CA2179711C

CA2179711C - Fluid cooled and perfused tip for a catheter

Info

Publication number: CA2179711C
Application number: CA002179711A
Authority: CA
Inventors: Greg G. Brucker; Jerome Philip Saul; Steven D. Savage
Original assignee: Cordis Webster Inc
Current assignee: Biosense Webster Inc
Priority date: 1993-12-21
Filing date: 1994-12-21
Publication date: 2004-08-03
Anticipated expiration: 2014-12-21
Also published as: EP0746372A4; US5643197A; DE69432671D1; CA2179711A1; US5462521A; JP3606328B2; WO1995017222A1; DE69432671T2; AU1866695A; EP0746372A1; AU682938B2; JPH09506808A; EP0746372B1; US6017338A

Abstract

The invention relates to an ablation catheter (20) which controls the temper ature and reduces the coagulation of biological fluids on a tip (26) of a catheter (20); prevents the impedance rise of tissue in c ontact with the catheter tip (26), and maximizes the ene rgy transfer to the tissue, thereby allowing an increase in the lesion size prod uced by the ablation. The ablation catheter includes a t ip (26) for applying electrical energy to biological tissue. Passages (48) are posit ioned within the tip (26) in a variety of manners for di recting a fluid flow through the tip (26) to the exterior surface of the tip (26) to c ontrol the temperature and form a protective fluid layer around the tip (26). Monitoring structure (47) is also positioned within the tip fo r measurement of the electrical potentials in a biologic al tissue. Ablation electrode structure (30) is also positioned within the tip (26) for application of ablative energy to the biological tissue . A flexible extended embodiment electrode (90) provides the capability to form deep, lin ear lesions along a portion of a heart wall during ablat ion for the treatment of particular arrhythmias.

Description

TUN-18-1996 15~57 P.~~42 FLUtD COQL$p AI~,~D PERPLrSEI7 TIP PpR A CATHETER
The invention relates to a flexible, fluid perfused elongated electrode far an ablation catheter to form linear lesions in tissue.
Back~r_otnd of the lnver,ti~n_t 'The pumping action of the heart is coritxolIed in an orderly manner by electrical stimulation of myocardial tissue. Stimulation a~ this tissue in the various regions of the heart is Controlled by a series of conduction pathways contained within the myocardial tissue. The impulse to stimulate is started at the sino-atrial (SA) node and is transmitted through the atria. The signals arrive at the atrio-ventricular (A'~i) node which is at the junction of the atria and ventricles. The signal passes through the AV
node Into the bundle of HIS, through the Purkinje fiber system and finally activates the ventricular muscle. At the completion of ventricular stimulation, heart tissue rests to allow the calls to recover for tha next stimulation. The stimulation is at the cellular level, and is a changing of the polarity of the cells from positive to negative.
Cardiac azrhythmias arise when the pattexn of the heartbeat is Changed by abnormal impulse initiation or conduction in the myocardial tissue. . The term tachycardia is used to describe an excessively rapid heartbeat resulting from repekitive stimulation of the heart muscle. Such disturbances often arise from additional conduction pathways which are present within the heart either from a congenital developmental abnormality or an acquired abnormality which changes the structure of the SUh!-18-1996 15:57 p, m7i~F2 -a-caadiac tissue, such as a myocardial infarction.
One of the ways to treat such dfsturbances is to identify the conductive pathways and to sever part of this pathway by destroying these cells which irxake up a portion of the pathway. Traditionally, this has been done by either cutting the pathway surgically, freezing the tissue, thus 3estroying the cellular membranes, or by heating the cells, thus denaturing - the Celdular proteins. The resulting destruction of the cells eliminates their electrical conductivity, thus destroying, or ablating, a certain portion of the pathway. 5y eliminating a portion of the pathway, the pathway no to longer conducts and the tachycasdia ceases.
One of the mast common ways to destroy tissue by heating i~aas been the xase o~ either electromagnetic energy or light. Typically, sources such as radiofrequency (ItP}, microwave, ultrasound, and laser extergy have been used. 'b4rith radiofrequency energy, a catheter with a conductive inner core and a metallic tip are placed izx contact with the myocardium and a circuit is completed with a patch placed on the patient's body behind the heart.
The catheter is coupled to a radiofrequency generator such that application of electrical energy creates localized heating in the tissue adjacent to the distal (emitting} electrode.
a0 Due of the nature of radiofrequency energy, both the metallic tip and the tissue axe heated simultaneously. The peak tissue temperatures during catheter delivered application of 12F energy to myocardixxrrx occur close to th.e endocardial surface, such that the lesion size produced is approximately limited by the thermodynamics of radial heat spread from TUN-18-199~,....is.~ P.88r42 the tip. The amount of heating which occurs is dependent on the area of contact bet<veen the electrode and the tissue and the lmpedanCe between the electrode and the tissue. Ttae higher the impedance, the lower the amount of energy transferred into the tissue.
Traditional electrode Configurations have a small cylindrical metal tip electrode with one or more thin ring electrodes near the tip either to aid with ablation or to measure the impedance itt nearby heart tissue. The size of the electrodes is limited because the catheter must remain flexible enough for the distal end of the catheter to be passed fihrough the cardiovascular system into the heart. Solid metal electrodes limit the flexibility of the catheter. These electrodes form a circular lesion at the point of contact on the surface of the heart tissue. The crass section of the lesion within the heart tissue is ellipsoidal in shape. These lesions are most effectivQ in the treatment of accessory pathways, .4V node re-entrant 25 tachycardias and some forms of idiopathic venixicular tachycardia.
Tiawev er, the treatment of a broader range of arrhythmias, such as atrial fibrillation and atrial flutter, may require linear lesions. An appropriate linear lesion would form a line on the surface of the heart and penetrate the fill thickness of the heart wall. 'With traditional tip electrodes described above, the only way to form such a linear lesion would be to move the catheter during ablation to create a Contiguous line from the discrete circular lesions. While this is theoretically possible, it is not practical to form such a line from the circular lesions because there are no visual mar&ers that would allow the positioning of one lesion with SLN-18-i9S6 15~57 -- P.OS.=42 ~ 2179711 respect to another lesion. Generally, the lesions are not visible under fluoroscopy.
s7ne of the major problems with radiofrequency energy is the coagulation of blood onto the tip of the catheter, creating a higher impedance or rE istance to passage of electrical energy into the tissue. As the impedance increases, more energy is passed through the portion of the tip without coagulation, creating even higher local temperatures and further increasing toagulum formation and the impedance. Eventually, enough blood is coagulated on the tip so that no energy passes into the (issue. The catheter must then be removed from the vascular system, the tip area cleaned and the catheter repositioned within the heart at the desired location. This process is not only rime consuming, but it is also difficult to return with precision to the previous ablation site because of (he reduced electrical activity in the regions whicte have been previously 25 ablated. TJse of temperahire sensors in the tip to modulate the power input to keep the electrode below the coagulation temperature of blood have been used. These systems inherently limit the amount of power which can be applied, others have used closed loop cooling systems to introduce water into the tip, but these systems are larger than necessary Zt~ because the coolant must be removed from the Catheter.
In some research, an increase of impedance was noted in radiofrequency (RF) ablation at power levels above 7 tvatts (IN) due to the formation of a thin insulating layer of blood degradation products on the electrode sur#ace. Wittkarnpf P. 1-I. et al., LiadiofrPa~,y-~. A'blation t~~th a JUh!-1~-1996 15:x -... p.lH;'42 wed PoroL t:yw~, Abstract, jACC, Vol. iI. No. 2, Page 17A
(1988). Wittkampf utilized an open lumen system at the distal electrode which had several hples perpendicular to the tentraI lumen which could be cooled by saline. Use of the saline kept the temperature of the electrode at a temperature low enough so that the blood pzodutts would not coagulate onto the tip of the electrode.
Impedance rise associated with caagulum fazmation during RF
catheter ablation was also noticed by Huang et al., TnCxeas~ s" ahe ~~w ath er for Radi fr a rencc, athat ~aa~. Abstract, Circ ,.~~~ Vol.
80, No. 4, page II-324 (1989). A quadropolar saline infusion intraluminal electrode tatheter was used to deliver RF energy at different levels.
The drawbacks of the existing catheter electrodes are that they do not minin~lze the contact of biological material with the tip of the catheter i5 along with the cooling of the tissue in the vicinity of the tip. While cooling will help to reduce coagulation of blood and tissue onto the catheter, the corxtinued contact of the biological material with the tip will result in further coagulation on the tip. This results in an increased electrical resistance and a further increase in local heating news the tip.
Another difficulty with existing catheter electrodes is that the lesions are limited in size and shape, it is only with great difficulty that such electrodes can be used to form appropriate lesions for many cardiac arrhythmias.

TIJI~F-18-1996 l~:Sg -..... p. t1: 42 $ 9>wrnma~y of the Invention The invention relates to a catheter tip for cardiac signal measurement and monitoring, including a tip structure which is positioned at the end of the catheter. Path means are formed within the tip structure for directing a fluid from the interior of fhe tip structure to portions of the tip structure exterior surface, thereby providing a fluid protective layer surrounding, the tip structure. l~:onitaring means are also included within the catheter tip structure far measurement of electrical potentials in a biological tissue.
The invention also relates to an ablation catheter which reduces the coagulation of biological fluids on a tip of a catheter, regulakes the impedance rise of tissue in contact with the catheter tip, and znaxin?_iaes the potential energy transfer to the tissue, producing a larger size lesion.
The ablation catheter includes a catheter body. The ablation catheter also includes a tip for monitoring electrical potentials, and applying electrical energy to a biological tissue. A fluid source is positioned at one end of the catheter tar supplying a fluid flow through the catheter to ahe tip means.
Passages are formed wvithin tkce t.lp for directing the fluid flow through the tip means to the exterior surface of the tip means to form a protective fluid layer around the tip. Monitoring zneans axe also positioned within tkae tip structure far measurement of the electrical potentials in a biological tissue.
Ablation means axe also positioned within the tip means far application of ablative energy to the biological tissue.
The invention also relates to an extended ablation catheter electrode that can produce a linear shaped lesion without moving the catheter from an initial position. The elongated electrode is preferably made from a fine metal mesh in electrical contact with the catheter handle. Construction of the extended electrode from the metal mesh allows the extended electrode to be sufficiently flexible that the extended electrode can be positioned within the heart. The inner surface of the mesh is in fluid communication with path means that directs fluid from the interior of the catheter through the mesh to form a protective fluid layer over the outer surface of the extended electrode.
In accordance with one embodiment of the present invention, there is provided a catheter tip for cardiac signal measurement and monitoring, comprising:
a) a tip structure positioned at an end of a catheter, the tip structure having an exterior surface;
b) means formed within the tip structure for providing fluid communication and ~ s commensurate flow of fluid originating inside the tip structure to portions of the tip structure exterior surface through a plurality of passages which direct the fluid flow from inside the tip structure over the exterior surface of the tip structure to provide a fluid protective layer surrounding the tip structure to minimize contact of the tip structure with biological materials; and 2o c) monitoring means within the tip structure for measurement of electrical potentials in a biological tissue.
In accordance with another embodiment of the present invention, there is provided a catheter tip for use in cardiac signal measurement, comprising:
a) a tip structure on a distal end of a catheter, the tip structure having an 25 interior and comprising a porous material;
b) a plurality of randomly disposed interstitial spaces formed within the porous material of the tip structure and in fluid communication with a source of fluid in the interior of the tip structure, the interstitial spaces directing a flow of fluid -7a-from the source of fluid in the interior of the tip structure over the exterior surface of the tip structure to provide a fluid protective layer surrounding the tip structure to minimize the contact of the tip with biological materials;
and c) monitoring means within the tip structure for measurement of electrical potentials in a biological tissue.
In accordance with another embodiment of the present invention, there is provided an ablation catheter which reduces the coagulation of biological materials on a tip of the catheter, reduces the impedance rise of tissue in contact with the catheter tip, and maximizes the energy transfer to the tissue, thereby allowing an increase in lesion size, the ablation catheter comprising:
a) a proximal end, a distal end, and a central lumen;
b) tip means having an exterior surface, the tip means being positioned at the distal end of the catheter for monitoring electrical potentials and applying energy to a biological tissue;
C) fluid source means positioned at the proximal end of the catheter body for supplying a fluid flow through the catheter to the tip means;
d) means formed within the tip means for directing the fluid flow through a plurality of passages which direct the fluid flow from the central lumen over the exterior surface of the tip to form a protective fluid layer around the tip 2o means to minimize contact of the tip means with biological fluids, reduce the coagulation of biological materials on the tip means and reduce resistance of energy transfer to the tissue;
e) monitoring means within the tip means for measurement of electrical potentials in a biological tissue; and f) ablation means within the tip means for application of energy to the biological tissue, the means for directing the fluid flow being formed within the ablation means.

-7 b-In accordance with another embodiment of the present invention, there is provided use of a catheter having a tip comprising a plurality of randomly disposed passages therethrough, whereby a fluid may be passed through the catheter and through the passages in the tip in an approximately radial s direction to produce a fluid flow originating within the catheter over the exterior surface of the tip and form around the catheter tip a fluid layer adapted to maintain biological materials at a distance from the catheter tip to reduce the coagulation of biological materials on the catheter tip and minimize resistance to energy transfer to tissue in communication with the catheter tip.
In accordance with another embodiment of the present invention, there is provided an ablation catheter which reduces the coagulation of biological materials on a tip of the catheter, reduces the impedance rise of tissue in contact with the catheter tip, and maximizes the energy transfer to the tissue, thereby allowing an increase in lesion size, comprising:
~s a) a catheter including a proximal end, a distal end, and a central lumen;
b) tip means having an exterior surface, the tip means being positioned at the distal end of the catheter for monitoring electrical potentials, and applying energy to a biological tissue;
c) fluid source means positioned at the proximal end of the catheter body for 2o supplying a fluid flow through the catheter to the tip means;
d) directional channel means formed within the tip means for directing the fluid flow through a plurality of passages which direct the fluid flow from the central lumen over the exterior surface of the tip means to form a protective fluid layer around the tip means to minimize contact of the tip with biological fluids, 25 reduce the coagulation of biological materials on the tip means and reduce the resistance to energy transfer to the tissue, wherein the directional channel means is a microporous structure;
e) monitoring means within the tip means for measurement of electrical potentials in a biological tissue; and -7c-f) ablation means within the tip means for application of energy to the biological tissue.
In accordance with another embodiment of the present invention, there is provided an ablation catheter that reduces coagulation of biological materials on a tip of the catheter by precluding ablation-inhibiting impedance rise of biological tissue adjacent the tip, the ablation catheter comprising:
a tip positioned at a distal end of the catheter to monitor electrical potentials and to apply ablation energy to a biological tissue, the tip having an exterior su rface;
a fluid source positioned to supply a fluid flow through the catheter to the tip;
and a structure defining a plurality of passages comprising interconnected interstitial spaces within the tip to direct fluid flow through the tip toward the exterior surface of the tip and to preclude ablation-inhibiting impedance rise of ~5 biological tissue adjacent the tip.
In accordance with another embodiment of the present invention, there is provided a catheter tip for signal measurement and monitoring, the catheter tip comprising:
an exterior surface;
2o means for providing fluid communication and commensurate flow of fluid from inside the tip to portions of the exterior surface of the tip through a plurality of randomly formed passages that direct the fluid flow from inside the tip over the exterior surface of tip; and monitoring means within the tip for measurement of electrical potentials in a 25 biological tissue.

-7d-In accordance with another embodiment of the present invention, there is provided An ablation catheter for application of energy to biological tissue, the ablation catheter comprising:
a proximal end, a distal end and at least one lumen;
s a tip at the distal end of the catheter, the tip including at least one electrode through which ablative energy is applied to the biological tissue, the electrode having an external surface;
a plurality of fluid paths disposed through the electrode, the fluid paths being between about 5 and about 20 microns in diameter and being constructed to direct fluid from the lumen through the electrode to the external surface of the electrode to form a protective layer of fluid around the electrode; and a fluid source for directing fluid through the lumen and the plurality of fluid paths to the external surface of the electrode.
In accordance with another embodiment of the present invention, there 15 is provided a catheter tip for ablation of tissue comprising:
a) an elongate shaft having shaft walls defining a shaft inner lumen and shaft wall outer surfaces, the shaft having a proximal attachment end portion and a distal tip portion;
b) an electrode portion comprised of porous metal having portions 2o mechanically connected to the shaft and electrically connected to a conductor within the shaft, the electrode placed circumferentially around a portion of the shaft and having an inner surface facing toward the shaft and an outer surface facing away from the shaft; and c) shaft wall structures defining fluid flow apertures extending from the shaft 2s inner lumen to the shaft wall outer surfaces; the apertures allowing the flow of fluid from the shaft inner lumen to the porous metal electrode inner surface, and the porous metal electrode defining fluid flow apertures suitable for the -7e-flow of the fluid through the fluid flow apertures to create a protective layer of fluid around the electrode outer surface.
Description of the Drawings Figure 1 is a side elevational view of an ablation catheter and tip.
s Figure 2 is a fragmentary enlarged section view of the catheter tip having a bulbous configuration.
Figure 3 is a fragmentary enlarged section view of the catheter tip 15 having a spherical configuration.
Figure 4 is a fragmentary enlarged section view of a catheter tip having an extended rectangular shape.
Figure 5 is a fragmentary enlarged section view of a catheter tip having a rectangular shape showing the electrical conduit.
Figure 6 is a fragmentary enlarged section view of a solid catheter tip having a multiplicity of discrete fluid flow passages.
15 Figure 7 is a fragmentary enlarged section view of a solid catheter tip having a passage extending the length of the catheter tip.
Figure 8 is a cross section view of the catheter tip showing axial 3UN-i8-19SF 15:58 . - P.13~42 _8_ channels extending the length of the catheter tip, Figure 9 is a cross secfion view of the catpteter tip showing a multipIiCfty of radially directed channels encircling the catheter tip.
Figure 10 is a fragmentary enlarged section view of a catheter tip made of a ceramic insulating material having monitoring members.
Figure 11 is a fragmentary enlarged section view of a catheter having ring electrodes which have path means.
Figure 12 is a fragmentary enlarged section view of an alternative embodiment of a catheter having a large central lumen and a smaller lumen.
Figure 13 is a cross section view taken along lane 13-23 of Figure 12.
Figure 14 is an enlarged fragmentary sectional view of a portion of the catheter tip and zing electrodes shown in Figures 2-5, 10, and 11..
Figure 25 is an enlarged fragmentary side perspective view of a catheter tip with an elongated flexible electrode, a tip electrode and several ring electrodes.
Figure I6 is a fragmentary enlarged section vi.w of a catheter tip with an extended flexible electrode, a tip electrode and several ring electrodes.
'p'hese figures, which are idealized, are not to scale and are intended to be merely illustrative and non-limiting.
netasled escrin son of the InvAnt;n.;
The invention relates to a catheter having a fpraid perfused or insulated tip, Fluid passes through the tip sfxucture, forming a fluid ,TUtJ-18-1956 15:59 ~ P.14i42 protective layer around the exterior surface of the tip structure. The fluid which permeates and surrounds the tip structure minimizes the amount of tha biological material which comes in contact w.~ith the catheter tip structure, as well as cools the tip structure. The cooling flund prevents a rise in the resistance (impedance) o~ the tissue to energy transfer frarxa an ablation energy source, and maximizes the potential energy transfer to the tissue in communication with the catheter tip. As a result, a larger lesioza Size in the tissue is produced.
Referring to Figure 1, a side elevational view of catheter 20 is shown having catheter body 22, a handle 24, and a tip stricture 26. Catheter body 22 may be of varying lengths, the length being determined by the application for catheter 2d. Catheter body 22 is preferably made of a flexible, durable anaterial, including, for example, thermoplastics such as nylon, in which a braiding is embedded. Preferably, catheter body 22 includes a large central lumen 28, such as a three French (P} lumen in a four F to twelve F, preferahly eight F catheter 2(?. Catheter body 22 may contain a plurality of ring electrodes 30 which surround the exterior surface of catheter body Z2 at selected distances from the distal end 32 proximate tip structure 26.
As shown in Figure 1, handle 24 is positioned on the proximal end 34 of catheter body 22. xIandle 24 may contain multiple ports, such as ports 36, 38. Port 36 may be utilized, in this embodiment, fax electrical connections bet~,~zen electrophysiological monitoring equipment and electrical potential sites of the tissue. Electrical connection means 40, ~N-18-1996 15: ~9 p. 15142 -lo-exiting through port 36, is positioned befween and connects tip structuze 26 and the electrpphysidlogical monitoring equipment. Port 36 is in communication with central lumen 28 of catheter body 22 and xnay also be used for the intzoduction and passage of devices 42 through catheter 20.
Port 38, in this embodiment, is connected to a fluid source and is also in fluid communication with central lumen 28 of catheter 20. Port 38 may be used for the entry of a fluid into catheter 20. Additional ports may be included on handle 24 which are in communication with central iumen 2$. port 36 may. for example, contain electrical connection means 40, and an additional port may contain device 42.
Referring to Figure 1, tip structure 26 is located at the distal end 32 of catheter body 22. Tip structure 26 may range from four (4) to twelve (12) Fzench catheter tips, Tip structure 26 includes at least one attachable electrode useful, for monitoring electrical potentials of the tissue, measuring cardiac signals, and mapping to locate the tissue to be ablated.
In addition, the tip Structure may include monitoring means for measuring, marutoring, and adjusting the rate of fluid flow through tip 26 relative to biological parameters, such as tip and tissue temperature.
As shown in Figures 2-5, the overall shape of tip structure 26 may have a variety of configurations. The various configuzations may be machined into the material comprising tip structure 26. Preferably, the shape of tip structure 26 permits catheter 20 to proceed readily through the vein or artery into which Catheter 2Q may be inserted. The shape of tip atructuxe 26 is determined by the application for which catheter 2g is SlJl~l-18-1996 15:~ .. p.16~'42 -m-designed. For example, Figure 2 is a fragmentary enlarged section view of tip structure 26 having wall portions 27 which extend beyond the diameter D of catheter portions proximal to the tip. For example, a bulbous or dumbbell Configuratiozt, as sho'cvn in Figure 2, may be useful in situations requiring access to pathway ablations which lie on tap of a valve or other relatively inaccessible site. Figure 3 illustrates a fragmentary enlarged section view of tip structure 26 which has a spherical or rounded configuration which ntay be advantageous, for example, in situations involving Cardiac pathways underneath. a valve. Figure 4 and Figure 5 illustrate fragmentary enlarged section views of tip structure 26 which vary in the length of tip structure 26. Tip structure 26 shown in Figure 4 may be useful in applications which Iie along the myocardiaP wall, and tip structure 26 illustrated in Figure 5 may be particularly advantagepus for uses such as eleCtrophysiological mapping.
Tip structure 26 may colztprise a variety of materials. Preferably, the material used for tip structure 26 in the different embodiments includes a plurality of apertures or path means which are either randomly or discretely formed in or spaced fltroughout tip structure 26. The diameter of the apertures or path means is substantially smaller than the averall diameter of tip structure 26. The diameter dimensions of the path means in the differenk embodiments discussed below may vary, and may include microporous slsuctures.
As illustrated in Figures 2-5, tip structure 26 is preferably made of a sintered metal which contains a pluralfity of randomly formed through-JUN-18-1996. 15:59 p.19i42 -i2-passages or path means 48 in tip structure 26. Generally, to create the sintered metal fox tip structure 26, spherical particles, such as finely pulverized metal powders, are mixed with alloying elements. This blend is subjected to pressure under high temperature conditions in a controlled reducing atmosphere to d temperature near the melting point of the base metal to sinter the blend. During sintering (heating), metallurgical bonds are formed between the particles within the blend at the point of contact.
The interstitial spaces between the points of contaci are preserved and provide path means for fluid flow, Paths means 48 in tip structure 26 comprise interstitial spaces forming structures which are randomly positioned, are of varying sizes, and are interconnected in a random manner with other interstitial spaces in tip structure 26 to provide fluid communication between central Lumen 28 of catheter 20 and the exterior surface 50 of tip structure 26. Path means 48 are generally five to twenty microns in diameter, although this may vary. The metal mnterial utilized for tip structure 26 should conduct heat well, have the ability to monitor electrical potentials from a tissue, and be economical to fabricate, such as stainless steel or platinum.
filtematively, as shown in Figure 6, tip structure 26 may comprise a solid metal material. Figure 6 is a fragmentary enlarged section view of catheter body 22 connected to tip structure 25. Tip structure 26 in this embod9ment comprises a solfd metal, such as stainless steel or platinum, having a multiplecity of specifically formed apertures or path means 52 within tip structure 26 which provide fluid communication between TIJN-18-1596 16:00 P.18i42 central lumen 28 of catheter 2fl and the exterior surface 50 of tip structure 26 for the passage of a fluid. The configuration of path means 52 is designed to provide a continuous layer of fluid over the exterior surface 50 of tip structure 26. Preferably, the apertures of path means 52 have a diameter less than five hundred microns, although this may vary. The metal material utilized for tip structure 26 shown in Figure 6 should conduct heat, as wren as have the ability to monitor electrical potentials from a tissue.
Figure 7 is a fragmentary enlarged section view illustrating catheter body 22 attached to tip structure 26. Tip structure 26, in this embodiment, is preferably made of a solid metal material which conducts heat well, and has the ability to monitor and measure electrical potentials of a tissue, such as stainless steel or platinum. Alternatively, fig structure 26 may comprise a dense ceramic material. As shown in Figure 7, a single orifice, channel or through path means 54 is f~rmed through the length L of tig structure 26. Path means 54 is in fluid communication with central lumen 28 of catheter 20. Preferably, the aperture of path means 54 has a diameter less than five hundred microns, although this may vary.
Figures 8 and 9 illustxate alternative cross section embodiments of tip structure 26. Figure 8 illustrates tip structure 26 having a plurality of grooves or directional channels 56 which extend in an axial direction along the length L of tip structure 26. Interconnecting channels may extend radially between channels 5b to aid in the fluid distribution over tip structure 26. Figure 9 illustrates a plurality of annular grooves nr JUN-12-1996 16:0D -.
P.19i42 directional channels 58 which encircle tip structure 26 in a radial manner.
As shown in Figure 9, channels 60 extend between path means 54 and Channels 58 to direct the fluid flow through central lumen 28 and path means 54 to the exterior surface 50 of tip structure 26. In these embodiments, chaxtnels 56, 58 are designed to communicate with path means 54 to provide a continuous, evenly distributed fluid protective layer over substantially the entire exterior surface 5Q of metallic tip structure 26.
Referring to Figure 1Q, an alternative embodiment of tip structure 26 is shown.- Figure 10 is a fragmentary enlarged section view of catheter body 22 attached to tip structure 26. Tip structure 26, in this embodiment, preferably comprises a ceramic insulating material which includes randomly formed path means 61. Path means 6I are generally ~ive to twenty microns in diameter, although this may vary. Path means 61 are in fluid communication with central lumen 28 of catheter 20. In addition, tip 25 26 includes at least one monitoring member b2 positioned throughout tip structure 2fi, ivlember(s) 62 may be of varying shapes and dimensions.
Preferably, members 62 are made of a conductive material suitable for monitoring electrica! activity and for application of electrical energy to a biological (issue, such as stainless steel or platinum. Tip structure 26, irt this embodiment, may contain axial or radial directional channels on exterior surface 50 of tip structure 26.
As shown in Figures 1 and 12, ring electrodes 30 may be attached to catheter body 22. Ring electrodes 30 axe connected to the mcnitorfng equipment by electrical connection means 64 through port 36 in handle 24.

TUhl-18-1996 16:EC1 P.20i42 Electrical connection means b4 are attached to ring electrodes 30, by, for example, soldering or other suitable mechanical means. Ring electrodes 30 may be made of a material which lxas path means similar to path means 48. 52, b0 as described above with. reference to tip structure 26 in Figures 2-and 10, and is preferably a sintered metal material. A plurality of ring electrodes 30 may be positioned at distal end 32 of catheter 20. Ring electrodes 30 may be used fox electrophysiological monitoring and mapping, as well as fox ablation. Fluid passes Front central lumen 28 through path means in ring electrodes 30 to forux a fluid protectfve layer around the exterior surface 65 of ring electrodes 30. In a mole flexible embadiment, ring electrodes 39 may be separated by flexible plastic material forming portions of catheter body 22. The electrodes may be spaced at various distances, buf in a flexible arrangemQnt may be about 1 mm to 2 mm apart.
Figure 12 and Figure 13 illustrate another embodiment of catheter 20. A central lumen 74 extends the length of catheter 20. Distal erwd 76 of catheter 20 znay include a smaller diameter lumen 78 relative to lumen 74 positioned substantially parallel and adjacent to central Lumen 74. Lumen 74 permits the introduction of a device, such as described above regarding device 42, Through the center of catheter ~0, as well as the passage of the fluid. Lumen 78 may be connected to port 38, and may also be used to direct the Fluid to tip structure 26, such that the fluid passes through path means 48, 52, 54, 61 in tip structure 25, as discussed above in relation to Ffgures 2-10. Non-permeable Layer 82, such as a plastic liner layer, may be .mra-ts-l9ss LG:e1 P.21i42 positioned between lumen 74 and lumen 78 to ensure that the fluid in, lumen 78 is directed through passages or path means 48, 52, 54, 61 ua tip structure 26 to the exterioz suzface 50 of tip structure 26. Ring electrodes may also be used in this embodiment to direct fluid to the exterior surface of tip structure 26 and catheter 20 to form the continuous and evenly distributed fluid protective Iayex 83 over substantially the entire exterior surface of the tip struchare_ Figure 14 illustrates an enlarged fragmentary section view of a portion of catheter tip structure 26 and/or rir~g electrodes 30 shocvn in Figures 2-5, 10, and 11. Substantially spherical particles $4, preferably biologically compatible metal particles, are positioned and arranged so as to form and create numerous interconnected, omnidizectional, tortuous path means 48, 52, and 61 (only 48 shown) through tip structure 26. Fluid flows thzough these tortuous Bath means 48, 52, 61 in the varied tip structzxre configurations to the exterior surface 50 of tip structure 26 or exterior surface 66 of ring electrodes 30 to uniformly and evenly distribute the fluid around tip structure 26. Substantially all path meazts 48, 52, 61 at surface of tip structure 26 or surface 66 of ring electrodes 30 are in fluid communication with central Iumen 28.
A :Flexible embodiment specifically designed to produce linear lesions is shown schematically in Figures 15 and 16. The elongated electrode 90 is preferably constructed from a porous or micraporous mesh 91 woven from small diameter metallic threads or merely configured with an appearance of a fine weave. The porous mesh can also be constructed JUN-18-1986 16:01 .1~.
P.22~42 from a series of small porous metal rungs Closely spaced to each other.
Preferably, the microporous mesh 91 covers an entire circumference near the distal end 32 of the ablation catheter. End portions of the mesh 91 are securely connected to the shaft theough mechanical clamps, connectors or adhesive bonds 9~.
The elongated electrode 90 is electrically connected to the handle 24, shown in Figure 1, through electrical connection means 64 preferably comprising at least one conducting wire attached to the electrical interface connection 40 at handle 24. Por ablation, appropriate electrical Current is supplied to elongated electrode 90 through electrical connection means 64.
The electrical current can be direct current or alternating current, and preferably is a radiofrequency signal. A, flexible, extended embodiment electrode provides the capability to form deep, linear lesions along a portion of a heart wall during ablation for the treatment of particular arrhythmias. The fluid insulating/protecting character of the invention is more important as the electrode length Increases due to the corresponding increase in possible localized uneven heating along the length of the electrode. Such uneven heating leads to the formation of hot spots which result in biological tissue Coagulation. However, creation of this continuous fluid protective layer reduces the possibility of areas of coagulation by maintaining a more even temperature and, when using conductive saline, creation of a conductive gap-filler material (the saline}
to provide more uniform electrical distribution of energy, The inside surface 94 of the elongated electrode 90 is exposed to the JUN-18-1996 16: L1 P.23i42 - 1e central lumen 28 via a plurality of macroscopic holes 96. Holes 96 axe preferably sized between about 0.1 millimeters (mm) to about 3 mm, and preferably about D.2 mm to about 1.D mm. Fluid flows from the proximal end 34 of the catheter dawn a fluid interface in the central lumen 28 to macroscopic holes 96, The pressure of the fluid within the central lumen 28 forces water to disperse in the annular space 98 between the shaft of the catheter and the fine weave forming the mesh 9I. The porosity of the mesh 91 is selected such that the resistance to the flow of fluid through the mesh 91 is significantly larger than the flow resistance at interconnecting 1D holes 96. This selection of porosity of the mesh 91 ensures that there is an essentially even flow of fluid over the outer surface IDO of the elongated electrode 90.
Generally, the length LS of elongated electrode 90 is significantly larger than the length LZ of the ring electrodes 30. The length of elongated electrode 90 is selected to produce the size of the linear lesion appropriate for the treatment o~ the patient. This length will preferably range from about 5 mm to about 5 centimeters (cm). This length wilt often more preferably range from about D.5 cm to about 1.5 cm.
A ring electrode 30 could not be constructed with a width 2D contemplated for the elongated electrode 9D because the ring electrode 30 would be too rigid. The elongated electrode 90 is flexible similar to or even more than the catheter body 22. This flexibility allows the elongated electrode 90 to have the appropriate width without limiting the capability of passing the distal end 32 of the catheter conveniently through the JUN-18-1996 16:01 - .. ~ .. P.24i42 _y9_ cardiovascular system info the heart.
The fluid introduced through ports 38, macroscopic holes 96 or other orifices, of catheter 2U is preferably a biologically compatible fluid, and znay be in a gaseous or liquid state. For example, the fluid may comprise carbon dioxide, nitxog2n, helium, water, and/or saline. Fluid enters through, for example, port 38 and is passed though central lumen 28 of catheter body 22. The fluid perfuses Eip structure 26 and/or ring electrodes 30 through the path means in tip structure 2b and/or ring electrodes 30, arid creates a fluid protective layer surrounding exterior surfaces of tip structure 2( or exterior surfaces of electrodes 30, 90 thereby minimizing contact of tip structure 26 or electrodes 30, 90 with biological material, such as blood.
The rate of fluid flow through central lumen 2$ of catheter 20 may vary and range From U.1 rnl/min, to 40 ml/min. Fluid flow through catheter 2U may be adjusted by a fluid infusion pump, if the fluid is liquid, or by pressure, if the fluid is a gas. The fluid flow is regulated by the infusion pump for the liquid fluid, ox by a needle valve if a gas, so as to maintain an optimal disbursing flow over the tip structure 26 and/or electrodes 30, 90 and maintain a desired Hp temperature. Preferably, the protective layer of fluid covers all or substantially all of the surface area of tip structure 26 and is betty een about O.U01 min arid 3. mm,, and more preferably, about O.U1 mm. in thickness, although this may vary depending an the application, and may vary in thickness during a given procedure.
Temperature sensing means 47 (for example as shown in Figures 3 JUN-18-1996 18:02 . P.25i42 and 4) may be incorporated into tip structure 26 ffor sensing and measuring the temperature of tip structure 2b and for sensing and measuring the temperature of the biological tissue in contact with tip structure 2b.
Temperature sensing means 47 may be incorporated in any of the tip structure embodiments shown in Figures 2-Ip, I5-I6. The temperature sensing means generally comprises at least one temperature sensor, such as a thermocouple ox theravstor. In addition, temperature sensing means 47 array be utilized as a feedback system to adjust the flow rate off the biologically compatible fluid to maintain the temperature of the tip structure at a particular temperature within a designated range of temperatures, such as 4D°C to g5°C. Also, temperature sensing means 47 may be used as a feedback system to adjust the flow rate of the biologically compatible fluid so as to maintain the temperature of the biological tissue in contact with tip structure 26 at a particular temperature within a '15 designated range of temperatures, such as 40°C to 95°C. The temperature of the tissue or tip structure 26 is controiIed by the temperature of the fluid, the distribution of the fluid xeIative to internal and external surfaces to the tip structure, the energy applied to the catheter, and the fluid flow rate.
Catheter 20 may include ablation means within tip structure 26.
Preferably, the ablation means may be a wire connected to an 1ZF energy source, although other types of electrical energy, including microwave and direct current, or ultrasound may be utilized. Alternatively, the ablation means may include optical fibers fox delivery of Iaser energy. The ablation ,TUhi-18-1996 16:02 - P.26i~2 -zz -means may be connected to an energy source through port 36, or an additional port.
As shown in Figure 1, device 42 may be passed through central luuten 28 of catheter 20. l7evice 42 may include, for example, a guidewire for ease of entry of catheter 2D into the heart or vascular system; a diagnostic device, such as an optical pressure sensor; a suction catkeeter for biopsy of biological material near the distal tip; an endoscope For direct viewing of the biological material in the vicinity o~ the distal tip of the catheter; or other devices.
ID In one example of operation, catheter body 22 of catheter 20 is preferably percutaneously inserted into the body. The catheter is positioned so that it lies against cardiac tissue such that the flexible poxnus elongated electrode 90 makes contact along its length with the tissue area that is to be ablated. tl,long the line of contact, energy will flow from the conductive source to the electrode and into the cardiac tissue.
Simultaneous fluid flow is maintained around the electrode creating a buffer between the tissue and the eleciaode. Tip structure ?6, as an electrode, may also be utilized to measure electrical potentials of the tissue and provide information regarding <ardfac signal measurement. Electrical connection means 40 extends from tip struCfure 2fi, through port 36, and is connected to monitoring equipment. Tip structure 26 may be utilized to map, monitor, and measure the cardiac signals and electrical potentials of the tissue, and locate arrhthymogenic sites.
A biologically compatible fluid is introduced through port 38. The JUN-18-199b 3E:02 P. ~ 42 fluid passes through a central lumen of catheter body 22 and is directed to tip structure 26. The fluid passes through Hp structure 26 and/or ring electrodes 30 and/or elongated electrode 90 through path means 4t3, 52, 54, 61 or holes 96 in a manner determined by the embodiment of distal end 32 used. Tl~,e fluid perfuses tip structure 26 and forms a fluid protective layer around exterior surface 50 of tip structure 26 and/or exterior surface 66 of ring electrodes 30 and/or the exterior surface of the elongated electrode 90.
The fluid layer formed around catheter tip structure 26 and/or ring electrodes 30 and/or elongated electrode 90 maintains biological materials, such as blood, at a distance Erom catheter tip structure 2b, thereby minimizing contact of catheter tip structure 26 witA the biological material, as well as cooling tip structure 2G and jor elongated electrode 90.
Since there is a consistent, controlled buffer layer between the biological material and catheter tip structure 26 and/or the elongated electrode 90, the coagulation of biological materials is reduced and the impedance or resistance to energy transfer of the tissue near the distal end 32 of the catheter 20 is regulated and minimized during ablation.
Once the site has been located by the monitoring of the electrophysiologicaI signals of the tissue, the ablative energy is activated.
As a result of the fluid protective layer, the transfer of electrical energy to the tissue is enhanced. increased destructfon of cardiac tissue also results from tip structure cooling since larger and deeper lesions in the cardiac tissue are achieved than have been previously possible. Zlse of the eloxZgated electrode 90 allows the production of deep linear lesions.

SL'IV-18-1996 16.:03 -P. 28%42 The ftow rate of the fluid over exterior surface 50 of Hp structure 26 ox exterior surface 66 of ring electrodes 30 or exterior surface of elongated electrode 90 may be accomplished in a controlled manner so that a thin fluid film is formed around exterior surface 50, 66, 100 of tip structure 26, ring electrodes 30 and elongated electrode 90. The maintenance of a controlled, stable, uniform fluid film along substantially the entire exterior surface of Hp 26, ring electrodes 30 and elongated electrode 90 may be accomplished by using the various embodiments of distal end 32 described above having a multiplicity of passages or path means 48, 52, 54, 61 or holes 96. Path means 4$, 52, S4, 61 and holes 96 permit an even, consistent distribution of minute quantities of a biologically ~aanpatible fluid over substantially the entire tip exterior surface 50 oz ring electrodes exterior surface 66.
The fluid can be pumped through tip structure 26, or heat generated by the electrical oz ablation process tare be Cased to expand the fluid and create a movement of ftuid to the exterior surface 50, 66 of tip structure 26 or ring electrodes 30 ox elongated electrode 90. This movement of fluid provides a buffer or protective insulating layer between the exterior surface of tip structure 26 and/or ring electrode 30 and/or elongated electrode 90 and the biologi:al matezial, such as blood, thereby reducing the coagulation of biological materials on tip structure 26 and/or ring electrode 30 andJor elongated electrode 90. In addition, the movement of fluid over and around tip structure 26 may be aided by passages or oha.~tnels 56, 58 on exterior surface, 50 of tip structure 26. Cooling of tip SUN-18-1996.-16:03 P.29i42 structure 26 and/or ring electrode 3D and/or elongated electrode 90 increases the lesion size produced by the ablation means since the point of maximum tissue temperature is likely moved away from tip structure 26, which allows for an altered tissue heat profile, as further described below.
Another advantage of the fluid layer buffering the surface area of tip structure 26 and/or ring electrodes 30 and/or elongated electrode 90 is that the fluid layer also cools the tissue adjacent tip structure 26 and elongated electrode 90 during ablation. In addition, the fluid aids in maintaining the tissue adjacextt tip structure 26 and elongated electrode 90 in a coaler and potentially more conductive state. which permits more electricity or ablative energy to enter the tissue. As a result, larger lesions are produced because a larger voltage can be applied, producing a larger electric field without producing excessive temperatures and coagulum formation at the tip/tissue interface. Lesions are produced with this invention in the form of a line measuring about 1 cm to about 4 cm in length and about 3 mm to about 5 mm in width while simultaneously maintaining the fluid protective layer. This is accomplished without having to move the catheter and without requiring several ablations. Also, the greater the pressure of the fluid, the more biological products are kept from the field of influence of, or area surrounding, tip structure 26 and/or elongated electrode 90.
A control system may be included for controlling and regulating the electrical potentials and temperatures in a mariner that allows for determination of the ablation effects in the tissue. It is possible to control SUhd-18-1996 16=03 .., -. ..

P.30i42 the distribution of tissue heating by controlling the temperature of tip structure 26 and/or elongated electrode 90 and the radiofrequency voltage, or other energy used, applied between tip structure 26 and/or elongated electrode 90 and a reference electrode on the surface of the body. The voltage may be set to achieve a desired electrical field strength, and the temperature of tip structure 26 and/or elongated electrode 90 may be set to provide a desired temperature distn'bution of the tissue. The temperature distribution will then determine the size of the lesion, i_e., the denatured pxatezn dimensions in the myocardium.
I0 The fluid flow rate can be regulated relative to biological parameters, sucks as tissue temperature, by the temperature sensing means.
Por instance, if the temperature of the tissue increases, the fluid Flow rate can be increased by the regulation of the fluid infusion pump or gas needle valve. If the tissue temperature adjacent tip structure 26 andlor elongated electrode 90 is not high eztough, the fluid flow rate can be decreased. This permits pawer to be set independently of temperature. It is significant to note that it is normally not necessary to remove the introduced fluid from the body.
It is also possible to generate reversible affects of ablation by use of a cooling fluid down the central lumen 28 of catheter 20 and tip structure 26, or by use of a low temperature controlled or elevational heating. An area in the heart tissue is quenched with a cold or icy fluid to produce a tissue temperature of 0°C to 30°C, ox heated with electrical energy with closed loop temperature controls as described above to produce tissue JUN-18-199b. .1.6:H3 P.31i42 teznperature5 ranging from 4D°C to 48°C_ Those cool and warm temperatures slow the conduction o~ signals and ternpararily and reversibly eliminate the conduction pathways. This technique may be advantageously used to see the affect on the tissue before the tissue is permanently of#ected. The heart tissue gradually heats or cools back to normal. This technique is also advantageous since no catheter exchange Would be required.
Various modifications and alterztivns of this invention will become apparent to those skilled in the art without dep«rring from the scope and spirit of this invention.

Claims

WHAT IS CLAIMED IS:

1. A catheter tip for cardiac signal measurement and monitoring, comprising:
a) a tip structure positioned at an end of a catheter, the tip structure having an exterior surface;
b) means formed within the tip structure for providing fluid communication and commensurate flow of fluid originating inside the tip structure to portions of the tip structure exterior surface through a plurality of passages which direct the fluid flow from inside the tip structure over the exterior surface of the tip structure to provide a fluid protective layer surrounding the tip structure to minimize contact of the tip structure with biological materials; and c) monitoring means within the tip structure for measurement of electrical potentials in a biological tissue.

2. The catheter tip of claim 1 wherein the tip structure comprises a metallic material.

3. The catheter tip of claim 1 wherein the tip structure comprises a ceramic material including metallic members.

4. The catheter tip of any one of claims 1 to 3, further comprising a plurality of directional channels disposed in the exterior surface of the tip structure to direct fluid flow in an axial direction over the exterior surface of the tip structure.

5. The catheter tip of any one of claims 1 to 3, further comprising directional channel means for directing fluid flow in a radial direction over the exterior surface of the tip structure.

6. The catheter tip of any one of claims 1 to 5 wherein the tip structure comprises a microporous material.

7. The catheter tip of any one of claims 1 to 6 wherein the fluid protective layer is between about 0.001 mm and one mm in thickness.

8. The catheter tip of any one of claims 1 to 7 wherein the monitoring means measures and adjusts the rate of fluid flow through the tip structure relative to biological parameters.

9. The catheter tip of any one of claims 1 to 8 further comprising temperature sensing means within the tip structure for sensing the temperature of the tip structure.

10. The catheter tip of claim 9 comprising temperature sensing means within the tip structure for sensing the temperature of the tip structure and adjusting the fluid flow rate to maintain the temperature of the tip structure within a designated range of temperatures.

11. The catheter tip of any one of claims 1 to 10 further comprising temperature sensing means within the tip structure for sensing the temperature of the biological tissue in contact with the tip structure.

12. The catheter tip of claim 11 further comprising temperature sensing means within the tip structure for sensing the temperature of the tissue and adjusting the fluid flow rate to maintain the temperature of the tissue within a designated range of temperatures.

13. The catheter tip of any one of claims 1 to 12, wherein the fluid is selected from the group consisting of biologically compatible liquids and gases.

14. The catheter tip of claim 13, wherein the fluid is selected from the group of fluids consisting of carbon dioxide, nitrogen, helium, water, and saline.

15. The catheter tip of any one of claims 1 to 14 wherein the monitoring means includes an electrode.

16. The catheter tip of any one of claims 1 to 15 wherein the means for providing fluid communication and fluid flow is disposed within the monitoring means.

17. The catheter tip of any one of claims 1 to 16 wherein the fluid protective layer is a continuous fluid protective layer.

18. The catheter tip of any one of claims 1 to 17 wherein the fluid protective layer covers all of the exterior surface of the tip structure.

19. A catheter tip for use in cardiac signal measurement, comprising:

a) a tip structure on a distal end of a catheter, the tip structure having an interior and comprising a porous material;

b) a plurality of randomly disposed interstitial spaces formed within the porous material of the tip structure and in fluid communication with a source of fluid in the interior of the tip structure, the interstitial spaces directing a flow of fluid from the source of fluid in the interior of the tip structure over the exterior surface of the tip structure to provide a fluid protective layer surrounding the tip structure to minimize the contact of the tip with biological materials;
and c) monitoring means within the tip structure for measurement of electrical potentials in a biological tissue.

20. The catheter tip of claim 19 wherein the monitoring means comprises metallic members.

21. The catheter tip of claim 19 or 20 further comprising a plurality of directional channels disposed in the exterior surface of the tip structure to direct fluid flow in an axial direction over the exterior surface of the tip structure.

22. The catheter tip of claim 19 or 20, further comprising directional channel means for directing fluid flow in a radial direction over the exterior surface of the tip structure.

23. The catheter tip of any one of claims 19 to 22 wherein the monitoring means measures and adjusts the rate of fluid flow through the tip structure relative to biological parameters.

24. The catheter tip of any one of claims 19 to 23 further comprising temperature sensing means within the tip structure for sensing the temperature of the tip structure.

25. The catheter tip of claim 24 further comprising temperature sensing means within the tip structure for sensing the temperature of the tip structure and adjusting the fluid flow rate to maintain the temperature of the tip structure within a designated range of temperatures.

26. The catheter tip of any one of claims 19 to 25 further comprising temperature sensing means within the tip structure for sensing the temperature of the biological tissue in contact with the tip structure.

27. The catheter tip of claim 26 comprising temperature sensing means within the tip structure for sensing the temperature of the tissue and adjusting the fluid flow rate to maintain the temperature of the tissue within a designated range of temperatures.

28. The catheter tip of any one of claims 19 to 27 wherein the fluid is selected from the group consisting of biologically compatible liquids and gases.

29. The catheter tip of claim 28 wherein the fluid is selected from the group of fluids consisting of carbon dioxide, nitrogen, helium, water, and saline.

30. The catheter tip of any one of claims 19 to 29 wherein the fluid protective layer is between about 0.001 millimeters (mm) and one mm in thickness.

31. The catheter tip of any one of claims 19 to 30 wherein the plurality of randomly disposed interstitial spaces are disposed within the monitoring device.

32. The catheter tip of any one of claims 19 to 31 wherein the fluid protective layer is a continuous fluid protective layer.

33. The catheter tip of any one of claims 19 to 32 wherein the fluid protective layer covers all of the surface area of the tip structure.

34. An ablation catheter which reduces the coagulation of biological materials on a tip of the catheter, reduces the impedance rise of tissue in contact with the catheter tip, and maximizes the energy transfer to the tissue, thereby allowing an increase in lesion size, the ablation catheter comprising:

a) a proximal end, a distal end, and a central lumen;

b) tip means having an exterior surface, the tip means being positioned at the distal end of the catheter for monitoring electrical potentials and applying energy to a biological tissue;

c) fluid source means positioned at the proximal end of the catheter body for supplying a fluid flow through the catheter to the tip means;

d) means formed within the tip means for directing the fluid flow through a plurality of passages which direct the fluid flow from the central lumen over the exterior surface of the tip to form a protective fluid layer around the tip means to minimize contact of the tip means with biological fluids, reduce the coagulation of biological materials on the tip means and reduce resistance of energy transfer to the tissue;

e) monitoring means within the tip means for measurement of electrical potentials in a biological tissue; and f) ablation means within the tip means for application of energy to the biological tissue, the means for directing the fluid flow being formed within the ablation means.

35. The catheter of claim 34 wherein the tip means comprises a metallic material.

36. The catheter of claim 34 wherein the tip means comprises a solid metal material having structure defining at least one passage therethrough.

37. The catheter of claim 34 wherein the tip means comprises a solid metal material having structure defining a plurality of passages therethrough.

38. The catheter of claim 34 wherein the tip means comprises a ceramic material having metallic pieces.

39. The catheter of any one of claims 34 to 37 wherein the ablation means is selected from the group of energy types consisting of RF, laser, microwave, ultrasound, and direct current.

40. The catheter of claim any one of claims 34 to 38 further comprising temperature sensing means within the tip means for sensing the temperature of the tip means.

41. The catheter of claim 40 further comprising temperature sensing means within the tip means for sensing the temperature of the tip means and adjusting the fluid flow rate to maintain the temperature of the tip means within a designated range of temperatures.

42. The catheter of any one of claims 34 to 41 further comprising temperature sensing means within the tip means for sensing the temperature of the biological tissue in contact with the tip means.

43. The catheter of claim 42 comprising temperature sensing means within the tip means for sensing the temperature of the tissue and adjusting the fluid flow rate to maintain the temperature of the tissue within a designated range of temperatures.

44. The catheter of claim 42 comprising temperature sensing means within the tip means for sensing the temperature of the tissue and adjusting the energy applied to the catheter to maintain the temperature of the tissue within a designated range of temperatures.

45. The catheter of any one of claims 34 to 44 further comprising control means within the catheter for regulating and controlling the distribution of tissue temperature to affect lesion size.

46. The catheter of claim 44 wherein the control means comprises a device for setting a voltage to a desired level to regulate and control the lesion size.

47. The catheter of any one of claims 34 to 46, wherein the fluid is selected from the group consisting of biologically compatible liquids and gases.

48. The catheter of claim 47 wherein the fluid is selected from the group of fluids consisting of carbon dioxide, nitrogen, helium, water, and saline.

49. The catheter of any one of claims 34 to 48 wherein the monitoring means includes an electrode.

50. The catheter of any one of claims 34 to 49 further comprising a device positioned within the central lumen of the catheter.

51. The catheter of any one of claims 34 to 50 wherein the fluid protective layer is between about 0.01 mm and one mm in thickness.

52. The catheter of any one of claims 34 to 51 further comprising directional channel means for directing fluid flow in a radial direction over the exterior surface of the tip means.

53. The catheter of any one of claims 34 to 52, wherein the means for directing fluid flow comprises a microporous structure.

54. The catheter of claim 53, wherein the means for directing fluid flow comprises apertures having a diameter less than five hundred microns.

55. The catheter of any one of claims 34 to 54, wherein the fluid protective layer is a continuous fluid protective layer.

56. The catheter of any one of claims 34 to 55 wherein the fluid protective layer covers all of the exterior surface of the tip structure.

57. Use of a catheter having a tip comprising a plurality of randomly disposed passages therethrough, whereby a fluid may be passed through the catheter and through the passages in the tip in an approximately radial direction to produce a fluid flow originating within the catheter over the exterior surface of the tip and form around the catheter tip a fluid layer adapted to maintain biological materials at a distance from the catheter tip to reduce the coagulation of biological materials on the catheter tip and minimize resistance to energy transfer to tissue in communication with the catheter tip.

58 The use of claim 57 wherein the fluid layer is a continuous fluid layer.

59. The use of claim 57 wherein the fluid layer covers all of the surface area of the tip.

60. An ablation catheter which reduces the coagulation of biological materials on a tip of the catheter, reduces the impedance rise of tissue in contact with the catheter tip, and maximizes the energy transfer to the tissue, thereby allowing an increase in lesion size, comprising:

a) a catheter including a proximal end, a distal end, and a central lumen;

b) tip means having an exterior surface, the tip means being positioned at the distal end of the catheter for monitoring electrical potentials, and applying energy to a biological tissue;

c) fluid source means positioned at the proximal end of the catheter body for supplying a fluid flow through the catheter to the tip means;

d) directional channel means formed within the tip means for directing the fluid flow through a plurality of passages which direct the fluid flow from the central lumen over the exterior surface of the tip means to form a protective fluid layer around the tip means to minimize contact of the tip with biological fluids, reduce the coagulation of biological materials on the tip means and reduce the resistance to energy transfer to the tissue, wherein the directional channel means is a microporous structure;

e) monitoring means within the tip means for measurement of electrical potentials in a biological tissue; and f) ablation means within the tip means for application of energy to the biological tissue.

61. An ablation catheter that reduces coagulation of biological materials on a tip of the catheter by precluding ablation-inhibiting impedance rise of biological tissue adjacent the tip, the ablation catheter comprising:
a tip positioned at a distal end of the catheter to monitor electrical potentials and to apply ablation energy to a biological tissue, the tip having an exterior surface;
a fluid source positioned to supply a fluid flow through the catheter to the tip;
and a structure defining a plurality of passages comprising interconnected interstitial spaces within the tip to direct fluid flow through the tip toward the exterior surface of the tip and to preclude ablation-inhibiting impedance rise of biological tissue adjacent the tip.

62. The ablation catheter of claim 61, further comprising ablation means at the tip for applying the ablation energy to the biological tissue.

63. The ablation catheter of claim 61, further comprising monitoring means at the tip for measuring electrical potentials within the biological tissue.

64. The ablation catheter of claim 61, wherein the structure defining the plurality of passages provides a fluid protective layer to minimize contact of the tip with biological materials.

65. A catheter tip for signal measurement and monitoring, the catheter tip comprising:
an exterior surface;
means for providing fluid communication and commensurate flow of fluid from inside the tip to portions of the exterior surface of the tip through a plurality of randomly formed passages that direct the fluid flow from inside the tip over the exterior surface of tip; and monitoring means within the tip for measurement of electrical potentials in a biological tissue.

66. The catheter tip of claim 65 wherein the means for providing fluid communication and flow provides a fluid protective layer at the exterior surface of the tip to minimize contact of the tip with biological materials.

67. The catheter tip of claim 66, wherein the fluid protective layer is a continuous fluid protective layer surrounding the tip.

68. The catheter tip of claim 67, wherein the fluid protective layer covers the entire exterior surface of the tip.

69. The catheter tip of claim 65, wherein the means for providing fluid communication and flow cools the tip to cool biological tissue adjacent the tip.

70. The catheter tip of claim 65, wherein the means for providing fluid communication and flow comprises structure defining a plurality of randomly disposed interstitial spaces.

71. An ablation catheter for application of energy to biological tissue, the ablation catheter comprising:
a proximal end, a distal end and at least one lumen;
a tip at the distal end of the catheter, the tip including at least one electrode through which ablative energy is applied to the biological tissue, the electrode having an external surface;
a plurality of fluid paths disposed through the electrode, the fluid paths being between about 5 and about 20 microns in diameter and being constructed to direct fluid from the lumen through the electrode to the external surface of the electrode to form a protective layer of fluid around the electrode; and a fluid source for directing fluid through the lumen and the plurality of fluid paths to the external surface of the electrode.

72. The ablation catheter of claim 71, wherein the electrode comprises a ring electrode.

73. The catheter of claim 71, wherein the electrode comprises a microporous structure.

74. A catheter tip for ablation of tissue comprising:
a) an elongate shaft having shaft walls defining a shaft inner lumen and shaft wall outer surfaces, the shaft having a proximal attachment end portion and a distal tip portion;
b) an electrode portion comprised of porous metal having portions mechanically connected to said shaft and electrically connected to a conductor within said shaft, said electrode placed circumferentially around a portion of said shaft and having an inner surface facing toward said shaft and an outer surface facing away from said shaft; and c) shaft wall structures defining fluid flow apertures extending from the shaft inner lumen to the shaft wall outer surfaces; the apertures allowing the flow of fluid from the shaft inner lumen to the porous metal electrode inner surface, and the porous metal electrode defining fluid flow apertures suitable for the flow of said fluid through the fluid flow apertures to create a protective layer of fluid around the electrode outer surface.

75. The catheter tip of claim 74 in which the porous metal electrode comprises a sintered metal material.

76. The catheter tip of claim 74 further comprising solid ring electrodes around said shaft near said porous metal electrode, said solid ring electrodes having an electrical connection to a conductor within said shaft.

77. The catheter tip of claim 74 further comprising a tip electrode at said distal tip of said shaft, said tip electrode having an electrical connection to a conductor within said shaft.

78. The catheter tip of claim 74 in which the electrode portion comprises porous metal ring electrodes separated by flexible plastic shaft wall segments.

79. The catheter tip of claim 74 in which the porous metal electrode portion comprises an elongated flexible woven mesh metal structure.

80. The catheter tip of any one of claims 74 to 79 further comprising temperature sensing means used as a feedback system for adjusting the flow rate of a fluid through the catheter tip.

81. The catheter tip of any one of claims 74 to 80 further comprising ablation means.