Abstract:
Cardiac catheterization is conducted using a probe having a balloon assembly, in which a spring has a resting axially elongated configuration and a torsed, axially shortened configuration. An inflatable balloon is twisted about the spring and mechanically linked to the spring. A flexible sheath is disposed about the spring within the balloon, the sheath and the wall of the balloon defining a chamber to contain a fluid flowing therein and thereout for inflation of the balloon and deflation of the balloon so as to energize and de-energize the spring.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    This invention relates to medical devices. More particularly, this invention relates to improvements in cardiac catheterization. 
         [0003]    2. Description of the Related Art 
         [0004]    Cardiac arrhythmias, such as atrial fibrillation, occur when regions of cardiac tissue abnormally conduct electric signals to adjacent tissue, thereby disrupting the normal cardiac cycle and causing asynchronous rhythm. 
         [0005]    Procedures for treating arrhythmia include surgically disrupting the origin of the signals causing the arrhythmia, as well as disrupting the conducting pathway for such signals. By selectively ablating cardiac tissue by application of energy via a catheter, it is sometimes possible to cease or modify the propagation of unwanted electrical signals from one portion of the heart to another. The ablation process destroys the unwanted electrical pathways by formation of non-conducting lesions. 
         [0006]    Circumferential lesions at or near the ostia of the pulmonary veins have been created to treat atrial arrhythmias. U.S. Pat. Nos. 6,012,457 and 6,024,740, both to Lesh, disclose a radially expandable ablation device, which includes a radiofrequency electrode. Using this device, it is proposed to deliver radiofrequency energy to the pulmonary veins in order to establish a circumferential conduction block, thereby electrically isolating the pulmonary veins from the left atrium. 
         [0007]    U.S. Pat. No. 6,814,733 to Schwartz et al., which is commonly assigned herewith and herein incorporated by reference, describes a catheter introduction apparatus having a radially expandable helical coil as a radiofrequency emitter. In one application the emitter is introduced percutaneously, and transseptally advanced to the ostium of a pulmonary vein. The emitter is radially expanded, which can be accomplished by inflating an anchoring balloon about which the emitter is wrapped, in order to cause the emitter to make circumferential contact with the inner wall of the pulmonary vein. The coil is energized by a radiofrequency generator, and a circumferential ablation lesion is produced in the myocardial sleeve of the pulmonary vein, which effectively blocks electrical propagation between the pulmonary vein and the left atrium. 
         [0008]    Another example is found in U.S. Pat. No. 7,340,307 to Maguire, et al., which proposes a tissue ablation system and method that treats atrial arrhythmia by ablating a circumferential region of tissue at a location where a pulmonary vein extends from an atrium. The system includes a circumferential ablation member with an ablation element and includes a delivery assembly for delivering the ablation member to the location. The circumferential ablation member is generally adjustable between different configurations to allow both the delivery through a delivery sheath into the atrium and the ablative coupling between the ablation element and the circumferential region of tissue. 
       SUMMARY OF THE INVENTION 
       [0009]    Commonly assigned copending application Ser. No. 14/578,807, which is herein incorporated by reference, describes how a balloon catheter may be injected with saline and used to ablate the ostium of a pulmonary vein. This and other applications of an improved balloon catheter are addressed herein. 
         [0010]    In embodiments of the present invention a spring, and a flexible protective sleeve for the spring are inserted into the balloon. In the deflated (fully evacuated) state of the balloon, the spring is uncompressed and untwisted, and is in its resting state. The untwisted, uncompressed spring is configured to retain the deflated balloon around the spring, so that the deflated balloon arranges compactly and tidily about the spring. 
         [0011]    The balloon is inflated by being injected with saline solution. The inflation forces the spring to compress and twist from its resting state. When the balloon is inflated the spring is in its compressed, twisted state and has torque. When the balloon is fully deflated, the spring is extended, untwisted and torsionless. 
         [0012]    By incorporating a spring which both compresses and twists as described above, embodiments of the present invention enable the deflated balloon to be stored efficiently and neatly for delivery through a guiding sheath, while the inflated balloon is maintained in its correct inflated shape. 
         [0013]    There is provided according to embodiments of the invention an ablation apparatus including a probe having a hollow shaft, a longitudinal axis and a distally disposed balloon assembly. The balloon assembly includes a spring having a resting axially elongated configuration and a torsed, axially shortened configuration. An inflatable balloon is mechanically linked to the spring. A flexible sheath is disposed about the spring within the balloon, the sheath and the wall of the balloon defining a chamber to contain a fluid flowing therein and thereout for inflation and deflation of the balloon. Inflation urges the spring into the torsed, axially shortened configuration and deflation permits the spring to return to the resting axially elongated configuration. 
         [0014]    In one aspect of the apparatus includes proximal and distal couplers attached to the balloon and the sheath. The proximal and distal couplers are independently rotatable about the longitudinal axis of the probe. 
         [0015]    According to yet another aspect of the apparatus, the proximal and distal couplers have a lumen for slidably receiving an extrusion therethrough. 
         [0016]    According to still another aspect of the apparatus, at least one of the proximal and distal couplers has ports formed therein to establish fluid communication between the chamber and a fluid source via the shaft. 
         [0017]    According to another aspect of the apparatus, in the resting axially elongated configuration the balloon is wrapped about the spring. 
         [0018]    According to a further aspect of the apparatus, the balloon assembly is deployable through the steerable guiding sheath. 
         [0019]    There is further provided according to embodiments of the invention a method which is carried out by inserting a probe having a hollow shaft, and a distally disposed balloon assembly into a heart of a subject. The balloon assembly includes a spring having a resting axially elongated configuration and a torsed axially shortened configuration, an inflatable balloon mechanically linked to the spring and enclosing the spring. The method is further carried out by urging the spring into the torsed axially twisted configuration by flowing a fluid into the chamber to thereby inflate the balloon, and deflating the balloon by removing the fluid from the chamber to allow the spring to assume the resting axially elongated configuration. 
         [0020]    According to another aspect of the method, the balloon assembly also includes proximal and distal couplers attaching to the balloon. 
         [0021]    According to an additional aspect of the method, the proximal and distal couplers are independently rotatable about the longitudinal axis. 
         [0022]    According to still another aspect of the method, the proximal and distal couplers have a lumen for slidably receiving an extrusion therethrough. 
         [0023]    According to yet another aspect of the method, at least one of the proximal and distal couplers has ports formed therein, and flowing a fluid is performed by passing the fluid between the chamber and a fluid source via the shaft. 
         [0024]    According to a further aspect of the method, in the resting axially elongated configuration the balloon is wrapped about the spring, and inflating the balloon comprises unwrapping the balloon about the spring. Deflating the balloon comprises wrapping the balloon about the spring. 
         [0025]    One aspect of the method includes deploying the balloon assembly through a steerable guiding sheath. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         [0026]    For a better understanding of the present invention, reference is made to the detailed description of the invention, by way of example, which is to be read in conjunction with the following drawings, wherein like elements are given like reference numerals, and wherein: 
           [0027]      FIG. 1  is a pictorial illustration of a system for performing catheterization procedures on a heart, in accordance with a disclosed embodiment of the invention; 
           [0028]      FIG. 2  is a view of the distal portion of the catheter shown in  FIG. 1  in accordance with an embodiment of the invention; 
           [0029]      FIG. 3  is another view of the distal portion of the catheter shown in  FIG. 1  in accordance with an embodiment of the invention; 
           [0030]      FIG. 4  is a pictorial series of three side elevations of a balloon assembly in accordance with an embodiment of the invention; 
           [0031]      FIG. 5  is a sectional view through the longitudinal axis of a probe in accordance with an embodiment of the invention; 
           [0032]      FIG. 6  is an elevation of a spring, which is incorporated in a balloon assembly in accordance with an embodiment of the invention; and 
           [0033]      FIG. 7  is a flow-chart of a method of cardiac catheterization in accordance with an embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0034]    In the following description, numerous specific details are set forth in order to provide a thorough understanding of the various principles of the present invention. It will be apparent to one skilled in the art, however, that not all these details are necessarily needed for practicing the present invention. In this instance, well-known circuits, control logic, and the details of computer program instructions for conventional algorithms and processes have not been shown in detail in order not to obscure the general concepts unnecessarily. 
       System Description. 
       [0035]    Turning now to the drawings, reference is initially made to  FIG. 1 , which is a pictorial illustration of a system  10  for evaluating electrical activity and performing ablative procedures on a heart  12  of a living subject, which is constructed and operative in accordance with a disclosed embodiment of the invention. The system comprises a catheter  14 , which is percutaneously inserted by an operator  16  through the patient&#39;s vascular system into a chamber or vascular structure of the heart  12 . The operator  16 , who is typically a physician, brings the catheter&#39;s distal tip  18  into contact with the heart wall, for example, at an ablation target site. Electrical activation maps may be prepared, according to the methods disclosed in U.S. Pat. Nos. 6,226,542, and 6,301,496, and in commonly assigned U.S. Pat. No. 6,892,091, whose disclosures are herein incorporated by reference. One commercial product embodying elements of the system  10  is available as the CARTO® 3 System, available from Biosense Webster, Inc., 3333 Diamond Canyon Road, Diamond Bar, Calif. 91765. This system may be modified by those skilled in the art to embody the principles of the invention described herein. 
         [0036]    Areas determined to be abnormal, for example by evaluation of the electrical activation maps, can be ablated by application of thermal energy, e.g., by passage of radiofrequency electrical current through wires in the catheter to one or more electrodes at the distal tip  18 , which apply the radiofrequency energy to the myocardium. The energy is absorbed in the tissue, heating it to a point (typically above 60° C.) at which it permanently loses its electrical excitability. When successful, this procedure creates non-conducting lesions in the cardiac tissue, which disrupt the abnormal electrical pathway causing the arrhythmia. The principles of the invention can be applied to different heart chambers to diagnose and treat many different cardiac arrhythmias. 
         [0037]    The catheter  14  typically comprises a handle  20 , having suitable controls on the handle to enable the operator  16  to steer, position and orient the distal end of the catheter as desired for the ablation. To aid the operator  16 , the distal portion of the catheter  14  contains position sensors (not shown) that provide signals to a processor  22 , located in a console  24 . The processor  22  may fulfill several processing functions as described below. 
         [0038]    Wire connections  35  link the console  24  with body surface electrodes  30  and other components of a positioning sub-system for measuring location and orientation coordinates of the catheter  14 . The processor  22  or another processor (not shown) may be an element of the positioning subsystem. Catheter electrodes (not shown) and the body surface electrodes  30  may be used to measure tissue impedance at the ablation site as taught in U.S. Pat. No. 7,536,218, issued to Govari et al., which is herein incorporated by reference. Temperature sensors (not shown), typically a thermocouple or thermistor, may be mounted on ablation surfaces on the distal portion of the catheter  14  as described below. 
         [0039]    The console  24  typically contains one or more ablation power generators  25 . The catheter  14  may be adapted to conduct ablative energy to the heart using any known ablation technique, e.g., radiofrequency energy, ultrasound energy, and laser-produced light energy. Such methods are disclosed in commonly assigned U.S. Pat. Nos. 6,814,733, 6,997,924, and 7,156,816, which are herein incorporated by reference. 
         [0040]    In one embodiment, the positioning subsystem comprises a magnetic position tracking arrangement that determines the position and orientation of the catheter  14  by generating magnetic fields in a predefined working volume and sensing these fields at the catheter, using field generating coils  28 . The positioning subsystem is described in U.S. Pat. No. 7,756,576, which is hereby incorporated by reference, and in the above-noted U.S. Pat. No. 7,536,218. 
         [0041]    As noted above, the catheter  14  is coupled to the console  24 , which enables the operator  16  to observe and regulate the functions of the catheter  14 . Console  24  includes a processor, preferably a computer with appropriate signal processing circuits. The processor is coupled to drive a monitor  29 . The signal processing circuits typically receive, amplify, filter and digitize signals from the catheter  14 , including signals generated by sensors such as electrical, temperature and contact force sensors, and a plurality of location sensing electrodes (not shown) located distally in the catheter  14 . The digitized signals are received and used by the console  24  and the positioning system to compute the position and orientation of the catheter  14 , and to analyze the electrical signals from the electrodes. 
         [0042]    In order to generate electroanatomic maps, the processor  22  typically comprises an electroanatomic map generator, an image registration program, an image or data analysis program and a graphical user interface configured to present graphical information on the monitor  29 . 
         [0043]    Typically, the system  10  includes other elements, which are not shown in the figures for the sake of simplicity. For example, the system  10  may include an electrocardiogram (ECG) monitor, coupled to receive signals from one or more body surface electrodes, in order to provide an ECG synchronization signal to the console  24 . As mentioned above, the system  10  typically also includes a reference position sensor, either on an externally-applied reference patch attacked to the exterior of the subject&#39;s body, or on an internally-placed catheter, which is inserted into the heart  12  maintained in a fixed position relative to the heart  12 . Conventional pumps and lines for circulating liquids through the catheter  14  for cooling the ablation site are provided. The system  10  may receive image data from an external imaging modality, such as an MRI unit or the like and includes image processors that can be incorporated in or invoked by the processor  22  for generating and displaying images. 
       Balloon Assembly. 
       [0044]    Reference is now made to  FIG. 2 , which is an oblique view of the distal portion of a balloon assembly  38  at the distal end of shaft  40  of catheter  14  in accordance with an embodiment of the invention, in accordance with an embodiment of the invention. Extending through the lumen of the shaft  40  and protruding beyond the tip is a flexible polymer extrusion  42 . The extrusion  42  may be used for device access, for example a guidewire to assist in introducing the catheter. Ports  44  are provided for irrigation and for inflation of a polymer balloon  46 . The fluid is allowed to exit the inflated balloon through small pores  47   
         [0045]    A spring mechanism  48  comprises a piston-type coaxial compression spring  50 , overlying the extrusion  42 , is attached to the shaft  40  by couplers  52 ,  54 . The spring  50  is rigidly bonded to the proximal and distal ends of the balloon  46  or to the couplers  52 ,  54 . A flexible sleeve  56  connected to the couplers  52 ,  54  is enclosed by the balloon  46 . The sleeve  56  surrounds the spring  50  and prevents fluid in a chamber defined by the outer wall of the sleeve  56  and the inner wall of the balloon  46  from escaping through the interstices of the spring  50 . 
         [0046]    During manufacture, while the spring  50  is in its home position, and not influenced by external forces, the proximal end of the balloon  46  is secured to the proximal end of the balloon assembly  38  or the coupler  52 . The balloon  46  is then stretched axially by about 1 cm, and twisted axially (about one-half to one full twist) before being secured to the distal end of the balloon assembly  38  or the coupler  54 . When the balloon  46  is inflated, internal fluid pressure causes it to untwist and to shorten axially by about 1 cm. Since the balloon  46  is mechanically linked to the balloon  46 , an angular force is transmitted by the untwisting balloon through the couplers  52 ,  54  to the spring  50 , thereby producing torsion upon and compressing the spring  50 . As a result the spring  50  transitions from a resting axially elongated configuration into a torsed, axially shortened configuration, and the entire balloon assembly  38  becomes axially shortened and the balloon becomes radially enlarged. 
         [0047]    Reference is now made to  FIG. 3  which is a view of the distal portion of the catheter  14  ( FIG. 1 ) in accordance with an embodiment of the invention. A lasso guide  58  has been deployed through the catheter  14  and is engaged with the wall of pulmonary vein  60 . Balloon  46  has been inflated, and is stabilized by the lasso guide  58  that is anchored against the vessel wall. Correct placement of the balloon  46  in the pulmonary vein  60  can be verified by injecting a contrast agent through the catheter  14 . Additionally or alternatively the contrast agent may be injected into the balloon  46 . The balloon  46  may be provided with electrodes  62  as taught in the above noted application Ser. No. 14/578,807, The electrodes  62  can be used for mapping or ablation. 
         [0048]    Reference is now made to  FIG. 4 , which is a pictorial series of three side elevations of the balloon assembly  38  in various phases of inflation and deflation in accordance with an embodiment of the invention. The balloon  46  and spring mechanism  48  are enabled by the couplers  52 ,  54  to slide over and rotate freely and independently with respect to one another about the extrusion  42 , i.e., about the longitudinal axis of the catheter. The balloon  46  is inflated by pressure exerted by fluid entering the balloon  46  through pores  64 . The expanding balloon shortens along its longitudinal axis but increases in transverse diameter (line A-A). In the uppermost image the balloon  46  is fully inflated. As a result of internal fluid pressure and consequent deformation of the balloon, the spring  50  is urged into a fully compressed and maximally torsed state, effectively shortening its length dimension (D-D). 
         [0049]    In the middle image release of the internal fluid pressure, e.g., by a valve (not shown), has allowed the balloon  46  to partially deflate, aided by the restorative force of the spring  50 . The spring  50  attempts to return to its resting state by lengthening, untwisting and opposing the internal fluid pressure in the balloon  46 , thereby aiding the fluid to escape through the pores  64 . Additionally or alternatively the fluid may escape through pores  47 , In the middle image, the spring  50  is partially untwisted, and its length dimension (line E-E) is larger than its length dimension (line D-D) in the uppermost image. 
         [0050]    In the lowermost image, the balloon  46  is fully deflated and the balloon assembly  38  fully collapsed. In this configuration the balloon assembly  38  can be introduced through the lumen of a catheter and withdrawn upon completion of a medical procedure. The spring  50  is in a resting state, fully extended and exerting no torsion on the mechanism. Its length dimension (F-F) is maximal relative to the length dimensions D-D, E-E. 
         [0051]    Reference is now made to  FIG. 5 , which is a sectional view through the longitudinal axis of a probe  66 , in accordance with an embodiment of the invention. A hollow inner shaft  68  extends through the lumen of the probe  66 . Its functions are to support balloon assembly  70  and to provide ingress for a guidewire (not shown). Balloon  72  is adhered to a proximal section  74  of the probe  66  by a circumferential seal  76 . The balloon  72  adheres to a discontinuous distal section  78  by circumferential seal  80 . A lumen  82  leads into a manifold  84  that is defined by the outer surface of the shaft  68 , the inner surface  86  of the probe  66  and by seals  88 ,  90 . Pores  92  allow communication for fluid flowing through the lumen  82  and the manifold  84  to inflate and deflate the balloon  72 . 
         [0052]    Reference is now made to  FIG. 6 , which is an elevation of the spring  94 , which is incorporated in a balloon assembly in accordance with an embodiment of the invention. The spring  94  may be made of a resilient plastic material such as PEEK™ or metal such as nitinol or stainless steel. The spring  94  has a shaft  96  that may be twisted and untwisted about its longitudinal axis  98 , as shown by arrow  100 , so that the spring alternates between a relaxed elongated state and a torsed, compressed state. When transitioning into the compressed state interstices  102  that separate coils  104  become narrow, and the spring  94  shortens on the longitudinal axis  98 . A coupler  106  is attached to the shaft  96  aby either by a weld, to form one integral unit, or by other means. One of couplers is omitted in  FIG. 6 . A longitudinal slot  108  is formed in the shaft  96 . It provides a port to route the saline into the balloon. 
       Operation. 
       [0053]    Reference is now made to  FIG. 7 , which is a flow-chart of a method of cardiac catheterization using a balloon catheter in accordance with an embodiment of the invention. This example concerns operations at the pulmonary vein ostia; however, the method is applicable, mutatis mutandis, to other structures and procedures in the heart. The process steps are shown in a particular linear sequence for clarity of presentation. However, it will be evident that many of them can be performed in parallel, asynchronously, or in different orders. Moreover, not all illustrated process steps may be required to implement the method. The method is disclosed for clarity of exposition with reference to the preceding figures, but is applicable to other embodiments and configurations of the balloon assembly as well. 
         [0054]    At initial step  83  a cardiac catheter is conventionally introduced into the left atrium of a heart. A guiding sheath may be employed to deploy the lasso guide and balloon. The Destino™ 12-F steerable guiding sheath is suitable for this purpose. 
         [0055]    Next, at step  85  a lasso guide is deployed and positioned to engage the interior wall of a pulmonary vein. At this stage the spring  50  in the balloon assembly  38  is fully extended and in an untorsioned state. The balloon  46  and sleeve  56  are wrapped about and collapsed to their maximum extent. When the balloon  46  is fully inflated, the spring  50  is compressed and fully twisted with respect to its initial position. 
         [0056]    Next, at step  87  the balloon is extended over the lasso guide and inflated by causing a fluid flow through the ports  44  into a chamber that is defined by the inner wall of the balloon  46  and the sleeve  56 . As inflation occurs, saline enters the balloon  46  through the ports  44 . The spring  50  compresses and twists, in opposition to forces exerted by the expanding balloon. 
         [0057]    Next, at step  89  the balloon is navigated into circumferential contact with a pulmonary vein ostium in order to occlude the ostium. 
         [0058]    Next, at an optional step  91  a radio-opaque contrast agent is injected through the lumen of the catheter and through appropriate irrigation ports of the catheter into the pulmonary vein in order to confirm that the balloon is in a correct position against the pulmonary vein ostium. The contrast agent does not enter the balloon. 
         [0059]    Control now proceeds to decision step  93 , where it is determined if the balloon is correctly positioned. If the determination at decision step  93  is negative, then control returns to step  89  and another attempt is made to position the balloon. 
         [0060]    If the determination at decision step  93  is affirmative then control proceeds to step  95  where a medical procedure, e.g., mapping or ablation is performed using appropriate ablation electrodes on the catheter. 
         [0061]    After completion of the ablation, the procedure may be iterated using another pulmonary vein ostium by withdrawal of the balloon and the lasso guide  58 . Control may then return to step  85 . Alternatively, the procedure may end by removal of the catheter at final step  97 . Prior to removal of the catheter the balloon is deflated. Referring again to  FIG. 4 , the procedure is essentially a reversal of the inflation procedure, and assisted by the action of the spring  50 , which extends and untwists, thereby assisting the balloon to compress and fold about the spring  50  and the underlying shaft, e.g., extrusion  42 . The fluid contents of the balloon  46  leave the balloon through pores  47 . 
         [0062]    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 hereinabove. Rather, the scope of the present invention includes both combinations and sub-combinations of the various features described hereinabove, as well as variations and modifications thereof that are not in the prior art, which would occur to persons skilled in the art upon reading the foregoing description.