Multi-lumen catheter device

Abstract

The present invention provides a multi-lumen catheter device for delivery of microwave energy to a target region of tissue by way of a microwave radiation antenna electrically connectible via a microwave feedline to an electrical microwave system. The device includes an antenna-receiving chamber for accommodating the microwave radiation antenna, one or more orifices providing fluid connection between the antenna- receiving chamber and the outside of the device, a primary lumen configured to accommodate the microwave feedline and a first electrode connected to an electrical sensing system and to provide fluid flow to the antenna-receiving chamber, one or more substantially toroidal internal bores, each providing a flow gallery in fluid connection to the outside of the device by way of a first plurality of spaced orifices, and one or more secondary lumens separate to the primary lumen, each secondary lumen configured to accommodate a second electrode connected to the electrical sensing system, each secondary lumen in fluid connection with a flow gallery. Fluid flow along the secondary lumen(s) exits the device through the first plurality of spaced orifices via a flow gallery, and the electrical circuit created between the respective electrodes includes an ionic conductivity bridge between the second electrode(s) and the plurality of spaced orifices, which thus act as a saline ring electrode for sensing tissue response or for applying electrical signals for other purposes.

Description

Multi-lumen catheter deviceField of the invention

[0001] The present invention concerns a multi-lumen catheter device and a system including such a device, for use in treatment of medical conditions.Background of the invention

[0002] Approximately 18 million people die a year globally from cardiovascular disease. Up to a quarter of cardiovascular deaths occur suddenly due to a rapid and abnormal rhythm disorder from the muscular pumping chambers of the heart, referred to as ventricular arrhythmias (VA). Scarring in the heart, which may be caused by a heart attack for example, can result in rapid circuitous electrical conduction generating lethal VA.

[0003] Generally, catheter ablation is more effective than medications in controlling VA and preventing implantable cardioverter defibrillator (ICD) shocks. For example, radiofrequency (RF) ablation involves using catheters introduced in a minimally invasive way into the heart via the vasculature to identify and target critical portions that may give rise to VA.

[0004] However, in patients with scars in the ventricle, the acute procedural success rate for catheter ablation of VA in major trials is 49-75%, and long-term VA-free survival is less than 50%. This limited efficacy is due to the biophysical limitations of RF ablation.

[0005] Resistive heat production occurs only in a shallow subsurface region, approximately 1 mm deep, and heat conduction deepens the ablation lesion from this shallow region of direct heating. RF ablation techniques are ill-suited for producing deeper thermal lesions without overheating the myocardial surface, leading to complications. Essentially, much of the scar in the ventricle can be out of the reach of RF ablation. Consequently, it is very difficult to eradicate all VA circuits this way, with VA recurring in more than 50% of patients.

[0006] Even using state-of-the-art RF ablation catheters, lesions no more than approximately 6-8 mm deep can be created before the risk of complications becomeunacceptably high. Given that the ventricular myocardium can be 10-12 mm thick, the lesions produced cannot reach many scars.

[0007] Moreover, RF ablation penetration can be further impeded and thus ineffective when the cardiac tissue contains fibrosis, fat, or calcifications. Whilst epicardial catheter ablation can on occasion be used to reach scars that cannot be reached endocardially, epicardial fat and overlying coronary arteries often prevent effective and safe ablation.

[0008] Another drawback of RF ablation catheters is that the ablation electrode must be relatively large (typically around 3.5-4.0 mm long) in order to deliver sufficient electrical energy to the tissue. However, a single electrode of this type is of limited use in identifying scar tissue, and multiple smaller electrodes (1 -2 mm) generally provide a higher resolution when used in characterising scar tissue. It has therefore become conventional practice to use a separate catheter equipped with multiple small electrodes to first map the scar region, and then using an ablation catheter to treat the scar, and this can add significantly to cost and complexity of the whole operation.

[0009] In contrast to conventional RF ablation, microwave ablations utilise electromagnetic waves within the 2.45-GHz ISM band. Microwave energy can interact with biological tissues resulting in dielectric heating produced predominately by dipole oscillation of water molecules. Microwave radiation can be generated by passing alternating electrical currents to an antenna to create resonance. Because microwaves heat dielectrically, catheter antenna contact is not required during ablation. The coupling of the ablation energy to the surrounding region means that a relatively large volume of tissue can be heated directly, meaning that larger and deeper ablations are possible than can be achieved with RF energy, and this can be accomplished without tissue overheating.

[0010] PCT / AU2019 / 050754, the entire contents of which are herein incorporated by reference, describes an ablation lesion device to deliver microwave energy to a selected region of a tissue, for treatment or prevention or arrhythmias, the device including a microwave antenna within a catheter-receiving portion of the device and including fluid flow lumens and optimally located outlet flow orifices, thereby allowing flow of saline irrigant to the outside of the catheter. The device is provided with an electric sensing system including one or more wire electrodes positioned in the fluid flow lumens,configured such that in use an electric circuit is formed which incorporates an ionic conductivity bridge between the electrode(s) and the fluid exiting the orifices, the ionic conductivity bridge traversing the catheter antenna-receiving portion.

[0011] In use, the resulting "saline electrodes" act as microwave-tolerant current paths for sensing and pacing. The saline electrodes therefore constantly weep a small quantity of saline irrigant, which provides an acceptable conductor for electrogram sensing, as well as the ability to pace up to 4 mA using a specially crafted pacing system. The saline also provides a high permittivity environment around the antenna, which allows it to be shorter than would otherwise be possible yet still be of a suitable length to couple preferentially to cardiac tissue.

[0012] The particular device described in PCT / AU2019 / 050754 had a number of drawbacks. The antenna was not axisymmetric with the tip, it was instead offset to one side to accommodate all the components within the catheter, resulting in uneven ablation patterns. It was manufactured by extrusion techniques and required a skilled technician to prepare the components. Due to limitations of the design, the amount of saline available around the antenna shank was less than optimal, and an antenna length of 27 mm (from tip to braid end) was required in order to find an effective null return loss point in the 2.45 GHz ablation band.

[0013] Reference to any prior art in the specification is not an acknowledgment or suggestion that this prior art forms part of the common general knowledge in any jurisdiction or that this prior art could reasonably be expected to be understood, regarded as relevant, and / or combined with other pieces of prior art by a skilled person in the art.Summary of the invention

[0014] In one aspect of the invention, there is provided a multi-lumen catheter device for delivery of microwave energy to a target region of tissue by way of a microwave radiation antenna electrically connectible via a microwave feedline to an electrical microwave system, the device including: an antenna-receiving chamber for accommodating the microwave radiation antenna;one or more orifices providing fluid connection between the antenna-receiving chamber and the outside of the device; a primary lumen configured to accommodate the microwave feedline and a first electrode connected to an electrical sensing system and to provide fluid flow to the antenna-receiving chamber; one or more substantially toroidal internal bores, each providing a flow gallery in fluid connection to the outside of the device by way of a first plurality of spaced orifices; and one or more secondary lumens separate to the primary lumen, each secondary lumen configured to accommodate a second electrode connected to the electrical sensing system, each secondary lumen in fluid connection with a flow gallery.

[0015] Accordingly, fluid flow along the one or more secondary lumens from a proximal end of the device exits the device through the first plurality of spaced orifices via the one or more flow galleries, and the second electrode(s) within this fluid flow can be used to create an ionic conductivity bridge with the plurality of spaced orifices, to act as a saline ring electrode.

[0016] The orifices of the first plurality of spaced orifices in fluid connection with each flow gallery may be substantially longitudinally coincident.

[0017] In a preferred form, the one or more orifices providing fluid connection between the antenna-receiving chamber and the outside of the device comprises a second plurality of spaced orifices angularly distributed around the device. The orifices of the second plurality of spaced orifices are preferably substantially longitudinally coincident and / or proximate a distal tip of the device.

[0018] In this way, the orifices can act as a saline ring electrode, to create an electrical dipole with another saline ring electrode, such as the saline ring electrode created by a plurality of spaced orifices in fluid connection with a flow gallery.

[0019] In a preferred form, at least one of the one or more secondary lumens connects to a respective flow gallery by way of multiple separate channels, the multiple separate channels splitting from the respective secondary lumen at a channel separation point.

[0020] The multiple separate channels may connect with a flow gallery at different connection points, selected to enhance uniformity of fluid delivery to the first plurality of spaced orifices.

[0021] For example, if a secondary lumen bifurcates into two separate channels, these may connect with a flow gallery at substantially diametrically opposite positions.

[0022] The electrode within one of the one or more secondary lumens is preferably positioned at or in the vicinity of the channel separation point.

[0023] Preferably, the plurality of multiple separate channels that separate from a secondary lumen are configured to have matched electrical impedances.

[0024] In a preferred form, the electric sensing system is independent of the electrical microwave system, wherein the electric sensing system includes an electric circuit between the electrode within the primary lumen and one or more of the electrodes within the one or more secondary lumens via the fluid exiting the first plurality of spaced orifices.

[0025] The multi-lumen catheter device preferably includes a mating section at the proximal end of the device with a reduced diameter, for sealing connection with a catheter sheath that accommodates the microwave feedline for connection to the electrical microwave system and wires connecting the first and second electrodes to the electrical sensing system.

[0026] The device preferably includes multiple secondary lumens and multiple flow galleries, each flow gallery associated with a first plurality of substantially longitudinally coincident spaced orifices providing fluid connection between the flow gallery and the outside of the device at different longitudinal positions.

[0027] In this form, each secondary lumen may connect to a respective flow gallery by way of at least two separate channels.

[0028] A secondary lumen of the multiple secondary lumens may connect to a respective first flow gallery of the multiple flow galleries by way of one or more flowchannels that pass within the inner circumference of a second flow gallery positioned more proximally than said first flow gallery.

[0029] In this way, the more proximally positioned flow galleries do not interfere with the channel or channels that feed one or more flow galleries that are more distally positioned.

[0030] In a further aspect, the present invention provides an elongated catheter device having a distal end and proximal end and a longitudinal centreline, the device including an inner chamber through which the longitudinal centreline runs, the inner chamber providing a first fluid flow connection from the proximal end of the device to the exterior of the device via one or more first flow orifices, the device also including a fluid flow gallery substantially surrounding the longitudinal centreline, the fluid flow gallery providing a second fluid flow connection from the proximal end of the device to the exterior of the device via one or more second flow orifices, within the device there being substantially no fluid flow connection between said inner chamber and said fluid flow gallery.

[0031] In a further aspect, the present invention provides a system to perform microwave ablation of a target region of tissue, including a catheter device as defined above.

[0032] Further aspects of the present invention and further embodiments of the aspects described in the preceding paragraphs will become apparent from the following description, given by way of non-limiting example and with reference to the accompanying drawings.Brief description of the drawings

[0033] Figure 1 schematically illustrates a medical system including an endovascular catheter device in accordance with the present invention;

[0034] Figures 2A-B, 3 and 4 illustrate a first embodiment of a catheter device in accordance with the present invention. In particular, Figure 2A provides a perspective view of the device, Figure 2B shows detail of the proximal end of the catheter device,Figure 3 shows the internal structure of the catheter device and Figure 4 shows detail of a part of said the internal structure.

[0035] Figures 5-7, 8A and 8B illustrate a second embodiment of a catheter device in accordance with the present invention. In particular, Figure 5 provides a perspective view of the device, Figures 6-8A show the internal structure of the catheter device, and Figure 8B shows detail of a distal part of the catheter device including the internal structure.Detailed description of the embodiments

[0036] The system shown in Figure 1 includes a catheter 10 connected at a handle 12 to a patient cable 14. At the proximal end 28 of patient cable 14, a microwave coaxial feedline (not shown) connects via a suitable connector 23 to a microwave generating source 50. In the system, electrical wires (not shown) are connected via a suitable connector 52 (such as one or more Redel 1 P plug-in connectors), to an electrical control module 54, such as an electrocardiogram processing / display module. Module 54 may include a signal processor and suitable monitors, displays and feedback means to assist use of the microwave catheter during an ablation procedure, alternatively or in addition it may be configured to provide electrical signals and measure responses, for use in cardiac pacing.

[0037] Further, connector means 56 (such as one or more Luer locks) connects a fluid control system 58 to irrigation lumens within catheter 10 (further described below). Fluid control system 58 includes suitable pump, control and flow measurement means, allowing selective adjustment of the irrigation fluid flow parameters. Fluid control system 58 may also be used to introduce other fluids such as drugs into the fluid flow lumens for delivery to the catheter tip.

[0038] Catheter 10 is flexible but substantially non-compressible along its length, to assist insertion and to minimise changes in impedance or fluid flow that might otherwise result from compression.

[0039] As will be understood, the catheter system may include other components and subsystems, such as a thermometry sensing system using a temperature sensing arrangement at the catheter distal end, to assist in monitoring operation during anablation procedure. For this purpose, the catheter may include a thermocouple for temperature monitoring, positioned within around 1 mm of the distal end of the microwave feedline (ie. the end of the coaxial cable shield braid). This may involve use of an additional lumen running the length of the catheter system, eg. connecting also through connector 52, not described in further detail herein.

[0040] Along its length the catheter system can be seen to comprise two portions, a distal portion (catheter 10) between a catheter tip 26 and handle 12 and a proximal portion (including patient cable 14, in this example around 2m in length) between handle 12 and proximal end 28.

[0041] The catheter system may include additional design features as required and known in the art, such as features to assist in steering or otherwise guiding of the catheter tip or to augment tracking of the catheter tip.

[0042] The majority of the length of catheter 10 provides a sheathed feedline (electric and fluid) to supply catheter tip portion 8, catheter tip portion 8 housing the microwave antenna (not shown). In an embodiment of the present invention developed by the inventors, catheter 10 has a diameter of around 8.5 Fr (about 2.7 mm).

[0043] As shown in Figure 2A, a first embodiment of catheter tip portion 8 includes an outer tubular insulating sheath 24, closed at tip 26, having two rings of spaced orifices (11 , 37) which provide irrigant fluid flow outlets, as described in further detail below.

[0044] As can be seen in Figures 2B and 3, catheter tip portion 8 is formed with internal bores, in particular with two internal lumens 15 and 16 which run in the longitudinal direction from the proximal end 21 of the catheter tip portion 8.

[0045] Lumen 16, of circular section, is the larger of the two internal lumens and extends from proximal end 21 to connect with an antenna-receiving chamber 31 in the distal part of the device (towards catheter tip 26), chamber 31 being defined by tubular sheath 24. The function of lumen 16 is to accommodate the microwave coaxial feedline cable (not shown), which terminates in a monopole microwave antenna (not shown) positioned within chamber 31 . As will be understood, the microwave antenna is configured to radiate microwave energy to the surrounding environment. The portion of catheter tip portion 8 from the proximal end 21 to the start of antenna receiving chamber31 constitutes the shank of the device, providing the connection to the feedline sheath and housing the lumens, as described further below.

[0046] Further, in assembling the device, a first wire (not shown), insulated along its length save for an uninsulated termination which acts as an electrode, is introduced into lumen 16, to position the electrode in the shank of catheter tip portion 8 proximal of the proximal end of antenna-receiving chamber 31 (approximately longitudinally aligned with bifurcation point 33 of lumen 15), as discussed further below. The first wire passes along the inside of the sheath of catheter 10 from electrical connector unit 52.

[0047] As can be seen in the figures, at the proximal end 21 lumen 16 is laterally offset from the centreline of the device, while antenna receiving chamber 31 is coaxial with the device. Hence, moving in the distal direction, lumen 16 gradually transitions from its offset position to a coaxial position, where it connects to antenna-receiving chamber 31 by way of a frustoconical transition section 45.

[0048] As Figure 3 shows, close to catheter tip 26 the outer wall of sheath 24 is provided with eight longitudinally coincident equispaced orifices 37 (in the embodiment developed by the inventors, around 2mm from tip 26). Orifices 37 are fed by bores that connect to antenna-receiving chamber 31 . As will be understood, the number of orifices can be selected as required, although too many orifices may unduly reduce the strength or compression resistance of the device.

[0049] Lumen 15 is also of circular section, and at the proximal end 21 is laterally offset from the centreline of the device, on the opposite side to lumen 16 (see Figure 2B). The function of lumen 15 is to provide irrigation fluid (saline solution) to ring gallery 68, while also accommodating a wire electrode, as described further below. Moving in the distal direction, lumen 15 narrows to a bifurcation point 33 at which it bifurcates into two separate irrigation lumens 47, 48.

[0050] As shown in Figures 3 and 4, just proximal of the transition section 45 of lumen 16, catheter tip portion 8 incorporates an annular bore of rectangular section, coaxial with the catheter centreline, to provide an irrigation ring gallery 68. The two irrigation lumens 47 and 48 terminate by connections 111 and 112 with the proximal face of ring gallery 68, connections 111 and 112 at diametrically opposite positions. As will beunderstood, ring gallery 68 takes the form of a hollow, substantially toroidal bore (ie. an annular void), allowing it to surround lumen 16 but remain isolated from lumen 16 and antenna-receiving chamber 31 . The outer diameter of ring gallery 68 is approximately equal to the internal diameter of antenna-receiving chamber 31 .

[0051] Ring gallery 68 is connected to the exterior of catheter tip portion 8 by eight angularly equispaced bores, which thus provide radially-directed outlet orifices 11 for irrigant fluid flow.

[0052] As will be understood, ring gallery 68 need not be wholly toroidal, provided it has a form that extends substantially around a substantial part of the circumference of the device. For example, it may take a C-shape, with a gap between the closed opposed ends of the gallery, through which the irrigant feed lumens 47, 48 may pass. Alternatively, ring gallery 68 may take the form of two separate half rings, each ring fed respectively by one of the two irrigant feed lumens 47, 48, and between which half rings irrigant feed lumens 47, 48 may pass. Ring gallery 68 may take any suitable substantially toroidal form (ie. a circular projection of any two dimension shape), and need not take a wholly regular form, provided it is able to feed the plurality of outlet orifices 11 .

[0053] In the embodiment developed by the inventors, at bifurcation point 33 lumen 15 has a diameter of approximately 0.7 mm, and lumen 16 a diameter of approximately 1 .3 mm. Catheter tip portion 8 has an outer diameter of 2.7 mm (as noted above) and a length - from proximal end 21 to tip 26 - of approximately 35 mm. Ring gallery 68 is positioned around 17 mm from tip 26.

[0054] As shown in Figures 2A and 2B towards its proximal end 21 , catheter tip portion 8 includes a mating part 32, which has a smaller outer diameter than the rest of the device, terminating in abutment shoulder 13. Mating part 32 thus provides a circumferential glue surface for the outer sheath of catheter 10, so the two may be adhesively sealed together while avoiding the risk of glue inadvertently entering and blocking lumens 15, 16. As the figures show, at their proximal ends lumens 15 and 16 open into cutaway sections in mating part 32, which aids in introducing the antenna and electrical feedline into lumen 16 and electrical wires into lumen 15 (as described further below).

[0055] Lumen 16 is sized such that once the antenna, electrical feedline and first electrode wire have been introduced, sufficient surrounding space remains to allow fluid flow to antenna-receiving chamber 31 . This irrigant fluid flow assists with removing localised heat caused by feedline current and provides a high permittivity environment around the microwave antenna. Further, the saline solution in antenna-receiving chamber 31 can be used to create virtual electrodes at the fluid outlet points of orifices 37, as discussed further below.

[0056] The antenna is insulated from the irrigant fluid that surrounds it by suitable encapsulation, such as a Teflon tube with an epoxy end cap, while the coaxial cable that provides the feedline is similarly insulated by a layer of thin heat shrink (such as Palladium™ thermoplastic elastomer). In two embodiments developed by the inventors, the monopole antenna used has a length of, respectively, 15mm and 23mm (from tip to braid end), fed by a Wellshow 1 .13mm Low Loss coaxial cable D113LWS5BT. The inventors have found that the 15mm antenna provides higher energy intensity (ie. a hotter ablation) while the 23mm antenna generates a longer lesion.

[0057] In assembling the device, a second wire (not shown), insulated along its length save for an uninsulated termination which acts as an electrode, is introduced into lumen 15 to position the electrode at or close to bifurcation point 33. The second wire passes along the inside of the sheath of catheter 10 from electrical connector unit 52.

[0058] In use, through the sheath of catheter 10, irrigant fluid (saline solution) from fluid control system 58 can be introduced to lumens 15 and 16. The fluid flow along lumen 16 thus passes through the space surrounding the electrical feedline, into antennareceiving chamber 31 , and radially outwardly to the exterior via the orifices 37. The fluid flow along lumen 15 splits into two flows at bifurcation point 33 and passes through the space surrounding the electrical feedline, along the two irrigation lumens 47 and 48, into ring gallery 68, and radially outwardly to the exterior via orifices 11 .

[0059] The device thus incorporates two virtual ring electrodes, by virtue of, firstly, the ionic conductivity bridge created between the first wire electrode and the fluid outflow points created by orifices 37 (or rather, the points at which the fluid flow meets the myocardium), and secondly, the ionic conductivity bridge created between the second wire electrode and the outlet orifices 11 of ring gallery 68 (or rather, the points at whichthe fluid flow meets the myocardium). These saline bridges and the resulting virtual electrodes therefore allow conduction of biological signals (in particular, the local electrogram) of the heart tissue to the clinician for diagnostic information.

[0060] The septated nature of catheter tip portion 8 (and the insulating function of the sheath material) provides electrical separation between the different fluid flows, which provides a high impedance circuit between electrodes. This arrangement thus provides a sensing electrode system independent of and electrically isolated from the microwave antenna element.

[0061] In addition to monitoring biological signals, the virtual electrodes created by use of the device can also be used to deliver of electrical signals (such as pacing signals) to the tissue, to be used for interrogation of local tissue properties (useful in locating target tissue areas) or for cardiac pacing study.

[0062] As will be understood, the use of ring electrodes provides significant advantages over using single point virtual electrodes (such as those provided by single fluid outlet orifices, eg. as described in PCT / AU2019 / 0507540) as, once the catheter tip is positioned in contact with the tissue, at least part of the ring electrode (ie. one or more of the virtual electrodes provided by the fluid outlet orifices) is in contact with the myocardium, and can thus gather the required sensing data (such as the local electrogram) from the surrounding tissue, avoiding the need to reorientate the catheter to ensure a suitable electrical connection.

[0063] As will be appreciated, split lumens 47 and 48 feed opposite parts of ring gallery 68 to distribute fluid more evenly (ie. to increase uniformity of fluid pressure around the ring gallery). It is important that the impedance of both lumens is matched as far as possible, accordingly the device is design such that the lumens are of equal diameter and length, their diameters being as large as practicable within the tight dimension constraints of the device. In the embodiment developed by the inventors, lumens 47 and 48 have a diameter of 300 pm.

[0064] In the device described, only two split lumens 47 and 48 are used, but more channels are possible (for example, up to six channels may extend to ring gallery 68 from a manifold connection to feed lumen 15). The more channels that are used, thesmaller diameter each channel needs to be. This can be advantageous, for example in regard to crush resistance. However, more channels can present challenges in design of the device. Further, a smaller channel has a higher impedance which can lead to limitations in application, as well as a higher friction head, reducing flow through the gallery and increasing the required pump pressure.

[0065] In the embodiment developed by the inventors, the bores that feed orifices 11 and 37 have a diameter of 200 pm, allowing the saline solution to provide sufficient pressure for effective fluid flow out of the orifices during ablation to prevent blood clot formation and effective wash-through of the catheter tip to prevent clot formation, as well as providing ‘jacking pressure’ to lift the tip away from contact with the myocardium surface and so reduce the risk of orifice blocking by such contact.

[0066] As will be understood, the particular form of mating part 32 minimises the risk of the parasitic load of the common saline path from reducing the amplitude of the local electrogram, while reducing the risk of current being shunted between the electrodes instead of interrogating the tissue outside the catheter (to measure the local electrogram).

[0067] In this regard, in assembly of the device, before introduction of the first and second electrode wires, lengths of plastic tubing are introduced to lumens 15 and 16 from the proximal end of catheter tip portion 8 and adhered into place. The purpose of these is to further increase the length of the parasitic electrical path between the separate fluid flows in the two lumens, by increasing the impedance of that path and thus reducing the undesirable shunting of current due to the common fluid feed.

[0068] The longitudinal position of ring gallery 68 is selected in accordance with the location of the tissue which is to be interrogated (ie. the location of the tissue relative to that of the antenna). The field strength of the microwave catheter ablation radiation is at its maximum at the longitudinal position of the proximal end of the antenna (ie. at the braid end of the coaxial shield conductor), hence the location of the ring gallery 68 in Figure 3 may be useful monitoring lesion development in that location.

[0069] However, the device preferably includes additional longitudinally spaced virtual ring electrodes, allowing monitoring of lesion development at different points along thecatheter tip portion 8, and the second embodiment described below was developed by the inventors with this in mind.

[0070] Figures 5-7, 8A and 8B illustrate this second embodiment of catheter tip portion 8. The components of the system in Figure 1 , described above with reference to the first embodiment, are shared with the second embodiment.

[0071] As shown in Figure 5, catheter tip portion 8 includes an outer tubular insulating sheath 24’, closed at tip 26’ and having six rings of spaced orifices (11 A-E, 37’) which provide irrigant fluid flow outlets, as discussed further below.

[0072] As Figures 6 and 7 show, catheter tip portion 8 is formed with internal bores, in particular with six internal lumens 15A-E and 16’ which run distally in the longitudinal direction from the proximal end 21 ’ of catheter tip portion 8.

[0073] Lumen 16’, of circular section, is significantly larger than the other internal lumens and extends from proximal end 21 ’ to connect with an antenna-receiving chamber 3T in the part of the device distal of the shank. Towards catheter tip 26’ the antenna-receiving chamber 3T includes a more distal chamber portion 70 of larger diameter. Lumen 16’ accommodates the microwave coaxial feedline cable (not shown), which terminates in a monopole antenna (not shown) positioned within chamber 31 ’ and distal chamber portion 70.

[0074] In a similar way to the first embodiment, lumen 16’ houses a first wire terminating in an exposed electrode (not shown), which passes along the inside of the sheath of catheter 10 from electrical connector unit 52. Also like the first embodiment, (and as most clearly seen in Figure 8A), at the proximal end 21’ lumen 16’ is laterally offset from the centreline of the device and transitions to a coaxial position for connection with antenna receiving chamber 3T.

[0075] In the vicinity of catheter tip 26’ the outer wall of sheath 24’ (around distal chamber portion 70) is provided with twelve longitudinally coincident equispaced orifices, orifices 37’ fed by bores which fluidly connect to chamber portion 70’.

[0076] Lumens 15A-E, of circular section, extend from proximal end 2T through the shank of catheter tip portion 8, and are laterally offset from the centreline of the device,on the opposite side to that of lumen 16’ (see Figure 8A). Lumens 15A-E provide irrigation fluid (saline solution) to ring galleries 68A-E and, like the first embodiment, accommodate wire electrodes, described further below. Moving in the distal direction, lumens 15A-E are isolated from one another, and each one extends in a substantially parallel orientation to bifurcation points 33’ at which each lumen 15A-E bifurcates into two separate irrigation lumens. In particular, lumen 15A bifurcates into irrigation lumens 47A and 48A, irrigation lumen 15B bifurcates into irrigation lumens 47B and 48B, irrigation lumen 15C bifurcates into irrigation lumens 47C and 48C, irrigation lumen 15D bifurcates into irrigation lumens 47D and 48D, irrigation lumen 15E bifurcates into irrigation lumens 47E and 48E (See Figures 6 and 7).

[0077] As shown in Figure 8A, moving in the distal direction, catheter tip portion 8 incorporates a plurality of annular bores of rectangular section, each coaxial with the catheter centreline, to provide irrigation ring galleries 68A-E. Each set of two irrigation lumens (47A-48A, 47B-48B, 47C-48C, 47D-48D, 47E-48E) terminate by connections (111 A-112A, 111 B-112B, 111 C-112C, 111 D-112D, 111 E-112E) with the inner surface of each ring gallery 68A-E. For each ring gallery, these connections (111 A-112A, 111 B- 112B, 111 C-112C, 111 D-112D, 111 E-112E) are at diametrically opposite positions.

[0078] To accommodate all the split lumens 47A-E, 48A-E, they all take a generally helical form from the bifurcation points 33’ to the longitudinal position of the start of antenna-receiving chamber 3T, from which position they continue parallel to the device centreline. In this way, the lumens are distributed around the full circumference of catheter tip portion 8 (see Figure 8A), thus minimising the overall radial space they take up and leaving sufficient space for the microwave antenna. Hence, each pair of split lumens (eg. 47D, 48D) is angularly offset from each other pair of split lumens (eg. 47D, 47E) within the longitudinal extent of antenna-receiving chamber 3T, with all the split lumens (except for those that feed proximal ring gallery 68A, ie. lumens 47A, 48A) passing within the ring galleries that feed the more proximal ring galleries (for example, split lumens 47E, 48E, that feed distal ring gallery 68E, pass within the annulus of the next ring gallery 68D).

[0079] As shown in Figure 7, irrigation lumens 47A and 48A terminate by connections 111 A and 112A with the inner face of ring gallery 68A, irrigation lumens 47B and 48Bterminate by connections 111 B and 112B with the inner face of ring gallery 68B, irrigation lumens 47C and 48C terminate by connections 111 C and 112C with the inner face of ring gallery 68C, irrigation lumens 47D and 48D terminate by connections 111 D and 112D with the inner face of ring gallery 68D, irrigation lumens 47E and 48E terminate by connections 111 E and 112E with the inner face of ring gallery 68E.

[0080] As will be understood, ring galleries 68A-E are substantially toroidal in form, allowing each one to surround lumen 16’ but remain isolated from lumen 16’, antennareceiving chamber 3T and distal chamber portion 70. The inner diameter of ring galleries 68A-E is larger than the internal diameter of antenna-receiving chamber 3T and the lumens 47A-E, 48A-E are arranged to allow space for the microwave antenna in antenna-receiving chamber 3T. As can be seen from Figures 7-8A, the outer diameter of ring galleries 68A-E is approximately equal to the internal diameter of distal chamber portion 70.

[0081] Each ring gallery 68A-E is connected to the exterior of catheter tip portion 8 by 12 angularly equispaced bores, which thus provide radially-directed outlet orifices 11 A- E for irrigant fluid flow.

[0082] Like the first embodiment, ring galleries 68A-E need not be wholly toroidal, and can take different forms (including different forms for different ring galleries), provided they have a form that extends substantially around most of the circumference of the device.

[0083] As can be seen from the figures, in this embodiment the ring galleries are not evenly spaced on the longitudinal direction. In the device developed by the inventors, ring galleries 68A and 68B are spaced 2mm apart, as are ring galleries 68C and68D, while ring galleries 68B is spaced 4mm from ring gallery 68C, with the same separation between ring galleries 68D and 68E. Distal ring gallery 68E is spaced 2mm from the ring of spaced orifices 37’. The reason for this arrangement of ring electrodes is discussed further below.

[0084] Like the first embodiment, this embodiment also includes a mating part 32’ (see Figure 6) terminating in abutment shoulder 13’ providing a circumferential glue surface for the outer sheath of catheter 10, and cutaway sections, which aids in introducing theantenna and electrical feedline into lumen 16’ and electrical wires into lumens 15A-E (shown in Figure 5).

[0085] In a similar way to the first embodiment, once the antenna (insulated by suitable encapsulation), the electrical feedline and the wire electrode have been introduced into lumen 16’, fluid flows in the antenna-receiving chamber 3T and distal chamber portion 70, the fluid assisting with removing localised heat caused by microwave radiation and providing a high permittivity environment around the microwave antenna. The saline solution in antenna-receiving chamber 31 and distal chamber portion 70 can be used to create a ring of virtual electrodes at the fluid outlet points of orifices 37’, as discussed further below.

[0086] In assembling the device, five wires (not shown), insulated along their length save for an uninsulated termination which acts as an electrode, are introduced into each lumen 15A-E to position the electrodes at or close to their respective bifurcation points 33’. As will be understood, these five wires are connected at their proximal end to electrical connector 52.

[0087] In use, irrigant fluid (saline solution) from fluid control system 58 can be introduced inside catheter sheath 10 into lumens 15A-E and 16’. The fluid flow along lumen 16’ thus passes through the space surrounding the electrical feedline, into antenna-receiving chamber 3T and distal chamber portion 70, and radially outwardly to the exterior via the orifices 37’. The fluid flow along each lumen 15A-E splits into two flows at bifurcation points 33’ (for a total of 5 pairs of irrigation lumens 47A-E, 48A-E) and passes through the space surrounding the electrical feedline, along each set of two separate irrigation lumens (47A-48A, 47B-48B, 47C-48C, 47D-48D, 47E-48E), into ring galleries 68A-E, and radially outwardly to the exterior via orifices 11 A-E.

[0088] The device of this embodiment thus incorporates six virtual ring electrodes, by virtue of the ionic conductivity bridge created between the wire electrode within lumen 16’ and the fluid outflow points created by orifices 37’ (or rather, the points at which the fluid flow meets the myocardium), and the five ionic conductivity bridge created between the wire electrodes inside lumens 15A-E and the outlet orifices 11 A-E of ring galleries 68A-E (or rather, the points at which the fluid flow meets the myocardium). These saline bridges therefore allow conduction of biological signals (in particular, the localelectrogram) of the heart tissue to the clinician for diagnostic information. Like the first embodiment, due to the septated structure of catheter tip 8, the sensing electrode system is independent and electrically isolated from the microwave antenna element.

[0089] These virtual electrodes can be used to deliver electrical signals (such as pacing signals) to the tissue for interrogation of local tissue properties (useful in locating target tissue areas) or for cardiac pacing study. As will be understood, the clinician using the device may elect to use all or some of the virtual ring electrodes associated with ring galleries 68A-E (simultaneously or separately) to collect the local electrogram from the surrounding tissue in order to monitor lesion development. Like the first embodiment, the ring electrodes 37’ and 68A-E allow gathering sensing data (such as the local electrogram) from the surrounding tissue, without the need to reorientate the tip.

[0090] As will be understood, all the flow paths are electrically isolated from each other, meaning that in certain applications the clinician may elect not to use an ionic conductivity path between any of the virtual ring electrodes, including a path that does not include the virtual electrode provided by outlet orifices 11 A-E (in electrical connection with the wire electrode within lumen 16’). In other words, sensing may be conducted using an electrical path between two different virtual ring electrodes associated with two different ring galleries selected from ring galleries 68A-E.

[0091] Each set of two separate irrigation lumens (47A-48A, 47B-48B, 47C-48C, 47D- 48D, 47E-48E) feed opposite parts of each ring gallery 68A-E to distribute fluid more evenly (ie. to increase uniformity of fluid pressure around the ring gallery). These irrigation lumens are of equal diameter. As these irrigation lumens connect with the inner surface of each ring electrode 68A-E, their diameter is as large as practicable, limited by the space available between the inner surface of each ring electrode 68A-E and the surrounding antenna receiving chamber 3T. In the embodiment developed by the inventors, each irrigation lumen (47A-48A, 47B-48B, 47C-48C, 47D-48D, 47E-48E) has a diameter of 300 pm. As will be understood, more irrigation lumens for each ring electrode are possible, and more ring galleries are possible. However, such increases create more challenges for the design of the device.

[0092] In the device developed by the inventors in accordance with this embodiment of the invention, the bores that feed orifices 11 A-E and 37’ have a diameter of 200 pm (like the first embodiment), allowing the saline solution to provide sufficient pressure to the tissue during ablation to prevent blood clot formation, and to prevent contact against the myocardium surface and so reduce the risk of orifices being blocked if the device is pressed against the myocardium.

[0093] In a similar way to the first embodiment, in assembly of the device lengths of plastic tubing are introduced into lumens 15A-E and 16 at the proximal end of catheter tip 8, into which the electrode wires are passed, in order to increase impedance and thus reduce shunting of current between the electrodes by way of the common fluid feed.

[0094] The longitudinal positions of ring galleries 68A-E is selected in accordance with the location of the tissue which is to be interrogated. The particular 2+2+2 arrangement of the ring galleries of the embodiment illustrated is based on the arrangement of metal ring electrodes used in conventional RF catheters. As noted above, the physician using the device can select the ring galleries to use to collect the local electrogram from the surrounding tissue, in order to monitor the lesion development.

[0095] Catheter tip portion 8 of the second embodiment has similar overall dimensions to those of the first embodiment, ie. 2.7 mm (8.5 Fr) by 35mm. Both the embodiments described above can be fabricated by 3D printing techniques (using, for example, an UpNano 3D printer). The process achieves a spatial resolution of 200 pm, defining the smallest printable feature. In this way, the inventors were able to fabricate devices in accordance with both the embodiments disclosed herein, integrally incorporating all the features described above, including, in the second embodiment, the multiple lumen channels 47A-E, 48A-E that run longitudinally along the device to feed the respective ring galleries. As will be understood, these multiple lumens take the form of tubes that run within antenna-receiving chamber 3T, but in an alternative form more be formed of longitudinal bores in the wall of the device (ie. formed in the material of the device, between the outer diameter of antenna-receiving channel 3T and the inner diameter of ring galleries 68A-E).

[0096] Suitable materials for fabrication of catheter tip device 8 include bloodcompatible, thermally stable, flexible, microwave safe resins, such as specialised 2PP (2 photon polymerisation) photopolymers, which provide strong cross linking of the cured resin. In high resolution printers such material can be used to fabricate extremely high resolution products (potentially in the sub-micron range).

[0097] As discussed above, the device of the present invention allows the clinician to perform and monitor a microwave ablation more efficiently as the device enable to collect the local electrogram that informs on the progress of the tissue ablation without the need for the clinician to reposition the device. This is because in the present invention, the saline solution creates an ionic conductivity bridge that flows in multiple directions to the biological tissue via the multiple orifices connected to each ring electrode, thus reducing the need for the clinician to reposition the catheter to monitor the progress of the ablation.

[0098] It will be understood that the invention disclosed and defined in this specification extends to all alternative combinations of two or more of the individual features mentioned or evident from the text or drawings. All of these different combinations constitute various alternative aspects of the invention.

[0099] As used herein, except where the context requires otherwise, the term "comprise" and variations of the term, such as "comprising", "comprises" and "comprised", are not intended to exclude further additives, components, integers or steps.

Claims

CLAIMS1 . A multi-lumen catheter device for delivery of microwave energy to a target region of tissue by way of a microwave radiation antenna electrically connectible via a microwave feedline to an electrical microwave system, the device including: an antenna-receiving chamber for accommodating the microwave radiation antenna; one or more orifices providing fluid connection between the antenna-receiving chamber and the outside of the device; a primary lumen configured to accommodate the microwave feedline and a first electrode connected to an electrical sensing system and to provide fluid flow to the antenna-receiving chamber; one or more substantially toroidal internal bores, each providing a flow gallery in fluid connection to the outside of the device by way of a first plurality of spaced orifices; and one or more secondary lumens separate to the primary lumen, each secondary lumen configured to accommodate a second electrode connected to the electrical sensing system, each secondary lumen in fluid connection with a flow gallery.

2. The multi-lumen catheter of claim 1 , wherein the orifices of the first plurality of spaced orifices in fluid connection with each flow gallery is substantially longitudinally coincident.

3. The multi-lumen catheter of claim 1 or claim 2, wherein the one or more orifices providing fluid connection between the antenna-receiving chamber and the outside of the device comprises a second plurality of spaced orifices angularly distributed around the device.

4. The multi-lumen catheter of claim 3, wherein the orifices of the second plurality of spaced orifices are substantially longitudinally coincident and / or proximate a distal tip of the device.

5. The multi-lumen catheter of any preceding claim, wherein at least one of the one or more secondary lumens connects to a respective flow gallery by way of multipleseparate channels, the multiple separate channels splitting from the respective secondary lumen at a channel separation point.

6. The multi-lumen catheter of claim 5, wherein the multiple separate channels connect with a flow gallery at different connection points, selected to enhance uniformity of fluid delivery to the first plurality of spaced orifices.

7. The multi-lumen catheter of claim 5 or claim 6, wherein if a secondary lumen bifurcates into two separate channels, these connect with a flow gallery at substantially diametrically opposite positions.

8. The multi-lumen catheter of any one of claims 5 to 7, wherein the electrode within one of the one or more secondary lumens is positioned at or in the vicinity of the channel separation point.

9. The multi-lumen catheter of any one of claims 5 to 8, wherein the plurality of multiple separate channels that separate from a secondary lumen are configured to have matched electrical impedances.

10. The multi-lumen catheter of any preceding claim, wherein the electric sensing system is independent of the electrical microwave system, and the electric sensing system includes an electric circuit between the electrode within the primary lumen and one or more of the electrodes within the one or more secondary lumens via the fluid exiting the first plurality of spaced orifices.11 . The multi-lumen catheter of any preceding claim, including a mating section at the proximal end of the device with a reduced diameter, for sealing connection with a catheter sheath that accommodates the microwave feedline for connection to the electrical microwave system and wires connecting the first and second electrodes to the electrical sensing system.

12. The multi-lumen catheter of any preceding claim, including multiple secondary lumens and multiple flow galleries, each flow gallery associated with a first plurality of substantially longitudinally coincident spaced orifices providing fluid connection between the flow gallery and the outside of the device at different longitudinal positions.

13. The multi-lumen catheter of claim 12, wherein each secondary lumen connects to a respective flow gallery by way of at least two separate channels.

14. The multi-lumen catheter of claim 12 or claim 13, wherein a secondary lumen of the multiple secondary lumens connects to a respective first flow gallery of the multiple flow galleries by way of one or more flow channels that pass within the inner circumference of a second flow gallery positioned more proximally than said first flow gallery.

15. A system to perform microwave ablation of a target region of tissue, including the multi-lumen catheter device of any one of claims 1 to 14.

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