Surgery – Instruments – Cyrogenic application
Reexamination Certificate
1999-07-19
2001-08-07
Peffley, Michael (Department: 3739)
Surgery
Instruments
Cyrogenic application
C606S024000
Reexamination Certificate
active
06270493
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
Not applicable.
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH
Not applicable.
FIELD OF THE INVENTION
The present application relates to cryocatheters and wands, i.e. to catheters and wands which are used to treat tissue by cooling contact. Such implements, henceforth generically referred to herein as “cryocatheters ” or simply “catheters” have an elongated body through which a cooling fluid circulates to a tip portion which is adapted to contact and cool tissue. In general, cooling catheters may be used to lower the temperature of tissue, such as cardiac wall tissue, to an extent such that signal generation or conduction ceases and allows one to map or confirm that the catheter is positioned at a particular lesion or arrhythmia conduction site. More recently, cryocatheters have been configured for ablation treatment, to cool the tissue to a much lower level at which freezing destroys the viability of the tissue, and, in the case of cardiac tissue, permanently removes it as a signal generating or signal conducting locus. Such devices are also useful for tissue destruction in other contexts, such as the ablation of tumorous, diseased, precancerous or congenitally abnormal tissue.
Cryocatheters may be adapted for endovascular insertion, or for insertion along relatively confined pathways, for example through a body lumen, or through a small incision to and around intervening organs, to reach an intended ablation site. As such, they are characterized by a relatively elongated body through which the cooling fluid must circulate, and a tip or distal end portion where the cooling is to be applied. The requirement that the coolant be localized in its activity poses stringent constraints on a working device. For example when the catheter contact must chill tissue to below freezing, the coolant itself must attain a substantially lower temperature. Furthermore the rate of cooling is limited by the ability to supply coolant and circulate it through the active contact region, and the efficacy of the contact region itself is further limited by geometry and physical properties that affect its ability to conduct heat into the tissue. The rate of cooling may change depending upon the effectiveness of thermal contact, e.g. upon the contact area and contact pressure between the catheter and the tissue, and may be further influenced by ice accumulations or other artifacts or changes due to the freezing process itself. Moreover, it is a matter of some concern that proximal, adjacent or unintended tissue sites should not be exposed to harmful cryogenic conditions. These somewhat conflicting requirements make the actual implementation of an effective cryocatheter complex.
One approach has been to provide a phase change coolant which is pumped as a liquid to the tip of the catheter and undergoes its phase change in a small chamber located at the tip. The wall of the chamber contacts adjacent tissue directly to effect the cooling or ablation treatment. Such a device can treat or achieve a relatively high rate of heat energy transfer. Moreover, by employing a phase change refrigerant which may be injected at ambient temperature along the body of the catheter and undergo expansion at the tip, the cooling effect may be restricted to the localized treatment region surrounding the tip portion of the device. The dimensions of catheter construction, particularly for an endovascular catheter, require that the phase change coolant be released from a nozzle or tube opening at a relatively high pressure, into a relatively small distal chamber of the catheter. After the fluid expands in the distal chamber and cools the walls, it is returned through the body of the catheter to a coolant collection system, preferably in the form of a recirculation loop.
However, the high pressure release of coolant in a relatively small chamber at the tip of the catheter and its recirculation back via a return conduit from the tip region involve relatively turbulent fluid flow conditions, so that the precise rate of heat transfer that occurs may be subject to rather wide variations. For cardiac ablation, the injection is controlled from a low rate of delivery for cold mapping or treatment site confirmation, to a higher rate of delivery used for tissue ablation at the mapped or confirmed sites. For other applications such as thermal angioplasty, proper treatment may require precise control of the cooling in other temperature ranges. The wide range of required energy transfer rates as well as differences in size, shape or construction of different catheters increases the difficulty of achieving uniform or repeatable catheter cooling rates. This in turn has resulted in instruments that operate in restricted temperature ranges and with wide variations in their cooling characteristics.
Accordingly, there remains a need for a cryocatheter tip construction that more effectively controls the flow of thermal transfer fluid.
There is also a need for a cryocatheter construction that ablates tissue more effectively, or in shorter times.
There is further a need for a cryocatheter construction, which is controllable to provide uniform and repeatable cooling over a range of thermal energy transfer rates.
SUMMARY OF THE INVENTION
One or more of the foregoing desirable objects are achieved in accordance with the present invention by a cryocatheter for treatment of tissue wherein a coolant line communicates with a cryochamber having a coolant receiving interior and a thermally conductive wall for contacting and conductively treating tissue. A return line returns spent coolant, and a body in the chamber controls or conditions the coolant flow. This may be a partition in the cryochamber that channels or directs the fluid as it enters via the coolant line to enhance the cooling efficacy. The partition may be configured to reduce fluctuations and produce a regular flow such that cooling regimens are dependably achieved without substantial variation when directly controlling only one or a few variables, such as coolant injection pressure, cycle time or the like. In various embodiments, the partition may extend axially to define an elongated sub-chamber of the tip interior that is preferentially cooled, and/or it may isolate one side of the tip to define an inert or uncooled side of the cryochamber. The partition may also be configured to define a flow or expansion sub-chamber that extends along a segmented length around a partial circumference of the catheter tip, or may be configured to channel the coolant from a central region outwardly against the peripheral wall of the cryochamber. The body may also be a shaped flow conditioner that controls the flow path and flow characteristics to the return port. Preferably, the return line is a vacuum return line. In another embodiment, the catheter includes a fluid warming provision for warming the catheter tip to heat the treated tissue. The catheter then operates to remove and to supply heat energy so as to effect a freeze/thaw or a cool/warm regimen for tissue ablation or mapping. This heating may be implemented by a heater in thermal contact with a fluid supply line, which may be either the coolant supply line or a separate line that carries a separate warming fluid. In one embodiment of this aspect, a switching valve connects a warming fluid supply passage such that the passage functions as an additional return line during application of coolant to the cryochamber, and the valve switches its connection at the start of a warming cycle to supply warming fluid in a reverse direction of flow through that line to the tip after the tissue has been cooled. The catheter may further include sensors for sensing contact orientation of the cooling tip against adjacent tissue. Such sensors may include a first impedance sensing electrode on a first side of the cryochamber, and a second impedance sensing electrode on a second side of the cryochamber, which operate in conjunction with one or more body surface electrodes to define a determinable sensing path or otherwise indicate
Carroll Sean
Klein George
Lalonde Jean-Pierre
Lueckge Claudia
Martin Robert
Cryocath Technologies Inc.
Gunster, Yoakley & Stewart, P.A.
Peffley Michael
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