WO2013164820A1

WO2013164820A1 - Cyrocatheter with coolant fluid cooled thermoelectric module

Info

Publication number: WO2013164820A1
Application number: PCT/IL2013/050363
Authority: WO
Inventors: Avi BERGER; Avri Hazan
Original assignee: Berger Thermal Research Ltd
Priority date: 2012-04-30
Filing date: 2013-04-30
Publication date: 2013-11-07
Also published as: US11160596B2; US9820795B2; IL219477A0; EP2988690A1; EP2988690A4; US20150112195A1; US20180071007A1

Abstract

Cryocatheter including an elongated flexible catheter member having a short rigid catheter tip for introduction to a therapy site, a thermoelectric module, and a heat exchange arrangement for freezing the catheter tip to a cryo-temperature from between about -15°C to about -30°C for freezing human tissue at the therapy site.

Description

CRYOCATHETER WITH COOLANT FLUID COOLED THERMOELECTRIC MODULE

Field of the Invention

The invention relates to catheters in general and cryocatheters for cryotherapy at a therapy site in particular.

Background of the Invention

The invention is directed toward catheters having an elongated flexible catheter member and a short rigid catheter tip. Catheter members are typically about 0.5 m to 1.5 m long depending on its intended clinical application. Rigid catheter tips are typically about 0.8 cm to 1.5 cm long. The catheter members and the catheter tips have a 2.3 mm to 3.3 mm outside diameter corresponding to French Gauge 7-10. Catheter tips terminate in a leading catheter dome typically formed from bio-compatible materials such as platinum, iridium, and the like. For certain surgical procedures, catheter tips are intended to be introduced into a human lumen via an externally accessible access port to be steered therealong to a therapy site for therapy thereat before being pulled back along the human lumen to leave therefrom at the access port in a single clinical procedure. In greater particularity, the present invention is directed towards cryocatheters for cryotherapy at a therapy site at cryo-temperatures which in the context of the present invention are sub-zero tip temperatures of -10°C and colder.

Cryocatheters are presently implemented employing the Joule-Thomson effect, namely, passing a liquid, gas or vapor refrigerant through a pressure line at 70 bar to 150 bar to exit through a restriction at a catheter tip to cause a loss of pressure with consequent loss of heat and rapid cooling to freeze a catheter tip to a cryo-temperature. Exemplary prior art patent publications include inter alia US Patent No. 5,807,391 to Wijkamp entitled Cryo-Ablation Catheter, US Patent Application Publication No. 2011/0196359 entitled Catheter with Cryogenic and Electrical Heating Ablation, PCT International Publication No. WO 2010/121739 entitled Cryosurgical Instrument particularly suitable for transbronchial biopsy, and the like.

Cryocatheters are commercially available from Medtronic CryoCath, Inc. w w w .cryocath .com under several trade names including inter alia Freezor® MAX Cardiac CryoAblation Catheter, and Arctic Front® Cardiac CryoAblation Catheter. The cryocatheters employ nitrous oxide or argon refrigerant and are capable of heat transfer of several dozens of watts of thermal energy from human tissue over a period of 4 to 5 minutes for freezing a catheter tip to as low as -150°C to create a so-called ice ball of up to a size of 20 mm diameter for high cryoenergy purposes, for example, cryoablation, and the like. The cryocatheters are also operated at partial cryocapacities for low and mid cryoenergy purposes, for example, ice mapping procedures at a typically narrow temperature range of -10°C to -20°C, and the like. The cryocatheters are considered to be less steerable than their non-cryo counterparts because of their construction to withstand high pressure which can lead to greater difficulty to steer them to a desired therapy site. Moreover, the cryocatheters are highly expensive.

Summary of the Invention

The present invention is directed towards cryocatheter systems including cryocatheters having an elongated flexible catheter member and a short rigid catheter tip for cryotherapy at a therapy site. The catheter tips are typically introduced into a human lumen via an externally accessible access port to be pushed therealong to a therapy site for cryotherapy thereat before being pulled back along the human lumen to leave therefrom at the access port in a single clinical procedure. The cryocatheters of the present invention include at least one thermoelectric module for directly freezing an external surface of a catheter tip to a cryo-temperature of from -10°C to -30°C in the immediate vicinity of a 37 °C human body temperature therapy site to temporarily freeze human tissue for a cryogenic procedure before defrosting same to permit removal of the cryocatheter from the human lumen. The cyrocatheters of the present invention additionally include a heat exchange arrangement in flow communication with an external coolant fluid source for providing a downstream coolant fluid flow for passing a coolant fluid flow therethrough for cooling a thermoelectric module hot side of the at least one thermoelectric module for freezing the catheter tip's exterior surface.

Non-cryocatheters have long employed thermoelectric modules for cooling and/or heating a catheter tip for therapy at a therapy site. Exemplary prior art patent publications include inter alia US 7,238 184, WO 94/19833 entitled Thermoelectric Devices with Recuperative Heat Exchangers, WO 02/080766 entitled Treatment of Lipid Pool, and the like. Such non- cryocatheters have employed a range of heat sink techniques to cool a thermoelectric module hot side of a thermoelectric module opposite a thermoelectric module cold side of the thermoelectric module for cooling its catheter tip to below human body temperature but far above the cryo- temperatures achievable by the cryocatheters of the present invention. Heat sink techniques include inter alia a conductive solid core heat sink, the use of a blood pool in the immediate vicinity of a therapy site, and the like.

WO 02/080766 page 6 line 11 discloses a catheter assembly 70 having a "cold" bottom side 200 having a "cold" bottom side 200 for solidifying or "freezing" inflamed and unstable lipid pools 110 located within artery 100. WO 02/080766 catheter assembly 70 could employ thermoelectric modules, for example, commercially available from TEC Microsystems GmbH, Berlin- Adlershof, Germany, www, tecmicro s y stems .com. Suitable thermoelectric modules include inter alia 1MD03-008-4, 1MD03-036-4 and the like, which have a 25% to 30% thermal efficiency at a 30°C to 40°C temperature difference across their thermoelectric module hot and cold sides. Larger temperature differences across a thermoelectric module considerably deteriorate its thermal efficiency and are considered unpractical. The WO 02/080766 catheter assembly 70 is cooled by blood flow and accordingly it can be shown that the aforesaid thermoelectric modules operating at, say, 15% to 20% thermal efficiency are capable of cooling the bottom side 200 to, say, about 10 °C sufficient to solidify inflamed or unstable lipid pools but incapable of cooling the bottom side 200 to sub-zero temperatures.

The present invention is based on the realization that it is possible to design heat exchange arrangements for sufficient heat transfer from a thermoelectric module hot side over a 3 to 4 minute duration to freeze an exterior surface of a catheter tip to a cryo-temperature in the region of from - 10°C to -30°C in the immediate vicinity of a 37°C human body temperature therapy site for producing different shapes and different dimensions of frozen human tissue at a therapy site. Such cryocapability is capable of freezing human tissue to form ice balls of 6.0 mm to 8.0 mm diameter suitable for low and mid cryoenergy cryotherapy procedures, for example, blocking biological activity in the human tissue, providing a 50 gram anchoring force, and the like. Cryocatheters of the present invention are incapable of supplying the same high cryogenic energy as aforesaid described Joule-Thomson cryocatheters but it is envisaged they will be considerably less expensive than the Joule-Thomson cryocatheters and therefore the preferred option for low and mid cryoenergy cryotherapy procedures. Moreover, the thermoelectric module based cryocatheters of the present invention are more readily controllable than Joule- Thomson effect cryocatheters.

It can be shown that it requires heat transfer from about 1.5 Watt to about 2.0 Watt thermal energy over a duration of 3 to 4 minutes to freeze local human tissue to from about -10°C to about -25°C at a 37°C human body temperature therapy site. Accordingly, based on an aforesaid practical 30% thermal efficiency, a heat exchange arrangement of the present invention is required to heat transfer from about 6.5 Watt to 7.5 Watt thermal energy from a thermoelectric module hot side of an at least one thermoelectric module. This thermal energy takes into account the thermal energy needed to be absorbed from the human tissue to be frozen and the electrical energy applied to operate the at least one thermoelectric module. In order for a thermoelectric module cold side of a thermoelectric module to have a cryo-temperature of between from about -10°C to -30°C, its thermoelectric module hot side has to have a temperature of about 10°C as dictated by aforesaid 30°C to 40°C temperature difference across a thermoelectric module hot side and a thermoelectric module cold side. The downstream coolant fluid flow can be cooled to no less than near freezing temperature of, say, about 3°C to prevent its possible freezing before delivery to a catheter tip. Accordingly, the downstream coolant fluid flow has a downstream temperature, of say, about 5°C on average after its delivery to a catheter tip to leave an about 5°C temperature difference between the downstream coolant fluid flow and a thermoelectric module hot side. Depending on lengthwise or widthwise deployment of a thermoelectric module in a catheter tip, its thermoelectric module hot side has a hot side footprint area of 20+10 mm². Lengthwise and widthwise deployments of a thermoelectric module are correspondingly co-directional with or transverse to a longitudinal axis of a catheter member. Typically lengthwise thermoelectric modules have greater hot side footprint areas than widthwise thermoelectric modules. Accordingly, the heat exchange arrangement of the present invention is necessarily designed to be able to absorb 7.5W thermal energy from a 20+10 mm² thermoelectric module hot side which represents a considerable heat density dissipation of from about 250 Kw/m² to 750 Kw/m².

The present invention includes two types of heat exchange arrangements to achieve this high degree of heat transfer as follows: First, a so-called heat sink module. And second, a so-called jet impingement module.

The former includes a heat sink in thermal energy connection with a thermoelectric module hot side of an at least one thermoelectric module. The heat sink is made from highly heat conductive materials typically having a heat conduction coefficient of at least 170 w/m°C. Suitable materials include inter alia metal, carbon based thermal conductive materials, and the like. The heat sink is designed with a total heat exchange area of at least four times greater than the hot side footprint area in order to absorb the about 7.5 Watt thermal energy. The present invention envisages several different implementations of heat sinks as follows: A finned heat sink. A coil heat sink. A heat sink stack of wire mesh discs. A porous heat sink. The latter employs a coolant fluid supply line providing one or more coolant fluid jets preferably directly against a thermoelectric module hot side in order to heat transfer the 7.5 Watt thermal energy from the thermoelectric module hot side. Reference is made to two jet impingement papers regarding the principles of the use of jets for thermal energy dissipation which are incorporated herein by reference. The jet impingement papers are as follows: Local Heat Transfer to Impinging Liquid Jet in the Initially Laminar, Transitional and Turbulent Regimes" by B. Elison and B. W. Webb, Journal of Heat and Mass Transfer Vol. 37 No. 8, 1994. Convective Heat Transfer by Impingement of Circular Liquid Jets" by X. Liu and J.H. Lienhard and J.S. Lombara, Journal of Heat Transfer, August 1991, Vol.113/571. Alternatively, a thermoelectric module hot side may be covered by an impingement plate in direct thermal contact with its underlying thermoelectric module hot side.

The cryocatheter systems of the present invention can be implemented as either open irrigation catheter systems or circulation catheter systems. In the former, coolant fluid is open irrigated into an internal human surrounding at a therapy site and therefore the coolant fluid is necessarily a bio-compatible liquid, for example, 0.9% NaCl saline, and the like. In the latter, a cryocatheter includes a coolant fluid return line co-extensive with a coolant fluid supply line for transporting coolant fluid from a catheter tip to an external coolant fluid destination. The coolant fluid destination is preferably connected to the coolant fluid source for recirculation. The coolant fluid is not necessarily a biocompatible liquid and it can alternatively be a gas, for example, nitrous oxide, argon, and the like.

The cyrocatheters of the present invention can deploy one or more thermoelectric modules either lengthwise and/or widthwise in a catheter tip. The thermoelectric modules of a cryocatheter in accordance with the present invention can include a single Peltier device or a stack of two or more Peltier devices with a thermoelectric module hot side of one Peltier device facing the thermoelectric module cold side of another Peltier device. Brief Description of Drawings

In order to understand the invention and to see how it can be carried out in practice, preferred embodiments will now be described, by way of non- limiting examples only, with reference to the accompanying drawings in which similar parts are likewise numbered, and in which:

Fig. 1 is a block diagram of an open irrigation cryocatheter system including an open irrigation cryocatheter including a widthwise thermoelectric module and a heat exchange arrangement for forming an ice ball at a therapy site;

Fig. 2 is a transverse cross section of Figure l 's open irrigation cryocatheter along line A- A in Figure 1 ;

Fig. 3 is a block diagram of a circulation cryocatheter system including a circulation cryocatheter for forming an ice ball at a therapy site;

Fig. 4 is a transverse cross section of Figure 3's circulation cryocatheter along line B-B in Figure 3;

Fig. 5 is a longitudinal cross section of Figure l 's catheter tip including a lengthwise thermoelectric module and a heat sink module;

Fig. 6 is a longitudinal cross section of Figure l 's catheter tip including a widthwise thermoelectric module and a coil heat sink;

Fig. 7 is a top elevation view of a Figure 6's coil heat sink;

Fig. 8 is a longitudinal cross section of Figure l 's catheter tip including a lengthwise thermoelectric module and a porous heat sink;

Fig. 9 is a longitudinal cross section of Figure l 's catheter tip including a lengthwise thermoelectric module and a finned heat sink;

Fig. 10 is a transverse cross section of Figure 9's finned heat sink along line C-C in Figure 9;

Fig. 11 is a longitudinal cross section of Figure 3's catheter tip including a widthwise thermoelectric module and an alternative coil heat sink;

Fig. 12 is a top elevation view of Figure 11 's coil heat sink;

Fig. 13 is a longitudinal cross section of Figure 3's catheter tip including a widthwise thermoelectric module and a heat sink stack of wire mesh discs; Fig. 14 is a top elevation view of a wire mesh disc of Figure 13 's heat sink stack;

Fig. 15 is a perspective cross section of Figure l 's catheter tip including a widthwise thermoelectric module and a jet impingement module with a single jet nozzle;

Fig. 16A is a front elevation view of Figure 15's jet impingement module;

Fig. 16B is a top elevation view of an impingement zone of a jet nozzle of Figure 15's jet impingement module on the thermoelectric module hot side;

Fig. 17 is a longitudinal cross section of Figure l 's catheter tip including a lengthwise thermoelectric module and a jet impingement module with three jet nozzles;

Fig. 18 is a transverse cross section of Figure 17's catheter tip along line E-E in Figure 17;

Fig. 19 is a perspective cross section of Figure 3's catheter tip including a widthwise thermoelectric module and a jet impingement module with a single jet nozzle;

Fig. 20 is a longitudinal cross section of a Figure 3's catheter tip for freezing a trailing section of the catheter tip;

Fig. 21 is a longitudinal cross section of a Figure l 's catheter tip including a lengthwise thermoelectric module and a widthwise thermoelectric module and a heat sink module;

Fig. 22 is a block diagram of an open irrigation cryocatheter system including a cryocatheter and a RF ablator for RF ablation at a therapy site;

Fig. 23 is a transverse cross section of Figure 22's catheter member along line F-F in Figure 22;

Fig. 24 is a block diagram of an open irrigation cryocatheter system including a cryocatheter having a catheter tip with a sensor;

Fig. 25 is a transverse cross section of Figure 24's catheter member along line G-G in Figure 24; Fig. 26 is a longitudinal cross section of an open irrigation cryocatheter including a pair of vacant lumens for introduction of surgical tools at a therapy site; and

Fig. 27 is a transverse cross section of Figure 26's catheter member along line H-H in Figure 26.

Detailed Description of Preferred Embodiments of the Invention

Figure 1 shows an open irrigation cryocatheter system 100 A for use with an open irrigation cryocatheter 130 A including an open irrigation elongated flexible catheter member 131 A and an open irrigation short rigid catheter tip 132 A for forming an ice ball IB at a therapy site. The cryocatheter system 100A necessarily employs a bio-compatible liquid for cooling purposes in view of open irrigation into internal human tissue at a therapy site. The biocompatible liquid is preferably 0.9% NaCl saline, and the like.

The catheter member 131 A has an about 0.5 m to 1.5 m length denoted

E depending on its intended cryotherapy application. The catheter tip 132 A has an about 0.8 cm to 1.5 cm length. The catheter member 131 A and the catheter tip 132 A have an about 2.3 mm to 3.3 mm outside diameter. The catheter tip 132 A terminates at a leading catheter dome 133. The catheter dome 133 can have a smooth spherical shape. Alternatively, the catheter dome 133 can be formed with different finishes and shapes similar to commercially available RF ablation catheters and diagnostic catheters. For example, Medtronic FREEZOR® cryoablation catheter and St. Jude Medical's INQUIRE® diagnostic catheter have different shaped catheter domes 133.

The catheter tip 132A includes a widthwise thermoelectric module 134 transverse to a longitudinal axis of the catheter member 131 A. Suitable thermoelectric modules 134 include, for example, TEC Microsystems GmbH part number 1MD03-008-4 commercially available from TEC Microsystems GmbH, Berlin-Adlershof, Germany, www.tecmicrosystems.com. The thermoelectric module 134 has a thermoelectric module hot side 136 and a thermoelectric module cold side 137 during its operation for freezing the catheter tip 132A. The catheter tip 132A includes a heat exchange arrangement 138 for heat transfer from the thermoelectric module hot side 136. The catheter tip 132 A includes a thermistor 139 for monitoring the temperature of the thermoelectric module hot side 136 or the thermoelectric module cold side 137. The catheter tip 132 A includes one or more irrigation holes 141 for enabling flow of coolant fluid from the catheter tip 132 A to an internal human surrounding at the therapy site. The catheter tip's 132A heat exchange arrangement 138 can be implemented as either a heat sink module or a jet impingement module as described hereinbelow.

The catheter dome 133 is in highly thermal conductive contact with the thermoelectric module cold side 137 for freezing human tissue to form the ice ball IB. The catheter dome 133 is formed from bio-compatible highly thermal conductive materials with a thermal conductivity coefficient k of at least > 50 w/m°C and preferably higher. Suitable catheter dome materials include metals, for example, platinum, iridium, gold, etc and highly conductive plastics. Gold is particularly suitable for some applications since it has an extremely high thermal conductivity coefficient k > 250 w/m°C. The catheter dome 133 is preferably glued onto the thermoelectric module cold side 137 using a highly thermal conductive filling material to reduce a temperature drop from the thermoelectric module cold side 137 to the catheter dome 133. Suitable commercially available high grade gap filling materials have a high thermal conductivity coefficient k in the range of about 10 w/m°C.

Figure 2 shows the catheter member 131 A has an extruded construction including the following longitudinal lumens: First, a central lumen 142 for housing a coolant fluid supply line 143 for delivering a downstream coolant fluid flow to the catheter tip 132A. Second, a pair of opposite lumens 144 for housing steering wires 146 for assisting the navigation of the catheter tip 132A to a therapy site. Third, a lumen 147 for housing an electrical power lead pair

148 connected to the thermoelectric module 134. And fourth, a lumen 149 for housing a thermistor lead pair 151 connected to the thermistor 139. The lumen

149 can also be employed for housing additional control wires. The cryocatheter system 100 A includes an external coolant fluid source 101 for delivering bio-compatible coolant fluid to the cryocatheter 130A for freezing the catheter tip 132A, a thermoelectric module power source 102 connected to the electrical power lead pair 148 and a controller 103 for controlling the operation of the external coolant fluid source 101 and the thermoelectric module power source 102. The controller 103 includes an ON/OFF switch 104, an ICING control 106 for freezing the catheter tip 132A and a DEFROST control 107 for defrosting the catheter tip 132A and a TEMPERATURE level control 108 and is connected to the thermistor lead pair 151. The DEFROST control 107 reverses the polarity of the electrical power lead pair 148 for cooling the thermoelectric module hot side 136 and the heating the thermoelectric module cold side 137.

The external coolant fluid source 101 includes a coolant fluid reservoir 109, for example, a 0.9% NaCl saline infusion bag at 17°C to 24°C ambient temperature. The external coolant fluid source 101 includes a cooling device 111 for cooling the saline to preferably near freezing temperature, say, 3°C to 4°C to ensure the saline does not freeze. The cryocatheter system 100A is operable at higher coolant fluid temperatures, say, 10°C but this linearly reduces its cryocapability. The external coolant fluid source 101 also includes a peristaltic pump 112 for delivering the downstream coolant fluid flow to the cryocatheter 130A at an acceptable maximal flow rate of about 35 cc/min in view of open irrigation to an internal human surrounding.

The coolant fluid supply line 143 has a typical internal diameter in the range of 0.4 mm to 0.7 mm. The fluid velocity of the downstream coolant fluid flow in the coolant fluid supply tube 143 is about 1.5-4.5 m/s such that it has a Reynolds number of about 700-1200 in the laminar range. This flow rate typically causes a pressure drop as high as 40-70 psi which is near the maximum allowable for standard medical grade tubing set.

The catheter member 131A has a proximal end 152 opposite its leading catheter tip 132A including a termination arrangement 153. The termination arrangement 153 can include a handle 154 connected to the steering wires 146, a Luer connection 156 for connection to the external coolant fluid source 101 and an electrical connector 157 for connection to the controller 103.

Figure 3 show a circulation cryocatheter system 100B including a circulation cryocatheter 130B having a circulation catheter member 13 IB and a circulation catheter tip 132B for forming an ice ball IB at a therapy site. The cryocatheter system 100B is similar in construction and operation to the cryocatheter system 100 A and therefore similar parts are likewise numbered. The circulation cryocatheter system 100B can employ a coolant fluid in the form of gas, vapor or liquid as opposed to the open irrigation cryocatheter system 100 A. The present cryocatheter system 100B is described with reference to a liquid coolant. A cryocatheter system 100B employing a gas coolant can be readily modified from the present system. A gas based cryocatheter system 100B includes a gas pump instead of the peristaltic pump. A gas based cryocatheter system 100B operates at high pressure but not as high as Joule-Thomson effect cryocatheter systems.

The circulation cryocatheter system 100B differs from the open irrigation cryocatheter system 100 A insofar as the former 100B includes a coolant fluid destination 113. The cryocatheter 130B differs from the cryocatheter 130A insofar as the former's catheter member 131B includes another lumen 158 for housing a coolant fluid return line 159 (see Figure 4) and its catheter tip 132B does not have irrigation holes. The coolant fluid return line 159 is connected to the coolant fluid destination 113 which is in turn preferably connected to the coolant fluid reservoir 109. The coolant fluid supply line 143 and the coolant fluid return line 159 typically have a smaller cross section area in the cryocatheter 130B in comparison to the cryocatheter 130A's coolant fluid supply line 143 due to external cryocatheter diameter constraints. The catheter tip 132B's heat exchange arrangement 138 can be implemented as either a heat sink module or a jet impingement module to cool the thermoelectric module hot side 136 as described hereinbelow.

The use of the cryocatheter system 100A is as follows: A surgeon introduces the catheter tip via an externally accessible access port into a human lumen. The surgeon navigates the catheter tip to a therapy site. The surgeon switches the controller to ICING mode for about 3 to 5 minutes to freeze the catheter tip at the therapy site. The catheter tip freezes human tissue at the catheter tip to form an ice ball which binds the human tissue to the catheter tip. The freezing process itself may be the desired cryotherapy or alternatively a surgeon may perform an additional medical procedure. At the end of the medical procedure, the surgeon switches the controller to DEFROST mode for about 30-60 second to defrost the human tissue at the catheter tip to prevent tissue laceration particularly in a vascular procedure if a catheter tip is pulled from human tissue while still iced thereto.

Thermodynamic Analysis of the Heat Exchange Arrangement

The heat exchange arrangement 138 has an incoming downstream coolant fluid flow and an outgoing coolant fluid flow to either internal human surroundings in an open irrigation cryocatheter system 100 A or a coolant fluid destination 113 in a circulation cryocatheter system 100B.

The heat exchange arrangement 138 has the following specification: h: heat transfer coefficient

Ah: heat exchange area

The following symbols are used:

Q is the total thermal energy, namely, about 7.5 Watts, required to undergo heat transfer from a thermoelectric module hot side to a coolant fluid flow in a heat exchange arrangement. The total thermal energy Q = Ql + Q2 where Ql is the human thermal energy required to be absorbed from the human tissue to be frozen and Q2 is the electrical energy required to operate the at least one thermoelectric module.

Tin is the temperature of an incoming downstream coolant fluid flow on arrival at the heat exchange arrangement 138. Tin is estimated at 4°C to 5 °C based on its initial cooling to, say, 2°C to 3°C before introduction into a cryocatheter and its subsequent heating during its travel along a catheter member.

Tout is the temperature of an outgoing coolant fluid flow on leaving the heat exchange arrangement 138. Tout is estimated at 6°C to 9°C after being heated directly or indirectly by the thermoelectric module hot side 136.

Thot is the temperature of the thermoelectric module hot side 136 of the at least one thermoelectric module of a cryocatheter tip where

(l)Thot = Tin + Atl + Δΐ2 + ··· + Δΐη where Δΐΐ, Δΐ2 ... Δΐη are temperature differences depending on a construction of a catheter tip and its heat exchange arrangement

Tcold is the temperature of the thermoelectric module cold side 137 where for practical considerations

(2) Tcold = Thot - 35 °C

Δΐΐ is the convection temperature difference between a coolant fluid flow passing through the heat exchange arrangement 138 and a heat exchange area Ah calculated as follows:

Q

(3) Ml = , ,

J h x Ah

The heat exchange arrangement 138 is required to be capable of developing a convection temperature difference Δΐΐ in the range of from about 4°C to about 10°C such that a heat exchange arrangement 138 is capable of heat transfer from a thermoelectric module hot side 136 for freezing an exterior surface of a catheter tip 133 to a cryo-temperature from between about -15°C to about -30°C for freezing human tissue at a therapy site.

The heat sink implementations of a heat exchange arrangement of the present invention have a relatively low heat transfer coefficient h and therefore are designed to have a large heat exchange area Ah compared to a thermoelectric module hot side footprint area Af. The jet impingement implementations of a heat exchange arrangement of the present invention have a relatively high heat transfer coefficient h and therefore can be designed to employ the available hot side footprint area Af of a thermoelectric module as the heat exchange area Ah without the need for additional heat exchange area as per heat sink implementations.

Heat Sink Implementations of Heat Exchange Arrangement

Figure 5 shows an open irrigation catheter tip 132A including a lengthwise thermoelectric module 134 co-directional with a longitudinal axis of the catheter member 131 A and a heat sink module 200 constituting the heat exchange arrangement 138. An exemplary thermoelectric module 134 is the TEC Microsystems GmbH part number 1MD03-036-4 with a thermoelectric module hot side footprint area of a near 20 mm².

The catheter tip 132 A is designed for ensuring minimal temperature differences across adjacent components to facilitate freezing of human tissue. Accordingly, the catheter tips 132 A employs high grade gap filling material having a thermal conductivity coefficient k in the range of about 10 w/m°C. Suitable gap filling material includes inter alia AI thecnology, Inc.'s Ultra high thermally conductive epoxy paste adhesive ME7159 www.aithecnologv.com.

The catheter tip 132 A includes a catheter side wall 180 with a lengthwise cutout 181 extensive with the catheter side wall 180 for receiving the lengthwise thermoelectric module 134 and the heat sink module 200. The thermoelectric module 134 has a thermoelectric module hot side 136 opposite a thermoelectric module cold side 137 facing the catheter side wall 180 to freeze the catheter side wall 180 to freeze the catheter dome 133. The catheter tip 132A includes a first gap filling material layer 182 for mounting the thermoelectric module cold side 137 on the catheter side wall 180 and a second gap filling material layer 183 for mounting the heat sink module 200 on the thermoelectric module hot side 136. The gap filling material layers 182 and 183 have a thickness L typically in the range of from 50 μηι to 100 μηι. The heat sink module 200 has a lowermost wall 201 facing the thermoelectric module hot side 136. This catheter tip construction introduces two additional temperature differences Δΐ2 and Δΐ3 such that the hot side temperature Thot is calculated as follows:

(1) Thot = Tin + Atl + At2 + At3

where Δΐ2 is the temperature difference across the second gap filling layer 183 and is calculated as follows:

Ql x L

At2 =

K x Af

and where Δΐ3 which is the temperature difference across the lowermost surface 201 of the heat sink module 200 and is estimated to be 3 °C due to the very high heat flux density of about 400 Kw/m from the thermoelectric module hot side 136 to the lowermost wall 201.

Assuming the heat sink module 200 has a heat transfer coefficient h = 10000 w/m^2oC and a heat exchange area Ah equal to the thermoelectric module's hot side footprint area of 20 mm² = 20 x 10^"6 m², then according to equation (3).

Q 7.5

Atl =— -— = Ξ 37°

h Ah 10000 X 20 X 10-⁶

Based on the above technical details, Δΐ2 is calculated as follows:

7.5 x 50 x 10^~6

M2 = = 2°C

10 X 20 X 10^~6

On substitution of the values of Tin, Δΐΐ, Δΐ2 and Δΐ3 into equation (1), the thermoelectric module hot side 136 has a hot side temperature Thot as follows:

Thot = Tin + Atl + At2 + At3 = 5°C + 2°C + 3°C + 37°C = 47°C such that its thermoelectric module cold side 137 has an above freezing temperature according to equation (2):

Tcold = Thot - 35°C = 47°C - 35°C = +12°C For illustrative purposes, to freeze the catheter tip 132A to -17 °C, the hot side temperature Thot has to be capped at 18 °C. This can be achieved by provision of a heat sink module 200 having a heat exchange area Ah of 94 mm² such that the convection temperature difference Δΐΐ is: Q 7.5

Λ _j- 1 _ ~ °C

h x Ah 10000 X 94 X 10-^{6 ~}

and the hot side temperature Thot is therefor:

Thot = Tin + Atl + At2 + At3 = 5°C + 2°C + 3°C + 8°C = 18°C resulting in the desired thermoelectric module cold side cryo temperature:

Tcold = Thot - 35°C = 18°C - 35°C = -17°C The first gap filling material layer 182 mounting the thermoelectric module cold side 137 on the catheter side wall 180 transfers the human thermal energy Ql to be absorbed from the human tissue to be frozen to the heat exchange arrangement 138. As mentioned above, Ql is between about 1.5W and 2W which is about a quarter of the thermal energy Q required to be dissipated from the thermoelectric module hot side 136 to the heat exchange arrangement 138. The first gap filling material layer 182 leads to a negligible about 0.5 °C temperature drop thereacross such that catheter side wall 180 and the catheter dome 133 are nearly the same temperature as the thermoelectric module cold side 137.

Figures 6 to 14 show five different heat sink modules 200 which can be readily designed to have a heat exchange area of at least four times greater than the hot side footprint area of a thermoelectric module.

Figures 6 and 7 show a catheter tip 132 A with a width wise thermoelectric module and a heat sink module 200 implemented as a coil heat sink 202. The coil heat sink 202 includes a coil 203 spiraled around a central cylindrical core 204 mounted on the thermoelectric module hot side 136. The coil 203 has an average diameter AD1 of about 2.5 mm and an overall tube length LI where:

Ll=n x AD1 x N

where N is the number of turns around the core 204. A coil heat sink 202 with 8 turns has a heat exchange area Ah = Π x 0.5 x 63 = 99 mm².

Figure 8 shows a catheter tip 132A having a lengthwise thermoelectric module 134 and a heat sink module 200 implemented as a porous heat sink 206. The porous heat sink 206 can be formed from a range of thermal conductive materials such as metal, carbon based materials, and the like. The porous heat sink 206 has a heat exchange area determined by its material specific area (m gram).

Figures 9 and 10 show a catheter tip 132 A having a lengthwise thermoelectric module 134 and a heat sink module 200 implemented as a finned heat sink 207. The finned heat sink 207 includes a base member 208 with a multitude of fins 209. The finned heat sink 207 has a heat exchange area Ah where Ah = 2 x [NF x B + (NF-1) x S ] x L wherein NF is the number of fins, B is fin height, S is the spacing between fins and L is fin length.

Figures 11 and 12 show a catheter tip 132B with a widthwise thermoelectric module 134 and a heat sink module 200 also implemented as a coil heat sink 202. The coil heat sink 202 includes a coil 211 with two or more windings 212 mounted on the thermoelectric module hot side 136 in a thermal conductive bonding process such as welding. The coil 211 has an internal tube diameter of about 0.5 mm and an overall tube length of between about 40 mm to -60 mm such that its heat exchange area equals is about 90 mm².

Figures 13 and 14 show a catheter tip 132B with a widthwise thermoelectric module 134 and a heat sink module 200 implemented as a heat sink stack 213 of horizontal wire mesh members 214. Figures 13 and 14 show wire mesh members 214 in the form of wire mesh discs typically have an about 2 mm to 3 mm diameter and are formed from 0.11 mm thick metal. Heat sink stacks 213 can include equally upright wire mesh members. Wire mesh members can be formed in different shapes including inter alia rectangle, oval, and the like.

The wire mesh discs 214 typically have a mesh density of 100 wires per inch. For example, part number 100xl00C0022W48T made from copper commercially available from TWP, Inc., Berkeley CA 94710, USA. The heat sink stack 213 includes about 30 discs with an overall height of 3 mm to 3.5 mm. The heat sink stack 213 has a heat exchange area determined by N x AS when N is the number of disks and AS is the overall surface area of each wire mesh disc. Jet Impingement Implementations of Heat Exchange Arrangement

Jet impingement modules are based on impingement of one or more coolant fluid jets on an impingement surface for affording more efficient heat transfer than a heat sink module such that jet impingement modules are capable of freezing a catheter tip to colder cryo-temperatures than a heat sink module.

Figures 15, 16A and 16B show an open irrigation cryocatheter 130A having a catheter tip 132A with a widthwise thermoelectric module 134 and a jet impingement module 300 constituting the heat exchange arrangement 138 for forming an ice ball IB. The jet impingement module 300 includes a housing 301 sealed on the thermoelectric module 134 to form a heat exchange cavity 302. The housing 301 can be formed from non-thermally conductive material such as bio-plastics which is considerably less expensive than biocompatible materials such as platinum iridium, and the like. The housing 301 may be manufactured by suitable low cost processes for medical parts, for example, micro-injection molding. Moreover, because the housing 301 can be made from plastics with a low thermal expansion co-efficient compatible with the ceramic plates of thermoelectric modules to reduce thermal stresses during operation.

The jet impingement module 300 includes a single jet nozzle 303 for impinging a coolant fluid jet preferably directly onto the thermoelectric module hot side 136 constituting the impingement surface at an impingement site 304. The jet nozzle 303 has an internal jet nozzle diameter D and an impingement height H from the thermoelectric module hot side 136. Jet nozzles typically have an internal jet nozzle diameter D in the range of 0.3 mm to about 0.7 mm and an impingement height H in the range of from about 0.3 mm to about 0.7 mm.

Figure 16B shows each a coolant fluid jet causes heat transfer over an imaginary circular impingement zone 306 having an impingement zone radius R although the shape of an actual impingement zone 306 is bound by a housing 301. But each coolant fluid jet has an effective imaginary circular impingement zone 307 having a maximum impingement zone radius twice the size of an internal jet nozzle diameter D beyond which heat transfer is considerably reduced in the annular area between the impingement zones 306 and 307. Accordingly, it is thermodynamically worthwhile to add jet nozzles if R > 3D to preferably eliminate any annular area beyond the impingement zone 307. Thus, jet impingement modules 300 can include a single jet nozzle 303 or an m x n array of jet nozzles 303 where at least one of m and n > 1 depending on the size and dimensions of a thermoelectric module hot side 136.

The jet impingement module 300 has a heat transfer coefficient h which depends on two ratios as follows:

First, a ratio H/D which is preferably in the range of from about 0.5 to about 1.5 when the velocity of the coolant fluid jet exiting from the jet nozzle 303 is in the range of from about 1.5 m/sec to about 7.0 m/sec for maximal volumetric flow of 35 cc/min and a specific nozzle diameter.

And second, the ratio R/D preferably in the range of 2 < R/D < 4 because jet nozzles too close to each other complicate manufacturing and can cause their respective coolant fluid jets to interfere with one another.

The aforesaid jet impingement papers set out that a jet impingement module 300 has a heat transfer coefficient h according to equation:

Nu x k

(4) h =— where Nu is a so-called Nusselt number, k is the thermal conduction coefficient of jet impingement fluid and D is the internal jet nozzle diameter in meters. For example, 0.9% NaCl saline has a thermal conduction coefficient k ~ 0.58 w/m°C.

The aforesaid jet impingement papers also set out that a Nusselt number Nu is calculated according to equation (5):

(5) Nu = 0.75 x Re¹/² x Pr¹/³

where Re is a Reynold number and Pr is a Prantel number.

Jet impingement modules 300 in accordance with the present invention have a Reynold number in the range of from about 400 to about 1400, a Prantel number in the range of from about 9 to about 11 and a heat transfer coefficient h in the range of from about 35,000 w/m^2oC to about 55,000 w/m^2oC which is between three and six times larger than a heat sink module's heat transfer coefficient.

In contrast to the heat sink module 200, the jet impingement module 300 has a single temperature difference between the hot side temperature Thot and the coolant fluid, namely, the convection temperature difference Δΐΐ such that Thot = Tin + Δΐΐ . The convection temperature drop Δΐΐ is calculated as per equation (3) where the heat exchange area A equals the hot side footprint area.

Figures 17 and 18 show an open irrigation catheter tip 132 A including a jet impingement module 311 having a 1 x 3 array 312 of jet nozzles 313 for heat transfer from the same TEC Microsystems GmbH part number 1MD03- 036-4 thermoelectric module 314 as Figure 5's heat sink module 200. Each jet nozzle 313 has an internal jet nozzle diameter D = 0.40 mm and an impingement height H = 0.40 mm such that each jet nozzle 313 has a ratio D/H = 1 within the range of 0.5 < D/H< 1.5. The TEC Microsystems GmbH part number 1MD03-036-4 has a 2.8 mm width, a 6.6 mm length and a near 20 mm hot side footprint area.

The jet impingement module 311 requires three jet nozzles 313 to effectively conduct heat transfer along the length of thermoelectric module 314 as now explained with reference to the following calculations:

The jet impingement module 311 has three equi-distanced spaced jet nozzles 313 along its length such that each impingement zone radius R = 1.15, adjacent jet nozzles 313 are spaced 2.3 mm apart and the two end jet nozzles 313 are each spaced 1.15 mm from the opposite ends of the thermoelectric module 314. Thus, the ratio R/D would be 1.15 / 0.40 = 2.75 which is in the range of the optimal value of R/D and therefore acceptable.

The jet impingement module 311 can employ requires a single jet nozzle 313 to effectively conduct heat transfer along the width of thermoelectric module 314 as now explained in the following second calculation: The jet impingement module 311 has a single central jet nozzle 313 along its width such that its impingement zone radius R = 2.8 mm / 2 = 1.4 mm and the ratio R/D is 1.4 / 0.40 = 3.5 which is in the acceptable R/D range.

In the case of the jet impingement module 311, the Reynold number has a 410 value and the Prantel number has a l l value such that according to equation (5) Nu = 34 and according to equation (4) its heat transfer coefficient h= 34 x 0.58 / 0.4 x 10^"3=49000 w/m^2oC. As already defined, in jet impingement cooling Ah=Af and therefore according to equation (3), the jet impingement module 314 has a convection temperature difference Atl :

Q 7.5

Atl = , , = = 8°C

h x Ah 49000 X 20 X 10-⁶

The thermoelectric module hot side 136 has a hot side temperature Thot

= Tin + Atl = 5°C + 8°C = 13°C such that the thermoelectric module cold side 137 has a cold side temperature Tcold = Thot - 35°C = 13°C - 35°C =-22°C which is in the intended cryo-temperature range.

Figure 19 shows a circulation catheter tip 132B having a widthwise thermoelectric module 134 and a jet impingement module 300 with a single jet nozzle 303.

Cryocatheter Designs

Figures 20 to 27 show different features of cryocatheters in accordance with the present invention. The features are not mutually exclusive and cryocatheters can include combinations of one or more features. Moreover, the cryocatheters can include lengthwise or widthwise thermoelectric modules. Also, the cryocatheters can include heat sink modules or jet impingement modules.

Figure 20 is a longitudinal cross section of a circulation cryocatheter

130B for freezing a trailing section of a catheter tip 132B for forming an ice ball IB deployed trailing its leading catheter dome 133. The cryocatheter 130B includes a metal plate 160 in high conductive thermal contact with the thermoelectric module cold side 137. The metal plate 160 has a peripheral cylindrical surface 160A for freezing human tissue in contact therewith. The length of the catheter tip 132B extending from the metal plate 160 to the catheter dome 133 is preferably made from non-highly heat conductive materials such as polyamide. The catheter dome 133 may be made from metal for clinical applications requiring electrical conductivity.

Figure 21 is a longitudinal cross section of an open irrigation cryocatheter 130A with a catheter tip 132A including a lengthwise thermoelectric module 134 A and a widthwise thermoelectric module 134B and a heat exchange arrangement 138 for simultaneous heat transfer from both the thermoelectric modules 134 A and 134B. The thermoelectric modules 134 A and 134B can be considered to have a single hot side with a hot side footprint area equal to the sum of their individual hot side footprint areas.

Figures 22 and 23 show an open irrigation cryocatheter system 100 A including an open irrigation cryocatheter 130A and a RF ablator 114 for RF ablation at a therapy site the RF ablator 114 is connected to the dome 133 with conductor wire 150.

Figures 24 and 25 show an open irrigation cryocatheter system 100 A including an open irrigation cryocatheter 130A having a catheter tip 132A with an acquisition device 161 for acquiring patient information at the therapy site. Exemplary acquisition devices 161 include inter alia a sensor for sensing a physiological parameter, a camera, and the like. Exemplary sensors include inter alia an ultrasound sensor, a pressure gauge, and the like. The controller 103 is connected to the acquisition device 161 by a signal wire 162.

Figures 26 and 27 show a circulation cryocatheter system 100B including vacant lumens 163 for introduction of a surgical tool at a therapy site. Such surgical tools could be, for example, a biopsy needle 165 connected to an external suction pump.

While the invention has been described with respect to a limited number of embodiments, it will be appreciated that many variations, modifications, and other applications of the invention can be made within the scope of the appended claims.

Claims

CLAIMS:

1. A cryocatheter for use in a cryocatheter system including an external coolant fluid source for delivering a downstream coolant fluid flow, the cryocatheter comprising:

(a) an elongated flexible catheter member having a short rigid catheter tip for introduction to a therapy site;

(b) at least one thermoelectric module having a thermoelectric module hot side and a thermoelectric module cold side, said thermoelectric module cold side being in highly conductive thermal contact with a highly thermal conductive exterior surface of said catheter tip;

(c) a coolant fluid supply line in flow connection with the external coolant fluid source for delivering the downstream coolant fluid flow to said catheter tip; and

(d) a heat exchange arrangement at said catheter tip for receiving an incoming downstream coolant fluid flow from said coolant fluid supply line for cooling said thermoelectric module hot side and delivering an outgoing coolant fluid flow,

said heat exchange arrangement having a heat transfer coefficient h and a heat exchange area Ah and capable of developing a convection temperature difference Atl between a coolant fluid flow passing therethrough and said thermoelectric module hot side in accordance with the relationship

where Q is a total thermal energy required to undergo heat transfer from said thermoelectric module hot side to said coolant fluid flow and Atl is in the range of from about 4°C to about 10°C such that said heat exchange arrangement is capable of freezing said exterior surface of said catheter tip to a cryo-temperature from between about -15°C to about -30°C for freezing human tissue at the therapy site.

2. The cryocatheter according to claim 1 wherein said heat exchange arrangement is constituted by a heat sink module in thermal contact with said thermoelectric module hot side, said heat sink module having a heat transfer coefficient h in range of from about 5000 w/m^2oC to about 10,000 w/m^2oC, and said thermoelectric module hot side having a hot side footprint area Af and said heat sink module having a heat exchange area Ah where at least four times greater than said hot side footprint area Af .

3. The cryocatheter according to claim 2 wherein said heat exchange arrangement includes a finned heat sink.

4. The cryocatheter according to claim 2 wherein said heat exchange arrangement includes a coil heat sink.

5. The cryocatheter according to claim 2 wherein said heat exchange arrangement includes a heat sink stack of wire mesh members.

6. The cryocatheter according to claim 2 wherein said heat exchange arrangement includes a porous heat sink.

7. The cryocatheter according to claim 1 wherein said heat exchange arrangement includes a jet impingement module including at least one jet nozzle for impinging a coolant fluid jet on an impingement surface in thermal contact with said thermoelectric module hot side for heat transfer therefrom, wherein at least one jet nozzle of said at least one jet nozzle has an internal jet nozzle diameter D and an impingement height H from said impingement surface for defining a ratio D/H in the range of from about 0.5 to about 1.5.

8. A cryocatheter according to any one of claims 1 to 7 for freezing a trailing section of said catheter tip instead of its leading catheter dome.

9. A cryocatheter according to any one of claim 1 to 8 wherein said at least one thermoelectric module includes a lengthwise thermoelectric module and a widthwise thermoelectric module.

10. A cryocatheter according to any one of claims 1 to 9 wherein said catheter tip includes a RF electrode for ablation purposes.

11. A cryocatheter according to any one of claims 1 to 9 wherein said catheter tip includes an acquisition device for acquiring patient information at the therapy site.

12. A cryocatheter according to any one of claims 1 to 9 wherein said catheter member includes at least one vacant lumen for introduction of a surgical tool to the therapy site.

13. A cryocatheter system for use with a cryocatheter according to any one of claims 1 to 12.