Abstract:
An embolic protection device comprises an intravascular flow-interactive surface supported by an expandable, substantially cylindrical frame, wherein the frame is configured to expand and engage the luminal surface of the ascending aortic arch, wherein said frame defines a longitudinal channel generally parallel to predominant blood flow vectors, and wherein a flow-modulating element is configured to alter fluid dynamics in a manner that redirects the cranial trajectory of embolic particles originating from the heart through and beyond the longitudinal channel. The embolic protection device may also comprise a plurality of independent or interconnected flow-modulating elements serially spaced apart along the longitudinal axis of the primary vessel. The interstitial space between flow-modulating elements allows blood flow passage between one another in a direction generally perpendicular to the longitudinal channel. The open central channel allows interval passage and manipulation of transcatheter instruments while maintaining the integrity of radially positioned flow-modulating surfaces.

Description:
[0001]    This application is a national stage entry under 35 U.S.C. §371 of PCT Application No. PCT/US2013/032222, filed Mar. 15, 2013, which claims the benefit of U.S. Provisional Application No. 61/623,989, filed Apr. 13, 2012. The entire contents of PCT Application No. PCT/US2013/032222 and U.S. Provisional Application No. 61/623,989 are incorporated herein by reference. 
     
    
     TECHNICAL FIELD 
       [0002]    The invention relates to implantable medical devices and, more particularly, vascularly-implantable medical devices for preventing cardio-embolic stroke. 
       BACKGROUND 
       [0003]    Stroke is the third leading cause of death in the United States and otherwise a frequently disabling neurologic condition. The American Heart Association estimates an annual stroke incidence of 500,000 new patients and prevalence of 4 million stroke survivors. Many of these patients require chronic rehabilitation and specialized care, and frequently require long-term hospitalization. 
         [0004]    Cerebral embolic stroke represents approximately 10-24% of all stroke types, the remainder of which are atherothrombotic or hemorrhagic in origin. Mechanisms responsible for particle embolization from cardiac structures to the cranial circulation include thrombosis from flow stagnation secondary to arrhythmias and post-myocardial infarction left ventricular dysfunction, intracardiac mechanical prosthesis-blood interface coagulation activation, infective or non-infective endocarditis, and instrument thrombosis related to left-sided endocardial ablations, valvuloplasties, and transcatheter valve replacements. 
         [0005]    Current therapies targeting the pro-thrombotic state of atrial arrhythmias include chronic oral anticoagulation and more recently mechanical isolation of the thrombus-prone left atrial appendage for patients deemed to have elevated bleeding risk. Mainstay oral anticoagulation involves variable-dose daily medication with weekly to monthly serum level surveillance for therapeutic effect. Novel anticoagulation with set dosing and no blood level surveillance has recently entered clinical practice, although currently no reversal agents exist in the event of catastrophic bleeding complications. Left atrial appendage occlusion or isolation devices target the essential elimination of the structure most recognized as a culprit region with flow stagnation in atrial arrhythmias, ultimately leading to thrombus formation and potential dislodgment and embolization to the cranial circulation, i.e. stroke. These devices either fill the structural void of the appendage from an intracardiac plug approach, or ligate the segment from a combined epicardial approach such as that augmented with magnetic guidance. 
         [0006]    Surgically implanted mechanical prosthetic intracardiac valves require lifelong oral anticoagulation to halt the coagulation cascade and resulting thrombosis activated at the device interface. Under certain clinical circumstances such as bleeding, when reversal of anticoagulation is required to prevent excessive blood loss, the mechanical device in contact with the patient&#39;s circulating blood becomes particularly susceptible to thrombosis, and again, embolization leading to potential stroke. 
         [0007]    Transcatheter aortic valve replacement or implantation (TAVR/TAVI) is gaining popularity as a minimally invasive alternative method for treating severe aortic stenosis (AS) in patients deemed to have prohibitive surgical risk. TAVR is a procedure whereby a catheter-loaded bio-prosthetic aortic valve is delivered either percutaneously via peripheral arteries or surgically via a mini-thoracotomy with trans-apical or trans-aortic approach to the native aortic valve region, following balloon valvuloplasty. The most significant adverse outcome associated with this approach is stroke, both at the time of procedure and up to 2 years post-procedure, despite dual antiplatelet therapy. 
         [0008]    The Placement of Aortic Trans-catheter Valves (PARTNER) trial, published in 2010 in The New England Journal of Medicine, found that in high-risk patients with symptomatic severe AS, including those deemed unsuitable candidates for surgery, TAVR, as compared to standard therapy (i.e. balloon valvuloplasty), significantly reduced cardiac symptoms, repeat hospitalization, and all-cause mortality. However, this trial revealed a higher incidence of major strokes and vascular events with TAVR, at both thirty days and one year post-implant. Follow-up data from this trial has demonstrated persisting stroke risk beyond 2 years. Both subclinical athero-embolization (detected by diffusion-weighted magnetic resonance imaging of the brain) and clinically evident stroke are potential complications of TAVR, and carry the greatest implications in patient outcome and peri-procedural cost from additional care and hospitalization. Proposed mechanisms for increased risk of embolic events during and after TAVR include the aortic luminal trauma during catheter and device transit, balloon valvuloplasty, deployment-related mechanical disruption of the aorta and native aortic valve causing fragmentation and embolization, potential valvular micro-thrombi, and atrial fibrillation (AF) following TAVR. 
         [0009]    Additionally, left-sided or systemic circulation endocardial ablation procedures target elimination of electrophysiologic channels, pathways, and foci responsible for arrhythmias including atrial fibrillation, atypical left-sided flutter, atrial tachycardia, bypass tracts, and ventricular tachycardia. These procedures require either trans-septal or trans-aortic instrument transit to targeted ablation site, exposing instrument surfaces to blood, and yielding potential for thrombus formation and embolic events. 
       SUMMARY 
       [0010]    In general, embolic protection devices and methods for using such devices are described. An embolic protection device engages the inner wall of a blood vessel, such as the aortic arch, and includes one or more embolic flow-modulating elements, which may comprise angled flow-modulating or deflective surfaces. The embolic protection device defines a longitudinal passageway through the device, and the flow-modulating elements modulate blood flow such that emboli shift trajectory based on modulated blood flow streamlines. The shift in embolic trajectory may occur with or without contact with the surface of a flow-modulating element. The emboli pass through the device via the longitudinal passageway, downstream and away from the cranial circulation. Blood may pass through the device in a direction generally transverse to the longitudinal passageway, e.g., to enter branches of the primary blood vessel. The longitudinal passageway is sized so that catheters or other instruments for performing cardiac procedures, e.g., aortic valvuloplasty, TAVR, coronary angiography or intervention, or endocardial ablation, may pass through the passageway while the protection device is seated in its functional position. The embolic protection device may remain implanted after such a procedure is performed, e.g., chronically. 
         [0011]    In one example, an embolic protection device comprises an expandable and substantially cylindrical frame. The frame is configured to expand to engage an inner wall of a blood vessel. The frame defines a longitudinal passageway through the frame when expanded, and wherein the expanded frame includes an inner circumference. The embolic protection device further comprises a flow-modulating element within the frame. The flow-modulating element extends around a portion of the inner circumference of the frame less than the entire inner circumference. The flow-modulating element comprises a leading surface and a trailing surface, and the leading surface and the trailing surface form a hydrofoil shape. 
         [0012]    In another example, an embolic protection device comprises an expandable and substantially cylindrical frame. The frame is configured to expand to engage an inner wall of a blood vessel. The frame defines a longitudinal passageway through the frame when expanded. The embolic protection device further comprises a plurality of embolic flow-modulating elements within the frame. The embolic flow-modulating elements are spaced apart and located at respective longitudinal, e.g., axial or along the longitudinal axis, positions along the frame. The spacing apart of the flow-modulating elements allows blood to pass between the flow-modulating elements and through the frame in a direction generally transverse to the longitudinal passageway. The flow-modulating elements are configured to deflect emboli and direct the emboli through the frame via the longitudinal passageway. 
         [0013]    In another example, an embolic protection device comprises an expandable and substantially cylindrical frame configured to expand to engage an inner wall of a blood vessel, and a helical embolic flow-modulating element within the frame. The flow-modulating element has an outer diameter and an inner diameter. The inner diameter defines a longitudinal passageway through the frame when the frame is expanded. The helical embolic flow-modulating element comprises a deflective surface between the outer diameter and the inner diameter, the deflective surface configured to face the flow of blood within the vessel and deflect emboli and direct the emboli through the frame via the longitudinal passageway when the embolic protection device is implanted within the vessel. The helical embolic flow-modulation allows blood to pass through the frame in a direction generally transverse to the longitudinal passageway. 
         [0014]    In another example, a method comprises inserting an embolic protection device into a common vascular access, deploying an embolic protection device to engage the inner wall of a target vessel, inserting a procedure instrument into the common vascular access, advancing the procedure instrument through the longitudinal passageway of the embolic protection device and to a procedure target, performing a procedure using the procedure instrument with embolic protection device engaged to the inner wall of the target vessel, and withdrawing the procedure instrument through the longitudinal passageway of embolic protection device. The embolic protection device may remain implanted chronically, with the potential for later retrieval. 
         [0015]    The details of one or more examples are set forth in the accompanying drawings and the description below. Other features, objects, and advantages will be apparent from the description and drawings, and from the claims. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0016]      FIG. 1A  is a conceptual cross-sectional diagram illustrating an example embolic protection device implanted within the aortic arch. 
           [0017]      FIG. 1B  is a conceptual cross-sectional diagram illustrating an example embolic protection device in conjunction with an instrument. 
           [0018]      FIG. 2A  is a conceptual cross-sectional diagram illustrating the embolic protection device of  FIG. 1B  in conjunction with an embolus. 
           [0019]      FIG. 2B  is a conceptual cross-sectional diagram illustrating another example embolic protection device in conjunction with an embolus. 
           [0020]      FIG. 3A  is a perspective diagram illustrating another example embolic protection device. 
           [0021]      FIG. 3B  is a perspective diagram further illustrating a flow-modulating element of the example embolic protection device of  FIG. 3A . 
           [0022]      FIG. 4  is a conceptual diagram illustrating an example frame for an embolic protection device. 
           [0023]      FIG. 5A  is a conceptual diagram illustrating another example embolic protection device. 
           [0024]      FIG. 5B  is a perspective diagram illustrating an example flow-modulating element for the embolic protection device of  FIG. 5A . 
           [0025]      FIG. 5C  is a cross-sectional diagram further illustrating the example flow-modulating element of  FIGS. 5A and 5B . 
           [0026]      FIG. 6  is cross-sectional diagram illustrating another embolic protection device 
           [0027]      FIG. 7A  is a conceptual diagram illustrating blood flow in an aortic arch. 
           [0028]      FIG. 7B  is a conceptual diagram illustrating blood flow and particle trajectory around a flow-modulating element. 
           [0029]      FIG. 7C  is a conceptual diagram illustrating blood flow and particle trajectory around a plurality of flow-modulating elements. 
           [0030]      FIG. 7D  is a conceptual diagram illustrating blood flow and particle trajectory around another example embolic protection device. 
           [0031]      FIG. 8  is a conceptual diagram illustrating another example embolic protection device implanted within a blood vessel. 
           [0032]      FIG. 9  is a conceptual diagram illustrating another example embolic protection device implanted within a blood vessel. 
           [0033]      FIG. 10  is a conceptual diagram illustrating another example embolic protection device. 
           [0034]      FIG. 11  is a flow diagram illustrating an example method of implanting an embolic protection device and performing a cardiac procedure. 
           [0035]      FIG. 12  is a flow diagram illustrating an example method of implanting an embolic protection device for stroke prophylaxis. 
           [0036]      FIG. 13  is a flow diagram illustrating an example method for implanting an embolic protection device and performing an aortic valve procedure. 
           [0037]      FIG. 14A  is a conceptual diagram of a cross-sectional view of an example embolic protection device. 
           [0038]      FIG. 14B  is conceptual diagram of an orthogonal view of the embolic protection device of  FIG. 14A . 
           [0039]      FIG. 14C  is a conceptual diagram of a side view of the embolic protection device of  FIGS. 14A and 14B . 
       
    
    
     DETAILED DESCRIPTION 
       [0040]    This disclosure describes devices, systems, and techniques for stroke prevention. In various examples, one or more flow-modulating elements is implanted within a patient&#39;s aortic arch. The flow-modulating element interrupts the flow of blood through the patient&#39;s primary vessel (i.e. aortic arch) while still allowing blood to pass freely through the vessel to the cranially-directed branch vessels and beyond to the rest of the body. When laminar blood flow encounters the modulating element&#39;s surface, blood flow streamlines converge at the leading edge of the flow-modulating element and then diverge as the blood flows along the trailing edge of the flow-modulating element. A particle, such as an embolus, that is traveling in a particular streamline shifts to an adjacent streamline and continues downstream past a branch vessel ostium rather than following a streamline into said branch vessel. The shift in trajectory of the particle may occur with or without direct contact with the surface of the flow-modulating element. 
         [0041]    In some examples, a flow-modulating element is implanted on the greater curvature of the aortic arch proximal to the brachiocephalic takeoff. A stent-like frame may support the flow-modulating element. In some examples, the flow-modulating element may encircle the inner aspect of the frame, resulting in a deflective surface that is symmetrical around the vessel. In some examples, the flow-modulating element covers less than, e.g., approximately half of, the circumference of the frame, resulting in a deflective surface that is radially asymmetrical within the vessel. In some examples, an embolic protection device may include a series of axially oriented rings, each ring including a flow-modulating surface. One or more of the flow-modulating elements may partially block one or more ostia. 
         [0042]    In various examples, the embolic protection device may be implanted temporarily within a patient. For example, the device may be implanted prior to a cardiac procedure, such as TAVR or endocardial ablation. The embolic protection device may help prevent stroke from emboli resulting from the cardiac procedure. After the procedure is completed, the embolic protection device may also be removed. 
         [0043]    In other examples, the embolic protection device may be permanently implanted. For example, the embolic protection device may be implanted in a patient at increased long-term risk for stroke. In some examples, the frame of the embolic protection device may be configured to allow endothelial cellular growth to further anchor the device. 
         [0044]      FIG. 1A  is a conceptual cross-sectional diagram illustrating an example embolic protection device  10  implanted within the aortic arch  12 . Embolic protection device  10  engages the inner wall  14  of aortic arch  12 . In some examples, embolic protection device  10  may be compressed and loaded onto a catheter-tip, having a smaller initial profile, e.g., diameter, for delivery through the vasculature to a target vascular location, e.g., the aortic arch. Embolic protection device  10  may then expand to engage the inner wall  14  of the target vessel. Embolic protection device  10  may, as examples, be expanded by inflation of a balloon or other inflatable element, or by being released from a restraining element that maintains the embolic protection device  10  in its compressed state. 
         [0045]    In the illustrated example, embolic protection device  10  comprises a plurality of flow-modulating elements  16 . In the illustrated example, embolic protection device  10  is positioned such that flow-modulating elements  16  divert emboli from entering the cranially-supplying branch arteries  18  from aortic arch  12 . Embolic protection device  10  is positioned such that at least some of flow-modulating elements  16  partially block ostia  20  of the cranially-supplying branch arteries  18 . However, flow-modulating elements  16  are spaced such that blood may flow between the elements and enter the cranially-supplying branch arteries via the ostia. When deployed in the aortic arch, the device may partially cover the ostia of the brachiocephalic trunk, left common carotid, and left subclavian arteries, or any anatomic variant of such blood vessels. The series of flow-modulating rings may act to protect the distal cranial circulation from particulate or thromboembolic matter that would otherwise follow fluid flow cranially and, potentially, result in stroke. 
         [0046]    Embolic protection device  10  and embolic flow-modulating elements  16  are configured, e.g., sized, to provide a longitudinal passageway  30  ( FIG. 1B ) through the embolic protection device. Blood flow  22  to the systemic circulation may occur through the longitudinal passageway  30 . Furthermore, flow-modulating elements  16  are configured to deflect emboli approaching the ostia  20  such that the emboli proceed through the longitudinal passageway  30  rather than entering the ostia  20 . Flow-modulating elements  16  may comprise an angled flow-modulating surface to deflect the emboli into the longitudinal passageway  30 . 
         [0047]      FIG. 1B  is a conceptual cross-sectional diagram illustrating an embolic protection device  11  in conjunction with a cardiac-directed procedure instrument  28 . As illustrated in  FIG. 1B , procedure instrument  28  may be advanced through longitudinal passageway  30  to the heart in the direction of arrow  32 . Embolic protection device  11  and flow-modulating element  11  may be configured, e.g., sized, such that longitudinal passageway  30  is large enough to allow a variety of procedure instruments  28  to pass freely through embolic protection device  11  via passageway  30 . Example procedure instruments  28  include guidewires, coronary catheters, sheaths, balloons, stents, or any instrument used for cardiac procedures, such as TAVR, valvuloplasty, or endocardial ablation. 
         [0048]    In some examples, embolic protection device  11  may be positioned within the aortic arch  12  so that flow-modulating element  17  is directly proximal to an ostium  20 . The trailing edge of the flow-modulating element may be positioned close to the edge of ostium  20 . 
         [0049]      FIG. 2A  is a conceptual cross-sectional diagram illustrating flow-modulating element  17  of  FIG. 1B  in conjunction with an embolus  34 . As illustrated in  FIG. 2A , embolus  34  may enter the aortic arch via the aortic valve  36 , or due to a procedure performed on or proximal to aortic valve  36 . Embolus  34  then travels through aortic arch  12  and toward ostia  20  ( FIGS. 1A and 1B ) of cranially-supplying branches  18  via path  38 . 
         [0050]    According to Bernoulli&#39;s principle, as laminar fluid flow approaches a curve, velocity at the greater or outer curvature (concavity)  24  ( FIG. 1A ) is slower, while velocity at the lesser or inner curvature (convexity)  26  ( FIG. 1A ) is faster. Slower velocity is accompanied by higher pressure, while faster velocity is accompanied by lower pressure. Additionally, slower velocity is accompanied by relatively more laminar flow (relatively lower Reynolds number), while faster velocity is accompanied by more turbulent flow (relatively higher Reynolds number). Ultimately, it is the pressure gradient formed from the outer curvature  24  to the inner curvature  26  that drives flow  22  ( FIG. 1A ) around the curve of the aorta to supply blood to the body. Flow is additionally driven by a pressure gradient formed from the outer curvature of the aortic arch towards the intracranial circulation. Given the curvature and multiple takeoff points from the main channel of the aorta into the ostia  20  of cranially-supplying vessels  18 , vortices of flow at divergence points additionally factor into the fluid dynamics of the aortic arch  12 . Streamlines illustrating blood flow through the aortic arch before implantation of a flow-modulating element is shown in  FIG. 7A , and discussed below. 
         [0051]    As embolus  34  exits the heart, it is propelled by the systolic pulse on a trajectory toward the aortic arch  12 . More particularly, embolus  34  preferentially follows path  38  initially directed toward the outer concave curvature (greater diameter)  24  of the aortic arch  12  toward the location of cranial-supplying arterial ostia  20 , then shifts away from said ostia, continuing downstream away from the brain. In a mechanically-unprotected scenario, pressure at the aortic arch directs flow, and may direct the embolus, down a pressure gradient, through a cranial-supplying arterial ostium, and toward the brain, leading to stroke. 
         [0052]    Embolic protection devices as described herein may be deployed prior to or during medical procedures that may impose elevated risk of embolic stroke, such as TAVR, valvuloplasty, or endocardial ablation. Embolic protection devices may also be deployed in patients with elevated stroke risk from arrhythmia, e.g., AF, deemed otherwise high-risk candidates for anticoagulation. An embolic protection device may also be deployed within or adjacent a medical device that increases the risk of embolic stroke, such as a ventricular assist device (VAD). 
         [0053]    An example application for embolic protection devices as described herein is aortic arch implantation prior to TAVR and/or valvuloplasty. Embolic protection devices may be implanted chronically or otherwise for an extended period of time, e.g., remaining implanted after the TAVR or valvuloplasty procedure. The longitudinal passageway of the embolic protection device facilitates such long duration implantation in that the passageway allows interval access through embolic protection device  10  with wires, catheters and other instruments, both during the procedure, and for any subsequent procedures that occur while the device remains implanted. Ultimately, by allowing device delivery just prior to and via the same access point as TAVR or valvuloplasty, faster overall procedure times are achieved, with the temporal benefit of “protected” cerebral circulation throughout the entirety of the procedure and beyond, into the extended peri-procedural risk period for stroke. 
         [0054]    Another application of the embolic protection devices described herein is stroke prophylaxis for the population of patients with cardiac arrhythmias, such as AF, that predispose them to elevated risk of thromboembolic events. Currently, such patients are risk-stratified for long-term thromboembolic risk based on the “CHADS2” scoring system, which stratifies patients&#39; stroke risk based on a score that indicates that recommended level of anticoagulation therapy to reduce patients&#39; stroke risk. In some patients with elevated CHADS2 scores, which would otherwise indicate recommended anticoagulation, the bleeding risk from anticoagulation equals or outweighs their stroke risk. 
         [0055]    Embolic protection devices as described herein may avoid interfering with cerebral blood flow and relative pressure, e.g., due to the spacing between flow-modulating elements. The longitudinal passageway of embolic protection devices as described herein may provide a relatively unobstructed passage of catheters and other instruments through and beyond the device without disrupting the positioning and function of the embolic protection device. Additionally, the overall structure of embolic protection devices as described herein may be more fixed and less compliant, and thus more applicable to an arterial pressure environment. Embolic protection devices may nevertheless conform to a variety of vessels, such as the aortic arch. 
         [0056]    In some examples, the embolic protection devices are radially symmetric, which may facilitate implantation, obviating the need for a particular rotational orientation of the device in the vessel, e.g., aortic arch. In other examples, embolic protection devices may only have deflective surfaces at the superior aspect of the device, e.g., along greater curvature of the aortic arch  24  ( FIG. 1A ) proximal to the cranially-supplying arterial ostia. The portion of the device proximal to the lesser curvature of the aortic arch  26  ( FIG. 1A ) may be relatively flat and free of elements protruding into the longitudinal passageway.  FIGS. 8 and 9 , discussed below, show a radially symmetrical embolic protection device and a radially asymmetrical embolic protection device, respectively. 
         [0057]      FIG. 2B  is a conceptual cross-sectional diagram illustrating another example embolic protection device  13  in conjunction with an embolus. Embolic protection device  13  is implanted in a branch vessel  18 , and flow-modulating element  19  encircles ostium  20 . As embolus  34  exits the heart, it is propelled by the systolic pulse on a trajectory toward the aortic arch  12 . More particularly, embolus  34  preferentially follows path  38  directed toward the outer concave curvature (greater diameter)  24  of the aortic arch  12 , and toward the location of cranial-supplying arterial ostia  20 . In a mechanically-unprotected scenario, pressure at the aortic arch directs flow, and may direct the embolus, down a pressure gradient, through a cranial-supplying arterial ostium, and toward the brain, leading to stroke. 
         [0058]    In the example of  FIG. 2B , flow-modulating element  19  deflects the path of embolus  34  way from ostia  20 , while still allowing blood to flow through branch vessel  18 . In the example of  FIG. 2B , embolic protection device  13  may be a cuffed sleeve, wherein the cuff is flow-modulating element  19 . Embolic protection device  13  may be self-expanding or a balloon-expandable stent. As shown in  FIG. 2B  embolic protection device  13  may be deployed at a proximal segment of a cranially-directed vessel  18 . Flow-modulating element  13  may be a circumferential cuff or bumper extending around ostium  20  into the lumen of the primary vessel (such as the aortic arch). The extension into the primary vessel acts as flow-modulating element  19 . In addition, the flow-modulating element may anchor the embolic protection device to prevent distal dislodgment toward the brain. The orientation of embolic protection device  12  may provide 360-degree flow modulation surrounding vessel ostium  20 , such that flow that would otherwise facilitate embolization of threatening particles traveling with diastolic retrograde aortic trajectory is also disrupted and redirected. 
         [0059]      FIG. 3A  is a perspective diagram illustrating another example embolic protection device. As illustrated in  FIG. 3A , embolic protection device  50  comprises a frame  52 , and a plurality of flow-modulating elements  54  within and coupled to the frame  52 . Flow-modulating elements  54  have a ring-like or generally annular profile. The configuration of flow-modulating elements  54  and frame  52  provides a longitudinal passageway through embolic protection device  50 —generally along the longitudinal axis of embolic protection device  50 . The construction and/or materials of frame  52  and flow-modulating elements  54  may be compressed and loaded onto a catheter-tip, allowing embolic protection device  50  to assume a relatively smaller profile, e.g., diameter, for delivery through the vasculature to a target vessel, e.g., the aortic arch, and to be expanded to engage the wall of the target vessel, e.g., the aortic arch. 
         [0060]    The ring-shape platform upon which the deflective surfaces are based allows the device to be deployed in any radial orientation, and once deployed, allows relatively unobstructed transit of wires, catheters, and other intravascular instruments through the device without interfering with the function of the device. Also, the expansion of embolic protection device  50  to engage or very nearly engage the inner surface of the vessel, e.g., aorta, facilitates an open channel. The number of flow-modulating elements  54  depicted in  FIG. 3A  is merely an example. In some examples, embolic protection devices as described herein may include at least two flow-modulating elements, which may be positioned proximal to one or more branches of the vessel in which the device is implanted, e.g., proximal to the cranially-supplying arterial branches of the aortic arch. 
         [0061]    As illustrated in  FIG. 3A , embolic protection device  50  may comprise a series of embolic flow-modulating elements  54  maintained spaced-apart in formation along the longitudinal axis of embolic protection device  50  by an outer scaffolding, e.g., frame  52 , which may be similar to a stent. Each of the embolic flow-modulating elements  54  is axially separated from the adjacent flow-modulating elements by an optimal distance determined by computational fluid dynamics of the target vessel and branch vessels, e.g., in the aorta and cranially-supplying vessels. The separation between the adjacent flow-modulating elements  54  allows open channels for blood flow to branch vessels, e.g., to the brain, while weighted embolic particles are more likely deflected or otherwise directed downstream to generally less clinically critical locations as compared to the brain. 
         [0062]      FIG. 3B  is a perspective diagram further illustrating a flow-modulating element  54  of embolic protection device  50  of  FIG. 3A . As illustrated in  FIG. 3B , flow-modulating element  54  comprises a first ring  60  with a first, relatively larger diameter, and a second ring  62 , with a second, relatively smaller diameter. A deflective surface  64  is disposed between, e.g., bridges, the first ring  60  and the second ring  62 . When flow-modulating element  54  is implanted within a vessel, e.g., the aortic arch, second ring  62  is more distally located relative to blood flow  66 , e.g., more distally located within the aortic arch. Accordingly, deflective surface  64  faces primary blood flow  66 . Based on the difference between the first and second diameters of the first ring  60  and the second ring  62 , deflective surface  64  is oriented at an angle  68  with respect to the longitudinal axis of embolic protection device  50 . Angle  68  may be between ten and eighty degrees, between 30 and 60 degrees, or a similar value that is otherwise deemed optimal per associated simulation and testing. As illustrated in  FIG. 3B , flow-modulating element  54  may take the shape resembling a frustum of a cone. 
         [0063]      FIG. 4  is a conceptual diagram illustrating an example configuration of frame  52  of embolic protection device  50  of  FIG. 3A . Frame  52  is cylindrical, and may be largely fenestrated, as shown in  FIG. 6 . In general, frame  52  may comprise a plurality of linked elements configured to allow frame  52  to be compressed to a smaller profile, e.g., diameter, and to be expand to engage or nearly engage a vessel wall. In this manner, frame  52  may be constructed similar to a stent. In the illustrated example, frame  52  comprises a plurality of circumferential elements  70  that are circuitous and are linked by a plurality of struts  72  arranged along the longitudinal axis of the frame. In other examples, the longitudinal elements may be circuitous, or both the longitudinal and circumferential elements may be circuitous. In general, frame  52  may be constructed using any elements, techniques, or materials known for stents. 
         [0064]    Embolic protection devices as described herein, e.g., one or both of frame  52  or flow-modulating elements  54 , may be formed of nitinol and/or another composite or other material capable of collapse and memory shape re-assumption or retention. Deflective surfaces  64  may be comprised of the same material as the rings  60 ,  62  and/or frame  52 , or any fabric or other material, including, but not limited to, polytetraflouroethylene (PTFE, Teflon®), expanded PTFE (GoreTex®), polyethylene (PE), polyethylene terephthalate (PETE), or some other polymer. Embolic protection devices, and particularly deflective surfaces  64 , could be formed of or coated with bovine, porcine, ovine, or other species-derived pericardium. Depending on the construction and materials of deflective surfaces  64 , e.g., if mesh-like, the deflective surfaces may act initially as a filter and/or flow modulator, and then transition to flow-modulating-only, depending on the degree of endothelialization of the deflective surfaces. 
         [0065]      FIG. 5A  is conceptual diagram illustrating another example embolic protection device  500 . As shown in  FIG. 5A , embolic protection device  500  includes a plurality of flow-modulating elements  80 . In the example shown, embolic protection device  500  includes 3 flow-modulating elements  80 . However, embolic protection device  500  may have more or less flow-modulating elements  80 . As illustrated in  FIG. 5A , each of the flow-modulating elements  5 A is position proximal to an ostium  20 . Each ostia  20  leads to a branch vessel  18 . The flow-modulating elements divert the flow of emboli away from ostia  20 , thereby preventing the occurrence of a stroke. In addition, as shown, flow-modulating elements  80  are radially asymmetrical. 
         [0066]      FIG. 5B  is a perspective diagram illustrating another example flow-modulating element  80  for an embolic protection device.  FIG. 5C  is a cross-sectional diagram further illustrating flow-modulating element  80  of  FIGS. 5A and 5B . Flow-modulating element  80  is an example of a radially-asymmetric flow-modulating element. A plurality of flow-modulating elements  80  may be axially spaced within a frame to form a radially-asymmetric embolic protection device as shown in  FIG. 5A . In some examples, an embolic protection device may comprise a single flow-modulating element  80 . 
         [0067]    Flow-modulating element  80  has a first portion  82 , which may be positioned superiorly along the greater aortic arch  24  when implanted in the aortic arch  12 . Flow-modulating element  80  also comprises a second portion  84 , which may be positioned inferiorly along the lesser aortic arch  26  when implanted in the aortic arch  12 . First portion  82  comprises a deflective surface  86 , while second portion  84  comprises a relatively flat surface  88 . Although in the illustrated example approximately half of the circumference of flow-modulating element  80  includes deflective surface  86 , in other examples a greater or lesser portion of the circumference may comprise a deflective surface. Furthermore, in some examples, non-contiguous portions of the circumference may comprise deflective surfaces. 
         [0068]    Deflective surface  86  faces the primary flow of blood. A trailing surface  90  faces away from the flow of blood. Deflective surface  86 , trailing surface  90 , and surface  92  meet at a peak  94 , the entirety of which resembles a hydrofoil shape, as illustrated in  7 B, for example. The angles of deflective surface  86  and trailing surface  90  may be chosen based on a desired hydrofoil shape. In addition, in some examples, deflective surface  86  is relatively smaller than trailing surface  90 , resulting in peak  94  being positioned towards the front of flow-modulating element  80  with respect to blood flow. This placement may result in less turbulence along the trailing surface  90 . In the illustrated example, an outer surface  96  of deflective element  80  is generally annular, in contrast to the frustum shape of the outer surface of flow-modulating element  54  illustrated in  FIG. 3B . The generally annular shape of outer surface  96  may be selected for reasons of manufacturability, in some cases. In some examples, outer surface  96  may be blood permeable. In some examples, outer surface  96  may be fenestrated. For example, outer surface  96  may be made up of struts and circumferential elements as illustrated in  FIG. 4 . 
         [0069]    Deflective surface  86  and trailing surface  90  may be oriented at respective angles,  202  and  204 , with respect to the longitudinal axis of the embolic protection device. The angles may be the same, or different. In the illustrated example, the angle  202  of deflective surface  86  is greater than angle  204  of trailing surface  90 . The angled trailing surface  90 , and relative angles of deflective surface  86  and trailing surface  90 , may affect the flow of blood through the center of flow-modulating element  80 , and through a longitudinal passageway of an embolic protection device including flow-modulating elements  80 . The blood flow, as affected by flow-modulating elements  80 , may cause emboli to preferentially travel through the center or inferior portions of the longitudinal passageway, avoiding superiorly-located arterial branches, e.g., ostia  20  of branches  18  ( FIGS. 1A and 1B ). 
         [0070]    In some examples, deflective surface  86  and trailing surface  90  may form a hydrofoil shaped flow-modulating element. The hydrofoil-shaped flow-modulating element may be configured to limit or avoid additional turbulence. A smooth hydrofoil-shaped flow-modulating element may also maintain the integrity of laminar flow at the outer curvature of the vessel. Minimizing additional turbulence is desirable, particularly for flow-modulating elements implanted for long periods of time for stroke prophylaxis. In particular, additional turbulence within the aortic arch may lead to additional embolic complications. 
         [0071]      FIG. 6  is a perspective diagram illustrating another example embolic protection device  200 . Embolic protection device  200  includes a flow-modulating element  160  and a frame  162 . Flow-modulating element  160  is positioned along inner wall  14  of greater aortic arch  24 . Embolic protection device  200  may be positioned so that flow-modulating element  160  is proximal to the first cranially-directed arterial ostium  20  after aortic valve  36 , i.e., between the aortic valve  36  and the arterial ostia  20  most proximal to aortic valve  36  or, in other words, more proximal relative to the aortic value than the arterial ostia most proximal to the aortic valve. Frame  162  may be substantially similar to frame  52  as illustrated in  FIG. 4 . In some examples, embolic protection device  200  may be substantially similar to flow-modulating element  80  discussed above with respect to  FIGS. 5A ,  5 B, and  5 C. For example, flow-modulating element  160  may have a hydrofoil like shape similar to that of flow-modulating element  80 . 
         [0072]      FIG. 7A  is a conceptual diagram illustrating blood flow in an aortic arch  12 . According to Bernoulli&#39;s principle, as laminar fluid flow  23  approaches a curve, velocity at the greater or outer curvature (concavity)  24  ( FIG. 1A ) is slower, while velocity at the lesser or inner curvature (convexity)  26  ( FIG. 1A ) is faster. Slower velocity is accompanied by higher pressure, while faster velocity is accompanied by lower pressure. Additionally, slower velocity is accompanied by relatively more laminar flow (relatively lower Reynolds number), while faster velocity is accompanied by more turbulent flow  25  (relatively higher Reynolds number). In order to minimize turbulent flow, in some examples, flow-modulating elements are placed asymmetrically around the aortic arch, so that flow-modulating elements encounter laminar flow  23 , and not the already turbulent flow  25  near the inner curvature of the aortic arch. 
         [0073]      FIG. 7B  is a conceptual diagram illustrating blood flow and particle trajectory around a flow-modulating element. The flow-modulating element  17  of  FIG. 7B  includes a leading (deflective) surface and a trailing surface with relative angles. More particularly, the flow-modulating element of  FIG. 7B  has a hydrofoil-like shape. Ideally, fluid would flow in a laminar pattern as shown, presuming the hydrofoil&#39;s angle of attack does not exceed the threshold beyond which vortices will form and create turbulence and drag. A solid particle of different size/density traveling towards the same surface will be deflected and, due to the hydrofoil shape, assume a new trajectory assisted by an adjacent streamline, thus avoiding the branch vessel, as illustrated in  FIG. 7B . In some examples, the deflection of the particle occurs without the particle coming in contact with the leading surface of the flow-modulating element. The flow-modulating element interrupts the fluid flow, causing the fluid streamlines to converge as they approach the deflective surface and diverge along the trailing surface. The solid particle may shift into an adjacent streamline. As shown in  FIG. 7B , the trajectory  41  of a solid particle shifts from a first streamline  40 A to a second, adjacent, streamline  40 B. The shift in streamline results in the particle avoiding branch vessel  18 . 
         [0074]      FIG. 7C  is a conceptual diagram illustrating blood flow and particle trajectory around a plurality of flow-modulating elements. The flow-modulating elements  300  include a leading surface and a trailing surface with relative angles. The trajectory  302  of a solid particle  34  may start in a first streamline  298 A and upon approaching each of the plurality of flow-modulating elements, shift direction. In some examples, particle  34  may shift from a first streamline  298 A to a second streamline  298 B that is farther away from the plurality of flow-modulating elements  300 . In some examples, trajectory  302  may follow the modulation of a particular streamline. 
         [0075]      FIG. 7D  is a conceptual diagram illustrating blood flow and particle trajectory around another example embolic protection device. Flow-modulating element  304  deflects streamline  306 . In addition, particle trajectory shifts from a first streamline  306 A to a second streamline  306 B as blood flow comes in contact with flow-modulating element  304 . 
         [0076]      FIG. 8  is a conceptual diagram illustrating another example embolic protection device  100  implanted within a blood vessel  102 . Embolic protection device  100  includes superior flow-modulating elements  104 A and inferior flow-modulating elements  104 B (collectively, “flow-modulating elements  104 ”). Flow-modulating elements  104  include deflective surfaces  106  that face blood flow  108  through the vessel  102 . Embolic protection device  100  engages, or nearly engages, the inner wall of vessel  102 , and is positioned such that flow-modulating elements  104  are proximal to branch vessel  110 . As illustrated in  FIG. 8 , an embolus  112  may be deflected off of a deflective surface  106 , and thereafter follow a trajectory with blood flow  108  through the longitudinal passageway of embolic protection device  100  that avoids branch vessel  110 . 
         [0077]      FIG. 9  is a conceptual diagram illustrating another example embolic protection device  120  implanted within blood vessel  102 . While embolic protection device  100  may be symmetric, e.g., radially symmetric, in that it includes both superior and inferior flow-modulating elements  106 , embolic protection device  120  may be asymmetric, e.g., radially asymmetric. In particular, embolic protection device  120  includes flow-modulating elements  104 A on the superior (cranial) portion of the device. However, an inferior portion of the device includes a relatively flat inner surface  122 , or longitudinal passageway wall. 
         [0078]    In some examples, embolic protection devices, e.g., embolic protection devices  100 ,  120 , may appear on a macroscopic level to be similar to a standard stent structure. However, rather than a flat low profile scaffolding structure on both the luminal and vessel-opposing surfaces, there are tilted or angled flow-modulating elements formed on the inner or luminal side of the stent structure, providing a deflective surface or series of deflective surfaces. 
         [0079]      FIG. 10  is a conceptual diagram illustrating another example embolic protection device  130 . Embolic protection device  130  includes a frame  132 , which may be similar to or the same as frame  52  ( FIG. 4 ). Embolic protection device  130  further includes an embolic flow-modulating element  134  within and coupled to frame  132 . 
         [0080]    Embolic flow-modulating element  134  is helical. More particularly, embolic flow-modulating element  134  may include an outer helix structure with a first diameter, and an inner helix structure with a second, smaller diameter. A deflective surface may be formed between or otherwise span the helix structures. The outer helix structure may be coupled to frame  132 . The diameter of the inner helix structure may define, and may be selected to provide, a longitudinal passageway through embolic protection device  130 , which may be sufficient for passage of various procedure instruments. 
         [0081]      FIG. 11  is a flow diagram illustrating an example method for implanting an embolic protection device to prior to or during any left-sided or systemic circulation cardiac procedure. As discussed below with respect to  FIGS. 12 and 13 , in various examples, a clinician inserts an embolic protection device as described herein into a common vascular access point ( 210 ). The clinician may then advance the embolic protection device to a target vessel, such as the aortic arch ( 212 ). In other examples, the embolic protection device may be advanced to one of the branch vessels. The embolic protection device may be delivered using a catheter or other catheter-based delivery mechanism. 
         [0082]    The clinician may then deploy the embolic protection device, e.g., to engage the inner wall of the aortic arch or other target vessel ( 214 ). The embolic protection device may be self-expanding, e.g., may expand upon release from the delivery mechanism. Embodiments in which the embolic protection device comprises nitinol may be capable of self-expansion. In some examples, the embolic protection device may be expanded by balloon or other expandable element of the delivery mechanism. In some examples, the embolic protection device may be radiopaque or include radiopaque elements to facilitate visualization during implantation. Visualization may be of particular importance in the case of asymmetric embolic protection devices, for which orientation of flow-modulating elements and deflective surfaces proximal to branch vessels is desired. In some examples, the clinician may position the embolic protection device so that the flow-modulating element is located prior to the first ostia  20  on the greater curvature  24 . In other examples, the clinician may position the embolic protection device so that a portion of the embolic protection device is placed within a branch vessel, while the flow-modulating element encircles the ostium of the branch vessel and extends partially into the lumen of the aortic arch. After the embolic protection device is implanted, the clinician may withdraw the embolic protection device delivery mechanism, e.g., through the common access ( 216 ). After the clinician has withdrawn the embolic protection device delivery system, the clinician may proceed with a cardiac directed procedure ( 218 ). The embolic protection device may remain in place while the valvuloplasty, TAVR, endocardial ablation, or other cardiac procedure is performed. The use of an embolic protection device may be indicated for various cardiac procedures with a relatively high stroke risk. After the cardiac procedure is completed, the embolic protection device may be removed. In other examples, the embolic protection device may remain in place for a period of time after the cardiac procedure is concluded. 
         [0083]      FIG. 12  is a flow diagram illustrating an example method for implanting an embolic protection device to provide stroke prophylaxis. In some examples, an embolic protection device may be implanted in a patient based on an increased likelihood of stroke. The use of the embolic protection device may be indicated when a patient is deemed high-risk for use of other stroke prevention techniques, namely anticoagulation therapy. As discussed above with respect to  FIG. 11 , in various examples, a clinician inserts an embolic protection device as described herein into a common vascular access point ( 220 ). The clinician may then advance the embolic protection device to a target vessel, such as the aortic arch ( 222 ). The embolic protection device may be delivered using a catheter or other catheter-based delivery mechanism. 
         [0084]    The clinician may then deploy the embolic protection device, e.g., to engage the inner wall of the aortic arch or other target vessel ( 224 ). The embolic protection device may be self-expanding, e.g., may expand upon release from the delivery mechanism. Embodiments in which the embolic protection device comprises nitinol may be capable of self-expansion. In some examples, the embolic protection device may be expanded by balloon or other expandable element of the delivery mechanism. In some examples, the embolic protection device may be radiopaque or include radiopaque elements to facilitate visualization during implantation. Visualization may be of particular importance in the case of asymmetric embolic protection devices, for which orientation of flow-modulating elements and deflective surfaces proximal to branch vessels is desired. In some examples, the clinician may position the embolic protection device so that the flow-modulating element is located prior to the first ostia  20  on the greater curvature  24 . After the embolic protection device is implanted, the clinician may withdraw the embolic protection device delivery mechanism, e.g., through the common access ( 226 ). The clinician may leave the embolic protection device implanted in the patient in order to provide stroke prophylaxis ( 228 ). In some examples, a frame of the embolic protection device may be made of a porous material that allows endothelialization and enhanced anchoring of the device. 
         [0085]      FIG. 13  is a flow diagram illustrating an example method for implanting an embolic protection device and performing an aortic valve procedure. According to the example method, a clinician inserts an embolic protection device as described herein into a common vascular access point ( 140 ). The clinician may then advance the embolic protection device to a target vessel, such as the aortic arch ( 142 ). The embolic protection device may be delivered using a catheter or other catheter-based delivery mechanism. 
         [0086]    The clinician may then deploy the embolic protection device, e.g., to engage the inner wall of the aortic arch or other target vessel ( 144 ). The embolic protection device may be self-expanding, e.g., may expand upon release from the delivery mechanism. Embodiments in which the embolic protection device comprises nitinol may be capable of self-expansion. In some examples, the embolic protection device may be expanded by balloon or other expandable element of the delivery mechanism. In some examples, the embolic protection device may be radiopaque or include radiopaque elements to facilitate visualization during implantation. Visualization may be of particular importance in the case of asymmetric embolic protection devices, for which orientation of flow-modulating elements and deflective surfaces proximal to branch vessels is desired. In some examples, the clinician may position the embolic protection device so that the flow-modulating element is located prior to the first ostium  20  on the outer arch  24  with respect to aortic valve  36 . After the embolic protection device is implanted, the clinician may withdraw the embolic protection device delivery mechanism, e.g., through the common access ( 146 ). 
         [0087]    The clinician may then insert a procedure instrument, e.g., for valvuloplasty or TAVR, into the common vascular access ( 148 ), and advance the procedure instrument through the longitudinal passageway of the embolic protection device ( 150 ). The clinician may then perform the aortic valve procedure with the embolic protection device in place in the aortic arch ( 152 ). In some examples, the procedure preformed by the clinician may be another procedure requiring access through the aortic arch, such as a left-sided endocardial ablation. When the procedure is completed, the clinician may withdraw the aortic valve procedure instrument through the longitudinal passageway of the embolic protection device ( 154 ). The common vascular access may be closed, and the embolic protection device may remain implanted, e.g., chronically ( 156 ). 
         [0088]    The embolic protection device may be implanted percutaneously via peripheral vessels or surgically via trans-apical or trans-aortic approach via catheter in the aortic arch, spanning the ostia of the cranially-supplying arterial branches. If ex-plantation becomes necessary, the embolic protection device may be retrieved via catheter or other means. 
         [0089]      FIG. 14A  is a conceptual diagram of a top view of an example embolic protection device  400 . Embolic protection device  400  includes a flow-modulating element  402  and a frame  404 . As shown, flow-modulating element  402  covers approximately half of the circumference of frame  404 . When implanted the flow-modulating element  402  may be positioned so that it is located along the greater curvature of the vessel in which it has been implanted. 
         [0090]      FIG. 14B  is conceptual diagram of an orthogonal cross-sectional view, taken along line  15 B in  FIG. 14A , of the embolic protection device  400  of  FIG. 14A . As shown in  FIG. 14B , the longitudinal axis  406  of embolic protection device  400  is open. When implanted in a vessel, flow-modulating element  402  has a hydrofoil shape facing the predominant flow of blood along the longitudinal axis  406 . 
         [0091]      FIG. 14C  is a conceptual diagram of a side view of the embolic protection device of  FIGS. 14A and 14B . Embolic protection device  400  includes flow-modulating element  402  and frame  404 . Frame  404  may be comprised of circumferential portions and struts. In some examples, the composition of frame  404  may allow for expansion of frame  404  once it has been delivered to a target vessel. 
         [0092]      FIG. 15  is a conceptual diagram of another example embolic protection device  13 . Embolic protection device  13  comprises a flow-modulating element  19  and a frame  53 . Frame  53  is substantially cylindrical and may be largely fenestrated. In general, frame  53  may comprise a plurality of linked elements configured to allow frame  53  to be compressed to a smaller profile, e.g., diameter, and to be expand to engage or nearly engage a vessel wall. In this manner, frame  53  may be constructed similar to a stent. In the illustrated example, frame  53  comprises a plurality of circumferential elements that are circuitous and are linked by a plurality of struts arranged along the longitudinal axis of the frame. In other examples, the longitudinal elements may be circuitous, or both the longitudinal and circumferential elements may be circuitous. In general, frame  53  may be constructed using any elements, techniques, or materials known for stents. 
         [0093]    In addition, flow-modulating element  19  may be attached to one end of the frame  53 . In some examples, element  19  may be made of the same material as frame  53 . Embolic protection devices as described herein, e.g., one or both of frame  53  or flow-modulating element  19 , may be formed of nitinol and/or another composite or other material capable of collapse and memory shape re-assumption or retention. Deflective surfaces of the flow-modulating element may be comprised of the same material, or any fabric or other material, including, but not limited to, polytetraflouroethylene (PTFE, Teflon®), expanded PTFE (GoreTex®), polyethylene (PE), polyethylene terephthalate (PETE), or some other polymer. Embolic protection devices, and particularly deflective surfaces such as that of flow-modulating element  19 , could be formed of or coated with bovine, porcine, ovine, or other species-derived pericardium. Depending on the construction and materials of deflective surface, e.g., if mesh-like, the deflective surfaces may act initially as a filter and/or flow modulator, and then transition to flow-modulating-only, depending on the degree of endothelialization of the deflective surfaces. 
         [0094]    Various examples have been described. However, one of ordinary skill in the art will appreciate that various modifications may be made to the described examples. For example, although described primarily with respect to application in an implantable embolic protection device, the frame and flow-modulating element structures described herein may find application in a variety of contexts, such as for deflection, separation, or direction of any of a variety of particles or fluids (liquids or gases). As one example, the frame and flow-modulating element structures described herein may be used for deflection, separation, or direction of agricultural materials, such as grain or seed, or for deflection, separation, or direction of oil and gas, such as for isolating oil from oil sands. These and other examples are within the scope of the following claims.