US 20080314394 A9
Devices and methods for creating a series of percutaneous myocardial revascularization (PMR) channels in the heart. One method includes forming a pattern of channels in the myocardium leading from healthy tissue to hibernating tissue. Suitable channel patterns include lines and arrays. One method includes anchoring a radiopaque marker to a position in the ventricle wall, then using fluoroscopy repeatedly to guide positioning of a cutting tip in the formation of multiple channels. Another method uses radiopaque material injected into each channel formed, as a marker. Yet another method utilizes an anchorable, rotatable cutting probe for channel formation about an anchor member, where the cutting probe can vary in radial distance from the anchor. Still another method utilizes a multiple wire radio frequency burning probe, for formation of multiple channels simultaneously. Still another method utilizes liquid nitrogen to cause localized tissue death.
1. A method for increasing blood perfusion to heart muscle wall by forming a plurality of channels in the myocardium comprising the steps:
marking a first location within said heart muscle wall by securing a radiopaque marker to said heart muscle wall;
positioning a radiopaque, channel forming tip at a second location with a chamber of said heart;
viewing said first and second locations fluoroscopically;
adjusting said second location relative to said first position; and
forming said channel in said myocardium at said second location using said treatment tip.
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8. A method for increasing blood availability to heart muscle myocardium having healthy, hibernating, and infarcted dead tissue comprising:
providing a treatment tip having the capability of forming a channel in said myocardium from within said heart;
selecting a first location in said healthy tissue;
selecting a second location in said hibernating tissue; and
forming a plurality of channels utilizing said treatment tip in said myocardium in a pattern extending from said first location to said second location.
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17. A method for increasing blood availability to heart muscle by forming a plurality of channels in the myocardium comprising the steps:
providing a myocardial channel forming device having an anchoring member, at least one treatment member, and means for rotating said treatment member about said anchoring member, wherein said treatment member includes means for forming a channel in said myocardium;
attaching said anchoring member to a first position in said myocardium;
rotating said treatment member to a desired rotational angle relative to said anchor; and
forming a channel in said myocardium.
18. A method for increasing blood availability to heart muscle as recited in
said channel forming device has a longitudinal axis extending through said anchoring member,
said treatment member has a distal tip displaced a radial distance from said longitudinal axis,
said channel forming device includes means for controlling said treatment member distal tip radial distance,
further comprising setting said treatment member radial distance.
19. A method for increasing blood availability to heart muscle as recited in
20. A method for increasing blood availability to heart muscle as recited in
21. A method for increasing blood availability to heart muscle as recited in
22. A device for creating a plurality of myocardial channels comprising:
an elongate tube having a distal port;
an anchoring member slidably disposed within said elongate tube, said anchoring member having a pointed distal end extending from said elongate tube distal port, said pointed distal end adapted to penetrate into said myocardium;
a treatment member slidably disposed within said elongate tube, said treatment member having an arcuate distal region having a cutting tip thereon, said arcuate distal region being biased to increase in radius when not constrained within said tube, such that said distally extending said elongate tube causes said treatment member distal end to decrease in radial distance from said anchor member and proximally retracting said elongate tube causes said treatment member distal end to increase in radial distance from said anchor member.
23. A method as recited in
The present application is a Continuation of application Ser. No. 10/231,033, filed Aug. 30, 2002, which is a Continuation of application Ser. No. 09/536,068, filed on Mar. 24, 2000, now U.S. Pat. No. 6,491,689 B1, and claims the benefit of U.S. Provisional Patent Application No. 60/064,169, filed Nov. 4, 1997.
The present application is related to devices and methods for promoting blood circulation to the heart muscle. Specifically, the present invention is related to percutaneous myocardial revascularization (PMR) devices and methods for forming multiple channels in the myocardium.
A number of techniques are available for treating cardiovascular disease such as cardiovascular by-pass surgery, coronary angioplasty, laser angioplasty and atherectomy. These techniques are generally applied to by-pass or open lesions in coronary vessels to restore and increase blood flow to the heart muscle. In some patients, the number of lesions are so great, or the location so remote in the patient vasculature that restoring blood flow to the heart muscle is difficult. Percutaneous myocardial revascularization (PMR) has been developed as an alternative to these techniques which are directed at by-passing or removing lesions.
Heart muscle may be classified as healthy, hibernating and “dead”. Dead tissue is not dead but is scarred, not contracting, and no longer capable of contracting even if it were supplied adequately with blood. Hibernating tissue is not contracting muscle tissue but is capable of contracting, should it be adequately re-supplied with blood. PMR is performed by boring channels directly into the myocardium of the heart.
PMR was inspired in part by observations that reptilian hearts muscle is supplied primarily by blood perfusing directly from within heart chambers to the heart muscle. This contrasts with the human heart, which is supplied by coronary vessels receiving blood from the aorta. Positive results have been demonstrated in some human patients receiving PMR treatments. These results are believed to be caused in part by blood flowing from within a heart chamber through patent channels formed by PMR to the myocardial tissue. Suitable PMR channels have been burned by laser, cut by mechanical means, and burned by radio frequency current devices. Increased blood flow to the myocardium is also believed to be caused in part by the healing response to wound formation. Specifically, the formation of new blood vessels is believed to occur in response to the newly created wound.
What remains to be provided are improved methods and devices for increasing blood perfusion to the myocardial tissue. What remains to be provided are methods and devices for increasing blood flow to myocardial tissue through controlled formation of channel patterns in the myocardium.
The present invention includes devices and methods for creation of multiple holes in the myocardium of a human heart for percutaneous myocardial revascularization. A pattern of holes is optimally created extending from healthy tissue to hibernating tissue, thereby increasing the supply of blood to hibernating heart muscle tissue. Creating a controlled pattern of channels rather than simply a plurality of channels of unknown location can be accomplished using various methods and devices. Holes can be considered the space left after a volumetric removal of material from the heart wall. Channels have a depth greater than their width and craters have a width greater than their depth.
One method includes marking a first location in the heart muscle wall with a radiopaque marker, then positioning a radiopaque cutting tip relative to the radiopaque marker using fluoroscopy and cutting channels in the myocardium where appropriate. Suitable markers can be secured to the endocardium mechanically with barbs or pigtails or injected into the myocardium. Suitable channel patterns include lines, arrays, and circular clusters of channels.
Another method includes injecting radiopaque material into the newly formed channels, thereby marking the positions of the channels already formed. The radiopaque material should be held in place with polymeric adhesives for the duration of the treatment. The channels formed can be viewed under fluoroscopy using this method. The marker can remain throughout the procedure or only long enough to record the position for mapping.
Yet another method can be accomplished by providing a myocardial channel forming device having an anchoring member, a treatment member with a cutting tip, means for rotating the cutting member about the anchoring member, and means for controlling the radial displacement of the cutting tip from the anchoring member. The anchoring member can be implanted in a heart chamber wall using a pigtail, and the radial and rotational displacement of the cutting tip controlled to sequentially form a circular cluster of channels about the anchoring member. The circular cluster preferably includes both healthy and hibernating tissue areas, which can be mapped using conventional techniques. A variant of this technique utilizes a device having a spline and corresponding star shaft, which restricts the number of possible rotational angles and provide predictable arc rotations around the spline for the treatment member about the anchoring shaft.
Still another method utilizes a bundle of fibers within a sheath as the cutting device. Preferred fibers are formed of Nitinol wire and carry radio frequency current to effect burning channels in the myocardium. Optical fibers carrying laser light for burning are used in another embodiment. The splay of fibers out of the distal end of the sheath can be controlled by controlling the bias of the fibers. The bias of the fibers can be controlled by utilizing shape memory materials, such as Nitinol wire. The splay of fibers can also be controlled by controlling the length of fiber exposed at the distal end, by controlling the retraction of the sheath over the fibers.
A variant device utilizes a magnetically responsive anchoring member, which can be pulled against the heart wall by an external magnetic force. The heart wall can have movement lessened during this procedure and other procedures generally, by inserting a catheter having a magnetically responsive distal region into a coronary artery. Force can be brought to bear upon the heart wall region having the catheter disposed within by applying a magnetic force on the catheter. The applied force can exert a pulling force on the catheter, reducing movement of the beating heart wall in that region.
Another device includes an outer positioning tube having several side channels in the distal region and means for securing the distal region against movement within the heart chamber. One securing means includes a suction orifice near the distal end supplied with vacuum by a vacuum lumen extending the length of the outer tube. Another securing means includes a magnetically responsive portion of the outer tube. The suction orifice can be secured to the heart chamber wall by applying vacuum and the magnetically responsive portion can be forced into the chamber wall by applying an external magnet field. The inner tube can contain an intermediate guide tube and the guide tube can contain an inner PMR cutting wire with a arcuate biased distal region. As the arcuate distal region is moved through the outer tube distal region and over the side channels, the PMR wire distal region can extend through a side channel and to the heart chamber wall. The PMR wire can be moved past undesired side holes by rotating the wire such that the arcuate wire region is oriented away from the side holes.
Another device includes a tube-in-a-tube configuration, having an outer tube disposed about an intermediate tube disposed about an inner PMR cutting probe. The inner PMR probe can be preformed to have a distal region arcuate or angled bias, bent away from the longitudinal axis of the probe. The PMR probe distal region can extend through a side channel in the distal region of the intermediate tube and is slidable within the intermediate tube, thereby exposing a varying length of distal PMR probe outside of the intermediate tube. The intermediate tube is slidably disposed within the outer tube which has an elongate slot to allow passage of the PMR probe therethrough. Thus, the radial extent or length of extending PMR probe can be varied by sliding the PMR probe within the intermediate and outer tubes, the longitudinal position of the PMR probe can be varied by sliding the intermediate tube within the outer tube, and the rotational position can be varied by rotating the outer tube from the proximal end. Varying the amount of a preformed, bent PMR probe extending from the intermediate tube can also change the longitudinal position of the PMR probe distal end.
Another device includes an elongate rod having a distal region secured to an outer collar, such that the outer collar can be pushed and pulled. The outer collar is slidably disposed over an intermediate tube. An inner PMR cutting probe is slidably disposed within the intermediate tube. The inner PMR probe and intermediate tube together have a distal region arcuate or bent bias or preform, such that distally advancing the outer collar over the intermediate tube straightens out the intermediate tube and proximally retracting the outer collar allows the arcuate bias or bend to be exhibited in the distal region shape of PMR probe and intermediate tube. The preform can exist in the PMR probe, intermediate tube, or both. The device includes means for anchoring the device to the ventricle wall. Circles or arcs of myocardial channels can be formed by rotating the outer tube, extending the inner PMR probe, and varying the amount of arc to form distal of the outer collar.
Yet another device includes an anchoring member and a positionable cryanoblative treatment tube. The treatment tube can be formed of metal and be either closed or open ended. In use, the device is anchored within a heart chamber and a cryogenic substance such a liquid nitrogen delivered through the tube and to the tube distal end. The liquid nitrogen can cause localized tissue death, bringing about the desired healing response. Still another device includes a plurality of splayed, cryanoblative tubes within a sheath. The tubes can be supplied with liquid nitrogen, which can be delivered through the tube lumens to the tube distal ends so as to cause localized myocardial tissue death at multiple sites substantially simultaneously.
In yet another embodiment, a catheter assembly is provided including a guide wire having a proximal end and a distal end. An expandable member, which may be a wire loop, is disposed at the distal end of the guide wire. The expandable member is moveable between a first position and a second position. In the first position, the member is collapsed to move through a lumen of a guide catheter. In a second position, the expandable member has a transverse diameter, with respect to the length of the guide wire, greater than the transverse diameter of the guide catheter lumen. An elongate catheter having a proximal end and a distal end is disposed on the guide wire. A therapeutic device is connected to the distal end of the catheter. The therapeutic device can be a needle, hypotube, electrode or abrasive burr to form holes or craters in the myocardium of the patient's heart.
Referring now to
The use of PMR device 20 may now be discussed, with reference to
In addition to cutting a series of channels radially outward from anchoring shaft 26, cutting tip 32 can also describe an arc about treatment shaft lumen 31, best visualized with reference to
Outer shaft 22 can also be rotated relative to anchoring shaft 26, thereby enabling the cutting of a regular series of channels in a circle about anchoring shaft 26. In a preferred embodiment, an intermediate star shaft such as shaft 24 is disposed between anchoring shaft 26 and outer shaft 22. Star shaft 24 can serve to restrict the rotational positions possible for outer shaft 22 relative to inner, anchoring shaft 26. Outer shaft 22 having internal splines, is not freely rotatable about the vertices of start shaft 24. In order for outer shaft 22 and carried treatment shaft 30, to be rotated about anchor shaft 26, star shaft 24 can be star shaped only is a limited distal region, and outer shaft 22 only splined in a limited distal region. In a preferred embodiment, star shaft 24 and outer shaft 22, at a location proximal of the cross section of
Cutting tip 32 can form a substantially regular pattern of channels. Cutting tip 32 preferably is formed of a wire such as Nitinol or elgiloy or stainless steel, and is capable of delivering the radio frequency current used for cutting channels in the myocardium. A suitable device for radio frequency cutting is described in co-pending U.S. patent application Ser. No. 08/810,830, filed Mar. 6, 1997, entitled RADIOFREQUENCY TRANSMYOCARDIAL REVASCULARIZATION APPARATUS AND METHOD. By restricting the movement of cutting tip 32 to movements relative to anchor tip 28, a more regular pattern of channels can be formed, even with limited fluoroscopic feedback, relative to the pattern formed by a cutting tip operating independent of the anchoring tip.
Referring now to
In use, probe 50 can be positioned near the ventricle wall region to be revascularized, and RF current delivered through distal cutting tips 56. The resulting myocardial channels can be formed substantially at the same time, and a similar pattern delivered to an adjacent ventricular wall area soon thereafter.
In another embodiment of the invention, not requiring illustration, a radiopaque marker can be delivered and secured to a position in the ventricular wall. Suitable radiopaque materials include barium, bismuth, tungsten and platinum. Markers believed suitable include metal markers having barbs or pigtails to securely engage the ventricle wall. Other markers, such as radiopaque gels injected into the ventricular wall, are suitable provided they stay in place for the length of the procedure. Such markers are preferably injected from within the ventricle utilizing a catheter. A preferred method utilizes the cutting tip to first plant or inject a marker, followed by the cutting of a series of channels in the myocardium. By utilizing a radiopaque distal cutting tip and a fixed, implanted radiopaque marker, the relative positions of the two can be viewed fluoroscopically and adjusted fluoroscopically, thereby allowing formation of a controlled pattern of channels. The radiopaque marker provides a reference point for forming a pattern of channels in the myocardium.
In another embodiment of the invention, the cutting tip injects radiopaque material in conjunction with the cutting of a channel. In this embodiment, as each channel is formed, a radiopaque marker is left, creating a pattern of radiopaque markers viewable fluoroscopically. The pattern of channels formed in the myocardium are thus immediately viewable, giving feedback to the treating physician as to the progress and scope of the pattern of channels. Suitable materials for injection into the myocardium are preferably biodegradable or absorbable into the body soon after the procedure, allowing the myocardial channels to be perfused with blood. A device suitable for cutting and injection of material is described in copending U.S. patent application Ser. No. 08/812,425, filed Mar. 16, 1997, entitled TRANSMYOCARDIAL CATHETER AND METHOD, herein incorporated by reference.
Referring now to
In use, magnets 84 can be used in conjunction with axially moving anchoring shaft 26 to plant anchoring shaft 26 in the desired location. Pairs of magnets in all three dimensions may not be required as the goal is to pull the anchoring shaft against a ventricle wall, not necessarily to suspend it in place using the magnets. The magnets, in conjunction with a radiopaque anchoring shaft tip and fluoroscopy, can be used to guide the anchoring shaft into position and maintain position during treatment. In the embodiment illustrated, an anchoring spike 82 lies at the distal end of anchoring shaft 26. Anchoring spike 82, drawn larger in
Referring now to
Referring now to
In use, magnetically responsive catheter 100 can be advanced with aid of fluoroscopy through the aorta and into a coronary artery. Catheter distal region 106 preferably includes radiopaque materials to aid positioning under fluoroscopy. Once in position, distal region 106 is effectively located in the heart wall. When stabilization is desired, external magnets such as magnet 84 can be positioned near catheter distal region 106. By exerting a strong pull on distal region 106, the movement of the heart wall in the vicinity of catheter distal region 106 can be lessened.
Stabilization can be used during intravascular PMR procedures, minimally invasive PMR procedures, and heart procedures generally. When used during PMR procedures, the stabilization can serve to lessen heart wall movement in the area being cut. When used during other medical procedures, the stabilization can serve to minimize heart wall movement in areas being operated on or otherwise treated. When used during intravascular PMR procedures, a second, PMR catheter should be provided.
Referring now to
Disposed within positioning tube 120 is a guide catheter 142 extending from positioning tube proximal end 126 to distal region 124. Disposed within guide catheter 142 is a PMR cutting wire 132, proximally electrically connected to an RF energy source 136 and terminating distally in a cutting tip 33. PMR wire 132 includes a distal arcuate or bent region 144 proximate distal cutting tip 33. Arcuate region 144 can be bent or arced so as to have a preformed shape or bias to extend laterally away from the longitudinal axis of the PMR wire. In one embodiment, PMR wire lies within positioning tube 120 directly, without a guide catheter. In a preferred embodiment, a guide catheter such as guide catheter 142 is disposed about the PMR wire. PMR wire 132 is slidably disposed within guide catheter 142 and can be rotated by applying torque to the proximal end.
In use, positioning tube 120 can be preloaded with guide catheter 142 containing PMR wire 132. PMR wire 132 can be retracted such that arcuate region 144 is retracted either to a position proximal of channels 138 or within positioning tube distal region 124 but retracted within guide catheter 142. In this retracted position, PMR wire arcuate region 144 does not extent from channels 138. With PMR wire retracted, positioning tube 120 can be advanced through the vasculature into a heart chamber such as the left ventricle. Positioning tube distal end 122 can be advanced down into the ventricle and up a ventricular wall. With distal end 122 in a desired position, anchoring means 130 can be used to anchor distal end 122 to the ventricular wall. In embodiments where anchoring means 130 is magnetically responsive or where positioning tube distal region 124 is magnetically responsive, an external magnetic force can be applied to pull or push anchoring means 130 and distal region 124 into the wall. In embodiments where anchoring means 130 is a suction tip, vacuum can be applied to the vacuum lumen in communication with the suction tip.
With positioning tube distal region 124 in place, guide catheter 142 containing PMR wire 132 can be advanced to push tube distal end 122 and PMR wire arcuate region 144 distally out of guide catheter 142. PMR wire 132 can be rotated such that cutting tip 33 is oriented toward channels 138, and guide catheter 142 and PMR wire 132 retracted together until cutting tip 33 can be pushed out of channel 138. Cutting tip 33 can be advanced through channel 138 and a channel cut into the myocardium. In a preferred embodiment, PMR wire 132 has a depth stop 146 proximal of arcuate region 144 that limits the length of wire passed through channels 138, such that the depth of a PMR formed myocardial channel is limited. After myocardial channel formation, PMR wire 132 can be retracted through the channel and the next, more proximal channel entered. In a preferred embodiment, arcuate region 144 is radiopaque and a series of radiopaque marker bands separate channels 138 to aid in positioning cutting tip 33. In one embodiment, PMR wire 132 can be rotated to cut more than one myocardial channel per positioning tube channel. In this manner, a series of myocardial channels in a regular pattern can be formed over the length of positioning tube distal region 124.
Referring now to
Referring now to
Intermediate tube 184 has a channel 194 formed through the tube wall sufficiently large to allow passage of PMR probe 182. In a preferred embodiment, channel 194 is formed in a side tube wall in a distal portion of intermediate tube 184, as illustrated in
Referring again to
In use, PMR positioning device 180 can be advanced into the left ventricle and anchoring tip 200 forced against some portion of the vermicular wall. Intermediate tube 184 can be slid within outer tube 186 to a desired position. Inner PMR probe 182 can be advanced out of channel 194 until the desired length of PMR probe is exposed. A desired position of cutting tip 188 can be reached by adjusting the length of PMR probe 182 exposed, the length of intermediate tube 184 advanced into outer tube 186, and the rotation of outer tube 186. In one method, a series of arcs of myocardial channels are formed substantially transverse to the longitudinal axis of positioning device 180. In this method, outer tube 186 is rotated such that cutting tip 188 describes an arc. As each arc is completed, intermediate tube 184 is slid relative to outer tube 186 and a new arc of channels is burned into the ventricular wall.
Referring now to
In one embodiment, elongate rod 226 and anchoring member 230 are both slidably disposed in a dual lumen tube 227 substantially coextensive with intermediate tube 222. Dual lumen tube 227 can terminate the lumen containing elongate rod 226 in a skived portion 229, continuing the tube as a single lumen portion 231. Single lumen portion 231 allows elongate rod 226 to freely travel with outer collar 224. Outer collar 224 preferably is slidably disposed over single lumen portion 231.
Intermediate sleeve 238 and inner PMR probe 182 together have an arcuate or bent bias or preform, as illustrated at 238. In one embodiment, intermediate sleeve 222 has a preformed shape which can be imparted with an embedded shape wire as illustrated by wire 189 in
In one embodiment, intermediate tube 222 can be rotated within outer collar 224. In another embodiment, intermediate tube is restricted in rotation corresponding ridges and grooves between outer collar 224 and intermediate tube 222. In one embodiment, outer collar has internal ridges fitting within external grooves in a region of intermediate tube 222. Restricting the rotation of intermediate tube 222 within collar 224 can aid in causing rotation about anchoring member 230 rather than about the center of outer collar 224.
In use, outer collar 224 can be extended distally over intermediate sleeve 222, such that collar 224 is proximate intermediate sleeve distal end 240. Inner PMR probe 182 can be preloaded within intermediate sleeve 222. With outer collar 224 distally extended, arcuate region 238 is substantially restrained and straightened. Device 220 can be advanced within the vasculature and into a heart chamber such as the left ventricle. Elongate anchoring member 230 can be advanced distally and rotated, thereby rotating pigtail 232 into the ventricle wall and securing anchoring member 230. With intermediate sleeve 222 and PMR cutting tip 188 positioned as indicated at “E” in
In one embodiment, distal cryanoblative tip 332 includes a distal orifice in communication with the treatment shaft lumen, such that liquid nitrogen can be delivered through the orifice and to the heart chamber wall. In another embodiment, tube 330 is close ended and initially under vacuum, allowing liquid nitrogen to be delivered to the tube distal region, causing the tube to become very cold without allowing liquid nitrogen to enter the myocardium. The cryanoblative tip can be inserted into the heart chamber wall, penetrating the wall, and into the myocardium prior to delivery of liquid nitrogen. The delivery of liquid nitrogen to the heart chamber wall can cause localized tissue death, bringing about the same healing response as laser and radio-frequency current PMR.
Referring now to
The coverage of the cutting tips in
In a variation of the methods previously described, a radiopaque contrast media is used to determine the depth of channels formed in the myocardium. The contrast medium is injected or “puffed” into or near the channel formed in the myocardium. The heart can be visualized under fluoroscopy to determine the depth of the channel formed thus far. After visualization, the channel can be further deepened. The cycle of channel formation, contrast medium puffing, and fluoroscopic visualization can be repeated until the channel has the desired depth.
Contrast medium could be injected using a lumen such as the lumen of guide catheter 142 of
In addition to using the device as described herein above to form channels in the myocardium, the device could be used to form craters in the myocardium. That is, to form a wound in the myocardium having a width greater than its depth. The crater can be formed by controlling the depth of insertion of, for example, a radiofrequency device and/or controlling the power delivered to the distal tip of the device such that a crater is formed. Those skilled in the art can also appreciate that mechanical devices, laser devices or the like could be used to form craters.
In use, the above methods and devices can be used to form a pattern of channels leading from healthy myocardial tissue to hibernating tissue. This can operate by multiple mechanisms to supply hibernating tissue with an increased blood supply. First, channels in the myocardium can perfuse tissue directly from the ventricle, through the patent channel formed by the cutting tip. Second, the channels formed by the cutting tip can become newly vascularized by operation of a healing response to the channel injury. The new blood vessels thereby increase further the supply of hibernating tissue by ventricular blood. Third, the series of newly formed vessels caused by the healing response can form interconnections or anastomoses between the series of injured areas, forming a network of blood vessels, which, by connecting with healthy area vessels, can be supplied by blood originating from coronary arteries in addition to blood supplied directly by the ventricle.
The materials to be used, and the methods of fabrication, to make catheter assembly 400 will be known to one skilled in the art in view of the uses to which catheter assembly 400 are put. As shown in
In order to move loop 404 between first position A and second position B, guide wire 402 should be relatively rigid in comparison to loop 404 and actuator member 406. With that configuration, actuator 406 can be pulled proximately to move loop 404 from second position B to first position A. In turn, actuator member 406 can be moved distally to deploy loop 404.
It can be appreciated that each of the devices disclosed herein can be bi-polar as well as mono-polar. To make a bi-polar configuration, a ground electrode would need to be disposed on the device proximate the electrode(s) shown.
Numerous characteristics and advantages of the invention covered by this document have been set forth in the foregoing description. It will be understood, however, that this disclosure is, in many respects, only illustrative. Changes may be made in details, particularly in matters of shape, size, and arrangement of parts without exceeding the scope of the invention. The inventions's scope is, of course, defined in the language in which the appended claims are expressed.