Patent Description:
A medical catheter defining at least one lumen has been proposed for use with various medical procedures. For example, in some cases, a medical catheter may be used to access and treat defects in blood vessels, such as, but not limited to, lesions or occlusions in blood vessels. This treatment may involve drawing fluid through the medical catheter. <CIT> discloses a double-tube injection and aspiration catheter device. This catheter comprises an alignment element indicating a predetermined position of the inner catheter relative to the outer catheter when the inner catheter is received within the outer catheter distal opening, wherein when the inner catheter is at the predetermined position, at least one of its sidewall openings remains positioned within the outer catheter lumen and at least one other sidewall opening is positioned distal to the outer catheter distal opening.

<CIT> discloses a telescoping surgical probe. <CIT> discloses a valved self-perfusing guiding catheter. <CIT> discloses a method for administering a liquid medical substance in a vein.

In some aspects, this disclosure describes example aspiration catheter systems configured to provide suction from and continuous flow of fluid through an aspiration catheter even when a distal opening of the aspiration catheter is blocked by a tissue. Aspiration catheter systems include an inner catheter with sidewall openings that allow fluid to flow into a lumen of the inner catheter when a distal opening of the inner catheter is blocked by the tissue. An outer catheter surrounding the inner catheter provides a flow path for aspiration fluid to a site of the tissue and through the sidewall openings of the inner catheter, ensuring continuous flow into the lumen of the inner catheter for removing any portions of the tissue that may come loose. A clinician can adjust the position of the inner catheter relative to the outer catheter to achieve a desired flow characteristic. In this way, a clinician may more effectively remove the tissue from vasculature of the patient when compared to aspiration catheters that provide reduced or no flow during engagement of a tissue.

According to the invention, an aspiration catheter system includes an outer catheter and an inner catheter configured to be positioned within the outer catheter lumen, and an alignment element. The outer catheter defines an outer catheter lumen and an outer catheter distal opening. The inner catheter defines an inner catheter lumen, an inner catheter distal opening, and a plurality of sidewall openings proximal to the inner catheter distal opening. The alignment element is configured to indicate a predetermined position of the inner catheter relative to the outer catheter when the inner catheter is received within the outer catheter distal opening. When the inner catheter is at the predetermined position, at least one sidewall opening of the plurality of sidewall openings remains positioned within the outer catheter lumen and at least one other sidewall opening of the plurality of sidewall openings is positioned distal to the outer catheter distal opening. The catheter system further comprises a fluid circulation system coupled to a proximal portion of the outer catheter and a proximal portion of the inner catheter, wherein the fluid circulation system is configured to deliver fluid through the outer catheter lumen and receive fluid through the inner catheter lumen.

In some examples, the alignment element comprises a visible marker on the inner catheter.

In some examples, the alignment element comprises an alignment structure extending from the inner catheter and is configured to engage with a proximal end of the outer catheter.

In some examples, the alignment element comprises a plurality of markers, each marker corresponding to a predetermined position of at least one sidewall opening of the plurality of sidewall openings of the inner catheter relative to the outer catheter distal opening.

In some examples, an inner circumference of the outer catheter is between about <NUM> microns and about <NUM> microns greater than an outer circumference of the inner catheter. In some examples, at least one sidewall opening of the plurality of sidewall openings comprises a one-way valve configured to permit flow of fluid into the inner catheter lumen.

In some examples, the one-way valve is configured to open in response to a differential pressure between the outer catheter lumen and the inner catheter lumen being greater than or equal to a predetermined threshold value.

In some examples, the one-way valve comprises a duckbill valve, a slit valve, or a flexible flap positioned at the respective sidewall openings.

:In some examples, the distal-most sidewall opening of the plurality of sidewall openings is positioned between about <NUM> centimeters and about <NUM> centimeters proximal to the inner catheter distal opening.

In some examples, the fluid comprises saline.

In some examples, the sidewall openings of the plurality of sidewall openings are circumferentially distributed around an outer perimeter of the inner catheter.

In some examples, the sidewall openings of the plurality of sidewall openings are distributed axially along the inner catheter.

Other features, objects, and advantages of the invention described in this disclosure will be apparent from the description and drawings, and from the claims.

The disclosure describes aspiration catheter systems, configured to maintain suction and continuous flow of fluid on an engaged thrombus, as well as aspiration systems including the aspiration catheter system and methods of using the aspiration systems.

Thrombosis occurs when a thrombus (e.g., a blood clot or other embolus) forms and obstructs vasculature of a patient. To treat a patient with thrombosis, a clinician may position an aspiration catheter in a blood vessel of the patient near the thrombus, apply suction to the aspiration catheter, and engage the thrombus with a tip of the aspiration catheter. Once the tip of the aspiration catheter has engaged the thrombus, the clinician may remove the aspiration catheter with the thrombus attached to the tip or suction off pieces of the thrombus through the aspiration catheter until the thrombus is removed from the blood vessel of the patient. The aspiration of the thrombus may be part of an aspiration procedure, such as, but not limited to, a medical procedure using A Direct Aspiration first Pass Technique (ADAPT) for acute stroke thrombectomy, or any other aspiration of thrombus or other material from the neurovasculature or other blood vessels.

During suctioning of the thrombus, the clinician may deliver aspiration fluid to the site of the thrombus and suction fluid through a lumen of the aspiration catheter into a canister located external to the patient. Prior to engagement of the thrombus by the aspiration catheter, this flow and suction of fluid near the thrombus may create turbulence at a surface of the thrombus and remove loose pieces of the thrombus from the surface. However, once the clinician has engaged the thrombus, the thrombus may block the distal opening of the aspiration catheter (e.g., at a tip of the aspiration catheter) and cause a reduction or cessation of flow through the lumen of the aspiration catheter. As a result, the flow of fluid at the surface of the thrombus may be reduced or ceased, and pieces of the thrombus may not be removed as effectively.

According to the invention, an aspiration catheter system includes an outer catheter and an inner catheter positioned within the outer catheter. A space between the inner catheter and the outer catheter enable fluid to be delivered near a distal tip of the aspiration catheter system. The inner catheter includes a plurality of sidewall openings proximal to an inner catheter distal opening. When the inner catheter is at a predetermined position relative to the outer catheter, as indicated by an alignment element, at least one sidewall opening is positioned within the outer catheter and at least one other sidewall opening is positioned outside the outer catheter to enable fluid to flow into an inner catheter lumen when an inner catheter distal opening is blocked, such as by the thrombus. In this way, the clinician may maintain both suction on an engaged thrombus and continuous flow of fluid on the engaged thrombus, which may result in more effective removal of the thrombus from the vasculature of the patient.

<FIG> is a schematic diagram illustrating an example aspiration system <NUM> that includes an aspiration catheter system <NUM> configured to maintain suction and continuous flow of fluid on an engaged thrombus. Aspiration system <NUM> includes aspiration catheter system <NUM> and a fluid circulation system <NUM>. Aspiration catheter system <NUM> includes an outer catheter <NUM> and an inner catheter <NUM> positioned in outer catheter <NUM>. Fluid circulation system <NUM> includes an aspiration pump <NUM> and aspiration tubing <NUM>. Aspiration tubing <NUM> is coupled to a proximal portion of outer catheter <NUM> and a proximal portion of inner catheter <NUM>, such that aspiration pump <NUM> is in fluidic communication with lumens of both outer catheter <NUM> and inner catheter <NUM>. While shown as a single unit, aspiration tubing <NUM> may include a plurality of sections of aspiration tubing, such as a first section of tubing coupled to the proximal portion of outer catheter <NUM> and a second section of tubing coupled to the proximal portion of inner catheter <NUM>.

Fluid circulation system <NUM> is configured to deliver fluid from aspiration pump <NUM> through an outer catheter lumen of outer catheter <NUM> and receive fluid through an inner catheter lumen of inner catheter <NUM> into aspiration pump <NUM>. An aspiration fluid, such as saline, may be delivered out of an outer catheter distal opening of outer catheter <NUM> by positive pressure created by aspiration pump <NUM>, the outer catheter distal opening being an opening to an inner lumen of outer catheter <NUM>. Fluid within vasculature of, such as blood, an aspiration fluid, or a mixture thereof, may be drawn into an inner lumen of the inner catheter via an inner catheter distal opening and/or sidewall opening of inner catheter <NUM> by negative pressure created by pump <NUM>, the inner catheter distal opening and sidewall opening being openings to the inner lumen of inner catheter <NUM>. The aspiration fluid, e.g., saline, may be selected to be less viscous than blood so that delivery of the aspiration fluid into the vasculature of the patient via outer catheter <NUM> may help create turbulence in the inner lumen of inner catheter <NUM> as the aspiration fluid is aspirated through the inner lumen of the inner catheter.

Aspiration catheter system <NUM> may be configured to be advanced through vasculature of a patient via a pushing force applied to a proximal portion of aspiration catheter system <NUM> with minimal or no buckling, kinking, or otherwise undesirably deforming (e.g., ovalization). Aspiration catheter system <NUM> may be used to remove a thrombus, such as a clot or other material such as plaques or foreign bodies, from vasculature of a patient. In such examples, a positive pressure may be applied, such as by aspiration pump <NUM>, to the proximal end of outer catheter <NUM> to deliver aspiration fluid to the site of the thrombus and a negative pressure may be applied, such as by aspiration pump <NUM>, to the proximal end of inner catheter <NUM> to draw a thrombus into the inner lumen of inner catheter <NUM> through one or more distal openings. Aspiration catheter system <NUM> may be used in various medical procedures, such as a medical procedure to treat an ischemic insult, which may occur due to occlusion of a blood vessel (arterial or venous) that deprives brain tissue, heart tissue or other tissues of oxygen-carrying blood.

In some examples, aspiration catheter system <NUM> is configured to access relatively distal locations in a patient including, for example, the middle cerebral artery (MCA), internal carotid artery (ICA), the Circle of Willis, and tissue sites more distal than the MCA, ICA, and the Circle of Willis. The MCA, as well as other vasculature in the brain or other relatively distal tissue sites (e.g., relative to the vascular access point), may be relatively difficult to reach with a catheter, due at least in part to the tortuous pathway (e.g., comprising relatively sharp twists or turns) through the vasculature to reach these tissue sites. Each of outer catheter <NUM> and inner catheter <NUM> may be structurally configured to be relatively flexible, pushable, and relatively kink- and buckle-resistant, so that it may resist buckling when a pushing force is applied to a relatively proximal section of a respective outer catheter <NUM> and inner catheter <NUM> to advance aspiration catheter system <NUM> distally through vasculature, and so that it may resist kinking when traversing around a tight turn in the vasculature. In some examples, outer catheter <NUM> may be a guide catheter that is introduced into the vasculature before inner catheter <NUM>, and may define a pathway through which inner catheter <NUM> may be navigated to a target treatment site.

In some examples, aspiration catheter system <NUM> is configured to substantially conform to the curvature of the vasculature. In addition, in some examples, aspiration catheter system <NUM> may have a column strength and flexibility that allows at least the distal portion of aspiration catheter system <NUM> to be navigated from a femoral artery, through the aorta of the patient, and into the intracranial vascular system of the patient, e.g., to reach a relatively distal treatment site. Alternatively, the elongated body can have a column strength (and/or be otherwise configured) to allow the distal portion of the elongated body to be navigated from a radial artery, through the aorta of the patient or otherwise to a common carotid or vertebral artery, and into the intracranial vascular system of the patient, e.g., to reach a relatively distal treatment site.

Although primarily described as being used to reach relatively distal vasculature sites, aspiration catheter system <NUM> may also be configured to be used with other target tissue sites. For example, aspiration catheter system <NUM> may be used to access tissue sites throughout the coronary and peripheral vasculature, the gastrointestinal tract, the urethra, ureters, fallopian tubes, veins and other body lumens.

In some examples, aspiration catheter system <NUM> may be described in terms of the working length of an elongated body of outer catheter <NUM> and/or inner catheter <NUM>. The working length of aspiration catheter system <NUM> may depend on the location of the target tissue site within the body of a patient or may depend on the medical procedure for which aspiration catheter system <NUM> is used. For example, if aspiration catheter system <NUM> is a distal access catheter system used to access vasculature in a brain of a patient from a femoral artery access point at the groin of the patient, the elongated body of outer catheter <NUM> and/or inner catheter <NUM> may have a working length of about <NUM> centimeters (cm) to about <NUM> or more, such as about <NUM>, although other lengths may be used. The distal portion may be about <NUM> to about <NUM> in length. The proximal portion may be about <NUM> to about <NUM> in length, depending on the length of the distal portion.

In some cases, a clinician may steer aspiration catheter system <NUM> through the vasculature of a patient by pushing or rotating a hub and/or the proximal portion of outer catheter <NUM> and/or inner catheter <NUM> to navigate the distal portion of aspiration catheter system <NUM> through the vasculature of a patient. The clinician may apply torque to the hub and/or the proximal portion of outer catheter <NUM> and/or inner catheter <NUM> to rotate the distal portion of the respective outer catheter <NUM> and inner catheter <NUM>.

Aspiration pump <NUM> is configured to create a positive pressure (i.e., outflow) on outer catheter <NUM>, e.g., to deliver fluid through an inner lumen of outer catheter <NUM> into vasculature of a patient. Aspiration pump <NUM> is also configured to create a negative pressure (i.e., vacuum or suction) on inner catheter <NUM>, e.g., to draw fluid through an inner lumen of inner catheter <NUM> into a reservoir of aspiration pump <NUM>. For example, aspiration pump <NUM> may include one or more ports configured to couple to aspiration tubing <NUM>, such that the positive or negative pressure created by aspiration pump <NUM> may be applied to the respective port and through aspiration tubing <NUM> and other portions of a fluid pathway between aspiration tubing <NUM> and a respective inner lumen of outer catheter <NUM> and/or inner lumen of inner catheter <NUM>. A variety of pumps may be used for aspiration pump <NUM> including, but not limited to, positive displacement pumps, centrifugal pumps, and the like. While illustrated as a single pump, aspiration pump <NUM> may include a plurality of pump units, such as a first pump for creating the positive pressure and a second pump for creating the negative pressure.

<FIG> is a schematic diagram illustrating example aspiration catheter system <NUM> of <FIG>. Outer catheter <NUM> defines an outer catheter lumen <NUM> and an outer catheter distal opening <NUM>. Outer catheter <NUM> may include various structural components, such as an inner liner, an outer jacket, and a structural support member, such as a coil and/or or a braid, positioned between at least a portion of the inner liner and at least a portion of the outer jacket.

Outer catheter lumen <NUM> is configured to transport fluid, such as aspiration fluid, blood, and particulates in the fluid, from a proximal end of outer catheter <NUM>, such as from aspiration pump <NUM> of <FIG>, to a distal end of outer catheter <NUM>, such as outer catheter distal opening <NUM>. Outer catheter lumen <NUM> is sized to receive at least a portion of inner catheter <NUM> while allowing aspiration fluid under a positive pressure provided by an aspiration pump to be delivered to outer catheter opening <NUM>. In some examples, outer catheter <NUM> may have an inner diameter D<NUM> between or equal to about <NUM> inches (about <NUM> millimeters (mm)) and/or about <NUM> inches (about <NUM>), which corresponds to the circumference of outer catheter lumen <NUM>. In some examples, the inner diameter and/or inner circumference of outer catheter lumen <NUM> may be relatively constant (e.g., constant or nearly constant) from a proximal end of outer catheter <NUM> to outer catheter opening <NUM>.

Outer catheter distal opening <NUM> is an opening of outer catheter lumen <NUM> at a distal end of outer catheter <NUM>. Outer catheter distal opening <NUM> is configured to receive inner catheter <NUM>, such that at least a portion of inner catheter <NUM> may be positioned within outer catheter lumen <NUM>. Outer catheter <NUM> also includes an outer catheter proximal opening <NUM>. Outer catheter proximal opening <NUM> may be an opening of outer catheter lumen <NUM> at a proximal end of outer catheter <NUM>. Outer catheter proximal opening may be configured to receive inner catheter <NUM>, such that at least a portion of inner catheter <NUM> may be positioned outside outer catheter lumen <NUM>. This portion of inner catheter <NUM> proximal to outer catheter proximal opening <NUM> may, for example, be used by a clinician to operate a position of inner catheter <NUM> relative to outer catheter <NUM>. As such, a length of inner catheter <NUM> may be sufficiently longer than outer catheter <NUM> to extend past outer catheter distal opening <NUM> to provide suction and continuous flow into inner catheter lumen <NUM> and to extend past outer catheter proximal opening <NUM> to provide a surface for a clinician or other operator to use to operate inner catheter <NUM> relative to outer catheter <NUM>.

In some examples, one or more portions of an inner surface of outer catheter <NUM> may be lubricious to facilitate the introduction and passage of inner catheter <NUM>, a therapeutic agent, or the like, through outer catheter lumen <NUM>. Examples of therapeutic agents include, but are not limited to, an oxygenated medium or a pharmaceutical agent, which may be, for example, a vasodilator such as nifedipine or sodium nitroprusside, or a tissue plasminogen activator (t-PA), which can be used to break down blood clots. In some examples, the material from which portions of the inner surface is formed may itself be lubricious (e.g., PTFE). For example, a lubricious inner surface that may allow relatively easy movement of inner catheter <NUM> and/or fluid through outer catheter lumen <NUM>. In addition to, or instead of, being formed from a lubricious material, in some examples, an inner surface of may be coated with a lubricious coating such as a hydrophilic coating. The inner surface may be formed from any suitable material including, but not limited to, polytetrafluoroethylene (PTFE), expanded PTFE a fluoropolymer, perfluoroalkyoxy alkane (PFA), fluorinated ethylene propylene (FEP), polyolefin elastomer, and the like.

Inner catheter <NUM> defines an inner catheter lumen <NUM>, an inner catheter distal opening <NUM>, and a plurality of sidewall openings 24A and 24B (collectively "sidewall openings <NUM>") proximal to inner catheter distal opening <NUM>. Inner catheter <NUM> may include an inner liner, an outer jacket, and a structural support member, such as a coil and/or or a braid, positioned between at least a portion of the inner liner and at least a portion of the outer jacket. Inner catheter <NUM> may include other structures, such as an expandable member configured to radially expand within a vessel of a patient, e.g., to engage a clot within the vessel.

Inner catheter lumen <NUM> is configured to transport fluid, such as aspiration fluid, blood, and particulates in the fluid, from a distal end of inner catheter <NUM>, such as from inner catheter distal opening <NUM> and/or the plurality of sidewall openings <NUM>, to a proximal end of inner catheter <NUM>, such as to aspiration pump <NUM>. Inner catheter <NUM> may be sized to be housed in outer catheter lumen <NUM> while still enabling aspiration fluid under a positive pressure provided by an aspiration pump to be delivered to outer catheter opening <NUM> (in the space between an inner surface of outer catheter <NUM> and an outer surface of inner catheter <NUM>) and allowing fluid and/or particles from a site of a thrombus to pass through inner catheter lumen <NUM>. In some examples, inner catheter <NUM> may have an outer diameter D<NUM> between or equal to about <NUM> inches (about <NUM>) and/or about <NUM> inches (about <NUM>). In some examples, the outer diameter and/or outer circumference of inner catheter <NUM> may be relatively constant (e.g., constant or nearly constant) from a proximal end of inner catheter <NUM> to inner catheter opening <NUM>. In other examples, inner catheter <NUM> may taper in distal direction or otherwise vary in outer diameter along its length.

Inner catheter distal opening <NUM> is an opening of inner catheter lumen <NUM> at a distal end of inner catheter <NUM>. In some examples, one or more portions of an inner surface of inner catheter <NUM> may be lubricious to facilitate the introduction and passage of a medical device, particulates such as pieces of a clot/thrombus, a therapeutic agent, or the like, through inner catheter lumen <NUM>. In some examples, the material from which portions of the inner surface is formed may itself be lubricious (e.g., PTFE). For example, a lubricious inner surface that may allow relatively easy movement of a guidewire, particulates, and/or fluid through inner catheter lumen <NUM>. In addition to, or instead of, being formed from a lubricious material, in some examples, an inner surface of may be coated with a lubricious coating such as a hydrophilic coating. The inner surface may be formed from any suitable material including, but not limited to, polytetrafluoroethylene (PTFE), expanded PTFE a fluoropolymer, perfluoroalkyoxy alkane (PFA), fluorinated ethylene propylene (FEP), polyolefin elastomer, and the like.

In some examples, one or more portions of an inner surface of inner catheter lumen <NUM> at a distal end of inner catheter <NUM> may be configured to have a relatively high affinity to a clot material by, for example, using a suitable surface treatment (e.g., a coating and/or etching) on inner liner <NUM> to promote mechanical or chemical engagement with the clot. (Such affinity may be measured, for example, with a DMA (dynamic mechanical analyzer) equipped with a shear sandwich clamp. ) For example, the inner surface of a distal section on inner catheter lumen <NUM> may be treated with a surface coating, etching, or other roughening mechanism, so that the distal section better engages with the clot, such that the inner surface of the distal section may be configured to promote at least one of mechanical or chemical clot engagement. A roughened or less lubricious surface of an inner surface that is brought in contact with the clot may allow for the clot to stick better to the inner surface, which may allow the clot to be pulled into inner catheter <NUM> more effectively. Examples of suitable coating materials to increase the affinity of the clot to an inner surface of inner catheter lumen <NUM> may include, for example, a thermoplastic elastomer such as ChronoPrene™ (AdvanSource Biomaterials, Wilmington, Massachusetts); a polyolefin elastomer such as ethylene-octene or ethylene-butene copolymer, or the like.

As mentioned above, inner catheter <NUM> is configured to be positioned within outer catheter lumen <NUM>. As such, an outer diameter or circumference of inner catheter <NUM> and an inner diameter or circumference of outer catheter lumen <NUM> may be selected or configured relative to each other. In some examples, an inner circumference of outer catheter <NUM> may be between about <NUM> microns and about <NUM> microns greater than an outer circumference of inner catheter <NUM>.

The plurality of sidewall openings <NUM> are configured to flow fluid from at least one of outer catheter lumen <NUM> and a volume of space (e.g., in a blood vessel) external to outer catheter distal opening <NUM> into inner catheter lumen <NUM>. Various factors of the sidewall openings <NUM>, such as a number of sidewall openings <NUM>, one or more positions of sidewall openings <NUM> around and along inner catheter <NUM>, one or more sizes of sidewall openings <NUM>, and the like, may be selected to provide desired and/or predetermined flow characteristics of fluid from outer catheter lumen <NUM> through outer catheter distal opening <NUM>, from outer catheter lumen <NUM> into inner catheter lumen <NUM>, and/or from a volume distal to outer catheter distal opening <NUM> into inner catheter lumen <NUM>.

In some examples, each of the plurality of sidewall openings <NUM> comprises a one-way valve configured to permit flow of fluid into inner catheter lumen <NUM>. For example, sidewall openings <NUM> may be configured to allow flow of fluid from outer catheter lumen <NUM> into inner catheter lumen <NUM> through sidewall openings <NUM>, such as in response to a positive pressure in outer catheter lumen <NUM> being greater than a negative pressure in inner catheter lumen <NUM>, but not allow (i.e., no substantial amount of) flow of fluid from inner catheter lumen <NUM> into outer catheter lumen <NUM> through sidewall openings <NUM>. The one-way valve can have any suitable configuration. For example, in some examples, the plurality of sidewall openings <NUM> comprise a duckbill valve, a slit valve, or a flexible flap positioned at one or more (e.g., all) of the sidewall openings of the plurality of sidewall openings. In some examples, the one-way valve does not protrude axially outward from outer catheter <NUM>. For example, the one-way valve may be flush with or below an exterior surface of outer catheter <NUM>. In this way, an exterior surface of outer catheter <NUM> may be relatively smooth and/or free of protrusions such that the valves may not catch on, for example, the vasculature of the patient or cause unwanted turbulence or flow resistance through outer catheter lumen <NUM>.

In some examples, the plurality of sidewall openings may be configured to open in response to a differential pressure between outer catheter lumen <NUM> and inner catheter lumen <NUM> (i.e., a difference between a positive pressure in outer catheter lumen <NUM> and a negative pressure in inner catheter lumen <NUM>) being greater than or equal to a predetermined differential pressure threshold value. For example, prior to engagement of a thrombus at inner catheter distal opening <NUM>, it may be desired for a majority of aspiration fluid to be delivered through outer catheter distal opening <NUM> into a volume outside outer catheter distal opening <NUM> near the thrombus and through inner catheter distal opening <NUM> from suction in inner catheter lumen <NUM>. However, once the thrombus is engaged with inner catheter <NUM> and blocking inner catheter distal opening <NUM>, the differential pressure between outer catheter lumen <NUM> and inner catheter lumen <NUM> may increase. For example, the thrombus may block flow of aspiration fluid from outer catheter lumen <NUM> into inner catheter lumen <NUM>, causing an increase in either or both a positive pressure in outer catheter lumen <NUM> or a negative pressure in inner catheter lumen <NUM>. Once the differential pressure is greater than or equal to the predetermined differential pressure threshold, fluid may flow from outer catheter lumen <NUM> and/or the volume outside outer catheter distal opening <NUM> into inner catheter lumen <NUM>.

In some examples, the plurality of sidewall openings <NUM> may have different differential pressure thresholds. For example, sidewall openings <NUM> that are more likely to be positioned outside outer catheter distal opening <NUM> may have a lower differential pressure threshold than sidewall openings that are more likely to be positioned within outer catheter distal opening <NUM>, such that a flow of fluid through sidewall openings closer to the thrombus is higher than flow of fluid further away from the thrombus. The differential pressure threshold for a particular sidewall opening <NUM> may be selected according to a variety of factors including, but not limited to, expected arterial blood pressure, positive pressure from aspiration pump <NUM>, negative pressure from aspiration pump <NUM>, and the like. For example, the differential pressure may be selected such that the blood pressure in the vessel does not result in flow of fluid into inner catheter lumen <NUM> via one or more sidewall openings <NUM>.

The plurality of sidewall openings <NUM> may have a variety of sizes (e.g., diameters, circumferences, lengths, widths, shapes, etc.). In some examples, all sidewall openings of the plurality <NUM> have substantially the same size (e.g., may only differ by manufacturing variances). In some examples, some sidewall openings of the plurality of sidewall openings <NUM> have different sizes. In some examples, a size and distribution of the plurality of sidewall openings may be selected according to a particular surface area of a distal end of inner catheter <NUM>. For example, a number of sidewall openings <NUM> and surface area of each of sidewall openings <NUM> may be selected so that the plurality of sidewall openings may have a percentage of a surface area of a distal portion (e.g., distal-most <NUM> centimeters) of inner catheter <NUM>, such as greater than about <NUM>%.

In some examples, sidewall openings <NUM> may have a median largest surface dimension (e.g., length, width, diameter, or area defined by the boundary of the respective opening) that is less than or equal to about <NUM>% of the diameter of inner catheter lumen <NUM> in order to help minimize the potential of blocking inner catheter lumen <NUM> and restricting flow through inner catheter lumen <NUM>. In some examples, sidewall openings <NUM> may have a median surface area that is less than about that corresponding to a diameter of <NUM> inches (about <NUM>). For example, a median surface area may correspond to a flow rate of fluid into inner catheter lumen <NUM> for a particular positive pressure, negative pressure, position of inner catheter <NUM> relative to outer catheter <NUM>, such that a median surface area may be selected to balance suction provided at inner catheter distal opening <NUM> (i.e., near the thrombus) when inner catheter distal opening <NUM> is not blocked, such that adequate fluid is flowing near the thrombus, with flow through sidewall openings <NUM> when inner catheter distal opening <NUM> is blocked, such that adequate fluid is flowing into inner catheter lumen <NUM>. Sidewall openings <NUM> may also have a minimum size, such as, but not limited to, about <NUM> inches (about <NUM>), which may help aid manufacturability of catheter <NUM>. In some examples, the plurality of sidewall openings <NUM> include between <NUM> sidewall openings and <NUM> sidewall openings.

In some examples, the distal-most sidewall opening 24B of the plurality of sidewall openings <NUM> may be positioned at a length Li between about <NUM> centimeters and about <NUM> centimeters proximal to inner catheter distal opening <NUM>. For example, a length Li greater than about <NUM> centimeters proximal to inner catheter distal opening <NUM> may correspond to a distance at which the distal-most sidewall opening is unlikely to be plugged (e.g., covered or otherwise blocked) by a thrombus drawn into inner catheter lumen <NUM>. As another example, a length L<NUM> less than about <NUM> centimeters proximal to inner catheter distal opening <NUM> may correspond to a distance at which fluid flowing through sidewall openings <NUM> may have a flow rate or position adequate (e.g., maximum residence time, minimum Reynolds number, minimum flow rate, etc.) for providing suction, circulation, and/or turbulence to a volume within inner catheter lumen <NUM> near inner catheter distal opening <NUM>.

In some examples, the plurality of sidewall openings may be distributed axially along inner catheter <NUM> (i.e., along a longitudinal axis <NUM> of catheter <NUM>). For example, as shown in <FIG>, distal-most sidewall opening 24B is distal to proximal-most sidewall opening 24A. While only two axially-distributed sidewall openings are shown, inner catheter <NUM> may include more than two axially-distributed sidewall openings, such as three, four, five or more axially distributed sidewall openings. In some examples, a size of sidewall openings may vary according to an axial distribution. For example, a size of sidewall openings may increase or decrease along a distal direction.

In some examples, the plurality of sidewall openings may be distributed around the outer perimeter of inner catheter <NUM>, e.g., circumferentially distributed in the case of inner catheter <NUM> having a circular cross-section (the cross-section being take in a direction orthogonal to the longitudinal axis of inner catheter <NUM>). <FIG> is a schematic axial cross-sectional diagram illustrating example aspiration catheter system <NUM> of <FIG> that includes outer catheter <NUM> and inner catheter <NUM>. As shown in <FIG>, sidewall opening 24C is at a different radial position than sidewall opening 24D. In some examples, a position and/or size of the sidewall openings may be relatively even or constant according to a radial distribution around inner catheter <NUM>. For example, consistency in position and/or size at different radial positions may provide a more even flow of fluid into inner catheter lumen <NUM>. In some examples, a position and/or size of sidewall openings may vary according to a radial distribution around inner catheter <NUM>. For example, variation in sidewall opening sizes at different radial positions may encourage more turbulent flow, as the flow may be less uniform.

Referring back to <FIG>, aspiration catheter system <NUM> includes an alignment element <NUM>. Alignment element <NUM> is configured to indicate a predetermined position P<NUM> of inner catheter <NUM> relative to outer catheter <NUM> when inner catheter <NUM> is received within outer catheter inner lumen <NUM>. When inner catheter <NUM> is at the predetermined position P<NUM>, at least one sidewall opening 24A of the plurality of sidewall openings <NUM> remains positioned within outer catheter lumen <NUM> and at least one other sidewall opening 24B of the plurality of sidewall openings <NUM> is positioned distal to outer catheter distal opening <NUM>. This predetermined position P<NUM> may correspond to a configuration that allows both suction and continuous flow through inner catheter lumen <NUM>. While only one predetermined position is shown, in some examples, aspiration catheter system <NUM> may include a variety of predetermined positions corresponding to various configurations of sidewall openings positioned within outer catheter distal opening <NUM> and distal to outer catheter distal opening <NUM>. In these examples, alignment element <NUM> may include a plurality of alignment elements, each alignment element corresponding to a respective predetermined position of inner catheter <NUM> relative to outer catheter <NUM>.

In some examples, the predetermined position P<NUM> may correspond to various flow paths of fluid from outer catheter lumen <NUM> to inner catheter lumen <NUM>. For example, when inner catheter <NUM> is at the predetermined position P<NUM>, aspiration catheter system <NUM> may define (<NUM>) a first flow path of fluid from outer catheter lumen <NUM> through outer catheter distal opening <NUM> and inner catheter distal opening <NUM> to inner catheter lumen <NUM>; (<NUM>) a second flow path of fluid from outer catheter lumen <NUM> through outer catheter distal opening <NUM> and sidewall opening 24B to inner catheter lumen <NUM>; and (<NUM>) a third flow path of fluid from outer catheter lumen <NUM> directly through sidewall opening 24A to inner catheter lumen <NUM>. When inner catheter distal opening <NUM> may be at least partially blocked, aspiration catheter system <NUM> may be configured to deliver the fluid from outer catheter lumen <NUM> to inner catheter lumen <NUM> through at least one of the second flow path or the third flow path.

Alignment element <NUM> can be positioned on inner catheter <NUM>, on outer catheter <NUM>, or on both inner catheter <NUM> and on outer catheter <NUM>. As discussed in further detail below, alignment element <NUM> may be a visible element, e.g., a visible marker on outer catheter <NUM> and/or inner catheter <NUM>. In these examples, alignment element <NUM> may not protrude from a surface of the respective catheter <NUM>, <NUM>, and may be flush (e.g., printed on or embedded in) with the outer surface of the respective catheter <NUM>, <NUM>. In other examples, however, alignment element <NUM> may include a structure that protrudes from one or both catheters <NUM>, <NUM>, e.g., and engages the other catheter in order to indicate the predetermined position of inner catheter <NUM> relative to outer catheter <NUM>. As shown in <FIG>, alignment element <NUM> may indicate an alignment position M<NUM> that corresponds to outer catheter proximal opening <NUM>.

Aspiration catheter systems discussed herein can be configured to maintain suction and continuous flow of fluid on an engaged thrombus. As an illustration, <FIG> are schematic longitudinal cross-sectional diagrams illustrating an example aspiration catheter system <NUM> that includes an outer catheter <NUM> and an inner catheter <NUM>. Aspiration catheter system <NUM>, outer catheter <NUM>, inner catheter <NUM>, an outer catheter lumen <NUM>, an outer catheter distal opening <NUM>, an inner catheter lumen <NUM>, an inner catheter distal opening <NUM>, and a plurality of sidewall openings <NUM> may correspond to aspiration catheter system <NUM>, outer catheter <NUM>, inner catheter <NUM>, outer catheter lumen <NUM>, outer catheter distal opening <NUM>, inner catheter lumen <NUM>, inner catheter distal opening <NUM>, and plurality of sidewall openings <NUM> of <FIG>, respectively.

In <FIG>, outer catheter <NUM> and inner catheter <NUM> are positioned near a thrombus <NUM> prior to engagement of aspiration catheter system <NUM> with thrombus <NUM>. When inner catheter distal opening <NUM> is not blocked by thrombus <NUM> (or partially blocked by thrombus <NUM> such that adequate flow of fluid is maintained through inner catheter distal opening <NUM>), an aspiration pump, such as aspiration pump <NUM>, may deliver aspiration fluid through outer catheter lumen <NUM> between an inner surface of outer catheter <NUM> and an outer surface of inner catheter <NUM>. The aspiration fluid may be delivered out of outer catheter distal opening <NUM> into a volume of space outside outer catheter distal opening <NUM>, such as near thrombus <NUM>. In some examples (not shown), the aspiration fluid may be delivered through sidewall openings <NUM> into inner catheter lumen <NUM>, even when thrombus <NUM> is not engaged, such as if sidewall openings <NUM> do not have a differential pressure (i.e., difference between positive pressure and negative pressure) threshold (i.e., minimum differential pressure) or the differential pressure threshold has been reached. The aspiration fluid (or combination of fluids) may flow near a surface of the unengaged or partially engaged thrombus <NUM>, such that pieces of thrombus <NUM> may be loosened and removed from thrombus <NUM>. Aspiration pump <NUM> may draw the pieces of thrombus <NUM>, along with fluid, into inner catheter lumen <NUM>. As such, the fluid flow shown in <FIG> may characterize a first flow path of fluid from outer catheter lumen <NUM> through outer catheter distal opening <NUM> and inner catheter distal opening <NUM> to inner catheter lumen <NUM>.

<FIG> illustrate outer catheter <NUM> and inner catheter <NUM> after engagement of thrombus <NUM>. When inner catheter distal opening <NUM> is blocked by thrombus (or partially blocked by thrombus <NUM> such that adequate flow of fluid is not maintained through inner catheter distal opening <NUM>), aspiration pump <NUM> may deliver aspiration fluid through outer catheter lumen <NUM> between an inner surface of outer catheter <NUM> and an outer surface of inner catheter <NUM>. However, the aspiration fluid may be delivered through sidewall openings <NUM> into inner catheter lumen <NUM>, even though inner catheter distal opening <NUM> is blocked by thrombus <NUM>. For example, aspiration fluid may be delivered from outer catheter inner lumen <NUM> through a sidewall opening <NUM> within outer catheter distal opening <NUM> into inner catheter lumen <NUM> and/or delivered through outer catheter distal opening <NUM> into a volume outside outer catheter distal opening <NUM>, such as near thrombus <NUM>, and through a sidewall opening <NUM> outside outer catheter distal opening <NUM>. In some examples, the aspiration fluid may be delivered through sidewall openings <NUM> in response to a differential pressure (i.e., difference between positive pressure and negative pressure) exceeding a differential pressure threshold (i.e., minimum differential pressure) of the sidewall openings <NUM>. The aspiration fluid (or combination of fluids) may flow near a surface of the engaged thrombus <NUM> within inner catheter lumen <NUM>, such that pieces of thrombus <NUM> may continue to be loosened and removed from thrombus <NUM>. As such, the fluid flow shown in <FIG> may characterize a second flow path of fluid from outer catheter lumen <NUM> through outer catheter distal opening <NUM> and at least a first sidewall opening of the plurality of sidewall openings <NUM> to inner catheter lumen <NUM>, and a third flow path of fluid from outer catheter lumen <NUM> directly through a second sidewall opening of the plurality of sidewall openings <NUM> to inner catheter lumen <NUM>.

Aspiration pump <NUM> may draw the pieces of thrombus <NUM>, along with fluid, into inner catheter lumen <NUM> for removal of the pieces of thrombus <NUM>. In this way, aspiration catheter system <NUM> may maintain both suction and -partial flow through inner catheter lumen <NUM> on engaged thrombus <NUM> to remove thrombus <NUM>, even when distal opening <NUM> is partially or fully blocked by thrombus <NUM>.

In some examples, the sidewall openings discussed herein may include one-way valves having a variety of opening mechanisms. <FIG> are schematic diagrams illustrating various valve configurations for sidewall openings. <FIG> is a schematic diagram illustrating an example duckbill valve <NUM>. Duckbill valve <NUM> may include two or more flaps <NUM> extending from an inner catheter <NUM>. Duckbill valve <NUM> may be configured to open in response to a differential pressure threshold being reached or exceeded. <FIG> is a schematic diagram illustrating an example slit valve <NUM>. Slit valve <NUM> may include two or more sides in inner catheter <NUM>. Slit valve <NUM> may be configured to deform in response to a differential pressure threshold being exceeded. <FIG> is a schematic diagram illustrating an example flap valve <NUM>. Flap valve <NUM> may include one or more flaps <NUM> extending from inner catheter <NUM>. Flap valve <NUM> may be configured to open in response to a differential pressure threshold being exceeded and may be aided by a direction of fluid flow past the flaps <NUM>.

The alignment elements discussed herein may have a variety of configurations. <FIG> are schematic longitudinal cross-sectional diagrams illustrating example aspiration catheter systems <NUM>, <NUM>, <NUM> having various example alignment elements for positioning an inner catheter at one or more predetermined positions within an outer catheter. Each aspiration catheter system <NUM>, <NUM>, <NUM> may be functionally similar to, for example, aspiration catheter system <NUM> of <FIG>.

<FIG> is a schematic longitudinal cross-sectional diagram illustrating example aspiration catheter system <NUM> that includes visible markers as an alignment element. Aspiration catheter system <NUM> includes an outer catheter <NUM>, an inner catheter <NUM> within outer catheter <NUM>, a plurality of sidewall openings <NUM> at a distal portion <NUM> of aspiration catheter system <NUM>, and an alignment element at a proximal portion <NUM> of aspiration catheter system <NUM>, the alignment element including an inner catheter visible marker <NUM> on inner catheter <NUM>. When inner catheter visible marker <NUM> is aligned with an outer catheter proximal opening <NUM> of outer catheter <NUM>, inner catheter <NUM> may be at the predetermined position P<NUM> relative to outer catheter <NUM>. In this way, a clinician operating aspiration catheter system <NUM> may adjust aspiration catheter system <NUM>, such as by operating a proximal portion of inner catheter <NUM>, using an easy to view visual indication. While visible marker <NUM> is described at proximal portion <NUM>, in some examples, visible marker <NUM> may be located at other locations, such that a clinician may more easily observe a relationship between visual marker <NUM> and outer catheter proximal opening <NUM>. In other examples, outer catheter <NUM> may include a visual marker, such that visual marker <NUM> may be aligned with the outer catheter visual marker.

<FIG> is a schematic longitudinal cross-sectional diagram illustrating example aspiration catheter system <NUM> that includes an alignment element including a plurality of visible markers. Aspiration catheter system <NUM> includes an outer catheter <NUM>, an inner catheter <NUM> within outer catheter <NUM>, a plurality of sidewall openings <NUM> at a distal portion <NUM> of aspiration catheter system <NUM>, and an alignment element at a proximal portion <NUM> of aspiration catheter system <NUM> that includes three inner catheter visible marker 332A, 332B, 332C on inner catheter <NUM>. Each marker 332A, 332B, 332C corresponds to a respective predetermined position P<NUM>, P<NUM>, P<NUM> of at least one sidewall opening of the plurality of sidewall openings of the inner catheter relative to the outer catheter distal opening when the respective marker <NUM> is at a respective marker position M<NUM>, M<NUM>, M<NUM> aligned with an outer catheter proximal opening <NUM> (or, alternatively, a visual marker on outer catheter <NUM>). When outer catheter proximal opening <NUM> is aligned with a respective inner catheter visible marker 332A, 332B, 332C, aspiration catheter system <NUM> may be at the respective predetermined position P<NUM>, P<NUM>, P<NUM>. For example, each predetermined position may have certain flow characteristics due to the proportion of sidewall openings <NUM> that are distal to the distal opening of outer catheter <NUM> (compared to the total number of sidewall openings <NUM> (including those within the outer catheter lumen <NUM>)). In this way, a clinician operating aspiration catheter system <NUM> may adjust aspiration catheter system <NUM> using an easy to view visual indication to a variety of different predetermined positions.

<FIG> is a schematic longitudinal cross-sectional diagram illustrating example aspiration catheter system <NUM> that includes an alignment element including alignment structures. Aspiration catheter system <NUM> includes an outer catheter <NUM>, an inner catheter <NUM> within outer catheter <NUM>, a plurality of sidewall openings <NUM> at a distal portion <NUM> of aspiration catheter system <NUM>, and an alignment element at a proximal portion <NUM> of aspiration catheter system <NUM>, the alignment element including an inner catheter alignment structure <NUM> extending from an outer surface of inner catheter <NUM> and an outer catheter alignment structure <NUM> extending from an inner surface of outer catheter <NUM>. Inner catheter alignment structure <NUM> may configured to engage with outer catheter alignment structure <NUM>.

When inner catheter alignment structure <NUM> and outer catheter alignment structure <NUM> are engaged, inner catheter <NUM> may be at the predetermined position P<NUM> relative to outer catheter <NUM>. In this way, a clinician operating aspiration catheter system <NUM> may adjust aspiration catheter system <NUM> and determine sidewall openings <NUM> are positioned at the desired location relative to the outer catheter distal opening without having to divert her gaze to observe a relative position of inner catheter <NUM> and outer catheter <NUM>. While alignment structures <NUM>, <NUM> are shown at proximal end <NUM>, in some examples, alignment structures <NUM>, <NUM> may be located at other locations. While alignment structures <NUM>, <NUM> are shown as interlocking structures, in other examples, the alignments structures may include other mechanisms that limit travel of inner catheter <NUM> within outer catheter <NUM>, such as a single structure at a proximal portion of inner catheter <NUM> that interacts with an edge of an outer catheter proximal opening <NUM> of outer catheter <NUM>.

<FIG> is a flow diagram of an example method of using an aspiration catheter system that includes an outer catheter and an inner catheter configured to maintain suction and continuous flow of fluid on an engaged thrombus. The methods and techniques described herewith do not form part of the present invention. The techniques of <FIG> are described with reference to the various aspects of aspiration system <NUM> of <FIG> for illustrative purposes; however, such descriptions are not intended to be limiting, and the techniques of <FIG> may be used with other examples of the aspiration systems disclosed herein, or otherwise. The technique of <FIG> includes introducing aspiration catheter system <NUM> into vasculature of a patient (<NUM>), positioning inner catheter <NUM> within outer catheter <NUM> at a predetermined position (<NUM>), and delivering a fluid through outer catheter lumen <NUM> into outer catheter distal opening <NUM> and/or a sidewall opening <NUM> of inner catheter <NUM> (<NUM>), thereby maintaining suction and continuous flow of fluid on an engaged thrombus. In some examples, the techniques described herein include removing aspiration catheter system <NUM> from the vasculature of the patient once the procedure is complete.

In some examples, introducing at least a portion of outer catheter <NUM> and inner catheter <NUM> into vasculature of a patient (<NUM>) may be aided by initially introducing a guidewire, guide catheter or another guide member into the vasculature of the patient to a target treatment site. In some examples, outer catheter <NUM> is a guide catheter that is initially introduced into the vasculature of the patient, e.g., over a guidewire and advanced to the target treatment site. Inner catheter <NUM> may then be introduced through an inner lumen of the guide catheter. In other examples, outer catheter <NUM> and inner catheter <NUM> may be navigated to a target treatment site inside of a separate guide catheter.

In some examples, aspiration catheter system <NUM> is inserted into vasculature of the patient prior to attachment of a remainder of aspiration system <NUM>, while in other examples, aspiration catheter system <NUM> may be inserted into vasculature of the patient with a remainder of aspiration system <NUM> already attached, such as through aspiration tubing <NUM>.

The technique of <FIG> may include various steps for initiating aspiration to remove a thrombus. For example, a distal end of aspiration catheter system <NUM> may be introduced into an intracranial blood vessel (or other blood vessel) and positioned so that inner catheter distal opening <NUM> is adjacent to and/or proximal of a thrombus. Once inner catheter distal opening <NUM> is positioned at a position corresponding to an estimated location of the thrombus, a clinician may deliver a fluid through outer catheter lumen <NUM>. For example, a clinician operating aspiration system <NUM> may operate aspiration pump <NUM> to generate a positive pressure in outer catheter lumen <NUM> and a negative pressure in inner catheter lumen <NUM>.

The technique of <FIG> can include positioning inner catheter <NUM> within outer catheter lumen <NUM> at the predetermined position P<NUM> such that at least one sidewall opening of the plurality of sidewall openings <NUM> remains positioned within outer catheter lumen <NUM> and at least one other sidewall opening of the plurality of sidewall openings <NUM> is positioned distal to outer catheter distal opening <NUM>. For example, the clinician may adjust inner catheter <NUM> within outer catheter <NUM> until alignment element <NUM> indicates the predetermined position P<NUM>.

In some examples, the technique of <FIG> may include positioning inner catheter distal opening <NUM> proximate to the thrombus in the vasculature so that the thrombus substantially covers inner catheter distal opening <NUM>. In response to the thrombus substantially covering inner catheter distal opening <NUM>, the fluid may be delivered through the at least one sidewall opening <NUM> into inner catheter lumen <NUM>. In some examples, the fluid is delivered through outer catheter lumen <NUM> through the at least one sidewall opening <NUM> into inner catheter lumen <NUM> in response to a differential pressure between outer catheter lumen <NUM> and inner catheter lumen <NUM> being greater than or equal to a predetermined threshold value.

At least a portion of the fluid entering inner catheter lumen <NUM> through the at least one sidewall opening <NUM> may contact a surface of the thrombus. This continuous flow of fluid on the thrombus may cause loose particles to be removed from the surface of the thrombus. For example, the continuous flow of fluid may be relatively turbulent, such that the flow of fluid may exert an impacting force on the thrombus. Additionally, a suction from inner catheter lumen <NUM> may draw fluid from the surface of the thrombus and remove the fluid through inner catheter lumen <NUM>.

In some examples, a clinician operating aspiration system <NUM> may adjust aspiration catheter system <NUM> to a second predetermined position corresponding to a different configuration of the plurality of sidewall openings <NUM> outside outer catheter lumen <NUM> (e.g., distal of distal opening <NUM>) and within outer catheter lumen <NUM> (e.g., proximal of distal opening <NUM>). For example, the clinician may desire that a higher flow rate of aspiration fluid passes through sidewall openings <NUM> that are distal of outer catheter distal opening <NUM>; in such a case, the clinician may select a predetermined position corresponding to an increased number of sidewall openings proximal of catheter distal opening <NUM> (e.g., within lumen <NUM>).

As pieces of the thrombus are removed, the thrombus may block inner catheter distal opening <NUM> to a lesser extent, such that flow of fluid into inner catheter distal opening <NUM> may increase. In response, the clinician may reposition aspiration catheter system <NUM>, such as by advancing aspiration catheter system in a distal direction, to continue to remove the thrombus.

Catheter <NUM> may be removed from the vasculature once the procedure is complete.

In some examples, inner catheter <NUM> may be used during a medical procedure with all of sidewall openings <NUM> in a blood vessel of a patient distal to or otherwise not within outer catheter <NUM> or another outer catheter. For example, inner catheter <NUM> may be used on its own without outer catheter <NUM>, although a guide catheter may be used to deliver inner catheter <NUM> to a treatment site within the vasculature of a patient. In some of these examples, inner catheter <NUM> may be used as an aspiration catheter. For example, aspiration pump <NUM> may create a negative pressure on inner catheter <NUM> to draw fluid into inner catheter lumen <NUM>, e.g. to aspirate a thrombus from a blood vessel. In some of these examples, sidewall openings <NUM> may be configured to enable flow of fluid from the blood vessel into inner catheter lumen <NUM> through sidewall openings <NUM>, such as in response to a positive pressure in the blood vessel being greater than a negative pressure in inner catheter lumen <NUM>. In some examples, the plurality of sidewall openings <NUM> may be configured to open in response to a differential pressure in the blood vessel and in inner catheter lumen <NUM> (i.e., a difference between a positive pressure in the blood vessel and a negative pressure in inner catheter lumen <NUM>) being greater than or equal to a predetermined differential pressure threshold value. This may enable fluid to flow into inner catheter lumen <NUM> when inner catheter distal opening <NUM> is blocked, such as by the thrombus. In this way, the clinician may maintain both suction on an engaged thrombus and continuous flow of fluid on the engaged thrombus, which may result in more effective removal of the thrombus from the vasculature of the patient.

Claim 1:
An aspiration catheter system (<NUM>) comprising:
an outer catheter (<NUM>) defining an outer catheter lumen (<NUM>) and an outer catheter distal opening (<NUM>,<NUM>);
an inner catheter (<NUM>) configured to be positioned within the outer catheter lumen (<NUM>), the inner catheter (<NUM>) defining an inner catheter lumen (<NUM>), an inner catheter distal opening (<NUM>), and a plurality of sidewall openings (<NUM>,<NUM>) proximal to the inner catheter distal opening (<NUM>); and
an alignment element configured to indicate a predetermined position of the inner catheter (<NUM>) relative to the outer catheter (<NUM>) when the inner catheter (<NUM>) is received within the outer catheter distal opening (<NUM>,<NUM>),
wherein when the inner catheter (<NUM>) is at the predetermined position, at least one sidewall opening (24B) of the plurality of sidewall openings (<NUM>,<NUM>) remains positioned within the outer catheter lumen (<NUM>) and at least one other sidewall opening (24A) of the plurality of sidewall openings (<NUM>,<NUM>) is positioned distal to the outer catheter distal opening (<NUM>,<NUM>), the aspiration catheter further comprising:
a fluid circulation system (<NUM>) coupled to a proximal portion of the outer catheter (<NUM>) and a proximal portion of the inner catheter (<NUM>),
wherein the fluid circulation system is configured to deliver fluid through the outer catheter lumen (<NUM>) and receive fluid through the inner catheter lumen (<NUM>).