U.S. patent application number 15/001347 was filed with the patent office on 2016-05-12 for system and apparatus comprising a multisensor guidewire for use in interventional cardiology.
The applicant listed for this patent is THREE RIVERS CARDIOVASCULAR SYSTEMS INC.. Invention is credited to Luc Bilodeau, Eric Caron.
Application Number | 20160128583 15/001347 |
Document ID | / |
Family ID | 55077962 |
Filed Date | 2016-05-12 |
United States Patent
Application |
20160128583 |
Kind Code |
A1 |
Caron; Eric ; et
al. |
May 12, 2016 |
SYSTEM AND APPARATUS COMPRISING A MULTISENSOR GUIDEWIRE FOR USE IN
INTERVENTIONAL CARDIOLOGY
Abstract
A system and apparatus comprising a multisensor guidewire for
use in interventional cardiology, e.g. for Transcatheter Valve
Therapies (TVT), comprises a plurality of optical sensors for
direct measurement of cardiovascular parameters, e.g. transvalvular
blood pressure gradients and flow. A conventional outer coil
contains a shaped core wire having a cross-section defining helical
grooves extending along its length, which accommodate optical
fibers and optical sensors within a diameter D.sub.core of the core
wire. Advantageously, the diameter and material of the core wire
provides the guidewire with sufficient stiffness for use as a
support guidewire for valve replacement, e.g. Transcatheter Aortic
Valve Implantation (TAVI), while accommodating multiple sensors and
optical fibers within a guidewire of outside diameter .ltoreq.0.89
mm. An optical connector couples the guidewire to a control system.
Optionally, the guidewire includes a contact force sensor; a
pre-formed tip; and/or a separable micro-connector for proximal
mounting of over-the-guidewire components.
Inventors: |
Caron; Eric; (Toronto,
CA) ; Bilodeau; Luc; (US) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
THREE RIVERS CARDIOVASCULAR SYSTEMS INC. |
Toronto |
|
CA |
|
|
Family ID: |
55077962 |
Appl. No.: |
15/001347 |
Filed: |
January 20, 2016 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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PCT/IB2015/055240 |
Jul 10, 2015 |
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15001347 |
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62023891 |
Jul 13, 2014 |
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62039952 |
Aug 21, 2014 |
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Current U.S.
Class: |
600/486 |
Current CPC
Class: |
A61B 2562/228 20130101;
A61F 2/2427 20130101; A61F 2/24 20130101; A61F 2/2418 20130101;
A61B 2560/0462 20130101; A61B 5/6851 20130101; A61B 5/02154
20130101; A61B 2560/066 20130101; A61B 5/02158 20130101; A61B 5/042
20130101 |
International
Class: |
A61B 5/0215 20060101
A61B005/0215 |
Claims
1. 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 a flexible coil (coil), the coil having a
length extending between a proximal end and a distal end, an
outside diameter of .ltoreq.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 D.sub.core 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.
2. The multisensor guidewire of claim 1, wherein the plurality of
grooves are symmetrically spaced around the core wire.
3. The multisensor guidewire of claim 2, wherein the grooves are
helical grooves.
4. The multisensor guidewire of claim 3, wherein the helical
grooves have a pitch of at least 25 mm (1 inch).
5. The multisensor guidewire claim 1, wherein the grooves have a
depth that accommodates each optical fiber and optical sensor
within a respective groove of the core wire without protruding
beyond the diameter D.sub.core of the core wire.
6. The multisensor guidewire of claim 5, wherein, at sensor
positions in the distal end portion, the grooves are enlarged to
accommodate optical sensors having an external diameter greater
than that of the optical fibers.
7. The multisensor guidewire of claim 1, wherein surfaces of the
core wire defining the grooves are radiused to no less than a
minimum radius R.sub.min for formation of the grooves by a
wire-drawing process.
8. The multisensor guidewire of claim 1, wherein each optical fiber
is adhesively bonded to the core wire within its respective groove
at a point adjacent the sensor location.
9. The multisensor guidewire of claim 1, wherein the coil has an
outside diameter of .ltoreq.0.89 mm (.ltoreq.0.035 inch).
10. The multisensor guidewire of claim 1, for use as a support
guidewire for transcatheter valve replacement, wherein the core
wire comprises a medical grade stainless steel alloy and the
diameter D.sub.core of the core wire provides the guidewire with
predetermined stiffness characteristics defined by a standard
guidewire descriptor, said guidewire descriptor being one of stiff,
super-stiff and ultra-stiff.
11. The multisensor guidewire of claim 1, for use as a support
guidewire for transcatheter valve replacement, wherein the core
wire comprises a medical grade stainless steel alloy and the
diameter D.sub.core of the core wire in at least the distal end
portion provides a flexural modulus of 60 GPa or more.
12. The multisensor guidewire of claim 1, configured for measuring
a transvalvular blood pressure gradient within the heart during a
minimally invasive cardiac intervention, wherein said plurality of
optical sensors comprise Fabry-Perot 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 tricuspid 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.
13. The multisensor guidewire claim 1, wherein the plurality of
optical sensors further comprises an optical flow sensor.
14. The multisensor guidewire of claim 1, for use as a support
guidewire for transcatheter valve replacement, comprising at least
three optical sensors and respective optical fibers, wherein the
distal end portion of the coil has an external diameter
.ltoreq.0.89 mm (.ltoreq.0.035 inch), and the core wire provides a
guidewire having a flexural modulus of 60 GPa or more.
15. The multisensor guidewire of claim 1, wherein apertures are
provided in the coil adjacent each optical pressure sensor for
fluid contact therewith, and optionally, radiopaque markers are
provided adjacent each optical pressure sensor.
16. The multisensor guidewire of claim 1, wherein the 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.
17. The multisensor guidewire of claim 1, wherein 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.
18. The multisensor guidewire of claim 1, wherein the flexible
distal tip comprises a pre-formed atraumatic tip comprising one of:
a straight soft tip; a pre-formed J-tip, a pre-formed spiral tip or
other two dimensionally curved tip; a pre-formed tip having a three
dimensional curved form; a pre-formed tip having a helical
structure; and a pre-formed tip having a tapered helical structure,
resembling the form of a snail shell.
19. A core wire for a multisensor guidewire as defined in claim 1,
wherein the multisensor guidewire has a flexible coil having an
external diameter of .ltoreq.1 mm and comprises a plurality of
optical sensors and a corresponding plurality of optical fibers,
the core wire being formed from a medical grade metal alloy, having
a diameter D.sub.core and an external surface 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 D.sub.core of the
core wire, and wherein D.sub.core is sized to fit slideably with
the flexible coil of a guidewire.
20. The core wire of claim 19, wherein the plurality of grooves
extend helically along the length of the core wire.
21. The core wire of claim 19, wherein the plurality of grooves are
spaced symmetrically around the core wire.
22. The core wire of claim 19, wherein surfaces of the grooves have
at least a minimum radius for formation of the grooves by
wire-drawing.
23. The core wire of claim 19, fabricated from a stainless steel
alloy.
24. A method of assembly of a multisensor guidewire as defined in
claim 1, 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 and 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 coil of the guidewire.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] 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.
[0002] 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.
TECHNICAL FIELD
[0003] 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.
BACKGROUND
[0004] 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).
[0005] 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.
[0006] 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.
[0007] 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.
[0008] 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. .ltoreq.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.
[0009] 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.
[0010] 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.
[0011] 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. .ltoreq.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.
[0012] 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.
[0013] 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.
[0014] 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.
[0015] 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.
[0016] 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.
[0017] 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.
[0018] 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.TM. pre-shaped TAVI guidewire has a
double curve tip, and the Medtronic Confida.TM. Brecker Curve.TM.
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.
[0019] 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.
[0020] 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.
SUMMARY OF INVENTION
[0021] 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.
[0022] 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 .ltoreq.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 D.sub.core 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.
[0023] 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 D.sub.core of the core
wire.
[0024] 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 D.sub.core that provides a required stiffness,
typical of a support guidewire for transcatheter valve
replacement.
[0025] 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 D.sub.core of the core wire. The fibers and
sensors are thereby protected within the grooves, during assembly
and in use of the guidewire.
[0026] 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.
[0027] 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 D.sub.core.
[0028] 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 R.sub.min to enable fabrication of the grooves by
a wire-drawing process.
[0029] 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.
[0030] The coil preferably has an outside diameter of .ltoreq.0.89
mm (.ltoreq.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 D.sub.core of the core wire, in at least the distal end
portion, provides a flexural modulus of a predetermined stiffness
to the guidewire.
[0031] Typically, the guidewire stiffness is described by guidewire
manufacturers using standard guidewire descriptors such as "stiff"
or "super stiff".
[0032] 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 D.sub.core 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.
[0033] In some embodiments, the core wire comprises a medical grade
stainless steel alloy and the diameter D.sub.core 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 D.sub.core of
the core wire in at least the distal end portion provides a
flexural modulus of 60 GPa or more.
[0034] 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-Perot 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.
[0035] 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.
[0036] 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 L.sub.FS 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.
[0037] 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
.ltoreq.0.89 mm (.ltoreq.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.
[0038] 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.
[0039] 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.
[0040] 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.
[0041] 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.
[0042] 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.
[0043] 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.
[0044] In some embodiments, to accommodate a plurality of optical
sensors within a guidewire of diameter .ltoreq.0.89 mm
(.ltoreq.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.
[0045] 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.
[0046] 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 .ltoreq.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
D.sub.core, 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 D.sub.core
of the core wire, and wherein D.sub.core is sized to fit slideably
with the outer flexible coil of a guidewire.
[0047] 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.
[0048] 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.
[0049] 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.
[0050] 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.
[0051] 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.
[0052] 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.
BRIEF DESCRIPTION OF THE DRAWINGS
[0053] In the drawings, identical or corresponding elements in the
different Figures have the same reference numeral.
[0054] FIG. 1 illustrates schematically a system according to a
first embodiment, comprising a multisensor guidewire apparatus
optically coupled to a control unit;
[0055] FIG. 2 illustrates schematically a longitudinal
cross-sectional view of an apparatus comprising a multisensor
support guidewire comprising a plurality of optical sensors
according to a first embodiment of the present invention;
[0056] FIG. 3 illustrates schematically an enlarged longitudinal
cross-sectional view showing details of the distal end portion of
the multisensor guidewire illustrated in FIG. 2;
[0057] FIGS. 4A, 4B, 4C and 4D show enlarged axial cross-sectional
views of the multisensor guidewire illustrated in FIG. 2 taken
through planes A-A, B-B, C-C and D-D respectively;
[0058] FIG. 5 illustrates schematically a longitudinal
cross-sectional view of an apparatus comprising a multisensor
guidewire comprising a plurality of optical sensors according to
another embodiment of the present invention;
[0059] FIG. 6A illustrates schematically an enlarged longitudinal
cross-sectional view showing details of the distal end portion of
the multisensor guidewire illustrated in FIG. 5; and FIG. 6B shows
an enlarged and simplified cross-sectional view along the axis of a
groove, such as through plane X-X of FIG. 6A;
[0060] FIGS. 7A, 7B, 7C, 7D and 7E show enlarged axial
cross-sectional views of the multisensor guidewire illustrated in
FIG. 5 taken through planes A-A, B-B, C-C D-D and E-E
respectively;
[0061] FIGS. 8A, 8B, 8C, 8D and 8E show enlarged axial
cross-sectional views of the multisensor guidewire similar to those
shown in FIGS. 7A to 7E, for an embodiment comprising fibers and
grooves of different dimensions;
[0062] FIG. 9 shows an enlarged axial cross-sectional view of a
core wire of another embodiment;
[0063] FIGS. 10A and 10B, show enlarged axial cross-sectional views
of core wires of other embodiments;
[0064] FIG. 11A shows a schematic diagram of a human heart to
illustrate placement within the left ventricle of a multisensor
guidewire, similar to that shown in FIG. 2, for use as: a) a
guidewire during a TAVI procedure; and b) for directly measuring a
blood pressure gradient across the aortic heart valve before and
after the TAVI procedure;
[0065] FIG. 11B shows a schematic diagram of a human heart to
illustrate placement within the left ventricle of a multisensor
guidewire, similar to that shown in FIG. 5, for use as: a) a
guidewire during a TAVI procedure; and b) for directly measuring a
blood pressure gradient across the aortic heart valve before and
after the TAVI procedure, wherein a flow sensor is provided for
measuring blood flow upstream of the aortic valve;
[0066] FIGS. 12A, 12B and 12C show corresponding schematics of a
human heart illustrating three potential approached for placement
of the multisensor guidewire through the mitral valve, for use as:
a) a support guidewire during a transcatheter valve replacement
procedure; and b) as a diagnostic tool for directly measuring a
blood pressure gradient across the heart valve before and after the
transcatheter valve replacement procedure;
[0067] FIG. 13 shows a corresponding schematic of a human heart
illustrating placement of the multisensor guidewire through the
tricuspid valve, for use as: a) a support guidewire during a
transcatheter valve replacement procedure; and b) for directly
measuring a blood pressure gradient across the heart valve before
and after the transcatheter valve replacement procedure;
[0068] FIG. 14 shows a corresponding schematic of a human heart
illustrating placement of the multisensor guidewire through the
pulmonary valve, for use as: a) a support guidewire during a
transcatheter valve replacement procedure; and b) for directly
measuring a blood pressure gradient across the heart valve before
and after the transcatheter valve replacement procedure;
[0069] FIG. 15 shows a chart, known as a Wiggers diagram, showing
typical cardiac blood flow and pressure curves during several heart
cycles, for a healthy heart;
[0070] FIGS. 16A, 16B and 16C show simplified schematics
representing the aortic heart valve and left ventricle in a healthy
heart, with the multisensor guidewire inserted through the aortic
valve with first and second optical pressure sensors P1 and P2
positioned within the ventricle and the third optical pressure
sensor P3 positioned within the aorta for measurement of a
transvalvular pressure gradient through the aortic valve in a
healthy heart, with the heart valve in closed, semi-closed/open and
open positions respectively;
[0071] FIGS. 17A, 17B and 17C show similar simplified schematics
representing the aortic heart valve and left ventricle, in which
shaded areas represent stenoses, with the multisensor guidewire
inserted through the aortic valve with first and second optical
pressure sensors P1 and P2 positioned within the ventricle and the
third optical pressure sensor P3 positioned within the aorta for
measurement of a transvalvular pressure gradient through the aortic
valve in a diseased heart, with the heart valve in closed,
semi-closed/open and open positions respectively;
[0072] FIG. 18 shows a chart showing typical variations to the
blood flow or pressure curves, during several cardiac cycles, due
to cardiac stenosis;
[0073] FIG. 19 illustrates schematically a view of the male and
female connectors of the micro-optical coupler for optically
coupling the distal and proximal parts of the multisensor
guidewire;
[0074] FIG. 20 illustrates schematically an enlarged longitudinal
cross-sectional view of the male part of the multisensor guidewire
optical connector illustrated in FIG. 19;
[0075] FIGS. 21A, 21B, 21C and 21D show enlarged axial
cross-sectional views of the multisensor guidewire optical
connector illustrated in FIG. 20 taken, respectively, through
planes A-A, B-B, C-C and D-D indicated in FIG. 20;
[0076] FIG. 22 illustrates schematically a side perspective view an
optical contact force sensor (strain gauge) for use in a
multisensor guidewire for cardiovascular use such as for TVR;
[0077] FIG. 23 illustrates a longitudinal cross-sectional view of
the optical contact force sensor (strain gauge) of FIG. 22;
[0078] FIG. 24 illustrates schematically a longitudinal
cross-sectional view showing details of the distal end portion of a
multisensor guidewire of a third embodiment comprising a contact
force sensor such as illustrated in FIG. 22;
[0079] FIGS. 25A and 25B show enlarged axial cross-sectional views
of the multisensor guidewire comprising a contact force sensor
illustrated in FIG. 23 taken, respectively, through planes A-A and
B-B indicated in FIG. 24;
[0080] FIG. 26 shows a schematic diagram of a human heart to
illustrate placement within the left ventricle of a multisensor
guidewire, similar to that shown in FIG. 23, for sensing a contact
force, e.g. during a TAVI procedure or during measurement of
cardiovascular parameters before, during and after the TAVI
procedure;
[0081] FIGS. 27A and 27B, show enlarged views of the distal end of
a guidewire wherein the tip comprises pre-formed helical tip of a
first embodiment;
[0082] FIG. 28 shows a schematic diagram of a human heart to
illustrate placement of within the left ventricle of a guidewire
comprising a flexible pre-formed helical tip as shown in FIGS. 27A
and 27B;
[0083] FIGS. 29A and 29B show enlarged views of views of the distal
end of a guidewire wherein the tip comprises a pre-formed helical
tip of another embodiment; and
[0084] FIG. 30 shows a schematic diagram of a human heart to
illustrate placement within the left ventricle of a multisensor
support guidewire, comprising a pre-formed helical tip as shown in
FIGS. 29A and 29B.
DETAILED DESCRIPTION OF EMBODIMENTS
[0085] 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.
[0086] Firstly, referring to FIG. 1, this schematic represents a
system 1 comprising an apparatus 100 comprising a multisensor
guidewire for use in transcatheter valve replacement procedures,
coupled to a control system 150, which houses a control unit 151
and user interface, such as the illustrated touch screen display
152. The apparatus 100 comprises a proximal part 101 and distal
part 102. 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
stiffness to act as a "support guidewire" for TAVI, i.e. for
over-the-wire delivery of a replacement valve. Typically, for TAVI,
the coil has an outside diameter of 0.035 inch (0.89 mm) or less,
the guidewire has a suitable stiffness for transcatheter or
intra-vascular insertion, and extends to distal tip 120, such as a
flexible J-tip, or other atraumatic curved tip, to facilitate
insertion. By way of example, a guidewire for transcatheter valve
replacement may typically be about 2 m to 3 m in length, e.g. 2.6
m.
[0087] 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 FIG. 1), located within the distal end portion 103,
near the distal tip 120. For example, as will be described in
detail with reference to FIG. 2 and FIG. 3, three optical pressure
sensors 10a, 10b and 10c are provided in a length L of the distal
end portion 103 spaced by distances L.sub.1 and L.sub.2.
Optionally, as illustrated in FIG. 2, the sensor arrangement also
includes an optical flow sensor 20, e.g., positioned proximally of
the flow sensors by a distance L.sub.FS. Thus, internally, the
distal part 102 provides optical coupling of the optical sensors
10a, 10b, 10c and 20, through a plurality of optical fibers 11, to
an optical coupler 140 at its proximal end, as will also be
described in detail with reference to FIGS. 2, 3, 4A, 4B, 4C and
4D.
[0088] 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.
[0089] The internal structure of the multisensor guidewire
apparatus 100 will now be described in more detail with reference
to FIGS. 2 and 3.
[0090] FIG. 2 illustrates schematically a longitudinal
cross-sectional view of the apparatus 100 according to the first
embodiment of the invention, comprising a multisensor guidewire.
The apparatus 100 extends from the optical input/output connector
112 at the proximal end 110 through the proximal part 101 to the
distal part 102 which extends to the distal tip 120.
[0091] 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 FIG. 2, in
this embodiment, the coil wire is formed from a flat ribbon wire
having a rectangular cross-section. If required, the outer coil of
guidewire may comprise a coating of a suitable biocompatible
material, e.g. to facilitate insertion and steering control. The
coating may be a hydrophobic coating, such as PTFE or silicone, or
a hydrophilic material. For example, in some instances, the
guidewire has a hydrophobic coating along its length and the distal
end portion and distal tip has a hydrophilic coating.
[0092] 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.
[0093] For example, for measuring a transaortic pressure gradient,
the optical pressure sensors 10a, 10b, 10c are arranged spaced
apart by distances L.sub.1 and L.sub.2, 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
FIGS. 2 and 5B) is positioned to measure flow in the aorta before
the main branches from the aorta, e.g. in the ascending aorta,
about 50 mm to 80 mm downstream of the aortic valve 511 or a
distance L.sub.FS of about 20 mm from the nearest pressure sensor
10b or 10c (see FIGS. 2, 5B, 11A and 11B).
[0094] FIG. 3 shows an enlarged longitudinal cross-sectional view
of the distal end portion 103 of the multisensor guidewire 100
illustrated in FIG. 2. As illustrated, in FIG. 2 and FIG. 3, to
accommodate the plurality of optical sensors 10a, 10b, 10c and 20
and their respective optical fibers 11 while maintaining the
required stiffness to the guidewire, the core wire is provided with
a corresponding plurality of helical grooves 32. The helical
grooves 32 extend along the length of the core wire 31 from the
optical coupler 140 to near the distal tip 120. The helical grooves
32 are sized to accommodate the optical fibers along the length of
the distal part 102 and accommodate the optical sensors at sensor
locations spaced apart along the length L of the distal end portion
103. To simplify illustration, the three optical sensors 10a, 10b,
10c are shown in FIG. 2 and FIG. 3 as spaced apart lengthwise on
one side of the core wire. The sensors may preferably be
distributed around the core wire, as shown, for example, in FIG. 4C
and FIG. 4D. As illustrated, the multisensor guidewire 100 is
capable of measuring blood pressure simultaneously at several
points, in this case three points, using the three optic
fiber-based pressure sensors 10a, 10b, 10c arranged along the
length L of the distal end portion 103 of the multisensor
guidewire. For TAVI, the sensor locations are arranged to allow for
the optical pressure sensors to be placed upstream and downstream
of the aortic valve during measurements.
[0095] Accordingly, in this embodiment, the two more distal sensors
10a and 10b are spaced apart by a distance L.sub.1 and sensors 10b
and 10c are spaced apart by a distance L.sub.2, where
L.sub.2>L.sub.1. 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 D.sub.core 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 FIG. 2, the fine wire forming the
flexible outer coil 35 of the distal portion 102 is tightly coiled
along most of its length to form a tubular covering layer of the
distal portion of the guidewire along most of its length. The
guidewire coil 35 is more loosely coiled, or otherwise structured,
in the distal end portion 103 to provide apertures 36 between the
coils of the wire of the guidewire coil near each of the optical
pressure sensors. The apertures allow for fluid contact with the
optical pressure sensors 10a, 10b, and 10c.
[0096] As shown in FIG. 3, a marker, such as a radiopaque marker
14, is provided near each sensor, e.g. placed in the helical groove
32 distally of the sensor, to assist in locating and positioning
the sensors in use, i.e. using conventional radio-imaging
techniques, when introducing the guidewire and positioning the
sensors in a region of interest, e.g. upstream and downstream of
the aortic valve. The radiopaque markers 14 are preferably of a
material that has a greater radiopacity than the material of the
core wire. For example, if the core wire 31 and outer coil 35 are
stainless steel, a suitable heavy metal is used as a radiopaque
marker, e.g. barium, tantalum, gold or platinum. However, if the
core wire has sufficient radiopacity for visualizing and
positioning the sensor arrangement in a region of interest, markers
may not be required. If required, the coil of guidewire may have a
conventional coating of a suitable biocompatible material, e.g. to
facilitate insertion.
[0097] FIGS. 4A, 4B, 4C and 4D show enlarged axial cross-sectional
views of the multisensor guidewire 100 taken through planes A-A,
B-B, C-C and D-D respectively, of FIG. 2. FIG. 4A shows the four
optical fibers 13 within the tubing 51 and jacket 52 of the
proximal part 101. FIGS. 4B, 4C and 4D show the core wire 31 within
the outer coil 35 to illustrate the location of the optical fibers
11 in grooves 32, and the location of pressure sensors 10a, 10c
within enlarged groove portion 34 of the grooves 32 in the core
wire 31.
[0098] 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
D.sub.core 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 D.sub.core 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.
[0099] 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 D.sub.core of
the core wire, as illustrated in the schematic cross-sectional view
shown in FIG. 4B. As mentioned above, if needed, the grooves are
enlarged to form a recess or cavity 34 in the sensor locations, as
illustrated schematically in FIGS. 4C and 4D. The optical fibers
and sensors are therefore protected within the grooves. The grooves
are preferably formed with rounded or bevelled edges, i.e. to avoid
sharp edges of the core wire that may damage the optical fibers and
sensors during assembly or use. For similar reasons, the flexible
outer coil may alternatively be formed from round wire rather than
rectangular wire. To provide more protection to the optical fibers
and sensors, the grooves may be deeper than the diameter of the
fibers and/or sensors, provided the core wire can provide the
required stiffness to the guidewire. Preferably, for a high
stiffness guidewire, the core wire has a cross-sectional profile
that defines grooves of the appropriate depth and dimensions to
accommodate the optical fibers and optical sensors, while
maximizing the cross-sectional area and effective diameter of the
core wire.
[0100] 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.TM. or Ultra Stiff.TM.
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.
[0101] FIG. 4A shows a corresponding cross-sectional view through
the proximal portion 101, which comprises the bundle of optical
fibers 13 contained within flexible tubing 51 and jacket 52. Since
the proximal part 101 simply provides a flexible optical coupling
to the control unit 150, it does not require the same stiffness or
torque characteristics as the distal part 102 comprising the
guidewire, and thus does not need to include a core wire. When the
distal part is twisted or torqued to guide the guidewire
intravascularly, a longer and more flexible proximal part 101 may
assist with manoeuvrability of the guidewire.
[0102] The structure of the multisensor assembly is shown in
cross-section along its length from the connector 112 to the distal
tip 120 in FIG. 2. However for simplicity, the internal structure
of the connector 112 is not shown. It will be appreciated that the
optical fibers 13 of the proximal part 101 extend through the
connector 112 to optical inputs/outputs 113 of the connector, as is
conventional.
[0103] The optical pressure sensors 10a, 10b and 10c are preferably
Fabry-Perot 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 .mu.m). Typically, they would be coupled to an
optical fiber with an outside diameter of 0.100 mm (100 .mu.m) to
0.155 mm (155 .mu.m). 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.
[0104] As illustrated schematically in FIGS. 4B to 4D, assuming the
coil 35 has an outside diameter of 0.89 mm (0.035 inch) including
any coating, and is formed from 0.002 inch thick coil wire, which
would provide a coil with an inside diameter of about 0.787 mm
(0.031 inch), then a core wire having a maximum outside diameter of
about 0.736 mm (0.029 inch) could be accommodated within, allowing
for clearance between the core wire and the coil. Preferably the
coil and the core of the guidewire are made from stainless steel
having high stiffness and tensile strength, e.g. 304V stainless
steel, or other approved types of stainless steel for medical
applications. Other biocompatible metal alloys with suitable
mechanical characteristics may alternatively be used. Typical
medical grade nitinol alloys would not offer sufficient stiffness
for a core wire for a multisensor support guidewire for
transcatheter valve replacements. On the other hand, medical grade
nitinol alloys may provide sufficient stiffness as a core wire for
a multisensor guidewire for other percutaneous procedures where a
more flexible guidewire is desirable, e.g. for intravascular
insertion into smaller blood vessels or coronary arteries, or for a
multisensor guidewire for diagnostic measurements only, such as
described in the second embodiment. Since the fibers sit within the
grooves of the core wire, for a guidewire of a given external
diameter, e.g. 0.89 mm (0.035 inch), allowing for a standard
thickness of the coil and the necessary clearance between the core
wire and the coil, the core wire can have maximum outside diameter
D.sub.core similar to that of a core wire for a conventional
support guidewire. The helical grooves are sized to accommodate
standard optical fibers, e.g. standard low cost fibers of 0.155 mm
diameter, or more preferably smaller diameter 0.100 mm optical
fibers, as illustrated schematically in FIGS. 4C and 4D.
[0105] 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 FIG. 4B, for
0.100 mm diameter optical fibers, the minimum diameter of the core
wire D.sub.min, at the centre of the grooves, is approximately 0.5
mm, while the major part of the core wire (i.e. approx.
270.degree./360.degree.=75%) has a maximum diameter D.sub.core of
0.736 mm, which contributes significantly to the stiffness of the
core wire.
[0106] 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.
[0107] 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.
[0108] 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 FIGS. 2 and
5B) at a suitable position in or near the distal end portion 103 to
measure the blood flow velocity. The optical flow sensor comprises,
for example, an optical thermoconvection sensor or other suitable
optical flow sensor, coupled by a respective optical fiber to the
optical/input output connector. The optional optical flow sensor 20
may comprise an optical thermoconvection flow sensor, e.g. as
described in U.S. patent application Ser. No. 14/354,588.
[0109] 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 FIGS. 4B, 4C, and
4D) so that the distal part 102 of the guidewire has sufficient
stiffness to act as a support guidewire for transcatheter valve
replacements.
[0110] 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.
[0111] 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.
[0112] A multisensor guidewire 200 of a second embodiment is
illustrated in FIGS. 5, 6 and 7A to 7E. Many elements of the
multisensor guidewire 200 are similar to those of the multisensor
support guidewire 100 illustrated in FIGS. 2 and 3 described above,
and like parts are numbered with the same reference numeral. In
this embodiment, the multisensor guidewire 200 comprises three
optical sensors, that is, two optical pressure sensors 10a and 10b,
an optical flow sensor 20, and their respective optical fibers 11.
Accordingly, the core wire 131 has a cross-sectional profile
comprising three grooves 32 along its length, to provide a
guidewire having an axial cross-section as illustrated in FIGS. 7A,
7B, 7C and 7D. The grooves 32, and respective cavities 34 for the
sensors, have a depth that accommodate the sensors 10a, 10b and 20,
coupled to their respective optical fibers 11, within the diameter
D.sub.core of the core wire.
[0113] Referring back to FIG. 5, similar to the apparatus 100 shown
in FIG. 2, the apparatus 200 comprises a proximal part 101 and
distal part 102. 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 131
within the outer coil 35. The outer diameter and mechanical
properties of both the outer coil 35 and the core wire 131 are
selected to provide the required stiffness to act as a guidewire
for TAVI. Typically, for TAVI, the coil has an outside diameter of
0.035 inch or 0.89 mm or less, the guidewire has a suitable
stiffness for transcatheter or intra-vascular insertion, and
extends to distal tip 120, such as a flexible J-tip, or other
atraumatic curved tip, to facilitate insertion.
[0114] As illustrated in the schematic cross-section shown in FIG.
7B, to accommodate three standard optical fibers of diameter 0.155
mm, the grooves take up a significant portion of the
cross-sectional area of the core wire. By comparison, for a core
wire of the same material and diameter D.sub.core, the structure
shown in FIG. 4B will provide superior stiffness. As described for
the apparatus 100 of the first embodiment, to provide the
appropriate stiffness and mechanical properties for use as a
support guidewire, coil 35 and core wire 131, are typically
fabricated from a medical grade stainless steel, e.g. 304V. On the
other hand, for other TVT procedures, e.g. if the multisensor
guidewire is to be used only for diagnostic measurements, and not
as a support guidewire for valve replacement, a high stiffness
guidewire may not be required. For some TVT procedures, a more
flexible guidewire may be preferred. In the latter case, other
alloys may be suitable, e.g. medical grade metal alloys including
nitinol, which are commonly used for cardiovascular guidewires.
[0115] As illustrated in FIG. 5 and FIG. 6, the coil wire 35 is
closely wound along most of its length to form a tubular covering
layer and in the distal end portion 103 containing the sensor
arrangement 130, the coil wire is more loosely wound or structured
to provide apertures 36 near each pressure sensor for fluid
contact. The coil wire 35 in this embodiment is shown with a
circular cross-section.
[0116] As shown in FIG. 5 and FIG. 6A, the distal part 102 contains
a sensor arrangement 130 comprising the two optical pressure
sensors 10a and 10b located within a length L of the distal end
portion 103, near the distal tip 120. The optical flow sensor 20 is
located proximally of the pressure sensors by a distance L.sub.FS.
Internally, the distal part 102 provides optical coupling of the
three optical sensors, through the plurality of optical fibers 11
to an optical coupling 145 at the proximal end of the
guidewire.
[0117] For simplicity of illustration, the sensors 10a, 10b and 20
are shown in FIG. 6A as spaced apart lengthwise along one side of
the core wire. In practice, since the grooves 32 are helical, the
sensors may alternatively be distributed around the core wire 131
to position the sensors at the appropriate sensor locations and
spacings.
[0118] FIG. 6B shows an enlarged and simplified schematic
cross-sectional view through a central part of plane X-X of FIG.
6A, that is, along the axis of the helical groove 32. It will be
appreciated that using the graphics software currently available to
the Applicant, it was difficult to accurately illustrate the
geometry of a cross-sectional slice of the core wire along helical
groove X-X. FIG. 6B therefore shows a very simplified schematic,
wherein the helical groove is represented as a straight so as to
illustrate the positioning of the optical fiber 11 within the
groove 32, with sensor 10b within an enlarged part of the groove,
i.e. cavity 34, so that both the fiber and the sensor can sit
within the groove, protected within diameter D.sub.core. As
illustrated schematically, the fiber 11 may be affixed to the core
wire 131, e.g. in the groove 32 by adjacent the sensor 10a, by a
spot of adhesive or encapsulant 118.
[0119] 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 FIG. 1). Thus, the proximal part 101 contains a
corresponding plurality of three optical fibers 13 which are
optically coupled to optical fibers 11 of the distal part 102 at
optical coupling 145. The proximal part has a tubular flexible
covering layer 51 and a protective layer or jacket 52. The optical
coupling 145 may be fixed or separable, and its body may be sized
to form a handle or hub for manoeuvring the guidewire. The proximal
part 101 has, at its proximal end 110, an optical input/output 112.
In this embodiment, the optical input/output 112 takes the form of
three optical connectors 114. Each optical fiber 13 of the proximal
part is coupled through a flexible optical coupling, e.g. through a
length of flexible tubing or optical cable 116, to an individual
one of the three optical connectors 114. The latter may be
conventional optical fiber connectors for ends 113 of each optical
fiber.
[0120] As illustrated schematically in the enlarged longitudinal
cross-sectional view in FIG. 6A, the three optical sensors 10a, 10b
and 20, coupled to their respective optical fibers 11, are located
in the distal end portion 103, near the distal tip 120. The sensors
10a, 10b and 20 are spaced by distances L and L.sub.FS
respectively. Each fiber 11 is secured to the core wire 131 at a
point near each sensor, e.g. using a spot of adhesive 118 (see FIG.
6B). Preferably, the fibers 11 lie freely within their respective
groove 32 along most of the length of the core wire, and they may
be similarly secured to the core wire near the distal end. Thus,
after assembly of the guidewire, each optical fiber has some
freedom to move or slide within its groove when the guidewire is
flexed or twisted, e.g. to spread stresses and strains along the
length of each optical fiber.
[0121] 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.
[0122] 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.
[0123] 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.
[0124] 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 L.sub.1 and L.sub.2, 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 FIG. 5) is positioned
proximally of the pressure sensors to measure flow in the aorta
before the main branches from the aorta, e.g. in the ascending
aorta, about 50 mm to 80 mm downstream of the aortic valve 511 or
at a distance L.sub.FS of about 20 mm to 30 mm from the nearest
pressure sensor 10b (see FIGS. 5 and 6A).
[0125] FIGS. 7A, 7B, 7C, 7D and 7E show enlarged axial
cross-sectional views of the multisensor guidewire 200 taken
through planes A-A, B-B, C-C, D-D and E-E respectively, of FIG. 5.
FIG. 7A shows the optical fibers 13 with tubing 51 and jacket 52 of
the proximal part 101. To accommodate optical sensors 10a, 10b and
20, and their respective optical fibers 11, while maintaining the
required stiffness to the guidewire, the core wire has helical
grooves 32 as shown in the axial cross-sectional views in FIGS. 7B,
7C and 7D. The grooves 32 extend along the length of the core wire
131 from the optical coupler 145 to near the distal tip 120.
[0126] 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 D.sub.core of the core
wire 131 (see FIGS. 7B, 7C and 7D for example). 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 adhesively attached to the core
wire 131 near each sensor, e.g. with a suitable biocompatible and
hemo-compatible adhesive 39, before the core wire is inserted into
the coil wire 35. To accommodate the sensors 10a, 10b and 20, which
may be larger in diameter than the optical fibers 11 themselves, if
required, the grooves are enlarged in the region where the sensors
10a, 10b and 20 are located, i.e. to form a cavity or recess at
each sensor location. For example, a cavity or recess 34 is ground
in the core wire, as shown schematically in FIGS. 6, 7C and 7D, to
provide space for the sensors 10a, 10b and 20. The guidewire coil
35 may be more loosely coiled, or otherwise structured, in the
distal end portion 103 to provide apertures 36 between the coils of
the wire of the guidewire coil near each of the optical pressure
sensors that allow for fluid contact with the optical pressure
sensors 10a and 10b.
[0127] FIGS. 7A, 7B, 7C, 7D, and 7E show schematic enlarged axial
cross-sectional views of the multisensor guidewire 200 taken
through planes A-A, B-B, C-C, D-D and E-E respectively, of FIG. 5
for a core wire sized to accommodate standard sized optical fibers,
such as those used for telecommunications, having a diameter of
0.155 mm. Correspondingly, FIGS. 8A, 8B, 8C, 8D, and 8E show
schematic enlarged axial cross-sectional views of the multisensor
guidewire 200 taken through planes A-A, B-B, C-C, D-D and E-E
respectively, of FIG. 5 for a multisensor guidewire with a core
wire 231 sized to accommodate optical fibers having a smaller
diameter, i.e. of 0.100 mm. Since the optical fibers do not
contribute significantly to the stiffness of the guidewire, for
superior stiffness required for a guidewire of a given outside
diameter, e.g. .ltoreq.0.89 mm (0.035 inch), the diameter core wire
D.sub.core is preferably as large as can be reasonably be
accommodated within the outer coil of the guidewire (e.g.
D.sub.core=0.029 inch) for a coil wire of 0.002 inch.times.0.012
inch. As illustrated schematically, if, for example, the optical
fibers are of 0.100 mm (0.0039 inch) diameter, the grooves 32 in
the core wire are sized accordingly to accommodate the optical
fibers 11 in the space or channel between groove surface of the
core wire 131 and outer coil 35. The three grooves are
symmetrically spaced around the circumference of the core wire.
[0128] FIG. 9 shows a core wire 331 of an alternative embodiment,
having another cross-sectional profile where the core wire surface
is contoured, e.g. by wire drawing, to form two grooves 32 within
the diameter D.sub.core of the core wire, which can accommodate two
optical fibers. As illustrated, and as mentioned above, in this
context, for a wire with a cross-section that is not entirely
circular, the diameter D.sub.core of the core wire refers to the
diameter of the circle into which the wire will fit. To avoid
adversely affecting the torque characteristics of the core wire for
guiding and steering the guidewire, the core wire preferably has
rotational symmetry about the axis of the core wire. Thus, to
accommodate a plurality of optical fibers, it is preferable that
the groove structure of the core wire is has at least two fold
rotational symmetry, as illustrated in FIG. 9 for core wire 331.
More preferably, the core wire has three-fold or four-fold
rotational symmetry. For example, core wire 431 shown in FIG. 10A
has three grooves and accommodates three fibers, each within its
own groove, and within the core wire diameter D.sub.core.
Similarly, core wire 531 shown in FIG. 10B, has four grooves, each
groove accommodating an individual optical fiber within the
diameter D.sub.core. Thus, the core wire surface defines a
cross-sectional profile that provides multiple grooves along the
length of the core wire, each groove accommodating a single fiber
and optical sensor, and with the grooves spaced symmetrically
around the circumference of the core wire. Preferably, the grooves
extend helically around the length of the core wire.
[0129] Advantageously, each optical fiber and its respective
optical sensor are accommodated within an individual groove within
the diameter D.sub.core 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.
[0130] Optical Micro-Coupler
[0131] 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).
[0132] 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.
[0133] 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.
[0134] The micro-coupler 140 of the first embodiment will now be
described in more detail with reference to FIG. 19. As illustrated
in FIG. 19, the micro-coupler 140 comprises male and female parts,
142 and 144 respectively, to provide for optical coupling of each
optical pressure sensor 10a, 10b, 10c and optical flow sensor 20
via their respective individual optical fibers 11 of the distal
part 102 to respective individual fibers 13 of the proximal part
101. Notably, the male portion 142 of the micro-optical coupler has
the same outside diameter D as the coil 35 of the guidewire to
enable components for transcatheter valve replacement to be mounted
on or over the guidewire. The female portion 144 of the
micro-optical coupler is of larger diameter and may be formed to
act as a hub 44 that can be grasped facilitate handling and torque
steering of the guidewire, and as well as to facilitate engaging
and disengaging distal part 102. An alignment means, such as facet
43 of the male part 142, which aligns to a corresponding facet (not
visible) in the female part 144 ensures that individual fibers 11
are indexed, aligned and correctly optically coupled to respective
corresponding individual fibers 13 for optical data communication.
The connector 140 may also include a suitable fastening means for
securely attaching and locking/unlocking the two parts 142 and 144
of optical coupler 140.
[0135] FIG. 20 shows a cross-sectional view of the proximal end of
distal part/guidewire 102 showing the internal structure of the
male part 142 of connector 140. As illustrated schematically, the
core wire 31 is tapered to form a core 37 at its end that inserts
into the ferrule 42 of connector part 142 so that the individual
optical fibers 11 are guided from the grooves 32 in the core wire
31 into and through the ferrule 42 of the connector part 142. The
internal structure of the male connector part 142 is shown through
lines A-A, B-B, C-C and D-D in subsequent FIGS. 21A, 21B, 21C and
21D.
[0136] 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.
[0137] 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.
[0138] 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.
[0139] 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.
[0140] 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.
[0141] 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.
Alternative Embodiments
[0142] For multisensor guidewires of some embodiments, for example,
as illustrated in FIG. 5, for the multisensor guidewire 200 of the
second embodiment, the optical micro-coupler connecting the
proximal part 101 and distal part 102 may be replaced with a larger
optical coupling 145, either a separable optical coupler or fixed
coupling. The body of optical coupling 145 may be sized to act as a
handle or hub for insertion and torque steering of the guidewire.
In the latter arrangement, any components for insertion, such as a
replacement heart valve, would be placed over the guidewire from
the distal tip, before intravascular insertion of the guidewire
into the patient.
[0143] 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.
[0144] For the multisensor support guidewire 100 illustrated in
FIG. 2, a single optical connector 114 is shown for the
input/output 112 for each of the optical fibers 13. In other
embodiments, an alternative connector or coupling arrangement may
be provided. The optical input/output 112 and the control unit port
153 may comprise several individual optic fiber connectors, e.g. as
illustrated in FIG. 5 for the multisensor guidewire 200 of the
second embodiment. In further embodiments, not illustrated, the
input/output 112 may optionally include circuitry allowing wireless
communication of control and data signals between the multisensor
guidewire and the control unit 151. Optionally one or more
electrical connectors for peripheral devices, or for additional or
alternative electrical sensors, may be provided.
[0145] Referring to FIG. 11A, this shows schematically the
placement of the distal end portion 103 of the guidewire 102 within
the left ventricle 512 in the human heart 500. For transcatheter
valve replacement procedures, the distal tip 120 is preferably of a
suitable structure, such as a flexible and specially curved tip or
J-tip, to assist in firmly anchoring the distal end of the
guidewire in position in the ventricle, without causing trauma to
the ventricular wall, the valve or other tissues within the heart.
Anchoring of the guidewire, in a stable but atraumatic manner, is
particularly important during valve replacement procedures, i.e. to
ensure accurate and optimum placement of replacement valve and to
hold the valve in position during valve implantation and/or during
other therapeutic or diagnostic procedures before or after
implantation. This also facilitates precise positioning of the
sensors in the region of interest for more accurate and reliable
measurements of parameters such as blood pressure, transvalvular
pressure gradient, and blood flow, before, during and/or after the
transcatheter valve replacement procedure.
[0146] FIG. 11B shows a schematic diagram of a human heart 500 to
illustrate placement within the left ventricle 512 of a multisensor
guidewire 102, similar to that shown in FIG. 5, for use as both: a)
a guidewire during a TAVI procedure and b) for directly measuring a
blood pressure gradient across the aortic heart valve 511 before
and after the TAVI procedure, wherein a flow sensor 20 is provided
for measuring blood flow upstream of the aortic valve 511. The
multisensor guidewire 102 comprises two optical pressure sensors
10a, 10b, which are spaced apart by a suitable distance, e.g. at
least 20 mm to 50 mm apart and more preferably about 70 mm to 80 mm
apart, so that one sensor can be located upstream and one sensor
located downstream of the aortic valve 511. The flow sensor 20 is
located further downstream of the aortic valve 511, in the root of
the aorta, e.g. a distance L.sub.FS of about 20 mm to 30 mm from
the nearest pressure sensor 10b.
[0147] 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.
[0148] For comparison, FIGS. 12A, 12B and 12C show, schematically,
three approaches for positioning of the distal end portion 103 of
the guidewire 102 through the mitral valve 513. Correspondingly,
FIGS. 13 and 14 show placement through the tricuspid valve 522 and
through the pulmonary valve 224, respectively. Each of these
Figures indicates how the three optical pressure sensors 10a, 10b,
10c would be placed for measurement of a transvalvular pressure
gradient.
[0149] 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.
[0150] Transvalvular Pressure Measurements in Interventional
Cardiology
[0151] 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 FIG. 11A), a conventional guidewire is first inserted into
a peripheral artery, such as the femoral, brachial, or radial
artery, using known techniques, and advanced through the ascending
aorta 510 into the left ventricle 512. A catheter is then slid over
the guidewire. The operator then advances and positions the
catheter into the left ventricle 512, using a known visualization
modality, e.g. X-ray imaging along with radio-opaque markers 14 on
the distal end, or contrast agent. The operator then replaces the
guidewire with the multisensor guidewire 100 in the lumen of the
catheter. The operator advances the multisensor guidewire 100
through the catheter and positions the distal end portion 103 of
the multisensor guidewire 100 into the left ventricle 512 using
visualization devices such as the radio-opaque markers 14 on its
distal end 103. Then, the operator pulls back the catheter over the
guidewire. Once the multisensor guidewire 100 is properly
positioned, and is coupled to the control unit 151 to activate the
optical sensors, the optical pressure sensors 10a, 10b and 10c
directly measure the transvalvular pressure gradient of the aortic
valve 511. As illustrated schematically in FIG. 11A, two pressure
sensors 10a, 10b are positioned in the left ventricle 512 and one
pressure sensor 10c is positioned in the aorta 510 just downstream
of the aortic valve 511, to allow simultaneous measurements of
pressure at three locations, i.e. both upstream and downstream of
the valve. A series of measurements may be taken during several
cardiac cycles. Although not illustrated in FIG. 11A, a flow sensor
20 may also be provided for simultaneous flow measurements.
Measurements results may be displayed graphically, e.g. as a chart
on the touch screen display 152 of the system controller 150 (see
FIG. 1) showing the pressure gradient and flow. The control system
may provide for multiple measurements to be averaged over several
cycles, and/or may provide for cycle-to-cycle variations to be
visualized. Thus, the operator can quickly and easily obtain
transvalvular pressure gradient measurements. The valve area may
also be computed when blood flow measurements are also available.
Measurements may be made, for example, before and after valve
replacement or valve repair procedures.
[0152] FIGS. 16A, 16B and 16C and FIGS. 17A, 17B and 17C are
simplified schematics of the aortic heart valve 511 and left
ventricle 512, illustrating the concept of aortic transvalvular
pressure gradient as measured by the multisensor guidewire 100
using the method of the first embodiment described above, for a
healthy heart and for a heart with stenoses 531, 532 and 533. In
this particular example, the aortic transvalvular pressure gradient
is the blood pressure measured by sensors at locations P1, P2
within the left ventricle 512 and P3 within the aortic root
510.
[0153] 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.
[0154] 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 FIG. 15, which shows curves typical of a healthy
heart. The cardiac cycle is coordinated by a series of electrical
impulses 610 that are produced by specialized heart cells. The
ventricular systole 601 is the period of time when the heart
muscles (myocardium) of the right 523 and left ventricles 512
almost simultaneously contract to send the blood through the
circulatory system, abruptly decreasing the volume of blood within
the ventricles 620. The ventricular diastole 602 is the period of
time when the ventricles 620 relax after contraction in preparation
for refilling with circulating blood. During ventricular diastole
602, the pressure in the left ventricle 640 drops to a minimum
value and the volume of blood within the ventricle increases
620.
[0155] The left heart without lesions, illustrated in FIGS. 16A,
16B and 16C, would generate aortic and ventricular pressure curves
similar to curves 630 and 640, respectively, in FIG. 15. However,
the heart illustrated in FIGS. 17A, 17B and 17C has multiple sites
of potential blood flow 530 obstructions 531, 532 and 533. In some
cases, the operator of the multisensor guidewire 100 might want to
measure the blood pressure at several locations, within the root of
the aorta 510 in order to assess a subvalvular aortic stenosis 533
or a supravalvular aortic stenosis 531.
[0156] 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. FIG. 18
illustrates typical differences between the aortic 630 and
ventricular 640 pressure curves due to intracardiac obstructions.
Some of those variations include the maximal difference 605 and the
peak-to-peak difference 606 between curves 630 and 640. The area
607 between the aortic pressure curve 630 and ventricle pressure
curve 640 is also used to assess the physiological significance of
stenosic lesions. The difference between the amplitude 603, 604 of
the aortic 630 and ventricle 640 pressure curves is also key
information for the clinician.
[0157] 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 FIG. 18, along with analysis of the curves, are provided
on pages 647 to 653 of the reference book entitled Grossman's
cardiac catheterization, angiography, and intervention by Donald S.
Baim and William Grossman.
[0158] As indicated, when the valve is closed as shown in FIG. 16A,
the pressures P1 and P2 measured by first and second sensors 10a
and 10b placed in the left ventricle would be equal and lower than
the pressure P3 measured by the third sensor in the aorta during
the ventricular diastole 302. During the ventricular systole 301,
when the aortic valve begins to open, FIG. 16B, the pressures P1,
P2 and P3 increase and when the aortic valve is fully open, FIG.
16C, P1, P2 and P3 are similar. The specific form of the pressure
traces P1, P2, P3 generated by each sensor provides the
interventional cardiologist with direct, real-time data to aid in
diagnosis and assessment of valve performance before and after
TVR.
[0159] However, as illustrated schematically in FIGS. 17A, 17B and
17C, when the heart has subvalvular aortic stenosis 533, for
example, the pressure traces P1, P2 and P3 will differ. To detect
and assess the severity of subvalvular stenosis 533, the two distal
pressure sensors at locations P1 and P2 must be located in the left
ventricle on each side of stenosis 533 while the proximal pressure
sensor P3 must be located within the root of the aorta 510 at a
certain distance from the aortic valve 511. Therefore, as shown,
the distance L.sub.1 (typically about 20 mm) between sensors 10a,
10b is shorter than the distance L.sub.2 (typically about 50 mm or
60 mm) between sensors 10b, 10c, which length is determined by the
dimensions of the heart or vascular region to be monitored. As
illustrated schematically in FIGS. 17A, 17B and 17C, when the heart
has subvalvular aortic stenosis 533, for example, the pressure
traces P1, P2 and P3 will differ.
[0160] 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.
[0161] Manufacturability
[0162] 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 .ltoreq.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.
[0163] 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
.ltoreq.1 mm comprising a grooved core wire which accommodates
multiple optical fibers and optical sensors.
[0164] 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.
[0165] Manufacturing a sub-millimeter diameter core wire with
straight or helical grooves along its length to accommodate
individual optical fibers of approximately 100 .mu.m diameter,
presents challenges for conventional core wire manufacturing
facilities.
[0166] 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.
[0167] 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.
[0168] 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.
[0169] 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.
[0170] 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.
[0171] 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 FIG. 2 and FIG. 5. It is also known, to form at least part of
outer flexible tubular member from a flexible metal hypotube. That
is, a metal hypotube that is spirally cut or slotted to provide the
required flexibility, as described for example, in U.S. Pat. No.
6,107,004, The hypotube is, for example, stainless steel or
nitinol, which is cut using processes, such as, laser cutting,
laser microject cutting, electrostatic discharge machining (EDM),
and chemical milling or etching. The term "coil", as used herein,
is therefore intended to encompass an elongate flexible tubular
member comprising a conventional outer coil of a guidewire wound
from fine wire and/or a spirally cut metal hypotube and/or a
slotted metal hypotube, and combinations thereof.
[0172] It is envisaged that in the future, a technique such as
laser cutting may potentially be used for formation of the grooved
core-wire.
[0173] 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
D.sub.core 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.
[0174] 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.
[0175] 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.
[0176] 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.
[0177] Contact Force Sensor
[0178] 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 FIGS. 22, 23, 24, 25A and 25B, e.g. an
optical strain gauge type of sensor, located at a suitable position
in or near the distal end portion 103. For example, as illustrated
in FIGS. 22 and 23, the optical contact force sensor 60 comprises a
Fabry-Perot MOMS sensor 61 which is located in the distal end
portion 103 and is coupled by a respective optical fiber 11 to an
input output optical connector, e.g. to the micro-optical connector
140 as previously described. The cavity 62 and diaphragm 63 of the
Fabry-Perot MOMS sensor 61 is also coupled to a length L.sub.CS of
a second optical fiber 64 which extends from the sensor 61 along
the length L.sub.CS of the distal end of the guidewire, towards the
flexible tip 120. As illustrated in FIGS. 25A and 25B, the second
optical fiber 64 sits in a helical groove 32 in the core wire which
is enlarged to form a recess 34 at A-A to accommodate the sensor
61. As indicated in FIG. 23, the sensor 61 and the end of fiber 64
are fixed to the core wire at points 66. This arrangement allows
for the sensor 61 to detect and measure a contact force applied
along a length L.sub.CS of the guidewire when it contacts the
internal heart walls 215 of the heart as indicated schematically in
FIG. 24. Such a contact force sensor 60 provides information and
feedback to the cardiologist regarding the force F being applied,
e.g. when a detected contact force approaches or exceeds a
threshold F.sub.t that may cause tissue damage, or potentially even
cause fatal injuries during TVR, an alert may be provided to the
operator.
[0179] Thus, for example, the guidewire 100 may comprises three
optical pressure sensors 10a, 10b, 10c as described above with
reference to FIGS. 2 and 3, optionally a flow sensor 20 located in
the distal end portion, and a contact force sensor 60 located in a
region between the distal end portion 103 containing the optical
pressure sensors and the flexible distal tip 120, to sense a
contact force applied near the end of the guidewire, along the
length L.sub.CS indicated by the dotted line in FIG. 26.
[0180] Flexible Preformed Three-Dimensional Curved Tip
[0181] 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.
FIGS. 27A and 27B show two views of a pre-formed flexible tip 400-1
having a three-dimensional form, specifically in this embodiment, a
pre-formed helical tip, of coil diameter D.sub.T, e.g. 5 cm, which
resembles part of a telephone cord or a pigtail. A tip 400-2 of
another embodiment, as illustrated in FIGS. 29A and 29B, comprises
a pre-formed helix that is tapered to resemble the form of a snail
shell. FIGS. 28 and 30, respectively, represent schematically the
placement of these pre-formed helical tips 400-1 and 400-2 in the
left ventricle 512 for TVR or for diagnostic measurements using the
optical pressure sensors 100. This three-dimensional pre-formed
structure is proposed for improved support of the guidewire in each
of the X, Y and Z directions during TVR procedures. Such a
structure can assist in providing support for the guidewire in a
safer manner.
Further Embodiments
[0182] 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.
[0183] 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
D.sub.core. For support guidewires for TVR, the guidewire can then
be provided with the required stiffness, e.g. a flexural modulus of
.about.60 GPa, in a guidewire having a diameter of .ltoreq.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.
[0184] 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.
[0185] 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.
[0186] 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.
[0187] 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.
INDUSTRIAL APPLICABILITY
[0188] 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.
[0189] 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.TM. 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.
[0190] 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.
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