FFR catheter with suspended pressure sensor

A catheter for measuring a pressure distal of a stenosis includes a shaft including a housing in a distal portion of the shaft. A flexible printed circuit board is coupled to the housing. A pressure sensor is coupled to the flexible printed circuit board and is suspended within the housing. An aperture enables blood flow into the housing and into contact with the pressure sensor.

FIELD OF THE INVENTION

The present invention relates to systems, and methods for manufacturing systems for calculating a Fractional Flow Reserve (FFR). More particularly, the present invention relates to a distal shaft of an FFR device with a pressure sensor coupled to a flexible printed circuit board (PCB) and suspended thereon.

BACKGROUND OF THE INVENTION

The severity of a stenosis or lesion in a blood vessel may be assessed by obtaining proximal and distal pressure measurements relative to the given stenosis and using those measurements for calculating a value of a Fractional Flow Reserve (FFR). FFR is defined as the ratio of a first, or distal pressure Pdmeasured on the distal side of the stenosis to a second, or proximal pressure Pameasured on the proximal side of the stenosis, usually within the aorta. Conventionally, a sensor is placed on a distal portion of a guidewire or FFR wire to measure the distal pressure Pd, while an external pressure transducer is fluidly connected via tubing to a guide catheter to measure the proximal, or aortic (AO) pressure Pa. Calculation of the FFR value provides a stenosis specific index of the functional severity of the stenosis in order to determine whether the blockage limits blood flow within the vessel to an extent that treatment is needed. An optimal or normal value of FFR in a healthy vessel is 1.00, while values less than about 0.80 are generally deemed significant and in need of an interventional treatment. Common interventional treatment options include balloon angioplasty and/or stent implantation.

If an interventional treatment is required, the interventional device, such as a balloon catheter, is tracked over a guidewire to the site of the stenosis. Conventional FFR wires generally are not desired by clinicians to be used as guidewires for such interventional devices. Accordingly, if an intervention treatment is required, the clinician generally removes the FFR wire, inserts a conventional guidewire, and tracks the interventional device to the treatment site over the conventional guidewire.

To address this concern, efforts have been made to utilize catheters (micro-catheters) to take pressure measurements for calculating FFR. Using an FFR catheter with a pressure sensor mounted within a distal portion of the catheter to measure the distal pressure Pd, a clinician may use a preferred guidewire for tracking the FFR catheter to the site of the stenosis. If an interventional treatment is required, the guidewire used with the FFR catheter may remain in situ and the interventional device may be tracked over the existing guidewire to the site of the stenosis.

The pressure sensor is a sensitive device that can be affected by external stresses as well as stresses emanating from the pressure sensor itself. More precisely, the FFR catheter experiences stresses and strains, or torsional forces as the FFR catheter is advanced through the tortuous vasculature of a patient. These torsional forces on the FFR catheter may be transferred to the pressure sensor mounted thereon. The transferred torsional forces may deflect the diaphragm of the pressure sensor and may result in errors in the measured distal pressure Pd, which in turn will may result in inaccurate FFR calculations. Thus, in order to provide a stable pressure output of the pressure sensor, it is desirable to minimize or eliminate stresses on the pressure sensor.

Additionally, manufacture of a distal portion of the FFR catheter with the pressure sensor mounted therein may be difficult. For example, threading of a sensor wire through the distal shaft portion, mounting of the pressure sensor, and connection of the sensor wire to the pressure sensor in a confined space inside the distal portion during manufacture provides both build and maintenance challenges.

Accordingly, there is a need for systems and methods for the manufacture of reduce inaccurate readings resulting from torsional deflection of a pressure sensor of a distal portion of an FFR catheter or a distal portion of an FFR guidewire.

BRIEF SUMMARY OF THE INVENTION

Embodiments hereof are directed to a catheter for measuring a pressure distal of a stenosis. The catheter includes a shaft including a housing in a distal portion of the shaft. A flexible printed circuit board is coupled to the housing. A pressure sensor is coupled to the flexible printed circuit board and suspended within the housing. An aperture is configured to allow blood flow into the housing and into contact with the pressure sensor. In some embodiments, the flexible printed circuit board is coupled to the housing at a fixation point. In some embodiments, the flexible printed circuit board is coupled to the housing at a plurality of fixation points. In some embodiments a cover coupled to the housing, the cover including a first configuration wherein the cover covers the pressure sensor. In some embodiments, the aperture is formed between an inner surface of the cover and an outer surface of the housing.

In some embodiments, a sensor lumen extends through the shaft of the catheter, and the flexible printed circuit board is disposed in the sensor lumen. In some embodiments, at least one through-hole extends radially through the distal portion of the shaft to the sensor lumen. In some embodiments, the at least one through hole is configured to enable access to couple the flexible printed circuit board to the housing. In some embodiments, the housing includes a guidewire lumen.

In some embodiments, the housing includes an open seat and the pressure sensor is suspended within the open seat. In some embodiments, the catheter includes a sensor lumen extending through the shaft. In some embodiments, the sensor lumen includes a first portion proximal of the open seat and a second portion distal of the open seat. In some embodiments, a first portion of the flexible printed circuit board is disposed in the first portion of the sensor lumen, a second portion of the flexible printed circuit board is disposed in the second portion of the sensor lumen, and a third portion of the flexible printed circuit board with the sensor coupled thereto is suspended in the open seat between the first and second portions of the sensor lumen. In some embodiments, a through-hole extends through the housing to the first portion of the sensor lumen. In some embodiments, the second portion of the sensor lumen is sized and shaped to fit the third portion of the flexible printed circuit board with the pressure sensor coupled thereto within the second portion of the sensor lumen.

Embodiments hereof are also directed to a system for calculating a Fractional Flow Reserve of a stenosis in a blood vessel. The system includes a catheter including a shaft with a housing in a distal portion of the shaft. A distal pressure sensor is suspended within the housing. An aperture is configured to provide blood flow to the distal pressure sensor suspended within the housing. The system further includes a proximal pressure-sensing device configured to measure a proximal blood pressure proximal of the stenosis. The system further includes a processing device in communication the distal pressure sensor and the proximal pressure-sensing device. The catheter is configured for placement within a blood vessel such that the housing is distal of the stenosis and blood distal of the stenosis flows through the aperture into the housing and in contact with the distal pressure sensor such that the distal pressure sensor measures a distal blood pressure distal of the stenosis. The processing device is configured to calculate the Fractional Flow Reserve based on the distal blood pressure relative to the proximal blood pressure.

Embodiments hereof are also directed to a system for calculating a Fractional Flow Reserve of a stenosis in a blood vessel. The system includes a guidewire including a housing in a distal portion of the guidewire. A distal pressure sensor is suspended within the housing. An aperture is configured to provide blood flow to the distal pressure sensor suspended within the housing. The system further includes a proximal pressure-sensing device configured to measure a proximal blood pressure proximal of the stenosis. The system further includes a processing device in communication the distal pressure sensor and the proximal pressure-sensing device. The guidewire is configured for placement within a blood vessel such that the housing is distal of the stenosis and blood distal of the stenosis flows through the aperture into the housing and in contact with the distal pressure sensor such that the distal pressure sensor measures a blood pressure distal of the stenosis. The processing device is configured to calculate the Fractional Flow Reserve based on the distal blood pressure relative to the proximal blood pressure.

Embodiments hereof are also directed to a method of manufacturing an FFR catheter. The method includes forming a shaft including a housing in a distal portion of a shaft, a guidewire lumen, and a sensor lumen. The method further includes forming an open seat in the housing. The method further includes coupling a pressure sensor to a flexible printed circuit board and to a sensor trace of the flexible printed circuit board. The method further includes positioning the flexible printed circuit board within the sensor lumen such that the pressure sensor coupled to the flexible printed circuit board is suspended within the open seat of the housing. In some embodiments, the method further includes coupling the flexible printed circuit board to the housing at a fixation point. In some embodiments, the method further includes after the step of positioning the flexible printed circuit board, sliding a cover from a first position proximal or distal of the housing to a second position wherein the cover is positioned over the open seat, and after sliding the cover to the second position, attaching the cover to the housing. In some embodiments, the method further includes forming an aperture in the distal portion of the shaft, wherein the aperture enables blood flow into the open seat with the cover in the second position.

In some embodiments, the sensor lumen includes a first portion proximal of the open seat and a second portion distal of the open seat. In some embodiments, the method includes positioning the flexible printed circuit board such that a first portion of the flexible printed circuit board is in the first portion of the sensor lumen, a second portion of the flexible printed circuit board is in the second portion of the sensor lumen, and a third portion of the flexible printed board with the pressure sensor coupled thereto is distal of the second portion of the sensor lumen. In some embodiments, the method further includes sliding the flexible printed circuit board proximally such that the pressure sensor slides through the second portion of the sensor lumen and into the open seat. In some embodiments, the method further includes coupling the flexible printed circuit board to the housing at a fixation point. In some embodiments, the flexible printed circuit board is coupled to the housing at a first fixation point proximal of the open seat and a second fixation point distal of the open seat.

DETAILED DESCRIPTION OF THE INVENTION

Specific embodiments of the present invention are now described with reference to the figures, wherein like reference numbers indicate identical or functionally similar elements. The terms “distal” and “proximal”, when used in the following description to refer to a catheter or delivery system are with respect to a position or direction relative to the treating clinician. Thus, “distal” and “distally” refer to positions distant from, or in a direction away from the treating clinician, and the terms “proximal” and “proximally” refer to positions near, or in a direction toward the clinician. The terms “distal” and “proximal” used in the following description to refer to a vessel or a stenosis are used with reference to the direction of blood flow. Thus, “distal” and “distally” refer to positions in a downstream direction with respect to the direction of blood flow, and the terms “proximal” and “proximally” refer to positions in an upstream direction with respect to the direction of blood flow.

The following detailed description is merely exemplary in nature and is not intended to limit the invention or the application and uses of the invention. Although the description of the invention is in the context of treatment of blood vessels such as the coronary arteries, the invention may also be used in any other body passageways where it is deemed useful such as but not limited to peripheral arteries, carotid arteries, renal arteries, and/or venous applications. Furthermore, there is no intention to be bound by any expressed or implied theory presented in the preceding technical field, background, brief summary or the following detailed description.

FIG. 1is a schematic partial side and partial perspective illustration of a system100for calculating a Fractional Flow Reserve (FFR) according to an embodiment hereof. The system100includes an FFR catheter or FFR micro-catheter102, a proximal pressure-sensing device (not shown), and a processing device104. The FFR catheter102is configured to be disposed with a proximal portion thereof extending outside of a patient and a distal portion thereof positioned in situ within a lumen LU of a vessel VS having a stenosis ST. In an embodiment, the vessel VS is a blood vessel such as but not limited to a coronary artery. The stenosis ST is generally representative of any blockage or other structural arrangement that results in a restriction to the flow of fluid through the lumen LU of the vessel VS. The stenosis ST may be a result of plaque buildup, including without limitation plaque components such as fibrous, fibro-lipidic (fibro fatty), necrotic core, calcified (dense calcium), blood, fresh thrombus, and mature thrombus. Generally, the composition of the stenosis ST will depend on the type of vessel being evaluated. In that regard, it is understood that embodiments hereof are applicable to various types of blockages or other narrowing of a vessel that results in decreased fluid flow.

The FFR catheter102includes shaft103including a proximal portion106(also referred to as a “proximal shaft portion”) and a distal portion108(also referred to as a “distal shaft portion”). A pressure sensor110, shown inFIG. 1and in greater detail inFIGS. 2-4, is suspended within a housing112of the distal portion108. The pressure sensor110may mounted onto a flexible printed circuit board114(hereafter referred to as a “flex PCB” for simplicity). The flex PCB114is coupled to the housing112within a sensor lumen116of the distal portion108such that the pressure sensor110is suspended within an open seat122of the housing112. The pressure sensor110is covered by a cover118. The cover118is a separate component attached to the housing112of the distal shaft108during manufacture to simplify manufacturing of the distal portion108with the pressure sensor110suspended therein. As used herein, the term “separate” when used to describe that the cover118is a “separate” piece attached to the distal shaft110during manufacture, it is meant that the cover118is not formed as part of the distal portion108of shaft103. Instead, the two pieces are separate and are attached as described below during manufacture. For example, and not by way of limitation, a distal shaft portion that is formed with a portion covering a pressure sensor would not be a “separate” cover. Similarly, a “cover” that is co-formed with a “distal shaft portion”, such as by molding, is not considered a “separate” cover attached to the distal shaft portion.

In the embodiment shown inFIG. 1, the shaft103is a multi-lumen extrusion including a guidewire lumen120extending through the proximal portion106and the distal portion108. The guidewire lumen120is configured to receive a guidewire GW. However, instead of the over-the-wire configuration shown inFIG. 1, the FFR catheter102may have a rapid exchange configuration wherein the guidewire lumen120extends through the distal portion108and a portion of the proximal portion106, and the guidewire GW exits through a rapid exchange port (not shown) in a distal portion of the proximal portion106. The FFR catheter102also includes the sensor lumen116extending through the proximal portion106and a proximal portion of the distal portion108. In an embodiment, the sensor lumen116is of a consistent cross-sectional profile along the entire length of the sensor lumen116. In other embodiments, the sensor lumen116may have a larger cross-sectional profile distal of the open seat122for simplifying the installation of the flex PCB114and the pressure sensor110mounted thereon, and a smaller cross-sectional profile proximal of the open seat122for receiving only the flex PCB114. The shaft103includes a proximal end124coupled to a hub or luer126. The shaft103may be formed of polymeric materials, non-exhaustive examples of which include polyethylene, polyether block amide (PEBA), polycarbonate, acrylonitrile butadiene styrene (ABS), polyether ether ketone (PEEK), polyamide, polyimide, and/or combinations thereof, either blended or co-extruded.

As shown inFIGS. 2-3, the distal portion108of shaft103includes the housing112, a distal portion of the flex PCB114, the pressure sensor110, the cover118, a tip134, and an aperture136. The shaft103includes a distal end132at a distal end of the distal portion108. A distal portion of the guidewire lumen120extends through the distal portion108. A distal portion of the sensor lumen116extends through the housing112of the distal portion108. The distal portion108is configured for measuring a pressure distal of a stenosis. More specifically, the distal portion108is configured such that the pressure sensor110and the tip134are disposed on the distal side DS of the stenosis ST such that the pressure sensor110can measure a distal pressure Pddistal of the stenosis ST, as shown inFIG. 1.

In the embodiment ofFIGS. 1-4, the housing112of the distal portion108is of a generally tubular shape having a proximal end and a distal end140, as shown inFIGS. 3 and 4. The housing112defines the open seat122, extending from an outer surface156of the housing112inward. The open seat122is configured to receive the pressure sensor110and a portion of the flex PCB114and is sized to allow for movement of the pressure sensor110suspended therein. The open seat122is further configured to receive a fluid therein from the aperture136. The housing112further defines a through-hole142, extending from the outer surface156of the housing112inward to the sensor lumen116. The through-hole142is configured to provide access to the sensor lumen116to aid in the coupling of the flex PCB114to the housing112within the sensor lumen116.

While the proximal portion106and the distal portion108of the shaft103of the FFR catheter102are described herein as a single extrusion, this is not meant to be limiting, and in another embodiment, the proximal portion106and the distal portion108may be separate components with a proximal end of the distal portion108coupled to a distal end of the proximal portion106. If formed as separate components, the distal portion108may be coupled to the proximal portion106by methods such as, but not limited to adhesives, fusing, welding, or any other method suitable for the purposes described herein

In the embodiment ofFIGS. 3 and 4, the open seat122is shown as a generally rectangular cuboid. However, this is not meant to be limiting. The open seat122may be of any shape suitable to house the pressure sensor110and the flex PCB114onto which the pressure sensor110is mounted and provide sufficient space for fluid to enter the open seat122such that the pressure sensor110may measure a pressure of the fluid. The open seat122may be formed in the housing112of the distal portion108by various methods, non-limiting examples of which include the open seat122formed as part of a molding process, a skiving process, machining, laser ablation, punching, or other suitable methods.

Although shown inFIGS. 3 and 4with one (1) through-hole142positioned proximal of the open seat122, in alternative embodiments, more than one (1) through-hole142may be utilized with the housing112and positioned proximal and/or distal of the open seat122in any combination. Even further, while the through-hole142is shown as a generally circular aperture, this is not meant to be limiting and the through-hole142may be of any shape suitable to provide access to the sensor lumen116for the purposes described herein. The through-hole142may be formed in the housing112by various methods, non-limiting examples of which include a skiving process, machining, laser-etching, punching, or other suitable methods.

In an embodiment shown in greater detail inFIG. 5, the flex PCB114is a flexible printed circuit board including the sensor traces146laminated between layers of polymer such as, but not limited to polyethylene terephthalate (PET), polyimide, and adhesive sandwich. The pressure sensor traces146may be formed of suitable materials such as, but not limited to copper. Alternatively, the flex PCB114may be formed by photolithography. The flex PCB114is configured to be coupled to the housing112of the distal portion to suspend the pressure sensor110within the open seat122of the distal portion108of shaft103, as best shown inFIGS. 3 and 4. The flex PCB114is sized to be received within the sensor lumen116. With the flex PCB114disposed within the sensor lumen116and coupled to the distal portion108, the pressure sensor110is suspended within the open seat122by the flex PCB114and is isolated from both external stresses on the FFR catheter102and from stresses emanating from the pressure sensor110, itself. More specifically the pressure sensor110is isolated from external stresses on the distal portion108generated by advancement through and positioning within the often tortuous vasculature. Thus, stresses imparted on the distal portion108are not transmitted to the pressure sensor110and the sensor readings of the pressure sensor110are not affected by the stress loads on the distal portion108of the FFR catheter102. The flex PCB114is coupled to the housing112of the distal portion108at a proximal fixation point148proximal of the open seat122and a distal fixation point150distal of the open seat122. While described as having two (2) fixation points148,150, this is not meant to be limiting, and the flex PCB114may be coupled to the housing112at more or fewer fixation points either proximal or distal of the open seat122, in any combination. The flex PCB114may be coupled to the housing112within the sensor lumen116by methods such as, but not limited to adhesives, a mechanical interlock, thermal reflow, or other suitable methods.

The pressure sensor110includes a pressure-sensing surface144, as best shown inFIG. 3. The pressure sensor110may be a piezo-resistive pressure sensor, a piezo-electric pressure sensor, a capacitive pressure sensor, an electromagnetic pressure sensor, an optical pressure sensor, and/or combinations thereof suitable for the purpose described herein. While the pressure sensor110is shown inFIG. 3configured with the pressure-sensing surface144facing radially outward, the pressure-sensing surface144may face in other directions to measure distal pressure Pdof a fluid outside the distal portion108that has entered the open seat122through the aperture136. The pressure sensor110is further configured to communicate a measured distal pressure Pdwith the processing device104through sensor traces146of the flex PCB114, shown inFIG. 3. The sensor traces146form a wired connection similar to the wired connection as described in U.S. Patent Application Publication No. 2015/0305633 A1 to McCaffrey et al., incorporated by reference herein in its entirety. The pressure sensor110is coupled to the flex PCB114and suspended within the open seat122of the distal portion108. The pressure sensor110may be coupled to the flex PCB114, for example, and not by way of limitation, by adhesives, fusing, welding, or any other method suitable for the purposes of the present disclosure. The pressure sensor110is further coupled to the sensor traces146of the flex PCB114. The pressure sensor110may be coupled to the sensor traces146for example, and not by way of limitation, by soldering, fusing, welding, for any other method suitable for the purposes of the present disclosure. While shown with three (3) sensor traces146, this is not meant to be limiting, and the flex PCB114may include more or fewer sensor traces146.

In an embodiment, the tip134is of a generally frusto-conical shape. The tip134includes the proximal end152coupled to the distal end140of the housing112, and a distal end154, as best shown inFIG. 3. The tip134may be formed of polymeric materials, non-exhaustive examples of which include polyethylene, polyether block amide (PEBA), polycarbonate, acrylonitrile butadiene styrene (ABS), polyether ether ketone (PEEK), polyamide and/or combinations thereof, or other materials suitable for the purposes described herein.

In an embodiment, the cover118is of a generally tubular shape with a proximal end162, a distal end164, and a cover lumen166, as shown inFIG. 6. The cover lumen166extends through the cover118between the proximal end162and the distal end164. The cover118may be disposed in a second configuration, as shown inFIG. 3, wherein the cover118is not coupled to the housing112and is disposed proximal of the open seat122. The second configuration is used during manufacture to simplify installation of the flex PCB114and the pressure sensor110. The cover118is moved during manufacture to a first configuration shown inFIG. 7, wherein the cover118is coupled to the housing112such that a portion of the housing112, the open seat122(obscured by the cover118inFIG. 7), and the pressure sensor110(obscured by the cover118inFIG. 7) are disposed within the cover lumen166. The cover118is configured to protect the pressure sensor110when the cover118is in the first configuration. The cover118may be coupled to the housing112by various methods, including, but not limited to adhesives, heat shrink tubing, swage coupling, interference fit, mechanical interlock, or other suitable methods. The cover118may be formed of various materials, non-limiting examples including stainless steel, gold, platinum, and/or iridium, and alloys thereof. In some embodiments, the cover may be formed of or include radiopaque materials (e.g., gold, platinum, and/or iridium) such that the cover118may act as a marker band. While described as a tube or cylinder, the cover118may include alternative shapes such as, but not limited to a half-cylinder.

As noted above, the aperture136is in fluid communication with the open seat122, as shown inFIGS. 2, 3, and 4. The aperture136is an opening extending from the outer surface156of the housing112and extending into the open seat122of the distal portion108. The aperture136is configured to allow fluid therethrough to the pressure sensor110. More specifically, the aperture136is configured to enable fluid flow from outside the housing112through the aperture136and into the open seat122, and into contact with the pressure-sensing surface144of the pressure sensor110. In an embodiment shown inFIG. 7, the aperture136is formed between an inner surface of the cover118and the outer surface156of the housing112at a distal end158of the open seat122. More precisely, the aperture136is formed via a longitudinal groove or depression160disposed within a proximal portion of the tip134and extending proximally within a distal portion of the housing112to the distal end158of the open seat122(obscured from view inFIG. 7by the cover118, but visible inFIG. 3). The longitudinal groove160provides fluid flow to the aperture136, and the aperture136provides the fluid flow to the open seat122and the pressure sensor110, suspended therein. The aperture136is sized such that a sufficient amount of blood flows into the open seat122of the housing112. In an embodiment, the aperture136is in the range of 100 to 500 microns in diameter. aperture136may be formed as an integral component of the housing112and the tip134of the distal portion108or may be formed by removing material from the housing112and the tip134by any suitable method such as, but not limited to heat processes with mandrels and dies, cutting, machining, laser ablation, or other methods suitable for the purposes described herein. The aperture136is shown as generally tubular, but this is not meant to limit the design, and other shapes may be utilized. Moreover, while only one (1) aperture136is shown, this is not meant to be limiting, and more than one (1) aperture136may be utilized, and disposed at other locations of the distal portion108.

With an understanding of the components above, it is now possible to describe their interaction as a system to provide stable, accurate distal pressure measurements for accurate FFR calculations by reducing torsional forces transmitted to the pressure sensor110from the shaft103, and in particular the distal portion108of the shaft103.

Referring toFIG. 8, the system100is shown disposed through a guide catheter200, which is utilized as the proximal pressure-sensing device, as explained below. The guide catheter200and the guidewire GW are advanced through the vasculature to a desired site. The guidewire GW may be back-loaded into the FFR catheter102(i.e., the proximal end of the guidewire GW is loaded into the distal end of guidewire lumen120at the distal end132of the shaft103. The FFR catheter102may then be advanced over the guidewire GW and through a lumen206of the guide catheter200to the desired treatment site. In particular, with a distal end204of the guide catheter200disposed at a desired site proximal of the stenosis ST, such as in the aortic sinus AS, the FFR catheter102is advanced through the lumen206and distal of the distal end204of the guide catheter200. The FFR catheter102is advanced such that the housing112with the pressure sensor110disposed therein is disposed distal of the stenosis ST of the vessel VS. Blood flow from the aortic sinus AS fills the lumen206and tubing214via a port210of a proximal portion212of the guide catheter200. The blood pressure Paat the distal end204of the guide catheter200is measured by an external pressure transducer250via the fluid (blood) column extending through the lumen206and the tubing214. Thus, the external pressure transducer250is configured to measure proximal, or aortic (AO) pressure Paat the distal end204of the guide catheter200.

The external pressure transducer250is configured to communicate the measured proximal pressure Pato the processing device104via a pressure transducer wire252, as shown inFIG. 8. While the pressure transducer250is shown inFIG. 8as communicating the measured proximal pressure Pawith the processing device104via the pressure transducer wire252, this is not meant to limit the design and the pressure transducer250may communicate with the processing device104by any means suitable for the purposes described, including, but not limited to, electrical cables, optical cables, or wireless devices.

Simultaneously, blood on the distal side DS of the stenosis ST flows through the aperture136and into the open seat122. The blood within the open seat122is in contact with the pressure-sensing surface144of the pressure sensor110, suspended therein. The pressure of the blood within the open seat122is equal to the pressure on the distal side DS of the stenosis ST.

The suspension of the pressure sensor110within the open seat122isolates the pressure sensor110from torsional forces on the shaft103, in particular the distal portion108thereof, that are transferred to a directly mounted pressure sensor. As used herein, the term “directly mounted” is meant to indicate that a portion of the pressure sensor is in contact with the shaft, and that stresses imparted on the shaft are transmitted to the pressure sensor and deflect the diaphragm of the pressure sensor. The deflected diaphragm of the pressure sensor may result in sporadic and inaccurate pressure measurement. Thus, the suspended pressure sensor110provides a stable and accurate measured distal pressure Pdas the pressure sensor110is not affected by stresses on the distal portion108of the shaft103. The measured distal pressure Pdsensed by the pressure sensor110is communicated to processing device104. The processing device104calculates the Fractional Flow Reserve (FFR) based on the measured distal pressure Pddivided by the measured proximal/aortic pressure Pa, or FFR=Pd/Pa.

FIG. 9is a schematic partial side and partial perspective illustration of a system300for calculating a Fractional Flow Reserve (FFR) according to another embodiment hereof. The system300includes an FFR guidewire302, a proximal pressure-sensing device (not shown), and a processing device304. The FFR guidewire302is configured to be disposed with a proximal portion thereof extending outside of a patient and a distal portion thereof positioned in situ within a lumen LU of a vessel VS having a stenosis ST. In an embodiment, the vessel VS is a blood vessel such as but not limited to a coronary artery.

The FFR guidewire302includes a proximal portion306and a distal portion308. A pressure sensor310, shown inFIG. 9and in greater detail inFIG. 10, is disposed within a housing segment312of the distal portion308. The pressure sensor310is mounted onto a flexible printed circuit board314(hereafter referred to as a “flex PCB” for simplicity), and the flex PCB314is coupled to a housing344of the housing segment312within an open seat316. The pressure sensor310suspended within the open seat316of the housing344. The proximal portion306of the FFR guidewire302includes a proximal end320and a distal end322. The proximal portion306may be a generally tubular shaped hypotube configured to have sufficient pushability to advance the FFR guidewire302through the tortuous vasculature to a desired treatment site. A proximal portion of a sensor lumen324extends from the proximal end320to the distal end322within the proximal portion306.

In the embodiment shown inFIG. 9, the distal portion308includes a proximal end326coupled to the distal end322of the proximal portion306, and a distal end328. An inner wire330extends from the proximal end326to the distal end328of the distal portion308. The distal portion308further includes the housing segment312disposed between a proximal segment332and a distal segment334of the distal portion308, as best viewed inFIG. 10. A distal end336of the proximal segment332is coupled to a proximal end338of the housing segment312, and a distal end340of the housing segment312is coupled to a proximal end342of the distal segment334. The distal portion308of the FFR guidewire302further includes a distal portion of the sensor lumen324extending through the proximal segment332and a portion of the housing segment312of the distal portion308. The sensor lumen324is configured to receive the flex PCB314. In an embodiment, the sensor lumen324is of a consistent cross-sectional profile along the entire length of the sensor lumen324. In other embodiments, the sensor lumen324may have a larger cross-sectional profile within the housing segment312for simplifying installation of the flex PCB314and the pressure sensor310, and a smaller cross-sectional profile proximal of the housing segment312for receiving only the flex PCB314.

In the embodiment shown inFIG. 10, the proximal segment332of the distal portion308includes a helically wound outer wire339, a proximal portion of the inner wire330, a proximal end343(not visible inFIG. 10), the distal end336, and a corresponding portion of the sensor lumen324. The corresponding portion of the sensor lumen324extends from the proximal end343to the distal end336of the proximal segment.

In the embodiment ofFIG. 10, the housing segment312includes the proximal end338, the distal end340, the housing344, and a corresponding portion of the inner wire330(obscured by the pressure sensor310, the flex PCB314, and the sensor lumen324inFIG. 10). The housing segment312further includes a corresponding portion of the sensor lumen324. The housing segment312is configured to provide a platform to mount the flex PCB314to suspend the pressure sensor310, which is coupled to the flex PCB314, within the open seat316. The pressure sensor310is thereby isolated from external stresses on the FFR guidewire, and in particular the distal portion308thereof, as described previously with respect to the suspended pressure sensor110and the distal portion108ofFIGS. 1-8. The housing344of the housing segment312of the distal portion308is of a generally tubular shape. The housing344defines the open seat316, extending from an outer surface of the housing344inward. The open seat316is configured to receive the suspended pressure sensor310and a portion of the flex PCB314therein. The open seat316is further configured to receive a fluid therein from an aperture348. The open seat316may be formed as an integral component of the housing344or may be formed by removing material from the housing344by any suitable method such as, but not limited to heat process with mandrels and dies, cutting, machining, or other methods suitable for the purposes described herein. The housing344may be formed of various materials, non-limiting example of which include metals, metal alloys, polymers, composites, or other suitable materials.

As shown in the embodiment ofFIG. 10, the distal segment334of the distal portion308includes the proximal end342, a distal end350, a helically wound outer wire352, and a distal portion of the inner wire330.

The proximal, distal, and housing segments332,334,312may each include structures to vary the level of stiffness, flexibility, and torquability of each segment. Thus, the flexibility of each segment may be different than the other segments. Further, the flexibility of each segment may vary along its length. For example, the distal segment334may have a greater flexibility at the distal end350than at the proximal end342to enhance atraumatic advancement of the FFR guidewire302thorough the tortuous vasculature. In another example, the housing segment312may have increased stiffness to support the flex PCB314and the pressure sensor310suspended therein. In an example, the distal segment334may be 3 centimeters (cm) in length, the housing segment312may be between 0.3 centimeter (CM) and 1.5 centimeters (cm) inclusive, and the proximal segment332may be 30 centimeters (cm). The overall length of the FFR guidewire302may be in the range of 170 cm for a rapid exchange configuration and 300 cm for an over the wire configuration.

Components of the proximal, housing, and distal segments332,312,334may be formed of various materials including, but not limited to metals, metal alloys, polymers, composites, or other suitable materials. The proximal, housing, and distal segments332,312,334may be coupled to the adjacent segment by various methods, non-limited examples of which include adhesives, fusing, welding, mechanical couplers, or other suitable methods. The proximal segment332of the distal portion308may be coupled to the proximal portion306by methods such as, but not limited to adhesives, fusing, welding, mechanical couplers, or other suitable methods.

The flex PCB314is similar to the flex PCB114described with the embodiment ofFIG. 1. Consequently, the details and alternatives of the flex PCB314will not be repeated. The flex PCB314is coupled to the housing344at a proximal fixation point360proximal of the open seat316and a distal fixation point362distal of the open seat316. While described as having two (2) fixation points360,362, it will be understood that the flex PCB314may be coupled to the housing344at more or fewer fixation points either proximal or distal of the open seat316, in any combination. The flex PCB314may be coupled to the housing344by methods such as, but not limited to adhesives, or other suitable methods.

The pressure sensor310is similar to the pressure sensor110described previously. Therefore, details of the pressure sensor310will not be repeated here.

As noted above, the housing344includes the aperture348in fluid communication with the open seat316. The aperture348is an opening extending from an outer surface of the housing344into the open seat316. The aperture348is configured to enable fluid flow therethrough. Thus, fluid outside the housing segment312may flow through the aperture348, into the open seat316, and into contact with the pressure-sensing surface340of the pressure sensor310. While the aperture348is shown with a specific shape, this is not meant to be limiting, and the aperture348may have other shapes and sizes such that a sufficient amount of blood flows into the open seat316. The aperture348may be formed as an integral component of the housing344or may be formed by removing material from the housing344by any suitable method such as, but not limited to heat process with mandrels and dies, cutting, machining, or other methods suitable for the purposes described herein.

Referring toFIG. 11, a method400of manufacturing a distal portion108of an FFR catheter102with a suspended pressure sensor110for measuring a distal pressure according to an embodiment hereof is described.

In step402, the shaft103, including the distal portion108, the proximal portion106, the guidewire lumen120, and the sensor lumen116, is formed by an extrusion process. In step404, the distal portion108of the shaft103is processed to form the open seat122and the through-hole142.

In step406, the pressure sensor110is coupled to the flex PCB114and the sensor traces146of the flex PCB114. In step408, the flex PCB114is threaded through the sensor lumen116of the shaft103. In one embodiment, the flex PCB114is threaded through the sensor lumen116without the sensor mounted on the flex PCB114. A distal portion of the flex PCB114extends distally beyond a distal end of the housing112, as shown inFIG. 12. The pressure sensor110may then be mounted on the flex PCB114. Next, the flex PCB114with the sensor110mounted thereon may be moved proximally through the portion of the sensor lumen116distal of the open seat122until the pressure sensor110is disposed within the open seat122(as shown inFIG. 4). In another embodiment, the pressure sensor100may be coupled to the flex PCB114prior to threading the flex PCB114through the sensor lumen116. In such an embodiment, after the sensor110is coupled to the flex PCB114, a proximal end of the flex PCB114is inserted into a distal end of the sensor lumen116, and the flex PCB114is advanced proximally until the sensor110is adjacent the distal end140of the housing112, as shown inFIG. 12. Next, the flex PCB114with the sensor110mounted thereon may be moved proximally through the portion of the sensor lumen116distal of the open seat122until the pressure sensor110is disposed within the open seat122(as shown inFIG. 13).

Next, in step410, the flex PCB114is coupled to the housing112of the distal portion108. More precisely, the flex PCB114is coupled at the proximal fixation point148to an inner surface of the housing112within the sensor lumen116, proximal of the open seat122. Access to the proximal fixation point148is available via the through-hole142, as shown inFIG. 14. Further, the flex PCB114is coupled at the distal fixation point150to the inner surface of the housing112within the sensor lumen116, distal of the open seat122. Access to the distal fixation point150is available via the sensor lumen116at the distal end140of the housing112, as shown inFIG. 13.

In step412, the tip134is coupled to the distal end140of the housing112in a step412.

In step414, the aperture136is created by processing the housing112and the tip134of the distal portion108to form the longitudinal groove160.

In step416, the cover118is positioned over the open seat122of the housing112with the pressure sensor110suspended therein by distally sliding or translating the cover118in a direction indicated by arrow170over the housing112of the distal portion108, as shown inFIG. 15.

In a next step418, the cover118is coupled to the housing118or the distal portion108.

Although the method describes a particular order of the steps of the method ofFIG. 11, the order may be different. For example, and not by way of limitation, the aperture136may be formed at any time. Further, while the method describes creating the aperture136via the formation of the longitudinal groove160in both the tip134and the housing112, this is not meant to limit the method, and step414may alternatively include creating the aperture136in the tip134, in the housing112, and/or in the cover118, in any combination thereof. Even further, more than one aperture136may be created.

While only some embodiments according to the present invention have been described herein, it should be understood that they have been presented by way of illustration and example only, and not limitation. Various changes in form and detail can be made therein without departing from the spirit and scope of the invention. Further, each feature of each embodiment discussed herein, and of each reference cited herein, can be used in combination with the features of any other embodiment. All patents and publications discussed herein are incorporated by reference herein in their entirety.