Abstract:
A fluid delivery catheter configured to allow optimal fluid distribution through each electrode by varying the diameter of a catheter lumen is disclosed. Uniform or different fluid flow rates through longitudinally spaced apart elution holes may be achieved. Exemplary fluids for use with the catheter include a cooling fluid, a therapeutic fluid, and a medication.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is related to U.S. patent application Ser. No. 11/696,657 filed Apr. 4, 2007, the entire disclosure of which is hereby expressly incorporated by reference in its entirety. 
     FIELD OF THE INVENTION 
     The field of the invention is catheters. 
     BACKGROUND OF THE INVENTION 
     Ablation catheters using RF (radio frequency) energy are known. A typical ablation catheter has electrodes located at the catheter tip and ean delivers RF energy to ablate selected tissue areas in a patient. For example, patients with arrhythmia experience irregular heart beats caused by arrhythmogenic electrical signals generated in cardiac tissues. Such patients may be treated by ablating those cardiac tissues that generate such unintended electrical signals with RE energy. With the help of sensing and mapping tools, an electrophysiologist can determine the region of cardiac tissue targeted for ablation. Once determined, a catheter tip having one or more electrodes is positioned over the targeted tissue. Then, the user sends RF energy from the generator to the electrodes, creating sufficient heat to damage the targeted tissue. By damaging and scarring the targeted tissue, aberrant electrical signal generation or transmission is interrupted. 
     Application of curative energy is currently performed endocardially with the objective of reaching the epicardium to create a fully transmural. This is important in all arrhythmias especially during ablation for atrial fibrillation and ventricular tachycardia. In the former case, transmural lesions are required to create conduction block to isolate relevant structures while in the latter case the arrhythmogenic substrate is located often in the epicardial layer of ventricular walls. Delivery of the energy is limited by the increase of temperature at the interface between catheter tip and endocardial surface and there is a good correlation between thrombus formation and high temperature. A temperature sensor is typically provided near the tip of the catheter so the user may monitor the operating temperature to ensure that overheating does not occur in the catheter tip and in the surrounding tissues. One known solution to prevent overheating is by having an irrigation system embedded within the catheter. In brief, a typical irrigation system includes a delivery lumen inside of the catheter body to supply cooling fluid, such a saline, from a pump to the catheter tip. An irrigation system may internally irrigate the catheter tip, where the cooling fluid circulates within the catheter tip. Another type of irrigation system delivers cooling fluid from within the catheter tip to the outside of the catheter tip which also cools the surrounding tissues. Catheters with an irrigated tip allow the delivery of more energy with a lower temperature at the tissue/catheter interface thus minimizing thrombus formation while maximizing deep lesion creation in the tissue. Despite numerous desirable properties, however, known irrigated catheters have several disadvantages. For example, because the temperature of the catheter tip region can vary depending on factors such as its proximity to an electrode and irrigation duct, it is difficult to monitor and ensure that all heated surfaces along the catheter tip are adequately cooled. Often the catheter tip is positioned not perpendicularly to the tissue but tangentially to increase the tip/tissue contact area as for example during ablation of the inferior part of the right sided pulmonary vein. In this situation and in every other situation where a tip side/tissue contact is required, a uniform cooling of the catheter tip would further reduce thrombus formation while allowing development of larger electrodes to more efficiently deliver energy for ablation. In this way the entire electrode surface can be used to ablate a pathological tissue without overheating any portion of the catheter tip and causing thrombus formation. 
     The coronary sinus (CS) is increasingly recognized as one of the major structures contributing in many types of supraventricular tachycardias including atrial fibrillation. In this case many anatomical and electrophysiological features can promote atrial fibrillation maintenance, especially in patients with a long-standing arrhythmia. As a matter of fact, the CS connects anatomically and electrophysiologically the right atrium and the left atrium with special characteristics of slow and anisotropic conduction, allowing micro- and macro-reentry during organized and unorganized atrial fibrillation. On the right atrial side, broad and thick muscular connections can be observed at the CS ostium, while different anatomic studies have demonstrated the existence of discrete and multiple connections (average 5±2) between the CS body and the LA postero-inferior and postero-lateral walls. This muscular extension of the left atrial wall into the CS shows marked anisotropy, and mapping their insertion with conventional bipolar and quadripolar catheters is relatively difficult given also the oblique insertion of these sleeves across the posterior pericardial space. 
     The role of the CS is increasingly recognized in maintaining persistent and permanent atrial fibrillation which constitute up to 70% of the atrial fibrillation cases in the population referred for catheter ablation. On one side during ablation of long-standing atrial fibrillation, disconnection of the coronary sinus from both the left and right atrium can be required in up to 60% of cases to interrupt the arrhythmia or to organize the electrical activity in a discrete mappable atrial tachycardia. On the other side, mitral isthmus ablation to create a bi-directional line of block is increasingly performed to organize the substrate during chronic atrial fibrillation ablation. To create a bi-directional block, ablation within the CS has to be performed in 30-50% of cases. The role of CS as a critical part of left atrial tachycardia is also increasingly known. Effective mitral isthmus block in the settings of perimitral atrial flutter can require ablation in the CS in up to 50% of cases to interrupt the arrhythmia and make it no longer inducible. The CS is also important in the ablation of postero-septal and left-sided accessory pathways, as in many cases the ventricular and/or atrial insertion of the accessory pathway is too epicardial for endocardial ablation using a conventional catheter. Furthermore mapping the CS body with a conventional multi-polar catheter is not quite efficient since this type of catheter is not able to deliver radiofrequency energy. 
     Thus, there remains a need for a balloon or a mesh expandable catheter that could be inserted deeply inside the CS, inflated and then slowly pulled back towards the CS ostium while delivering equatorially curative energy source such as radiofrequency or therapeutic ultrasound to fully disconnect the CS musculature from the left and right atrium in atrial fibrillation, atrial tachycardia or WPW ablation. It would be more beneficial clinically if this balloon catheter consists of multiple ablating irrigated electrodes where the irrigation pattern is controlled to provide desired relative uniform cooling to the ablating electrodes to minimize coagulum formation and create larger and longer lesions safely. 
     SUMMARY OF THE INVENTION 
     Embodiments of catheters, systems and methods are disclosed that, provide, among other things, substantially uniform cooling of ablation electrodes and/or the surrounding tissues in use. The catheter may include an elongated tubular catheter body having a distal end, a proximal end, and a lumen extending longitudinally within the catheter body. A number of elution holes may be provided in each electrode, and these holes are in fluid communication with the lumen through ducts. As such, a cooling fluid may be delivered from a pump, through the lumen, through the ducts, and out of the holes to the environment outside of the catheter. 
     Contemplated catheters may have at least one electrode positioned at the distal end, and the lumen may have varying diameters throughout so as to provide a desired fluid outflow pattern when flowing out of elution holes. Of the many contemplated patterns, it is desired that the varying lumen diameters is configured such that fluid outflow rate at all of the elution holes is substantially the same. Among the many different possibilities contemplated, the lumen may have a diameter that is smaller at a distal end than at a proximal end. Further, it is contemplated that the decrease in diameter may be defined by a tapered section in the lumen. 
     The ducts may be positioned at a tilted angle from the main lumen, or can be substantially perpendicular to the main lumen. In exemplary embodiments the ducts and the main lumen are formed at angles between 35 to 90 degrees, more specifically, 45 to 90 degrees, even more specifically between 80 to 90 degree angles, and even substantially 90 degrees. In embodiments where the ducts are tilted, they can tilt forward and also backward. 
     Contemplated lumen diameters may vary from about 0.005 inches to about 0.045 inches, and the tapered section may decrease the diameter by about 5% to about 40% when comparing the two diameters immediately adjacent the tapered section. In other embodiments, there are no such tapered sections, and the diameter gradually decreases along the distal region of the catheter. 
     In some embodiments of the contemplated device, the catheter may have at least six ducts at a single junction with the main lumen, and these ducts may be evenly and radially spread out, evenly angled from each other to form a complete circle of 360 degrees. 
     The ducts optionally have an inner surface with a surface pattern that causes the outflow of cooling fluid to form an irregular pattern upon exiting the holes. For example, the pattern is a spiral groove, so that the spraying pattern is an outwardly spraying swirl. 
     The catheter may also include at least one inflatable balloon. In some embodiments, the balloon may be attached to less than 60% of a circumference of a section of the catheter body, instead of completely surrounding a longitudinal section of the catheter body; or in another embodiment, the balloon may be attached to less than 52% of a circumference of a section of the catheter body. 
     The optional balloons can have an inflated shape such as a half-dome. Other suitable shapes can also be implemented depending on the shape and size of the body lumen and tissue area intended for treatment. 
     Further, the balloons can be positioned opposite to elution holes and/or electrodes so that the inflatable balloon can assist in physically pressing the electrodes to the targeted tissue for ablation. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
         FIG. 1  is a perspective view of an irrigation catheter system according to an aspect of the inventive subject matter. 
         FIG. 2  is a perspective view of the catheter distal region according to an aspect of the inventive subject matter. 
         FIG. 3  is a perspective view of the catheter tip according to an aspect of the inventive subject matter. 
         FIG. 4  is a side view of the catheter tip according to an aspect of the inventive subject matter. 
         FIG. 4A  is a cross sectional view of the catheter tip of  FIG. 4  at line A-A, according to an aspect of the inventive subject matter. 
         FIG. 4B  is a cross sectional view of the catheter tip of  FIG. 4  at line B-B, according to an aspect of the inventive subject matter. 
         FIG. 5  is a longitudinal cross sectional view of the catheter tip of  FIG. 4  at line C-C, according to an aspect of the inventive subject matter. 
         FIG. 6  is a longitudinal cross section view of a catheter tip illustrating varied lumen diameter, according to an aspect of the inventive subject matter. 
         FIG. 7  is a longitudinal cross section view of a catheter tip illustrating varied lumen diameter, according to an aspect of the inventive subject matter. 
         FIG. 8  is a longitudinal cross section view of a catheter distal section illustrating an embodiment having multiple lumens for fluid delivery, according to an aspect of the inventive subject matter. 
         FIG. 9  is a longitudinal cross section view of a catheter distal section illustrating an embodiment having multiple lumens for fluid delivery, according to an aspect of the inventive subject matter. 
         FIG. 10  is a diagramatic illustration of side channel configuration, according to an aspect of the inventive subject matter. 
         FIG. 11  is a diagramatic illustration of side channel configuration, according to an aspect of the inventive subject matter. 
         FIG. 12  is a diagramatic illustration of side channel configuration, according to an aspect of the inventive subject matter. 
         FIG. 13  is a diagramatic illustration of side channel configuration, according to an aspect of the inventive subject matter. 
         FIG. 14  is a perspective top view of the catheter distal region having inflatable balloons fully inflated, according to an aspect of the inventive subject matter. 
         FIG. 15  is a perspective bottom view of the catheter distal region having inflatable balloons fully inflated, according to an aspect of the inventive subject matter. 
         FIG. 16  is a top view of the catheter distal region having inflatable balloons fully inflated, according to an aspect of the inventive subject matter. 
         FIG. 17  is a cross sectional view of the catheter distal region of  FIG. 16  at line E-E, according to an aspect of the inventive subject matter. 
     
    
    
     DETAILED DESCRIPTION 
     The invention can now be better understood by turning to the following detailed description of numerous embodiments, which are presented as illustrated examples of the invention defined in the claims. It is expressly understood that the invention as defined by the claims may be broader than the illustrated embodiments described below. 
     Many alterations and modifications may be made by those having ordinary skill in the art without departing from the spirit and scope of the invention. Therefore, it must be understood that the illustrated embodiment has been set forth only for the purposes of example and that it should not be taken as limiting the invention as defined by the following claims. For example, notwithstanding the fact that the elements of a claim are set forth below in a certain combination, it must be expressly understood that the invention includes other combinations of fewer, more or different elements, which are disclosed herein even when not initially claimed in such combinations. 
     As used herein, the term “duct” is synonymous with “side channel”, both are used herein to describe fluid delivery paths branching off of the main lumen of the catheter. 
     Referring now to  FIG. 1 , which illustrates a catheter system  10 , having a control unit body  12 , tubing sets  14  and  16 , and an elongated catheter body  18  with a distal region  20 . Tubing sets  14  and  16  can be connected to any suitable known devices in the art such as, for example, a monitor/display, RF generator, signal processor, fluid pump, etc. The system  10  may also use a temperature sensor and mapping tool such as that described in U.S. Pat. No. 6,217,573. 
     In  FIG. 2 , catheter distal region  20  has bands of electrodes  22  positioned spaced apart in different longitudinal sections. Each band of electrodes  22  has elution holes  25  located in the same longitudinal sections. At the terminal end is catheter tip  21 , also having electrodes. Catheter tip  21  can be manufactured separately and attached to the rest of the elongated catheter body. 
     The contemplated catheter tip  21  can be made of suitable biocompatible materials to conduct RF energy and to withstand temperature extremes. Suitable materials include natural and synthetic polymers, various metals and metal alloys, naturally occurring materials, textile fibers, glass and ceramic materials, sol-gel materials, and all reasonable combinations thereof. In one embodiment, the catheter tip  21  is made of 90% platinum with 10% iridium. 
       FIG. 3  shows an exemplary embodiment of the catheter tip  21 , having a through hole  26  and groove  28 . Hole  26  and groove  28  are used to help attaching the catheter tip  21  to the catheter body  18 . Catheter body  18  has corresponding structures to matingly couple to the groove  28  and hole  26 . 
       FIG. 4  is a side view of the catheter tip  21 . Exemplary embodiments of the catheter tip  21  have two rows of elution holes  25 . In this figure, line A-A represents the first row of the elution holes and line B-B represents the second row of elution holes. The terminal end of the tip can be in any configuration, and may be spherical. The distance K 1  between the most distal tip of the spherical end to the center of the first row of elution holes may be about 0.039 inches in one embodiment. The distance K 2  between edge  29  to the center of the second row of elution holes may be about 0.020 inches. The diameter of both rows of elution holes may be about 0.016 inches. As for arrangement of electrodes, mapping devices and sensors, these can be referenced from known ablation catheters such as U.S. Pat. No. 6,611,699. 
     The number and configuration of elution holes  25  depends on the intended use of the catheter. For example,  FIG. 4  shows a configuration where six elution holes  25  are provided in each of the two rows. Each elution hole  25  is fluidly connected with main lumen  23  via ducts  24 . Referring to  FIGS. 4A and 4B , this configuration provides six ducts  24  radially spread out and spaced evenly from each other in substantially the same degree of angle. This configuration allows all around irrigation and cooling. In comparing  FIGS. 4A and 4B , the two rows of elution holes are offset by about 15 degrees. By doing so, the offset rows of elution holes provide more evenly distributed irrigation. It is also contemplated that these two rows may be offset by between 15-45 degrees, or more specifically, by about 30 degrees. 
       FIG. 5  provides exemplary dimensions of the various elements in the catheter tip  21 . In one embodiment, the diameter D 1  of the distal portion of the main lumen may be about 0.019 inches, and the proximal portion of the lumen, after the tapered flow constrictor  27 , may have a diameter D 2  of about 0.028 inches. The diameter D 3  of the main lumen at the neck portion of the catheter tip  21  may be about 0.034 inches. In other embodiments, the diameter of main lumen may range from about 0.005 inches to about 0.045 inches, and the tapered section may decrease the diameter by about 5% to about 40% comparing the two diameters immediately adjacent the tapered section. 
     The terminal end of the main lumen may end in a flat cone shape, and the distance Li from the edge of the flat cone to the proximal end of the neck portion may be about 0.194 inches. The distance L 2  from the tip of the spherical end to the edge  29  may be about 0.158 inches. The distance L 3  of the neck from the end of the neck to the edge  29  may be about 0.065 inches. The distance L 4  from the edge of the flat cone to the terminal tip of the sphere may be about 0.030 inches. Distance L 5  is measured from the larger edge of the tapered flow constrictor  27  to the end of neck, and it may be about 0.135 inches. 
       FIGS. 6 and 7  illustrate different possible configurations of the flow constrictor  27 . The flow constrictor  27  limits or constricts the volume of fluid as the fluid passes toward the distal end of the catheter tip. By decreasing the main lumen  23  diameter using a flow constrictor  27  located substantially equidistant from the first row and from the second row, as shown in  FIG. 6 , the volume of fluid reaching the first row of elution holes  25  is effectively decreased, causing fluid output in the first row of elution holes  25  to be substantially the same volume as the fluid output in the second row. That is, all rows of the elution holes  25  that are disposed along the length of the electrode region may have substantially the same outflow rate. Without a flow constrictor  27 , the irrigation system will have an imbalanced outflow pattern where more fluid outflow occurs at the first row. A number of factors are involved in designing an irrigation system with even distribution rate along all of the elution holes. Some of these factors include: size of lumen diameter, percentage differences in diameter decrease, distance between adjacent rows of ducts, diameter of ducts, and tilt angle (if any) of the ducts relative to the main lumen. It is contemplated that the irrigation path described may be modified as dictated by the functional needs of particular applications. For example, in some medical applications more irrigation may be desired in the proximal end and any one or more of the above factors may be adjusted to create an irrigation system to provide more output flow in the proximal region. 
     In some embodiments, the ducts  24  may have walls with spiral grooves, influencing flow pattern of the fluid flowing through the ducts  24 . With such spiral grooves, the fluid comes out of elution holes  24  with an outwardly spraying swirl. This spraying pattern tends to minimize direct impact of the fluid on vessel walls. The spiral grooves can be formed by using an appropriate drill bit. The duct wall can alternatively have other irregular patterns to create other outflow patterns. 
     In  FIG. 7 , the flow constrictor  27  is a gradual taper that gradually decreases the main lumen diameter, as opposed to a relatively more abrupt taper seen in  FIG. 6 . Either abrupt taper or gradual taper, both are preferred over straight angle drop in diameter, because a straight angle drop in diameter can create undesirable eddy currents in the main lumen. 
       FIGS. 8 ,  9 , and  10  show yet other embodiments of the present invention. These embodiments have two separate lumens  123 A,  123 B, with each lumen supplying fluid to corresponding rows of ducts  124 . These embodiments are perhaps less desirable because multiple lumens take up precious cross sectional space in catheter body  118 . However, it is recognized that even distribution of fluid can be achieved by having separate fluid delivery lumens for separate rows of ducts, with each lumen being precisely pressure and volume flow controlled. 
     As will be illustrated in connection with  FIGS. 10-13 , the irrigation system can be advantageously enhanced by arranging the angle of the ducts  24  relative to the main lumen  23 . A flow constrictor is omitted from these figures but it is contemplated that a flow constrictor may be required depending on the type of flow output desired. An angle between a longitudinal axis of each of the plurality of ducts  24  and the longitudinal axis of the main lumen may be formed, for example, between 35 to 90 degrees, more specifically between 45 to 90 degrees, and even more specifically between 80 to 90 degrees. In  FIG. 10 , the ducts  24  are substantially perpendicular to the main lumen  23 . In  FIG. 11 , all of the ducts  24  are tilted towards the distal end, creating a general flow towards the front. In  FIG. 12 , all of the ducts  24  are tilted towards the proximal end, creating a general flow towards the back. In  FIG. 13 , a mixture of all three types is provided, creating a general flow away from the ablation area. 
     In  FIG. 14-17 , three inflatable balloons  230 A,  230 B,  230 C can be optionally provided to the electrode catheter as discussed above. Alternatively, this can be a balloon catheter with optional electrodes for ablation. The balloons  230  help navigate and position the electrode  222  to the targeted ablation site. As discussed earlier, elution holes  225  may be provided for irrigation purposes, and the catheter has a catheter tip  221 . The catheter is first inserted into the patient while the balloon  230  is deflated. Once the user finds the targeted ablation location, the balloon  230  inflates, pushing the electrode side  222  of the catheter region against or closer to the ablation area. As opposed to electrodes described above, these embodiments have electrodes  222  on only the top side of the catheter distal portion. The underside has inflatable balloons  230 . 
     Contemplated devices may have just a single balloon  230 , or a plurality of balloons  230 . Where a plurality of balloons  230  are provided, the balloons can be of the same size and shape, or alternatively, each balloon  230  can have a distinct shape and size. An exemplary embodiment includes three balloons  230 A,  2308 ,  230 C, with the smallest one at the distal end, and the largest one on the proximal end. This configuration facilitates manipulation of the catheter in a funnel-shaped vessel. When in a funnel-shaped vessel closely corresponding to shape of the balloon catheter distal region when inflated, the balloon catheter in  FIGS. 14-17  can more fittingly secure itself and position the electrode at the ablation region. Exemplary balloons may be half-dome shaped, and may have a cross-sectional shape resembling a half circle. Also contemplated is a configuration having at least one inflatable balloon, where at least one balloon has an inflated shaped that resembles a longitudinally-dissected cone, or half-cone. By providing one balloon, or a plurality of balloons, an overall general shape that may be provided that corresponds to a funnel-shaped vessel. This overall general shape can be a longitudinally dissected cone shape, a longitudinally dissected oval (egg-like) shape where a distal end is smaller than the proximal end, or any other shapes where the cross-sectional area is smaller at the distal portion of the overall shape than at its proximal portion. The device may use typical controlling parts and other related configuration for using and positioning the balloon  230 , such as those disclosed in U.S. Pat. Nos. 7,137,395 and 6,780,183. 
     Balloon catheter devices are well known and general features (e.g. size, shape, materials) of the balloons  230  may be in accordance with conventional balloons. In one embodiment, the balloons  230  may be made of flexible medical-grade silicone rubber. Alternatively, the balloon  230  may be made of other biocompatible and distendable materials, such as polyethylene terepthalate (PET). 
     While the various embodiments of the irrigation system is herein disclosed as suitable for ablation catheters that perform tissue ablation, and the fluid being suitable cooling fluid such as saline, the same uniform distribution concept can be applied to drug delivery catheters desiring to delivery therapeutic fluid at a uniform rate among the many delivery bores on the catheter distal region. Thus, specific embodiments and applications of multi-electrode irrigated catheters with balloons have been disclosed. It should be apparent, however, that many more modifications besides those already described are possible without departing from the inventive concepts herein. The inventive subject matter, therefore, is not to be restricted except in the spirit of the appended claims.