as shown in fig1 , a catheter 10 comprises an elongated catheter body 12 , a distal section having an inflatable cryoablation assembly 13 with a balloon member 24 and one or more micro - peltier cooling modules 15 in and / or on its outer surface , and a deflection control handle 16 attached to the proximal end of the catheter body 12 . the catheter 10 may function in combination with a further distal electrode assembly , for example , a lasso electrode assembly 17 , for which the inflatable assembly 13 can function as an anchor and / or stabilizer when the lasso electrode assembly 17 is in use , such as when inserted in a pulmonary vein pv of the left atrium , as shown in fig2 . the catheter body 12 comprises an elongated tubular construction , having a single , axial or central lumen 18 , as shown in fig3 . the catheter body 12 is flexible , i . e ., bendable , but substantially non - compressible along its length . the catheter body 12 can be of any suitable construction and made of any suitable material . a presently preferred construction comprises an outer wall 22 made of a polyurethane , or pebax . the outer wall 22 comprises an imbedded braided mesh of high - strength steel , stainless steel or the like to increase torsional stiffness of the catheter body 12 so that , when the control handle 16 is rotated , the tip section 14 of the catheter 10 will rotate in a corresponding manner . the outer diameter of the catheter body 12 is not critical , but is preferably no more than about 8 french , more preferably about 7 french . likewise the thickness of the outer wall 22 is not critical , but is thin enough so that the central lumen 18 can accommodate components , including , for example , one or more puller wires , electrode lead wires , irrigation tubing , and any other wires and / or cables . the inner surface of the outer wall 22 is lined with a stiffening tube 20 , which can be made of any suitable material , such as polyimide or nylon . the stiffening tube 20 , along with the braided outer wall 22 , provides improved torsional stability while at the same time minimizing the wall thickness of the catheter , thus maximizing the diameter of the central lumen 18 . the outer diameter of the stiffening tube 20 is about the same as or slightly smaller than the inner diameter of the outer wall 22 . polyimide tubing is presently preferred for the stiffening tube 20 because it may be very thin walled while still providing very good stiffness . this maximizes the diameter of the central lumen 18 without sacrificing strength and stiffness . as would be recognized by one skilled in the art , the catheter body construction can be modified as desired . for example , the stiffening tube can be eliminated . the intermediate deflection section comprises a shorter section of tubing 19 , which as shown in fig4 , has multiple lumens , for example , off - axis lumens 31 , 32 , 33 and 34 . in some embodiments , the tubing 19 is made of a suitable non - toxic material more flexible than the catheter body 12 . a suitable material for the tubing 19 is braided polyurethane , i . e ., polyurethane with an embedded mesh of braided high - strength steel , stainless steel or the like . the outer diameter of the deflection section 14 is similar to that of the catheter body 12 . the size of the lumens is not critical and can vary depending on the specific application . various components extend through the catheter 10 . in some embodiments , as shown in fig3 and fig4 , the components include one pair of lead wires 28 and 29 for each micro - peltier cooling module 15 . the components also include one or more puller wires 26 and 27 for deflecting the deflection section 14 , a cable 44 for an electromagnetic position sensor 46 ( not shown ) housed in suitable location in a distal portion of the catheter . the components further include a feeder fluid tubing 38 for passing fluid distally along the catheter and into the balloon member 24 for inflation and cooling , a return fluid tubing 39 for passing fluid from the balloon member proximally along the catheter , and a guidewire tubing 45 . these components pass through the central lumen 18 of the catheter body 12 , as shown in fig3 . it is understood that a return fluid tubing is optional where fluid is used for balloon member inflation purposes during procedures of shorter duration , for example , about 10 mins or less . for procedures of longer duration , the feeder fluid tubing 38 and the return fluid tubing 39 enable circulation of the fluid within the balloon member to maintain efficacy of cryogenic cooling of the micro - peltier modules . in the deflection section 14 , different components pass through different lumens of the tubing 19 as shown in fig4 . in some embodiments , the lead wires 28 and 29 and cable 44 for electromagnetic position sensor 46 pass through first lumen 31 . the first puller wire 26 passes through second lumen 32 . the feeder fluid tubing 38 passes through third lumen 33 . the return fluid tubing 39 passes through a fourth lumen 34 . a second puller wire 27 passes through fifth lumen 35 . the guidewire tubing 45 passes through a sixth lumen 43 . the second and fifth lumens 32 and 35 are diametrically opposite of each other to provide bi - directional deflection of the intermediate deflection 14 . the distal ends of the puller wires 26 and 27 can be attached to sidewall of the tubing 19 at or near its distal end , for example , with the use of t - bars , as known in the art . such a design is described in u . s . pat . no . 9 , 101 , 733 , the entire disclosure of which is incorporated herein by reference . each puller wire 26 and 27 is anchored at its proximal end in the control handle 16 . in some embodiments , the puller wires are made of any suitable metal , such as stainless steel or nitinol , and are preferably coated with teflon ® or the like . the coating imparts lubricity to the puller wires . a compression coil 36 is situated within the catheter body 12 in surrounding relation to each puller wire 26 and 27 , as shown in fig3 . the compression coils 36 extend from the proximal end of the catheter body 12 to at or near the proximal end of the deflection section 14 . the compression coils 36 are made of any suitable metal , preferably stainless steel . each compression coil is tightly wound on itself to provide flexibility , i . e ., bending , but to resist compression . the inner diameter of the compression coil is preferably slightly larger than the diameter of the puller wire . a teflon ® coating on each puller wire allows it to slide freely within the compression coil . if desired , particularly if the lead wires 28 and 29 are not enclosed by a protective sheath , the outer surface of the compression coils 36 can be covered by a flexible , non - conductive sheath ( not shown ), e . g ., made of polyimide tubing , to prevent contact between the compression coils 36 and any other wires within the catheter body 12 . the puller wire 26 extends through the second lumen 32 of the tubing 19 and the puller wire 27 extends through the fifth lumen 35 of the tubing 19 . within these lumens , each puller wire extends through a respective plastic , preferably teflon ®, sheath 37 ( see fig4 ), which prevents the puller wires from cutting into the wall of the tubing 19 when the deflection section 14 is deflected . longitudinal movement of the puller wires 26 and 27 relative to the catheter body 12 , which results in deflection of the tip section 14 , is accomplished by suitable manipulation of the control handle 16 . a suitable control handle design for use with the present invention is described in u . s . pat . no . 8 , 287 , 532 , the entire disclosure of which is incorporated herein by reference . if desired , the catheter can be uni - deflectional , i . e ., having only one puller wire . as shown in detail in fig5 a , distal of the deflection section 14 is the inflatable cryoablation assembly 13 including the balloon member 24 which can serve as a substrate on which one or more micro - peltier modules 15 are provided . the balloon member 24 has a membrane 40 which is flexible and if appropriate or desired , also elastic . fixedly attached to an outer surface of the balloon membrane 40 are one or more micro - peltier cooling (“ mpc ”) modules 15 . as shown in fig5 a , each of mpc modules 15 a - 15 i includes one or more mpc units 50 a - 50 n . as shown in fig6 , each unit 50 i has an n - type semiconductor n and a p - type semiconductor p that are configured thermally in parallel to each other by thermally - conducting layers or surfaces 41 and 42 , and electrically in series at junctions x and y defined by , respectively , first and second electrically - conducting members 51 and 52 at their opposing ends . when a voltage is applied to the n - type and the p - type semiconductors of any unit 50 i via the first and second electrically - conducting members 51 and 52 forming a circuit with a current / voltage source 60 , a dc current flows across junctions x and y of the n - type and p - type semiconductors ( as shown by arrows a ) causing a temperature difference between the junctions x and y of the unit 50 i . with the current / voltage source 60 and the circuit configured such that the current flows first into the n - type semiconductor and then out of the p - type semiconductor , the junction y is the “ hot ” junction with the first surface 41 being the “ hot ” ( or relatively hotter ) side , and the junction x with the second surface 42 being the “ cold ” ( or relatively colder ) side , wherein the “ cold / colder ” side absorbs heat which is then moved to the other side of the unit 50 i where the “ hot / hotter ” side is . where the mpc unit 50 is configured such that the cold side 42 faces outwardly on the balloon membrane 40 of the balloon member 24 , the cold side functions as cryoablation surface of the inflatable assembly 13 adapted for tissue contact . with the hot side 41 facing inwardly , it is in closer proximity to the balloon membrane 40 and hence adapted for thermal conduction ( directly or indirectly ) with a heat sink that includes heat - absorbing fluid entering and exiting the interior cavity 25 of the balloon member 24 via feeder fluid tubing 38 and return fluid tubing 39 . voltage / current source 60 of the peltier circuit can be adjusted to create a temperature difference between the junctions x and y ranging between about 50 degrees celsius , preferably about 60 degrees celsius , and , more preferably about 70 degrees celsius . the fluid can be any suitable fluid , including , for example , water or saline . in some embodiments , the mpc circuit can be adjusted such that the hot side 41 is at body temperature , namely , about 37 celsius , therefore achieving about − 33 celsius on the cold side 42 . with chilled water or saline at about 0 c being the temperature of the hot side 41 , the cold side 42 can be about − 70 c which is a temperature well suited for cryoablation . as shown in fig5 a and fig6 , one or more mpc units 50 a - 50 n are cascaded together for form an mpc module 15 for lower temperature , with the n - type semiconductor of a first mpc unit 50 a being connected to one hot wire 28 and the p - type semiconductor of a last mpc unit 50 n being connected to a neutral wire 29 for forming one peltier cooling circuit driven by the voltage / current source 60 with a current direction as shown by arrow a . as shown in fig6 , adjacent mpc units 50 i and 50 ( i + 1 ) of a mpc module 15 share a common “ hot ” junction y such that the units 50 a - 50 n are joined with current flowing from the p - type semiconductor of a downstream mpc unit 50 i to the n - type semiconductor of an upstream mpc unit 50 ( i + 1 ). with a plurality of n mpc units 50 and a plurality of m mpc modules 15 , a matrix of “ n × m ” mpc units 50 may be provided on any tissue contacting surface of a catheter , as shown in fig7 . the mpc modules 15 a - 15 m can be connected in parallel , all driven by a single voltage / current source 60 via a pair of lead wires 28 and 29 . in other embodiments , each mpc module 15 i of mpc modules 15 a - 15 m may have its respective voltage / current source 60 i , and lead wires 28 i and 29 i , as shown in fig8 . it is understood that a catheter may have any one or more combinations of mpc modules sharing a voltage / current source , as desired or appropriate . the assembly 13 includes one or more feeder and return lead wires 28 and 29 . they may extend along the outer surface of the balloon membrane 40 , affixed thereto , to reach the first and last mpc units 50 a and 50 n of each mpc module 15 i , as shown in fig5 a . as described hereinabove , the lead wires 28 and 29 extend through the central lumen 18 of the catheter shaft 12 and the first lumen 31 of the tubing 19 of the deflection 14 before emerging through apertures ( not shown ) formed in , for example , the wall of a distal section of the tubing 19 . in an alternate embodiment , the lead wires 28 and 29 may extend into the interior cavity 25 of the balloon member 13 and emerge through fluid - tight apertures ( not shown ) formed in the balloon membrane 40 . in other embodiments as shown in fig9 , fig1 and fig1 , a focal catheter 100 has a distal tip section 113 having one or more end and / or side surfaces 110 adapted for tissue contact . provided on the surfaces 110 are one or more mpc units 50 forming one or more one or more mpc modules 15 . the one or more units 50 and modules 15 may be arranged in any suitable pattern , including , for example , linear , nonlinear , circular , concentric , nonconcentric patterns and combinations thereof . fig9 illustrates an embodiment of a parallel linear pattern on a distal end surface of the catheter . fig1 illustrates an embodiment of longitudinal radial patterns on distal end and circumferential surfaces of the catheter . fig1 illustrates an embodiment of a circular spiral pattern on a distal dome surface . while the mpc modules 15 of fig5 a are arranged in a longitudinal pattern in fig5 a , the mpc modules 15 of fig5 b are arranged in a latitudinal pattern which is suited for ablating ring lesions in an ostium of a pulmonary vein . for a focal catheter 100 , the distal tip section 113 whose outer surface supports the mpc modules may be configured as a shell 122 with a sidewall 123 and an interior cavity 125 , as shown in fig1 , wherein the cavity 125 , as an internal heat sink , is adapted to contain circulating cooling fluid passing through feeder and return fluid tubings ( not shown ), as described above . hot and neutral lead wires 128 and 129 may extend through the interior cavity 125 and apertures 126 formed in the sidewall 123 for connection to a first mpc unit 50 a and a last mpc unit 50 n , respectively , of an mpc module 15 i . the apertures 126 are sealed and fluid - tight . a thermally and electrically insulating sheath 130 surrounds each wire 128 and 129 . it is understood that for any embodiments of the catheter of the present invention , the “ hot ” side 41 counterpart to the “ cold ” side 42 may be the surface on which the mpc units and modules are supported . for example , the balloon membrane 40 of the balloon member 24 or the side wall 123 of the distal tip shell 122 ( either as the substrate for the mpc units ) may be the “ hot ” side 41 , if they are constructed of a suitable material that is thermally conductive but electrically insulative . it is also understood that the first and second members 51 and 52 are constructed of material ( s ) that are both electrically - and thermally - conductive , whereas the “ hot ” and “ cold ” layers 41 and 42 are constructed of material ( s ) that are thermally - conductive but electrically - insulative , so that there is no intended current path through the mpc units from the fluid contained in the interior cavity 125 or from blood or other conductive tissue or bodily fluids near the mpc units . in that regard , the layers 42 may be coextensive in forming a generally contiguous layer that extends over and across the mpc units and modules , sealing them on the substrate and leaving no surface thereof ( or at least no surface of conductive components thereof ) exposed to unintended current paths . in some embodiments , the membrane 40 is constructed of a thermoplastic material with a low durometer ranging between about 50a and 55d , and preferably between about 80a and 50d . a suitable material includes pebax or pellethane , a medical - grade thermoplastic polyurethane elastomer , with superior resilience , low temperature properties / low thermal conductivity , low electrical conductivity ( i . e ., insulative dielectric properties ), and exceptionally smooth surfaces . another suitable material is flexible polyimide films . suitable materials for lead wires 28 , 29 , 128 and 129 include electrically conductive materials with low resistivity to prevent joule heating and undesired loss in cooling efficiency , including , for example , copper . the n - type and p - type semiconductors may include any thermoelectric material with large peltier coefficients , including appropriately doped bismuth telluride , silicon - germanium and bismuth - antimony . the components of the mpc units may be assembled on and / or affixed to the support surface by any suitable methods , including , for example , electrochemical deposition , mems ( micro - electro - mechanical systems ) techniques including photolithography , masking , etching and the like . fig1 , fig1 a and fig1 b illustrate another embodiment of a focal catheter 200 of the present invention . the catheter 200 has a dome distal tip section 213 having an mpc unit 250 , wherein the unit has an n - type wire 228 , a p - type wire 229 , an electrically conductive inner concave layer 252 ( defining a distal or first junction x with distal ends of the wires 228 and 229 ), and an electrically - insulative and thermally - conductive outer convex layer 242 sealing the layer 252 . it is understood that the layer 252 is optional and ed by directly cooling the y junction the dome distal tip section 213 is made of an electrically - insulative material , and the material may also be thermally - insulative . the layers 252 and 242 are embedded in a recess 260 , which may be located , for example , at a distal end of the section 213 . in the illustrated embodiment , distal ends the wires 228 and 229 are electrically connected to the layer 252 and extend through respective passages 271 and 272 , and through respective lumens 281 and 282 in a tubing 219 proximal of shell 213 . the wires 228 and 229 extend through a central lumen of a catheter shaft ( not shown ) and emerge proximally of the control handle 16 where the proximal or second junction y of the two wires is thermally coupled to an external heat sink 290 , for example , immersed in a bath . electrified by a voltage / current source 260 , with current flowing toward the layer 252 via the n - type wire 228 , junction x is configured as the “ cold / colder ” junction with junction y configured as the “ hot / hotter ” junction . with adjustment of the voltage / current , the temperature difference between the junctions x and y can range between at least about 50 degrees celsius , preferably at least 60 degrees celsius , and more preferably about 70 degrees celsius . accordingly , where the temperature of the “ hot / hotter ” junction y is regulated at about − 196 celsius by the bath 290 containing , for example , liquid nitrogen or liquid carbon dioxide , the temperature of the “ cold / colder ” junction x can reach about − 266 celsius . where the bath 290 contains dry ice ( with a temperature of about − 78 . 5 celsius ), the temperature of junction x can reach about − 148 . 5 celsius . it is understood that in other embodiments the layers 252 and 242 may be configured as an elongated body extending along the longitudinal axis of the distal tip section 213 to resemble and function as a needle 214 ( shown in broken lines in fig1 a ) extending distally from the distal end of the section 213 . as shown in fig1 c , another embodiment of a focal catheter 300 is shown with a distal section 313 having an mpc unit 350 and an internal heat sink . the internal heat sink includes an interior cavity 325 that is circulated with a fluid of a predetermined temperature that enters and exits the interior cavity 325 via feeder and return fluid tubings 338 and 339 . the mpc unit 350 has an n - type semiconductor n and a p - type semiconductor p that are configured thermally in parallel to each other by thermally - conducting , electrically insulative proximal and distal layers or surfaces 341 and 342 , and electrically in series at cold and hot junctions x and y defined by , respectively , first and second electrically - conducting members 351 and 352 at their opposing ends . the tissue contact surface of the catheter includes the distal layer or surface 342 . hot lead wire 328 is electrically connected to the n - type semiconductor n and the neutral lead wire 329 is electrically connected to the p - type semiconductor p , such that the first member 351 is the hot side or junction and the second member 352 is the cold side or junction of the mpc unit 350 . the thermally - conducting , electrically insulative layers 341 and 342 prevent any unintended current path through the mpc unit from fluid contained in the interior cavity 325 or from blood or other conductive tissue or bodily fluids near the mpc units . the first member 351 or hot side is in closer proximity to the interior cavity 325 as a heat sink such that its temperature is regulated by the fluid contained in the interior cavity 325 via thermal conduction across the layer 341 . thus , the second member 352 presenting the cold side is in closer proximity to the distal layer 342 which is configured for tissue contact . it is understood that the catheter 313 may include any number of mpc units 350 sharing the interior cavity 325 and fluid as their common heat sink , wherein the respective second members 352 of the units 350 are presented as the cold side for tissue contact . in yet other embodiments , the layers 252 and 242 may be deposited electrochemically on a flexible polyimide film 280 , as shown in fig1 a , rolled into a cylindrical body 291 , with the layer 252 facing outwardly and the film 280 facing inwardly , as shown in fig1 b , and assembled as component of a tip section 213 extending longitudinally and distally of the tip section 213 , as shown in fig1 . a distal end of the cylindrical body 291 may be capped and sealed with a sealant 295 , for example , polyurethane or epoxy . as part of an mpc circuit , the wires 228 and 229 are constructed of electrical conductors . in some embodiments , one or both of these wires may be constructed of drawn and appropriately - doped bismuth telluride , silicon - germanium and bismuth - antimony , for example , n - doped bismuth telluride for an n - type wire 228 and p - doped bismuth telluride for p - type wire 229 . it is understood that the present invention includes embodiments wherein the voltage / current source and the mpc components and / or circuit are configured such that the current direction is in the opposite direction , where the hot side faces outwardly or is the outer contact surface and the cold side faces inwardly or is the inner surface of the distal portion of the catheter , as desired or appropriate . the preceding description has been presented with reference to presently disclosed embodiments of the invention . workers skilled in the art and technology to which this invention pertains will appreciate that alterations and changes in the described structure may be practiced without meaningfully departing from the principal , spirit and scope of this invention . as understood by one of ordinary skill in the art , the drawings are not necessarily to scale and any feature or combinations of features described in any one embodiment may be incorporated into any other embodiments or combined with any other feature ( s ) of other embodiments , as desired or needed . accordingly , the foregoing description should not be read as pertaining only to the precise structures described and illustrated in the accompanying drawings , but rather should be read consistent with and as support to the following claims which are to have their fullest and fair scope .
a catheter has a cooling distal section for freezing tissue to sub - zero temperatures with one or more miniature reverse thermoelectric or peltier elements , also referred to herein as micro - peltier cooling units or electrodes . the mpc units may be on outer surface of an inflatable or balloon member or a tip electrode shell wall that has a fluid - containing interior cavity acting as a heat sink . each mpc unit has a hot junction and a cold junction whose temperatures are regulated by the heat sink , and a voltage / current applied to the mpc units . a temperature differential of about 70 degrees celsius may be achieved between the hot and cold junctions for extreme cooling , especially where the mpc units include semiconductor materials with high peltier co - efficients . an outer coating of thermally - conductive but electrically - insulative material seals the mpc units to prevent unintended current paths through the mpc units .