Abstract:
A device and method for treatment of intracranial vasospasm is provided. The device is a microcatheter having a steeply tapered end and is thicker walled, and in a preferred embodiment is braided to provide greater pushability. In order to achieve a thicker walled catheter, in one embodiment, the inner lumen diameter can be reduced, leaving the outer diameter the same while in another embodiment the catheter is larger in outer diameter. In one embodiment, the microcatheter is coated with performance enhancing lubricant, such as a hydrophilic coating. Further, the microcatheter can also be coated with drugs and serve as a drug delivery device, drugs being embedded into vessel intima. In the use of the method of treatment, the device is fed into the smaller arterial vessels in the brain simultaneously dilating arteries of various caliber along the path of the catheter to relieve vasospasm; pharmacological agents can then be delivered by the microcatheter to further effect treatment.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     The present invention concerns a device and method for relieving vasospasm affecting the intracranial arteries. More particularly the present invention concerns a device and method of performing non-balloon angioplasty within tiny arteries so as to relieve intracranial vasospasm.  
         [0002]     The arterial make up of the head, and more specifically of the brain, includes important routes that are, of necessity, small and tortuous in character. As such, intracranial brain artery networks are comprised of vessels having small diameters and almost “hairpin”-like turns.  
         [0003]     Patients with ruptured brain aneurysms, known as subarachnoid hemorrhage (or SAH) can develop intracranial vasospasm as a delayed complication. In vasospasm, the arteries supplying the brain are narrowed as a result of constriction and/or thickening of the blood vessel wall. Because the narrowed vessel lumen restricts blood flow, lack of blood supply to the brain distally can result in a stroke.  
         [0004]     Current management of vasospasm utilizes a combination of mechanical dilatation (angioplasty) and pharmacological intervention of the spastic vessels. Mechanical angioplasty is commonly performed with a microcatheter with a small balloon attached at its end. Balloon angioplasty is widely accepted to be a safe, effective and durable treatment for vasospasm, but it is limited in that the balloon microcatheters are by design larger diameter and stiffer than simple microcatheters. As such, these microcatheters usually cannot be steered into vessels that are smaller or more tortuous. In addition, these balloons are chosen based on the diameter when maximally inflated and it is difficult to inflate a balloon to a diameter less than its designed maximum. For these reasons, angioplasty of affected arteries is usually reserved for larger, proximal vessels, while smaller, more tortuous, more distal vessels are not mechanically treated.  
         [0005]     At present, most angioplasty of arteries affected by intracranial vasospasm is performed with specialized low-radial-pressure, compliant balloon microcatheters, such as the Sentry, manufactured by Target/Boston Scientific and the Equinox, manufactured by MicroTherapeutics, Inc. However, even these specialized balloon microcatheters have not overcome all of the noted shortcomings in that the tip profile and stiffness of these devices still prevents them from being steered into small, tortuous vessels. Moreover, the balloons tend to inflate in an all-or-nothing manner, making it less desirable to, for example, use a 3.5 mm diameter balloon to dilate a vessel with a 2.5 mm normal diameter due to the potential risk of over dilatation.  
         [0006]     In rare occurrences, some individual practitioners have performed angioplasty of small, tortuous, distal arteries simply by passing a microcatheter (without a balloon) through the vessel. However, this technique is often not helpful because currently available microcatheters have generally blunt tips and in general have too small an outer diameter to accomplish much angioplasty.  
         [0007]     Chemical or pharmacological intervention is also practiced. For example, the affected arteries can be infused with vasodilating drugs, to facilitate opening of the arteries. Infusion can be carried out by direct infusion through use of a catheter or by placement of such chemicals on, for example, an angioplasty balloon such that the chemical is placed onto the affected area of the arteries. However, there are inherent limitations in that the bathing of tissue with dilating chemicals, while effective, is generally effective for only the short period while the chemical is present or is present in an effective amount.  
       BRIEF SUMMARY OF THE INVENTION  
       [0008]     In accordance with the present invention, a microcatheter comprising a steep taper with a large shaft is provided. The microcatheter is thicker walled, and in a preferred embodiment is braided to provide greater pushability. In order to achieve a thicker walled catheter, in one embodiment, the inner lumen diameter can be reduced, leaving the outer diameter the same. In one embodiment, the microcatheter is coated with performance enhancing lubricant, such as a hydrophilic coating. Further, the microcatheter is also coated with drugs and serves as a drug delivery device, drugs being embedded into vessel intima. Such drugs as heparin, anti-platelet drugs and vasoactive drugs are used. The present invention comprises a microcatheter with no balloon, but designed with a wall thickness, tapered outer diameter and tip profile that would allow angioplasty of smaller, more tortuous vessels by the outer surface of the microcatheter shaft.  
         [0009]     These and other features and advantages of the present invention will be apparent from the following detailed description, in conjunction with the appended claims. 
     
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS  
       [0010]     The benefits and advantages of the present invention will become more readily apparent to those of ordinary skill in the relevant art after reviewing the following detailed description and accompanying drawings and photographs, all of which are referred to as figures, wherein:  
         [0011]      FIG. 1  is a schematic representation of the vascular anatomy of the brain showing typical branching pattern and vessel lumen diameters.  
         [0012]      FIG. 2  is a schematic representation of the vascular anatomy of a healthy brain without vasospasm.  
         [0013]      FIG. 3  is a schematic representation of the vascular anatomy of a brain with moderate vasospasm of the distal interior carotid artery, proximal anterior cerebral artery and proximal middle cerebral artery.  
         [0014]      FIG. 4   a  is an elevational view of a known microcatheter used for dilatation when a balloon microcatheter cannot be advanced into a spastic vessel.  
         [0015]      FIG. 4   b  is an elevational view of an uninflated balloon microcatheter.  
         [0016]      FIG. 4   c  is an elevational view of an inflated balloon microcatheter.  
         [0017]      FIG. 4   d  is a schematic representation of the vascular anatomy of the brain of  FIG. 3  after treatment by angioplasty with a typical balloon catheter showing improved diameter of the interior cerebral artery and a segment (M 1 ), but in which areas (A 1 , A 2  and M 2 ) were unable to be treated, that is, illustrating that caliber is improved proximally but not distally.  
         [0018]      FIG. 5  is a schematic representation of the vascular anatomy of a brain with severe vasospasm of the distal interior carotid artery, proximal anterior cerebral artery and proximal middle cerebral artery.  
         [0019]      FIG. 6  is a schematic representation of the vascular anatomy of the brain of  FIG. 5  following angioplasty with a typical microcatheter (illustrating that caliber is improved distally by not proximally).  
         [0020]      FIG. 7  is an elevational view of the device of the present invention.  
         [0021]      FIG. 8  is another elevational view of the device of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0022]     While the present invention is susceptible of embodiment in various forms, there is shown in the drawings and will hereinafter be described a presently preferred embodiment with the understanding that the present disclosure is to be considered an exemplification of the invention and is not intended to limit the invention to the specific embodiment illustrated.  
         [0023]     It should be further understood that the title of this section of this specification, namely, “Detailed Description Of The Invention”, relates to a requirement of the United States Patent Office, and does not imply, nor should be inferred to limit the subject matter disclosed herein.  
         [0024]     Referring to the figures, and in particular to  FIGS. 1 and 2  there is shown the vascular anatomy  10  of a healthy brain, that is one not suffering from vasospasm, with a typical branching patterns and indications of vessel lumen diameters. It will be understood by persons having skill in the art that the  FIG. 1  is a schematic representation of the brain and is not meant to be drawn to exact scale or be an exact representation of all healthy brain tissue.  
         [0025]     As shown, the Internal Carotid Artery (ICA)  12  is a relatively large vessel having a vessel lumen diameter of about 4 mm to 5 mm. The two carotid arteries along with the two vertebral arteries are, in most patients, the four larger arteries at the base of the skull. The ICA  12  branches into the Middle Cerebral Artery (MCA)  14  and the Anterior Cerebral Artery (ACA)  16 , each of which in turn branches into smaller arterial segments and passageways (first, second and third order branches).  
         [0026]     The MCA  14  includes M 1  segments  14   a  having vessel lumen diameters of about 2.5 mm to 3 mm and branches into a M 2  segments  14   b  each of which has a reduced vessel lumen diameter of about 1.5 mm to 2.0 mm. ACA  16 , as shown in  FIG. 1 , includes A 1  segments  16   a  having vessel lumen diameters of about 1.5 mm to 2.0 mm and A 2  segments  16   b  having reduced vessel lumen diameters of about 1.2 mm to 1.5 mm. As shown in  FIGS. 1 and 2 , other artery segments are also present having even smaller vessel lumen diameters.  
         [0027]     Referring now to  FIG. 3 , another schematic representation of the vascular anatomy of the brain  20  is shown. As illustrated the vessels are affected by moderate vasospasm. Vasospasm is represented by the narrowing of the vessels; specifically ICA  22  is narrowed at the distal segment  22   a ; MCA  24  is narrowed at the proximal segment  24   a ; and ACA  26  is narrowed at proximal segment  26   a . This narrowing can be a byproduct of an event such as a ruptured brain aneurysm, known as subarachnoid hemorrhage (or SAH). Subsequent to the SAH a patient can develop intracranial vasospasm. As noted above, in vasospasm, the arteries supplying the brain are narrowed as a result of constriction and/or thickening of the blood vessel wall. Because the narrowed vessel lumen restricts blood flow, lack of blood supply to the brain distally can result in a stroke.  
         [0028]     Referring to  FIGS. 4   a ,  4   b ,  4   c  and  4   d , the prior devices and methods used to treat vasospasm are shown so as to provide a departure for the discussion of the device and method of the present invention. As shown in  FIG. 4   a , a microcatheter  30  is shown of a type well known in the art, that while designed as a delivery system for coils or liquid agents, has in rare reports also been used to perform mechanical dilatation of smaller diameter branches in vasospasm. The diameter of the microcatheter  30  however would be too small to accomplish angioplasty in larger vessels in vasospasm (see, e.g.,  FIG. 6 ). Catheter  30  can be advanced in a vessel to point of narrowing of the vessel and, by virtue of its size, dilate the vessel. Further, catheter  30  may also be utilized as a delivery device for pharmacological agents that can dilate the vessel. However, in order to be effective, catheter  30  must be of a configuration, size and flexibility to reach to the point of constriction without damaging vessel walls.  
         [0029]      FIGS. 4   b  and  4   c  are, respectively, depictions of a balloon microcatheter  32 , in a first uninflated state and a second inflated state. In the use of microcatheter  32 , the catheter  32  is advanced into the vessel to the narrowed point and the balloon  34  is then inflated to dilate the narrowed vessel. The balloon  34  can be coated with pharmacological agents that, in cooperation with the inflation effect of the balloon, deliver dilating agents to the vessel&#39;s interior walls when inflated.  
         [0030]     However, as set forth above, such balloon catheters suffer from limited (large) diameters and stiffnesses that prevent use in small or more tortuous arterial networks.  FIG. 4   d  illustrates the schematic arterial representation post angioplasty using the devices of  FIG. 4   b / 4   c . It will be seen in  FIG. 4   d  that the use of the balloon catheter  32  provides adequate treatment of the ICA  22  and MCA segment M 1   24   a , but does not allow treatment of narrowed smaller diameter segments of the ACA  26  (segments  26   a ) and the MCA  24  (segments  24   a ).  
         [0031]     Referring to  FIG. 5 , another schematic representation of the vascular anatomy of the brain  50  is shown. In this instance the vessels are suffering from severe vasospasm. Vasospasm is represented by the narrowing of the vessels; specifically ICA  52  is narrowed at the distal segment  52   a ; MCA  54  is narrowed at the proximal segment  54   a ; and ACA  56  is narrowed at proximal segment  56   a .  FIG. 6  shows a best-case scenario of the treatment, using the microcatheter  30  of  FIG. 4   a . A comparison of the vascular anatomy of  FIGS. 1, 5 , and  6  shows that the treatment used, that is the use of catheter  30  ( FIG. 4   a ) resulted in improved diameters in ACA segments A 1  ( 56 ) and A 2  ( 56   a ) and MCA segment M 2  ( 54   a ), as well as minimal or mild improvements in M 1  segment ( 54 ) of MCA, but no significant improvement in ICA ( 52 ). The limited benefit in M 1  segment ( 54 ) of MCA and the lack of improvement in ICA ( 52 ) is due to the catheter  30  having, initially, a smaller diameter than the narrowed segment  52   a  and therefore offering no dilation therein.  
         [0032]     Referring now to  FIG. 7 , the improved catheter  60  of the present invention is shown. It will be seen that catheter  60  tapers, more steeply than prior art catheters, from its proximal end  60   a  to its distal end  60   b . Further, catheter  60  has a larger shaft than prior art catheters, a smaller tip, a steeper or more severe taper and thicker walls. The catheter can be braided to permit the catheter to be pushed further without kinking.  
         [0033]     As seen in  FIG. 7 , the inner lumen  66  diameter D 66  of catheter  60  can be reduced to achieve thicker walls. Catheter  60 , in a preferred embodiment, can be coated with performance enhancing lubricants  62 , such as hydrophilic coating and with pharmacological agents  64  such as heparin, anti-platelet drugs, vasoactive drugs and the like. It will be understood that catheter  60  can be coated with other lubricating agents and other drugs and pharmacological agents, as well as other agents that can produce desirable effects (whether understood at present or not) without departing from the novel scope of the present invention.  
         [0034]     In the use of the device of the present invention, catheter  60  is advanced into the vascular system shown in any of the previous figures. Because of the taper and the narrow, non-blunt tip, the catheter can be used to physically dilate smaller, more tortuous vessels while the larger proximal segment simultaneously dilates the larger M 1  segment of MCA and the ICA. The advancement of catheter  60 , thereby, dilates a significantly larger amount of the vascular system shown, while not causing damage that prior art catheters may be prone to cause. Additionally, catheter  60  can be used to deliver pharmacological agents further into the vascular system, as well, either through delivery as an injection through the end-hole or through imbedding the drug coating the catheter into the vessel wall inner lining in the process of angioplasty.  
         [0035]     As seen in  FIG. 8 , a presently contemplated catheter  60  has a length L 60  of about 120 cm to 150 cm, preferably about 130 cm. The diameter of the catheter is about 3 mm at the base or proximal end  60   a  D 6Oa  and tapers to a diameter D 60b  about 0.67 mm at the distal end  60   b . The tapering of the catheter  60  occurs at about the distal most 20 cm to 30 cm (indicated at  60   c ), likely at about the distal most 20 cm. As discussed above, the diameter of the lumen D 66  is less than known catheters. The lumen  66  of the presently contemplated catheter has a diameter of about 14 thousandths of an inch (mils) to about 22 mils. It is anticipated that the catheter  60  is not necessarily used for the delivery of solid materials such as particulate agents or coils. Rather, the catheter may be used to deliver fluids such as drugs, and as such, the lumen diameter D 66  can remain relatively small. In such an arrangement, a lead wire  70  having a diameter of about 10 mils to 18 mils can be used.  
         [0036]     It is anticipated that the thicker walls of the catheter  60  (in part permitted by the smaller lumen  66 ) will permit manipulating the catheter  60  into vessels that otherwise could not be reached by known catheters and dilating these vessels by movement of the catheter  60  therein. Advantageously, because the outside diameter of the proximal portion  60   a  of the present catheter  60  is larger and tip or distal portion  60   b  is smaller, the taper is steeper or more severe than known catheters. And, in that the taper occurs over the distal most 20 cm to 30 cm of the catheter, the present catheter  60  allows simultaneous dilatation of the various (caliber) cerebral arteries as the catheter is urged into the arterial system (e.g., toward and into the first, second and third order branches).  
         [0037]     Those skilled in the art will recognize that the present device can be used in a like manner to effect improvement in vasospasm involving the vertebrobasilar system, and as such, the device and methods and use of the device and methods for such use are within the scope and spirit of the present invention.  
         [0038]     In one embodiment of catheter  60 , a catheter having no taper is provided with an expandable jacket at its distal end. As the catheter is advanced into narrowed segments of vessels, the jacket can be expanded into the tapered shape desired to effect dilation.  
         [0039]     All patents referred to herein, are hereby incorporated herein by reference, whether or not specifically done so within the text of this disclosure.  
         [0040]     In the present disclosure, the words “a” or “an” are to be taken to include both the singular and the plural. Conversely, any reference to plural items shall, where appropriate, include the singular.  
         [0041]     From the foregoing it will be observed that numerous modifications and variations can be effectuated without departing from the true spirit and scope of the novel concepts of the present invention. It is to be understood that no limitation with respect to the specific embodiments illustrated is intended or should be inferred. The disclosure is intended to cover all such modifications as fall within the scope of the claims.