Abstract:
A PMR catheter including an elongate shaft having a proximal end and a distal end, and a conductor extending therethrough. An insulator disposed around the conductor. At least one conductive loop disposed at the distal end of the shaft. The conductive loop having an electrode disposed at its distal end.

Description:
RELATED APPLICATIONS 
     This application is a continuation of application Ser. No. 09/035,737, filed Mar. 5, 1998, now U.S. Pat. No. 6,093,185. 
     The present application is related to. U.S. patent application Ser. No. 08/812,425, filed on Mar. 6, 1997, entitled TRANSMYOCARDIAL REVASCULARIZATION CATHETER AND METHOD, now U.S. Pat. No. 5,968,059, U.S. patent application Ser. No. 08/810,830, filed Mar. 6, 1997, entitled RADIOFREQUENCY TRANSMYOCARDIAL REVASCULARIZATION APPARATUS AND METHOD, herein incorporated by reference, now U.S. Pat. No. 5,938,632 and U.S. patent application Ser. No. 09/035,625, filed on Mar. 5, 1998, entitled PMR DEVICE AND METHOD, now U.S. Pat. No. 6,056,793. 
    
    
     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 distal loops 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 relatively wide holes in the wall of a heart chamber. Such a device would be capable of forming holes having a greater width than depth and thus limit the potential of perforation of the heart wall. 
     SUMMARY OF THE INVENTION 
     The present invention pertains to a device and method for performing percutaneous myocardial revascularization (PMR). The device includes an electrode which in most embodiments has a width greater than its depth such that it can be used to form craters in the myocardium of a patient&#39;s heart rather than channels. Craters are wounds in the myocardium of a patient&#39;s heart which have a width greater than their depth whereas channels can be considered to have a depth greater than their width. Holes in the myocardium are volumetric removals of material. The embodiments also include a loop to limit the penetration of the electrode. 
     In one embodiment, a catheter assembly is provided including an elongate shaft having a proximal and a distal end and a conductor extending through the shaft. An insulator is disposed around the conductor. A conductive loop is disposed at the distal end of the shaft. The conductive loop in turn has an electrode disposed at its distal end. 
     The catheter shaft can include a proximal portion and a more flexible distal portion. The proximal and distal portions can be stainless steel and Nitinol hypotubes respectively. 
     The loop is preferably formed from Nitinol which can be heat set to expand on introduction of the loop into a chamber of a patient&#39;s heart. The loop is preferably insulated with a material such as PTFE which can withstand high temperatures. The distal end of the loop, however, can act as an electrode if uninsulated. 
     The electrode can be positioned at the distal end of the loop. Preferably the electrode is substantially radiopaque such that it can readily be viewed by fluoroscopy. 
     In yet another embodiment, the loop is disposed proximate and proximally of the distal end of the shaft. An electrode is disposed at the distal end of the shaft. The shaft defines an elongate lumen. The lumen continues through the electrode such that contrast medium, growth factors or other drugs can be delivered to the wound created by the PMR procedure. The loop, if insulated, can act as a stop to limit the penetration of the electrode. 
     In yet another embodiment, the loop is retractable within the catheter shaft. In this embodiment, an elongate reciprocating shaft is disposed within a lumen defined by the catheter shaft. The reciprocating shaft is connected to at least one end of the loop, the reciprocating shaft is moveable between a first position and a second position such that in the second position, the loop has a greater transverse dimension than in the first position. In the first position, the reciprocating shaft is used to withdraw the loop into the catheter shaft lumen to reduce the transverse dimension of the loop for delivery and withdrawal from the heart. 
     In the method in accordance with the present invention, a catheter assembly is provided including an elongate shaft having a proximal end and a distal end. A transversely expandable conductive loop is disposed at the distal end of the shaft. An electrode is disposed on the loop. The loop is advanced to the myocardium of the patient&#39;s heart where the transverse dimension of the loop is allowed to expand as the loop enters a chamber of the patient&#39;s heart. The electrode is advanced to the endocardium and energized to form a crater in the myocardium. The electrode can be repeatedly advanced to the myocardium to form a plurality of craters. The electrode is preferably energized with radiofrequency energy to create an arc which ablates or removes tissue. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a longitudinal, cross-sectional view of a PMR catheter in accordance with the present invention; 
     FIG. 2 is a perspective view of an alternate embodiment of the distal end of the PMR catheter; 
     FIG. 3 is a perspective view of yet another alternate embodiment of the distal end of the PMR catheter; 
     FIG. 4 is a perspective view of yet another alternate embodiment of the distal end of the PMR catheter; 
     FIG. 5 is a perspective view of yet another alternate embodiment of the distal end of the PMR catheter; and 
     FIG. 6 is a view of the distal end of the PMR catheter of FIG. 5 shown in a deployed position. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring now to the drawings wherein like reference numerals represent like elements throughout the several views, FIG. 1 is a longitudinal, cross-sectional view of a catheter  10  in accordance with the present invention. Catheter  10  includes an elongate shaft  11  having a proximal portion  12  and a distal portion  14 . A loop  16  is connected to catheter  10  at the distal end of shaft  11 . Proximal portion  12  of shaft  11  is preferably formed from a metallic member such as a stainless steel hypotube. Portion  14  is preferably formed from a metallic member such as a Nitinol hypotube. Loop  16  is preferably formed from, for example, a Nitinol ribbon having a cross section of about 0.003 inches by about 0.005 inches as well. The connections between proximal shaft  12 , distal shaft  14  and loop  16  should be formed from a solder or other conductive material such that a conductive path can be formed through shaft  11  to loop  16  for conductance of RF energy. 
     As one skilled in the art would recognize, an RF generator can be connected to the proximal end of shaft  11  to deliver radio frequency energy to loop  16 . The strength of the RF field delivered to loop  16  should be sufficient to create the desired wound in a patient&#39;s myocardium when performing percutaneous myocardial revascularization (PMR). 
     To guard against injury to the vasculature through which catheter  10  is advanced, shaft  11  is insulated. Proximal portion  12  can be insulated by a layer of polyethylene  18 . Distal portion  14  can be insulated by a layer of polyimide  20 . These insulative materials are illustrative examples only, as other biocompatible materials may advantageously be used as insulators. 
     Loop  16  is preferably heat set to expand from a compressed position to be passed through a guide catheter to, for example, the left ventricle of the patient&#39;s heart. Loop  16  is preferably heat set such that as loop  16  enters the left ventricle, it will expand to a size greater than the diameter of the guide catheter lumen through which loop  16  was advanced. 
     A radiopaque marker  22  is preferably disposed at the distal end of loop  16 . Marker  22  is preferably formed from a radiopaque material such as gold or platinum. Marker  22  should be conductively connected to loop  16  to enable marker  220  to act an electrode to deliver RF energy to a patient&#39;s myocardium. If it is desired to form craters in the patient&#39;s myocardium, the distance which marker  22  extends distally from loop  16  should be less than the maximum transverse dimension of marker  22  (a crater is a hole having a width greater than its depth). 
     To focus the RF energy on marker  22 , loop  16  can be insulated with a material such as heat shrink PTFE. If a portion of loop  16 , for example, adjacent its distal end, is left uninsulated, the uninsulated portion of loop  16  can act as an electrode. In such an instance, a very wide crater can be formed. The width of the crater being approximately equal to the transverse dimension of the uninsulated portion of loop  16 . Since loop  16  can have a transverse dimension greater than that of the guide catheter lumen through which it is advanced, the crater can have a width which is in turn, greater than the diameter of the guide catheter lumen. It can be appreciated that to the extent that the transverse portion of loop  16  is insulated, it can act as a stop limiting the penetration of marker  22 . 
     It should be noted that marker  22  and loop  16  can be pressured against the endocardium during the PMR procedure. During the PMR procedure, since the heart continues to beat, marker  22  will be motion when in contact with the heart. To absorb the movement of the heart and keep marker  22  in contact with the heart wall, it can be appreciated that loop  26  can act as a shock absorber to dampen the change in force incident to marker  22  as the heart beats. 
     FIG. 2 is a perspective view of a distal end of an alternate embodiment  100  of a catheter in accordance with the present invention. Catheter  100  includes a shaft  111  and a loop  116  extending distally therefrom having a radiopaque marker  122  disposed on the distal end thereof. A second loop  124  extends from the distal end of shaft  111  to proximate, and proximal of the distal end of loop  116 . It can be appreciated that if a portion of second loop  124  were not insulated and it were connected to ground or a lower voltage than loop  116 , that it could act as a second pole to create a bi-polar RF ablation device (a second pole could be added to each of the other embodiments disclosed herein as well). A distal portion of loop  116 , as well as marker  122 , can be used as an electrode if left uninsulated. Insulating loop  124 , loop  124  can act as a stop limiting penetration of loop  116  into the myocardium during the PMR procedure. The various components of catheter  100  can be formed from the same materials as catheter  10  and assembled in a similar manner. 
     FIG. 3 shows a perspective view of a distal end of yet another embodiment  210  of the catheter in accordance with the present invention. Catheter  210  includes a shaft  211  and a distal shaft extension  226 . Disposed at the distal end of extension  226  is a tip  228 . Shaft  226  is preferably formed from a metal such as Nitinol. Tip  228  can be a ball shaped tip formed from, for example, stainless steel. Shaft extension  226  and ball tip  228  are connected to shaft  211  by soldering or other means to form a conductive path from shaft  211  through extension  226  into ball tip  228 . Ball tip  228  can then act as an electrode to form holes in the myocardium of the patient&#39;s heart during the PMR procedure. 
     Catheter  210  includes a first loop  216  and a second loop  224 . Preferably loops  216  and  224  as well as extension  226  are insulated by a material such as heat shrink PTFE. When loops  216  and  224  are insulated, they can act as stops limiting the penetration of tip  228  into the myocardium of the patient&#39;s heart. 
     FIG. 4 shows a perspective view of the distal end of yet another embodiment  310  of the catheter in accordance with the present invention. Catheter  310  is substantially similar to catheter  210 , having a shaft  311 , a conductive shaft extension  326  and electrode tip  328 . Catheter  310  also includes first and second loops  316  and  324 , respectively. 
     Each of the elements  310  are formed from the same materials in essentially the same way as that of the previous embodiments and, in particular, of catheter  210 . Tip  326 , however, includes a truncated surface  330 . In addition, a lumen extends through the entire length of the catheter exiting at opening  332  in tip  328 . During PMR, contrast media, growth factor or other drugs can be delivered to the myocardium of the patient&#39;s heart through the lumen. 
     FIG. 5 shows a distal end of yet another embodiment  410  of the catheter in accordance with the present invention. Catheter  410  includes a shaft  411  which defines a lumen  413  extending between the proximal and distal ends of shaft  411 . Loop  416  extends distally from lumen  413 . Loop  416  has a first end  434  and a second end  436  which extends to the proximal end of shaft  411 . End  434  is anchored to shaft  411  proximate the distal end of shaft  411 . A marker  422  can be disposed on loop  416 . Loop  416  is preferably formed from a metallic ribbon such as a Nitinol ribbon having cross-sectional dimensions of about 0.003 inches by about 0.005 inches. At least one end of loop  416  is connected to a radio frequency generator. Loop  416  can also be stainless steel, cold worked and heat treated into the desired geometry. 
     As shown in FIG. 5, loop  416  is disposed in an advancement position A. In FIG. 6, loop  416  is shown in a deployed position B. Loop  416  can be shifted from position A to position B by advancing end  436  distally. Loop  416  can be shifted from position B to position A by pulling end  436  proximally. 
     As can be seen in FIG. 6, loop  416  has a substantial transversely extending distal portion. This configuration can be obtained by heat setting or pre-forming loop  416  as known to those skilled in the art. It can be appreciated that if the substantially transversely extending portion of loop  416  is left uninsulated to form an electrode, an electrode can be delivered during the PMR procedure which is substantially wider than the diameter of the guide catheter lumen through which it is advanced. Loop  416  can, however, be insulated such that only marker  422  acts as an electrode. 
     In use, each of the catheters of the present invention is preferably advanced percutaneously through a guide catheter extending through the aorta into the left ventricle of a patient&#39;s heart. It can be appreciated that the various embodiments can be advanced into other heart chambers as well. Once the electrode has been advanced to the patient&#39;s heart, RF energy is delivered to the electrode. The electrode is then repeatedly advanced into the patient&#39;s myocardium to create holes therein. 
     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.