totally occlude the pulmonary vein. However, ostial sizes can vary greatly, both within the same patient (for example, each of the patient&#39;s pulmonary vein ostia may be a different size) and between patients. Currently, a surgeon must have a multitude of differently sized catheters on hand in order to accommodate this variety. Further, a surgeon may have to try several non-reusable catheters to find the right fit, which can be costly and time consuming. 
     It is therefore desirable to provide a system that includes a treatment element that is adjustable to accommodate any of a variety of ostial sizes. 
     SUMMARY OF THE INVENTION 
     The present invention advantageously provides a system, device, and method for treating cardiac conditions such as cardiac arrhythmia. The system may generally include a device having a treatment element having a first balloon defining a chamber and a second balloon disposed about the first balloon, the first balloon and second balloon defining an interstitial space therebetween, a first fluid injection lumen in fluid communication with the chamber and a first fluid reservoir, and a second fluid injection lumen in fluid communication with the interstitial space and a second fluid reservoir. The first balloon may be inflatable to a first diameter by fluid delivered to the chamber from the first fluid reservoir through the first fluid injection lumen and the second balloon being expandable to a second diameter by liquid delivered to the interstitial space by the second fluid reservoir through second fluid injection lumen, the second diameter being greater than the first diameter. The device may further include one or more sensors on the treatment element, such as pressure sensors, and the second diameter may correspond to a diameter of a pulmonary vein ostium within the patient&#39;s heart, with the diameter of the pulmonary vein ostium being determined at least in part by signals from the one or more pressure sensors. The second balloon may be substantially compliant and the first balloon may be substantially noncompliant. The device may further include a fluid injection element and/or a heating element disposed within the chamber. The second balloon may have a uniform wall thickness, or it may have one or more portions having a first wall thickness and one or more portions having a second wall thickness. 
     The device may be used for occluding a pulmonary vein, and may generally include a treatment element including a first balloon defining a chamber and a second balloon disposed about the first balloon, the first balloon and second balloon defining an interstitial space therebetween, a first fluid injection lumen in fluid communication with the chamber, and a second fluid injection lumen in fluid communication with the interstitial space, the first balloon being inflatable to a first diameter by a first fluid delivered to the chamber from the first fluid injection lumen and the second balloon being expandable to a second diameter by a second fluid delivered to the interstitial space by the second fluid injection lumen, the second diameter being greater than the first diameter. For example, the second fluid may be a liquid. The device may further comprise a plurality of pressure sensors on the outer balloon. Further, the second fluid may be at a temperature that causes ablation of tissue. 
     The method may be used for occluding a pulmonary vein, and may generally include positioning a treatment element in contact with an ostium of the pulmonary vein ostium, the treatment element including a first balloon defining a chamber, a second balloon disposed on the outside of the first balloon, and an interstitial space defined between the first balloon and the second balloon, delivering fluid to the chamber to inflate the first balloon and cause the treatment element to have a first diameter, determining whether the treatment element completely occludes the pulmonary vein ostium, and delivering fluid to the interstitial space to expand the second balloon to cause the treatment element to have a second diameter when it is determined that the pulmonary vein ostium is not completely occluded. The chamber may be in fluid communication with a first fluid injection lumen and a first fluid recovery lumen and the interstitial space is in fluid communication with a second fluid injection lumen and a second fluid recovery lumen. The method may further include, after delivering fluid to the interstitial space to expand the second balloon, determining whether the pulmonary vein is completely occluded, and activating the treatment element when it is determined that the pulmonary vein is completely occluded. Activating the treatment element may include circulating a liquid coolant within the interstitial space, the liquid coolant delivered from the second fluid injection lumen and evacuated by the second fluid recovery lumen. Alternatively, activating the treatment element may include heating a thermal coil within the chamber to increase the temperature of the fluid within the interstitial space and/or delivering a liquid to the interstitial space that is heated to a temperature sufficient to cause ablation of tissue. The treatment element may further include a plurality of pressure sensors on the outer second balloon, the plurality of pressure sensors recording at least one of pressure signals generated by contact between the plurality of pressure sensors and the pulmonary vein and pressure signals generated by a lack of contact between the plurality of pressure sensors and the pulmonary vein. The amount of fluid delivered to the interstitial space to expand the second balloon may be determined at least in part on the pressure signals recorded by the plurality of pressure sensors. Further, fluid may be delivered to the interstitial space in fixed-volume increments. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A more complete understanding of the present invention, and the attendant advantages and features thereof, will be more readily understood by reference to the following detailed description when considered in conjunction with the accompanying drawings wherein: 
         FIG. 1  shows an exemplary system including a medical device having an adjustable treatment element; 
         FIG. 2  shows an adjustable treatment element in an uninflated (delivery) configuration; 
         FIG. 3A  shows a cross-sectional view of a first embodiment of an adjustable treatment element in a first inflated (treatment) configuration; 
         FIG. 3B  shows a cross-sectional view of a first embodiment of an adjustable treatment element in a second inflated (treatment) configuration, with fluid injected into the interstitial space between the inner balloon and outer balloon; 
         FIG. 4A  shows a cross-sectional view of a second embodiment of an adjustable treatment element in a first inflated (treatment) configuration; 
         FIG. 4B  shows a cross-sectional view of a second embodiment of an adjustable treatment element in a second inflated (treatment) configuration, with fluid injected into the interstitial space between the inner balloon and outer balloon; 
         FIG. 5  shows an adjustable treatment element in a first inflated configuration positioned at and occluding a pulmonary vein ostium; 
         FIG. 6A  shows an adjustable treatment element in a first inflated configuration positioned at and failing to occlude a pulmonary vein ostium; and 
         FIG. 6B  shows an adjustable treatment element in a second inflated configuration positioned at and occluding the pulmonary vein ostium of  FIG. 6A . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring now to  FIG. 1 , a first and second embodiment of a system including a medical device having an adjustable treatment element are shown. The system  10  generally includes a medical device  12  for ablating tissue and a console  14  that houses various system  10  controls. The system  10  may be adapted for cryoablation and/or hot balloon ablation. Additionally or alternatively, the system  10  may be adapted for radiofrequency (RF) ablation and/or phased radiofrequency (PRF) ablation, ultrasound ablation, laser ablation, microwave ablation, or other energy modalities or combinations thereof. 
     The treatment device  12  may be a catheter having ablation capabilities, and may include mapping capabilities or be usable with a mapping device. As a non-limiting example, the device  12  may be advanceable over a mapping catheter  16 . Further, the device  12  may generally include a handle  18 , an elongate body  20  having a distal portion  22  and a proximal portion  24 , and one or more treatment elements  26  for ablating or thermally treating tissue. For example, the treatment element  26  shown in  FIGS. 1-6B  include at least an inner balloon and an outer balloon  30 . Additionally, the device  12  may include one or more mapping elements for recording electrophysiological signals or may be configured for use with a separate mapping device  16 . For example, the device treatment  12  may include one or more lumens through which a mapping device  16  may be disposed (for example, as shown in  FIG. 1 ). The mapping device  16  may be advanced into a pulmonary vein and used to record electrical activity as myocardial cells polarize and depolarize. The treatment device  12  may then be advanced over the mapping device  16  (as in an over-the-wire system) until the treatment element  26  is in contact with the pulmonary vein ostium Alternatively, one or more mapping elements  32  may be disposed on or coupled to the treatment device  12 . 
     The treatment device  12  may have a longitudinal axis  34 . Likewise, if a separate mapping device  16  is used, the mapping device  16  may also have a longitudinal axis that is substantially coaxial with the longitudinal axis  34  of the treatment device  12 . The one or more treatment elements  26  may be coupled to or disposed on at least a portion of the distal portion  22  of the elongate body  20 . For example, the one or more treatment elements  26  (such as a cryoballoon as shown in  FIGS. 3A and 3B  or a Toray-Satake hot balloon as shown in  FIGS. 4A and 4B ) may include an inner balloon  28  and an outer balloon  30 . As is shown and described in greater detail in the non-limiting examples of  FIGS. 3A and 3B , a liquid coolant may be injected into the interstitial space between the first  28  and second  30  balloons when in an inflated configuration to increase the diameter of the treatment element  26 . 
     The treatment device  12  may include a shaft  36  that is disposed within a main lumen  38  of the elongate body  20 . In embodiments wherein the shape of the treatment element  26  is adjustable, the shaft  36  may be slidably disposed within the main lumen  38 . Further the shaft  36  may define a lumen through which a mapping device  16  may be advanced (for example, as shown in  FIG. 1 ). If the treatment device  12  is a cryoablation catheter (as shown in  FIGS. 1, 3A , and  3 B), the elongate body  20  may include a main lumen  38 , a first fluid injection lumen  40  in fluid communication with a first fluid reservoir  42 , a fluid injection element  44 , and a first fluid exhaust lumen  46  in fluid communication with a first fluid return reservoir  48 . The treatment device  12  may further include a second fluid injection lumen  50  in fluid communication with a second fluid reservoir  52  and a second fluid exhaust lumen  51  in fluid communication with a second fluid return reservoir  54  (as shown in  FIGS. 3A and 3B ). Alternatively, the second fluid exhaust lumen  51  may be in fluid communication with the first fluid return reservoir  48 . 
     If the treatment device  12  is a hot balloon ablation catheter (as shown in  FIGS. 4A and 4B ), the elongate body  20  may include a main lumen  38 , first fluid injection lumen  40  in fluid communication with a first fluid reservoir  42 , a first fluid exhaust lumen  46  in fluid communication with a first fluid return reservoir  48 , and a second fluid injection lumen  50  in fluid communication with a second fluid reservoir  52  and a second fluid exhaust lumen  51  in fluid communication with a second fluid return reservoir  54  (as shown in  FIGS. 4A and 4B ). Alternatively, the second fluid exhaust lumen  51  may be in fluid communication with the first fluid return reservoir  48 . Electrical elements (such as a heating or thermal coil  56 ) within the hot ablation balloon may be in electrical communication with a power source  58  through one or more wires disposed within the main lumen or another lumen of the elongate body  20  (not shown). In some embodiments, one or more other lumens may be disposed within the main lumen, may be disposed within the elongate body  20  along the longitudinal axis  34  parallel to the main lumen  38 , and/or the main lumen  38  may function as the fluid injection lumen or the fluid return lumen. If the treatment device  12  additionally includes, for example, electrodes capable of transmitting RF, ultrasound, microwave, electroporation energy, or the like, these elements may also be in electrical communication with one or more power sources  58  via one or more wires disposed within a lumen of the elongate body  20  (not shown). 
     The console  14  may be in electrical and/or fluid communication with the device  12  and may include one or more fluid (such as coolant, saline, water, or contrast medium) reservoirs  42 ,  52 , fluid return reservoirs  48 ,  54 , power sources  58  (for example, a power source for warming a thermal coil  56  in a hot ablation balloon, or an RF or electroporation energy generator), and one or more computers  60  with displays  62 , and may further include various other displays, screens, user input controls, keyboards, buttons, valves, conduits, connectors, power sources, and computers for adjusting and monitoring system  10  parameters. The computer  60  may be in electrical communication with the one or more treatment elements  26  and the one or more recording electrodes  32 . Further, the computer  60  may include a processor  64  that includes one or more algorithms executable to evaluate signals received from the one or more mapping elements  32 , one or more temperature sensors, pressure sensors, or the like located within or on the treatment device  12  and/or system  10 , and to control, monitor, and/or suggest repositioning of the one or more treatment elements  26 . 
     The computer  60  may further be able to determine a fixed volume of fluid for injecting into the interstitial space between the inner balloon  28  and outer balloon  30  when a larger diameter treatment element  26  is required for pulmonary vein occlusion. As a non-limiting example, the computer may be programmable to incrementally inject the fluid until complete occlusion is achieved. Occlusion may be evaluated by using radiography, magnetic resonance imaging, or similar imaging techniques with a contrast medium. The contrast medium may be expelled from the distal portion of the treatment device into the pulmonary vein. If contrast medium is seen leaking into the left atrium of the heart, then the treatment element  26  must be repositioned until complete occlusion is achieved. Once complete occlusion is visually confirmed, no more fluid may be injected between the balloons  28 ,  30 . Additionally or alternatively, the mapping device may form a loop that is in contact with a circumference of the inside of the pulmonary vein. The computer may use this circumference to determine the diameter of the pulmonary vein and a predicted diameter of the ostium. Then, the computer may determine the required volume of fluid that would sufficiently expand the treatment element to occlude the pulmonary vein, and confirm with imaging. Additionally or alternatively, the treatment element  26  may include one or more sensors  65 , for example, on the outer surface of the outer balloon  30 . As a non-limiting example, the one or more sensors  65  may be discrete sensors distributed around one or more circumferences of the balloon, as shown in  FIG. 1 . The one or more sensors  65  may be, for example, pressure sensors, force sensors, temperature sensors, impedance sensors, or other sensors useful in assessing contact between the treatment element  26  and tissue. Further, the one or more sensors  65  may send signals to the computer  60  that the computer  60  may use to assess contact between the treatment element  26  and the pulmonary vein ostium. As a non-limiting example, the computer  60  may be programmable to stop the delivery of fluid to the treatment element  26  once signals transmitted by one or more pressure sensors  65  indicate that the treatment element  26  is occluding the pulmonary vein ostium. Again, contact may be visually confirmed using one or more imaging techniques. Other sensors may also be positioned throughout the system to monitor system operation (for example, pressure or temperature sensors). Additional fluid may be added or fluid may be removed from between the balloons  28 ,  30  as necessary. 
     Referring now to  FIG. 2 , an adjustable treatment element in an uninflated (delivery) configuration is shown. At least the treatment element  26  and a portion of the elongate body  20  may be passed through the patient&#39;s vasculature and into the patient&#39;s heart via femoral, brachial, radial, or other access means. The septal wall of the heart may be punctured (for example, by another device or delivery sheath) to allow the treatment element  26  of the device  12  to pass therethrough and access the left atrium. During delivery, the inner and outer balloons  28 ,  30  of the treatment element  26  may be uninflated and, for example, folded, wound, compressed, or otherwise disposed about the elongate body  20  and shaft  36  in a low-profile manner (as shown in  FIG. 2 ). Once within the left atrium, the inner balloon  28  may be inflated with a treatment fluid, such as a liquid or gas coolant (if, for example, a cryoballoon is used), water, or saline (if, for example, a hot ablation balloon is used). Saline may include a mixture of water and a salt. Further, the treatment element  26  may be fully or partially retracted within a delivery sheath (not shown) during delivery through the patient&#39;s vasculature. As used herein, the term “inflate” refers to expansion of the treatment element  26  from a delivery configuration to a treatment configuration (as shown in  FIGS. 3A-4B ) through the inflation of the inner balloon  28  with a fluid. The outer balloon  30  will also expand along with the inner balloon  28 . 
     Referring now to  FIG. 3A , a cross-sectional view of a first embodiment of an adjustable treatment element in a first inflated (treatment) configuration is shown. The treatment element  26  shown in  FIGS. 3A and 3B  may be configured for use in cryoablation or cryotreatment procedures. The treatment element  26  may include an inner balloon  28  and an outer balloon  30  that have a similar shape, at least when there is no fluid in the interstitial space  66  between the balloons  28 ,  30 . As used herein, the term “interstitial space” may refer to the interface between the inner balloon  28  and outer balloon  30 , whether fluid is injected between the inner  28  and outer  30  balloons or not. When fluid is injected between the balloons  28 ,  30 , the interstitial space is increased as the fluid separates the outer balloon  30  from the inner balloon  28 . So, in the absence of fluid in the interstitial space  66 , the inner  28  and outer  30  balloons may be in contact with each other along the treatment surface  67  (or the area over which the balloons  28 ,  30  are not affixed to each other, the shaft  36 , or the elongate body  20 ), whereas the balloons  28 ,  30  may be substantially separated from each other along the treatment surface  67  when fluid is in the interstitial space  66 . 
     The inner balloon  28  may have a fixed shape and outer diameter when inflated, and may be composed of, for example, a noncompliant or low-compliant material such as polyethylene terephthalate (PET) or nylon. Alternatively, the inner balloon  28  may be composed of a shape memory material that expands to an “inflated” shape upon being warmed by the patient&#39;s body temperature or using another mechanism to control the shape of the inner balloon  28  (for example, extending the shape memory material to have a small diameter of inner balloon). In this case, the inner balloon may not be in fluid communication with a first fluid injection lumen  40  or a first fluid exhaust lumen  46 . Conversely, the outer balloon  30  may be composed of, for example, a compliant or highly compliant material such as polyethylene (PE) or other polyolefins, polyurethanes, or polyvinylchloride (PVC). The compliant nature of the outer balloon  30  may allow it to conform to the shape of the inner balloon  28  when the inner balloon  28  is inflated. 
     The inner balloon  28  may define a fluid chamber  68  into which a fluid (liquid or gas) may flow to inflate the inner balloon  28 . As a non-limiting example, the fluid may be a biocompatible liquid, such as water, saline, contrast medium, or combination thereof. As the outer balloon  30  substantially conforms to the shape of the inner balloon  28  in this configuration, the outer balloon  30  may also be referred to as defining the fluid chamber  68 . Although the inner  28  and outer  30  balloons are shown as being separated by a gap in  FIG. 3A , this is to illustrate the interstitial space  66  that may later be filled with a liquid coolant. In practice, the inner  28  and outer  30  balloons may be in contact with each other in this configuration, with the interstitial space  66  being defined as fluid is injected between the balloons  28 ,  30 . Fluid may enter the chamber  68  from the injection element  44  through the first fluid injection lumen  40 , and may exit the chamber  68  through the fluid exhaust lumen  46 . For example, the fluid recover lumen  46  may be in communication with a vacuum source  70 . 
     Each of the balloons  28 ,  30  may include a distal neck portion  72 ,  74  and a proximal neck portion  76 ,  78  that are affixed to the device  12  at a connection point or bond joint. As a non-limiting example, at least part of the distal neck portion  72 ,  74  of each balloon  28 ,  30  may be affixed to a distal portion  80  of the shaft  36 . Further, an inner surface of the outer balloon distal neck  74  may also be affixed to an outer surface of the inner balloon distal neck  72 . Likewise, at least a part of the proximal neck portion  76 ,  78  of each balloon  28 ,  30  may be affixed to a distal portion  22  of the elongate body  20 . Further, an inner surface of the outer balloon proximal neck  78  may also be affixed to an outer surface of the inner balloon distal neck  76  (as shown in  FIG. 3A ). However, it will be understood that other balloon attachment means and configurations may be used. If the surgeon determines that the diameter of the balloon in this configuration is sufficient to occlude the pulmonary vein, the treatment procedure may be performed without additional expansion of the outer balloon (that is, without injecting fluid between the inner  28  and outer  30  balloons  30 ). In that case, the inner balloon  28  may be filled with the fluid coolant. When the procedure is over, the inner balloon  28  may be deflated by removing fluid from the chamber  68 . Optionally, removed fluid may be stored, for example, in a fluid return reservoir  48 . 
     Referring now to  FIG. 3B , a cross-sectional view of a first embodiment of an adjustable treatment element in a second inflated (treatment) configuration, with fluid injected into the interstitial space between the inner balloon and outer balloon is shown. The fluid may be injected into the interstitial space  66  between the balloons  28 ,  30  from a second fluid reservoir  52 . For example, a volume of fluid determined by the computer  60  may pass from the second fluid reservoir  52  through the second fluid injection lumen  50  into the interstitial space  66 . As a non-limiting example, the computer  60  may be programmable to stop the delivery of fluid to the interstitial space  66  once signals transmitted by the one or more pressure sensors  65  indicate that the treatment element  26  is occluding the pulmonary vein ostium. Likewise, fluid may be removed from the interstitial space  66  through the second fluid exhaust lumen  51 , which may be in communication with a vacuum source  70 . The fluid injected into the interstitial space  66  may be a liquid coolant. The outer balloon  30  may reach temperatures capable of ablating tissue by virtue of the temperature of the liquid in the interstitial space  66 . This liquid may be a liquid coolant that is pre-cooled by the console  14  or a liquid (either a liquid coolant or other liquid that is capable of being cooled to ablation temperatures) that is, for example, cooled by virtue of a fluid coolant circulating within the chamber  68  of the inner balloon  28 . Alternatively, the liquid within the interstitial space  66  may be cooled by a combination thereof. The computer may determine a fixed volume of liquid coolant to inject, and may inject that amount of fluid into the interstitial space  66  incrementally until complete pulmonary vein occlusion is confirmed. Further, the system  10  may include an adjustment fluid reservoir  82  that is supplied from the second fluid reservoir  52  and one or more valves. As a non-limiting example, a valve between the interstitial space  66  and the adjustment fluid reservoir  82  may be closed while a valve between the second fluid reservoir  52  and the adjustment fluid reservoir  82  is open. This allows the adjustment fluid reservoir  82  to be filled with a fixed amount of fluid before the coolant is allowed to pass into the interstitial space  66 . Once the adjustment fluid reservoir  82  is filled with the fixed fluid volume, the valve between the adjustment fluid reservoir  82  and the interstitial space  66  may be opened and the valve between the adjustment fluid reservoir  82  and the second fluid reservoir  52  may be closed. 
     The outer balloon  30  may have a uniform thickness or may have various thicknesses that determine the shape of the outer balloon  30  and/or maximum outer diameter. For example, the outer balloon  30  may include one or more areas having a first thickness and one or more areas having a second thickness. Depending on the desired outer balloon  30  characteristics, the one or more areas of first and second thicknesses may be positioned partially or entirely around a circumference of the balloon and/or may be discrete areas of various sizes and shapes. This may allow the outer balloon  30  to assume different shapes, depending on the size and/or location of wall thickness differences and the volume of fluid injected into the interstitial space  66 . 
     Referring now to  FIGS. 4A and 4B , a cross-sectional view of a second embodiment of an adjustable treatment element in a second inflated (treatment) configuration is shown, both without ( FIG. 4A ) and with ( FIG. 4B ) fluid in the interstitial space  66  between the first balloon  28  and second balloon  30 . The adjustable treatment element  26  shown in  FIGS. 4A and 4B  are generally as shown and described in  FIGS. 1-3B , except that the treatment element  26  may be usable for hot balloon ablation, such as the Toray-Satake balloon. As such, the inner balloon  28  may include a thermal coil  56  that, when activated, heats fluid within the fluid chamber  68  of the inner balloon  28 . Heat from the fluid chamber  68  is transmitted through the first  28  and second  30  balloons to the tissue being treated. Heat from the fluid chamber  68  may warm fluid within the interstitial space  66  to ablation temperatures, or the fluid injected into the interstitial space  66  may be pre-warmed by the system  10  before injection. Like the adjustable treatment element  26  of  FIGS. 3A and 3B , the adjustable treatment element  26  of  FIGS. 4A and 4B  includes first  40  and second  50  fluid injection lumens and first  46  and second  51  fluid exhaust lumens. Fluid, such as a gas or a liquid (for example, water, saline, mixture of water and saline, or other thermally conductive fluids), may be introduced into the fluid chamber  68  from the first fluid injection lumen  40  and removed from the fluid chamber  68  from the first fluid exhaust lumen  46 . Likewise, liquid (such as water, saline, contrast medium, or other biocompatible fluids and mixtures thereof) may be injected into the interstitial space  66  between the first  28  and second balloons  30  from the second fluid injection lumen  50  and removed from the interstitial space  66  from the second fluid exhaust lumen  51 . For example, fluid may be added and removed from the interstitial lumen  66  for adjusting the outer diameter of the treatment element  26 . 
     Referring now to  FIGS. 5-6B , an adjustable treatment element is shown at a pulmonary vein ostium. As shown in  FIG. 5 , the adjustable treatment element  26  may have a sufficient outer diameter to completely occlude a pulmonary vein ostium when the inner balloon  28  is inflated and no fluid is injected into the interstitial space  66  between the inner  28  and outer  30  balloons. The device  12  is shown in  FIG. 5  without a mapping device  16 , although it will be understood that one may be used (for example, as shown in  FIGS. 6A and 6B ). In contrast,  FIG. 6A  shows a scenario in which the pulmonary vein ostium is wider than the diameter of the adjustable treatment element  26  when the treatment element  26  is inflated but with no interstitial fluid. In this case, the treatment element  26  will not occlude the pulmonary vein. The outer diameter of the treatment element  26  is determined by the maximum inflation volume of the inner balloon  28 , as the compliant outer balloon  30  assumes the shape of the inflated inner balloon  28  before fluid is injected into the interstitial space  66 . As shown in  FIG. 6B , the injection of fluid into the interstitial space  66  may increase the outer diameter of the treatment element  26 , allowing the treatment element  26  to completely occlude the pulmonary vein. Fluid may be injected in a single fixed volume or incrementally in fixed volumes. The amount of fluid injected may be determined by the computer  60  (for example, using signals received from one or more pressure sensors  65  to determine contact with the pulmonary vein ostium) and/or determined manually by the user. Complete occlusion may be visually confirmed using one or more imaging techniques. Additionally, fluid may be added or removed (for example, by opening the second fluid exhaust lumen  51  to a vacuum source  70 ) as required to achieve complete occlusion. 
     It will be appreciated by persons skilled in the art that the present invention is not limited to what has been particularly shown and described herein above. In addition, unless mention was made above to the contrary, it should be noted that all of the accompanying drawings are not to scale. A variety of modifications and variations are possible in light of the above teachings without departing from the scope and spirit of the invention, which is limited only by the following claims.