WO2017098198A1

WO2017098198A1 - Microcatheter apparatus

Info

Publication number: WO2017098198A1
Application number: PCT/GB2016/053409
Authority: WO
Inventors: Paul Weinberger; Graham Scott Gutsell; Ahmed ELGHAMAZ; Connor O'brien; Michael Dunning; Eoin BRENNAN
Original assignee: Diasolve Ltd
Priority date: 2015-12-07
Filing date: 2016-11-03
Publication date: 2017-06-15
Also published as: GB2538124B; GB2538124A; GB201521552D0

Abstract

Microcatheter apparatus (10) is disclosed which comprises a microcatheter shaft (60) defining a microcatheter lumen (64) and having a radiopaque distal tip (72); a hub (20) attached to a proximal end (62) of the microcatheter shaft; and a strain relief sleeve (80) extending distally from the hub along the microcatheter shaft. The hub comprises a first port (34) to admit a pressure wire to the microcatheter lumen through the hub, and a second port (30) for fluid connection to the microcatheter lumen, and an axial lumen (38) in fluid communication with the microcatheter lumen. The axial lumen comprises a distal end section (42) having a diameter substantially equal to the diameter of the microcatheter lumen, a proximal section having a larger diameter, and a tapered section (40) therebetween. Also disclosed are apparatus for use in coronary catheterisation procedures, comprising the microcatheter.

Description

Microcatheter Apparatus

Field of Invention

This invention relates to apparatus for use in catheterisation procedures. In particular, the invention relates to microcatheter apparatus for use in coronary catheterisation procedures. Background to the Invention

Coronary catheterisation procedures typically involve first inserting an elongate, flexible guide wire into a peripheral artery of the patient, for example by an incision in the wrist or groin. A guide catheter is then passed over the guide wire to position a distal end of the catheter at a site in or adjacent to the coronary artery of interest. The use of the guide wire can ease the initial guiding of the guide catheter through the patient's arterial network.

Once in place, the guide wire can be withdrawn, and a variety of other devices can then be advanced into the coronary artery through the lumen of the guide catheter for therapeutic or diagnostic purposes. For example, a pressure wire comprising an elongate, flexible wire with a miniature pressure sensor located at, or near, its distal tip can be advanced into the coronary arteries beyond the distal end of the guide catheter to measure the actual local blood pressure at different locations.

In another example, a pressure catheter may be used. Typically, a pressure catheter is a rapid exchange microcatheter with a miniature pressure sensor located at, or near, its distal tip, as described for example in US Patent Application Publication No. US 2010/0241008.

Such devices can be useful in a variety of clinical techniques. For example, in Fractional Flow Reserve (FFR) analysis of a coronary artery stenosis, the pressure wire or pressure catheter can be can be advanced through the structures of the heart to measure the actual local blood pressure downstream of an arterial stenosis. This local pressure can be compared to an aortic blood pressure measurement obtained using a proximal pressure sensor connected in a flow line at a point proximal of the guide catheter. The proximal sensor is positioned at the same elevation as the patient's heart, for example on a drip stand, to avoid systematic errors arising from a hydrostatic head of pressure. The signals from both pressure sensors are normally displayed in real-time on a pressure analyser/display unit. In addition to providing the cardiologist with instantaneous display of the patient's status, the unit may also calculate the ratio of the two pressures, which is used in FFR as a measure of the severity of a coronary stenosis.

It is desirable to perform FFR analysis under conditions of maximal myocardial hyperaemia. Hyperaemia can be stimulated by the administration of a hyperaemic agent, such as adenosine, by continuous intravenous infusion into, for example, a central femoral vein or a large antecubital peripheral cannula. In some cases, however, it is preferable to administer the hyperaemic agent directly into the coronary artery, for example to help to reduce the dose of agent required.

Accordingly, it may be convenient to use the guide catheter for the delivery of the hyperaemic agent directly to the site of interest in the coronary artery during the procedure, either by bolus injection or infusion, thus avoiding the need to obtain central venous access and making the procedure quicker and more comfortable for the patient.

It can also be desirable to use the guide catheter to deliver other fluids to the coronary artery, such as saline, other drugs in liquid form, and contrast agents for facilitating the imaging of the coronary artery using, for example, an x-ray imager. In a similar way, it may be desirable to extract liquid samples, for example for diagnostic purposes. One disadvantage of the use of the guide catheter for fluid delivery and/or extraction during FFR analysis and similar procedures is that the proximal pressure sensor generally only provides an effective means of measuring aortic pressure when there is no flow of liquid along the guide catheter, so that the prevailing conditions at the distal end of the guide catheter are replicated at the proximal sensor. When a liquid is being passed along the guide catheter, the proximal pressure sensor measurement no longer bears a simple relationship to the true aortic pressure. To avoid this erroneous situation, the proximal sensor is often isolated, normally by means of a valve, from the guide catheter during those parts of the procedure in which fluid is flowing along the guide catheter. This results in an interruption in monitoring of aortic blood pressure, which can be disadvantageous. For example, if a vasodilator drug such as adenosine is being introduced while the proximal sensor is in effect disabled, the exact time of maximal blood flow (hyperaemia) through the stenosis may occur when the pressure measurements for FFR are not being taken. As a result, the resultant data may have been obtained in less than ideal circumstances. An alternative proposal is described in Yoon et. al., American Heart Journal, 157 (6), 2009, p 1050-1056. In this case, a microcatheter is advanced along the guide catheter, alongside the pressure wire. With such an arrangement, the lumen of the microcatheter can be used for the delivery and/or extraction of fluids, thus avoiding fluid flow in the remaining portion of the lumen of the guide catheter. In this way, with the proximal pressure sensor fluidly connected to the lumen of the guide catheter, pressure transmission from the distal end of the guide catheter to the proximal pressure sensor is not affected or interrupted during infusion or sampling. In practice, however, such an arrangement introduces significant complexity and could be time consuming and complex to operate. Against this background, it would be desirable to provide apparatus and methods for use in catheterisation procedures in which fluid is delivered to a site whilst pressure measurements are simultaneously obtained. Summary of the Invention

According to a first aspect of the present invention, there is provided a microcatheter apparatus, comprising a microcatheter shaft defining a microcatheter lumen and having a radiopaque distal tip, a hub attached to a proximal end of the microcatheter shaft, and a strain relief sleeve extending distally from the hub along the microcatheter shaft. The hub comprises a first port to admit a pressure wire to the microcatheter lumen through the hub, a second port for fluid connection to the microcatheter lumen, and an axial lumen in fluid communication with the microcatheter lumen, the axial lumen comprising a distal end section having a diameter substantially equal to the diameter of the microcatheter lumen, a proximal section having a larger diameter, and a tapered section therebetween.

The microcatheter apparatus is suitable for use in cardiac catheterisation procedures, in which the microcatheter shaft can be advanced along a guide catheter, using the radiopaque tip to aid positioning. The microcatheter apparatus can then be used to provide access to a target site for a pressure wire by way of the first port and the microcatheter lumen, and to simultaneously deliver fluid, such as a hyperaemic agent, to the site by way of the microcatheter shaft and the second port. These operations can be performed without affecting fluid behaviour in the lumen of the guide catheter, so as to allow accurate monitoring of aortic blood pressure by means of a proximal pressure sensor connected to the lumen of the guide catheter. Furthermore, the pressure wire can be pre-loaded into the microcatheter apparatus before the microcatheter shaft is advanced along the guide catheter, thereby reducing the complexity and length of the procedure. Preferably, the first port is an axial port. Providing an axial port for the pressure wire allows easy insertion and manipulation of the pressure wire. The second port may be an inclined side port. The resulting shape of the microcatheter hub may be suitable for one-handed operation.

The hub comprises an axial lumen in fluid communication with the microcatheter lumen. The axial lumen includes a distal end section having a diameter substantially equal to the diameter of the microcatheter lumen, a proximal section having a larger diameter, and a tapered section therebetween. In this way, a smooth fluid flow path from the hub to the microcatheter lumen can be achieved, and the tapered portion can help to guide the pressure wire into the microcatheter lumen. The tapered portion preferably defines a cone angle of between 5° and 15°, more preferably approximately 10°.

The microcatheter shaft may be adhesively affixed to the hub. The hub may comprise a distal end formation having a shaft receiving passage for receiving a proximal end of the microcatheter shaft, and the strain relief sleeve may be attached or attachable to the distal end formation.

Preferably, the strain relief sleeve has a length of at least one half of the length of the hub. More preferably, the strain relief sleeve has a length of at least two thirds of the length of the hub. In one embodiment, the strain relief sleeve has a length of at least three quarters of the length of the hub. The provision of a relatively long strain relief sleeve helps to prevent kinking or other damage to the relatively thin microcatheter shaft.

The microcatheter shaft is preferably sized and shaped for compatibility with guide catheters that are typically used in coronary catheterisation procedures. To this end, the external diameter of the microcatheter shaft may be sized so that, in use, a sufficiently large space is provided for fluid between the microcatheter and the inner diameter of the guide catheter to allow an accurate measurement of the aortic pressure by a proximal pressure sensor connected to the guide catheter. The internal diameter of the microcatheter lumen is preferably sufficiently large to allow complete filling of the microcatheter lumen in a relatively short time period and to avoid a substantial pressure drop along the lumen during delivery of a hyperaemic agent. The wall thickness of the microcatheter shaft is preferably sufficient to provide enough strength to avoid kinking or other damage in use, whilst maintaining flexibility. With these considerations in mind, the inventors have determined that a microcatheter shaft having an external diameter of approximately 1 mm and/or an internal diameter of approximately 0.8 mm may be optimum for some applications, including FFR analysis. The microcatheter shaft, in particular the proximal end of the microcatheter shaft, may be strengthened to help prevent kinking or squashing with consequent restriction of fluid flow, for example by thickening, reinforcing or using a stiffer material. The microcatheter shaft may be of a thermoplastic elastomer material, such as a polyether block amide material. The material of the microcatheter shaft may have a Shore D hardness of between 60 and 80. Similarly, the strain relief sleeve may be of a thermoplastic elastomer material such as a polyether block amide material, and may have a Shore D hardness of between 20 and 50.

The radiopaque tip is preferably of a material having a lower hardness than the material of the microcatheter shaft, so as to reduce or avoid trauma in the event that the tip contacts biological structures in use. For the same reason, the radiopaque tip may comprise a rounded or chamfered distal end. The tip may be of a thermoplastic elastomer material filled with a metal to provide radiopacity. In one example, the tip is of a material comprising tungsten and a polyether block amide material. Alternatively or additionally, a metal band around the tip may be used. For example, for some applications the material of the tip may not be metal-loaded, and instead the tip may include a radiopaque marker band, such as a platinum/iridium marker band. The tip material may have a Shore D hardness of between 30 and 60. The radiopaque tip may be heat bonded to the microcatheter shaft. The microcatheter shaft may have a working length of between 1.1 m and 1 .4 m, for compatibility with guide catheters that typically have a length of approximately 1 m and with pressure wires that typically have a length of approximately 1.75 m. Preferably, the microcatheter shaft has a working length of at least 1 .15 m. To aid positioning of the microcatheter in use, the microcatheter shaft may comprise at least two marker bands that are visually distinguishable from one another. The microcatheter apparatus may comprise a haemostasis valve attached or attachable to the first port. The valve may attach or be attachable by a threaded fitting, for example of the Tuohy-Borst type. Alternatively, a push on/pull off (quick release) type valve could also be used. The apparatus may also comprise a pressure wire for admission to the microcatheter lumen through the first port, and/or a fluid delivery device, such as an infusion pump, for fluid connection to the microcatheter lumen through the second port.

In another aspect, the present invention resides in apparatus for use in coronary catheterisation procedures. The apparatus comprises microcatheter apparatus according to the first aspect of the invention, a guide catheter defining a lumen for receiving the microcatheter shaft, a pressure wire for admission to the microcatheter lumen by way of the first port, fluid delivery means for connection to the microcatheter lumen, and proximal pressure sensing means for connection to the guide catheter lumen.

Preferred and/or optional features of the first aspect of the invention may be used, alone or in appropriate combination, in the second aspect of the invention also. In a further aspect, the present invention provides a method for performing a catheterisation procedure on a patient which comprises using microcatheter apparatus or apparatus according to the first and/or second aspects respectively of the invention. The method is preferably a coronary catheterisation procedure, more preferably a Fractional Flow Reserve (FFR) analysis procedure. A preferred FFR procedure of the present invention comprises the steps of: introducing a guide catheter into the arterial system of the patient through a suitable peripheral artery, guiding the distal end of the guide catheter to a desired position in or near a coronary artery on one side of a stenosis, and connecting the lumen of the guide catheter to a proximal pressure sensor of a Fractional Flow Reserve pressure monitoring and analysis apparatus;

advancing the microcatheter shaft along the guide catheter to position the distal end of the microcatheter shaft at or near the end of the guide catheter;

extending a pressure wire through the microcatheter shaft to position a pressure sensor in a desired location beyond the end of the guide catheter, on the far side of the stenosis;

delivering a hyperaemic agent through the microcatheter to the site of the stenosis; and

recording the pressure measured by the pressure wire and the proximal pressure to determine the FFR ratio.

The microcatheter apparatus may be pre-loaded with the pressure wire, and positioning of the microcatheter shaft at or near the end of the guide catheter may be aided by a radiopaque tip and/or marker bands.

The hyperaemic agent may be delivered by way of a side port of the microcatheter hub, as described above. The steps of the method of the present invention may be performed in any suitable order as appropriate, and are not necessarily limited to the order in which they are listed above. Brief Description of the Drawings

The invention will now be described, by way of example only, with reference to the accompanying drawings in which like reference numerals are used for like features, and in which:

Figure 1 shows a microcatheter assembly according to an embodiment of the present invention; Figure 2 is a cross-sectional view of the microcatheter assembly of Figure 1 ;

Figures 3(a) and 3(b) are side and cross-sectional views, respectively, of a hub of the microcatheter assembly of Figure 1 ; Figure 4 is a cross-sectional view of part of the hub of Figures 3(a) and 3(b) on an enlarged scale;

Figure 5 is a cross-sectional view of a strain relief sleeve of the microcatheter assembly of Figure 1 ; and

Figure 6 shows medial and proximal parts of a microcatheter shaft of the microcatheter assembly of Figure 1 ; and

Figure 7 shows a distal part of the microcatheter shaft of Figure 6.

Detailed Description of Embodiments of the Invention

Figures 1 and 2 show a microcatheter assembly 10 according to a first embodiment of the present invention. The microcatheter assembly 10 comprises a bifurcate microcatheter hub 20, an elongate, tubular microcatheter shaft 60, and a strain relief sleeve 80. As shown most clearly in Figure 2, a proximal end 62 of the shaft 60 is attached to a distal end formation 22 of the hub 20. The strain relief sleeve 80 is fitted over the distal end formation 22 and extends distally from the hub 20 along the microcatheter shaft 60.

The microcatheter shaft 60 is relatively thin, and is manufactured from a suitable biocompatible material, which may be transparent. For example, the shaft 60 may be of a thermoplastic elastomer material, such as a polyether block amide, also known as PEBAX (a registered trade mark of Arkema S.A., Colombes, France). One suitable grade of material is PEBAX 7233 SA 01 MED, which has a Shore D hardness of approximately 72. The microcatheter shaft has an outer diameter of approximately 1 mm (approximately 3F in the French scale system), an internal lumen diameter of approximately 0.8 mm, and a working length (i.e. the length of shaft that extends beyond the distal end of the strain relief sleeve) of approximately 1250 mm. In one specific case, the outer diameter is 1 .04 mm and the inner diameter is 0.79 mm.

Referring additionally to Figures 3(a) and 3(b), the hub 20 comprises a body 24 that is preferably of a medical grade plastics material, such as polycarbonate. The body 24 of the hub 20 is preferably formed as a single component, for example by injection moulding. The body 24 has a generally tubular axial portion 26 and a generally tubular inclined portion 28 that intersects with the axial portion 26 to define a side port 30. A support web 32 extends between the axial and inclined portions 26, 28 of the hub body 24 to support the side port 30. The side port 30 terminates in a female luer fitting.

The axial portion 26 of the hub body 24 extends proximally from the distal end formation 22 of the hub 20 and terminates in an axial port 34 at the proximal end of the hub 20. The axial port 34 is in the form of a threaded valve fitting arranged to accept a haemostatis valve 36, for example of the Tuohy-Borst type (shown only schematically in Figures 1 and 2). However, a push on/pull off (quick release) type valve could also be used. A passage or lumen 38 extends along the axial portion 26 of the hub body 24 from the distal end formation 22 to the axial port 34.

The axial lumen 38 of the hub 20 is of a generally constant, relatively large diameter along a major part of its length. However, in a minor, distal part 40, the lumen 38 tapers in the distal direction (i.e the diameter of the lumen 38 decreases moving towards the distal end of the hub 20). The axial lumen 38 terminates in a distal end section 42 having a relatively small diameter. The diameter of the lumen in the end section 42 is approximately equal to the diameter of the lumen of the microcatheter shaft 60. In the illustrated example, the major part of the axial lumen 38 has a diameter of approximately 3.3 mm, and the cone angle of the taper in the distal part 40 is approximately 10°, relative to the axis of the lumen 38. As shown most clearly in Figure 4, which is an enlarged view of the distal end of the hub 20, the distal end formation 22 is a generally tubular extension that projects distally from the hub body 24. A chamfer 44 is formed where the distal end formation 22 meets the axial portion 26 of the hub body 24. The distal end formation 22 defines a shaft receiving bore or passage 46. The shaft receiving passage 46 extends distally from, and is coaxial with, the end section 42 of the axial lumen 38. The internal diameter of the shaft receiving passage 46 is approximately equal to the outer diameter of the microcatheter shaft 20. Accordingly, a distally-facing step or shoulder 48 is defined where the shaft receiving passage 46 meets the end section 42 of the axial lumen 38. A locating collar 50 extends annularly around the cylindrical outer surface of the distal end formation 22.

Referring back to Figure 2, when assembled, the proximal end 62 of the microcatheter shaft 60 is received in the shaft receiving passage 46 of the distal end formation 22 of the hub 20, with the proximal end face of the shaft 60 in abutment with the shoulder 48. In this example, the shaft 60 is adhesively attached to the hub 20 by applying a suitable adhesive, such as a UV-curable adhesive, between the outer surface of the proximal end 62 of the shaft 60 and the inner surface of the shaft receiving passage 46.

In this way, the axial lumen 38 of the hub 20 is fluidly connected to the lumen 64 of the microcatheter shaft 60 to allow fluid flow therebetween. Because the end section of the axial lumen 38 has substantially the same diameter as the microcatheter lumen 64, the fluid flow path between the axial lumen 38 of the hub 20 and the microcatheter lumen 64 is relatively smooth where the microcatheter shaft 60 meets the hub 20. Furthermore, the tapered section 40 of the axial lumen 38 of the hub 20 provides a continuous transition for fluid flow from the relatively large diameter portion of the axial lumen 38 towards the relatively small diameter microcatheter lumen 64. These features help to encourage laminar fluid flow in the microcatheter lumen 64. The strain relief sleeve 80 serves to guard against kinking of the relatively thin flexible microcatheter shaft 60 by providing support to the shaft 60 close to the relatively large and heavy hub 20. The proximal end of the microcatheter shaft 60, may also be strengthened to help prevent kinking or squashing with consequent restriction of fluid flow, for example by thickening, reinforcing or using a stiffer material. The sleeve 80 also helps to protect the shaft 60 from other damage as may occur during handling or use. Referring additionally to Figure 5, which shows the strain relief sleeve 80 in isolation, the sleeve 80 is generally tubular to define an internal bore 82, and has an elongate, generally frustoconical shape that tapers from a relatively large-diameter proximal end 84 to a relatively small-diameter distal end 86. The sleeve 80 is of a thermoplastic elastomer such as a polyether block amide material, preferably with a Shore D hardness of approximately 35.

A proximal end portion 88 of the strain relief sleeve 80 is shaped and sized so as to couple to the distal end formation 22 of the hub 20. Accordingly, the internal diameter of the sleeve bore 82 is generally constant within the proximal end portion 88, except for an annular recess or groove 90 disposed adjacent to the proximal end 84 of the sleeve 80 and a chamfer 92 where the bore 82 meets the proximal end face of the sleeve 80. On assembly, the collar 50 of the distal end formation 22 locates in the groove 90 of the sleeve 80, thereby to secure the sleeve 80 to the hub 20. The chamfer 92 of the sleeve abuts the corresponding chamfer 44 of the hub 20. The sleeve 80 may also be adhesively or otherwise affixed to the hub 20.

The internal diameter of the bore 82 of the sleeve 80 decreases moving towards the distal end 86 of the sleeve 80. Before assembly, the internal diameter of the bore 82 at the distal end 86 of the sleeve 80 is approximately 0.3 mm. When assembled, the sleeve 80 elastically deforms to accommodate the microcatheter shaft 80 within its internal diameter. In this way, the sleeve 80 grips the microcatheter shaft 80 to provide mechanical support against kinking, bending or other deformation or damage. The sleeve 80 also serves to shroud and protect the junction between the microcatheter shaft 60 and the proximal end formation 22 of the hub 20.

To provide effective support, the strain relief sleeve 80 is relatively long. In the illustrated example, the strain relief sleeve 80 is approximately 47 mm long, which is approximately three-quarters of the axial length of the hub 20 (approximately 65 mm in this example). More generally, the strain relief sleeve 80 has a length that is preferably at least half of the length of the hub 20, more preferably at least two-thirds of the length of the hub 20, and most preferably at least three-quarters of the length of the hub 20. The design of the hub 20 and the provision of the strain relief sleeve 80 allow the microcatheter assembly 10 to be easily and accurately manoeuvred by an operator using a single hand, leaving the operator's other hand free to perform other tasks. Referring to Figures 1 and 6, the microcatheter shaft 60 is provided with first and second marker bands 66, 68. The first marker band 66 is positioned at a distance M1 of approximately 900 mm from the distal end 70 of the microcatheter shaft 60, and has a length L1 of approximately 5 mm. The second marker band 68 is positioned at a distance M2 of approximately 1000 mm from the distal end 70 of the microcatheter shaft 60, and has a length L2 of approximately 10 mm. The marker bands 66, 68 are preferably pad-printed onto the microcatheter shaft 60, using any suitable ink. In use of the microcatheter apparatus 10, the marker bands 66, 68 provide a useful indication to the operator of the position of the distal end 70 of the microcatheter shaft 60, and the different lengths L1 , L2 of the marker bands 66, 68 allow the operator to distinguish between the marker bands 66, 68. Figure 7 shows the distal end of the microcatheter shaft 60, which is fitted with a radiopaque tip 72 with a length LT of approximately 8 mm. The tip 72 is preferably of a metal-loaded polymeric material. Use of a tip material comprising a tungsten-loaded polyether block amide material has been found to be particularly advantageous. For example, a 60:40 mixture by weight of tungsten in PEBAX with a Shore D hardness of approximately 40 may be used. In this case, the tungsten provides radiopacity, allowing the tip 72 of the microcatheter shaft 60 to be observed by X-ray angiography during a procedure and to be distinguished from other components and structures that may be present in the same area, such as a guide catheter and a pressure wire. Alternatively or additionally, a metal band around the tip 72 may be used. For example, for some applications the material of the tip 72 may not be metal-loaded, and instead the tip 72 may include a radiopaque marker band, such as a platinum/iridium marker band. The material of the tip 72 is preferably of a lower hardness (durometer) than the material of the microcatheter shaft 60. In this way, despite the presence of tungsten metal, the tip 72 is relatively soft and therefore less likely to cause trauma in the event that it comes into contact with a blood vessel wall or other biological structure in use. For the same reason, the tip 72 is chamfered or rounded at its distal end 70, to avoid the possibility of sharp edges or corners causing trauma in the event of contact with delicate biological structures. To form the tip 72, an extruded tube of the tip material is manufactured with an internal diameter equal to the internal diameter of the microcatheter shaft 60, and an external diameter that, in this example, is approximately 0.02 mm greater than the external diameter of the microcatheter shaft 60. Thus the wall thickness of the tip extrusion is slightly greater than the wall thickness of the microcatheter shaft 60. The distal end of the bare microcatheter shaft 60 is then heat-tapered by locally warming the shaft 60 and using a suitable heat- shrink material to apply an inward concentric pressure to the shaft 60. This reduces the external diameter of the distal end of the shaft 60. The tip extrusion is then overlaid onto the end of the shaft and heat and concentric pressure are again applied, to cause heat bonding of the tip 72 to the shaft 60. The distal end 70 of the tip 72 is also shaped during this process to form the chamfered edge. During the heat bonding process, the tip 72 tends to elongate slightly and thin under the concentric pressure applied by the heat shrink. However, this thinning is accounted for by the increased wall thickness of the tip extrusion, so that, when bonded to the shaft, the resulting wall thickness and outer diameter of the tip 72 is close to that of the remainder of the shaft 60.

The microcatheter apparatus 10 is intended for use with a guide catheter (not shown) and a pressure wire 94, for example to perform FFR analysis during a coronary catheterisation procedure. To this end, the dimensions of the microcatheter shaft 60 are such that the shaft 60 can be advanced along guide catheters of the type preferred for radial and femoral cardiac cathetersiations, which typically have a diameter of around 2 mm (6F) or around 1 .7 mm (5F). For FFR analysis, the guide catheter would be fitted with a suitable end fitting having a haemostasis valve port to accept the microcatheter shaft and a fluid connection (for example through a side port) for connection of a proximal pressure sensor. In turn, the haemostasis valve 36 of the microcatheter hub 20 allows the pressure wire 94 to be extended through the axial lumen 38 of the hub 20 and through the lumen 64 of the microcatheter shaft 60. The tapered region 40 of the axial lumen 38 of the hub 20 helps to guide the pressure wire 94 into the microcatheter lumen 64. With a pressure wire 64 of suitable length, the pressure sensor (not shown) at the tip of the pressure wire 94 can be positioned beyond the tip 72 of the microcatheter shaft 60 in a desired site in a coronary artery. Preferably, the pressure wire 94 has a diameter of approximately 0.36 mm (1 F). Commercially-available pressure wire systems, such as are available under the trade marks PressureWire Certus and Prestige from St. Jude Medical, Inc. (St. Paul, MN, USA), may be suitable for use with the apparatus.

Conveniently, the pressure wire 94 can be pre-loaded into the microcatheter apparatus 10 before the microcatheter shaft 60 is advanced through the guide catheter, thus reducing the complexity and duration of the procedure.

The microcatheter apparatus 10 also provides for simultaneous delivery of a fluid, such as a hyperaemic agent, through the lumen 64 of the microcatheter shaft 60. Accordingly, the luer fitting of the side port 30 of the hub 20 can be connected to a suitable fluid delivery device (not shown), such as an infusion pump, a syringe, or to other fluid handling systems as may be generally known in the art. In this way, the functional parts of the catheterisation apparatus are arranged in a generally concentric arrangement in use, with the microcatheter shaft 60 extending through the lumen of the guide catheter, and the pressure wire 94 extending through the lumen 64 of the microcatheter shaft 60. The space between the inner wall of the guide catheter and the outer wall of the microcatheter shaft 60 is filled with static liquid (such as saline or blood) and can therefore be used to transmit the aortic pressure to the proximal pressure sensor. The lumen 64 of the microcatheter shaft 60 provides a separated flow path for delivery of hyperaemic agents or other fluids, such that fluid flow within the microcatheter apparatus 10 does not affect the aortic pressure measurement at the proximal pressure sensor. Similarly, because the pressure wire 94 is routed along the microcatheter lumen 64, movement of the pressure wire 94 during the procedure does not affect the pressure measurement at the proximal pressure sensor.

Use of the microcatheter apparatus 10 during an FFR analysis procedure for a coronary stenosis may proceed as follows. First, the microcatheter apparatus 10 is pre-loaded with a pressure wire 94. The pressure wire 94 is initially positioned with the tip of the pressure wire 94 positioned in the microcatheter lumen 64, proximal to the distal end 70 of the microcatheter shaft 60.

A guide catheter is then introduced to the arterial system of the patient through a suitable peripheral artery, and the distal end of the guide catheter is guided to a desired position in or near a coronary artery, on one side of the stenosis. This procedure may be performed using a guide wire, or by other suitable means. The lumen of the guide catheter is connected to the proximal pressure sensor of a known FFR pressure monitoring and analysis apparatus. With the guide catheter in place, the microcatheter shaft 60, with the pre- installed pressure wire 64, is then advanced along the guide catheter. The distal end 70 of the microcatheter shaft 60 is positioned at or near the end of the guide catheter, using the radiopaque tip 72 and the marker bands 66, 68 to aid positioning. The relatively soft and atraumatically-shaped tip 72 helps to avoid trauma should the microcatheter shaft 60 extend out of the end of the guide catheter.

The pressure wire 94 is then extended to position the pressure sensor at the tip of the pressure wire 94 in a desired location beyond the end of the guide catheter, on the far side of the stenosis.

A hyperaemic agent is then delivered through the microcatheter lumen 64, by way of the side port 30 of the microcatheter hub 20. In this way, the agent is delivered directly to the site of the stenosis, to encourage maximum localised hyperaemia. The distal end 70 of the microcatheter shaft 60 can be repositioned as necessary before or during delivery of the agent. The pressure recorded by the pressure wire and the proximal pressure sensor can then be monitored and analysed to determine the FFR ratio.

It will be appreciated that the steps of the procedure could be modified and/or performed in a different order as may be clinically appropriate. It should be understood that, in the above-described example, the dimensions of the microcatheter shaft 60, in particular the internal and outer diameters (and consequently the wall thickness) of the microcatheter shaft 60 have been selected for optimal performance in an FFR or similar procedure. In particular, the inventors have determined that, with the dimensions indicated above, and when used with a 6F (2 mm) guide catheter, the outer diameter of the microcatheter shaft 60 is sufficiently small that the presence of the microcatheter shaft 60 in the lumen of the guide catheter does not cause substantial damping or other modification of the pressure transmission along the fluid in the lumen of the guide catheter, which might otherwise affect the pressure reading taken by the proximal pressure sensor. At the same time, the internal diameter of the microcatheter lumen 64 is sufficiently large that, even when a pressure wire 94 is present in the microcatheter lumen 64, complete filling of the microcatheter lumen 64 can occur in a reasonably short time period (preferably no more than 30 seconds) so as not to cause undue delays in the procedure. Furthermore, the internal diameter of the microcatheter lumen 64 is sufficiently large that, when the microcatheter lumen 64 is connected to an infusion pump, continuous infusion can occur through the microcatheter lumen 64 during the course of a procedure (typically several minutes in duration) without causing such a pressure drop as to trigger an infusion alarm from the infusion pump. At the same time, the material selected for the microcatheter shaft 60 and the wall thickness are chosen so that sufficient strength is provided to avoid kinking or other damage due to handling or manipulation in use, and to meet regulatory requirements for tensile strength, whilst allowing the necessary degree of flexibility and manouuverability for routine use.

It will also be appreciated that the length of the microcatheter shaft 60, and the positions of the markers 66, 68, in the above-described example have been selected for compatibility and ease of use with typical guide catheters (which are generally approximately 1000 mm in length, or 1 100 mm in certain cases), taking into account the length of the guide catheter end fitting and the haemostasis valve, and with typical pressure wires (which are usually around 1750 mm in length). Various modifications of the apparatus are possible. In particular, whilst the above-described apparatus has been described for use in FFR and similar procedures, the microcatheter apparatus 10 of the present invention could be used in a variety of other catheterisation procedures and the dimensions, materials and properties of the components may vary from those described above in accordance with the requirements of other applications and uses.

For example, different materials may be selected for the microcatheter shaft 60 and/or the radiopaque tip 72. For instance, thermoplastic elastomer materials with a Shore D hardness in the range from about 60 to about 80 may be suitable for the microcatheter shaft 60. Metal-loaded thermoplastic elastomer materials with a Shore D hardness in the range from about 30 to about 60 may be suitable for the tip 72. Any suitable ratio of metal to elastomer may be used. For example, a 65:35 mixture by weight of metal in elastomer (such as tungsten in PEBAX) may be used. For some applications, the material of the tip 72 is not metal-loaded, and instead the tip may include a radiopaque marker band, such as a platinum/iridium marker band. Further modifications and variations of the above-described embodiments are also possible without departing from the scope of the invention as defined in the appended claims.

Claims

1 . Microcatheter apparatus, comprising:

a microcatheter shaft defining a microcatheter lumen and having a radiopaque distal tip;

a hub attached to a proximal end of the microcatheter shaft; and a strain relief sleeve extending distally from the hub along the microcatheter shaft;

wherein the hub comprises a first port to admit a pressure wire to the microcatheter lumen through the hub, and a second port for fluid connection to the microcatheter lumen, and an axial lumen in fluid communication with the microcatheter lumen, the axial lumen comprising a distal end section having a diameter substantially equal to the diameter of the microcatheter lumen, a proximal section having a larger diameter, and a tapered section therebetween.

2. Microcatheter apparatus according to claim 1 , wherein the first port is an axial port and the second port is an inclined side port. 3. Microcatheter apparatus according to claim 1 or 2, wherein the microcatheter shaft is adhesively affixed to the hub.

4. Microcatheter apparatus according to any preceding claim, wherein the hub comprises a distal end formation having a shaft receiving passage for receiving a proximal end of the microcatheter shaft, and wherein the strain relief sleeve is attached or attachable to the distal end formation.

5. Microcatheter apparatus according to any preceding claim, wherein the strain relief sleeve has a length of at least one half of the length of the hub, preferably at least two thirds of the length of the hub.

6. Microcatheter apparatus according to any preceding claim, wherein the microcatheter shaft has an external diameter of approximately 1 mm.

7. Microcatheter apparatus according to any preceding claim, wherein the microcatheter shaft has an internal diameter of approximately 0.8 mm.

8. Microcatheter apparatus according to any preceding claim, wherein the microcatheter shaft is of a thermoplastic elastomer material having a

Shore D hardness of between 60 and 80.

9. Microcatheter apparatus according to any preceding claim, wherein the strain relief sleeve is of a thermoplastic elastomer material having a Shore D hardness of between 20 and 50.

10. Microcatheter apparatus according to any preceding claim, wherein the radiopaque tip is of a material comprising a thermoplastic elastomer material and tungsten and having a lower hardness than the material of the microcatheter shaft.

1 1 . Microcatheter apparatus according to any preceding claim, wherein the radiopaque tip is heat bonded to the microcatheter shaft. 12. Microcatheter apparatus according to any preceding claim, wherein the radiopaque tip comprises a rounded or chamfered distal end.

13. Microcatheter apparatus according to any preceding claim, wherein the microcatheter shaft has a working length of between 1 .1 m and 1 .4 m.

14. Microcatheter apparatus according to any preceding claim, wherein the microcatheter shaft comprises at least two marker bands that are visually distinguishable from one another. 15. Microcatheter apparatus according to any preceding claim, further comprising a haemostasis valve attached or attachable to the first port. Microcatheter apparatus according to any preceding claim, further comprising a pressure wire for admission to the microcatheter lumen through the first port.

Microcatheter apparatus according to any preceding claim, further comprising a fluid delivery device for fluid connection to the microcatheter lumen through the second port.

Apparatus for use in coronary catheterisation procedures, comprising: microcatheter apparatus according to any of Claims 1 to 15; a guide catheter defining a lumen for receiving the microcatheter shaft;

a pressure wire for admission to the microcatheter lumen by way of the first port;

fluid delivery means for connection to the microcatheter lumen; and

proximal pressure sensing means for connection to the guide catheter lumen. 19. A method for performing a catheterisation procedure on a patient which comprises using microcatheter apparatus according to any one of claims 1 to 17 or apparatus according to claim 18.

20. A method according to claim 19 wherein the catheterisation procedure is a coronary catheterisation procedure.

21 . A method according to claim 19 or 20 wherein the catheterisation procedure is a Fractional Flow Reserve analysis procedure. 22. A method according to claim 21 which comprises the steps of:

introducing a guide catheter into the arterial system of the patient through a suitable peripheral artery, guiding the distal end of the guide catheter to a desired position in or near a coronary artery on one side of a stenosis, and connecting the lumen of the guide catheter to a proximal pressure sensor of a Fractional Flow Reserve pressure monitoring and analysis apparatus;

recording the pressure measured by the pressure wire and the proximal pressure to determine the Fractional Flow Reserve ratio.

A method according to claim 22 wherein the microcatheter apparatus is pre-loaded with the pressure wire.

A method according to claim 22 or 23 wherein positioning the microcatheter shaft at or near the end of the guide catheter is aided by a radiopaque tip and/or marker bands.

A method according to claim 22, 23 or 24 wherein the hyperaemic agent is delivered by way of a side port of the microcatheter hub.