Patent Application
20160128583
The present invention relates to a system and apparatus comprising a multisensor guidewire for use in interventional cardiology, e.g. for Transcatheter heart Valve Therapies (TVT), such as, for Trans-catheter Aortic Valve Implantation (TAVI) and for related diagnostic measurements.
If a heart valve is found to be malfunctioning because it is defective or diseased, minimally invasive methods are known for repair and replacement of the heart valve, by introduction of a catheter intravascularly into the heart to access the heart valve. Percutaneous procedures for minimally invasive transcatheter heart valve repair and replacement avoid the need for open heart surgery. These procedures may be referred to as Transcatheter Valve Therapies (TVT).
TVT for valve repair include, for example, procedures such as, balloon valvuloplasty to widen an aortic valve which is narrowed by stenosis, or insertion of a mitral clip to reduce regurgitation when a mitral valve fails to close properly. Alternatively, if the valve cannot be repaired, a prosthetic replacement valve may be introduced. Minimally invasive Transcatheter heart Valve Replacement (TVR) procedures, including, Transcatheter Aortic Valve Implantation (TAVI) and Transcatheter Mitral Valve Implantation (TMVI), have been developed over the last decade and have become more common procedures in recent years.
While there have been many recent advances in systems and apparatus for TVT and for related diagnostic procedures, interventional cardiologists who perform these procedures have identified the need for improved apparatus for use in TVT, including apparatus for heart valve replacement. They are also seeking improved diagnostic equipment that provides direct measurements, i.e. within the heart, of important hemodynamic cardiovascular parameters before, during and after TVT.
The above referenced related PCT application No. PCT/IB2012/055893 (Publication No. WO/2013/061281), having common inventorship and ownership with the present application, discloses a multisensor micro-catheter or guidewire which comprises a distal end portion containing multiple optical sensors arranged for measuring blood pressure at several sensor locations, simultaneously in real-time. It optionally includes a sensor for measuring blood flow. In particular, the multisensor micro-catheter or guidewire is designed for use in minimally invasive surgical procedures for measurement of intra-vascular pressure gradients, and more particularly, for direct measurement of a transvalvular pressure gradient within the heart.
To obtain accurate measurements of hemodynamic parameters such as blood pressure, blood flow, a blood pressure gradient, or other parameters within the heart, it is desirable that the sensor guidewire does not interfere with normal operation of the heart and the heart valves. Thus, beneficially, a fine diameter guidewire, e.g. ≦0.89 mm diameter, with a flexible tip, facilitates insertion through a heart valve without trauma, and reduces interference with valve operation. That is, when the sensor guidewire is inserted through the valve, it preferably causes minimal interference with the movement of the valve and/or does not significantly perturb the transvalvular pressure gradient or other parameters. For example, in use, a multisensor guidewire may be introduced via the aorta, through the aortic valve, and positioned so that the optical pressure sensors are located both upstream and downstream of the aortic valve, for direct measurement of the transvalvular blood pressure gradient, and optionally also blood flow, with minimal disruption of the normal operation of the aortic valve. Accordingly, a fine gauge guidewire minimizes disruption of the heart valve activity during measurement, to obtain accurate measurements of the transvalvular pressure gradient or other parameters.
A reliable measurement of a transvalvular pressure gradient through several cardiac cycles is an important parameter to assess whether the heart valve is functioning well or malfunctioning. An optical multisensor pressure sensing guidewire of this structure provides a valuable tool that an interventional cardiologist can use to facilitate direct measurements of cardiovascular parameters, including a transvalvular pressure gradient. Such measurements provide information relating to parameters, such as, an aortic regurgitation index, stenotic valve orifice area and cardiac output.
As described in the above referenced related patent applications, typically, a conventional support guidewire used for a transcatheter valve replacement procedure, such as TAVI, comprises an outer tubular layer in the form of a flexible metal coil, and a central metal core wire or mandrel to provide stiffness and torque characteristics. The outer metal coil and inner core wire act together to provide a suitable combination of flexibility and stiffness, which, together with a suitably shaped tip, allow the guidewire to be directed or guided through the blood vessels, i.e. intravascularly, into the heart.
In the multisensor guidewire disclosed in the above referenced PCT International Application No. PCT/IB2012/055893, the optical sensors, e.g. 3 or 4 optical pressure sensors, are located in a distal end portion of the sensor guidewire, and coupled by respective individual optical fibers to an optical input/output at the proximal end of the guidewire. It will be appreciated that to fit a plurality of optical sensors and optical fibers within a guidewire comprising a small gauge outer coil, e.g. ≦0.89 mm (0.035 inch), the diameter of core wire is made as small as possible, i.e. to allow sufficient space around the core wire to accommodate the optical fibers and sensors between the core wire and the coil. For example, standard optical fibers have a diameter of 0.155 mm, which would require a core wire having a diameter of only 0.5 mm for a 0.89 mm outside diameter guidewire. Since the stiffness of a wire varies as the fourth power of its diameter, the small diameter core wire significantly reduces the stiffness of the multisensor guidewire. That is, the optical fibers and sensors take up space within the micro-catheter or guidewire coil but do not contribute significantly to the stiffness.
In testing of prototype multisensor guidewires, it has been found that the strong blood flow and turbulence within the heart can be sufficient to displace a small-gauge flexible guidewire, and tends to push the guidewire back into the aorta. Thus, during measurement of a transvalvular pressure gradient, movement of the guidewire may create difficulty in positioning the sensors and the cardiologist may need to readjust the positioning of the guidewire to maintain the pressure sensors each side of the heart valve. On the other hand, in a multisensor guidewire of this structure, to accommodate a plurality of optical sensors and respective optical fibers around a larger diameter stiffer core wire would require a larger outside diameter outer coil, i.e. larger than 0.89 mm. While a larger gauge, stiffer guidewire would be less easily displaced during measurements, for measurement of transvalvular pressure gradients, it would tend to interfere more with normal heart valve operation, and may increase the risk of tissue damage. Accordingly, a need for further improvements has been identified.
If diagnostic measurements of hemodynamic/cardiac parameters indicate the need for valve replacement, minimally invasive transcatheter valve replacement procedures, such as TAVI, can be performed to insert a replacement or prosthetic valve, e.g. comprising leaflets made of biologic tissue supported within an expandable metal frame.
Examples of current prosthetic valves and valve delivery systems are illustrated and described and illustrated in an article entitled “Current Status of Transcatheter Aortic Valve Replacement”, by John G. Webb, MD, David A. Wood, MD, Vancouver, British Columbia, Canada; Journal of the American College of Cardiology, Vol. 60, No. 6, 2012.
Very briefly, the TAVI procedure requires that a support guidewire, which is a relatively stiff guidewire (TAVI guidewire) with a flexible tip, is introduced into the heart and through the aortic valve. For example, the interventional cardiologist introduces the support guidewire through a catheter inserted into the femoral artery, i.e. in the groin, and moves it up through the aorta into the heart. The tip of the TAVI guidewire is introduced into the aorta, through the malfunctioning aortic valve, and into the left ventricle of the heart. Once the support guidewire is anchored within the ventricle, a delivery device holding the replacement valve is passed over the support guidewire. The cardiologist guides the delivery device carrying the replacement valve over the support guidewire and manoeuvres the valve into position within the aortic valve. The replacement valve is expanded, so that the patient's malfunctioning aortic valve is pushed out of the way. The valve frame may be self-expandable or balloon-expandable, depending on the valve type and the delivery system. Once expanded, the metal frame engages the wall of the aorta and holds the replacement valve in position. When the delivery system is withdrawn, the leaflets on the replacement valve are able to unfold and then function in a manner similar to the leaflets of the natural aortic valve.
Commercial availability of an optical multisensor guidewire or multisensor micro-catheter as described in the above referenced related U.S. patent application Ser. No. 14/354,624, (now issued to U.S. Pat. No. 9,149,230), would provide the interventional cardiologist with a useful tool for directly measuring a pressure gradient before and after such a procedure for valve repair or replacement, e.g. for TAVI. For example, it is envisaged that the interventional cardiologist would introduce the fine gauge multisensor guidewire to measure a transvalvular pressure gradient, and optionally blood flow, to assess pre-implantation functioning of the heart and the damaged or malfunctioning aortic valve. After withdrawing the multisensor guidewire, the cardiologist would perform a transcatheter heart aortic valve implantation procedure using a specialized, more robust and stiffer support guidewire (TAVI guidewire) to deliver the valve implant into the heart and perform the implantation. Subsequently, after completing the TAVI procedure, the TAVI guidewire would be withdrawn. The multisensor guidewire would then be reintroduced to measure a transvalvular pressure gradient and flow, to assess post-implant functioning of the replacement valve.
For TAVI, a relatively stiff support guidewire, typically 0.035 inch (0.89 mm) in diameter, is required. For example, guidewire manufacturers may use a descriptive term, such as, “stiff” or “super stiff” to provide an indication of the guidewire stiffness. Based on experience, an interventional cardiologist will select a guidewire with an appropriate stiffness and/or other mechanical characteristics to suit a particular transcatheter valve replacement procedure. Such a description of stiffness or flexibility can be related in mechanics to a measurement of a flexural modulus, which is a ratio of stress to strain in flexural deformation, or, what may be described as the tendency for a material to bend.
During a TAVI procedure, the support guidewire must be firmly anchored within the left ventricle for insertion of the valve delivery system and so that the replacement valve can be accurately positioned and held firmly in place while it is expanded. When a stiff support guidewire is introduced into the left ventricle of the heart through the aortic valve, if too much force is applied to the guidewire or it is pushed too far, there is some risk that the guidewire could cause damage or trauma to the heart tissues, e.g. damage to the aortic wall or ventricular perforation and pericardial effusion resulting in pericardial tamponade. Moreover, there is increased risk of trauma or damage to the heart wall in a diseased, weakened or calcified heart. To reduce risk of trauma or ventricular perforation, typically the tip of the support guidewire is relative soft and flexible. It may be pre-formed as a J-tip or it may be resiliently deformable so that it can be manually shaped as required by the cardiologist. Recently, specialized TAVI guidewires have become commercially available with pre-formed curved tips of other forms. For example, the Boston Scientific Safari™ pre-shaped TAVI guidewire has a double curve tip, and the Medtronic Confida™ Brecker Curve™ guidewire has a spiral tip. Reference is also made, by way of example, to structures described in US patent publication No. US2012/0016342 and PCT Publication No. WO2010/092347, each to Brecker, entitled “Percutaneous Guidewire”; PCT Publication No. WO2014/081942, to Mathews et al., entitled “Preformed Guidewire”; and PCT Publication No. 2004/018031 to Cook, entitled “Guidewire”. See also, an article by D. A. Roy et al., entitled “First-in-man assessment of a dedicated guidewire for transcatheter aortic valve implantation”, EuroIntervention 2013; 8, pp. 1019-1025.
While significant advances have recently been made, interventional cardiologists have identified a need for further improvements or alternatives to available guidewires and diagnostic tools for use in minimally invasive intravascular procedures and cardiac interventions, such as TAVI, or other TVT. In particular, it is desirable to have improved apparatus to simplify or facilitate transcatheter valve replacement procedures, including apparatus that will assist in reducing the risk of tissue trauma, e.g. damage to the aorta, the valve or the ventricular wall when much force is exerted on the support guidewire. Additionally, improved systems and apparatus that would provide for direct (in situ) diagnostic measurements within the heart, before, during and after at least some TVT procedures would potentially assist in understanding factors that contribute to successful outcomes and/or issues that may contribute to mortality or need for re-intervention.
Thus, an object of the present invention is to provide for improvements or alternatives to multisensor guidewires, including support guidewires for transcatheter valve replacement procedures and/or to multisensor diagnostic guidewires that enable direct measurements of cardiovascular parameters at multiple locations within the heart, such as, measurement of a transvalvular pressure gradient.
The present invention seeks to mitigate one or more disadvantages of known systems and apparatus for measuring cardiovascular parameters, and/or for performing interventional cardiac procedures, including transcatheter valve therapies (TVT), for heart valve repair and/or replacement.
A first aspect of the invention provides a multisensor guidewire for measuring blood pressure concurrently at multiple locations during a minimally invasive intravascular or cardiac intervention, comprising:
a tubular covering layer comprising an outer flexible coil, the coil having a length extending between a proximal end and a distal end, an outside diameter of ≦1 mm, a core wire extending within the coil from the proximal end to the distal end, and the distal end comprising a flexible distal tip;
a plurality of optical sensors and a plurality of optical fibers; a sensor end of each optical fiber being attached and optically coupled to an individual one of the plurality of optical sensors;
the core wire having an external surface with a cross-sectional profile defining a plurality of grooves extending along a length of the core wire, each groove accommodating an individual optical fiber and a respective optical sensor within a diameter Dcore of the core wire and providing a sensor arrangement with said plurality of optical sensors positioned at respective sensor locations within a distal end portion of the guidewire;
a proximal end of each of the plurality of optical fibers being coupled to an optical input/output connector at the proximal end of the guidewire for connection to an optical control system; and
the plurality of optical sensors of the sensor arrangement including at least two optical pressure sensors at respective sensor locations spaced apart lengthwise along a length of said distal end portion.
Thus, a specially shaped core wire is provided which is grooved to accommodate and position the optical fibers and their respective sensors with the diameter Dcore of the core wire.
In embodiments comprising a multisensor support guidewire, the grooved core wire accommodates a plurality of optical fibers within a standard diameter multisensor guidewire with a core wire of a diameter Dcore that provides a required stiffness, typical of a support guidewire for transcatheter valve replacement.
The plurality of optical fibers and optical sensors sit within the grooves formed in the surface of the core wire, and the grooves preferably have a depth that is sufficient that the fibers and sensors are accommodated completely within the grooves and within a diameter Dcore of the core wire. The fibers and sensors are thereby protected within the grooves, during assembly and in use of the guidewire.
If required, e.g. if the sensors are of larger diameter than the optical fibers, at sensor positions in the distal end portion, recesses or cavities may be formed in the core wire at sensor locations to accommodate the optical sensors, e.g. by enlarging the grooves at sensor locations. The cavities optionally include radiopaque markers adjacent each sensor for locating the sensors in use, e.g., by conventional radio-imaging techniques.
Beneficially, the grooves are symmetrically spaced around the core wire. That is, the core wire preferably has rotational symmetry, e.g. three-fold or four-fold symmetry, with a corresponding plurality of three or four grooves spaced symmetrically around the circumference of the core wire. This provides rotationally symmetric stiffness and torque characteristics to the core wire for flexing and steering the guidewire. Preferably the grooves have some rotation around the core wire, e.g. they are helical grooves. For example, the helical grooves have a pitch of at least 25 mm (1 inch). Accordingly, a multisensor guidewire is provided with a helically grooved core wire that can accommodate multiple fibers and optical sensors while optimizing the stiffness and torque characteristics of the multisensor guidewire comprising a core wire of a particular diameter Dcore.
The core wire may be formed by wire-drawing, from a medical grade metal alloy, such as stainless steel. In this case, surfaces of the core wire defining the grooves are radiused to no less than a minimum radius Rmin to enable fabrication of the grooves by a wire-drawing process.
Each optical fiber may be adhesively bonded to the core wire at least at one point, e.g. within its respective groove at a point adjacent the sensor location and optionally also at the proximal end of the core wire.
The coil preferably has an outside diameter of ≦0.89 mm (≦0.035 inch). The outer coil and the optical fibers do not contribute significantly to the stiffness of the guidewire. Thus, the stiffness of the guidewire is primarily determined by the material and the diameter of the core wire. The material and diameter Dcore of the core wire, in at least the distal end portion, provides a flexural modulus of a predetermined stiffness to the guidewire.
Typically, the guidewire stiffness is described by guidewire manufacturers using standard guidewire descriptors such as “stiff” or “super stiff”.
For example, when the multisensor guidewire is for use as a support guidewire for TVR, the core wire may comprise a medical grade stainless steel alloy and the diameter Dcore of the core wire provides the guidewire with predetermined stiffness characteristics, such as, defined by a standard guidewire descriptor, said guidewire descriptor being one of stiff, super-stiff and ultra-stiff.
In some embodiments, the core wire comprises a medical grade stainless steel alloy and the diameter Dcore of the core wire in at least the distal end portion provides a flexural modulus of 60 GPa+/−10%. In some embodiments, the core wire comprises a medical grade stainless steel alloy and the diameter Dcore of the core wire in at least the distal end portion provides a flexural modulus of 60 GPa or more.
In an embodiment, the multisensor guidewire is configured measuring a transvalvular blood pressure gradient within the heart during a minimally invasive cardiac intervention, wherein said plurality of optical sensors comprise Fabry-Pérot MOMS pressure sensors and said sensor locations are spaced apart lengthwise along said length of the distal end portion to provide for one or more of:
a) placement of at least one pressure sensor in the aorta downstream of the aortic valve and placement of at least one pressure sensor in the left ventricle, upstream of the aortic valve for measurement of a transvalvular blood pressure gradient for the aortic valve; b) placement of at least one pressure sensor in the left atrium upstream of the mitral valve and placement of at least one pressure sensor in the left ventricle, downstream of the mitral valve for measurement of a transvalvular blood pressure gradient for the mitral valve; c) placement of at least one pressure sensor in the right atrium upstream of the tricuspid valve and placement of at least one pressure sensor in the right ventricle, downstream of the tricuspid valve, for measurement of a transvalvular blood pressure gradient for the triscuspid valve; and d) placement of at least one pressure sensor in the right ventricle upstream of the pulmonary valve and placement of at least one pressure sensor in the pulmonary artery, downstream of the pulmonary valve for measurement of a transvalvular blood pressure gradient for the pulmonary valve.
Thus, the plurality of optical sensors, including two or more optical pressure sensors at sensor locations spaced apart along a length of the distal end portion of the core wire, are positioned for placement upstream and downstream of a heart valve for measuring pressure at a plurality of sensor locations, concurrently, to provide a transvalvular pressure gradient.
Optionally, the plurality of optical sensors further comprises an optical flow sensor for monitoring blood flow in addition to measurement of blood pressure and blood pressure gradients, e.g. to enable computation of the valve area. In one embodiment, the optical flow sensor is positioned proximally of the pressure sensors, i.e. to measure blood flow in the ascending aorta downstream of the aortic valve and before the branches from the aorta, e.g. about 50 mm to 80 mm from the aortic valve or a distance LFS of about 20 mm upstream from the most proximal optical pressure sensor. Multisensor guidewires of alternative embodiments, comprising other spacings of two or more pressure sensors and a flow sensor, are also disclosed.
In a multisensor guidewire of an embodiment for use as a support guidewire for TVR, the multisensor guidewire comprises three or four optical sensors and respective optical fibers, wherein the distal end portion of the coil has an external diameter ≦0.89 mm (≦0.035 inch), and the core wire provides a guidewire having a flexural modulus of 60 GPa or more. The optical sensors comprise for example two optical pressure sensors and optionally, an optical flow sensor.
Where required, apertures are provided in the coil adjacent each optical pressure sensor for fluid contact therewith, and radiopaque markers are provided adjacent each optical pressure sensor.
Where the multisensor guidewire is to be used as a support guidewire for transcatheter valve replacement, to enable over-the-wire delivery of components, the multisensor guidewire may comprise separable distal and proximal parts connected by a micro-optical coupler. The multisensor guidewire forms the distal part and the proximal part comprises a flexible optical coupling to the control system. Thus, the distal part comprises a male connector of the optical coupler and the proximal part comprises a female connector of the optical coupler, the male connector having an outside diameter no greater than the outside diameter of the coil of the guidewire. For example, a proximal end of the core wire comprises a tapered portion that extends to form a core of the male connector and the plurality of optical fibers emerge from the grooves and extend around the tapered portion, around the core, and through a surrounding body or ferrule of the male connector which has an outside diameter of no greater than 0.89 mm. Preferably, the micro-optical coupler comprises alignment means and/or fastening means to facilitate quick connection/re-connection, with optical alignment of the multiple optical fibers, and to securely lock together the proximal and distal parts of the guidewire apparatus.
In an embodiment, the multisensor guidewire comprises separable distal and proximal parts connected by an optical coupler, said optical coupler securely fastening together the distal and proximal part, with optical alignment and coupling of the individual ones of the plurality of optical fibers of the distal part to corresponding individual ones of a plurality of optical fibers of the proximal part, and the proximal part being more flexible than the distal part for optically coupling the distal part to the control system.
In another embodiment, the multisensor guidewire comprises separable distal and proximal parts, and further comprising a separable micro-optical coupler comprising a female connector and a male connector coupling the proximal and distal parts, the distal part carrying the male connector, and the male connector having a diameter no greater than the outside diameter of the coil, to enable proximal mounting of components on/over-the-guidewire.
Optionally, the plurality of optical sensors further comprises an optical contact force sensor adjacent to, or within, the distal tip, the optical contact force sensor being configured for sensing a force applied by the distal end portion of the guidewire to surrounding tissue. A system comprising a sensor guidewire with a contact force sensor allows for a control system to monitor the contact force applied to said length of the distal end portion and provides feedback indicative of the contact force.
The contact force sensor monitors a contact force applied to a length of the distal end portion of the guidewire, e.g. to provide feedback to the interventional cardiologist when a threshold contact force is reached and to assist in avoiding tissue trauma or perforation. The system may provide an alert when the contact force exceeds a predetermined threshold value, e.g. during insertion of the support guidewire into the left ventricle for TAVI, to assist the cardiologist in avoiding tissue trauma.
In some embodiments, to accommodate a plurality of optical sensors within a guidewire of diameter ≦0.89 mm (≦0.035 inch) and with a core wire providing a required stiffness, the number sensors may be limited to a maximum of two, three or four sensors. For example, for some applications, if only three sensors can be accommodated, it may be preferred to provide two optical pressure sensors and one flow sensor to enable measurements of a transvalvular pressure gradient and blood flow. If a fourth sensor can be accommodated, while still providing sufficient stiffness, it may be another pressure sensor, or a contact force sensor.
Beneficially, to assist in anchoring of the guidewire during TVR, e.g. anchoring the guidewire within the left ventricle for TAVI, the flexible distal tip comprises an atraumatic tip such as a J-tip or other pre-formed curved tip. The flexible distal tip may comprise a pre-formed atraumatic tip, for example, comprising one of: a J-tip, spiral or another two dimensional curved shape; a three dimensional curved form; a helical structure, e.g. resembling a pigtail or phone cord; and a tapered helical structure, e.g. resembling the form of a snail shell.
Another aspect of the invention provides a core wire for a multisensor guidewire, wherein the multisensor guidewire has an outer flexible coil having an external diameter of ≦1 mm and the guidewire contains a plurality of optical sensors and a corresponding plurality of optical fibers, the core wire being fabricated from a medical grade metal alloy and having a diameter Dcore, an external surface of the core wire defining a plurality of grooves extending along the length of the guidewire, each groove having a depth that can accommodate an individual one of said plurality of optical fibers within the diameter Dcore of the core wire, and wherein Dcore is sized to fit slideably with the outer flexible coil of a guidewire.
Preferably, the plurality of grooves have some rotation around the core wire, e.g. extend helically along the length of the core wire, and the plurality of grooves are spaced symmetrically around the core wire.
For a multisensor guidewire with high stiffness, e.g. for use as a support guidewire, the core wire comprises a medical grade stainless steel alloy, such as 304V. To facilitate formation of the grooves by wire-drawing, radiused surfaces of the grooves have at least a minimum radius required for wire drawing.
Another aspect of the invention provides a method of assembly of a multisensor guidewire including a flexible outer coil and a core wire extending therethrough, the method comprising: providing a core wire having an external surface and cross-sectional profile defining a plurality of grooves defined along its length; providing a plurality of optical fibers, each optical fiber having at its distal end an optical sensor; attaching the optical fibers and their respective optical sensors to the core wire to form a sub-assembly with optical sensors spaced apart lengthwise along a distal end portion of the core wire, and with each optical fiber and its respective sensor sitting within a respective groove of the core wire; and inserting the sub-assembly into the outer coil of the guidewire.
Thus, apparatus and systems comprising a multisensor guidewire are provided that mitigate one or more problems with known systems and apparatus for TVT. In particular, some embodiments provide a multisensor support guidewire, with high stiffness, which can be used for minimally invasive transcatheter valve replacement procedures and which also provides for direct measurement of hemodynamic parameters, such as intravascular or transvalvular pressure gradients and flow, before and after the valve replacement. In other embodiments more flexible multisensor guidewires are provided for other percutaneous, minimally invasive intravascular procedures, comprising diagnostic measurements of hemodynamic parameters including blood pressure gradients.
Also provided is a grooved core wire which can provide high stiffness for multisensor support guidewires, and methods of fabrication of multisensor guidewires with improved stiffness and torque characteristics.
The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description, taken in conjunction with the accompanying drawings, of embodiments of the invention, which description is by way of example only.
In the drawings, identical or corresponding elements in the different Figures have the same reference numeral.
A system and apparatus comprising a multisensor guidewire for use in interventional cardiology, which may include diagnostic measurements of cardiovascular parameters and/or transcatheter valve replacement or repair, according to an embodiment of the present invention will be illustrated and described, by way of example, with reference to a system comprising a support guidewire for use in a TAVI procedure, for aortic valve replacement.
Firstly, referring to
To provide the appropriate stiffness and other mechanical properties, coil 35 and core wire 31 are typically stainless steel, although other suitable medical grade metals or alloys may alternatively be used. The distal part 102 differs from a conventional guidewire in that, internally, it also contains a sensor arrangement 130 comprising a plurality of optical sensors (not visible in
The proximal part 101 of the apparatus 100 provides for optical coupling of the distal part 102 to the control unit 151. The proximal part 101 has at its proximal end 110 an optical input/output 112, such as a standard type of optical fiber connector which connects to a corresponding optical input/output connector 153 of the control unit 151. Thus, the proximal part 101 is effectively an elongate, flexible optical coupler, e.g. a tubular flexible member containing a plurality of optical fibers, with the optical coupler 140 at its distal end for optical coupling of the distal part 102, i.e. the multisensor guidewire. The control unit 151 houses a control system comprising a controller with appropriate functionality, e.g. including a processor, data storage, and optical source and optical detector, and it provides a user interface, e.g. a keypad 154, and touch screen display 152, suitable for tactile user input, and for graphical display of sensor data. The user interface cable 155 (e.g. a standard USB cable) is used to transfer data between the control unit 151 to the touch screen display 152. The control unit 151 and touch screen display 152 may optionally be integrated within a single housing or module.
The internal structure of the multisensor guidewire apparatus 100 will now be described in more detail with reference to
The distal part 102 takes the form of a multisensor guidewire and comprises components of a conventional guidewire comprising a tubular outer layer in the form of a flexible fine metal coil 35 and an inner mandrel or core wire 31 within the outer coil 35. The outer coil 35 and the core wire 31 each have a diameter and mechanical properties to provide the required flexibility and stiffness to act as a support guidewire for TAVI. Typically, for TAVI, the coil forms a flexible tubular covering layer of the guidewire and has an outside diameter of 0.035 inch or 0.89 mm or less. To provide the appropriate stiffness and other mechanical properties, such as torque characteristics, for a support guidewire, coil 35 and core wire 31, are typically stainless steel, although other suitable metals or alloys may alternatively be used. As illustrated schematically in
In this embodiment, the sensor arrangement 130 comprises a plurality of optical sensors, i.e. three optical pressure sensors 10a, 10b, 10c arranged along a length L of a distal end portion 103 near the distal tip 120, for measuring pressure concurrently at each sensor location. Each of the optical pressure sensors is attached and optically coupled to a sensor end (i.e. a distal end) of a respective individual optical fiber 11. That is each optical fiber carries an individual sensor, e.g. bonded to the sensor end of the fiber or integrally formed therewith. Optionally, another type of optical sensor, e.g. an optical flow sensor 20 as mentioned above, may be provided in or near the distal end portion 103, and coupled to another respective optical fiber 11.
For example, for measuring a transaortic pressure gradient, the optical pressure sensors 10a, 10b, 10c are arranged spaced apart by distances L1 and L2, e.g. 20 mm and 50 mm to 60 mm respectively, for placement of the sensors upstream and downstream of the aortic valve. Optionally, a flow sensor 20 (see
Accordingly, in this embodiment, the two more distal sensors 10a and 10b are spaced apart by a distance L1 and sensors 10b and 10c are spaced apart by a distance L2, where L2>L1. The dimensions and pitch/angle of the helical grooves 32 in the surface of the core wire 31 are selected to provide a space or channel between the grooved surface of the core wire 31 and coil 35. Each groove is deep enough that the fiber sits within the groove. Preferably, the grooves are sized so that the optical sensors 10a and 10b and the optical fibers 11 do not protrude beyond the external diameter Dcore of the core wire 31. Each sensor and optical fiber may be fixed to the core wire, e.g. adhesively fixed to the core wire, at one or more points. For example, during assembly, optical fibers 11 are inserted into the grooves 32 and held in place in the grooves 32 in the core wire 31, e.g. with a suitable biocompatible and hemo-compatible adhesive, before the core wire is inserted into the coil wire 35. To accommodate the sensors 10a, 10b, 10c and 20, which may be larger in diameter than the optical fibers 11 themselves, if required, each groove 32 may be enlarged to form a cavity or recess 34 in the region where the sensor is located, i.e. at each sensor location. As shown schematically in
As shown in
Since the outer coil of the guidewire is quite flexible, the stiffness of the guidewire is determined predominantly by the stiffness of the core wire. Also, the optical fibers do not contribute significantly to the stiffness of the guidewire. For superior stiffness, which is required for a support guidewire of a given outside diameter, e.g. 0.89 mm, the outside diameter core wire is preferably as large as can be reasonably be accommodated within the inside diameter of the outer coil of the guidewire, allowing for the required clearance between the core wire and the outer flexible coil. Accordingly, the helical grooves 32 in the core wire preferably have a minimal size to accommodate the optical fibers and sensors within the grooves and within the diameter Dcore of the core wire. In this context, by convention, the wire gauge or diameter D of a wire refers to the diameter D of the circle into which the wire will fit. It will be appreciated that the maximum diameter Dcore must also fit within the inside diameter of the outer flexible coil of the guidewire, with an appropriate clearance between the core wire and optical fibers and sensors and the coil, which is, for example, at least 1 mil or 25 microns.
The helical form of the grooves 32 reduces longitudinal and point stresses/strains in the individual fibers when the guidewire is flexed. For example, if the grooves were straight along the length of the fiber, when the guidewire is flexed, optical fibers on the inside curve of the bend would be subject to more compressive forces and fibers on the outside of the curve would be subject to more tensile forces. While the ends of the fibers and the sensors may be adhesively fixed to the core wire within the grooves 32, and/or at one or more intermediate points, when the guidewire is flexed, the helical structure of the grooves tends to spread compressive and tensile forces over a length of each fiber and reduces localized stresses and strains. Thus it is preferably that the fibers have some freedom to move or slide within the grooves. Desirably, to optimize the core wire stiffness relative to the outside diameter of the guidewire, i.e. the diameter of the outer coil, there is a minimal required spacing between the core wire 31 and the coil 35, and therefore, preferably, the helical grooves are at least deep enough to accommodate the optical fibers and sensors without protruding beyond the diameter Dcore of the core wire, as illustrated in the schematic cross-sectional view shown in
The stiffness of a guidewire may be quantified by a flexural modulus, e.g. as described in an article by G. J. Harrison et al., entitled “Guidewire Stiffness: What's in a Name?” J. Endovasc. Ther. 2011, pp. 797-801. As an example, for, a stainless steel coil and core wire providing a guidewire having an outside diameter of 0.89 mm (0.035 inch), a TAVI guidewire desirably provides a flexural modulus of at least 60 GPa or 65 GPa. That would be similar to that of an Amplatz Super Stiff™ or Ultra Stiff™ guidewires (0.89 mm or 0.035 inch) which were reported in the above referenced article to have a flexural modulus of 60 GPa and 65 GPa, respectively. For some procedures, the operator may require or prefer a guidewire in the range 60 GPa±10%, or alternatively may require a significantly stiffer guidewire. For some procedures, e.g. a multisensor guidewire for diagnostic measurements only, a more flexible guidewire may be preferred.
The structure of the multisensor assembly is shown in cross-section along its length from the connector 112 to the distal tip 120 in
The optical pressure sensors 10a, 10b and 10c are preferably Fabry-Pérot Micro-Opto-Mechanical-Systems (FP MOMS) pressure sensors. As an example, a suitable commercially available FP MOMS pressure sensor is the Fiso FOP-M260. These FP MOMS sensors meet specifications for an appropriate pressure range and sensitivity for blood pressure measurements. They have an outside diameter of 0.260 mm (260 μm). Typically, they would be coupled to an optical fiber with an outside diameter of 0.100 mm (100 μm) to 0.155 mm (155 μm). Accordingly, for 0.155 mm optical fibers, the helical grooves would have a depth of 0.155 mm along their length with an enlarged depth of 0.260 mm at each sensor location, plus any required clearances between the core wire and outer coil and around the fibers and the sensors. The pitch of the helical grooves is, for example, about 25 mm (1 inch) or more to reduce stress on the optical fibers.
As illustrated schematically in
The helical grooves 32 will somewhat reduce the stiffness of the core wire relative to a conventional cylindrical core wire of the same outer diameter, but the grooved core wire structure accommodates multiple optical fibers and sensors while optimizing the stiffness for a given multisensor guidewire of a particular diameter. For example, as illustrated schematically in
By comparison, to accommodate a plurality of similarly sized optical fibers and sensors in a cylindrical space between a conventional core wire and the outer coil, the core wire diameter would have to be reduced to about 0.5 mm to accommodate the fibers, and even further reduced in the sensor locations to accommodate the sensors. Since the stiffness of a round core wire varies as the fourth power of the diameter, such a reduction in the core wire diameter significantly reduces the stiffness of the guidewire. While the helical grooves in the core wire 31 will somewhat reduce the stiffness of the core wire, they will do so by a far less significant factor than using a smaller diameter conventional core wire having a circular cross-section of 0.5 mm.
When helical grooves are provided to accommodate the fibers and the optical sensors, the pitch of the helix may be 25 mm (1 inch) or more, for example, to avoid excessive bending or stress/strain on the optical fibers. In alternative embodiments (not illustrated) the grooves in the guidewire run straight along the length of the guidewire, or run helically with a larger pitch. The feasibility of using helical grooves with a smaller pitch may be limited by optical fiber characteristics, such as acceptable optical fiber bend radius.
The multisensor support guidewire apparatus 100 is preferably also capable of measuring blood flow, since quantification of blood flow restriction is related to the pressure difference/gradient and the blood flow velocity. Thus, optionally, it includes an integral fiber-optic flow sensor 20 (see
The guidewire coil 35 together with the mandrel or core wire 31 provide the torquable characteristics of the multisensor support guidewire 100 so that is capable of being shaped or flexed to traverse vascular regions in a manner similar to that a conventional support guidewire. To facilitate insertion, the distal tip 120 extends beyond the distal end portion 103 containing the pressure sensors 10a, 10b, 10c and optional flow sensor 20, and the tip 120 may be a flexible pre-formed J-tip or other appropriate atraumatic tip such as a resiliently deformable or flexible curved tip which is preformed or can be manually shaped. Typically the tip is contiguous with the guidewire. That is, the fine wire coil 35 extends along the length of the tip to a rounded end, and the core wire 31 is thinned within the tip to increase the flexibility of the tip relative to the main part of the support guidewire 102. The tip 120 may comprise a coating that can be pre-formed into a desired curved shape, e.g. a thermoplastic coating that can be thermoformed into a desire shape. Preferably, the core wire 31 has a maximum possible diameter within the coil 35 within distal end portion 103 that contains the sensors (e.g. see
For operation of the optical sensors, the micro-coupler 140 couples the distal part 102 forming the multisensor guidewire to the proximal part 101 which provides optical coupling to the control unit 151 for controlling operation of the optical sensors 10 and 20. The proximal part 101 simply provides a flexible optical coupling of the distal part of the guidewire 102 to the control unit 151. Thus, the proximal part 101 can have any suitable diameter and flexibility. It is not required to have guidewire elements, i.e. a coil 35 and core wire 31 to provide specific mechanical properties of a guidewire, such as such as the stiffness and torque characteristics. Thus, the proximal part may be more similar to a lower cost optical fiber cable, e.g. a bundle of plurality of optical fibers 13 enclosed within a tubular covering layer 51, such as a single layer or multilayer flexible polymer tubing. If required, it is protected by a thicker protective outer jacket or sleeve 52 for mechanical strength/reinforcement and to facilitate handling. The optical fibers 13 in the proximal part are optically coupled to connector 112 at the proximal end 110 and to the micro-optical coupler 140 at the distal end.
The optical fibers 11 in the distal part 102 reduce the cross-sectional area of the core wire 31, therefore reducing stiffness of the guidewire 102. It will be appreciated that the use of specialized higher cost optical fibers 11 with a smaller diameter, e.g. 0.100 mm or less, and correspondingly sized smaller grooves, improves the stiffness of the core wire, and therefore the stiffness of the guidewire 102. On the other hand, to reduce overall cost, in the proximal part 101, standard lower cost optical fibers 13 with a larger diameter can be used, e.g. 0.155 mm diameter optical fibers used for telecommunication.
A multisensor guidewire 200 of a second embodiment is illustrated in
Referring back to
As illustrated in the schematic cross-section shown in
As illustrated in
As shown in
For simplicity of illustration, the sensors 10a, 10b and 20 are shown in
The proximal part 101 of the apparatus 200 provides for optical coupling of the distal part 102 to the control unit 151 (e.g. see
As illustrated schematically in the enlarged longitudinal cross-sectional view in
During assembly, the fibers and sensors are affixed to the core wire to form a sub-assembly, which is then inserted into the flexible outer coil. For example, the fibers are secured to the surface of the core wire at a point adjacent each sensor, e.g. with a spot of adhesive within the groove, so that sensors are positioned at sensor locations with the required spacings, and/or so that each sensor is held within the sensor cavity of its groove. Since the grooves are helical, the optical fibers are wound around the core wire, so that the optical fibers are inserted into their respective groove around the core wire, and the proximal ends of the fibers are secured at the proximal end of the core wire. The sub-assembly of the core wire, sensors and their optical fibers is then inserted into the coil.
For protection of the sensors during assembly, it may be preferred to insert the sub-assembly from the distal end of the coil and subsequently form the optical connector at the proximal end, and then complete the distal tip. On the other hand, when the optical connector is pre-formed at the proximal end of the sub-assembly before insertion, the sensor end of the sub-assembly is inserted into the coil from proximal end of the coil. In either case, it is preferable that the guidewire components have rounded edges, i.e. to avoid sharp edges of the coil wire or core wire so that the subassembly with the sensors and optical fibers can slide smoothly into the outer coil without catching on sharp edges, to avoid mechanical damage to the sensors or optical fibers. For this reason, it is also preferable that the grooves are sufficiently deep that the fibers and sensors are protected within the grooves during assembly. For assembly, it may also be beneficial if the fibers are further secured, at least temporarily, in their grooves at multiple points along the length of the groove. However, in use of the multisensor guidewire, it is preferable that the fibers are fixed to the core wire adjacent the sensors but otherwise the fibers have some freedom to move or slide within the grooves when the guidewire is flexed.
If required, a marker, such as a radiopaque marker 14 is provided near each sensor, e.g. within the groove or cavity, to assist in locating and positioning the sensors in use, i.e. using conventional radio-imaging techniques, as described for the first embodiment. Apertures or openings in the coil wire adjacent the optical pressure sensors provide for fluid contact with the sensors. As mentioned for the first embodiment, if required, the outer coil of guidewire may have a coating of a suitable biocompatible coating, which may be, for example, a hydrophobic coating such as PTFE or silicone, or a hydrophilic coating. In some instances a hydrophilic distal tip may be preferred.
The spacings of the sensor locations are arranged for placement of a sensor each side, i.e. upstream and downstream, of a heart valve. As an example, for measuring a transaortic pressure gradient, the optical pressure sensors 10a, 10b, 10c are arranged spaced apart by distances L1 and L2, e.g. 20 mm and 60 mm respectively, for placement of the sensors upstream and downstream of the aortic valve. The flow sensor 20 (see
The dimensions of the grooves 32 in the surface of the core wire 131 are selected to accommodate the fibers 11 in between the core wire 131 and coil 35. The grooves 32 are sized so that the optical pressure sensors 10a, 10b and 20 and the optical fibers 11 do not protrude beyond the external diameter Dcore of the core wire 131 (see
Advantageously, each optical fiber and its respective optical sensor are accommodated within an individual groove within the diameter Dcore of the core wire to provide protection to the optical fibers and sensors during assembly and use. To facilitate fabrication, this enables the optical fibers carrying the optical sensors to be fixed to the core wire, e.g. by adhesively bonding the fibers to the surface of the core wire within a respective groove, to form an assembly of the core wire and the plurality of optical fibers and optical sensors, with the optical sensors appropriately spaced apart and positioned at the required sensor locations. Then, the assembly of the core wire, fibers and optical sensors can be inserted into the outer flexible coil. In preferred embodiments, the outer coil of the guidewire is fabricated from round coil wire, and all edges and surfaces of the grooves of the core wire and other components are radiused to avoid sharp edges that may catch on or damage the fibers and sensors during assembly.
Optical Micro-Coupler
The multisensor guidewire 100 of the first embodiment comprises a separable micro-optical coupler so that the distal part 102 comprising the multisensor support guidewire is separable from the proximal part 101 that provides an optical coupling to the control system. This arrangement enables proximal mounting of over-the-guidewire components, e.g. mounting of a replacement heart valve on the guidewire from the proximal end of the distal part 102 of the guidewire, in a manner similar to that used with a conventional support guidewire (i.e. without sensors).
That is, during known valve replacement procedures, such as TAVI, using a conventional support guidewire (i.e. without sensors), replacement valve components are mounted on the guidewire from the proximal end. For example, a support guidewire for TAVI is typically about 2.6 m to 3.0 m long and thus provides extra length at its proximal end to mount the valve components and delivery system on the guidewire. When the distal portion of the guidewire is initially introduced intravascularly into the patient, the extra proximal length of the guidewire holds the valve components and delivery system until the cardiologist is ready to introduce the replacement valve. However, since the optical multisensor guidewire must be optically coupled to the control system, if the distal part of the sensor guidewire is fixed to the larger diameter proximal part of the sensor guidewire, which carries the optical input/output connector for coupling to the control system, proximal mounting of components on the sensor guidewire is not possible.
For ease of manufacturing, ease of use, and user acceptance, it is advantageous if embodiments of the optical multisensor guidewire, as disclosed herein, can be manufactured and used in a manner that is similar to that for a conventional support guidewire. That is, it has an exterior form and characteristics, such as torque characteristics, similar to a conventionally structured support guidewire with which the medical staff is familiar, and which provides for proximal mounting of components over the wire in the usual manner. Accordingly, it is desirable to have a multisensor guidewire with separable distal and proximal parts that are coupled with a micro-optical coupler, such as described for the multisensor guidewire of first embodiment.
The micro-coupler 140 of the first embodiment will now be described in more detail with reference to
Notably, the micro-coupler 140 provides for disengagement of the distal part 102 from the proximal part 101 of the guidewire. Moreover, the male part 142 has the same outside diameter D as the coil 35 of the multisensor guidewire. Thus, the distal part 102 functions as a conventional support guidewire, in that, components such as a replacement valve and delivery system, or other components, can be mounted on/over the guidewire from the proximal end for guiding and delivery into the heart.
The female part 144 of the micro-connector 140 may have an outer hub 44 of larger diameter to facilitate handling, alignment and connection of the micro-coupler 140.
The connector 140 enables the distal part 102 of the sensor guidewire to be unlocked from the proximal part 101, i.e. to untether the distal part 102 of the apparatus from the control console (control unit 151). Then TVT components can be inserted over the male part of the micro-coupler at the proximal end of the multisensor guidewire 102. Then the distal part 102 of the sensor guidewire is recoupled to the control console by proximal part 101, and the connector is locked so that the distal part 102 is again optically coupled to the control system for making pressure and flow measurements. The micro-coupler 140 therefore provides for proximal mounting, as is conventional, for components for transcatheter valve repair, such as, balloon catheters for valvuloplasty, and the multisensor guidewire additionally enables measurements of blood pressure, concurrently at multiple locations, and optionally also flow measurements, e.g. before and/or during and/or after a the valve repair procedure.
For multisensor support guidewires of embodiments comprising a separable optical micro-coupler, heart valve replacement or repair components, such as, a replacement heart valve and delivery device for TAVI, may be mounted over the multisensor guidewire from its proximal end. The multisensor guidewire has a standard length of a support guidewire, e.g. around 2.6 m.
Typically, a patient is evaluated some time (e.g. days or weeks) prior to valve replacement or repair (minimally invasive or open heart procedures), to determine whether valve repair or replacement is necessary or appropriate. Where diagnostic measurements of transvalvular blood pressure gradient and flow, and other parameters, have been performed previously, and confirm need for valve replacement, the valve components may be pre-mounted on the multisensor support guidewire ready to perform a transcatheter valve replacement procedure in a conventional manner. The multisensor guidewire can additionally provide data for blood pressure measurements at multiple locations, and/or flow measurements at any time before, during or after the procedure, or continuously during the procedure.
Optionally, it is envisaged that the multisensor guidewire would be introduced initially for diagnostic measurements of a transvalvular pressure gradient and blood flow. If, for example, measurements confirm the need for an immediate valve replacement or repair, the micro-coupler is separated to enable proximal mounting of components over the guidewire, e.g. for further assessment, or for delivery of a replacement heart valve or repair components. The micro-coupler is then reconnected to enable similar diagnostic measurements of the transvalvular pressure gradient and blood flow to be made before or after the procedure, or continuously prior to the procedure, during the procedure, and for a monitoring period afterwards.
For multisensor guidewires of some embodiments, for example, as illustrated in
Conventionally, a typical length of standard guidewire is around 1.8 m. A support guidewire for transcatheter valve replacement is not only stiffer to hold the components firmly during delivery of the replacement valve, it has additional length, e.g. a total length of approximately 2.8 m. Thus, when the distal part of the guidewire is initially inserted into the patient, the additional length at the proximal end holds the heart valve components until the cardiologist is ready to deliver and insert the valve.
For the multisensor support guidewire 100 illustrated in
Referring to
For example, a sensor spacing of about 20 mm to 50 mm would be sufficient to place one sensor upstream and one downstream of a heart valve. However, blood pressure measurements may be affected by significant turbulence in the blood flow through the cardiac cycle. For this reason, a larger spacing, e.g. 70 mm to 80 mm, between the two sensor locations may be preferred to enable one sensor to be located further into the ventricle and another sensor to be located further upstream of the valve in the aorta, so that both sensors are located in regions of less turbulent flow, i.e. spaced some distance each side of the valve. Based on review of CT scans to assess dimensions of the heart of a number of subjects, an 80 mm spacing of two pressure sensors may be preferred. For paediatric use, a closer spacing of the sensors may be preferred.
For comparison,
In practice, it is desirable that a multisensor guidewire provides a plurality of optical pressure sensors, e.g. two or three pressure sensors, and optionally a flow sensor, that are optimally spaced for measurement of transvalvular pressure gradients and flow for any one of the four heart valves. For example, while multisensor guidewires may be individually customized for different TVT procedures, or, for example, smaller sized versions may be provided for paediatric use, it is preferred to have a standard arrangement, e.g., two, three or four sensors, which is suitable for various diagnostic measurements and for use during various TVT procedures.
Transvalvular Pressure Measurements in Interventional Cardiology
By way of example only, the use of a multisensor guidewire for transvalvular pressure measurement will be described with reference to the multisensor guidewire 100 of the first embodiment, and with reference to the aortic valve. For measuring and monitoring the blood pressure gradient across the aortic valve 511, i.e. the aortic transvalvular pressure gradient in a human heart 500 (see
The function of the heart is to move de-oxygenated blood from the veins to the lungs and oxygenated blood from the lungs to the body via the arteries. The right side of the heart collects de-oxygenated blood in the right atrium 521 from large peripheral veins, such as, the inferior vena cavae 520. From the right atrium 521 the blood moves through the tricuspid valve 522 into the right ventricle 523. The right ventricle 523 pumps the de-oxygenated blood into the lungs via the pulmonary artery 525. Meanwhile, the left side of the heart collects oxygenated blood from the lungs into the left atrium 514. From the left atrium 514 the blood moves through the mitral valve 513 into the left ventricle 512. The left ventricle 512 then pumps the oxygenated blood out to the body through the aorta 510.
Throughout the cardiac cycle, blood pressure increases and decreases into the aortic root 510 and left ventricle 512, for example, as illustrated by the pressure curves 630 and 640, respectively, in
The left heart without lesions, illustrated in
The cardiac hemodynamic data collected from a patient's heart allow a clinician to assess the physiological significance of stenosic lesions. The aortic and ventricular pressure curves from a patient's heart are compared with expected pressure curves.
The medical reference literature relating to cardiac catheterization and hemodynamics provides different possible variations of the aortic 630 and ventricular 640 pressure curves along with the possible causes in order to identify the proper medical diagnosis. For example, cardiac hemodynamic curves, such as shown in
As indicated, when the valve is closed as shown in
However, as illustrated schematically in
Importantly, the specific positioning of the multiple sensors enables measurements that permit the determination of whether the stenosis is strictly associated with the valve or not, and whether it is associated with a subvalvular stenosis (e.g. sub-aortic hypertrophic stenosis) or supravalvular stenosis. It also enables measurements that permit the determination of the functional severity of subvalvular stenosis.
Manufacturability
During prototyping, a number of challenges have been discovered in attempting to accommodate a plurality of optical sensors and optical fibers within a multisensor support guidewire having a required stiffness e.g. 60 GPa, and a sufficiently small outside diameter ≦1 mm, and typically 0.89 mm or 0.035 inch, for use in TVR, including TAVI. Until smaller diameter optical sensors and optical fibers are developed and characterized, a design of core wire is required to accommodate multiple fibers and sensors without unduly reducing the stiffness of the core wire.
In considering manufacturing tolerances for the optical components and for the guidewire coil and core wire, it has also been discovered that there are currently significant manufacturing challenges in providing multisensor guidewires of diameter ≦1 mm comprising a grooved core wire which accommodates multiple optical fibers and optical sensors.
Conventionally, core wires are circular in cross-section and manufactured by standard wire-drawing and/or wire-rolling processes, e.g., from suitable metals and alloys, usually medical grade stainless steel, or nitinol, to provide the required mechanical properties, e.g., stiffness, flexibility, tensile strength. Thus, conventionally, small diameter round core wires with sufficient stiffness for support guidewires are manufactured by drawing (pulling) a wire through successively smaller dies.
Manufacturing a sub-millimeter diameter core wire with straight or helical grooves along its length to accommodate individual optical fibers of approximately 100 μm diameter, presents challenges for conventional core wire manufacturing facilities.
Since medical guidewires are intended to be disposable, i.e. for single-use only, an alternative or lower cost manufacturing solution is desirable. However, for medical applications, it will also be appreciated that manufacturing facilities must also be capable of meeting required regulatory standards for medical devices. It also desirable to use materials, e.g., metals and alloys, such as medical grade stainless steel, which already have regulatory approval for medical use and for which extensive manufacturing experience is already available. It is envisaged that alternative materials, such as suitable polymer and composite materials could potentially be used for manufacture of core wires, e.g. if they provide appropriate stiffness and mechanical properties. However, conventional medical grade metals and alloys, that already have regulatory approval for medical use, are preferred.
During initial prototyping, the Applicant encountered several manufacturing challenges that had to be overcome in order to manufacture grooved stainless steel core wires of the required size and tolerances by known wire drawing processes, particularly with respect to forming a plurality of small grooves to accommodate individual fibers, and controlling rotation of grooves along the length of the wire, e.g. to form helical grooves of a pre-defined pitch.
For manufacturing reasons, a core wire having a single channel or groove accommodating multiple fibers was proposed the above referenced U.S. Provisional patent application No. 62/039,952, entitled “System And Apparatus Comprising a Multisensor Support Guidewire for Use in Trans-Catheter Heart Valve Therapies”, filed Aug. 21, 2014. For example, a core wire was disclosed having a D-shape cross-section or a contoured/scalloped groove for three fibers. However, a core wire with single groove containing multiple fibers along one side of the core wire is not optimum for providing rotationally symmetric torque characteristics. It was also discovered that, this structure did not effectively protect the optical fibers and sensors from damage during assembly since the optical components are exposed and tend to be dislodged, or catch on inner surfaces of the coil, during insertion of the core wire/optical fiber assembly into the coil, leading to damage of the optical components.
Accordingly, as disclosed herein, for an optical multisensor guidewire, beneficially the core wire has a plurality of grooves, spaced with rotational symmetry around the core wire, wherein each groove accommodates an individual optical fiber and its optical sensor. The grooves preferably have some rotation around the core wire, i.e. are helical, and are deep enough to accommodate the optical fibers within the diameter of the core wire, for protection of the optical fibers and sensors from mechanical damage during assembly and in use.
To facilitate manufacturing, it is desirable that the grooved core wire has a cross-sectional profile that can be formed by a wire-drawing process, i.e. similar to the processes currently used in manufacturing conventional round core wires for medical guidewires. The wire-drawing process may use high precision diamond wire drawing dies, as manufactured by Fort Wayne Wire Die, Inc. For example, surfaces of the core wire defining the grooves are radiused with at least a minimum radius for formation of the core wire by wire-drawing.
In embodiments described above, the outer flexible tubular member 35 of the guide wire, which is referred to as the outer flexible coil, or “coil”, is disclosed as a being wound from a coil of fine metal wire, i.e. a round or rectangular wire as illustrated in
It is envisaged that in the future, a technique such as laser cutting may potentially be used for formation of the grooved core-wire.
During assembly, the optical fibers and sensors are assembled and secured to the core wire, e.g. adhesively bonded, at least at one point near each sensor. Then, the sensor assembly, comprising the optical fibers and sensors secured to the core wire, is inserted into the outer coil. It is desirable to protect the optical fibers and sensors during assembly, and for this reason, it is preferred to provide an individual groove for each optical fiber and sensor, and for the groove structure to be sufficiently deep to entirely accommodate the fiber and the sensor within the diameter Dcore of the core wire. As mentioned above, it is also desirable to avoid sharp edges, and provide all components, including the coil wire and the core wire, with rounded edges to facilitate assembly, i.e. that the sub-assembly can slide smoothly into the coil, without catching on sharp edges, and also to protect the sensors and optical fibers from damage when the guidewire is flexed during use. Also, as explained above, it is preferable that the cross-sectional shape of core wire has at least three-fold rotational symmetry, and that the grooves have some rotation around the core wire, preferably extending helically around the core wire, for improved torque characteristics of the guidewire, and to distribute stresses/strains on the fibers when the guidewire is flexed.
Other factors for consideration are: regulatory requirements for medical devices, ease of use and safety. For these reasons, it is desirable that the multisensor guide wire is based on a conventional tried and tested external guidewire structure, i.e. based on a predicate device structure comprising an external flexible coil and core wire, which has regulatory approval and which is fabricated with materials, such as 304V stainless steel or nitinol, that already have regulatory approval for medical use in guidewires. It is also desirable that the multisensor guidewire can incorporate known safety features of conventional guidewires. For example, they are fabricated from materials having high tensile tensile strength to minimize the likelihood of stretching or fracturing, and typically include a structure such as a safety ribbon, which extends along its length and is welded to both ends of the guidewire to reduce the risk of separation of fragments in case of fracture.
As mentioned above, the grooved core wire structure also protects the optical fibers and sensors from mechanical damage during assembly and use. When each optical sensor sits fully within its groove in the core wire, or within an enlarged portion of the groove at the sensor location, the grooved core wire structure helps to reduce the risk of breakage or separation of the optical components in use. Also, each fiber is preferably adhesively bonded or otherwise secured to the core wire in the groove adjacent the respective optical sensor. This ensures the sensors are appropriated positioned and fixed in the sensor locations, i.e. at the required sensor spacing as well as retained within the groove to protect them from damage. When the sensors are bonded to the ends of the fibers, rather than integrally formed at the end of the fiber, if required, some additional adhesive or encapsulation material may be provided in the groove to protect and strengthen the junction/bond region between the fiber and sensor, e.g. to reduce risk of separation of the sensor from the fiber. For similar reasons, apertures in the coil wire adjacent the optical pressure sensor should be large enough to enable fluid contact for accurate sensing of blood pressure, but preferably, the apertures are sized to ensure that if an optical sensor were to separate, it would be captured and retained within the coil wire.
As mentioned above, a helical groove structure also helps to spread stresses and strains on the optical fibers along their length when the guidewire is flexed in use. For this reason, it may be preferred to fix the optical fibers only at ends of the guidewire, e.g. a spot of adhesive or encapsulant near sensor locations and another spot at the proximal end near the input/output connector. Each fiber then has some freedom to move or slide within its groove as the guidewire is flexed. This arrangement provides for the optical sensors to be secured in their respective sensor locations, at predetermined sensor spacings, so that pressure gradients can be accurately obtained.
Contact Force Sensor
Beneficially, for use in TVR, the multisensor guidewire 100 is also capable of measuring a contact force of the guidewire against the wall of the heart, e.g. the wall of a diseased left ventricle. Thus, a guidewire according to another embodiment comprises an integral fiber-optic contact force sensor 60 as illustrated schematically in
Thus, for example, the guidewire 100 may comprises three optical pressure sensors 10a, 10b, 10c as described above with reference to
Flexible Preformed Three-Dimensional Curved Tip
To assist in atraumatic insertion and anchoring of the guidewire 100 within the ventricle during TVR, it is desirable to use a flexible preformed tip such as a J-tip or other curved tip.
It will be appreciated that in alternative embodiments or variants of the multisensor guidewires of the embodiments described in detail above, one or more features disclosed herein may be combined in different combinations or with one or more other features disclosed herein and in the related patent applications referenced herein, depending on whether the multisensor guidewire is to be used as a multisensor support guidewire for transcatheter valve replacement, requiring a guidewire with high stiffness, or, as a multisensor guidewire for other TVT procedures where a more flexible multisensor guidewire is preferred.
In preferred embodiments, the multisensor guidewire comprises a core wire having multiple helical grooves along its length to accommodate a plurality of three or four optical sensors and optical fibers within a required maximum core wire diameter Dcore. For support guidewires for TVR, the guidewire can then be provided with the required stiffness, e.g. a flexural modulus of ˜60 GPa, in a guidewire having a diameter of ≦0.89 mm external diameter. Preferably the grooves are symmetrically arranged around the core wire and extend helically along the length of the core wire for rotationally symmetric stiffness and torque characteristics.
Additionally, for valve replacement, since the guidewire must be firmly anchored within the ventricle for accurate measurements and for positioning of a replacement valve, an optional three-dimensional pre-formed curved tip, such as a pre-formed “snail” tip, assists in positioning and anchoring the distal end of the multisensor guidewire in the ventricle during TAVI.
Furthermore, an optional contact force sensor near the tip provides important feedback to the interventional cardiologist relating to the force being applied or transferred internally to tissues of the heart wall. Feedback to the cardiologist to indicate when a contact force exceeds a threshold level, together with a specially shaped pre-formed flexible tip, assists in reducing trauma to the tissues of the heart, and in particular reduces risk of perforation the ventricular wall.
In a multisensor guidewire for percutaneous, minimally invasive intravascular procedures other than transcatheter valve replacement, which do not need the high stiffness of a conventional support guidewire, a more flexible multisensor guidewire may be desirable. For example, for initial diagnostic measurements within the heart, including transvalvular blood pressure measurements, a smaller diameter and/or more flexible and/or shorter multisensor guidewire may be appropriate. As an example, the latter may also be applicable for percutaneous, minimally invasive intravascular procedures such as diagnostic measurements requiring concurrent pressure measurements at multiple locations within smaller blood vessels, or within the coronary arteries for assessment of stenotic lesions.
Thus, the interventional cardiologist is offered multisensor guidewires according to various embodiments, which can be configured for intravascular diagnostic measurements and/or as a support guidewire for transcatheter valve replacement procedures, including TAVI. Options including a contact force sensor and a three dimensional atraumatic tip help to avoid trauma or perforations.
Currently, patient mortality rate after TAVI is significant, with some studies reporting mortality in a range of 10%-15%. As shown by a growing number of studies, interventional cardiologists need accurate data, i.e. measurements of cardiovascular parameters to assess the functional performance of a patient's heart valves before and after TAVI, to obtain a better understanding of the issues and to find solutions to reduce mortality and reduce the need for re-intervention after TAVI.
Systems and apparatus according to embodiments of the invention comprise multisensor support guidewires for use in transcatheter valve replacements, such as TAVI. These Smart Guidewires™ not only have the required mechanical characteristics to act as support guidewires for transcatheter valve replacements, they comprise sensors for making direct (in-situ) measurements of important parameters, including measurement of blood pressure concurrently at multiple locations within the heart, to obtain a transvalvular blood pressure gradient and optionally also measure blood flow, for evaluation of performance of the heart and the heart valves immediately before and after transcatheter valve replacement. A single-use disposable guidewire integrating multiple optical sensors allows for quickly providing real-time accurate quantitative data related to functional performance of heart valves right before and after TVT.
Although embodiments of the invention have been described and illustrated in detail, it is to be clearly understood that the same is by way of illustration and example only and not to be taken by way of limitation, the scope of the present invention being limited only by the appended claims.
This application is a Continuation-in-Part of PCT International Application No. PCT/IB2015/055240, entitled “System and Apparatus Comprising a Multisensor Guidewire for Use in Interventional Cardiology”, filed Jul. 10, 2015, designating the United States, and claiming priority from U.S. Provisional patent application No. 62/023,891, entitled “System And Apparatus Comprising a Multisensor Support Guidewire for Use in Trans-Catheter Heart Valve Therapies”, filed Jul. 13, 2014 and from U.S. Provisional patent application No. 62/039,952, entitled “System And Apparatus Comprising a Multisensor Support Guidewire for Use in Trans-Catheter Heart Valve Therapies”, filed Aug. 21, 2014; all said applications are incorporated herein by reference in their entirety. This application is related to U.S. patent application Ser. No. 14/354,624 which is a national stage entry of PCT International Application No. PCT/IB2012/055893, entitled “Apparatus, system and methods for measuring a blood pressure gradient”, filed Oct. 26, 2012, which claims priority from U.S. Provisional patent application No. 61/552,778 entitled “Apparatus, system and methods for measuring a blood pressure gradient”, filed Oct. 28, 2011 and from U.S. Provisional patent application No. 61/552,787 entitled “Fluid temperature and flow sensor apparatus and system for cardiovascular and other medical applications”, filed Oct. 28, 2011, all of which are incorporated herein by reference, in their entirety.
| Number | Date | Country | |
|---|---|---|---|
| 62023891 | Jul 2014 | US | |
| 62039952 | Aug 2014 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/IB2015/055240 | Jul 2015 | US |
| Child | 15001347 | US |
