Intravascular Guidewire with Hyper Flexible Distal End Portion

In one embodiment, a sensing guidewire for performing atraumatic intravascular physiologic measurements includes an elongated core wire and a sensor disposed at a distal end portion thereof. A flexure is disposed in the core wire proximal to the sensor housing. The flexure is substantially more flexible than regions of the core wire disposed on either side of the flexure, and enables a distal end portion of the guide wire to conform to and rest against a wall of vascular structure, such as an aneurism, without exerting an undue outward pressure thereon in response to making any contact with the wall.

DETAILED DESCRIPTION

In embodiments of the present disclosure, guidewires are provided for making physiologic measurements in a blood vessel or aneurism (where perforation or rupture is of significant concern) that reduce stress on the vessel/aneurism wall by placing one or more sensors located at the distal end portion of the guide wire with a hyper flexible core wire section proximal to the sensor housing, together with methods for making and using them.

FIG. 1is a partial cross-sectional elevation view of a conventional guidewire10having one or more sensors12, such as a blood pressure sensor and/or a blood flow sensor, located at its distal end and being introduced into an aneurism14on a blood vessel16, such as a vein or an artery, using a catheter18extending through the lumen20of the blood vessel16and into the aneurism14.

As illustrated inFIG. 1, in some instances, the distal end of the microcatheter18can be disposed near the wall of the aneurism14. When this occurs, a distal end portion of the guidewire10extending from the microcatheter18can come into contact with the wall of the aneurism14. If the distal end portion of the guidewire10is relatively stiff, the distal end portion of the guidewire10may try to straighten itself into the configuration indicated by the dashed line22, thereby causing the distal end portion of the guidewire10to apply an undesirable outward pressure on the wall of the aneurism14, as indicated by the arrow24, thereby potentially resulting in a perforation or rupture of the wall of the aneurism14.

An example embodiment of a conventional guidewire device100capable of performing physiologic measurements and other intravascular procedures such as that described above is illustrated inFIG. 2, which illustrates a “ComboWire 0.0,” available from the Volcano Corporation, Rancho Cordova, Calif. In the particular embodiment illustrated inFIG. 2, the guidewire device100can include an elongated guidewire10having two sensors12located within a housing102disposed at its distal end. In one embodiment, the two sensors12can comprise, for example, a distal-end-mounted ultrasound transducer that transmits ultrasound waves and receives returned Doppler signals to measure blood flow, and a pressure sensor disposed immediately proximal of the flow sensor. In some embodiments, the pressure sensor can comprise a semiconductor diaphragm disposed over a sealed cavity and bordered by a flexible rim, for example, such as described in U.S. Pat. No. 6,106,476 to Corl et al. It should be understood that the device100is also available in models having only one sensor12at the distal end. In some embodiments, the housing in which the sensor(s)12can be from about 0 centimeters (cm), i.e., no housing, to about 3 cm in length. In one form, the housing is a substantially rigid hypotube section having a length between 1.5-2.5 mm, although shorter or longer housings may be utilized. In alternative embodiment, the housing is a flexible tubular member that may have a length greater than 3 mm up to 3 cm. Additionally, in some embodiments, the guidewire10can have no sensors12at its distal end, and other embodiments, the guidewire10can incorporate more than2sensors12at its distal end.

As illustrated inFIG. 2, in addition to the foregoing, the example guidewire device100can also include a distal end portion that is shapeable and/or radiopaque for visualization under fluoroscopy, a torqueing device104, which can be used to rotate the guidewire10about its long axis, a connector body106configured to receive the proximal end of the guidewire10in a slide-in engagement, a connector body nose108for releasably locking the proximal end of the guidewire10in the connector body106, and an electrical cable and connector plug110for connecting the signals from the two sensors to a monitor station (not illustrated) incorporating, e.g., a touch-screen display, a recordable CD drive, a printer, memory for storing sensor output data and other signal monitoring, displaying and recording components.

Examples of combination sensor guidewire devices100can be found in commonly owned U.S. Pat. Nos. 8,277,386 and 8,231,537, both to M. Ahmed et al., the disclosure of each of which is incorporated herein in its entirety.

A procedure such as discussed above in connection withFIG. 1can be performed using a guidewire device100such as discussed above in connection withFIG. 2. Thus, in one example embodiment, the guidewire10of the device100is inserted into the aneurism14through a microcatheter, such as an Echelon-14 Microcatheter, available from Micro Therapeutics, Inc., Irvine Calif. The catheter18is initially delivered, which may be affected under fluoroscopy, into the aneurism14using a standard “front line” guidewire (not illustrated).

Once the microcatheter18is situated in the desired position, the front line guidewire is removed, and the guidewire10of the guidewire device100is inserted into the microcatheter18so that the distal end of the guidewire10is even with the distal end of the microcatheter18. In one possible embodiment, the microcatheter18can then be moved proximally for a short distance, for example, about 10 mm, thereby exposing a corresponding 10 mm length of the distal end portion of the guidewire10, without having to advance the guidewire10itself into the anatomy. Pressure, flow, and/or other measurements can then be made using, for example, the sensor(s)12disposed at the distal end portion of the guidewire10. Thus, signals from the sensors12at the distal end portion are conveyed through the length of the guidewire10to the connector part108by thin conductive wires, and thence, through the cable and connector plug100to, for example, a monitoring station of the type described above.

In some procedures, the guidewire10and catheter18can be pulled back short distances and additional measurements taken. With proper initial positioning, measurements can be taken at many locations within the aneurism14. At the completion of the procedure, the guidewire10can be withdrawn through the microcatheter18and out of the patient's body.

One drawback of conventional guidewires10is that they have relatively rigid distal end portions, i.e., the portion generally describing the distal-most 1-3 cm of the guidewire10. As illustrated inFIG. 2, in the guidewire device100described above, both the pressure sensor and the Doppler transceiver are positioned in a tubular sensor housing102located at the distal end of the guidewire10. In some embodiments, the sensor housing102can be approximately 2-3 mm long and can have a significant mass and rigidity, relative to the other components disposed at the distal end portion of the guidewire10. Guidewires10conventionally comprise a flexible coil disposed concentrically about an elongated distal “core wire,” which forms a backbone of the guidewire10. Thus, conventional guidewires10can have a distal core wire that includes a 1.5 centimeter (cm) long distal end “flat,” i.e., a flattened portion that is about 0.0017 inches (in.) thick.

A more flexible guidewire10, such as a PrimeWire, available from Volcano Corp., typically has a distal end flat that is also about 1.5 cm long but only approximately 0.0009″ thick, which renders the distal end portion of the PrimeWire guidewire10relatively softer and more flexible than the embodiment above. The core wires of both guidewires have a similar distal core grind, i.e., a 0.0055 in. base core diameter that tapers down to a 0.0024 in. diameter over a 5 cm long taper, with a final cylindrical end portion grind that is about 0.0024″ in diameter and 2 cm long.

As those of some skill will understand, flexibility of the distal end portion of the guidewire10is based on several factors, including distal core wire grind diameter, distal flat length, distal flat thickness, distal flat width, and distal end portion coil design, material, and spacing. The respective mechanical stiffnesses of the distal core wire and distal flat are both functions of their Area Moments of Inertia (I) which, in the case of circular cross-sections, is calculated from the equation,

where r is the radius of the circular cross-section, and in the case of rectangular cross-sections,

where W is the width of the cross-section and T is its thickness.

From the above equations, it can be seen that, in the case of a circular cross-section, decreasing the diameter (a fourth power function), has a substantial impact on the flexibility of the distal end portion, and in the case of a rectangular cross-section, a decrease in the thickness T (a third power function) of the flat has a greater impact on the distal end portion flexibility than decreasing the width W. Generally, the width W of the flat (the less impactful dimension) is not controlled but is a result of the initial round profile cross-sectional area (derived from the final core grind diameter) and the thickness to which the core wire distal end portion is flattened. Nevertheless, some increase in the flexibility of the distal portion of the core wire can be obtained by locally reducing the width of the distal flat.

As those of some skill will understand, having a stable distal end portion is necessary when navigating, e.g., coronary anatomy. Some guidewires10are prepared for such use by putting a slight bend in the distal end portion of the wire, referred to as a “J-shape, as illustrated in the enlarged breakout view ofFIG. 2. The “J” is typically 5-7 cm long and is bent at an angle of approximately 45 degrees. The actual size and angle of the bend can vary considerably, depending on the shaping method and the particular application at hand. The thicker distal end portion flat of a conventional guidewire10core wire, i.e., the mechanically flattened most distal portion of the core wire, typically about 1.5 cm long, makes the creation of the J-shape much more difficult. In the coronary and peripheral blood vessel anatomies, guidewires10can be “steered” by “torqueing,” i.e., rotating the direction which the J-shape points within the anatomy and advancing/retracting the guidewire10, both typically under fluoroscopy, possibly using contrast injections to verify distal end portion location. With the sensors and sensor housing102disposed at the distal end of the distal end portion, their position relative to the body of the guidewire10and the J-shape needs to remain relatively stable, so that the guidewire10exhibits a predictable behavior when rotated or advanced or retracted axially. While it is possible to decrease the diameter of the core wire in the distal end portion or to decrease the thickness of the distal end portion flat, thus making the guidewire10more flexible and atraumatic, this would decrease the steerability of the guidewire10by making it difficult for the guidewire10to maintain a prescribed J-shape and destabilizing the handling of the guidewire distal end portion when steering inputs, i.e., torqueing, are applied.

However, in the aneurism assessment application described above, the guidewire10was delivered to the measurement location, viz., an aneurism14, by passing it through a microcatheter18that had already been positioned using a frontline guidewire. Thus, as those of some skill will understand, it was not necessary to “steer” the guidewire10to its finally location. This is because the microcatheter18can have, for example, an internal lumen with a diameter of about 0.017 in., thus providing generous column support to the guidewire10, which in some embodiments, can have an outer diameter of about 0.0145 in. As a result, the guidewire10can easily be advanced distally through the microcatheter18as long as the guidewire10has sufficient support, which can be provided by the core wire portions other than the distal end portion, along with adequate lubricity, which is also independent of distal end portion design, between the guidewire10and the catheter18.

This delivery method therefore enables the creation of an improved guidewire10that has at least one flexible region, i.e., one or more “flexures,” disposed proximal to the distal sensor housing102, thereby reducing the straightening force exerted on the wall of, e.g., an aneurism14, when the guidewire10is exposed distally from the microcatheter18by the latter's withdrawal. This hyper flexible distal end portion design would, as discussed above, be detrimental to unaided steering of the guidewire10through, e.g., coronary anatomy, such as could occur, for example, in a typical percutaneous coronary intervention (PCI) procedure, but as discussed above, can be very beneficial in an atraumatic neuro/aneurism procedure, in which steerability of the distal end of the guidewire10is, as discussed above, of less importance.

FIG. 3is an enlarged partial cross-sectional view of a distal end portion of an example embodiment of a guidewire300having a hyper flexible distal end portion in accordance with the present disclosure, in which one or more flexures are incorporated into the core wire302posterior to a sensor housing304thereof to provide enhanced flexibility of the distal end portion.

As illustrated inFIG. 3, the example guidewire300comprises a core wire302and a sensor housing304disposed at the distal end of the guidewire300. As discussed above, the sensor housing304can contain one or more sensors for sensing physiologic parameters within coronary, peripheral and neural locations in the body. In the particular embodiment illustrated inFIG. 3, for example, the sensor housing304is shown containing two sensors, viz., a blood flow sensor306mounted at the distal end of the guidewire300, and a blood pressure sensor308mounted in a separate portion of the sensor housing304proximal to the flow sensor306. In some embodiments, the sensors306and308can be at least partially embedded in matrix of a “potting” material310. However, it should be understood that in other guidewire embodiments, other numbers, types and mountings of sensors could be implemented at or near, e.g., from approximately 0-3 cm, from the distal end of the guidewire300, depending on the particular application at hand.

A coil312is disposed coaxially about the core wire302. As discussed above, in some embodiments, the distal end portion of the coil12can be made radiopaque over a selected length to render it more visible under fluoroscopy. As illustrated inFIG. 3, in some embodiments, the spacing between the turns of the coil312at a distal end portion thereof can be increased to decrease the stiffness of a corresponding end portion of the guidewire300. Alternatively, or in addition, the coil312can be wound from a source material having a diameter, e.g., from 0.001 in. to 0.003 in., so as to reduce the axial stiffness of the coil312, and hence, the guidewire300.

The guidewire300can have many possible configurations. However, for purposes of explication, a configuration corresponding to those discussed above is illustrated inFIG. 3. Thus, in the particular example embodiment ofFIG. 3, the example core wire302includes a base or proximal core314having diameter316of 0.0055 in. The base core314tapers down over a distance318of 5 cm to a cylindrical portion320having a diameter322of 0.0024 in. and a length319of about 2 cm. As described above, a flat324is disposed at the distal end of the cylindrical portion320. The example flat324has a length326of 1.5 cm, a width328(W) of 0.0027 in., and as discussed above, can have a thickness330(T) of from 0.0009 in. to 0.0017 in. It should be understood that the above configurations and dimensions are given by way of an example only, and that the core wire302can have many other configurations and dimensions, depending on the particular application at hand.

As discussed above, in order to render a distal end portion of the guidewire300hyper flexible, it is desirable to dispose one or more flexures within the core wire302proximal to the sensor housing304, i.e., in a region of the core wire302disposed proximal to the arrows332. The flexure in the core wire302should be substantially more flexible than regions of the core wire302disposed on either side of the flexure. As discussed above, this can be effected by reducing the area moment of inertia I in the region of the flexure relative to the area moment of inertia I of the adjacent regions of the core wire302.

Thus, in one example embodiment, a substantial reduction in the flexibility of the distal end portion of the guidewire300can be effected by reducing the diameter, e.g., by grinding, of the cylindrical portion320of the core wire302to about 0.0015 in. If desired, the distal end portion of the cylindrical portion320could then be flattened to produce a flat of about 2 cm in length and about 0.0009-0.0017 in thickness.

This can be also be effected, for example, in the case of a flat324at the distal end of the core wire302by reducing at least one of the thickness T and/or the width W of the flat324in a region proximal to the sensor housing304. As illustrated in the enlarged side elevation detail view A ofFIG. 3, this can be effected, for example, by forming a pair of opposing notches334, one each in the upper and lower surfaces of the flat324, to reduce the thickness T of the flat324in that region, or, as illustrated in the top plan detail view B, by forming a pair of opposing notches334, one each in the opposite sides of the flat324, to reduce the width W of the flat324in that region, or by doing both.

As illustrated in detail side elevation view C, in some embodiments, it may be desirable to omit a distal flat324, and to extend the cylindrical portion320of the core wire302to the distal end thereof. In this instance, a reduction in the area moment of inertia I in the desired region of the flexure relative to the area moment of inertia I of the adjacent regions of the core wire302can be effected, for example, by grinding one or more circumferential grooves338in the cylindrical portion322to reduce the diameter at the desired location of the flexure.

As illustrated in the top plan detail view D ofFIG. 3, in yet another example embodiment, a pair of opposing notches336can be formed, e.g., by grinding, at the transition between the cylindrical portion320of the core wire302and a flat324at the distal end thereof.

As those of some skill in this art will understand, the above modifications to the core wire302can be effected in a number of known processes, including grinding, centerless grinding, conventional machining, micromachining, electrical discharge machining (EDM), pressing, and the like.

In some cases, it may be desirable to test guidewires with hyper flexible distal end portions made in accordance with the present disclosure at the prototype stage or during production to ensure that they exhibit the requisite degree of flexibility in their distal end portions.

FIGS. 4A and 4Billustrate a simple type of test that can be performed to obtain a first-order evaluation of the flexibility of the distal end portion404of a guidewire400.FIG. 4Ais a partial side elevation view of a conventional guidewire400being supported by a fulcrum402or the like at a selected distance proximal to its distal end, showing a downward deflection, or “droop,” of the distal end portion404thereof due to gravity. As discussed above, due to the stiffness of the distal end portion intentionally incorporated therein in order to obtain the requisite degree of steerability of the distal end of the guidewire400within an anatomical vessel or chamber, the distal end portion404of the conventional guidewire400supported at a distance of 3 cm from the distal tip will droop or deflect under its own weight relative to the central axis of the guidewire by an angle Θ that is only from about 0 degrees to less than about 3 degrees.

FIG. 4Bis a partial side elevation view of an example embodiment of a guidewire400in accordance with the present invention being supported at the same selected distance (3 cm) proximal its distal end, showing the downward deflection, or droop, of the distal end portion404thereof due to gravity. As illustrated, the guidewire is supported at a position proximal of the flexures or flex regions to allow gravity to act on the section of the guidewire distal of the flexure or flex regions. As illustrated inFIG. 4Band discussed above, by the provision of one or more flexures or flex regions in the core wire of the guidewire400proximal to its distal end, the hyper flexible distal end portion of the guidewire400can be configured to droop under its own weight relative to the central axis of the guidewire400through an angle Θ of from about 5 degrees to about 45 degrees, and preferably, within a range of 10 degrees to 35 degrees and still in a range of from about 15 degrees to about 25 degrees.

FIG. 5is a partial side elevation view of an example method and apparatus500for determining the amount of force necessary to obtain a given deflection in the distal end portion of a guidewire502. InFIG. 5, a test guidewire502is suspended vertically by a hypotube collar504. This orientation is selected because, as discussed above, the hyper flexible distal end portions of the guidewires502are configured to have very weak “necks” proximal to their distal end portions506, which, as discussed above, will tend to droop under their own weight if the guidewires were to be positioned horizontally. This vertical orientation makes it difficult to mount a fixture to a vertical tensile test machine, e.g., an Instron vertical test machine.

Accordingly, in the example method500illustrated, an arbor508is disposed adjacent to the guidewire502at a distance, e.g., about 10-30 mm, but in one example 20 mm posterior to the distal end portion of the guidewire502to create a fulcrum or pivot around which the guide wire502will bend when the distal end portion506is displaced laterally by moving, e.g., a wedge510disposed on a strain gauge or a load cell512in the direction of the arrow514and against the distal end portion506. The load measured on the load cell512needed to bend the guidewire502through an angular displacement indicated by the arrow516and to the position indicated by the dashed lines518can be used as a measure of the flexibility/stiffness of the distal end portion of the guidewire502.

As those of some skill appreciate, the designs for guidewires with hyper flexible distal end portions described herein can be applied to any measurement guidewire and used in any body locations, including many coronary, peripheral and neural locations in the body, where functional measurements are required.

The embodiments described above illustrate but do not limit the invention. It should also be understood that numerous modifications and variations are possible in accordance with the principles of the invention. Accordingly, the scope of the invention is defined only by the following claims and their functional equivalents.