referring now to the drawings wherein like reference numerals represent like elements throughout the several views , fig1 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 22 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 16 can act as a shock absorber to dampen the change in force incident to marker 22 as the heart beats . fig2 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 . fig3 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 . fig4 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 . fig5 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 fig5 loop 416 is disposed in an advancement position a . in fig6 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 fig6 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 .
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 .