Patent Application
20180085027
This invention relates to deflectable medical catheters. More particularly, this invention is related to medical injection catheters.
Traditionally, deflectable medical catheters have been used in interventional procedures to deliver therapies, such as RF energy, or implantables, such as leads or valves, into the body. Medical catheters have also been used for imaging and diagnostic purposes. Additionally, medical catheters, such as those with balloons, have been used to modify a patient's anatomy, such as during a structural heart application. An emerging catheter-based therapy is the delivery of liquids into tissue. An example of such a therapy is chemo-ablation, which is the destruction of cells via delivery of ethanol or a similar cytotoxic liquid into tissue. Chemo-ablation could be used to replace RF ablation for arrhythmia modification or for targeted chemotherapy of tumors. Another example is stem cell therapy, in which a solution containing stem cells and supporting liquids is delivered into the tissue to replace damaged cells. The aforementioned therapies require a precise method for delivering the solutions into the target tissue. This precision is predicated upon detailed tissue visualization and accurate navigation of the catheter tip to the target tissue location.
MRI has achieved prominence as a diagnostic imaging modality, and increasingly as an interventional imaging modality. The primary benefits of MRI over other imaging modalities, such as X-ray, include superior soft tissue imaging and avoiding patient exposure to ionizing radiation. The superior capability for imaging soft tissue using MRI has offered great clinical benefit with respect to diagnostic imaging. Similarly, interventional procedures, which have traditionally used X-ray imaging for guidance, stand to benefit greatly from soft tissue imaging only available with MRI. In addition, the significant patient exposure to ionizing radiation associated with traditional X-ray guided interventional procedures is eliminated with MRI guidance.
MRI uses three fields to image patient anatomy: a large static magnetic field, a time-varying magnetic gradient field, and a radiofrequency (RF) electromagnetic field. The static magnetic field and time-varying magnetic gradient field work in concert to establish both proton alignment with the static magnetic field and also spatially dependent proton spin frequencies (resonant frequencies) within the patient. The RF field, applied at the resonance frequencies, disturbs the initial alignment, such that when the protons relax back to their initial alignment, the RF emitted from the relaxation event may be detected and processed to create an image.
Each of the three fields associated with MRI presents safety risks to patients when a medical device is in close proximity to or in contact either externally or internally with patient tissue. One important safety risk is the heating that may result from an interaction between the RF field of the MRI scanner and the medical device (RF-induced heating), especially medical devices that have elongated conductive structures, such as braiding and pull-wires in catheters and sheaths.
The RF-induced heating safety risk associated with elongated metallic structures in the MRI environment results from a coupling between the RF field and the metallic structure. In this case several heating related conditions exist. One condition exists because the metallic structure electrically contacts tissue. RF currents induced in the metallic structure may be delivered into the tissue, resulting in a high current density in the tissue and associated Joule or Ohmic tissue heating. Also, RF induced currents in the metallic structure may result in increased local specific absorption of RF energy in nearby tissue, thus increasing the tissue's temperature. The foregoing phenomenon is referred to as dielectric heating. Dielectric heating may occur even if the metallic structure does not electrically contact tissue, such metallic braiding used in a deflectable sheath. In addition, RF induced currents in the metallic structure may cause Ohmic heating in the structure, itself, and the resultant heat may transfer to the patient. In such cases, it is important to attempt to both reduce the RF induced current present in the metallic structure and/or eliminate it all together by eliminating the use of metal braid and long metallic pull-wires.
The static field of the MRI will cause magnetically induced displacement torque on any device containing ferromagnetic materials and has the potential to cause unwanted device movement. It is important to construct the sheath and control handle from non-magnetic materials, to eliminate the risk of unwanted device movement.
When performing interventional procedures under MRI guidance, clinical grade image quality must be maintained. Conventional catheters and sheaths are not designed for the MRI and may cause image artifacts and/or distortion that significantly reduce image quality. Constructing the catheter from non-magnetic materials and eliminating all potentially resonant conductive structures allows the catheter to be used during active MR imaging without impacting image quality. Similarly, it is as important to ensure that the catheter control handle is also constructed from non-magnetic materials thereby eliminating potentially resonant conductive structures that may prevent the control handle being used during active MR imaging.
While there are many types of surgical instruments available, few are well-suited for use in an MRI environment. For example, deflectable (i.e., steerable) catheters and sheaths including multi-directional, bi-directional and uni-directional deflectable devices are known. However, many of these devices have ferromagnetic components that can result in undesired movement and a potential for patient injury, when placed in the strong magnetic field associated with MRI. The ferromagnetic components can also cause image distortions, thereby compromising the effectiveness of the procedure. Still further, such devices may include metallic components that may cause radiofrequency (RF) deposition in adjacent tissue and, in turn, tissue damage due to an extensive increase in temperature.
Conventional puncture and injection catheters have the same limitations. They either include ferromagnetic components that cause image distortion or include metallic components that cause RF deposition in tissue.
Moreover, it is difficult or impossible to track or visualize the location of the aforementioned devices in an MRI environment. In general, there are two types of device tracking useful for MRI guidance of interventional devices: active tracking and passive tracking. Active tracking is more robust and often preferable to passive tracking. However, active tracking is more difficult to implement in interventional devices and typically involves resonant RF coils that are attached to the device and directly connected to an MR receiver. These RF coils act as receive coils and allow for the determination of the three-dimensional coordinates of the coils within the scanner. To the inventors' knowledge neither active nor passive tracking techniques are presently utilized in conventional puncture/injection catheters.
Even with limited MRI compatible interventional devices currently available, a variety of MRI techniques are being developed as alternatives to X-ray imaging for guiding interventional procedures. For example, as a medical device is advanced through the patient's body during an interventional procedure, it is now possible to track its position so that the device can be visualized and delivered properly to a target site. Once delivered to the target site, the device and patient tissue can be monitored to improve therapy delivery. Thus, tracking the position of medical devices is useful in interventional procedures. Exemplary interventional procedures include, for example, cardiac electrophysiology procedures including diagnostic procedures for diagnosing arrhythmias and ablation procedures such as atrial fibrillation ablation, ventricular tachycardia ablation, atrial flutter ablation, Wolfe Parkinson White Syndrome ablation, AV node ablation, SVT ablations and the like. Tracking the position of medical devices using MRI is also useful in oncological procedures such as breast, liver and prostate tumor ablations; and urological procedures such as uterine fibroid and enlarged prostate ablations.
Thus, what is needed is an MR compatible puncture catheter so MR imaging can be utilized to ensure the precise delivery of therapeutic solutions into the target tissue. Such a device needs to be safe for use under MR guidance and allow for MR guidance and visualization.
In a first aspect of the MR compatible injection catheter in accordance with the invention, the injection catheter broadly includes an inner shaft; an outer shaft circumferentially surrounding said inner shaft; and a means for actively tracking the catheter in a patient within a MRI.
In another aspect of the invention the inner shaft slides within the outer shaft. The inner shaft is a long hollow tube that may consist of a braided catheter construction or a simple polymer extrusion. A puncture tip is operably connected to the distal tip of the inner shaft. The puncture tip includes a small, short cannula fixedly attached to the distal tip of the inner shaft. The cannula extends is a hollow tube that has a sharpened tip. The cannula is similar in shape to the distal tip section of a traditional transseptal needle. The connection between the puncture tip and the inner shaft is such that the lumen of the cannula is continuous with the lumen of the inner shaft. The inner diameter of the cannula lumen is preferably smaller than the inner diameter of the inner shaft lumen, but they could be the same size, or the lumen of the inner shaft could be smaller than the lumen of the cannula. The cannula could be constructed of metallic materials such as aluminum, inconel, nitinol, gold, etc. or of non-metallic materials such as PEEK, ceramic, zirconia, delrin, epoxy, etc. The puncture tip also contains a tracking coil and an O-ring. The distal end of the cannula terminates in a sharpened puncture tip.
The outer shaft is a long hollow tube that may consist of a braided catheter construction or a simple polymer extrusion. At the distal tip of the outer shaft is a tip support that includes a tracking coil. The tip support is preferably made of a non-metallic material such as PEEK, ceramic, zirconia, delrin, fiber reinforced epoxy, etc.
The inner shaft slides in relation to the outer shaft from a first retracted, proximal position to an extended distal position. In the retracted position, the puncture tip is completely housed within the tip support of the outer shaft. In the extended position, the cannula of the puncture tip is exposed and extends from the distal tip of the puncture catheter.
At the proximal end of the puncture catheter is a control handle. The control handle contains an advancement mechanism that allows the clinician to advance the inner shaft, which moves the puncture tip into the extended position. The advancement mechanism could be a sliding button, a control knob, etc. The lumen of the inner shaft terminates on the proximal end in the control handle. At this end there is an opening that allows for injection of solution into the inner shaft lumen. The opening could be a simple luer fitting, hemostasis valve, or stopcock assembly as is common in medical catheters.
As mentioned above, there are two tracking coils, one on the outer tip support and one on the puncture tip. These two tracking coils allow the puncture catheter to be navigated to the target tissue location under MR guidance. During the navigation step, the puncture tip is in the retracted position, which ensures that the sharp cannula tip doesn't damage any tissue. When the target tissue is reached, the clinician advances the inner shaft, which causes the puncture tip to move into the extended position and the cannula to penetrate the target tissue. Once the cannula is in the tissue, the clinician injects the therapy solution in the proximal opening of the inner shaft lumen. This solution then travels down the inner shaft lumen and enters the target tissue.
Each tracking coil is connected to a transmission line that travels the length of the respective shaft and exits at the control handle. In this aspect, the inner tracking coil moves with the inner shaft and the inner transmission line also moves. As a result, there may be some slack in the transmission line in the control handle to accommodate this movement. Alternatively, the termination of the tracking coil transmission line may move with the inner shaft eliminating the need for slack in the transmission line.
The advantage of locating one tracking coil on the puncture tip and the other tracking coil on the outer tip support is that the linear position of puncture tip in relation to the outer shaft can be precisely measured. This is because the space between the two tracking coils changes when the puncture tip goes from the retracted position to the extended position. With this configuration, the precise location of the tip of the cannula can be displayed to the clinician and the clinician can then use this information to control the depth of penetration of the cannula tip into the tissue. This would give the clinician a finer degree of control over the location and extent of solution delivery into the target tissue.
The purpose of the O-Ring on the puncture tip is to ensure that there is no fluid ingress between the puncture tip and the outer tip support, while still allowing the puncture tip to slide in relation to the outer tip.
Another advantage of this aspect is that because the cannula is fixedly attached to the puncture tip and will always be in a distal position in relation to the tracking coils, it can be fabricated out of metal, such as aluminum, inconel, nitinol, gold, etc. If any portion of the inner shaft that is located under either of the tracking coils were made out of metal, there is a potential for disruption or distortion of the tracking signal. Fabricating the cannula out of metal is advantageous because a metal tube can have a thinner wall than a nonmetallic tube and have superior strength and bending resistance. A thinner wall translates to a larger inner diameter for the cannula, which further translates to easier delivery of viscous solutions such as those that might be required for delivery of stem cells. Finally, it is easier to grind the tip of a metal tube into more complicated and sharper bevel shapes, which could reduce the puncture force required to penetrate the target tissue.
This aspect could be made deflectable by locating one or more pull wires in the wall of either or both of the inner shaft or the outer shaft. Utilizing a braided catheter shaft construction for one or both of the inner and outer shafts would mean that deflectable regions could be created by placing a lower durometer or softer material in the distal section of the shafts. The one or more pull wires would be connected in the control handle to a mechanism that would allow the clinician to deflect the distal tip of the puncture catheter. This mechanism could be a slide button, rotation knob, etc.
Those of skill in the art will recognize that alternative aspects achieving a similar purpose are possible. For instance, two tracking coils could be located in the outer shaft and both remain fixed. This would eliminate the need for an inner tip support and thus the inner shaft could be directly connected or bonded to the cannula section, which could still be constructed of a metallic material. The advantage of the design of this aspect is that it is simpler and easier to manufacture. The disadvantage is that the measurement of the distance between the two tracking coils remains fixed and therefore the extent of cannula extension, and the related amount of tissue penetration, cannot be measured by the tracking coil locations and displayed to the clinician.
In another aspect with fixed tracking coils on the outer shaft, the inner shaft could be made up of two coaxial tubes. Preferably, the outer tube would be made of a more rigid material such as ceramic or fiber-reinforced epoxy, while the inner tube would be made of a more flexible material, such as polyimide, PEBAX, grilamid, etc. A deflectable region within the rigid outer tube could be created by spiral-cutting, spine-cutting, etc. the tube in a short section near the distal tip of the tube. The inner tube is not spiral cut and therefore creates a continuous, solid inner lumen, which would contain the injected fluid. In other words, if the inner tube were not present, the fluid would escape through the channels in the outer tube created by the spiral cut. Those of skill in the art will appreciate that the tubes could be reversed such that the inner tube is the stiffer, spiral cut material, while the outer tube is the more flexible material. The advantage of constructing the inner shaft in this manner is that it simplifies the design by reducing the number of components in the inner shaft. It also allows for using stiffer materials to construct the inner shaft. Stiffer materials translate to more column strength which potentially translates to lower puncture force.
In a similar aspect, the inner shaft could be removable from the puncture catheter. To reintroduce the inner shaft, which could comprise an injection needle, into the injection catheter, the catheter could be outfitted with an inner lumen connected to a hemostasis valve located at the catheter handle.
In yet another aspect, inner shaft and puncture tip/cannula could remain in a fixed position in relation to the outer tip support and outer shaft. A sliding cannula cover piece could conceal the tip of the cannula while the catheter is being navigated to the target tissue. The sliding cannula cover piece could be biased in a position covering the tip of the cannula and a pull wire or some other mechanism could be used to expose the tip of the cannula for delivery of therapy.
The shortcomings of the present injection catheters are addressed by the device in accordance with the invention. The MR safety of the injection needle is provided by the materials from which the needle is constructed. The use on non-magnetic materials and limiting the use of conductive materials eliminates the risk associated with magnetic displacement force and RF heating associated with MR guided interventional procedures.
The MR safety of the MR tracking coils is provided by the construction of the tracking coil transmission line. One method for doing this is to incorporate transformers into the transmission line.
For puncture catheter with integrated electrodes, the MR safety of the electrodes is provided by the electrode wire assembly. Examples of electrode wire assemblies safe for use during MR imaging include those described in U.S. Pat. No. 8,588,934 and U.S. Pat. No. 8,588,938, which are hereby incorporated by reference in their entireties.
For a better understanding of the invention, and to show how the same may be carried into effect, reference will now be made, by way of example, to the accompanying drawings, in which:
Referring now to the figures,
The puncture catheter with a removable inner shaft includes a hemostasis valve and in the handle of the catheter that is connected to an inner lumen through which the inner shaft 401 can be inserted into the puncture catheter. The extent to which the sharpened tip 405 extends from the outer shaft 402 is controlled manually at the proximal end of the inner shaft 401 near the hemostasis valve where it enters the puncture catheter.
In reference to injection catheter 400,
Although inner shaft described in
The injection catheter described herein can be made safe from the risk of magnetic displacement force by use of non-magnetic materials. The risk of RF heating can be eliminated by limiting conductive materials to the puncture tip, RF safe electrode lines, and transmission lines with integrated transformers.
To facilitate electrophysiological measurements during an interventional procedure, the injection catheter can include one or more electrodes. To achieve RF safety of the electrodes, RF safe electrode lines such as those described in U.S. Pat. No. 8,588,934 and U.S. Pat. No. 8,588,938 may be used to connect the electrodes to a connector in the catheter handle.
In all of the various aspects of the injection catheter disclosed herein, two tracking coils are shown; however, those of skill in the art will appreciate that the invention is not necessarily limited to two tracking coils. Rather injection catheters utilizing only one tracking coil are also intended to fall within the scope of the invention.
Although the present invention has been described with reference to various aspects of the invention, those of ordinary skill in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/US16/29499 | 4/27/2016 | WO | 00 |
| Number | Date | Country | |
|---|---|---|---|
| 62153829 | Apr 2015 | US | |
| 62232902 | Sep 2015 | US |
