Patent Publication Number: US-6660003-B1

Title: Percutaneous myocardial revascularization basket delivery system and radiofrequency therapeutic device

Description:
RELATED APPLICATIONS 
     The present application is related to U.S. Provisional Patent Application Serial No. 60/064,210, filed Nov. 4, 1997, and entitled TRANSMYOCARDIAL REVASCULARIZATION GROWTH FACTOR MEDIUMS AND METHOD. The present application is a Divisional of pending U.S. application Ser. No. 09/035,738, filed Mar. 5, 1998, now U.S. Pat. No. 6,063,082 which is also related to U.S. patent application Ser. No. 08/812,425, filed on Mar. 6, 1997, entitled TRANSMYOCARDIAL REVASCULARIZATION CATHETER AND METHOD and U.S. patent application Ser. No. 08/810,830, filed Mar. 6, 1997, entitled RADIOFREQUENCY TRANSMYOCARDIAL REVASCULARIZATION APPARATUS AND METHOD, herein incorporated by reference. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates generally to medical devices for forming holes in heart chamber interior walls in percutaneous myocardial revascularization (PMR) procedures. More specifically, the present invention relates to intravascular PMR devices having expandable baskets deployable within heart chambers. 
     BACKGROUND OF THE INVENTION 
     A number of techniques are available for treating cardiovascular disease such as cardiovascular by-pass surgery, coronary angioplasty, laser angioplasty and atherectomy. These techniques are generally applied to by-pass or open lesions in coronary vessels to restore and increase blood flow to the heart muscle. In some patients, the number of lesions are so great, or the location so remote in the patient vasculature that restoring blood flow to the heart muscle is difficult. Percutaneous myocardial revascularization (PMR) has been developed as an alternative to these techniques which are directed at by-passing or removing lesions. 
     Heart muscle may be classified as healthy, hibernating and “dead”. Dead tissue is not dead but is scarred, not contracting, and no longer capable of contracting even if it were supplied adequately with blood. Hibernating tissue is not contracting muscle tissue but is capable of contracting, should it be adequately re-supplied with blood. PMR is performed by boring channels directly into the myocardium of the heart. 
     PMR was inspired in part by observations that reptilian hearts muscle is supplied primarily by blood perfusing directly from within heart chambers to the heart muscle. This contrasts with the human heart, which is supplied by coronary vessels receiving blood from the aorta. Positive results have been demonstrated in some human patients receiving PMR treatments. These results are believed to be caused in part by blood flowing from within a heart chamber through patent channels formed by PMR to the myocardial tissue. Suitable PMR holes have been burned by laser, cut by mechanical means, and burned by radio frequency current devices. Increased blood flow to the myocardium is also believed to be caused in part by the healing response to wound formation. Specifically, the formation of new blood vessels is believed to occur in response to the newly created wound. 
     What would be desirable is a device capable of forming multiple holes in the wall of a heart chamber but requiring minimal manipulation while positioned within the chamber. What would be desirable is a device capable of forming multiple holes in a short time period in the myocardium. 
     SUMMARY OF THE INVENTION 
     The present invention provides devices and methods for forming a plurality of holes in a heart chamber wall as part of a percutaneous myocardial revascularization (PMR) treatment. Devices according to the present invention have a basket, termed a PMR basket, formed of a plurality of arcuately biased flexible arms. The arms can assume an outwardly bowed configuration once freed of the confines of a shaft lumen. The fully deployed PMR basket arms can expand until the arms engage the walls of the heart chamber. Some devices provide for multiple, simultaneous myocardial hole formation. In such devices, cutting means such as RF electrodes are carried on the arms and disposed outwardly to engage the heart chamber walls. The term “cutting” as used herein, means penetration, including the formation of holes by burning and by other means. One device utilizes a PMR basket to anchor or stabilize a steerable PMR cutting probe within the heart chamber. 
     The present invention provides devices and methods for forming numerous holes in a heart chamber wall within a short time period. This reduces the amount of time the heart chamber is invaded by the foreign device. Some devices and methods according to the present invention allow for the formation of many holes while requiring minimal maneuvering once the devices are advanced into the heart chamber. 
     One group of PMR basket devices includes an elongate outer tubular shaft having a lumen, a proximal end and a distal end. A plurality of elongate flexible arms are secured together at their proximal and distal ends, the arms being biased so as to bow outward relative to an axis through the secured proximal and distal ends. The arms carry a plurality of cutting means disposed in an outward direction toward the chamber wall. One device arms have lumens therethrough and outwardly oriented apertures. This device includes electrical supply wires running though the arms lumens and electrode wires extending from the supply wires and through the arm apertures. This device can include arcuately biased electrode wires that can be formed of a shape memory material. The biased arms can extend radially outward away from the arm when unconstrained, especially when heated by body fluids. One device includes a single supply wire slidably disposed within the arm lumen and electrically connected to each of the electrode wires which are slidably disposed within an arm aperture. The electrode wires can be advanced away from the apertures by advancing the supply wire within the arm. A variation of this embodiment utilizes cutting probes having sharpened free ends capable of piercing the heart chamber wall and forming holes within the myocardium. 
     In another embodiment of the PMR basket, the basket includes a plurality of electrode groupings. The electrodes can also have a loop shape, which can be, for example, semi-circular. Both the electrode grouping and loop shaped electrodes can be used to form craters in the myocardium of a patient&#39;s heart rather than channels. Craters can be considered wounds which have a width greater than their depth, whereas channels can be considered to a have a depth greater than their width. A hole is the resulting space after volumetric removal of material has been made from the patient&#39;s heart wall. A hole can be either a crater or a channel. It is believed that forming craters, in some instances, provide better therapeutic value than forming channels in the myocardium as their formation can be better controlled to reduce the likelihood of heart wall perforation. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective, cutaway view of a human heart having a PMR basket device inserted over the aorta and into the left ventricle; 
     FIG. 2 is a fragmentary, perspective view of the PMR basket device of FIG. 1, having cutting probes and flexible arms in an expanded state; 
     FIG. 3 is an expanded, cutaway view of detail area  3  of FIG. 2, having a PMR basket cutting probe slidably disposed within an arm; 
     FIG. 4 is fragmentary, side view of a PMR basket cutting probe wherein the probe is an electrode protruding from an insulated arm; 
     FIG. 5 is fragmentary, side view of a PMR basket cutting probe wherein the probe is a needle having a lumen and a sharp point; 
     FIG. 6 is fragmentary, side view of a PMR basket arm wherein the cutting means including a water jet orifice supplied by the flexible arm lumen; 
     FIG. 7 is fragmentary, side view of a PMR basket arm having an insulated, electrical cutting probe; 
     FIG. 8 is a fragmentary, perspective view of a PMR basket anchor and steerable PMR cutting probe disposed within the basket; 
     FIG. 9 is a fragmentary, perspective view of a PMR brush device having a plurality of arcuately biased electrical cutting probes, the device being in an expanded state; 
     FIG. 10 is a fragmentary, side, cutaway view of the PMR brush device of FIG. 9 in a retracted, compact state; 
     FIG. 11 is the perspective view of a PMR basket having a plurality of electrode groupings disposed thereon; 
     FIG. 12 is a fragmentary view of an electrode grouping from FIG. 11; 
     FIG. 13 is a perspective view a PMR basket having a plurality of loop electrodes disposed thereon; and 
     FIG. 14 is a fragmentary view of a loop electrode from FIG.  13 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to FIG. 1, a human heart  22 , including an apex  38 , a left ventricle  22  and an aorta  32 , is illustrated having a PMR basket device  28  disposed within ventricle  22 . PMR basket device  28  includes an elongate outer shaft  26  lying within aorta  32  and a basket  30  disposed within left ventricle  22 . PMR basket  30  includes a distal portion  34  and a proximal portion  36 , with distal portion  34  disposed near apex  38 . 
     Referring now to FIG. 2, PMR device  28  is illustrated in more detail, having an inner shaft  40  slidably disposed within outer shaft  26 . PMR basket  30  includes a plurality of flexible arms  42  secured together at distal portion  34  and proximal portion  36 . In one embodiment, PMR device  28  is constructed in a similar manner to the electrophysiological mapping device disclosed in U.S. Pat. No. 5,628,313 (Webster, Jr.), herein incorporated by reference. In particular, the construction of arms  42 , shafts  26  and  40 , and their interconnections can be similar. Flexible arms  42  include several cutting probes  44  depicted generally in FIG.  2 . In a preferred embodiment, cutting probes  44  have a length “L” extending from flexible arms  42  that decreases with increasing distal distance along the device. Thus, in a preferred embodiment, the length of cutting probes  44  is least near distal portion  34 . A shorter cutting probe length is desirable as the heart wall is generally thinner near the apex. As can be appreciated, the basket might also be used as a probe to map conductive versus non-conductive myocardial tissue. 
     As can be seen from inspection of FIG. 2, proximally retracting inner shaft  40  within outer shaft  26  will result in arms  42  being proximally withdrawn into outer shaft  26 , thereby collapsing basket  30 . Conversely, distally advancing inner shaft  40  results in arms  42  being distally advanced as well, freeing arms  42  from the constraint of shaft  26 . Arms  42  have an arcuate outward bias as illustrated in FIG.  2 . The arcuate bias allows arms  42  to expand and form basket  30  once freed from the confines of outer shaft  26 . Arms  42  are preferably formed of a shape memory material such as Nitinol, which can assist in the formation of expanded basket  30 , as arms  42  re-attain an outwardly bowed, arcuate shape. As can be seen from inspection of FIG. 1, basket  30  can be further expanded by distally forcing inner shaft  40  against basket proximal portion  36 , thereby pushing basket distal portion  34  against the ventricle wall and forcing arms  42  even further apart. The longitudinally directed force of inner shaft  40  is thus partially transmitted into radially directed forces over cutting probes  44 . In embodiments where the cutting probes are sharpened needles, the radial force can operate to force the needles into the heart chamber wall. In embodiments where cutting probes are electrical, the radial force can operate to bring the cutting probes into sufficiently close proximity to the heart chamber wall to allow burning holes into the heart chamber wall and myocardium. 
     In one embodiment, cutting probes  44  are formed of Nitinol or other shape memory material and have a bias or preform of their own. One bias is an arcuate bias as illustrated in FIG.  2 . Cutting probes in this embodiment lie flat against arms  42  while the arms are retracted within outer shaft  26  and are allowed to assume a remembered, arcuate shape upon release from the constraint of outer shaft  26  and exposure to warm body fluids. Once in the arcuate position, cutting probes  44  are better able to contact the ventricle walls. In another embodiment, not requiring illustration, the cutting probes are formed of Nitinol and wound into a tight spiral which extends and lengthens the spiral into a less tightly wound spiral or straighter wire upon assuming the remember shape. The spiral wound embodiment also allows the cutting arms to extend to the ventricle walls. 
     Referring now to FIG. 3, an enlargement of cutting probe  44  illustrates an extensible length “L”, extending radially from the generally longitudinal orientation of arm  42 . Cutting probe  44  terminates in a cutting tip  45 . In a preferred embodiment, cutting probe  44  is an electrode and cutting tip  45  cuts into the ventricle wall due to the application of an electrical signal, preferably a radio frequency (RF) current, to the ventricle walls. A lumen  50  in arm  42  contains a first supply wire  46  which is bonded to, and electrically connected to, cutting probe  44 . In the embodiment illustrated, a second supply wire  48  also extends through arm  42 , for interconnection to a cutting probe. In one embodiment, more than one supply wire runs within arm lumen  50 . In one lumen, a unique supply wire can exist for every electrode wire. In a preferred embodiment, a single supply wire runs within each arm and is electrically connected to multiple electrode wire cutting probes. Unlike electrical mapping, delivery of current for burning multiple myocardial holes does not absolutely require distinct multiple supply wires. In one embodiment, supply wire  46  slides longitudinally within arm  42  and cutting probe  44  slides radially through an orifice  52  in arm  42 . Thus, longitudinally sliding the supply wire causes cutting probe  44  to slide radially toward the heart chamber wall, as indicated by the arrows in FIG.  3 . In a preferred embodiment, electrical insulation coats either the exterior of supply wire  46  or the interior of arm lumen  50 , or both. 
     Referring now to FIG. 4, another arm  58  and cutting means is illustrated in FIG. 4 in a cutting electrode  54  having an electrically insulating coating  56  over arm  58 , leaving only cutting electrode  54  exposed. The arm embodiment of FIG. 4 allows use of smaller diameter arms as no lumen is required as the insulation is external to the arm. This can allow more arms to be fit within outer tube  26  when retracted. A greater number of arms in the basket allows the formation of a greater number of holes simultaneously formed. In use, after expanding the PMR basket, cutting electrode  54  is brought into close proximity to the heart chamber wall and sufficient electrical potential supplied to a supply wire to burn a hole in the heart chamber wall. 
     Referring now to FIG. 5, another arm  60  is illustrated, having a cutting needle  62  terminating is a cutting tip  64 . In one embodiment, needle  62  is formed of a solid material such as stainless steel. In another embodiment, needle  62  contains a lumen and cutting tip orifice such that a lumen through arm  60  can supply a high pressure fluid through cutting needle  64  and cutting tip  64 . Needle  64  can be used in some methods to deliver angiogenic materials in conjunction with the hole formation by cutting tip  64 . For example, angiogenic material can be delivered into a hole recently burned by RF current delivered through needle  62 . Contrast media may also be delivered through needle  62 . 
     Referring now to FIG. 6, another arm  70  is illustrated, having a cutting orifice  72  used to deliver fluid under high pressure to form myocardial holes. Cutting orifice  72  supplies sufficiently high pressure fluid to form holes without requiring the use of electrodes or sharp needles. In use, arm  70  is brought into close contact with a heart chamber wall and high pressure fluid forced through the arm and other arms. 
     Referring now to FIG. 7, yet another embodiment is illustrated in an arm  74  having a burning electrode  76  protruding from an insulated housing  78 . Insulated housing  78  and electrode  76  allow a conventional electrophysiological mapping basket to be converted into a PMR cutting device. Insulating housing  78  can be formed of a material such as Teflon® or other thermoplastic such as PEBA. Burning electrode  76  has a rounded distal tip, to form a crater shaped burn in the heart chamber wall. Other cutting electrodes, in particular, longer and sharper tipped electrodes, can also be used with the embodiment of FIG.  7 . 
     Referring now to FIG. 8, a PMR basket device  80  is illustrated. PMR device  80  includes a basket  82  formed of a plurality of arms  83  terminating in distal portion  92  and proximal portion  94 . An outer shaft  84  is slidably disposed over an intermediate shaft  96  which can have an inner, steerable cutting probe  81  disposed within. In one embodiment, intermediate shaft  96  functions as a hub, having arms  83  secured thereto and steerable probe  81  slidably and rotatably received within. Steerable cutting probe  81  includes a shaft  86  preferably having a lumen therethrough. Basket  82  can be similar, in shape and arcuate bias of individual arms, to basket  30  in FIG. 1, but having no means for cutting mounted over the length of the arms. Basket proximal portion  94  is affixed to the distal end of intermediate shaft  96 . In one embodiment, as in shaft  96  in FIG. 8, the intermediate shaft is tubular, having cutting probe shaft  86  slidably disposed within. 
     In another embodiment, the intermediate shaft and cutting probe shaft  86  are both slidably disposed, side-by-side, within outer shaft  84 . Cutting probe shaft  86  is preferably arcuately biased and slidably disposed within outer shaft  84  such that the degree of arc exhibited by the probe can be controlled by longitudinally advancing or retracting the arcuately biased member within the constraints of outer shaft  84 . Allowing more of cutting probe shaft  86  to extend distally from outer shaft  84  allows more the arcuate shape to be attained. In one embodiment, cutting probe shaft  86  is formed of a shape memory material such as Nitinol. In another embodiment, cutting probe shaft  86  is formed of a spiral wound material such as woven stainless steel braid in a polymer which is biased to have an unconstrained arcuate shape. A cutting wire  90  is preferably slidably disposed within shaft  86  and can terminate in a distal cutting tip  90 . In another embodiment, an elastic fabric may be suspended around basket  82  to form a balloon-like enclosure. A plurality of apertures may be formed in the fabric such that cutting tip  88  can exit the basket to access the myocardium only through a hole in the fabric. The hole may be placed in a predetermined array to guide the arrangement of channels or craters to be formed during the PMR procedure. 
     In use, intermediate shaft  96 , basket  82  and cutting probe  81  can be proximally retracted within outer shaft  84  in preparation for placement. The distal end of outer shaft  84  can be advanced over the aorta and into a heart chamber such as the left ventricle. Intermediate shaft  96  can be advanced distally into the left ventricle, forcing basket  82  out from within outer shaft  84 . Cutting probe shaft  86  can also be advanced distally from outer shaft  84 , either separately or together with basket  82 . Basket  82 , freed from the constraint of outer shaft  84 , can assume the outwardly bowed arcuate shape imparted by arms  83 . Further bowing can be achieved by distally pushing intermediate shaft  96 , thereby forcing basket distal portion  92  against the ventricle wall near the apex. Basket  82  thus acts as an anchor, stabilizing the position of cutting probe  81  within the ventricle. 
     In one embodiment, the shape of cutting probe  81  can be controlled in part by imparting to cutting probe shaft  86  an arcuate bias and controlling the length of shaft  86  that is allowed to extend from within outer shaft  84  and inner shaft  96 . With the degree of arc thus controlled, cutting wire  90  can be advanced until contact with the heart chamber wall is effected. With cutting tip  88  in contact with the chamber wall, a suitable RF electrical current can be passed through cutting wire  90 , thereby burning a hole in the heart chamber wall. Cutting probe  81  can be rotated, allowing a circle or arc of myocardial holes to be formed within the heart chamber. Adjusting the longitudinal position of cutting probe  81  allows other series of holes to be formed. In one embodiment (not requiring illustration), an additional tube is slidably disposed over cutting probe shaft  86 , distally past intermediate shaft  94 , and within basket  82 , allowing control of the arc of cutting probe shaft  86  to be extended longitudinally. While anchoring basket  82  is preferably used in conjunction with electrical PMR cutting means, other cutting means, including sharp cutting tips, are used in other embodiments. 
     Referring now to FIG. 9, a PMR brush device  100  is illustrated, including an inner shaft  104  having a distal end  105  and a plurality of arcuate electrode wires  106  secured to distal end  105 . Inner shaft  104  is slidably disposed within an outer shaft  102 . Electrode wires  106  can terminate in a distal cutting tips  108  which, in one embodiment, are formed of metallic balls of platinum or gold brazed to the distal ends of electrode wires  106 . In one embodiment, electrode wires  106  are insulated except for cutting tip  108 . Electrode wires  106  can be formed of a shape memory material such as Nitinol. The electrodes can be formed into an initial arcuate shape, with the shape being remembered after the electrodes are freed from constraint and warmed to body temperature. Referring now to FIG. 10, inner shaft  104  is illustrated in a retracted position within outer shaft  102 . 
     In use, PMR brush device  100  can be put into a retracted position as illustrated in FIG.  10  and advanced over the aorta and into a heart chamber such as the left ventricle. Outer shaft  102  can be retracted, freeing electrode wires  106  of the restraint of shaft  102 , allowing the wires to assume an arcuate shape such that cutting tips  108  can engage the ventricle wall. With cutting tips  108  in position, a suitable electrical source can be switched, causing cutting tips  108  to burn holes into the heart chamber wall. In one embodiment, electrode wires  106  are supplied by a common supply wire and all electrodes fired simultaneously. 
     PMR brush device  100  can be made to engage the ventricle walls at varying depths within the ventricle. For example, PMR device  100  can have outer shaft  102  only partially retracted, keeping arcuate electrode wires  106  partially straightened and grouped together for engaging the ventricle wall near the apex. After burning a series of holes, outer tube  102  can be retracted further, allowing arcuate electrode wires  106  to splay further apart, allowing a superior, wider portion of the left ventricle to be treated. In one embodiment, electrode wires  106  are preformed to have an extreme arcuate shape such that superior, wide regions of the left ventricle can be treated from a central position in the ventricle. In some methods, brush device  100  may be pulled via inner shaft  104  to more completely treat the right wall of the left ventricle and pushed to more completely treat the left wall of the left ventricle. Upon completion of treatment, electrode wires  106  can be retracted within outer shaft  102  and brush device retracted from the left ventricle. 
     FIG. 11 shows yet another embodiment of a PMR basket  200 . Basket  200  is disposed at the distal end of an elongate catheter shaft  202  disposed within a guide catheter  204 . Basket  200  is formed from a plurality of wires  206  each having proximal ends and distal ends. The distal ends and proximal ends, respectively are connected to each other. Wires  206  are biased to expand basket  200  transversely when unconstrained. Extending generally transversely from wires  206  are a plurality of electrode groupings  208 . Each electrode grouping includes a plurality of individual elongate electrodes  210 . Each of the individual electrodes  210  preferably has a diameter of about 0.001 inches to 0.009 inches. A radiopaque marker  212  can be disposed at the distal end of basket  200 . FIG. 12 is a fragmentary view of an electrode grouping from FIG.  11 . 
     To conduct radiofrequency energy, catheter  202  must include or be formed from a conductor, such as stainless steel or other biocompatible metal. Likewise, wires  206  and electrodes  210  must be formed from a conductor such as stainless steel, Nitinol or other biocompatible material. If wires  206  are formed from Nitinol they can be heat set to expand upon introduction of basket  200  into the left ventricle of the patient. The conductor of catheter  200  and wires  206  should be insulated to concentrate the release of RF energy at electrode groupings  208 . Catheter  202  can be insulated by, for example, a surrounding layer of polyethylene, polyimide or PTFE. Wires  206  are preferably insulated by a heat shrink PTFE layer or other biocompatible insulator. Marker  212  can be formed from gold, platinum or other highly radiopaque material. Electrodes  210  can be plated with gold or other radiopaque material to enhance their visibility by fluoroscopy. Each electrode  210  can be insulated in a cylindrical ceramic housing to provide electrical insulation and thermal shielding from wires  206 . Each electrode  210  is preferably between about 0.0 to 0.1 inches in length. Electrodes  210  can include a spherically shaped tip having a diameter of about 0.01 to 0.039 inches. Each grouping  208  is preferably spaced about 0.19 to 0.078 apart. 
     In use, guide catheter  204  is advanced to a chamber of a patient&#39;s heart, such as a left ventricle. Basket  200  is advanced in a constrained and compressed configuration to the left ventricle. Upon being advanced out of guide catheter  204  into the left ventricle, basket  204  expands. The expanded size of basket  200  should be large enough to bring electrodes  210  in contact with the wall of the left ventricle. RF energy of a sufficient magnitude is then delivered to the heart wall by way of electrodes  210 . The small diameter electrodes  210  can deliver a high current density to the tissue. By placing electrodes  210  in groupings  208 , the tissue can be cratered, that is a wound can be formed in the tissue which has a width greater than its depth. 
     FIG. 13 is a perspective view yet another embodiment of a PMR basket  300 . PMR basket  300  is disposed at the distal end of a catheter  302 . Basket  300  is advancable to a patient&#39;s heart chamber through a guide catheter  304 . Basket  300  is formed from a plurality of wires  306  biased to expand basket  300  transversely when unconstrained. Each wire  306  has a distal end and a proximal end, the proximal ends and distal ends of each wire respectively are connected to form basket  300 . A plurality of loops  308  are disposed on each wire  306 . The wire forming each loop has a diameter of about 0.039 inches to about 0.197 inches. Loops  308  can have a semi-circular configuration. A radiopaque marker  312  can be disposed at the distal end of basket  300 . FIG. 14 is a fragmentary view of basket  300  showing a side view of a loop  308  on wire  306 . Each loop  308  is preferably contained within a cylindrical ceramic housing to provide electrical isolation and thermal shielding from wires  306 . 
     The various elements of the basket embodiment of FIGS. 13 and 14 can be formed from the materials cited above in connection with the embodiment of FIGS. 11 and 12. Basket  300  is intended to be used in essentially the same manner as basket  200  to form craters in the myocardium of a patient&#39;s heart. 
     If can be appreciated that each of the devices disclosed herein could be made bi-polar rather than mono-polar as shown. To make these devices bi-polar, a ground electrode can be disposed proximate the electrodes shown. 
     Numerous advantages of the invention covered by this document have been set forth in the foregoing description. It will be understood, however, that this disclosure is, in many respects, only illustrative. Changes may be made in details, particularly in matters of shape, size, and arrangement of parts without exceeding the scope of the invention. The inventions&#39;s scope is, of course, defined in the language in which the appended claims are expressed.